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An invasive riparian tree reduces stream ecosystem efficiency via a recalcitrant organic matter subsidy
Ecology
Abstract
A disturbance, such as species invasion, can alter the exchange of materials and organisms between ecosystems, with potential consequences for the function of both ecosystems. Russian olive (Elaeagnus angustifolia) is an exotic tree invading riparian corridors in the western United States, and may alter stream organic matter budgets by increasing allochthonous litter and by reducing light via shading, in turn decreasing in-stream primary production. We used a before-after invasion comparison spanning 35 years to show that Russian olive invasion increased allochthonous litter nearly 25-fold to an invaded vs. a control reach of a stream, and we found that this litter decayed more slowly than native willow. Despite a mean 50% increase in canopy cover by Russian olive and associated shading, there were no significant changes in gross primary production. Benthic organic matter storage increased fourfold after Russian olive invasion compared to pre-invasion conditions, but there were no associated changes in stream ecosystem respiration or organic matter export. Thus, estimated stream ecosystem efficiency (ratio of ecosystem respiration to organic matter input) decreased 14%. These findings show that invasions of nonnative plant species in terrestrial habitats can alter resource fluxes to streams with consequences for whole-ecosystem functions.
... Consequently, this is enabling invasive species to have spatially cascading effects on other ecosystems ( Fig. 1 and Table 1). For instance, the invasion of plants to forests is modifying the properties (for example, nutrient composition or lability) and magnitude of leaf detritus flowing from forests to streams, substantially influencing decomposition rates and ecosystem efficiency in streams [21][22][23] . Rats (Rattus spp.) invasive to islands are significantly reducing bird populations through predation, limiting the flow of nitrogen released in bird guano from islands to coral reefs, and consequently reducing the biomass of coral reef fish by up to 50% and critical ecosystem functions by three to four times 15,24,25 . ...
... Other stressor has shown such invasions can have spatially cascading effects into adjacent streams and ponds by altering the traits and, thus, quality of leaf detritus flowing into them [21][22][23][63][64][65][66][67][68][69][70][71][72][73][74][75][76] . Collectively, this growing body of evidence demonstrates the cross-ecosystem impact on adjacent freshwater ecosystems typically depends on the quality of invasive plant species leaf litter relative to native species. ...
... Invasive species with relatively low carbon:nitrogen (C:N) and/or structural content, such as Japanese knotweed (Reynoutria japonica), have been linked to higher leaf litter breakdown rates in freshwater ecosystems 64,65,68 , changes in community and food-web structure 64,72 , greater species richness 68,72,73 , and enhanced fitness and production of freshwater organisms 66,[73][74][75] . By contrast, the input of litter from invasive plant species with relatively high C:N and/or structural content, such as the invasive river red gum (Eucalyptus camaldulensis), results in an input of more recalcitrant litter into aquatic systems, which can significantly decrease leaf breakdown and recycling rates 21,22,63,65 , stream efficiency 21 , species richness 73 , and the fitness and production of freshwater organisms 66,67,73,74 . ...
Invasive species are pervasive around the world and have profound impacts on the ecosystem they invade. Invasive species, however, can also have impacts beyond the ecosystem they invade by altering the flow of non-living materials (for example, nutrients or chemicals) or movement of organisms across the boundaries of the invaded ecosystem. Cross-ecosystem interactions via spatial flows are ubiquitous in nature, for example, connecting forests and lakes, grasslands and rivers, and coral reefs and the deep ocean. Yet, we have a limited understanding of the cross-ecosystem impacts invasive species have relative to their local effects. By synthesizing emerging evidence, here we demonstrate the cross-ecosystem impacts of invasive species as a ubiquitous phenomenon that influences biodiversity and ecosystem functioning around the world. We identify three primary ways by which invasive species have cross-ecosystem effects: first, by altering the magnitude of spatial flows across ecosystem boundaries; second, by altering the quality of spatial flows; and third, by introducing novel spatial flows. Ultimately, the strong impacts invasive species can drive across ecosystem boundaries suggests the need for a paradigm shift in how we study and manage invasive species around the world, expanding from a local to a cross-ecosystem perspective.
... Invasive species can act synergistically to increase the rate and success of additional species introductions (Simberloff, 2006;Simberloff & Von Holle, 1999). For example, monocultures of invasive riparian trees can have particularly acute effects on both habitat and nonnative species introductions in riverine ecosystems (Heinrich et al., 2021;Katz & Shafroth, 2003;Mahoney et al., 2019;Mineau et al., 2012). Specifically, riparian invasion can alter sediment transport and retention, causing changes in channel morphology (West et al., 2020). ...
... Specifically, riparian invasion can alter sediment transport and retention, causing changes in channel morphology (West et al., 2020). In addition, invasive riparian trees can affect riverine food webs by altering the quality, timing and magnitude of leaf litter inputs (Going & Dudley, 2008;Mineau et al., 2012;Swan et al., 2008), as well as influencing terrestrial prey inputs (Roon et al., 2016). Therefore, understanding the role of invasive riparian trees in aquatic ecosystem function will enhance conservation and management of riverine ecosystems. ...
... These changes in the riparian community have increased bank vegetation cover from 10% in the 1930s to more than 90% in 2010s, contributing to channel restriction and incision (Bassett, 2015). In addition to changing channel morphology, olive has the potential to restructure riverine food webs by contributing large seasonal pulses of its fruit and litter (Mineau et al., 2012). ...
Russian olive ( Elaeagnus angustifolia ) is an invasive, fruit‐bearing riparian tree that dominates riparian zones of the San Juan River in the southwestern United States. Previous research in this river suggests olive fruit is common in diets of invasive channel catfish ( Ictalurus punctatus ), but its energetic importance is unknown (i.e. critical for catfish fitness vs. incidental consumption). We assessed Russian olive consumption in channel catfish diets bimonthly for 1 year, hypothesizing that olive consumption would be greatest during periods of high olive availability and low benthic aquatic invertebrate availability. We found that catfish consumed olive fruit throughout the year and that olive comprised up to 44% of total stomach contents by mass, with peaks in spring and fall. Regression models revealed the presence and mass of olive fruit in catfish stomachs were positively associated with catfish total length, with a significant interaction between water temperature and river discharge. Catfish were more likely to consume olive fruit during higher flows, regardless of temperature and at low discharge with higher temperature. Contrary to our hypothesis, neither olive nor benthic invertebrate availability were associated with olive presence in channel catfish diets. Nutrition analysis indicated that olive alone was a low‐quality diet item but has the potential to provide a reliable energy source. We used seasonal data to estimate the energetic contribution of olive fruit to catfish populations using a bioenergetic model, which estimated that olive fruit accounted for 35.6% of energy (Joules) consumed by catfish populations and satisfied 38% of their metabolic demand. Our results suggest that Russian olive fruit is a significant subsidy to channel catfish in the San Juan River. However, more research is needed to determine the indirect effects of this interaction on native fishes and ecosystem function.
... Factors that contribute to the establishment and spread of Russian olive include horticultural cultivation, its large seed size and seed longevity, and altered flow regimes (i.e., damming and irrigation water withdrawals) (Katz andShafroth 2003, Espeland et al. 2017). It is a deciduous tree that adds a large flux of recalcitrant allochthonous litter to streams along which it invades (Royer et al. 1999) and thus reduces the efficiency of organic matter processing within invaded stream ecosystems (Mineau et al. 2012). Russian olive also has a high capacity to fix N 2 through microbial association and has been associated with changes in in-stream N dynamics . ...
... Multiple reaches of Deep Creek were intensively studied when it served as a representative cooldesert stream during the International Biological Program (IBP) in the early 1970s (Minshall et al. 1972, 1973, Minshall 1978. The same reaches were recently studied after Russian olive invaded one of these sites (Mineau et al. , 2012. We hypothesized that the invasion of Russian olive facilitates the invasion of the common carp and that the synergistic impacts of these subsidized carp include consequences for in-stream primary producers, organic matter standing stocks, and nutrient dynamics. ...
... We focus on this site because of the Russian olive invasion and because previous work on its effects (e.g., increases in allochthonous inputs and benthic v www.esajournals.org organic matter, and changes in nutrient dynamics) was also conducted at this site (Mineau et al. , 2012. Fish population data were collected during the IBP, and our general observation of an increase in carp subsequent invasion of Russian olive was also part of the motivation for this study. ...
Abstract Multiple invasive species may interact, influencing one another and generating synergistic effects on food webs and ecosystem processes. We investigated the interaction between two non‐native species widespread in the western USA: common carp (Cyprinus carpio) and Russian olive (Elaeagnus angustifolia), an invasive riparian tree associated with di‐nitrogen fixation. Deep Creek, Idaho, was an International Biological Program site in the early 1970s; at that time, carp were rare and Russian olive was absent. Subsequently, Russian olive was introduced and established a dense stand, increasing allochthonous inputs and nitrogen‐rich benthic organic matter. Since 1971, carp density has increased ~4× (an increase our bioenergetic analysis suggests could not have been sustained in the absence of Russian olive). Carp gut contents in 2013–2014 revealed, on average, ~40% olives, and, similarly, stable isotope analyses revealed ~58% of carp tissues were derived from olives. A small‐scale, short‐term experimental exclusion of these subsidized carp caused ~3× increases in macrophytes and chlorophyll‐a, suggesting they may limit algae and macrophyte biomass. Moreover, carp that consumed olives excreted more nitrogen (~2× more ammonium, ~2× more total dissolved nitrogen, and ~3× more total nitrogen) compared to those that had not, which may amplify recycling and export from streams invaded by both species. This scenario is characteristic of an “invasional meltdown,” with attendant changes in food webs and ecosystem processes.
... This is particularly true in the case of stream-riparian forest meta-ecosystems. The invasion of riparian forests by alien woody species can deeply affect their biodiversity and functioning (Urgenson, Reichard & Halpern, 2009;Tererai et al., 2013;Gutiérrez-López et al., 2014;Constán-Nava et al., 2015), but it can also affect stream ecosystems given their large aquatic-terrestrial interface and strong dependency on riparian vegetation (Lecerf et al., 2007;Atwood et al., 2010;Hladyz et al., 2011;Mineau et al., 2012). Riparian vegetation is one of the most important factors controlling in-stream functioning: it provides shade, thus reducing the amount of solar radiation reaching the stream bed and controlling water temperature, which limits instream primary production; it provides organic matter as a food source and substrate for aquatic organisms; it provides habitat for aquatic organisms (e.g. ...
... Despite the small number of studies, and differences in the identity and functional type of the invasive species and in the type of the invaded ecosystem, it emerges as a general trend that the invasion of riparian areas by N-fixing species leads to higher N concentrations in stream water and sediments (Goldstein, Williard & Schoonover et al., 2009;Atwood et al., 2010;Mineau, Baxter & Marcarelli, 2011;Wiegner et al., 2013;Stewart et al., 2019) and lower N limitation of biofilms (Mineau et al., 2011;Wiegner et al., 2013). Changes in litter inputs (Mineau et al., 2012;Railoun, 2018), the N cycle (Mineau et al., 2011;Stewart et al., 2019), benthic invertebrate communities (Lowe et al., 2008) and food webs (Atwood et al., 2010) have also been reported (Table 1). ...
... ambient temperature, atmospheric N deposition). In this case, the beforeafter condition is compared for two sets of streams: streams that underwent invasion and streams that did not undergo invasion and still flow through native forests (Mineau et al., 2012). Conceptual framework to predict effects of invasion of temperate deciduous broadleaf forests by N-fixing species on streams by considering a continuum from early to advanced stages of invasion by N-fixing species (e.g. ...
Biological invasions are a major threat to biodiversity and ecosystem functioning. Forest invasion by alien woody species can have cross-ecosystem effects. This is especially relevant in the case of stream-riparian forest meta-ecosystems as forest streams depend strongly on riparian vegetation for carbon, nutrients and energy. Forest invasion by woody species with dissimilar characteristics from native species may be particularly troublesome. The invasion of temperate deciduous broadleaf forests with low representation of nitrogen (N)-fixing species by N-fixers has the potential to induce ecosystem changes at the stream level. Although effects of tree invasion on stream ecosystems have been under assessed, knowledge of native and invasive tree characteristics allows prediction of invasion effects on streams. Here we present a conceptual model to predict the effects of forest invasion by alien N-fixing species on streams, using as a background the invasion of temperate deciduous broadleaf forests by leguminous Acacia species, which are among the most aggressive invaders worldwide. Effects are discussed using a trait-based approach to allow the model to be applied to other pairs of invaded ecosystem-invasive species, taking into account differences in species traits and environmental conditions. Anticipated effects of N-fixing species invasions include changes in water quality (increase in N concentration) and quantity (decrease in flow) and changes in litter input characteristics (altered diversity, seasonality, typology, quantity and quality). The magnitude of these changes will depend on the magnitude of differences in species traits, the extent and duration of the invasion and stream characteristics (e.g. basal nutrient concentration). The extensive literature on effects of nutrient enrichment of stream water, water scarcity and changes in litter input characteristics on aquatic communities and processes allows prediction of invasion effects on stream structure and function. The magnitude of invasion effects on aquatic communities and processes may, however, depend on interactions among different pathways (e.g. effects mediated by increases in stream nutrient concentration may contrast with those mediated by decreases in water availability or by decreases in litter nutritional quality). A review of the literature addressing effects of increasing cover of N-fixing species on streams suggests a wide application of the model, while it highlights the need to consider differences in the type of system and species when making generalizations. Changes induced by N-fixing species invasion on streams can jeopardize multiple ecosystem services (e.g. good quality water, hydroelectricity, leisure activities), with relevant social and economic consequences.
... Invasive species studies also tend to focus on a single ecosystem function and fail to address the interacting and potentially reinforcing mechanisms underlying invasion-driven ecosystem change [11]. Resource subsidies, or fluxes of resources between ecosystems, can provide insight into the multiple ways invasive species alter biological communities [12,13]. ...
... Stable isotopes were measured at the Natural Resource Ecology Laboratory (Colorado State University, Fort Collins, Colorado, USA) using a Carlo Erba NA 1500 (Milan, Italy) coupled with a VG Isochrom continuous flow isotope ratio mass spectrometer (Isoprime Inc., Manchester, United Kingdom) to simultaneously determine nitrogen and carbon isotope composition. Ratios of the heavy isotope to its common lighter counterpart (i.e., 13 C/ 12 C and 15 N/ 14 N) were expressed in standard δ-notation relative to international standards (Vienna Peedee Belemnite and atmospheric nitrogen, respectively) in parts per mil (‰). For instance, δ 13 C sample = [( 13 C sample / 12 C sample )/( 13 C standard / 12 C standard )-1] x 1000, and likewise for δ 15 N [47]. ...
... The figure shows mean percent aquatic-derived carbon sampled from songbird species individually and overall (i.e., "community") for 2015 (grey) and 2016 (white). Results were determined using a single isotope mixing formula and δ13 C signatures of insect and fecal samples, pooled across reference and invaded sites. There were insufficient sample sizes (n<2 per year) to calculate means for Virginia's warbler in 2016. ...
Non-native plants can impact riparian ecosystem function through diverse terrestrial and aquatic pathways, with cascading effects on food webs. Invasion-mediated vegetation changes can depress terrestrial arthropod communities and alter arthropod flux across the aquatic-terrestrial interface. We investigated the effects of a non-native woody plant, Robinia neomexicana, on insect contributions to riparian songbird diets. This plant was introduced over 100 years ago to the Clear Creek drainage in northwestern Colorado (USA) from its native range, which extends into southern Colorado. We used stable isotope analysis of insects and avian feces to 1) assess whether the relative contributions of aquatic- and terrestrial-derived arthropod prey differed between reference sites and sites invaded by R. neomexicana, and 2) quantify the amount of aquatic- and terrestrial-derived resources consumed by an insectivorous songbird assemblage. Two species of insectivorous songbirds consumed more aquatic insects in invaded sites compared to reference sites. This change in terrestrial- and aquatic-derived prey in bird diets in response to a near-range plant invasion suggests that the introduction of novel species from more distant native ranges could produce similar or stronger effects. Overall, the songbird community consumed approximately 34% aquatic resources, which highlights the importance of these subsidies to riparian consumers. Our investigation of insect subsidies demonstrates how introduced species can indirectly affect food webs and provides insight into the plasticity of riparian consumer responses.
