Article

Constancy of local spread rates for buffelgrass (Pennisetum ciliare L.) in the Arizona Upland of the Sonoran Desert

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Abstract

In North American deserts, grass invasions threaten native vegetation via competition and altered fire regimes. Accurate prediction and successful mitigation of these invasions hinge on estimation of spread rates and their degree of constancy in time and space. We used high-resolution aerial photographs from 11 sites in the Santa Catalina Mountains, southern Arizona to reconstruct the spread of buffelgrass (Pennisetum ciliare), a C4 perennial bunchgrass, since 1980. The total area infested was fit to a logistic model and residuals of the model were compared to climatic factors of the corresponding and lagged time periods. Infestations grew from small colonizing patches in the 1980s to 66 ha in 2008, doubling every 2.26–7.04 years since 1988. Although buffelgrass germination, establishment and distribution are favored by wet summers and warm winters, climate variables did not predict spread rates. Buffelgrass has grown at a constant rate, at least since 1988, when much of its expansion took place. In the study area, minimum requirements are met almost every year for germination and reproduction, establishing a consistent baseline for spread that manifests as a constant spread rate.

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... Buffelgrass (Cenchrus ciliaris or Pennisetum ciliare) is an important pasture grass in many semi-arid regions of the world but it is also an invasive weed in some areas of North America [1]. In the Sonoran Desert of southern Arizona it has infested thousands of acres of public and private lands, including Saguaro National Park and the Coronado and Tonto National Forests [2][3][4]. The increased fire frequency and intensity in the infested areas is negatively affecting the native species including the iconic saguaro cactus [5]. ...
... The residue was then purified by TLC eluted with CHCl3-i-PrOH (98:2) to afford the derivative 12 ( (13) To epi-radicinol (4, 5 mg), dissolved in pyridine (100 µL), Ac2O (10 µL) was added. The reaction was carried out following the same procedure used for the conversion of 2 into 11 yielding the corresponding acetyl ester of 3-epi-radicinol (13,4 ...
... Results of the leaf puncture bioassay on buffelgrass (Cenchrus ciliaris) at a concentration of 2.5 × 10 −3 M for the hemisynthetic derivatives(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) and the natural compounds(1)(2)(3)(4)(5). ...
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Radicinin (1), is a fungal dihydropyranopyran-4,5-dione isolated together with some analogues, namely 3-epi-radicinin, radicinol, 3-epi-radicinol, and cochliotoxin (2–5), from the culture filtrates of the fungus Cochliobolus australiensis, a foliar pathogen of buffelgrass (Cenchrus ciliaris), an invasive weed in North America. Among the different metabolites 1 showed target-specific activity against the host plant and no toxicity on zebrafish embryos, promoting its potential use to develop a natural bioherbicide formulation to manage buffelgrass. These data and the peculiar structural feature of 1 suggested to carry out a structure-activity relationship study, preparing some key hemisynthetic derivatives and to test their phytotoxicity. In particular, p-bromobenzoyl, 5-azidopentanoyl, stearoyl, mesyl and acetyl esters of radicinin were semisynthesized as well as the monoacetyl ester of 3-epi-radicinin, the diacetyl esters of radicinol and its 3 epimer, and two hexa-hydro derivatives of radicinin. The spectroscopic characterization and the activity by leaf puncture bioassay against buffelgrass of all the derivatives is reported. Most of the compounds showed phytotoxicity but none of them had comparable or higher activity than radicinin. Thus, the presence of an α,β unsaturated carbonyl group at C-4, as well as, the presence of a free secondary hydroxyl group at C-3 and the stereochemistry of the same carbon proved to be the essential feature for activity.
... In addition to understanding dispersion pattern, it is critical to understand cumulative expansion rate in order to formulate an effective control strategy (Fensham et al. 2013;Lookingbill et al. 2014). Expansion rates inform land managers about the total resources needed to control expansion of an invasive species (Olsson et al. 2012a), they allow determination of areas at greatest risk for further invasion (Higgins et al. 1996;Cannas et al. 2016), and they help managers estimate the consequences of lags between detection and control efforts. ...
... The invasion success of P. ciliare, like most invasive grasses, is due in part to its seed dispersal (Ernst et al. 1992), low water requirements for germination (Ward et al. 2006), high drought tolerance, and quick uptake of water from senescence (Reynolds et al. 2004). Pennisetum ciliare can become dominant in the Sonoran Desert even without disturbances (Olsson et al. 2012b) but the cycle of dry-lightning-ignited fires fostered by P. ciliare threatens plant community conversion to an African-type grassland with little diversity and few native plants (McDonald and McPherson 2011;Olsson et al. 2012a;Lyons et al. 2013). ...
... Thus, even if a local P. ciliare population is removed, land managers must continue managing for seedling emergence from the seed bank and recruitment from regional sources, due to propagule pressure and seed dispersal radius. Olsson et al. (2012a) found that P. ciliare patches double in size an average of every 5.1 years, with a range of 2-7 years. However, the patches in the Olsson et al. (2012a) study were long-term, based on data collected from patches that had established 14 to 20 years before. ...
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Essential variables to consider for an efficient control strategy for invasive plants include dispersion pattern (i.e., satellite or invasion front) and patch expansion rate. These variables were demonstrated for buffelgrass [ Pennisetum ciliare (L.) Link], a C 4 perennial grass introduced from Africa, which has invaded broadly around the world. The study site was along a roadway in southern Arizona (USA). The P. ciliare plant distributions show the pattern of clumping associated with the satellite (nascent foci) colonization pattern (average nearest neighbor test, z -score −47.2, P<0.01). The distance between patches ranged from 0.743 to 12.8 km, with an average distance between patches of 5.6 km. Median patch expansion rate was 271% over the 3-yr monitoring period versus 136% found in other studies of established P. ciliare patches. Targeting P. ciliare satellite patches as a control strategy may exponentially reduce the areal doubling time, while targeting the largest patches may have less effect on the invasion speed.
... The grass was introduced to Australia and South, Central and North America, including the Sonoran Desert region, in the 1940s to provide livestock forage and mitigate soil erosion (Hanselka 1988). Since then, buffelgrass has aggressively spread into areas historically occupied by sparse native vegetation (McDonald and McPherson 2011;Olsson et al. 2012). Buffelgrass threatens ecosystems in its introduced range because, compared to native vegetation, it increases the fuel load and intensity of fires (Jackson 2005;Esque et al. 2006;Stevens and Falk 2009;Martin et al. 2015). ...
... Buffelgrass has been previously found to grow best on sandy loam soils with high fertility, but not in areas where there is high salinity, deep sand, or high clay content (Hanselka 1988;Van Devender and Dimmitt 2006;Abella et al. 2012). Buffelgrass has been found to be negatively correlated in density with other herbaceous species and is commonly found beneath woody plants, especially in the Arizona Upland vegetation type (Abella et al. 2012;Olsson et al. 2012). In Arizona, the invasive grass is commonly found in drainages, on south-facing slopes, and along arroyos in valley flats and disturbed roadsides (Van Devender and Dimmitt 2006). ...
... Among these vegetation types, the Sonoran Paloverde-Mixed Cacti Desert Scrub had the highest buffelgrass cover in both districts. This vegetation type likely provided opportunities for buffelgrass establishment and spread due to the large open interspaces between trees, shrubs and cacti (Abella et al. 2012;Olsson et al. 2012). Buffelgrass likely occupied other low elevation desert vegetation types because it is tolerant of drought and low soil nutrients, and can rapidly respond to pulses of moisture that are common in dryland regions (Marshall et al. 2012b). ...