... Findings include (1) lower bird species richness and diversity (Brown 1990;Knopf and Olson 1984) than in surrounding native plant species, (2) potential nesting habitat for the endangered southwestern willow flycatcher (Empidonax traillii extimus A. R. Phillips, Tyrannidae) (USDA 2012), and (3) significant nitrogen input to streams (Mineau et al. 2011) andsoils (DeCant 2008;Follstad Shah et al. 2010). Reviews by Katz and Shafroth (2003) Several studies indicate Russian-olive invasion is drastically altering aquatic ecosystem functioning (e.g., Kominoski et al. 2013;Mineau et al. 2011Mineau et al. , 2012. Streams invaded with Russian-olive are not as limited by nitrogen compared with uninvaded streams (Mineau et al. 2011). ...
... When coupled with anthropogenic sources of nitrogen from agriculture and urban-suburban areas where Russian-olive planting is common, additions of nitrogen from Russian-olive may contribute to stream nitrogen saturation, leading to eutrophication and oxygen deficiencies within the system (Mineau et al. 2011). Along Deep Creek in southeast Idaho, Mineau et al. (2012) determined that allochthonous organic matter inputs from Russian-olive leaf litter and the recalcitrant nature of Russian-olive leaves caused a decrease in ecosystem efficiency. In that study, inputs of allochthonous organic matter increased 25-fold after Russian-olive invasion and was most likely stored as benthic organic matter in the stream (Mineau et al. 2012). ...
... Along Deep Creek in southeast Idaho, Mineau et al. (2012) determined that allochthonous organic matter inputs from Russian-olive leaf litter and the recalcitrant nature of Russian-olive leaves caused a decrease in ecosystem efficiency. In that study, inputs of allochthonous organic matter increased 25-fold after Russian-olive invasion and was most likely stored as benthic organic matter in the stream (Mineau et al. 2012). ...
Russian-olive is a small tree or large multistemmed shrub that was introduced to Canada and the United States from Eurasia in the early 1900s. It was provisioned in large numbers during the last century to prairie farmers as a shelterbelt plant and remains a popular and widely available ornamental. Now invasive within some riparian ecosystems in the western United States, Russian-olive has been declared noxious in the states of Colorado and New Mexico. With traits including high shade tolerance and a symbiotic association with nitrogen-fixing bacteria, Russian-olive has the potential to dominate riparian vegetation and thus radically transform riparian ecosystems. Especially alarming is its capacity to influence nutrient dynamics within aquatic food webs. Our objective is to draw attention to Russian-olive as a potential threat to riparian ecosystems within Canada, especially in the southwest, where invasion is becoming commonplace. We review what is known about its biology and about the threats it poses to native organisms and ecosystems, and we summarize management and control efforts that are currently underway. We conclude by proposing a research agenda aimed at clarifying whether and how Russian-olive poses a threat to riparian ecosystems within western Canada. Nomenclature: Russian-olive; Elaeagnus angustifolia L. ELGAN.
... Riparian zones often support a higher percentage of non-native plants than upland habitats due to the combined effects of flood events that disturb riparian soils and landscape connectivity that links populations along riparian corridors (Tabacchi et al., 1996; Hood & Naiman, 2000). As a result, non-native plants in riparian forests are currently spreading in many locations, with notable invasions of Russian olive (Elaeagnus angustifolia) and tamarisk (Tamarix spp.) in the western United States (Royer et al., 1999; Sher et al., 2002; Friedman et al., 2005; Mineau et al., 2012), knotweeds (Fallopia spp.) in the United States and Europe (Braatne et al., 2007; Lecerf et al., 2007; Claeson et al., 2013), and willows (Salix spp.) in Australia (Read & Barmuta, 1999). Because riparian zones link terrestrial and aquatic ecosystems, the spread of non-native plants in riparian forests could affect stream organisms, food webs, and ecosystem function (Gregory et al., 1991; Hood & Naiman, 2000; Gessner & Chauvet, 2002). ...
... Collectively, these aquatic invertebrate communities support upper trophic level consumers like stream fishes (Wallace et al., 1997; Baxter et al., 2005). The spread of non-native plants can alter the timing, quantity, and quality of leaf litter inputs into streams (Abelho & Graça, 1996; Lecerf et al., 2007; Mineau et al., 2012). Non-native plants can differ in quality from native species, for example, through lower nutrient content, increased leaf toughness, or presence of secondary plant compounds (Irons et al., 1988; Cummins et al., 1989; Abelho & Graça, 1996; Motomori et al., 2001 ). ...
... Our results are supported by Baldy et al. (1995) who found that leaf litter breakdown decreased in main-stem habitats with higher stream flow than in headwater habitats due to decreased biological activity of aquatic bacteria and fungi responsible for conditioning leaf litter. Other studies examining the behavior of non-native leaf litter in streams often found non-native leaf litter broke down at a slower rate compared to native species (Sampaio et al., 2001; Kennedy & Hobbie, 2004; Braatne et al., 2007; Lecerf et al., 2007; Going & Dudley, 2008; Mineau et al., 2012). This is sometimes due to the presence of recalcitrant compounds (i.e., lignin and tannins) that can slow both physical fragmentation and leaf litter conditioning by aquatic bacteria and fungi (Webster & Benfield, 1986; Graça, 2001; Lecerf et al., 2007; Mineau et al., 2012). ...
European bird cherry (Prunus padus) (EBC) is an invasive ornamental tree that is spreading rapidly in riparian forests of urban Alaska. To determine how the spread of EBC affects leaf litter processing by aquatic invertebrate shredders, we conducted complementary leaf pack experiments in two streams located in Anchorage, Alaska. The first experiment contrasted invasive EBC with three native tree species—thin-leaf alder (Alnus tenuifolia), paper birch (Betula neoalaskana), and black cottonwood (Populus trichocarpa)—in one reach of Chester Creek; finding that EBC leaf litter broke down significantly faster than birch and cottonwood, but at a similar rate to alder. The second experiment contrasted EBC with alder in four reaches of Campbell and Chester creeks; finding that while EBC leaf litter broke down significantly faster than alder in Chester Creek, EBC broke down at a similar rate to alder in Campbell Creek. Although EBC sometimes supported fewer shredders by both count and mass, shredder communities did not differ significantly between EBC and native plants. Collectively, these data suggest that invasive EBC is not currently exhibiting strong negative impacts on leaf litter processing in these streams, but could if it continues to spread and further displaces native species over time.
... Russian olive biological, ecological or life history traits conferring some degree of competitive advantage over native trees such as cottonwood include: seedling recruitment that is not limited to large flooding events; superior drought tolerance; seedlings that are comparatively less shade intolerant; and mature trees that are injured or felled much less frequently by beavers (Shafroth et al. 1995;Lesica and Miles 1999Katz and Shafroth 2003;Reynolds and Cooper 2010). As a nitrogen-fixing species, Russian olive also potentially functions as a so-called 'transformer' invasive species (D' Antonio et al. 2004) due to its ability to alter both terrestrial and benthic nutrient and community dynamics in invaded riparian areas (Reynolds and Cooper 2010;Follstad Shah et al. 2010;Mineau et al. 2011Mineau et al. , -2012. ...
... A pre-and post-invasion comparison determined that Russian olive invasion was associated with a nearly 25-fold increase in recalcitrant stream litter input. Russian olive inputs were additionally associated with a 4-fold increase in streambed stored organic matter, but with no attendant changes in gross primary production or community respiration, estimated stream ecosystem efficiency declined by 14% (Mineau et al. 2012). ...
The primary goals of a two-day Russian olive symposium held in February 2014 were to disseminate current knowledge and identify data gaps regarding Russian olive biology and ecology, distributions, integrated management, and to ascertain the feasibility and acceptance of a proposed program for classical biological control of Russian olive. The symposium was hosted by the Northern Rockies Invasive Plant Council in conjunction with NRIPC's 3rd Invasive Species in Natural Areas Conference, held February 10-15, 2014, in Spokane, WA. Funding to support the Russian olive symposium was received through a USDA NIFA AFRI Foundational Program grant awarded in response to the 'Controlling Weedy and Invasive Plants' (A1131) program priority area. Talks delivered by invited research subject experts were interspersed with facilitated large group and smaller breakout group discussions. Key invited management and stakeholder representatives also discussed first-hand experiences with Russian olive as a conflict (invasive and beneficial) species in the western U.S., and provided details about the implementation and efficacy of current Russian olive IPM options. The symposium was ultimately initiated to help establish an atmosphere of dialogue and trust among researchers, policy makers, stakeholders and resource managers. This highly focused forum allowed participants to gain a common and updated understanding of many important aspects of the biology, ecology and management of Russian olive. This in turn contributed to productive dialogue, identifying, and hopefully mitigating conflicts of interests about the potential biological control of Russian olive. Nomenclature: Russian olive, Elaeagnus angustifolia L. ELGAN
... Successful invasion of riparian vegetation communities by exotic species can be detrimental for riparian biodiversity and ecosystem processes such as nutrient cycling, soil microbial processes, and substrate stability (Stohlgren et al. 1998, Richardson et al. 2007, DeMeester and Richter 2010. Likewise, alterations in riparian vegetation affect aquatic ecosystems, particularly streams and rivers (Mineau et al. 2012, Kominoski et al. 2013, Garc ıa et al. 2014). This is because many freshwater processes depend on surrounding riparian forests which provide shade, a physical barrier from uplands, channel stability, and litter inputs (Naiman and D ecamps 1997). ...
... systems (Bottollier-Curtet et al. 2011, Mineau et al. 2012, Garc ıa et al. 2014. Two competing hypotheses could explain either of the trends: (1) the "home-field advantage," suggesting that local decomposer fauna is adapted to local subsidies and thus native litter will be processed faster because it is the preferred substrate (Hunt et al. 1988, Freschet et al. 2012, and (2) invading plant taxa have traits which can be less deterrent to herbivores (e.g., reduced defense compounds in the leaves, higher N or phosphorus content) and thus will be processed faster (Baruch and Goldstein 1999, Allison and Vitousek 2004, Leishman et al. 2007. ...
Riparian habitats are highly susceptible to invasion and the spread of non-native plants. Many freshwater organisms and processes are dependent on allochthonous subsidies, and thus, riparian invasions are often associated with changes in aquatic ecosystems. We studied the potential effects of riparian plant invasions on instream decomposition and detritivore communities. We compared decomposition rates (k) of leaf litter from species native and invasive to coastal British Columbia, and the macroinvertebrate assemblages associated with the local and novel resource subsidy. Five native and five invasive species of riparian plants representing various growth forms (i.e., herbs, shrubs, and trees) were used in a litter bag experiment. Litter bags were distributed in stream-side experimental channels, ensuring similarity in background environmental conditions (substrate, flow, and temperature). Compared to native litter, the k-values of invasive plants were 2.6 times higher for herbs and 1.3 times higher for trees, while shrubs did not differ. Shrubs also decomposed significantly slower than trees and herbs. These patterns could be partially explained by the chemical properties of the litter. Throughout the whole experiment, decomposition rates were negatively related to the content of structural carbohydrates which tended to be higher in native leaves of herbs and shrubs. The k-values also had positive relationships with nitrogen content measured in the unconditioned and conditioned litter, and invasive plant species had some of the highest values of leaf nitrogen. We found no significant relationships between decomposition rates and the lignin content of the conditioned and unconditioned leaf litter. Taxonomic richness of all aquatic macroinvertebrates and densities of all aquatic macroinvertebrates and shredders were significantly higher on the invasive litter incubated for 21 but not for 53 d. Finally, richness of shredders explained the highest proportion of the variance in decomposition rates, when compared to other biological (all macroinvertebrate densities and richness) and litter chemistry variables. Our results indicate that riparian plant invasions are associated with changes in aquatic litter decomposition; however, the direction of the change is largely dependent on litter quality and plant identity rather than growth form or exotic status.
... Because riparian zones connect terrestrial and aquatic ecosystems, the spread of invasive plants in riparian forests has the potential to impact aquatic organisms and food webs linked through cross-ecosystem resource subsidies (Gregory et al. 1991;Hood and Naiman 2000;Baxter et al. 2005). This has been studied extensively in regards to the effects of invasive plants on leaf litter inputs and the aquatic invertebrate communities that depend on them (Lecerf et al. 2007;Mineau et al. 2012;Claeson et al. 2014;). However, less is known about the effects of invasive riparian plants on terrestrial invertebrate prey subsidies. ...
... This is especially true with invasive riparian plants that can cross ecosystem boundaries and impact both terrestrial and aquatic organisms linked through stream-riparian food webs (Baxter et al. 2005). While previous studies have examined the effects of riparian plants on leaf litter processing by aquatic invertebrate shredders (Mineau et al. 2012) or aquatic invasive species on stream-riparian food webs (Baxter et al. 2004(Baxter et al. , 2007Benjamin et al. 2013) or riparian invaders on aquatic insects (Burkle et al. 2012), this is the first attempt of which we are aware to document how the spread of an invasive riparian tree can affect stream fishes through a reduction in their terrestrial prey. While we documented that invasive EBC strongly affected terrestrial invertebrate communities in riparian forests, we did not see the reductions of terrestrial prey subsidies from invasive EBC extend to juvenile coho salmon. ...
The spread of invasive species in riparian forests has the potential to affect both terrestrial and aquatic organisms linked through cross-ecosystem resource subsidies. However, this potential had not been explored in regards to terrestrial prey subsidies for stream fishes. To address this, we examined the effects of an invasive riparian tree, European bird cherry (EBC, Prunus padus), spreading along urban Alaskan salmon streams, by collecting terrestrial invertebrates present on the foliage of riparian trees, their subsidies to streams, and their consumption by juvenile coho salmon (Oncorhynchus kisutch). Riparian EBC supported four to six times less terrestrial invertebrate biomass on its foliage and contributed two to three times lower subsidies relative to native deciduous trees. This reduction in terrestrial invertebrate biomass was consistent between two watersheds over 2 years. In spite of this reduction in terrestrial prey resource input, juvenile coho salmon consumed similar levels of terrestrial invertebrates in stream reaches bordered by EBC. Although we did not see ecological effects extending to stream salmonids, reduced terrestrial prey subsidies to streams are likely to have negative consequences as EBC continues to spread.
... Salix litter is neither as nitrogen rich as Alnus, and often not as palatable for consumers (Wipfli & Musslewhite, 2004;Going & Dudley, 2008). Increases in the abundance of more refractory litter will slow the overall speed of decomposition (Mineau et al., 2012;Handa et al., 2014). This in turn will potentially decrease the rate of release of finer particles supporting the productivity of the detrital component of the stream food web (Heard & Richardson, 1995;Jonsson & Malmqvist, 2005;Hladyz et al., 2011;Wallace et al., 2015). ...
... In cases where alder is not replaced by another tree species, the changes are likely to be even more profound. These changes can be projected from studies comparing forested and open streams (Stone & Wallace, 1998;Swank, Vose & Elliott, 2001;Kiffney, Richardson & Bull, 2003;McKie & Malmqvist, 2009;Schade et al., 2011;Mineau et al., 2012). These and several other studies show that loss of leaf litter input, shade and subsequent increase in radiation from sun have substantial effects on stream ecosystems. ...
1. Alder trees (Alnus spp.) are key nitrogen-fixing riparian species in the northern hemisphere.
Inputs of nitrogen-rich leaf litter from alder into stream food webs can contribute significantly to
nitrogen dynamics at local and landscape scales. Alder trees also provide habitats for terrestrial and
aquatic organisms, and help stabilize river banks.
2. Recently, substantial declines in alder stands have occurred along streams in Europe, with
damages observed in some parts of North America also. A major driver has been the invasive
oomycete pathogen Phytophthora alni species complex, which can spread rapidly along stream
networks.
3. This review synthesises information on the pathogen, processes of spread and infection, and its
impacts on alder. We further address the potential ecosystem-level and management consequences
of the decline of alder, and highlight research needs.
4. The alder dieback caused by P. alni is associated with reductions in shade and quality and
quantity of leaf litter. A decline in the structural integrity of branches and roots further threatens
bank stability. Stream banks dominated by other tree species or no trees at all will result in
ecosystem-level changes both above and below the waterline.
5. The P. alni taxonomic complex includes different species with varying phenotypes. An improved
understanding of their environmental tolerances, virulence and evolution, along with the processes
regulating the spread and impacts of the pathogen, would assist in identification of the riparian and
stream systems most vulnerable not only to invasion but also to the heaviest disease outbreaks and
ecosystem-level impacts.
6. Within the P. alni complex, the highly pathogenic hybrid species P. x alni is favoured by mild
winters and warm, but not excessively hot summer temperatures suggesting possible changes in
distribution and level of impact under future global climate change.
... For instance, inundation and temperature determine the recruitment and establishment of riparian species (Mosner et al., 2011) and influence the spread of exotics (Stokes et al., 2010). This can have consequences for in-stream detrital food webs when allochthonous material from invading riparian species is of lower nutritional quality (Hladyz et al., 2009;Hladyz et al., 2011;Mineau et al., 2012). Similarly, increased air temperature and atmospheric CO 2 concentrations can change the timing of leaf abscission and the palatability of leaf litter (Norby et al., 2003;Gunderson et al., 2012), with consequences for CPOM processing as well as for the composition and diversity of aquatic detritivores in streams (Kominoski et al., 2007;Dangles et al., 2011;Dray et al., 2014;Ferreira & Canhoto, 2014). ...
... All rights reserved. , 1996;Hassall et al., 2007;Doi, 2008;Rundio & Lindley, 2008;Brown et al., 2011Allan et al., 2003Chan et al., 2008Norby et al., 2003Gunderson et al., 2012Penuelas et al., 2007Kharuk et al., 2010;Stokes et al., 2010;Mineau et al., 2012;Perry et al., 2012 Community and species interactions: ...
Streams and adjacent terrestrial ecosystems are characterised by permeable boundaries that are crossed by resource subsidies. Although the importance of these subsidies for riverine ecosystems is increasingly recognised, little is known about how they may be influenced by global environmental change. Drawing from available evidence, in this review we propose a conceptual framework to evaluate the effects of global change on the quality and spatio-temporal dynamics of stream-terrestrial subsidies. We illustrate how changes to hydrologic and temperature regimes, atmospheric CO2 concentration, land-use, and the distribution of non-indigenous species can influence subsidy fluxes by affecting the biology and ecology of donor and recipient systems and the physical characteristics of stream-riparian boundaries.
... Similarly, within aquatic systems there is heterogeneity in resource use among subhabitats , with some demonstrating that carbon produced by periphyton is more readily transferred up food webs compared to phytoplankton-derived carbon (Bunn et al. 2003, Jardine et al. 2013). Diet quality is often poorly considered in food-web studies, and usually only includes aspects such as food lability and palatability (Marcarelli et al. 2011, Mineau et al. 2012 or search and handling times and energy gains from consuming certain prey (e.g., Baxter 2010, Giacomini et al. 2013). This is despite the fact that there are nutritional aspects of diet governed by its biochemical composition; including N and P content, protein, vitamins and minerals, and polyunsaturated fatty acids (PUFA), that, if not provided as required, constrain animal growth and reproduction (Holt 2011). ...
... Consideration of PUFA in food-web models becomes particularly important when environmental change alters the flow of organic matter and essential compounds to higher trophic levels (Bunn et al. 1999, Greig et al. 2011. Beyond the replacement of native with invasive species (Mineau et al. 2012), human-induced changes to aquatic ecosystems have the potential to limit PUFA supply to the top of the food web (Mu¨ller-Navarra et al. 2004). In-stream barriers to anadromous fish migration and large-scale clearing of riparian zones can interrupt PUFA delivery from subsidies. ...
Few studies measure multiple ecological tracers in individual organisms, thus
limiting our ability to differentiate among organic matter source pathways and understand
consequences of dietary variation and the use of external subsidies in complex food webs. We
combined two tracers, stable isotope (SI) ratios and fatty acids (FA), to investigate linkages
among ecological compartments (water column, benthos, riparian zone) in food webs in
waterholes of a dryland river network, the Border Rivers in southwestern Queensland,
Australia. Comprehensive analyses of sources (plankton, periphyton, leaf litter, riparian
grasses) and animals (benthic insects, mollusks, large crustaceans, fishes) for SI and FA
showed that all three zones contribute to animal biomass, depending on species and life stage.
Large fishes derived a subsidy from the riparian/floodplain zone, likely through the
consumption of terrestrial and semi-aquatic insects and prawns that fed on detritivorous
insects. Importantly, post-larval bony bream (Nematalosa erebi ) and golden perch (Macquaria
ambigua) were tightly connected to the water column, as evidenced by 13C-depleted, 15Nenriched
isotope ratios and a high content of plankton-derived polyunsaturated fatty acids
(eicosapentaenoic acid [EPA; 20:5x3] and docosahexaenoic acid [DHA; 22:6x3]). These
observations were consistent with expectations from nutritional requirements of fish early life
stages and habitat changes associated with maturity. These results highlight the importance of
high-quality foods during early development of fishes, and show that attempting to attribute
food-web production to a single source pathway overlooks important but often subtle
subsidies that maintain viable populations. A complete understanding of food-web dynamics
must consider both quantity and quality of different available organic matter sources. This
understanding can be achieved with a combined SI and FA approach, but more controlled
dietary studies are needed to estimate how FA profiles are modified by animals when
consuming a diverse range of diets of variable quality.
Key words: arachidonic acid; benthic habitat; Border Rivers, Queensland, Australia; diet quality;
docosahexaenoic acid; eicosapentaenoic acid; essential fatty acids; food-web subsidies; polyunsaturated fatty
acids; stable isotopes; terrestrial organic matter; water column.
... The loss or invasion of a species in one habitat can change fluxes of materials and organisms within habitats and to adjacent or distant habitats, with consequences for food webs and ecosystem processes (Baxter et al. 2005, Mineau et al. 2012. Kate Boersma and colleagues documented decreased trophic trait diversity, specifically, the disappearance of top predators, in arid river systems in response to habitat fragmentation. ...
... Initially, Colden Baxter and colleagues described how the invasion of western U.S. riparian areas by Russian olive has altered stream organic matter budgets and nutrient dynamics. They suggested these changes were due to the ability of the invader to fix nitrogen, and because Russian olive produces low-quality leaf litter which decomposes slowly and is underutilized by native stream animals (Mineau et al. 2012). Conversely, Weston Nowlin and colleagues documented increased leaf litter decomposition rates in the presence of an invasive armored catfish, Hypostomus, in Texas rivers. ...
... Additionally, invasive plants can alter soil properties, nutrient cycling, and microbial communities, which in turn affect the overall health and functionality of streams (Qu et al., 2021;Vujanović et al., 2022). Such alterations in riparian vegetation can have profound effects on stream baseflow and ecosystem efficiency (Mineau et al., 2012;Vanderklein et al., 2013). Therefore, understanding the effects of invasive alien plants on stream physical and chemical Acacia invasions also alter aquatic conditions by raising pH, reducing ammonium content through processes like nitrification, and increasing total dissolved solids . ...
Acacia invasion has shown a negative impact on the water resources of forest streams. Therefore, studies need to be conducted demonstrating the importance of managing invasive species to preserve stream and forest ecosystems. This study investigates the effects of Acacia invasion on the water quality of Kerangas forest streams in Brunei. Water samples were collected from an Acacia-invaded (IN) stream and a non-invaded (NIN) stream during the dry season at three locations along each stream. Water properties, including pH, conductivity, salinity, total dissolved solids (TDS), phosphate, nitrate, ammonia, and nitrite, were analyzed using in situ and laboratory methods. The results showed that Acacia invasion significantly increased pH (from 4.01 to 5.68), nitrate (by 256%), and phosphate (by 250%) levels, while reducing conductivity (by 208%) and salinity (by 20%) compared to non-invaded streams. These findings suggest that Acacia invasion alters water chemistry, potentially posing risks to aquatic ecosystems. Effective management strategies, such as controlling Acacia spread and restoring native vegetation, are essential to mitigate these impacts and preserve forest water resources.
... It is hypothesized that monocultures of riparian vegetation would alter ecosystems by altering trophic structure and biodiversity compared to native and more diverse vegetation communities. Some authors have studied the effect of changes in allochthonous inputs, nutrients and decay rates by plant species in the Pacific Northwest, however it is challenging to relate the change in plant composition to change in biological function, and the effect of invasive vegetation differs depending on the invasive species (e.g., Braatne et al., 2007;Mineau et al., 2012). Using an approach to relate the most common invasive weeds in the Western U.S. to biological function, Ringold et al. (2008) observed that instream biotic integrity was lower when even a single invasive plant target taxon was present than when invasive plant species were absent. ...
A companion to the Stream Function Assessment Method (SFAM) for Oregon User Manual, this Scientific Rationale documents the development and scientific underpinning of the method. It supports a deeper critical understanding of the method, provides transparency, facilitates the transfer and adaptation of SFAM, and promotes ongoing improvements as new data and information becomes available. SFAM was designed to evolve as science advances; the current document (Version 2.0) incorporates and describes data and research newly available since 2018 (Version 1.0).
To inform compensatory mitigation, an independent stream mitigation accounting protocol integrates assessment of functions and values using SFAM outputs, resulting in credit (offset) and debit (impact) calculations. The mitigation accounting protocol used with SFAM as well as Oregon’s statewide function and watershed-based stream mitigation program, were recently described (JAWRA: https://doi.org/10.1111/1752-1688.13225). SFAM components (User Manual, Scientific Rationale, Workbook, GIS Tool) can be accessed here: https://www.oregon.gov/dsl/wetlands-waters/pages/assessment-tools.aspx
... For instance, the invasion of riparian forests by nitrogen (N)-fixing species can increase aquatic N concentrations (e.g., Atwood et al., 2010;Goldstein et al., 2009;Mineau et al., 2011;Stewart et al., 2019;Wiegner et al., 2013) and alter N cycles (Mineau et al., 2011;Stewart et al., 2019), especially in ecosystems where N-fixers were formerly absent or present in low abundances. If N-fixing species differ in patterns of deciduousness from dominant native species, they can also alter litterfall dynamics in the riparian vegetation (Mineau et al., 2012;Railoun et al., 2021). ...
Small streams and their riparian vegetation are closely linked ecosystems. Thus, the invasion of native riparian forests with non-native species can impact stream ecosystems.
We assessed the effects of the invasion of broadleaf deciduous forests by evergreen, nitrogen-fixing Acacia species on seasonal variation of relevant instream environmental variables, litterfall in the riparian area, aquatic decomposers, and leaf litter decomposition, by comparing three streams flowing through native forests (native streams) and three streams flowing through invaded forests (invaded streams) in central Portugal. Invaded streams flow through forests composed (almost) of monospecific stands of Acacia trees.
Litterfall in the riparian area was sampled with fabric traps and sorted into five categories: leaf (including phyllodes), flower, fruit and seed, wood litter, and other materials. Aquatic hyphomycete conidia suspended in water were sampled to assess conidia concentration and community composition. Leaf litter of Quercus robur was enclosed in coarse-mesh bags and incubated in streams to assess decomposition rates and associated macroinvertebrate density and community composition. Samples from each variable were collected monthly from streams over 1 year.
Aquatic hyphomycete conidia concentration was higher in invaded streams in spring/summer when litter inputs, water temperature, and aquatic nutrient concentrations were higher. In contrast, conidia concentration was lower in invaded streams in autumn/winter as they received less native deciduous leaf litter in autumn than native streams. Aquatic hyphomycete community structure changed, and species richness was lower in invaded streams because aquatic nutrient concentrations were higher and leaf litter species richness was lower.
Macroinvertebrate and shredder density in decomposing leaf litter did not differ between native and invaded streams, but litter bags may have artificially increased densities by providing high quality food and/or refuges in streams with poor-quality resources. Nevertheless, macroinvertebrate community structure changed, and family richness was lower in invaded streams.
Finally, decomposition rates of Q. robur leaf litter in coarse-mesh bags were similar between stream types, despite differences in aquatic decomposer communities.
Overall, Acacia invasion changed water quality, litterfall seasonality and composition, and aquatic decomposer communities (especially aquatic hyphomycetes). However, Acacia effects on macroinvertebrate density and leaf litter decomposition rates were less pronounced, suggesting that higher trophic levels may be more resilient to invasion than basal levels, or the invasion time/extent in our invaded streams was not strong enough to affect macroinvertebrates and associated processes. Instream invasion effects on aquatic hyphomycete communities were more strongly mediated by changes in litter inputs rather than increases in aquatic nutrient concentrations because they remained oligotrophic in invaded streams. Simplification of riparian and aquatic communities may render them less efficient in coping with additional environmental changes. Acacia effects might be mitigated by the maintenance of a riparian corridor composed of native vegetation. The protection of non-invaded riparian galleries and restoration of invaded ones could protect and restore stream ecosystems.
... Elaeagnus angustifolia (Russian olive) is a major riparian invader in western North America, forming closed shrub canopies that inhibit plant establishment and change the habitat structure of river corridors (Stannard et al. 2002, Shafroth et al. 2010, Scott et al. 2018). This extensive invasion affects plant community trajectories and successional outcomes, and can alter both water and soil nutrients in riparian zones with persistent legacy effects (Katz and Shafroth 2003, Mineau et al. 2012, Tuttle et al. 2016, Schantz et al. 2017, Katz et al. 2020. For instance, Katz et al. (2020) detected low native and high exotic species cover and elevated soil N in formerly E. angustifolia-invaded plots relative to un-invaded plots three years after removal. ...
... As discussed earlier, riparian vegetation and its inputs of leaf litter into the stream are critical to the food web and biogeochemical dynamics in streams, so changes in dominant riparian vegetation species can influence these aspects of stream ecosystems as well. Russian olive (Elaeagnus angustifolia) is another invasive riparian tree species in the western US, and its presence is associated with 25 times more leaf litter input to streams, increasing benthic organic matter storage while decreasing the efficiency of stream respiration relative to organic matter input (Mineau et al., 2012). In-stream nutrient dynamics are also affected by the Russian olive as it is a nitrogen-fixer, and stream reaches invaded by it have greater N concentrations and reduced N limitation of stream biofilms (Mineau et al., 2011). ...
... Changes in the quantity or quality of these sources may have bottom-up effects on organisms that directly consume the allochthonous resource [e.g., microbial (bacteria, fungi, and microeukaryotes) communities and macroinvertebrate shredders] and on other functional feeding groups that directly and indirectly consume them, such as predators and collector-filterers (Cummins 1974;Wallace et al. 1997). Recent studies showed dense mats of sedges (Carex spp.) often dominated canopy gaps following EAB invasion of riparian forests , potentially altering in-stream leaf decomposition given the differences in leaf litter quality and quantity (Ehrenfeld et al. 2001;Knight et al. 2007;McNeish et al. 2012;Mineau et al. 2012). Additionally, dead ash trees will eventually result in an influx of CWM into forest ecosystems and potentially into stream ecosystems where CWM plays an important ecological role (Higham et al. 2017). ...