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Abstract Methods to detect and monitor the spread of invasive grasses are critical to avoid ecosystem transformations and large economic costs. The rapid spread of non‐native buffelgrass(Pennisetum ciliare) has intensified fire risk and is replacing fire intolerant native vegetation in the Sonoran Desert of the southwestern US. Coarse‐resolution satellite imagery has had limited success in detecting small patches of buffelgrass, whereas ground‐based and aerial survey methods are often cost prohibitive. To improve detection, we trained 2 m resolution DigitalGlobe WorldView‐2 satellite imagery with 12 cm resolution unmanned aerial vehicle (UAV) imagery and classified buffelgrass on Google Earth Engine, a cloud computing platform, using Random Forest (RF) models in Saguaro National Park, Arizona, USA. Our classification models had an average overall accuracy of 93% and producer's accuracies of 94–96% for buffelgrass, although user's accuracies were low. We detected a 2.92 km2 area of buffelgrass in the eastern Rincon Mountain District (1.07% of the total area) and a 0.46 km2 area (0.46% of the total area) in the western Tucson Mountain District of Saguaro National Park. Buffelgrass cover was significantly greater in the Sonoran Paloverde‐Mixed Cacti Desert Scrub vegetation type, on poorly developed Entisols and Inceptisol soils and on south‐facing topographic aspects compared to other areas. Our results demonstrate that high‐resolution imagery improve on previous attempts to detect and classify buffelgrass and indicate potential areas where the invasive grass might spread. The methods demonstrated in this study could be employed by land managers as a low‐cost strategy to identify priority areas for control efforts and continued monitoring.
... It is extremely competitive with native species in semi-arid ecosystems and is associated with increased wildfire [4]. Fire poses a serious and direct threat to the iconic saguaro cactus of the Sonoran Desert [5,6], and efforts to control buffelgrass there have been ongoing for many years [7]. However, effective buffelgrass control in the Sonoran Desert has been highly problematic for several reasons. ...
... Fish embryo acute and chronic toxicity on zebrafish (Brachydanio rerio) were evaluated for the most promising compound. (4) nil [19] cochliotoxin (5) high [19] chloromonilicin (6) not tested [20] chloromonilinic acid B (7) high [20] chloromonilinic acid C (8) high [20] chloromonilinic acid D (9) high [20] From Pyricularia grisea pyriculin A (10) low [21] pyriculin B (11) nil [21] (10S, 11S)-(−)-epi-pyriculol (12) high [21] trans-3,4-dihydro-3,4,8-trihydroxy-1(2H)-naphtalenone (13) nil [21] (4S)-(+)-isosclerone (14) nil [21] 1 For details on seedling bioassay procedure and on the relative results, see cited publications [19][20][21]. ...
... Fish embryo acute and chronic toxicity on zebrafish (Brachydanio rerio) were evaluated for the most promising compound. (4) nil [19] cochliotoxin (5) high [19] chloromonilicin (6) not tested [20] chloromonilinic acid B (7) high [20] chloromonilinic acid C (8) high [20] chloromonilinic acid D (9) high [20] From Pyricularia grisea pyriculin A (10) low [21] pyriculin B (11) nil [21] (10S, 11S)-(−)-epi-pyriculol (12) high [21] trans-3,4-dihydro-3,4,8-trihydroxy-1(2H)-naphtalenone (13) nil [21] (4S)-(+)-isosclerone (14) nil [21] ...
Article
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The fungal pathogens Cochliobolus australiensis and Pyricularia grisea have recently been isolated from diseased leaves of buffelgrass (Cenchrus ciliaris) in its North American range, and their ability to produce phytotoxic metabolites that could potentially be used as natural herbicides against this invasive weed was investigated. Fourteen secondary metabolites obtained from in vitro cultures of these two pathogens were tested by leaf puncture assay on the host plant at different concentrations. Radicinin and (10S, 11S)-epi-pyriculol proved to be the most promising compounds. Thus, their phytotoxic activity was also evaluated on non-host indigenous plants. Radicinin demonstrated high target-specific toxicity on buffelgrass, low toxicity to native plants, and no teratogenic, sub-lethal, or lethal effects on zebrafish (Brachydanio rerio) embryos. It is now under consideration for the development of a target-specific bioherbicide to be used against buffelgrass in natural systems where synthetic herbicides cause excessive damage to native plants.
... We calibrated the spatial spread of our invader with historical reconstruction of buffelgrass spread based on aerial photographs (Olsson et al. 2012a). Aerial photography is frequently used to map invasive species and reconstruct historical distributions of species (Browning et al. 2009;Franklin et al. 2006;Huang and Asner 2009;Lonsdale 1993), although discrimination among individual species is dependent on image quality, phenology, and physical characteristics of the species that may distinguish infested from uninvaded areas. ...
... Second, buffelgrass invasion has accelerated in this sector since the mid-1980s, but efforts to control the spread on CNF only started in the past 2 yr and thus can still be heavily influenced by decision support models. Third, a rich data set was available for the region, comprising remotely sensed and field surveys (Olsson et al. 2012a). This readily available information helped with the process of initializing and calibrating the simulation model. ...
... The Use of Historic Air Photos to Calibrate the Spread Rate Used in the Simulation Modeling. Olsson et al. (2012a) reconstructed buffelgrass spread at 11 sites in the Santa Catalinas using historical aerial photographs with a spatial resolution varying between 0.25 and 1 m (3.28 ft) and found populations doubling approximately every 2.66 to 7.04 yr. We identified the three sites with the longest and most complete time series of data to calibrate our spatially explicit spread model. ...
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Buffelgrass, a highly competitive and flammable African bunchgrass, is spreading rapidly across both urban and natural areas in the Sonoran Desert of southern and central Arizona. Damages include increased fire risk, losses in biodiversity, and diminished revenues and quality of life. Feasibility of sustained and successful mitigation will depend heavily on rates of spread, treatment capacity, and cost-benefit analysis. We created a decision support model for the wildland-urban interface north of Tucson, AZ, using a spatial state-and-transition simulation modeling framework, the Tool for Exploratory Landscape Scenario Analyses. We addressed the issues of undetected invasions, identifying potentially suitable habitat and calibrating spread rates, while answering questions about how to allocate resources among inventory, treatment, and maintenance. Inputs to the model include a state-and-transition simulation model to describe the succession and control of buffelgrass, a habitat suitability model, management planning zones, spread vectors, estimated dispersal kernels for buffelgrass, and maps of current distribution. Our spatial simulations showed that without treatment, buffelgrass infestations that started with as little as 80 ha (198 ac) could grow to more than 6,000 ha by the year 2060. In contrast, applying unlimited management resources could limit 2060 infestation levels to approximately 50 ha. The application of sufficient resources toward inventory is important because undetected patches of buffelgrass will tend to grow exponentially. In our simulations, areas affected by buffelgrass may increase substantially over the next 50 yr, but a large, upfront investment in buffelgrass control could reduce the infested area and overall management costs.
... 3 In the Saguaro National Park, the increased fire frequency caused by this weed is decimating the iconic saguaro cactus, and the Sonoran Desert ecosystem is becoming a grassland monoculture. 4,5 Physical removal with hand tools and the use of broadspectrum herbicides (e.g., glyphosate) are the two methods employed to manage the buffelgrass invasion. 6 Bioherbicide formulations based on the phytotoxins produced by pathogenic fungi of C. ciliaris could be adopted as an innovative biocontrol strategy to avoid the use of synthetic pesticides. ...
... Four other metabolites were isolated from the culture filtrates of P. grisea and identified as dihydropyriculol (1) and epi-dihydropyriculol (2), 3-methoxy-6,8-dihydroxy-3-methyl-3,4-dihydroisocoumarin (3), and (R)mevalonolactone (4). For the first three only, the relative configuration was previously reported, and thus, their AC was assigned for the first time by a combining ECD chiroptical spectroscopy and computational techniques. ...