Emerald ash borer (EAB) has killed millions of ash trees in the United States and Canada, yet impacts on terrestrial-aquatic linkages are largely unknown. Ash tree death along streams creates canopy gaps, increasing light to riparian plants and potentially affecting organic matter subsidies. Six EAB-related canopy gaps along streams across a gradient of timing of EAB invasion in Michigan were characterized for coarse woody material (CWM), terrestrial and aquatic leaf litter and their associated bacterial communities, and macroinvertebrates upstream, downstream, and at the center of the gap. Stream sites downstream of EAB-related canopy gaps had significantly lower dissolved oxygen and macroinvertebrate diversity than sites upstream and at the gaps. Yet there was no difference in CWM or aquatic leaf litter, likely due to downstream movement of organic matter from upstream riparian sources. Low abundance bacterial amplicon sequence variants unique to gap or forest were detected in leaves and leaf litter, suggesting that EAB-related canopy gaps altered leaf-associated bacterial communities. Overall, EAB invasion indirectly impacted some variables, while organic matter dynamics were resistant to change.
... Exotic plant invasions that alter the plant community in riparian forests can influence aquatic organisms and alter stream ecosystem function (e.g., Richardson et al. 2007). For example, invasive plant leaves may have different decay rates than native species, altering instream organic matter cycling (Swan et al. 2008;McNeish et al. 2012;Mineau et al. 2012). Some work suggests that riparian invasion alters stream geomorphology (Fei et al. 2014) and can result in additions of woody materials with unique characteristics into aquatic systems (Tabacchi and Planty-Tabacchi 2003). ...
The ecology of headwater streams is tightly linked to the riparian zone through organic matter subsidies which are highly susceptible to alteration due to biological invasion. Lonicera maackii is a non-native shrub that is a highly successful invader of headwater stream riparian zones in the American Midwest. We assessed effects on benthic macroinvertebrates across a gradient of invasion intensity from references sites with minimal invasion to a site that had a very heavy invasion. Benthic macroinvertebrates were sampled throughout the year and compositional differences were assessed using Non-metric Multidimensional Scaling ordination, and by comparing the prevalence of sensitive (Ephemeroptera, Plectoptera, and Trichoptera: EPT) and tolerant (Chironomidae) macroinvertebrate taxa. We found strong evidence of variation among macroinvertebrate communities across the invasion gradient (ANOSIM R = 0.215, P = 0.004) and particularly strong separation between one of our reference sites with minimal invasion and the site with the heaviest invasion. Analysis of EPT taxa indicated a significant overall effect and pairwise comparisons indicated that the site with the heaviest invasion had the lowest percentage of sensitive taxa (P < 0.05). Our analysis of chironomids did not yield a statistically discernable effect, although the pattern of the data suggest higher dominance in the site with the heaviest invasion. These stream-scale results bolster prior laboratory and field experiments and provide evidence that terrestrial invasion of L. maackii impacts the benthic community present in headwater streams. These results provide impetus to re-focus stream management recommendations to include practices that control invasive plants in riparian forests.
... Changes in the presence of a species within meta-ecosystem food webs could also lead to a change in the exchange of resources within the meta-ecosystem [6]. For example, the addition of an invasive plant in the riparian zone of a stream can increase the amount of transferred organic material to the freshwater ecosystem [7]. ...
Reciprocal subsidies link ecosystems into meta-ecosystems, but energy transfer to organisms that do not cross boundaries may create sinks, reducing reciprocal subsidy transfer. We investigated how the type of subsidy and top predator presence influenced reciprocal flows of energy, by manipulating the addition of terrestrial leaf and terrestrial insect subsidies to experimental freshwater pond mesocosms with and without predatory fish. Over 18 months, fortnightly addition of subsidies (terrestrial beetle larvae) to top-predators was crossed with monthly addition of subsidies (willow leaves) to primary consumers in mesocosms with and without top predators (upland bullies) in a 2 × 2 × 2 factorial design in four replicate blocks. Terrestrial insect subsidies increased reciprocal flows, measured as the emergence of aquatic insects out of mesocosms, but leaf subsidies dampened those effects. However, the presence of fish and snails, consumers with no terrestrial life stage, usurped and retained the energy within in the aquatic ecosystem, creating a cross-ecosystem bottleneck to energy flow. Thus, changes in species composition of donor or recipient food webs within a meta-ecosystems can alter reciprocal subsidies through cross-ecosystem bottlenecks.
... It is hypothesized that monocultures of riparian vegetation would alter ecosystems by altering trophic structure and biodiversity compared to native and more diverse vegetation communities. Some authors have studied the effect of changes in allochthonous inputs, nutrients and decay rates by plant species in the Pacific Northwest, however it is challenging to relate the change in plant composition to change in biological function, and the effect of invasive vegetation differs depending on the invasive species (e.g., Braatne et al., 2007;Mineau et al., 2012). Using an approach to relate the most common invasive weeds in the Western U.S. to biological function, Ringold and coauthors (2008) observed that instream biotic integrity was lower when even a single invasive plant target taxon was present than when invasive plant species were absent. ...
This Scientific Rationale, a companion to the Stream Function Assessment Method (SFAM) for Oregon (Nadeau et al., 2020) describes the scientific underpinning of the method, supports a deeper critical understanding and provides transparency. SFAM has been developed to provide a standardized, rapid, more function-based method for assessing stream function statewide. It is intended to further federal and state regulatory objectives by informing mitigation planning. The method development process, from conception through measure development, iterative field testing and statistical method (model) analysis, and the relationship of measures to assessed functions and values is described. A scientific rationale for individual function and value measures is provided, including a detailed description of the standard performance index for each function measure and establishment of a standard index scale to give ecological meaning to measure scores. The current version (1.1) reflects updates to maintain consistency with revisions made to other components of SFAM to produce SFAM Version 1.1.
... For instance, inundation and temperature determine the recruitment and establishment of riparian species (Mosner et al., 2011) and influence the spread of exotics ( Stokes et al., 2010). This can have consequences for in-stream detrital food webs when allochthonous material from invading riparian species is of lower nutritional quality ( Hladyz et al., 2009Hladyz et al., , 2011Mineau et al., 2012). Similarly, increased air temperature and atmospheric CO 2 concentrations can change the timing of leaf abscission and the palatability of leaf litter ( Norby et al., 2003;Gunderson et al., 2012), with consequences for CPOM processing as well as for the composition and diversity of aquatic detritivores in streams ( Kominoski et al., 2007;Dangles et al., 2011;Dray et al., 2014;Ferreira & Canhoto, 2014). ...
Stream and river ecosystems provide subsidies of emergent adult aquatic insects and other resources to terrestrial food webs, and this lotic–land subsidy has garnered much attention in recent research. Here, we critically examine a list of biotic and abiotic variables—including productivity, dominant taxa, geomorphology, and weather—that should be important in affecting the nature of these subsidy dynamics between lotic and terrestrial ecosystems, especially the pathway from emergent aquatic insects to terrestrial predators. We also explore how interactions between these variables can lead to otherwise unexpected patterns in the importance of aquatic subsidies to terrestrial food webs. Utilizing a match-mismatch framework developed previously, we identify how these variables and interactions may be affected by a broad suite of stressors in addition to contaminants: climate change, land-use conversion, damming and water abstraction, and species invasions and extinctions. These stressors may all act to modify and potentially exacerbate the effects of contaminants on subsidies. The available literature on many variables is sparse, despite strong theoretical underpinnings supporting their importance for lotic–land subsidies. Notably, these understudied variables include those related to physical geomorphology and the structure of the stream/river and floodplain/riparian zone as well as species-specific interactions between aquatic and terrestrial organisms. We suggest that more explicit characterization of these variables and more research directly linking broad-scale stressors to subsidy resource-consumer interactions can help provide a more mechanistic understanding to lotic–land subsidy dynamics within a changing environment.
... However, a study on the effects of riparian Russian olive (Elaeagnus angustifolia L.) on in-stream nutrient availability in Idaho and Wyoming showed invaded stream reaches had elevated total dissolved N concentrations (Mineau et al., 2011). The excessive N 2 fixation from Russian olive appeared to be delivering N and C to the streams via leaf litter and root leaching, thereby demonstrating how some riparian vegetation can be a source of N instead of an N sink (Mineau et al., 2012). There are only four studies that have characterized the influence of autumn olive stands on N loss in soil or stream water (Baer et al., 2006;Goldstein et al., 2009;Goldstein et al., 2010;Aljobeh et al., 2016). ...
Autumn olive (Elaeagnus umbellata Thunb.) is an invasive and exotic N2–fixing plant species found throughout the United States. Proliferation and spread of autumn olive have displaced native plants and raised concerns about the effects of N fixation and cycling on water quality in invaded areas. This study investigated the relationship between autumn olive cover and stream N concentrations. Twelve forested watersheds were selected and classified into edge, mid‐distance, and interior‐of‐the‐forest watersheds based on autumn olive density and distance from the permanent edge of invasion point along a major road corridor. For the 2012 vegetation survey, autumn olive cover in edge, mid, and interior watersheds ranged from 37 to 61%, 18 to 37%, and 4 to 10%, respectively. From 2006 to 2012, mean stream water NO3–N concentration in the edge watersheds was significantly higher (1.39 mg L⁻¹, p < 0.0001) than mid (0.37 mg L⁻¹) and interior (0.27 mg L⁻¹) watersheds. A linear relationship was found between NO3–N concentration and autumn olive cover (R² = 0.72, p = 0.0001). Mean stream water NH4–N, specific conductivity, and pH were significantly less in the interior watersheds than in the edge watersheds. Additionally, peak specific conductivity and NO3–N from edge watersheds coincided with peak stage for these watersheds, demonstrating that N flushing events were driven by surface and shallow subsurface flow pathways proximal to the stream. Results from this study demonstrate how encroachment of autumn olive can influence water quality and transform biogeochemical cycles in natural systems, which points to the need for effective management of autumn olive in the edge watersheds and riparian zones that are vulnerable to invasion and increased N export.
Core Ideas
Substantial autumn olive cover was found along riparian habitats in marginal forest.
Autumn olive invasion in interior‐of‐the‐forest watersheds was lowest.
Encroachment of autumn olive can influence water quality.
Autumn olive invasion can transform biogeochemical cycles in natural systems.
Autumn‐olive‐invaded edge watersheds had greatest N concentrations in stream water.
... Tamarix chinensis Lour cannot meet the needs of urban greening and Fraxinus velutina Torr, Robinia pseudoacacia L, Salix matsudana Koidz and E. angustifolia are introduced to be the ornamental tree species. Our results show that E. angustifolia cannot vegetatively reproduce and the young seedlings from seeds grow very slowly because of high soil salinity (results are not listed) and will be killed by the surrounding halophyte weeds without human intervention, which is different from that the species grow in invading riparian corridors in the western United States (Mineau et al. 2012) and in Nebraska (Miller et al. 2010). E. angustifolia on the Yellow River Delta cannot overcome two major barriers (survival and reproduction) without artificial assistance according to the unified framework (Blackburn et al. 2011) so it could not be a potential invasive plant on the Yellow River Delta. ...
Key message
Our manuscript showed that Elaeagnus angustifolia L. can be introduced to the Yellow River Delta of China and planting E. angustifolia was beneficial effects on the soil system.
Abstract
The saline soil of the Yellow River Delta of China is not suitable for the growth of crop and afforestation seedlings due to high salt content, high underground water level, and deficiencies in organic matter, nitrogen and phosphorus, which limits urban road greening around the Yellow River Delta. Elaeagnus angustifolia L. (E. angustifolia) is a member of the Elaeagnaceae family, which is a deciduous shrub or small tree. Due to its good resistance, E. angustifolia has been planted widely in the western region of China, and it has been used for wind breaking, landscaping and sand stabilization. Furthermore, E. angustifolia seedlings were introduced to the Yellow River Delta due to its strong stress and adaptive growth response, which were studied in 2014 and 2015. The results revealed that the seedlings of E. angustifolia grew well with high relative growth rates, big crowns, thick basal diameter, thick diameter at the breast height, and many branches, especially during the second year. Planting E. angustifolia on the Yellow River Delta significantly decreased its salt content, and increased its content of organic matter, nitrogen and phosphorus, as well as the number of fungus, bacteria, salt-tolerant bacteria, actinomycetes and salt-tolerant actinomycetes, especially after planting E. angustifolia for two consecutive years. In conclusion, E. angustifolia seedlings can grow well in the saline soil of the Yellow River Delta with a large biomass. In turn, planting E. angustifolia could improve saline soil properties. Hence, E. angustifolia can be a potential local greening tree species.
... within the 21 st century (Pearce and Smith 2001;Lesica and Miles 1999). As a N 2 -fixing species, Russian olive potentially functions as a so-called 'transformer' invasive species (D' Antonio et al. 2004) due to its ability to alter both terrestrial and benthic nutrient and community dynamics in invaded riparian areas (Mineau et al. 2012(Mineau et al. , -2011Shah et al. 2010;Reynolds and Cooper 2010). Indirect effects of Russian olive, such as the intensification of beaver attack on increasingly reduced stands of native tree species, can alter riparian vegetation community structure and composition (Lesica and Miles 2004). ...
An online survey was distributed through email lists provided by various stakeholder groups on behalf of the International Consortium for Biological Control of Russian Olive in spring of 2012. A total of 392 respondents replied from 24 U.S. states and 1 Canadian province. Questions posed in the survey were designed to identify and categorize 1) stakeholders by geographic location, profession and professional affiliation; 2) stakeholder perceptions of Russian olive as a problematic and/or beneficial organism; 3) by ecological, economic and geographic scale stakeholders' perceived benefits and/or detriments associated with Russian olive; and 4) potential benefits and/or risks stakeholders thought might arise from the implementation of a classical biological control program for Russian olive. The survey also asked stakeholders to suggest additional research to improve understanding both of Russian olive and Russian olive biological control. The survey link was widely distributed and respondents were given from February through May 2012 to complete the questionnaire. The questionnaire was highly informative because it included many opportunities for respondents to provide detailed responses in their own words. Nomenclature: Russian olive, Elaeagnus angustifolia L., ELGAN
... Whereas studies into the effects of naturalized Russian olive on bird communities remain contradictory (Fischer et al., 2012;Stoleson & Finch, 2001), it is clear that Russian olive leaf litter can significantly increase N input to soils (DeCant, 2008) and in some riparian settings, facilitate the invasion of other non-native plant species (Tuttle, Katz, Friedman, & Norton, 2016). Russian olive has been shown to dramatically increase organic matter inputs to streams (Mineau, Baxter, Marcarelli, & Minshall, 2012) and has the potential to influence aquatic ecosystems through shading, hydrologic, and geomorphic effects (Katz, 2016). Our results suggest that Russian olive was directly involved in the most recent episode of channel narrowing along the Escalante River, resulting in levee formation and channel simplification. ...
Along rivers, native and invasive species may establish and persist on active channel bedforms as part of channel narrowing. Using historical aerial photography and dendrochronology, we quantified spatial and temporal patterns of narrowing and vegetation expansion, including native Fremont cottonwood (Populus fremontii) and non‐native Russian olive (Elaeagnus angustifolia), along the largely unregulated Escalante River in southwestern USA. Russian olive establishment was examined with respect to hydrologic and climate variables. Narrowing along the Escalante River was initiated during a mid‐20th century drought. Cottonwood rapidly colonized higher, bar surfaces between the 1950s and 1981. Small numbers of Russian olive established in moist sites during this period as the channel narrowed by nearly 80%. After 1981, there was no obvious cottonwood establishment but low channel bars and banks were rapidly colonized by Russian olive. Hydroclimate predictors were equivocal but exponential growth of this large‐seeded, shade‐tolerant species lagged its introduction by 30 years, apparently because of delayed reproductive maturity, limited seed availability and widespread availability of favorable establishment sites following initial channel narrowing. Sediment trapping, levee formation and modification of channel form by dense, channel‐edge bands of Russian olive progressively limited new establishment sites and by 2000, recruitment declined sharply. Our results have implications for management of non‐native tree invasions along arid‐region rivers, including identification of low, moist, active channel bars where the establishment and physical impacts of Russian olive appear to be most pronounced and where focused management efforts are likely to be most effective.