Article
The fungal pathogen Pyricularia grisea has been studied to evaluate its production of phytotoxins for the biocontrol of the buffelgrass (Cenchrus ciliaris L.) weed. A first investigation allowed to isolate several new and known phytotoxic metabolites. However, the further investigation on the organic extract obtained from the fungus liquid culture showed the presence of other metabolites possibly contributing to its phytotoxicity. Thus, four known metabolites were isolated and identified by spectroscopic (nuclear magnetic resonance [NMR] and high‐resolution electrospray ionization mass spectrometry [HRESIMS]) methods as dihydropyriculol (1 ), epi‐dihydropyriculol (2 ), 3‐methoxy‐6,8‐dihydroxy‐3‐methyl‐3,4‐dihydroisocoumarin (3 ), and (R )‐mevalonolactone (4 ). The absolute configuration of 1 –3 was determined for the first time by a computational analysis of their electronic circular dichroism (ECD) spectra. When the isolated compounds were bioassayed at a concentration of 5 × 10–3 M in a buffelgrass coleoptile and radicle elongation test no toxicity was detected. On the contrary, compounds 1 and 3 showed a significant stimulating effect of radical elongation. Furthermore, the difference in growth stimulation between 1 and its epimer 2 highlights the tight relationship between absolute configuration and biological activity of these fungal metabolites.
... Its rapid growth, efficient seed production and dispersal ensure the rapid spread of buffel grass. Invasion of desert scrub displaces native species, threatening their conservation, a phenomenon that has been little studied (Brenner and Kanda 2013;Franklin and Molina-Freaner 2010;Olsson et al. 2012). In buffel grass active pastures, a 73% reduction of native species has been documented and many native species are unable to regenerate (Morales-Romero and Molina-Freaner 2008;Morales-Romero et al. 2012;Tinoco-Ojanguren et al. 2013). ...
... In buffel grass active pastures, a 73% reduction of native species has been documented and many native species are unable to regenerate (Morales-Romero and Molina-Freaner 2008;Morales-Romero et al. 2012;Tinoco-Ojanguren et al. 2013). Several studies have documented that buffel grass invasion reduces water potential, photosynthesis (Eilts and Huxman 2013), and recruitment (Bracamonte et al. 2017) of native species and often results in a reduction of native plant cover (Abella et al. 2012) and species richness (Olsson et al. 2012). Buffel grass has become an agent of local and regional change, making the control of buffel grass a critical issue for the protection and restoration of natural vegetation (Marshall et al. 2012). ...
Article
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Buffel grass (Cenchrus ciliaris L.) is an African grass used as forage for livestock that is also invasive. Several methods have been evaluated to remove invasive buffel grass, but the effect of removal on establishment of native plants is poorly understood. We explore the effect of buffel grass removal treatments on the germination and establishment of four Sonoran Desert tree species. We used three removal treatments and a control; after treatments were applied, we sowed seeds of Mariosousa willardiana, Parkinsonia microphylla, Olneya tesota, and Parkinsonia florida. For each treatment, we evaluated germination, plant survival and measured soil moisture, soil temperature, and light quantity. In a second experiment, we tested whether glyphosate, an herbicide used in removal treatments, had significant effects on the same native species. Additionally, in a third experiment, we evaluated the effect of glyphosate on a native annual species. Results showed that the herbicide treatment was effective killing buffel grass and promoting the regeneration of native species. Germination and survival rates for the four study species were greatest under the herbicide treatment and lower after manual removal treatments of buffel grass. However, the herbicide glyphosate significantly suppressed the survival and growth of seedlings of the studied tree species and the annual species. Given the effect of glyphosate on native seedlings and other known side effects, we suggest that it is used only to target buffel plants, avoiding contact with native vegetation.
... While SNP has mapped buffelgrass data from many years, there is active management occurring throughout the landscape, and therefore, no time series of unmanaged buffelgrass patch sizes was available to calibrate the dispersal kernel. Thus, instead of using SNP data, we calibrated the dispersal kernel for the STSM using a time series of spread data from unmanaged land in the nearby Santa Catalina Mountains (Olsson et al. 2012b). We varied the Weibull scale parameter (a) between 0.02 and 0.26 and the Weibull shape parameter (b) between 0.1 and 1.5 and then selected the parameter combination that resulted in a spread distribution most similar to the Santa Catalina Mountain time series data (a 0.14 and b 1.0). ...
... The workshop identified gaps in research (e.g., the rate of patch cover increase and patch expansion) with great uncertainty among experts. There are general estimates of patch expansion (i.e., spread) over time based on aerial photographs (Olsson et al. 2012b), but previous research has not considered patch cover increase. This STSM could be used to determine whether this gap in information is important in answering management questions (Cullinane Thomas et al. 2019). ...
Article
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Invasive species can alter ecosystem properties and cause state shifts in landscapes. Resource managers charged with maintaining landscapes require tools to understand implications of alternative actions (or inactions) on landscape structure and function. Simulation models can serve as a virtual laboratory to explore these alternatives and their potential impacts on a landscape. To be useful, however, managers need to participate in model development to ensure that model structure can evaluate the response of key resources to plausible actions. Here, we detail development of a state-and-transition simulation model (STSM) to evaluate buffelgrass (Cenchrus ciliaris L. syn Pennisetum ciliare (L.) Link) in Saguaro National Park (SNP), Arizona, USA, through collaboration between managers and researchers. We integrate expert knowledge and research to create and parameterize a stochastic, spatially explicit STSM to evaluate specific management objectives. We also develop a dynamic link between the STSM and a fire behavior model to allow exploration of potential novel processes introduced to the ecosystem by buffelgrass invasion. Our projections show that buffelgrass can be expected to increase on the landscape and that the integration of fire into the model accelerates the projected rate of invasion and increases degradation of resources of management concern. We highlight the benefit of engaging end users in the modeling process so that the model is targeted to evaluate management objectives, in this case retention of saguaro cacti (Carnegiea gigantea (Engelm.) Britton & Rose) on the landscape. Being able to integrate an external model that can help address the unique characteristics of a problem such as the introduction of fire into the SNP desert ecosystem increases the ability of simulations to address complex ecological and management questions.
... Remote sensing data could provide a practical and economical alternative to field-based methods for locating and monitoring buffelgrass infestations in remote areas of SNP, provided that the imagery shows both the presence and phenological status of the plants. Images collected via aircraft or unmanned aerial vehicles allow for fine-scale visual differentiation of vegetation types; researchers have tracked the spread of buffelgrass in the foothills of the Tucson mountains by identifying individual plants on high-resolution (sub 1-m pixel size) aerial imagery collected at irregular intervals over a 21-year period [19]. The phenological development stage, however, can only be determined from an imagery collection rate that is unfeasible with aerial campaigns given the economic limitations of most natural resource budgets. ...
... Pima Canyon is located in the Santa Catalina foothills on the northern edge of the city ( Figure 2) in geomorphic conditions similar to those of Saguaro National Park-East; i.e., mountainous terrain composed of felsic granitic and metamorphic rocks. The south-facing slope of the Santa Catalina Mountains, which includes the Pima Canyon area, has a particularly dense and widespread buffelgrass infestation [19]. The observations were collected by a single observer (co-author Weltzin) on a near-weekly basis from July 2010 to December 2014 using standardized protocols [35]; data were archived in the USA National Phenology Network (USA-NPN) database [36]). ...