... Riparian invasive plants can have substantial impacts on terrestrial-aquatic linkages via alteration of these subsidies (Greene 2014;McNeish et al. 2015). For example, Russian-olive (Elaeagnus angustifolia L.) is a riparian invasive tree in the western United States known to increase instream terrestrial organic matter subsidies and organic nitrogen, altering stream ecosystem efficiency and biogeochemistry (Mineau et al. 2011(Mineau et al. , 2012. Tree-of-heaven [Ailanthus altissima (Mill.) ...
Riparian plant invasions can result in near-monocultures along stream and river systems, prompting management agencies to target invasive species for removal as an ecological restoration strategy. Riparian plant invaders can alter resource conditions in the benthos and drive bottom-up shifts in aquatic biota. However, the influence of management activities on the structure and function of aquatic communities is not well understood. We investigated how removal of a riparian invader, Lonicera maackii (Amur honeysuckle), influenced aquatic macroinvertebrate community functional and taxonomic diversity in a headwater stream. We hypothesized that removal of L. maackii from invaded riparia would result in ( H1 ) increased aquatic macroinvertebrate abundance, density, and diversity; ( H2 ) a taxonomic and functional shift in community composition; and, in particular, ( H3 ) increased functional diversity. Aquatic macroinvertebrates were sampled monthly from autumn 2010 to winter 2013 in headwater stream riffles with a dense riparian L. maackii invasion and those where L. maackii had been experimentally removed. We found macroinvertebrate density was significantly higher in the L. maackii removal reach ( P <0.05) and that macroinvertebrate community structure and functional trait presence was distinct between stream reaches and across seasons ( P <0.05). The removal reach exhibited greater functional richness during spring and summer and had more unique functionally relevant taxa (20% and 85%) compared with the L. maackii reach (5% and 75%) during summer and autumn seasons. Our results suggest bottom-up processes link restoration activities in the riparian corridor and aquatic biota through alterations of functional composition in the benthic community.
... Biological invasions are stressors to ecosystem processes (Crooks 2002), and are an integral driver of global environmental change (Vitousek et al. 1997). Invasive species can greatly alter their surroundings by exploiting limiting resources (e.g., Kennedy and Hobbie 2004;Baxter et al. 2004), by altering nutrient cycles (e.g., Collins et al. 2011), and changing organic matter budgets (e.g., Mineau et al. 2012), to name a few. Although the negative effects of exotic species have been described for individuals and whole ecosystems alike, simultaneous investigations of impacts across biological levels of organization are rare (Simon and Townsend 2003). ...
Bighead carp (Hypophthalmichthys nobilis) are an invasive planktivore that can greatly deplete planktonic resources. Due to the inefficient conversion of food into fish tissue, large portions of consumed materials are egested and shunted to benthic habitats. We explored how bighead carp alter pools of organic matter between planktonic and benthic habitats, and across ecosystem boundaries. Here, we report evidence from a manipulative experiment demonstrating that bighead carp greatly reapportion pools of organic matter from planktonic to benthic habitats to such a degree that additional effects propagated across ecological boundaries into terrestrial ecosystems. Strong direct consumption by bighead carp reduced filamentous algae, biomass and production of zooplankton, and production of a native planktivorous fish within planktonic habitats. Reduced herbivory indirectly increased phytoplankton (chlorophyll a). Direct consumption of organic matter by bighead carp supported high carp production and concomitant losses of materials due to egestion. Perhaps in response to organic matter subsidies provided by fish egestion, ponds having bighead carp had higher standing crop biomass of Chironomidae larvae, as well as cross-boundary fluxes of their adult life stage. In contrast, we detected reduced cross-boundary fluxes of adult Chaoboridae midges in ponds having bighead carp. Consideration of bighead carp as mediators of organic matter exchanges provides a clearer framework for predicting the direct and extended impacts of these invasive planktivores in freshwater ecosystems. The perception of bighead carp must evolve beyond competitors for planktonic resources, to mediators and processors of nutrients and energy within and across ecosystems.
... The leaves of common buckthorn decompose five to seven times faster than common native species (green ash Fraxinus pennsylvanica, and American elm Ulmus americana; Freund et al., 2013) in headwater streams. This rapid decomposition of common buckthorn is in contrast to many previously studied riparian invasive trees (e.g., eucalyptus (Eucalyptus globus), Canhoto and Graça, 1996; melaleuca (Melaleuca quinquenervia), Martin et al., 2010; Russian olive (Elaeagnus angustifolia), Mineau et al., 2012) that have very tough or waxy leaves that make them more recalcitrant to decomposition. ...
Decomposition of allochthonous organic matter that enters shaded headwater streams during a short autumn leaf fall period provides much of the energy the streams receive throughout the year. As such, alterations of riparian communities, including those resulting from invasive species, should have a significant impact on these energy inputs and potentially alter microbial communities and the behavior of shredders that process leaf litter. We compared consumption of leaves of an abundant native species (green ash Fraxinus pennsylvanica) and nonnative species (common buckthorn Rhamnus cathartica) by the northern spring amphipod Gammarus pseudolimnaeus, with and without periods of stream conditioning. Amphipods consumed a very small proportion of the unconditioned leaves of common buckthorn and green ash and demonstrated no significant preference for the unconditioned leaves of either species. When leaves were stream-conditioned, there was a significant interaction between the effects of leaf species and days of stream conditioning on both the mass and area of leaf disks consumed by the amphipods. Overall there was a greater consumption of buckthorn leaves compared to ash, with peak consumption occurring during a narrower range of conditioning times for buckthorn. Common buckthorn's higher overall consumption level is expected to provide rapid and short-lived input of energy into the stream, in marked contrast to the slower and more sustained input from native green ash. These results suggest there may be significant changes in the organic matter dynamics of stream ecosystems throughout the Midwest as common buckthorn continues its expansion and green ash declines with the invasion of emerald ash borers (Agrilus planipennis).
... Merr.) is an invasive, nitrogen-fixing legume found in the southeastern USA, which significantly increased net N mineralization, nitrification, and nitric oxide emissions from invaded soils by more than 100% (Hickman et al. 2010). Mineau et al. (2012) found the riparian invasive tree Russian olive (Elaeagnus angustifolia L.) substantially increased terrestrial organic-matter subsidies and retention of leaf organic matter in a stream system, resulting in an estimated 14% decrease in stream ecosystem efficiency (ratio of ecosystem respiration to organic matter input). In a meta-analysis of 199 articles presenting data related to invasive species effects, it was found that, although presence of invasive species tends to result in a decline of local native species, many plant invasions result in increased ecosystem function (Vilà et al. 2011). ...
Invasive species are of global importance because of their impacts on ecological communities, habitat structure, native community dynamics, and ecosystem processes and function. Scientists and conservation managers are increasingly focusing on the biological impacts of invasive species and on devising management practices that emphasize the health of ecosystems based on measured biological processes. Amur honeysuckle (Lonicera maackii (Rupr.) Herder) is a highly successful invasive shrub in forests of eastern North America. The scientific literature surrounding this species has grown in the past several decades as researchers have investigated L. maackii impacts across multiple ecological scales. In this review we synthesized literature on (a) the key traits related to this species' invasion success, (b) the impacts this invasive species has at various ecological scales, (c) the outcomes of restoration efforts for this species, and (d) the connections of this weed to invasion ecology theories. Lonicera maackii impacts are complex and vary across ecosystems and spatial scales; we report findings from studies demonstrating a wide range of effects on species composition, community structure, ecosystem function, and successional trajectories. We end by providing a working ecological framework that may help guide future research and conservation efforts.
... Thus, the predicted stream ecosystem efficiency (i.e. ecosystem respiration/ organic matter input) reduced 14%, and it was a stress for the stream ecosystem [137,138]. The effects of nonnative species on recipient ecosystems may be quantity dependent. ...
Riparian zone provides a variety of resources to organisms, including availability of water and subsidies. Water availability in riparian areas influences species distribution and trophic interaction of terrestrial food webs. Cross-ecosystem subsidies as resource flux of additional energy, nutrients, and materials benefit riparian populations and communities (e.g. plants, spiders, lizards, birds and mammals). However, aquatic ecosystems and riparian zones are prone to anthropogenic disturbances, which change water availability and affect the flux dynamics of cross-system subsidies. Yet, we still lack sufficient empirical studies assessing impacts of disturbances of land use, climate change and invasive species individually and interactively on aquatic and riparian ecosystems through influencing subsidy resource availability. In filling this knowledge gap, we can make more effective efforts to protect and conserve riparian habitats and biodiversity, and maintain riparian ecosystem functioning and services.
... Russian olive (Elaeagnus angustifolia Linnaeus; Elaeagnaceae) is an exotic shrub/tree that has become invasive in many riparian ecosystems throughout the great basin and western North America, including southern British Columbia, Canada (Collette and Pither 2015). Despite its prevalence and the potentially dramatic impacts it can have on riparian and aquatic ecosystems (Katz and Shafroth 2003;Mineau et al. 2011Mineau et al. , 2012, little is known about the arthropods that associate with Russian olive, especially in comparison to those that associate with co-occurring native plants. To our knowledge, only two previous studies have surveyed arthropods associated with Russian olive. ...
Russian olive (
Elaeagnus angustifolia
Linnaeus; Elaeagnaceae) is an exotic shrub/tree that has become invasive in many riparian ecosystems throughout semi-arid, western North America, including southern British Columbia, Canada. Despite its prevalence and the potentially dramatic impacts it can have on riparian and aquatic ecosystems, little is known about the insect communities associated with Russian olive within its invaded range. At six sites throughout the Okanagan valley of southern British Columbia, Canada, we compared the diversity of insects associated with Russian olive plants to that of insects associated with two commonly co-occurring native plant species: Woods’ rose (
Rosa woodsii
Lindley; Rosaceae) and Saskatoon (
Amelanchier alnifolia
(Nuttall) Nuttall ex Roemer; Rosaceae). Total abundance did not differ significantly among plant types. Family richness and Shannon diversity differed significantly between Woods’ rose and Saskatoon, but not between either of these plant types and Russian olive. An abundance of Thripidae (Thysanoptera) on Russian olive and Tingidae (Hemiptera) on Saskatoon contributed to significant compositional differences among plant types. The families Chloropidae (Diptera), Heleomyzidae (Diptera), and Gryllidae (Orthoptera) were uniquely associated with Russian olive, albeit in low abundances. Our study provides valuable and novel information about the diversity of insects associated with an emerging plant invader of western Canada.
... For example, suitable habitat is predicted along the Fraser River from the town of Lytton to as far north as Williams Lake. The Fraser River hosts an economically important salmon fishery and, based on research conducted in the US (Mineau et al. 2011(Mineau et al. , 2012Kominoski et al. 2013), any future Russian olive establishment along it has the potential to alter aquatic ecosystem functioning. ...
Russian olive (Elaeagnus angustifolia L., Elaeagnaceae) has gained notoriety as an invasive tree in the United States (US), particularly owing to its impacts within western riparian ecosystems. In Canada, its potential for range expansion has yet to be assessed, despite alarming infestations in parts of southern British Columbia (BC). Existing niche model predictions are of limited utility because they are restricted to the US, were constructed in the absence of higher latitude records in Canada, and did not consider potentially important soil-related predictors. Here, we address these gaps, and include more than 1400 new occurrence records for Canada, most of which were collected using Google Street View. Our Maxent niche models achieved excellent performance (AUC > 0.9), and identified mean temperature of the coldest quarter and topsoil pH as the first and second-most important predictor variables, respectively, neither of which was included in previously published niche models. High habitat suitability is predicted in areas of western Canada that presently lack occurrence records, including along several major rivers in south-central BC. Our findings should prove valuable to nascent detection and management efforts in western Canada, and also highlight the benefits of basing niche model predictions on occurrence records encompassing as much of the invaded range as possible.
... Some studies suggested that invasive species can cause alterations at different levels in the structure and functioning of ecosystems (Ehrenfeld 2010). Moreover, the establishment of exotic riparian plants can alter the exchange of organic material between terrestrial and lotic ecosystems, both changing the quantity (Mineau et al. 2011(Mineau et al. , 2012 or the quality (B€ arlocher & Graça 2002) of terrestrial litter inputs, leading to alterations in the composition (Serra et al. 2013) and density (Lester et al. 1994) of benthic assemblages. Many studies have shown that, for instance, the introduction and spread of Eucalyptus globulus plantations in Spain had a strong effect on in-stream terrestrial detritus colonization and degradation (Chauvet et al. 1997;Pozo et al. 1998;Ferreira et al. 2006), while other studies have shown weak influence of exotic species on streams (Braatne et al. 2007). ...
Most of the energy input of low-order lotic food webs derives from non-living sources of terrestrial organic matter. For this reason, many studies have examined patterns of leaf breakdown; most recently, interest has focused on the importance of water quality or the nature (native versus exotic) of plant material. In this study, we combined both aspects by analyzing the breakdown process and macroinvertebrate colonization of leaf bags containing leaves of different plant types in two nearby sites with different levels of water quality. We exposed a total of 600 leaf bags made of five leaf types (three native: Alnus incana, Populus alba and Quercus robur; and two exotic: Reynoutria japonica and Robinia pseudoacacia) at two sites of the Pellice River (northwestern Italy). Leaf bags were retrieved after 10, 20, 30, 40, 50 and 60 days, leaf mass loss determined and the associated macroinvertebrates quantified. Significant differences were found in the mass loss and in the colonization of leaf bags between sites but not between native and exotic species. Dry mass loss was different among species but without any evident relation with exotic or native origin of plants. In our study sites, geographical origin of plant detritus is not per se central in shaping macroinvertebrate colonization and mass loss because the impact of wastewater treatment plant effluent seems to be much more important than plant origin in the breakdown process.
... However, exotic plants may colonize in those habitats as pioneers since they have plastic biological attributes, which are common to many weed species. For example, Russian-olive and saltcedar (Tamarix ramosissima Ledeb.) are two common exotic species, which are widely distributed at the riparian habitats in the US (Friedman et al. 2005;Mineau et al. 2012;. ...
Mapping forest resources is useful for identifying threat patterns and monitoring changes associated with landscapes. Remote Sensing and Geographic Information Science techniques are effective tools used to identify and forecast forest resource threats such as exotic plant invasion, vulnerability to climate change, and land-use/cover change. This research focused on mapping abundance and distribution of Russian-olive using soil and land-use/cover data, evaluating historic land-use/cover change using mappable water-related indices addressing the primary loss of riparian arboreal ecosystems, and detecting year-to-year land-cover changes on forest conversion processes. Digital image processing techniques were used to detect the changes of arboreal ecosystems using ArcGIS ArcInfo® 9.3, ENVI®, and ENVI® EX platforms.
Research results showed that Russian-olive at the inundated habitats of the Missouri River is abundant compared to terrestrial habitats in the Bismarck-Mandan Wildland Urban Interface. This could be a consequence of habitat quality of the floodplain, such as its silt loam and silty clay soil type, which favors Russian-olive regeneration. Russian-olive has close assemblage with cottonwood (Populus deltoides) and buffaloberry (Shepherdia argentea) trees at the lower elevations. In addition, the Russian-olive-cottonwood association correlated with low nitrogen, low pH, and high Fe, while Russian-olive- buffaloberry association occurred in highly eroded areas.
The Devils Lake sub-watershed was selected to demonstrate how both land-use/cover modification and climatic variability have caused the vulnerability of arboreal ecosystems on the fringe to such changes. Land-cover change showed that the forest acreage declined from 9% to 1%, water extent increased from 13% to 25%, and cropland extent increased from 34% to 39% between 1992 and 2006. In addition, stochastic modeling was adapted to simulate how land-use/cover change influenced forest conversion to non-forested lands at the urban-wildland fringes in Cass County. The analysis yielded two distinct statistical groups of transition probabilities for forest to non-forest, with high transition probability of unchanged forest (0.54≤ Pff ≤ 0.68) from 2006 to 2011. Generally, the land-uses, such as row crops, showed an increasing trend, while grains, hay, seeds, and other crops showed a declining trend. This information is vital to forest managers for implementing restoration and conservation practices in arboreal ecosystems.
... For example, Pickart et al. (1998) documented fertilization effects of an invasive lupine in similarly barren dune soils in California (USA); Myrica faya was responsible for fixing large amounts of nitrogen in recent volcanic soils in Hawaii, where no N-fixing plants were present pre-invasion (Vitousek and Walker 1989). Invasion of riparian nitrogen fixers may even affect water chemistry, biogeochemical cycling and ecosystem efficiency in streams (Mineau et al. 2011(Mineau et al. , 2012. ...
Floodplain vegetation is fundamental in fluvial systems, controlling river corridor geomorphology and ecology through a series of hydraulic, sedimentological, and biological processes. Changes caused by introduced plant species can thus result in shifts in river regime, succession trajectories and nutrient availability, affecting native biodiversity. The exotic bigleaf or marsh lupine Lupinus polyphyllus, introduced in Patagonia in the last decades, is aggressively invading fluvial corridors. It fills unoccupied ecological niches in southern Chilean rivers, due to its capacity for nitrogen fixation, its perennial habit, and high shoot density and leaf surface area.
... Changes in the quality of subsidies can influence CRC consumption (Marcarelli et al. 2011). For instance, Mineau et al. (2012) documented the invasion of the riparian Russian olive tree Elaeagnus angustifolia in the western US increases organic matter subsidies in temperate streams, yet because of Russian olive's poor quality, ecosystem efficiency within streams decreased following the invasion. As researchers identify other mechanisms that alter cross system resource fluxes, our ability to understand the factors that regulate them and to predict how these linkages will change in the face of current and future environmental stressors will improve. ...
Pulse subsidies account for a substantial proportion of resource availability in many systems, having and cascading effects on consumer population dynamics, and energy flow within and across ecosystem boundaries. Although the importance of pulsed resource subsidies is well-established, the mechanisms that regulate resource fluxes across ecosystem boundaries are not well understood. The aim of our study was to determine the extent that marsh consumers regulated a marsh prey subsidy to estuarine consumers in the oligohaline reaches of an Everglades estuary. We characterized a marsh pulsed subsidy of cyprinodontoid, invertebrate and sunfish prey that move into the upper estuary from adjacent drying
marshes. In response to the prey pulse, we examined the numerical, fitness and dietary responses of three focal consumers in the upper estuary; two marsh species (largemouth bass and bowfin) that accompanied the subsidy as a result of marsh drying, and one estuarine consumer (snook). At the onset of marsh drying and the prey subsidy, estuarine consumers switched diets to consume the larger marsh prey (sunfishes), while bass and bowfin maintained similar diets (cyprinodontoids and invertebrates respectively) than pre and post subsidy. From the consumption of this subsidy, bass (marsh species) and snook (estuarine species) exhibited fitness gains while bowfin did not. Although both marsh and estuarine consumers benefitted from the subsidy, we found evidence that freshwater consumers shunted some of the subsidy away from snook. Of the prey sampled in consumer stomachs, 41% of marsh prey biomass was eaten by marsh consumers, while 59% was consumed by the estuarine consumer. We conclude that the amount of the marsh prey available to estuarine consumers may be greater in the absence of marsh consumers, thus the magnitude of the prey subsidy could depend on the dynamics of the marsh consumers from donor communities.
Climate change is one of the main challenges that human societies are currently facing. Given that forests represent major natural carbon sinks in terrestrial ecosystems, administrations worldwide are launching broad‐scale programs to promote forests, including stands of non‐native trees. Yet, non‐native trees may have profound impacts on the functions and services of forest ecosystems, including the carbon cycle, as they may differ widely from native trees in structural and functional characteristics. Also, the allocation of carbon between above‐ and belowground compartments may vary between native and non‐native forests and affect the vulnerability of the carbon stocks to disturbances. We conducted a global meta‐analysis to compare carbon stocks and fluxes among co‐occurring forests dominated by native and non‐native trees, while accounting for the effects of climate, tree life stage, and stand type. We compiled 1678 case studies from 250 papers, with quantitative data for carbon cycle‐related variables from co‐occurring forests dominated by native and non‐native trees. We included 170 non‐native species from 42 families, spanning 55 countries from all continents except Antarctica. Non‐native forests showed higher overall carbon stock due to higher aboveground tree biomass. However, the belowground carbon stock, particularly soil organic carbon, was greater in forests dominated by native trees. Among fluxes, carbon uptake rate was higher in non‐native forests, while carbon loss rate and carbon lability did not differ between native and non‐native forests. Differences in carbon stocks and fluxes between native and non‐native trees were greater at early life stages (i.e. seedling and juvenile). Overall, non‐native forests had greater carbon stocks and fluxes than native forests when both were natural/naturalised or planted; however, native natural forests had greater values for the carbon cycle‐related variables than plantations of non‐native trees. Our findings indicate that promoting non‐native forests may increase carbon stocks in the aboveground compartment at the expense of belowground carbon stocks. This may have far‐reaching implications on the durability and vulnerability of carbon to disturbances. Forestry policies aimed at improving long‐term carbon sequestration and storage should conserve and promote native forests.
Networks of direct and indirect biotic interactions underpin the complex dynamics and stability of ecological systems, yet experimental and theoretical studies often yield conflicting evidence regarding the direction (positive or negative) or magnitude of these interactions. We revisited pioneering data sets collected at the deciduous forested Horonai Stream and conducted ecosystem‐level syntheses to demonstrate that the direction of direct and indirect interactions can change depending on the timescale of observation. Prior experimental studies showed that terrestrial prey that enter the stream from the adjacent forest caused positive indirect effects on aquatic invertebrates during summer by diverting fish consumption. Seasonal and annual estimates of secondary production and organic matter flows along food web pathways demonstrate that this seasonal input of terrestrial invertebrate prey increases production of certain fish species, reversing the indirect effect on aquatic invertebrates from positive at the seasonal timescale to negative at the annual timescale. Even though terrestrial invertebrate prey contributed 54% of the annual organic matter flux to fishes, primarily during summer, fish still consumed 98% of the aquatic invertebrate annual production, leading to top‐down control that is not revealed in short‐term experiments and demonstrating that aquatic prey may be a limiting resource for fishes. Changes in the direction or magnitude of interactions may be a key factor creating nonlinear or stabilizing feedbacks in complex systems, and these dynamics can be revealed by merging experimental and comparative approaches at different scales.
Invasive species can have disastrous ecological consequences, and management is often required to control these invasions and mitigate the damage. Yet in many systems, biological invaders can serve critical ecological roles, particularly where they have been long-established or effectively replaced functionally similar native species. In such cases, eradicating invasions can have unintended consequences on other components of the ecosystem, and potential control measures must be viewed within an ecosystem wide context to ensure they do not cause more harm than good. On the lower Snake River in eastern Washington, invasive Russian olive (Elaeagnus angustifolia) comprises 90% of the woody riparian vegetation in some areas. In this study, we experimentally removed half of the Russian olive from 0.5-ha plots using three configuration patterns that varied in the amount of interspersion of remaining vegetation (n = 9 replicates) to evaluate the short-term impact of a stepwise restoration strategy on breeding bird communities. We monitored plots for 5 yr and found that Russian olive removal on low interspersion treatments negatively affected occupancy rates for 50 of 52 species (96%) and significantly reduced richness by up to 2.41 (95% credible interval [CI] = 0.73, 4.14) species relative to control plots. These effects dampened with increasing interspersion, and occupancy rates of only 41 (79%) species decreased on high inter-spersion treatments, leading to non-significant richness reductions of only 0.99 (95% CI = À0.70, 2.75) species. Given the dominance of Russian olive in this region, removing it eliminates critical habitat for birds that require woody structure for nesting and foraging. Thus, we caution managers to consider the potential short-term negative impacts to the local fauna when planning invasive control efforts. However, we found that several riparian-dependent species known to breed in the region were noticeably absent from our study plots, and short-term losses in avian habitat may be tolerable where restoration of native vegetation supports greater diversity in the long term. In such restoration efforts, managers may be able to mitigate the negative effects of invasive shrub control by maintaining high interspersion among unmanip-ulated vegetation while waiting for native vegetation to re-establish.
The biology of headwater streams is intimately linked to that of the surrounding terrestrial environment through organic matter subsidies. Lonicera maackii, an invasive shrub that is becoming abundant in headwater stream riparian areas, deposits substantial quantities of organic matter into the aquatic system. This organic material has allelopathic effects on terrestrial plants and insects, and a growing body of work suggests strong connections between L. maackii invasion and aquatic biota. Lonicera maackii deposits fruit and flowers in quantities and timings that are unique, and we tested the hypothesis that these subsidies would negatively affect survival and growth of laboratory-cultured Hyalella azteca and field-collected Anthopotamus verticis and Allocapnia spp. Invertebrates were exposed to a gradient of fruit (reference sediment + 0, 0.31, 0.62, 1.25, or 2.5 g dry mass [DM]) and flower (reference sediment + 0, 0.30, 0.60, 1.2, or 2.4 g DM) biomass in laboratory and field sediment exposure tests. Hyalella azteca survival was significantly reduced by exposure to L. maackii fruit in the laboratory and in the field exposures, and a negative effect was observed for A. verticis (p< 0.05). Lonicera maackii flower biomass was associated with negative effects on survival of H. azteca in the field and laboratory exposures and of A. verticis in the laboratory exposure. During the laboratory exposures, dissolved O2 (DO) and pH were <2 mg/L and 5.5, respectively. In the field exposures, DO and pH were comparable to stream conditions during fruit exposures, declining significantly with increasing flower biomass. Our results suggest that L. maackii fruit and flowers, novel subsidies in these systems, can negatively affect benthic organism survival and growth. Research focused on verifying this novel subsidy hypothesis for L. maackii and other species could enhance our understanding of invasion biology and terrestrial–aquatic linkages.
Introduction:Elaeagnus spp. is one in the family of riparian trees growing near the rivers or water corridors. In this family, Elaeagnus angustifolia (Russian olive) is famous because of its medical applications.
Methods: A comprehensive review was performed to extract the related data from published literature.
Results: Traditionally, it has been used as an analgesic, antipyretic and diuretic herbal medicine. A large number of compounds have been derived from Russian olive and made this plant a source of flavonoids, alkaloids, minerals and vitamins. Although the purpose of most studies is to use this plant for preparation of herbal medicines and as an ingredient for drug formulation, there is no available drug dosage form commercially.
Conclusion: This review aimed to provide the most important documentary information on the active components of Elaeagnus spp. and their relation to the pharmacological properties and compare them with reported medicinal effects.
Riparian ecosystems support mosaics of terrestrial and aquatic plant species that enhance regional biodiversity and provide important ecosystem services to humans. Species composition and the distribution of functional traits – traits that define species in terms of their ecological roles – within riparian plant communities are rapidly changing in response to various global change drivers. Here, we present a conceptual framework illustrating how changes in dependent wildlife communities and ecosystem processes can be predicted by examining shifts in riparian plant functional trait diversity and redundancy (overlap). Three widespread examples of altered riparian plant composition are: shifts in the dominance of deciduous and coniferous species; increases in drought-tolerant species; and the increasing global distribution of plantation and crop species. Changes in the diversity and distribution of critical plant functional traits influence terrestrial and aquatic food webs, organic matter production and processing, nutrient cycling, water quality, and water availability. Effective conservation efforts and riparian ecosystems management require matching of plant functional trait diversity and redundancy with tolerance to environmental changes in all biomes.
Read More: http://www.esajournals.org/doi/abs/10.1890/120056
The reasons for nitrification inhibition in some soils are controversial We studied the effect of Elaeagnus angustifolia leaf litter (a host plant able to fix atmospheric nitrogen via root‐nodule symbiosis with an actinomycete of the genus Frankia) on the density and activity of nitrifying microorganisms present in degraded soils. Soils were incubated with and without leaf litter, and it was seen that increased denitrification, CO2‐induced inhibition, or nitrite and ammonia fixation by organic matter did not decrease nitrification. Our results suggest allelopathic inhibition by leaf litter and indicate that the introduction of E. angustifolia could improve degraded soils because it stimulates nitrogen conservation.
In this paper, the dynamics of primary production in the Daly River in tropical Australia are investigated. We used the diurnal-curve method for both oxygen and pH to calculate photosynthesis and respiration rates as indicators of whole-river productivity. The Daly River has maximum discharges during the summer, monsoonal season. Flow during the dry season is maintained by groundwater discharge via springs. The study investigated how primary production and respiration evolve during the period of low flow in the river (April–November). The relationship between primary production and the availability of light and nutrients enabled the role of these factors to be assessed in a clear, oligotrophic tropical river. The measured rate of photosynthesis was broadly consistent with the estimated mass of chlorophyll associated with the main primary producers in the river (phytoplankton, epibenthic algae, macroalgae, macrophytes). A significant result of the analysis is that during the time that plant biomass re-established after recession of the flows, net primary production proved to be ~4% of the rate of photosynthesis. This result and the observed low-nutrient concentrations in the river suggest a tight coupling between photosynthetic fixation of carbon and the microbial degradation of photosynthetic products comprising plant material and exudates.
Global environmental changes have direct effects on aquatic ecosystems, as well as indirect effects through alterations of adjacent terrestrial ecosystem structure and functioning. For example, shifts in terrestrial vegetation communities resulting from global changes can affect the quantity and quality of water, organic matter, and nutrient inputs to aquatic ecosystems. The relative importance of these direct and terrestrial-vegetation-mediated effects is largely unknown, but understanding them is essential to our ability to predict the consequences of global changes for aquatic ecosystems. Here, we present a conceptual framework for considering the relative strengths of these effects and use case studies from xeric, wet and temperate, and boreal ecosystems to demonstrate that the responses of aquatic ecosystems to drivers of global changes may not be evident when the pathways are studied separately. Future studies examining changes in aquatic ecosystem structure and functioning should consider the relative contributions of both direct and terrestrial-vegetation-mediated effects of global changes.
Biological invasions are a widespread and significant component of human-caused global environmental change. The extent of invasions of oceanic islands, and their consequences for native biological diversity, have long been recognized. However, invasions of continental regions also are substantial. For example, more than 2,000 species of alien plants are established in the continental United States. These invasions represent a human-caused breakdown of the regional distinctiveness of Earth's flora and fauna - a substantial global change in and of itself. Moreover, there are well-documented examples of invading species that degrade human health and wealth, alter the structure and functioning of otherwise undisturbed ecosystems, and/or threaten native biological diversity. Invasions also interact synergistically with other components of global change, notably land use change. People and institutions working to understand, prevent, and control invasions are carrying out some of the most important - and potentially most effective - work on global environmental change.
The ability of ecosystems to recover from external disturbances, that is, their stability, is a fundamental property of these systems. Quantification of the ability for various ecosystems to recover and understanding of the mechanisms behind stability are currently areas of major ecological research. In this paper we present an overview of how the stability concept has been used in ecology and a more specific discussion of the application of these ideas to stream ecosystems. This is followed by a case study in which we have been observing the stability of small streams in response to watershed logging and comparing stream stability to stability of the adjacent forest ecosystem.