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The increasing spread and abundance of an invasive perennial grass, buffelgrass (Pennisetum ciliare), represents a critical threat to the native vegetation communities of the Sonoran desert in southern Arizona, USA, where buffelgrass eradication is a high priority for resource managers. Herbicidal treatment of buffelgrass is most effective when the vegetation is actively growing, but the remoteness of infestations and the erratic timing and length of the species' growth periods confound effective treatment. The goal of our research is to promote buffelgrass management by using remote sensing data to detect where the invasive plants are located and when they are photosynthetically active. We integrated citizen scientist observations of buffelgrass phenology in the Tucson, Arizona area with PRISM precipitation data, eight-day composites of 250-m Moderate-resolution Imaging Spectroradiometer (MODIS) satellite imagery, and aerially-mapped polygons of buffelgrass presence to understand dynamics and relationships between precipitation and the timing and amount of buffelgrass greenness from 2011 to 2013. Our results show that buffelgrass responds quickly to antecedent rainfall: in pixels containing buffelgrass, higher correlations (R² > 0.5) typically occur after two cumulative eight-day periods of rain, whereas in pixels dominated by native vegetation, four prior 8-day periods are required to reach that threshold. Using the new suite of phenometrics introduced here-Climate Landscape Response metrics-we accurately predicted the location of 49% to 55% of buffelgrass patches in Saguaro National Park. These metrics and the suggested guidelines for their use can be employed by resource managers to treat buffelgrass during optimal time periods.
... where z is the distance from the cell (i, j) centre to the neighbouring cell centre and α is the dispersal constant, which is estimated to be 1 using a non-linear least squares regression using historical reconstructions of spread in the nearby Catalina Mountains (Olsson et al, 2012). This is a simple but widespread dispersal kernel model (Levin et al, 2003). ...
... Control of this invasive weed needs much more resources to be successful. The increased buffelgrass population could lead to the disappearance of many native species in the region (Rogstad, 2008;Olsson et al, 2012). It can also increase fire hazard, since the dry buffelgrass population could lead to the growth of burning areas by being a good conductor in spreading fire to saguaros and buildings (Bowers et al, 2006). ...
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In this paper, we formulate and analyse a long-term multi-objective dynamic model for controlling invasive species. This optimization framework is then applied to the case of buffelgrass control in the Arizona desert. The proposed model simultaneously optimizes three objectives corresponding to three different valued and threatened resources including saguaros (a native cactus species), buildings and vegetation. The model is used to decide the optimal allocation of labour to these resources to control the population of the species in a multi-period planning horizon. The computational method to solve this problem is based on multi-objective integer programming.
... The National Invasive Species Council (NISC) was established by Executive Order 13112 in 1999 to improve coordination of invasive species control programs. The Council's management plan stresses the importance of rapid response to invasive species and calls for the use of ''rapid-response teams'' to control new invasions before they spread (NISC 2001). Model results have direct implications for the staffing and deployment of rapid response teams to prevent buffelgrass establishment. ...
... First, the Management Plan of the National Invasive Species Council (NISC 2001) calls for ''rapid-response teams'' to control new invasions before they spread. Our first simulations quantified labor requirements needed for such teams to prevent new buffelgrass establishment. ...
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Buffelgrass (Pennisetum ciliare) is a fire-prone, African bunchgrass spreading rapidly across the southern Arizona desert. This article introduces a model that simulates buffelgrass spread over a gridded landscape over time to evaluate strategies to control this invasive species. Weed-carrying capacity, treatment costs, and damages vary across grid cells. Damage from buffelgrass depends on its density and proximity to valued resources. Damages include negative effects on native species (through spatial competition) and increased fire risk to land and buildings. We evaluate recommended "rule of thumb" control strategies in terms of their ability to prevent weed establishment in newly infested areas and to reduce damage indices over time. Two such strategies potential damage weighting and consecutive year treatment used in combination, provided significant improvements in long-term control over no control and over a strategy of minimizing current damages in each year. Results suggest specific recommendations for deploying rapid-response teams to prevent establishment in new areas. The long-run population size and spatial distribution of buffelgrass is sensitive to the priority given to protecting different resources. Land managers with different priorities may pursue quite different control strategies, posing a challenge for coordinating control across jurisdictions.
... In fire-sensitive systems, locations where human values conflict with fire (e.g., WUI, forests managed for timber production, recreation areas), or where shifts in fire regime have rendered ecosystems vulnerable, there may be a very low tolerance for even low-intensity fires. Vegetation communities that are not fire-adapted may experience increased threats from altered fire regimes due to anthropogenic influences such as the profusion of invasive non-native grasses [42,104,138] and increased ignition potential from human activity [139]. For example, in desert ecosystems of the western U.S., native perennial vegetation is extremely slow to regenerate after fire, and recovery is complicated by non-native species and additional direct effects of climate change [31,32]. ...
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As the effects of climate change accumulate and intensify, resource managers juggle existing goals and new mandates to operationalize adaptation. Fire managers contend with the direct effects of climate change on resources in addition to climate-induced disruptions to fire regimes and subsequent ecosystem effects. In systems stressed by warming and drying, increased fire activity amplifies the pace of change and scale of severe disturbance events, heightening the urgency for management action. Fire managers are asked to integrate information on climate impacts with their professional expertise to determine how to achieve management objectives in a changing climate with altered fire regimes. This is a difficult task, and managers need support as they incorporate climate adaptation into planning and operations. We present a list of adaptation strategies and approaches specific to fire and climate based on co-produced knowledge from a science–management partnership and pilot-tested in a two-day workshop with natural resource managers and regional stakeholders. This “menu” is a flexible and useful tool for fire managers who need to connect the dots between fire ecology, climate science, adaptation intent, and management implementation. It was created and tested as part of an adaptation framework used widely across the United States and should be applicable and useful in many fire-prone forest ecosystems.
... By 1930, annual cheatgrass (Bromus tectorum) had invaded~40 M ha in the Intermountain West of the United States (Mack 1981). In the Sonoran Desert, the annual red brome (Bromus rubens; Esque and Schwalbe 2002) and the perennials Lehmann's lovegrass (Eragrostis lehmanniana; Schussman et al. 2006) and buffelgrass (Pennisetum ciliare synonym Cenchrus ciliaris; Olsson et al. 2012) have increased in abundance. These exotic grasses reduce biodiversity and alter hydrological and fire regimes to promote further invasion (Ravi et al. 2009, Wilcox et al. 2012. ...
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Biological soil crusts (biocrusts) cover the soil surface of global drylands and interact with vascular plants. Biocrusts may influence the availability and nature of safe sites for plant recruitment and the susceptibility of an area to invasion by non‐native species. Therefore, to investigate the potential role of biocrusts in invasive species management, we sought to determine whether native and non‐native grass recruitments in two North American deserts were differentially affected by biocrusts. We conducted a series of coordinated experiments in field, semi‐controlled, and controlled environment settings in the Colorado Plateau and Sonoran Desert using contrasting biocrust and grass functional types. Experiments in field environments focused on early establishment of grass seedlings whereas controlled environment experiments focused on seedling emergence. Within each experiment, we compared responses (frequency, magnitude, and timing of emergence/establishment) both across species (biocrust types pooled) and across species and levels of biocrust development. Native grasses varied by experiment and included Aristida purpurea, A. purpurea var. longiseta, Bouteloua gracilis, and Vulpia octoflora. Emergence of non‐native Bromus tectorum was similar to that of native grasses on the Colorado Plateau. Differences in emergence of native vs. non‐native grasses in the Sonoran Desert were species‐ and response‐specific. Emergence of the non‐native Bromus rubens was comparable to that of native grasses whereas emergence frequency and magnitude of the non‐native Pennisetum ciliare was lower compared with two of four native species. Within a grass species, emergence was higher and faster on bare soil compared with biocrusts in the Sonoran Desert semi‐controlled and greenhouse environment experiments. However, the pattern was not consistent across other experiments. When comparing across Colorado Plateau and Sonoran Desert biocrusts in greenhouse experiments, we found that emergence of native grasses was higher on Colorado Plateau biocrusts. Based on the lack of consistent results across our experiments, grass recruitment on biocrusts appears to be driven more by species‐specific traits than species provenance. Our greenhouse experiments suggest that biocrust topographic relief is an important safe site trait influencing plant recruitment.
... In recent decades, buffelgrass has rapidly spread throughout the southwestern United States and beyond at elevations below 3000′ (Cox et al., 1988;Franklin & Molina-Freaner, 2010). As buffelgrass abundance increases, the amount of dry biomass to fuel fires accumulates, leading to devastating impacts to ecosystems that are not fire adapted (Jarnevich et al., 2019;Olsson et al., 2012). For example, Saguaro cacti (Carnegiea gigantea) populations are at extreme risk from widespread fires in the region. ...
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Abstract Buffelgrass (Cenchrus ciliaris syn. Pennisetum ciliare) was introduced to Sonoran Desert in the early 20th century and has become widespread at low elevations. This perennial bunchgrass accumulates abundant biomass that can carry fires through ecosystems not adapted to fire, resulting in devastating impacts for native cacti and other plant and animal life. Buffelgrass is most effectively managed through the application of herbicide when the grass is at least 50% green. Because the grass rapidly greens up following summer monsoon rainfall, it is possible to forecast green‐up using daily rainfall measurements. In 2019, the USA National Phenology Network (USA‐NPN) released daily Buffelgrass Green‐up Forecast maps for the state of Arizona based on the PRISM 4 km daily total precipitation product. The daily digital Buffelgrass Green‐up Forecast maps are a freely available data product and meet the FAIR principles of findability, accessibility, interoperability and reusability. They are permanently archived and publicly accessible as raster and image layers from the USA‐NPN website. These map layers support planning the timing of management activities to maximize buffelgrass treatment efficacy and researchers seeking to incorporate daily estimates of buffelgrass greenness in their analyses.
... Present conditions have an expanding front of non-native grasses that will promote an increase of fuels and connectivity at the wildland-urban interface and the Desertscrub/Semi-desert Grassland ecotone in the coming years and couple decades (Figure by MRS). (Olsson et al., 2012a) and elevates fire risk at the WUI (Olsson et al., 2012b). Buffelgrass burns hotter than most other native and non-native grasses, reaching fire temperatures of 800-900 • C (McDonald and McPherson, 2013). ...
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In the southwestern United States, non-native grass invasions have increased wildfire occurrence in deserts and the likelihood of fire spread to and from other biomes with disparate fire regimes. The elevational transition between desertscrub and montane grasslands, woodlands, and forests generally occurs at ∼1,200 masl and has experienced fast suburbanization and an expanding wildland-urban interface (WUI). In summer 2020, the Bighorn Fire in the Santa Catalina Mountains burned 486 km ² and prompted alerts and evacuations along a 40-km stretch of WUI below 1,200 masl on the outskirts of Tucson, Arizona, a metropolitan area of >1M people. To better understand the changing nature of the WUI here and elsewhere in the region, we took a multidimensional and timely approach to assess fire dynamics along the Desertscrub-Semi-desert Grassland ecotone in the Catalina foothills, which is in various stages of non-native grass invasion. The Bighorn Fire was principally a forest fire driven by a long-history of fire suppression, accumulation of fine fuels following a wet winter and spring, and two decades of hotter droughts, culminating in the hottest and second driest summer in the 125-yr Tucson weather record. Saguaro ( Carnegia gigantea ), a giant columnar cactus, experienced high mortality. Resprouting by several desert shrub species may confer some post-fire resiliency in desertscrub. Buffelgrass and other non-native species played a minor role in carrying the fire due to the patchiness of infestation at the upper edge of the Desertscrub biome. Coupled state-and-transition fire-spread simulation models suggest a marked increase in both burned area and fire frequency if buffelgrass patches continue to expand and coalesce at the Desertscrub/Semi-desert Grassland interface. A survey of area residents six months after the fire showed awareness of buffelgrass was significantly higher among residents that were evacuated or lost recreation access, with higher awareness of fire risk, saguaro loss and declining property values, in that order. Sustained and timely efforts to document and assess fast-evolving fire connectivity due to grass invasions, and social awareness and perceptions, are needed to understand and motivate mitigation of an increasingly fire-prone future in the region.
... Unlike many native warm-season grasses, buffelgrass will grow and reproduce in both the summer and winter rainy seasons when rainfall and temperatures are adequate. These characteristics allow it to outcompete most native flora and develop near monocultures over large swaths of previously highly biodiverse desert scrub ( Olsson et al. 2012 ). ...
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Invasive plants can have significant negative effects on human and ecological communities, including reduced productivity and biodiversity and increased fire risk. Effective mitigation of invasive species likely requires action by heterogeneous actors who span jurisdictions, sectors, and levels of governance. While there has been significant research to develop targeted mitigation techniques that slow or halt the spread of specific invasive plants, there has been relatively little complementary work to develop knowledge about the implementation of these management techniques through effective governance systems. To address this gap, we interviewed and conducted archival research on land managers involved in the mitigation of buffelgrass (Pennisetum ciliare, syn: Cenchrus ciliarus) invasion in southern Arizona to investigate how existing and emerging governance arrangements encourage or undermine individual and collective action to manage invasive plants. Our results show that a key challenge of managing invasive species is identifying the mechanisms that will allow heterogeneous actors to overcome internal barriers to coor- dination with others and enable collective action. These internal barriers are multifaceted, involving laws and policies, cultural traditions and mandates, the availability of monetary and human resources, and information on causes and consequences of species invasion and effective approaches to mitigation. Ap- proaches to solving these problems must include improved knowledge of internal institutional structures and the opportunities and barriers they present to collective action, the preferences of heterogeneous actors when presented with information about future ecosystem conditions absent coordination, the fac- tors that prevent individuals within different organizations from following through on commitments to participate in collective action institutions, and how each of these conditions affects the availability and persistence of resources for mitigation. Together, improved knowledge of the relationships between these factors may provide new approaches to proactive management of emerging resource management challenges, from invasive species to emerging diseases.
... The rate of buffelgrass infill is difficult to quantify because of the high variability in precipitation in the region. Olsson et al. 45 reported relatively constant increase in infestation area from 1980 to 2008 based on interpretation of aerial photographs for 11 sites, but there was variability between sites. Another study in the Arizona Sonoran Desert found variable patch expansion over time 46 . ...
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Ecological forecasts of the extent and impacts of invasive species can inform conservation management decisions. Such forecasts are hampered by ecological uncertainties associated with non-analog conditions resulting from the introduction of an invader to an ecosystem. We developed a state-and-transition simulation model tied to a fire behavior model to simulate the spread of buffelgrass (Cenchrus ciliaris) in Saguaro National Park, AZ, USA over a 30-year period. The simulation models forecast the potential extent and impact of a buffelgrass invasion including size and frequency of fire events and displacement of saguaro cacti and other native species. Using simulation models allowed us to evaluate how model uncertainties affected forecasted landscape outcomes. We compared scenarios covering a range of parameter uncertainties including model initialization (landscape susceptibility to invasion) and expert-identified ecological uncertainties (buffelgrass patch infill rates and precipitation). Our simulations showed substantial differences in the amount of buffelgrass on the landscape and the size and frequency of fires for dry years with slow patch infill scenarios compared to wet years with fast patch infill scenarios. We identified uncertainty in buffelgrass patch infill rates as a key area for research to improve forecasts. Our approach could be used to investigate novel processes in other invaded systems.
... Buffelgrass (Cenchrus ciliaris) is one of the most noxious invasive plant species in the southwestern United States. Since its introduction to the arid regions of North America from east Africa in the 1930s, buffelgrass has dramatically modified natural systems by reducing native plant cover, such as saguaro (Carnegiea gigantea), decreasing native plant community richness and enhancing fire fuel loads (Jackson 2005;Esque et al. 2006;Olsson et al. 2012). Buffelgrass dominance over native desert plant species is known to occur through several mechanisms. ...