The importance of terrestrial-aquatic linkages was evaluated by a large-scale, 3-year exclusion of terrestrial leaf litter
inputs to a forest stream. Exclusion of leaf litter had a strong bottom-up effect that was propagated through detritivores
to predators. Most invertebrate taxa in the predominant habitat declined in either abundance, biomass, or both, compared with
taxa in a nearby reference stream. However, fauna in moss habitats changed little, indicating that different food webs exist
in habitats of different geomorphology. Thus, the ecosystem-level consequences of excluding detrital inputs to an ecosystem
were demonstrated. Inputs of riparian detritus are essential for conservation or restoration of diverse stream food webs.
1. Large‐scale invasions of riparian trees can alter the quantity and quality of allochthonous inputs of leaf litter to streams and thus have the potential to alter stream organic matter dynamics. Non‐native saltcedar ( Tamarix sp.) and Russian olive ( Elaeagnus angustifolia ) are now among the most common trees in riparian zones in western North America, yet their impacts on energy flow in streams are virtually unknown.
2. We conducted a laboratory feeding experiment to compare the growth of the aquatic crane fly Tipula (Diptera: Tipulidae) on leaf litter from native cottonwood ( Populus ) and non‐native Tamarix and Elaeagnus . Tipula showed positive growth on leaf litter of all three species; however, after 7 weeks, larvae fed Tamarix leaves averaged 1.7 and 2.5 times the mass of those fed Elaeagnus and Populus , respectively. Tipula survival was highest on Populus , intermediate on Tamarix and lowest on Elaeagnus .
3. High Tipula growth on Tamarix probably reflects a combination of leaf chemistry and morphology. Conditioned Tamarix leaf litter had intermediate carbon : nitrogen values (33 : 1) compared to Populus (40 : 1) and Elaeagnus (26 : 1), and it had intermediate proportions of structural carbon (42%) compared to Elaeagnus (57%) and Populus (35%). Tamarix leaves are also relatively small and possibly more easily ingested by Tipula than either Elaeagnus or Populus .
4. Field surveys of streams in the western U.S.A. revealed that Tamarix and Elaeagnus leaf packs were rare compared to native Populus , probably due to the elongate shape and small size of the non‐native leaves. Thus we conclude that, in general, the impact of non‐native riparian invasion on aquatic shredders will depend not only on leaf decomposition rate and palatability but also on rates of leaf litter input to the stream coupled with streambed retention and subsequent availability to consumers.
Stream ecosystems consist of several subsystems that are spatially distributed concentrically, analogous to the elements
of a simple telescope. Subsystems include the central surface stream, vertically and laterally arrayed saturated sediments
(hyporheic and parafluvial zones), and the most distal element, the riparian zone. These zones are hydrologically connected;
thus water and its dissolved and suspended load move through all of these subsystems as it flows downstream. In any given
subsystem, chemical transformations result in a change in the quantity of materials in transport. Processing length is the length of subsystem required to “process” an amount of substrate equal to advective input. Long processing lengths
reflect low rates of material cycling. Processing length provides the length dimension of each cylindrical element of the
telescope and is specific to subsystem (for example, the surface stream), substrate (for instance, nitrate), and process (denitrification,
for example). Disturbance causes processing length to increase. Processing length decreases during succession following disturbance.
The whole stream-corridor ecosystem consists of several nested cylindrical elements that extend and retract, much as would
a telescope, in response to disturbance regime. This telescoping ecosystem model (TEM) can improve understanding of material
retention in running water systems; that is, their “nutrient filtration” capacity. We hypothesize that disturbance by flooding
alters this capacity in proportion to both intensity of disturbance and to the relative effect of disturbance on each subsystem.
We would expect more distal subsystems (for example, the riparian zone) to show the highest resistance to floods. In contrast,
we predict that postflood recovery of functions such as material processing (that is, resilience) will be highest in central
elements and decrease laterally. Resistance and resilience of subsystems are thus both inversely correlated and spatially
separated. We further hypothesize that cross-linkages between adjacent subsystems will enhance resilience of the system as
a whole. Whole-ecosystem retention, transformation, and transport are thus viewed as a function of subsystem extent, lateral
and vertical linkage, and disturbance regime.
Elaeagnus angustifolia L., a nonnative N2-fixer, has established within riparian corridors of the interior western United States and is now the fourth most frequently
occurring woody riparian plant in this region. We examined whether E. angustifolia alters pools and fluxes of soil inorganic N at eight sites dominated by Populus deltoides ssp. wislizeni along the Rio Grande in New Mexico over 2years. E. angustifolia contributed a small fraction of total leaf fall (<5% across sites) but accounted for a disproportionately high amount of
N (19%) that entered the system from P. deltoides and E. angustifolia leaf fall, due to the high N content (>2%) of E. angustifolia senesced leaves. Soil inorganic N concentrations and potential rates of nitrification and net N mineralization varied across
sites. E. angustifolia leaf fall explained 59% of the variation in soil inorganic N concentrations across years. This relationship suggests that
inputs of N-rich leaf litter from E. angustifolia may increase N availability in riparian soils. We detected no relationship between E. angustifolia leaf fall and fluxes of soil inorganic N, whereas others have measured both stimulation and inhibition of soil N cycling
by E. angustifolia. Greater abundance of N2-fixing species in riparian forests may augment growth of neighboring plants or increase N export to rivers. Given these possibilities,
ecosystem studies and restoration projects should further examine the potential for E. angustifolia to affect N pools and fluxes along western North American rivers.
Concern about spread of non-native riparian trees in the western USA has led to Congressional proposals to accelerate control efforts. Debate over these proposals is frustrated by limited knowledge of non-native species distribution and abundance. We measured abundance of 44 riparian woody plants at 475 randomly selected stream gaging stations in 17 western states. Our sample indicates that Tamarix ramosissima and Elaeagnus angustifolia are already the third and fourth most frequently occurring woody riparian plants in the region. Although many species of Tamarix have been reported in the region, T. ramosissima (here including T. chinensis and hybrids) is by far the most abundant. The frequency of occurrence of T. ramosissima has a strong positive relation with the mean annual minimum temperature, which is consistent with hypothesized frost sensitivity. In contrast the frequency of occurrence of E. angustifolia decreases with increasing minimum temperatures. Based on mean normalized cover, T. ramosissima and E. angustifolia are the second and fifth most dominant woody riparian species in the western USA. The dominance of T. ramosissima has been suspected for decades; the regional ascendance of E. angustifolia, however, has not previously been reported.
Dissolved organic carbon (DOC) is an abundant form of organic matter in stream ecosystems. Most research has focused on the
watershed as the source of DOC in streams, but DOC also comes from leaching of organic matter stored in the stream channel.
We used a whole-ecosystem experimental approach to assess the significance of leaching of organic matter in the channel as
a source of DOC in a headwater stream. Inputs of leaf litter were excluded from a forested Appalachian headwater stream for
3 years. Stream-water concentration, export, and instream generation of DOC were reduced in the litter-excluded stream as
compared with a nearby untreated reference stream. The proportion of high molecular weight (HMW) DOC (more than 10,000 daltons)
in stream water was not altered by litter exclusion. Mean DOC concentration in stream water was directly related to benthic
leaf-litter standing stock. Instream generation of DOC from leaf litter stored in the stream channel contributes approximately
30% of daily DOC exports in this forested headwater stream. This source of DOC is greatest during autumn and winter and least
during spring and summer. It is higher during increasing discharge than during base flow. We conclude that elimination of
litter inputs from a forested headwater stream has altered the biogeochemistry of DOC in this ecosystem.
Responses of detrital pathways to nutrients may differ fundamentally from pathways involving living plants: basal carbon resources can potentially decrease rather than increase with nutrient enrichment. Despite the potential for nutrients to accelerate heterotrophic processes and fluxes of detritus, few studies have examined detritus-nutrient dynamics at whole-ecosystem scales. We quantified organic matter (OM) budgets over three consecutive years in two detritus-based Appalachian (U.S.A.) streams. After the first year, we began enriching one stream with low-level nitrogen and phosphorus inputs. Subsequent effects of nutrients on outputs of different OM compartments were determined using randomized intervention analysis. Nutrient addition did not affect dissolved or coarse particulate OM export but had dramatic effects on fine particulate OM (FPOM) export at all discharges relative to the reference stream. After two years of enrichment, FPOM export was 340% higher in the treatment stream but had decreased by 36% in the reference stream relative to pretreatment export. Ecosystem respiration, the dominant carbon output in these systems, also increased in the treatment stream relative to the reference, but these changes were smaller in magnitude than those in FPOM export. Nutrient enrichment accelerated rates of OM processing, transformation, and export, potentially altering food-web dynamics and ecosystem stability in the long term. The results of our large-scale manipulation of a detrital ecosystem parallel those from analogous studies of soils, in which net loss of organic carbon has often been shown to result from experimental nutrient addition at the plot scale. Streams are useful model systems in which to test the effects of nutrients on ecosystem-scale detrital dynamics because they allow both the tracking of OM conversion along longitudinal continua and the integrated measurement of fluxes of transformed material through downstream sites.
Randomized intervention analysis (RIA) is used to detect changes in a manipulated ecosystem relative to an undisturbed reference system. It requires paired time series of data from both ecosystems before and after manipulation. RIA was applied to data from 12 lakes (3 manipulated and 9 reference ecosystems) over 3 yr. RIA consistently indicated changes after major manipulations and only rarely indicated changes in ecosystems that were not manipulated. Less than 3% of the data sets had equivocal results because of serial autocorrelation. -from Authors
Nutrient cycling and export in streams and rivers should vary with flow regime, yet most studies of stream nutrient transformation do not include hydrologic variability. We used a stable isotope tracer of nitrogen (15N) to measure nitrate (NO3) uptake, storage, and export in a mountain stream, Spring Creek, Idaho, U.S.A. We conducted two tracer tests of 2-week duration during snowmelt and baseflow. Dissolved and particulate forms of 15N were monitored over three seasons to test the hypothesis that stream N cycling would be dominated by export during floods, and storage during low flow. Floods exported more N than during baseflow conditions; however, snowmelt floods had higher than expected demand for NO{3 because of hyporheic exchange. Residence times of benthic N during both tracer tests were longer than 100 d for ephemeral pools such as benthic algae and wood biofilms. Residence times were much longer in fine detritus, insects, and the particulate N from the hyporheic zone, showing that assimilation and hydrologic storage can be important mechanisms for retaining particulate N. Of the tracer N stored in the stream, the primary form of export was via seston during periods of high flows, produced by summer rainstorms or spring snowmelt the following year. Spring Creek is not necessarily a conduit for nutrients during high flow; hydrologic exchange between the stream and its valley represents an important storage mechanism.
Habitat alteration and biotic invasions are the two leading causes of global environmental change and biodiversity loss. Recent innovative experiments have shown that habitat disturbance can have drastic effects that cascade to adjacent ecosystems by altering the flow of resource subsidies from donor systems. Likewise, exotic species invasions could alter subsidies and affect distant food webs, but very few studies have tested this experimentally. Here we report evidence from a large-scale field experiment in northern Japan that invasion of nonnative rainbow trout (Oncorhynchus mykiss) interrupted reciprocal flows of invertebrate prey that drove stream and adjacent riparian forest food webs. Rainbow trout usurped terrestrial prey that fell into the stream, causing native Dolly Varden charr (Salvelinus malma) to shift their foraging to insects that graze algae from the stream bottom. This indirectly increased algal biomass, but also decreased biomass of adult aquatic insects emerging from the stream to the forest. In turn, this led to a 65% reduction in the density of riparian-specialist spiders in the forest. Thus, species invasions can interrupt flows of resources between interconnected ecosystems and have effects that propagate across their boundaries, effects that may be difficult to anticipate without in-depth understanding of food web relationships.
All vegetation on Watershed 2 of the Hubbard Brook Experimental Forest was cut during November and December of 1965, and vegetation regrowth was inhibited for two years by periodic application of herbicides. Annual stream-flow was increased 39% the first year and 28% the second year. Large increases in streamwater concentration were observed for all major ions, except NHâ/sup +/SOâ/sup 2 -/ and HCOââ», approximately five months after the deforestation. Nitrate concentrations were 41-fold higher than the undisturbed condition the first year and 56-fold higher the second. Sulfate was the only major ion in stream water that decreased in concentration after deforestation. An inverse relationship between sulfate and nitrate concentrations in stream water was observed in both undisturbed and deforested situations. Average streamwater concentrations increased for Ca++, Mg++, K+ and Na+ during the two years subsequent to deforestation. 58 references, 8 tables, 15 figures.
Heavy shade presents serious challenges for primary producers and food-limited herbivores in forest streams. This study examines the response of periphyton and grazing snails (Elimia clavaeformis) to summer shade in White Oak Creek (WOC) in a Tennessee deciduous forest. Three experiments were performed: (1) in situ manipulation of light and snail density to test the effects of light limitation and grazing; (2) construction of photosynthesis-irradiance (P-I) curves to test for shade adaptation by periphyton; and (3) measurements of snail growth vs. irradiance. In the first experiment, light and snail densities were manipulated in a 2 x 2 factorial design. Snails at normal densities cropped periphyton biomass to low levels regardless of light regime, but periphyton productivity was higher at the open sites where snails grew faster and accumulated more lipid. Snail growth and lipid accumulation were strongly affected by intraspecific competition in both light regimes. In the second experiment, photosynthesis-irradiance curves for periphyton from shaded and open sites illustrated considerable shade adaptation: shaded periphyton was 2 times more efficient at low irradiance than with periphyton from open sites. Despite the greater efficiency of shaded periphyton at low irradiance, integrated primary production estimated with photosynthetic models was 4 times greater in the open because shade adaptation provided only partial compensation for the shade. In the third experiment, in situ snail growth again increased with decreasing shade. Bottom-up effects of light limitation were propagated very strongly in WOC, where the vertebrate fauna is dominated by a grazer that appears to escape top-down control. 68 refs., 4 figs., 3 tabs.
Net photosynthesis and respiration in the Madison River, Yellowstone National Park, was calculated using pH measurements to estimate CO 2 changes. The upstream‐downstream method was used on five successive reaches. Primary production and macrophyte standing crops decreased downstream and the ratio of gross to net photosynthesis also became less. The downstream decline in productivity was correlated with successively lower concentrations of free CO 2 . The decline in free CO 2 was due to photosynthetic removal during daylight and outward diffusion of CO 2 during all hours of the day and night.
When ecosystems are not suffering from unusual external perturbations, we observe certain well-defined developmental trends.
Since disturbance tends to arrest, or even reverse, these autogenic developments, we can anticipate some ecosystem responses
to stress. Trends expected in stressed ecosystems include changes in energetics, nutrient cycling, and community structure
and function.
Recent findings support reappraisal of the widely held belief that most streams are heterotrophic and dependent upon the input of terrestrial detritus. Autotrophic production is shown to play an important role in the economy of many streams, a fact which suggests the need to develop a more generalized theory of stream energy dynamics.
The ecosystem-level distress syndrome is manifest through changes in nutrient cycling, productivity, the size of dominant species, species diversity, and a shift in species dominance to opportunistic shorter-lived forms. These symptoms of ecosystem dysfunction are common in both terrestrial and aquatic systems under various stress impacts including harvesting, physical restructuring, pollutant discharges, introductions of exotic species, and extreme natural events (such as disastrous storms or volcanic activity). The progression of appearance of symptoms under intensifying stress levels may be interrupted temporarily as ecosystem homeostasis and homeorhetic mechanisms intercede. Inability to cope leads to further dysfunctions and, perhaps, to irreversible ecosystem breakdown.-from Authors
Whole-stream metabolism in a first-order stream was measured using upstream-downstream changes in dissolved oxygen (DO) concentration measured at 1-min intervals over a 40-h period. The measured change in DO was corrected for reaeration flux using a reaeration coefficient determined from injections of conservative and volatile tracers. The whole-stream metabolism measurement was compared in the spring with in situ chamber measurements performed a few days later in the same stream reach. Chamber measurements of community respiration extrapolated to a 24-h period (CR(24)) were about one third the whole-stream measurements, while gross primary production (GPP) measured at midday in the chambers was roughly 20% less than the whole-stream estimate. Whole-stream GPP was higher during the spring just prior to forest canopy closure than in summer or autumn. Community respiration exceeded whole-stream GPP on all dates and was greatest during the summer. Our results suggest that this whole-stream approach provides a measure of total stream metabolism that is relevant to other stream ecosystem processes measured on reach scales, such as nutrient spiralling.