Article
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Buffelgrass (Cenchus ciliaris) is a drought-tolerant invasive grass in the Americas and Australia that significantly impacts native plant communities and ecosystems. Despite the clear need to develop a comprehensive understanding of how buffelgrass is able to invade and rapidly establish in arid ecosystems, there is still a lack of knowledge as to if and how this weed might change the soil microbiome in a way that affects its dominance in the presence of management. We investigated the effect of buffelgrass on soil microbial communities in areas that have either been exposed to or not exposed to glyphosate in Saguaro National Park, Arizona USA. We found that buffelgrass roots in invaded areas are surrounded by a distinct soil community that includes a greater number of nitrifiers than in uninvaded soil. We also observed increases in arbuscular mycorrhizal fungi, ectomycorrhizal fungi and methanotrophs with buffelgrass invasion compared to uninvaded soil. Finally, we found no evidence of glyphosate effects on the soil microbiome. Overall, our study results suggest that buffelgrass can escape the limitation of nutrient availability in arid ecosystems by directly or indirectly modifying the soil microbiome. The competitive dominance of buffelgrass in arid systems might be indirectly enhanced by nitrifiers and fungal symbionts, which are often involved in rapid biomass accumulation. This work highlights the importance of soil microbiome considerations in weed science research.
... Total cover by C. ciliare, estimated from high-resolution aerial photography, showed an increase of 170% between 1994 and 2000 and an additional 69% in the next seven years (J. L. Betancourt and T. Bean, unpublished data; Olsson et al. 2012), especially near the top of Tumamoc Hill on the south, east, and west slopes. Competition with exotic grasses has also been shown to influence saguaro range expansion potential (Springer et al. 2015. ...
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Population demography is typically assumed to be strongly influenced by climatic factors, particularly with succulent plants and cacti. The saguaro cactus (Carnegiea gigantea) is a long-lived columnar cactus of the Sonoran Desert that experiences episodic recruitment and mortality. Previous studies have attributed long-term changes in saguaro populations to climatic factors, including increased germination and establishment during wet periods and mortality and reduced establishment during droughts and extreme freezes. We used a 48-yr data set of marked individuals at the Desert Laboratory in Tucson, Arizona, to test the hypothesis that local, temporal population trajectories are mediated by topographic heterogeneity that interacts with fluctuating climatic conditions. We tested the influence of local slope and aspect vs. climatic variability on a population of saguaro using >5800 marked individuals that have been measured since 1964. We examined the relationship between demography and climatic variables (drought, precipitation, and extreme temperatures) and found significant differences in growth and survival among aspects and among census periods. Saguaro population growth was higher during wet and cool periods (e.g., 1964-1970), and changes in age structures suggest that topographic differences interact with climatic fluctuations to produce unexpected demographic patterns including large recruitment events during periods of relatively unfavorable climate conditions. Our results highlight the importance of long-term data to detect demographic responses to climate that could not be predicted from short-term studies of plant physiology and population demography.
... Differences among sampling dates might be attributed in part of environmental changes associated with woody vegetation removal prior to stock-pile construction. Woody vegetation removal affects air movement patterns important to seed dispersing seeds such as Cenchrus ciliaris (buffelgrass [Olsson et al. 2012]) as well as light, temperature and moisture conditions at the soil surface which in turn can affect dormancy and germination (e.g., Wester 1995, Baskin andBaskin 2001). ...
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Topsoils often are removed from energy production sites and stock-piled for use later in restoration activities. Effects of this practice on soil seed banks are unknown. We examined seed bank size, species richness, and species composition of stock-piled topsoils as affected by sampling depth and sampling date at two study sites in the western Rio Grande Plains, TX, USA. Stock-piled topsoil and adjacent non-disturbed topsoil samples were collected at 0-10, 10-20, 20-30 and 30-40 cm depths on five dates over an 18-month period following stock-pile construction. Seed banks were assessed with the seedling emergence method. Sampling date had little effect on seed bank characteristics. We detected differences among depths on the stock-pile, and between stock-piles and undisturbed soil. Seed bank size and species richness generally decreased with increased stock-pile sampling depth at both sites. Differences between stock-piles and undisturbed soil varied between sites: at one site, stock-piling effects were common and were expressed in lower seed bank size and richness in stock-piles compared to undisturbed soils; at the other site, stock-piling had fewer effects on richness or seed bank size. Prevalence of exotic species varied between sites and likely reflected differences in surrounding vegetation. Therefore, site-to-site variability precludes strong generalizations. However, density of emerged native seedlings ranged from < 1 to 3.8 seedlings m-2 at both sites. Assuming acceptable species composition, stock-piles supported an adequate seed bank size at time of sampling for restoration without need for additional seed input. © 2018 by the Board of Regents of the University of Wisconsin System.
... This model was a spatially explicit STSM, developed using TELSA (Kurz et al. 2000), which included input and output maps of the P. ciliare over time, and distinguished between detected (and treatable) and undetected patches that would require resources to be detected. The model simulated dispersal of short-(i.e., neighbor-toneighbor) and long-distance dispersal of P. ciliare to other locations on the landscape based on time series of spread determined from aerial photography (Olsson et al. 2012). A map of the current known distribution of P. ciliare was derived from the same aerial photographs. ...
Chapter
State-and-Transition Simulation Modeling (STSM) is a quantitative analysis method that can consolidate a wide array of resource management issues under a “what-if” scenario exercise. STSM can be seen as an ensemble of models, such as climate models, ecological models, and economic models that incorporate human dimensions and management options. This chapter presents STSM as a tool to help synthesize information on social–ecological systems and to investigate some of the management issues associated with exotic annual Bromus species, which have been described elsewhere in this book. Definitions, terminology, and perspectives on conceptual and computer-simulated stochastic state-and-transition models are given first, followed by a brief review of past STSM studies relevant to the management of Bromus species. A detailed case study illustrates the usefulness of STSM for land management. As a whole, this chapter is intended to demonstrate how STSM can help both managers and scientists: (a) determine efficient resource allocation for monitoring nonnative grasses; (b) evaluate sources of uncertainty in model simulation results involving expert opinion, and their consequences for management decisions; and (c) provide insight into the consequences of predicted local climate change effects on ecological systems invaded by exotic annual Bromus species.
... In the Sonoran desert, 8% of natural desert scrub area has been converted to buffelgrass (Cenchrus ciliaris) and land transformation follows an exponential growth (Castellanos et al., 2002;Franklin et al., 2006). Besides, because of its rapid growth and efficient seed production and dispersal, buffelgrass is rapidly spreading, invading natural areas of desert scrub with visible effects on displacement of native species, threatening its conservation, a phenomenon that has been little studied (Brenner and Kanda, 2013;Franklin and Molina-Freaner, 2010;Olsson et al., 2012). ...
... Increases in aridity expected by climate change in this the Sonoran Desert region may ultimately result in less total perennial vegetation. The expansion of areas with low or no perennial vegetation cover in our study region could be studied further to inform where land degradation is likely to occur, including soil erosion losses (Sankey et al. 2013) and colonization by non-native plant species (Olsson et al. 2012). Our results demonstrate that the cover of grasses and woody plants in the future depends on the underlying topo-edaphic properties of the site, with shallow slopes and coarse-textured deep soils promoting woody plant drought resistance and fine-textured shallow soils encouraging rapid increases in grass cover following wet summers. ...
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Woody plant encroachment and overall declines in perennial vegetation in dryland regions can alter ecosystem properties and indicate land degradation, but the causes of these shifts remain controversial. Determining how changes in the abundance and distribution of grass and woody plants are influenced by conditions that regulate water availability at a regional scale provides a baseline to which compare how management actions alter the composition of these vegetation types at a more local scale and can be used to predict future shifts under climate change. Using a remote sensing-based approach, we assessed the balance between grasses and woody plants and how climate and topo-edaphic conditions affected their abundances across the northern Sonoran Desert from 1989 to 2009. Despite widespread woody plant encroachment in this region over the last 150 years, we found that leguminous trees, including mesquite (Prosopis spp.), declined in cover in areas with prolonged drying conditions during the early 21st century. Creosote bush (Larrea tridentata) also had moderate decreases with prolonged drying but was buffered from changes on soils with low clay that promote infiltration, and high available water capacity that allows for retention of water at depth. Perennial grasses have expanded and contracted over the last two decades in response to summer precipitation, and were especially dynamic on shallow soils with high clay that have large fluctuations in water availability. Our results suggest that topo-edaphic properties can amplify or ameliorate climate-induced changes in woody plants and perennial grasses. Understanding these relationships has important implications for ecosystem function under climate change in the southwestern U.S. and can inform management efforts to regulate grass-woody plant abundances. This article is protected by copyright. All rights reserved.
... Large-scale conversion of desert and thorn scrub to buffel grass pastures began in the 1970s and has continued with an almost exponential growth (Castellanos et al., 2002;Franklin et al., 2006). Thereafter, buffel grass has spread from pastures to disturbed habitats and into adjacent natural desert habitats (Olsson et al., 2012;Brenner and Kanda, 2013). Studies on the impact of buffel grass in ecosystems of NW Mexico have focused on the effect of conversion of natural vegetation to pasture for livestock grazing (Castellanos et al., 2002(Castellanos et al., , 2010Franklin et al., 2006). ...
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Cenchrus ciliaris is one of the most important invasive plants in northwestern México and southwestern United States, threatening the conservation of desert and thorn scrub. Our knowledge about the mechanisms that underlie its capacity for invasion is limited. Here, we evaluate the effect of light, temperature, gibberellic acid, osmotic potential, heat shock and experimental fire on caryopses germination from an invader population, exploring the hypothesis that fast germination under a wide range of environmental conditions facilitates survival in a plant species that invades desert environments. Results showed that caryopses of invasive plants were light-indifferent, and germinate under a wide range of temperatures (10 °C–40 °C). Germination initiates in less than 24 h, reaching a maximum in 3–6 days at 25 °C, with lower germination recorded below 15 °C. Germination occurred at osmotic potentials ranging from 0 to − 1.6 MPa. Some of the caryopses germinated only after the lemma and palea were removed and a fraction did not germinate even after covers were removed, suggesting the existence of physiological dormancy in these caryopses. Other seeds did not germinate even after gibberellins treatment. This variation in dormancy may promote a seed bank, increasing possibilities for persistence in time. Plasticity in germination responses to temperature and osmotic potential, as well as fast germination, might facilitate the invasion of buffel grass in arid and semiarid areas.
... This model was a spatially explicit STSM, developed using TELSA (Kurz et al. 2000), which included input and output maps of the P. ciliare over time, and distinguished between detected (and treatable) and undetected patches that would require resources to be detected. The model simulated dispersal of short-(i.e., neighbor-toneighbor) and long-distance dispersal of P. ciliare to other locations on the landscape based on time series of spread determined from aerial photography (Olsson et al. 2012). A map of the current known distribution of P. ciliare was derived from the same aerial photographs. ...
... In Central Australia plants required at least 58mm of rainfall to complete their life cycle (Slayter 1962 in Bosch andDudzinski 1984). Where minimum requirements are met for germination and reproduction, buffel spread at a constant rate (Olsson et al. 2012a). ...
... In Sonora, ranchers continue to bulldoze or burn native vegetation to plant buffelgrass in a process known as desmonte (Burquez-Montijo et al. 2002;Franklin et al. 2006;Brenner et al. 2012). Throughout the Sonoran Desert, buffelgrass has spread from planted pastures to disturbed roadsides, and then to washes and undisturbed hillsides (Olsson et al. 2012a;Brenner and Kanda 2013). Where buffelgrass colonizes outside pastures, its propensity to burn hotter and spread fire transforms the landscape ( The disruption of pollination and seed dispersal interactions by land transformation has likely occurred as key desertscrub and thornscrub plant species have been greatly reduced in abundance as a result of the clearing of native vegetation during the development of buffelgrass pastures. ...
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Biotic interactions are vital to ecosystem functioning. Interactions among individuals lie at the core of population and community dynamics, and therefore play a central role in the existence and persistence of species. Plants form the food base of most terrestrial ecosystems and are therefore not surprisingly involved in a substantial portion of biotic interactions. Plants, animals, and microbes face great challenges to survival in the desert environment, and these interactions play a critical role in the survival of many species. The Sonoran Desert flora is well documented and certain of its iconic interactions are well understood. For example, saguaros and the bats that pollinate them and disperse their fruits have become textbook examples of mutualisms (e.g., Shreve and Wiggins 1964; Turner et al. 2005). However, what do we know about plant-animal, plant-plant, and plant-microbe interactions in the Sonoran Desert more generally? What role do such interactions play in the ecology and evolution of the Sonoran Desert ecosystem? How are these interactions affected by global changes, and how can we conserve interactions? These questions inspired a discussion session convened at the Next Generation Sonoran Desert Researchers (NGSDR) 2012 Summit. Ultimately, participants identified the following five critical needs regarding research and conservation. We need to (1) improve our knowledge of the natural history (diversity, ecology, evolution) of interactions, both as individual entities and as players in the broader ecological community; (2) monitor interactions on broad spatio-temporal scales to be able to identify the consequences of climate change, especially for seasonal interactions involving migratory species; (3) identify the human activities with the greatest impacts on interactions; (4) develop criteria to compile a “priority interaction list” to improve and strengthen our ecosystem conservation efforts; and, finally, (5) use interactions to restore disrupted habitats and ecosystems. Here we provide a comprehensive yet concise overview of biotic interactions involving the flora, fauna, and microbiota of the Sonoran Desert, summarizing and expanding results of the NGSDR 2012 Summit discussion. We briefly present the broad categories of interspecific interactions involving Sonoran Desert plants, identify and describe threats known to negatively affect them as well as positive links with human activities, and present ongoing conservation needs and restoration efforts. We conclude by suggesting future research directions and recommendations required for urgent conservation and restoration efforts. All living organisms on Earth are involved in interactions with other organisms. Interactions are “mutualistic” when both organisms benefit and “antagonistic” when only one benefits at the expense of the other. They are “facultative” when participants do not strictly depend on one another and interact with several other species; they are “obligate” when at least one species relies on the other and rarely interacts with other species, making the interaction a matter of life and death in some cases. Although obligate interactions represent only a minor fraction of the immense web of biotic interactions, their more constant association and higher specificity make them easier to study (Davidson and McKey 1993; Futuyma and Agrawal 2009). In contrast, facultative interactions are both more common and complicated, since species interact with many partners and the associations can fluctuate between mutualistic and antagonistic (e.g., Bentley 1977; Ness 2006). Here, we focus on interspecific interactions in which Sonoran Desert plants regularly engage. We group them based on the harm or benefits animals and microbes confer. This includes two forms of antagonism, herbivory and parasitism, and five forms of mutualism, pollination, seed dispersal, biotic protection, facilitation, and microbe-mediated nutrition. These are detailed below. An extensive bibliography is provided in appendix 1. Plants are the most common terrestrial food resource for animals. Most plant-consuming animals are insects; among vertebrates, most are mammals (Herrera and Pellmyr 2002). Plants in desert habitats are particularly important for animal consumers, because they represent a critical source not only of nutrients but also water. Effects of herbivores on plant fitness differ depending on the plant parts consumed. For example, the loss of reproductive parts, such as flower buds, is worse for the plant than having some leaves eaten. In the Sonoran Desert, herbivory studies have focused on mammal consumption of woody legumes and cacti, insect...