Dynamics of headwater stream ecosystems are generally regarded as occurring at the interface of aquatic and terrestrial ecosystems. Terrestrial arthropod inputs can provide an energy subsidy and increase the abundance of predatory fish, and the ensuing effects potentially can cascade through the food web and ultimately affect primary producers. Nevertheless, the community-based effects of such inputs on stream food web dynamics are still poorly understood. We present experimental evidence that terrestrial arthropod inputs have an indirect but prominent effect on a stream benthic community by altering the intensity of fish predation in the food web. Two key elements of the stream food web, terrestrial arthropod inputs and the presence of predatory fish, were experimentally manipulated by using greenhouse-type covers and enclosures (or exclosures) in a forest stream located in northern Japan. When terrestrial arthropod inputs to the stream were experimentally reduced, fish predation pressure shifted dramatically from terrestrial to aquatic arthropods. The ensuing depletion of aquatic arthropods resulted in a subsequent increase in periphyton biomass. This field experiment revealed that terrestrial arthropod inputs were a primary factor controlling cascading trophic interactions among predatory fish, herbivorous aquatic arthropods, and benthic periphyton. These results provide empirical support for the perspective that transfers of energy and biomass from donor systems are frequently significant for the maintenance of biotic communities in recipient systems.
Rates of photosynthesis and community respiration were determined for benthic assemblages in Sycamore Creek, a Sonoran Desert stream in Arizona. Benthos in this stream can be separated into (1) mats of Cladophora glomerata and associated epiphytes and (2) assemblages of epipelic diatoms and blue‐green algae. Community respiration and net photosynthesis were measured for these assemblages using submerged light‐dark chambers in situ . Multiple regression analysis was used to predict (1) gross photosynthesis as a function of photosynthetically active radiation, temperature and chlorophyll‐α concentration; and (2) community respiration as a function of temperature and biomass.
Calculations suggest that Sycamore Creek is autotrophic during the summer ( P/R = 1.7) and that the rates of gross photosynthesis ( P =8.5 g O 2 m ⁻² day ⁻¹ ) and community respiration ( R = 5.1 g O 2 m ⁻² day ⁻¹ ) are high for a small stream. Considerable difference exists between the Cladophora mat assemblages, in which mean P is 12.5gO 2 m ⁻² day ⁻¹ and the P/R ratio is 2.3, and the epipelic assemblages in which mean P is 4.4 g O 2 m ⁻² day ⁻¹ and P/R is 0.96. The high rate of gross photosynthesis, low litter inputs, high biomass of algae and the intermittent but severe floods that characterize Sycamore Creek indicate that this stream and other similar desert streams are net exporters of organic matter and are, thereby, truly autotrophic stream ecosystems.
1. Experimental manipulations were performed to determine the biological, chemical and physical attributes that govern sediment respiration in the hyporheic zone of Sycamore Creek, a Sonoran Desert stream.
2. Hyporheic respiration per unit volume of sediment was inversely related to diameter of sediment particles, indicating that respiration is affected by availability of substrate for microbial colonization (i.e. sediment surfaces). Respiration rate per unit surface area on sediments was positively correlated with particle diameter, indicating greater metabolic activity of microbes on larger sediments.
3. Hyporheic respiration was more than twice as high in water collected from the surface flow than from subsurface flow. Further, hyporheic respiration was highest immediately following exposure of sediments to surface water and declined over time, presumably due to exhaustion of labile organic matter.
4. Microbial activity was stimulated by addition of algal leachate; however, amendments of leaf leachate had little effect. Respiration was also elevated with dextrose and leucine amendments, but not with inorganic nitrogen additions, indicating hyporheic respiration is carbon limited.
5. Water from the stream surface is probably enriched in labile organic matter derived from algae and stimulates respiration at points of hydrologic downwelling where surface water enters hyporheic sediments. The physical structure of sediments further affects metabolism by affecting the area available for microbial attachment.
1. Streams are highly connected to their landscapes and so are easily altered by multiple stressors that affect both uplands and riparian zones, and the streams themselves. These include dams and diversions, channelisation, deforestation, water pollution, biological invasions and climate change.
2. We review research conducted in Hokkaido Island, northern Japan, which measured the effects of many of these stressors on both stream food webs and fluxes of invertebrates to and from the riparian zone that feed aquatic and terrestrial consumers. About half the energy that sustains fish falls directly into streams as terrestrial invertebrates, and a quarter of the energy needs for riparian birds is supplied by adult aquatic insects emerging from the stream.
3. Single stressors in these Hokkaido streams, including deforestation, channelisation, erosion-control dams, biological invasions and climate change, have drastic effects on stream food webs, the fishes they support and riparian predators (spiders, birds, and bats). Most stressors caused 30–90% declines in foraging, growth, or abundance of aquatic or terrestrial predators. Indirect effects of stressors also cascaded throughout stream food webs and across the aquatic–terrestrial boundary.
4. Effects of individual stressors were largely concordant across spatial scale, through time during years of different productivity and among different food web components.
5. Two studies of multiple stressors revealed that each stressor alone reduced food web components like abundance of stream benthos or riparian spiders to low levels (35–83% reduction; mean 59%), beyond which an additional stressor had little effect. Synergism and antagonism are less relevant when individual stressors have such large effects.
6. Thematic implications: small streams in Hokkaido are highly sensitive to many individual stressors and have little resistance or resilience to their effects. Moreover, each stressor alone can reduce biota strongly, indicating that restoration will need to consider all simultaneously to protect biotic diversity.
1. Pelagic trophic structure and energy fluxes are evaluated predominantly on the basis of ingestion of particulate organic matter by living organisms and the effects of consumption on the population dynamics of trophic levels.
2. Population fluxes are not representative of the material and energy fluxes of either the composite pelagic region or the lake ecosystem. Metabolism of particulate and especially dissolved organic detritus from many pelagic and non-pelagic autochthonous and from allochthonous sources dominates both material and energy fluxes. Because of the very large magnitudes and relative chemical recalcitrance of these detrital sources, the large but slow metabolism of detritus provides an inherent ecosystem stability that energetically dampens the ephemeral, volatile fluctuations of higher trophic levels.
3. The annual time period is the only meaningful interval in comparative quantitative analyses of material and energy fluxes at population, community, and ecosystem levels.
4. Non-predatory death and metabolism by prokaryotic and protistian heterotrophs dominate. Continued application of animal-orientated relationships to the integrated, process-driven couplings of the aquatic ecosystems impedes understanding of quantitative ecosystem pathways and control mechanisms.
1. We investigated the impacts of saltcedar invasion on organic matter dynamics in a spring‐fed stream (Jackrabbit Spring) in the Mojave Desert of southern Nevada, U.S.A., by experimentally manipulating saltcedar abundance.
2. Saltcedar heavily shaded Jackrabbit Spring and shifted the dominant organic matter inputs from autochthonous production that was available throughout the year to allochthonous saltcedar leaf litter that was strongly pulsed in the autumn. Specifically, reaches dominated by saltcedar had allochthonous litter inputs of 299 g ash free dry mass (AFDM) m ⁻² year ⁻¹ , macrophyte production of 15 g AFDM m ⁻² year ⁻¹ and algal production of 400 g AFDM m ⁻² year ⁻¹ , while reaches dominated by native riparian vegetation or where saltcedar had been experimentally removed had allochthonous litter inputs of 7–34 g AFDM m ⁻² year ⁻¹ , macrophyte production of 118–425 g AFDM m ⁻² year ⁻¹ and algal production of 640–900 g AFDM m ⁻² year ⁻¹ .
3. A leaf litter breakdown study indicated that saltcedar also altered decomposition in Jackrabbit Spring, mainly through its influence on litter quality rather than by altering the environment for decomposition. Decomposition rates for saltcedar were lower than for ash ( Fraxinus velutina ), the dominant native allochthonous litter type, but faster than for bulrush ( Scirpus americanus ), the dominant macrophyte in this system.
The invasion of non-indigenous plants is considered one of the primary threats to rare and endangered species as well as to the integrity and function of North American ecosystems. However, many of the suspected negative ecosystem impacts are based on anecdotal evidence. For example, there is almost unanimous agreement among natural resource managers of the detrimental ecological impacts of species such as Lythrum salicaria (purple loosestrife), Phragmites australis (common reed) and Alliaria petiolata (garlic mustard) but convincing documentation is scarce. Experimental and theoretical ecology predicts large ecosystem impacts of the most widespread invasive species. However, it is difficult to prioritize control of species that occur at intermediate densities. Long-term monitoring before and during the invasion as well as before, during and after any control attempts can provide valuable ecological information. In particular, it is important to understand how changes in the abundance of species influence ecosystem properties and processes which, in turn, will help guide management decisions. Ideally, this monitoring has to go beyond 'simple impacts on plant communities, involve cross-disciplinary teams of scientists and should incorporate many different taxa and their interactions. Monitoring design and data collection should be sophisticated enough to allow statistically sound data analysis. The available information will be paramount in (1) developing new political and scientific guidelines in invasive species management, (2) helping resolve potential conflicts of interest and (3) helping change public attitudes regarding growth, sale, and control of non-indigenous species.
Russian olive (Elaeagnus angustifolia) is a non-native riparian tree that has become common and continues to rapidly spread throughout the western United States.
Due to its dinitrogen (N2)-fixing ability and proximity to streams, Russian olive has the potential to subsidize stream ecosystems with nitrogen (N),
which may in turn alter nutrient processing in these systems. We tested these potential effects by comparing background N
concentrations; nutrient limitation of biofilms; and uptake of ammonium (NH4-N), nitrate (NO3-N), and phosphate (PO4-P) in paired upstream-reference and downstream-invaded reaches in streams in southeastern Idaho and central Wyoming. We found
that stream reaches invaded by Russian olive had higher organic N concentrations and exhibited reduced N limitation of biofilms
compared to reference reaches. However, at low inorganic N background concentrations, reaches invaded by Russian olive exhibited
higher demand for both NH4-N and NO3-N compared to their paired reference reaches, suggesting these streams have the potential to retain the N subsidy from Russian
olive N2 fixation and diminish its downstream export and effects. Our findings demonstrate the potential for a non-native riparian
plant to significantly alter biogeochemical cycling in streams. Finally, we used our results to develop a conceptual model
that describes predicted effects of Russian olive and other non-native riparian N2 fixers on in-stream N dynamics.
Keywords
Elaeagnus angustifolia
–Russian olive–invasive species–nitrogen fixation–nutrient limitation–nutrient spiraling–subsidy–DON
Russian olive (Elaeagnus angustifolia L.) is an invasive non-native tree in western North America capable of nitrogen fixation through symbiotic actinorhizal associations.
The high abundance of the tree may have important effects on ecosystem nutrient dynamics and consequent community responses.
This study explored the influence of Russian olive on soil nitrogen along a section of the Rio Grande River riparian zone
in Rio Grande Valley State Park, Albuquerque, New Mexico. Cottonwood trees (Populus deltoides, var. wislizenii) without subcanopy trees were paired with cottonwood having a Russian olive under the canopy, and soil nitrogen
pools were assessed. Relative to open interplant areas, soils under subcanopy Russian olive showed a 55% increase in total
nitrogen and nearly four times the amount of available nitrogen compared to soils under cottonwood alone. Organic matter accumulation
followed a similar pattern relative to open areas with 73% more accumulation under subcanopy Russian olive compared with cottonwood
trees alone. Acetylene reduction and δ15N revealed that nitrogen fixation occurred in Russian olive at the site during the time of sampling, and foliar chemistry
averaged 2.58% nitrogen for Russian olive compared to 0.54% for cottonwood. Both soil texture and Russian olive presence proved
to be important factors affecting the observed soil nitrogen patterns. Despite these nitrogen inputs, cottonwood trees appeared
to utilize sources other than that derived from Russian olive. A soil respiration experiment assessed the influence of Russian
olive on soil microbial productivity, which revealed that soils at this location are carbon limited and not nitrogen limited.
Even after imposing a nitrogen limitation through the addition of carbon, Russian olive did not affect microbial productivity
despite higher nitrogen levels in soils associated with it. The results of this study show that Russian olive enhances soil
nitrogen resources in this semi-arid riparian environment, but the added nitrogen is not likely to facilitate cottonwood tree
growth or further exotic weed invasion. Russian olive may instead compete with cottonwood for other resources.
The Russian olive tree (Elaeagnus angustifolia L.) was brought to the western United States from Eurasia during the early to mid-1900s, and has since become a common member of many riparian communities in Idaho. We compared leaf chemistry and in-stream processing of Russian olive leaves (exotic) and various species of native leaves in one hardwater and one relatively softwater Idaho stream. Measurements using air-dried leaves showed that Russian olive contained the greatest concentration of nitrogen, approximately 1.6% of the dry mass, whereas the native species each contained less than 1.0% nitrogen. The C/N ratio of Russian olive was
Vertical inputs of allochthonous organic matter to streams can be estimated directly with traps; traps may be placed over the stream, in the riparian forest or at other locations in the catchment. In this study, we compared litter inputs estimated from traps located over the stream with those obtained from traps placed on the stream bank in two stretches (orders 2 and 3) of the Mera stream, with similar tree species composition and riparian forest structure. The amount of annual litter input measured with the traps on the stream was similar in the two stretches, 748 and 730 g m-2 yr-1, for orders 2 and 3, respectively. However, there appeared to be differences in the composition of litter; a lower percentage of leaves and a higher percentage of wood was found in the stretch of order 3 than in the stretch of order 2. In both sites, the mean input measured under the riparian forest was lower than the input recorded with the traps placed over the stream by approximately 10%. In relation to the traps located over the stream, the traps located on the bank overestimated the input from adjacent terrestrial tree species and, therefore, underestimated the input from riparian species.
Although the study of resource subsidies has emerged as a key topic in both ecosystem and food web ecology, the dialogue over their role has been limited by separate approaches that emphasize either subsidy quantity or quality. Considering quantity and quality together may provide a simple, but previously unexplored, framework for identifying the mechanisms that govern the importance of subsidies for recipient food webs and ecosystems. Using a literature review of > 90 studies of open-water metabolism in lakes and streams, we show that high-flux, low-quality subsidies can drive freshwater ecosystem dynamics. Because most of these ecosystems are net heterotrophic, allochthonous inputs must subsidize respiration. Second, using a literature review of subsidy quality and use, we demonstrate that animals select for high-quality food resources in proportions greater than would be predicted based on food quantity, and regardless of allochthonous or autochthonous origin. This finding suggests that low-flux, high-quality subsidies may be selected for by animals, and in turn may disproportionately affect food web and ecosystem processes (e.g., animal production, trophic energy or organic matter flow, trophic cascades). We then synthesize and review approaches that evaluate the role of subsidies and explicitly merge ecosystem and food web perspectives by placing food web measurements in the context of ecosystem budgets, by comparing trophic and ecosystem production and fluxes, and by constructing flow food webs. These tools can and should be used to address future questions about subsidies, such as the relative importance of subsidies to different trophic levels and how subsidies may maintain or disrupt ecosystem stability and food web interactions.
Sumario: The genesis of a concept -- The lake as a microcosm -- Transformation and development of the concept -- The International Biological Program -- Consolidation and extension of the concept -- Interpretations and conclusions Bibliografía: P. 225-248