... Spread of buffelgrass from polygons where it is present to neighboring polygons was simulated using a probability distribution of annual spread distances (i.e., dispersal kernel) with a Weibull distribution. We calibrated the dispersal kernel with time series spread data from the nearby Santa Catalina Mountains from Olsson et al. [21], because no time series data was available within the Monument. For calibration we varied the Weibull scale parameter (alpha; 0.04 to 0.2) and shape parameter (beta; 0.3 to 0.5), selecting the closest match to the observed data (alpha 0.05 and beta 0.33). ...
Article
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Resource managers are often faced with trade-offs in allocating limited resources to manage plant invasions. These decisions must often be made with uncertainty about the location of infestations, their rate of spread and effectiveness of management actions. Landscape level simulation tools such as state-and-transition simulation models (STSMs) can be used to evaluate the potential long term consequences of alternative management strategies and help identify those strategies that make efficient use of resources. We analyzed alternative management scenarios for African buffelgrass (Pennisetum ciliare syn. Cenchrus ciliaris) at Ironwood Forest National Monument, Arizona using a spatially explicit STSM implemented in the Tool for Exploratory Landscape Scenario Analyses (TELSA). Buffelgrass is an invasive grass that is spreading rapidly in the Sonoran Desert, affecting multiple habitats and jurisdictions. This invasion is creating a novel fire risk and transforming natural ecosystems. The model used in this application incorporates buffelgrass dispersal and establishment and management actions and effectiveness including inventory, treatment and post-treatment maintenance. We simulated 11 alternative scenarios developed in consultation with buffelgrass managers and other stakeholders. The scenarios vary according to the total budget allocated for management and the allocation of that budget between different kinds of management actions. Scenario results suggest that to achieve an actual reduction and stabilization of buffelgrass populations, management unconstrained by fiscal restrictions and across all jurisdictions and private lands is required; without broad and aggressive management, buffelgrass populations are expected to increase over time. However, results also suggest that large upfront investments can achieve control results that require relatively minimal spending in the future. 428 AIMS Environmental Science Volume 2, Issue 2, 427-447. Investing the necessary funds upfront to control the invasion results in the most efficient use of resources to achieve lowest invaded acreage in the long-term.
... A Minimum Noise Fraction (MNF) transformation was applied to the AVIRIS scene and MTMF was performed on the MNF-transformed image. Buffelgrass patches were previously mapped by Olsson et al. (2012a) using 0.3 m resolution aerial photography from 2002. A reference spectrum in the MNF-transformed image was derived from 11 pixels in areas of dense buffelgrass, chosen manually based on high estimates of buffelgrass cover derived from 2002 imagery. ...
Article
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This paper assesses the potential of a single HYSPIRI scene to estimate cover of the non-native invasive buffelgrass (Pennisetum ciliare) in a heterogeneous Sonoran Desert scrub ecosystem. We simulated HYSPIRI (60 m) along with two multispectral sensors, Thematic Mapper (TM; 30 m) and Advanced Space-borne Thermal Emission and Reflection Spectrometer (ASTER; 15 m), from high-resolution Airborne Visible/Infrared Imaging Spectrometer (AVIRIS; 3.2 m) imagery in an area infested by buffelgrass near Tucson, Arizona. We compared classification accuracies of all simulated sensors at spatial resolutions of 15 m, 30 m, and 60 m to evaluate tradeoffs of spectral and spatial resolution across the sensors. Although spectroscopically superior to Landsat TM and ASTER, ASTER easily outperformed HYSPIRI for small infestations (225 m2) on account of its spatial resolution. Shortwave-infrared bands near 2.2 µm were key indicators for both HYSPIRI and ASTER, highlighting the benefit of narrow-wave SWIR for mapping invasive species in arid ecosystems.
... Phenology data inform invasive species management by enabling the identification of reproduction and green-up windows-the two timeframes that are critical for mechanical removal or herbicide application. For example, in desert habitats of the southwestern US, the invasive perennial grass Pennisetum ciliare (buffelgrass) is expanding exponentially and threatens biodiversity by disrupting fire and soil moisture regimes (Olsson et al., 2012;Rogstad, 2008;Rutman et al., 2002). Managers seek to minimize inadvertent spread of propagules during mechanical control and to maximize photosynthetic uptake of herbicide during chemical control activities. ...
Article
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Changes in the timing of plant and animal life cycle events, in response to climate change, are already happening across the globe. The impacts of these changes may affect biodiversity via disruption to mutualisms, trophic mismatches, invasions and population declines. To understand the nature, causes and consequences of changed, varied or static phenologies, new data resources and tools are being developed across the globe. The USA National Phenology Network is developing a long-term, multi-taxa phenological database, together with a customizable infrastructure, to support conservation and management needs. We present current and potential applications of the infrastructure, across scales and user groups. The approaches described here are congruent with recent trends towards multi-agency, large-scale research and action.
... Visual interpretation can be highly accurate; it requires minimal image preparation and uses human knowledge to make logical decisions (Gergel et al. 2010). This method can be documented either by digitising infestations (Olsson et al. 2012) or by using visual standards to categorically record species cover at selected locations across the study site (Puckey et al. 2007). Digitising is extremely laborious but less subjective than visual cover standards (Gergel et al. 2010). ...
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We assess the feasibility of using airborne imagery for Buffel grass detection in Australian arid lands and evaluate four commonly used image classification techniques (visual estimate, manual digitisation, unsupervised classification and normalised difference vegetation index (NDVI) thresholding) for their suitability to this purpose. Colour digital aerial photography captured at approximately 5 cm of ground sample distance (GSD) and four-band (visible–near-infrared) multispectral imagery (25 cm GSD) were acquired (14 February 2012) across overlapping subsets of our study site. In the field, Buffel grass projected cover estimates were collected for quadrates (10 m diameter), which were subsequently used to evaluate the four image classification techniques. Buffel grass was found to be widespread throughout our study site; it was particularly prevalent in riparian land systems and alluvial plains. On hill slopes, Buffel grass was often present in depressions, valleys and crevices of rock outcrops, but the spread appeared to be dependent on soil type and vegetation communities. Visual cover estimates performed best (r 2 0.39), and pixel-based classifiers (unsupervised classification and NDVI thresholding) performed worst (r 2 0.21). Manual digitising consistently underrepresented Buffel grass cover compared with field- and image-based visual cover estimates; we did not find the labours of digitising rewarding. Our recommendation for regional documentation of new infestation of Buffel grass is to acquire ultra-high-resolution aerial photography and have a trained observer score cover against visual standards and use the scored sites to interpolate density across the region.
... (D) Habitat suitability model of P. ciliare derived from topographic variables plus NDVI. Because NDVI acts as a proxy for species actual distribution, the predicted suitability model identifies only areas where P. ciliare is already present, yet P. ciliare has been doubling in area at this site every 2-5 years since 1989 (Olsson et al., 2012). This model explained 38.1% of the variance (an "improvement" of model accuracy). ...
Article
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Remotely sensed datasets are increasingly being used to model habitat suitability for a variety of taxa. We review habitat suitability models (HSMs) developed for both plants and animals that include remote sensing predictor variables to determine how these variables could affect model projections. For models focused on plant species habitat, we find several instances of unintentional bias in HSMs of vegetation due to the inclusion of remote sensing variables. Notably, studies that include continuous remote sensing variables could be inadvertently mapping actual species distribution instead of potential habitat due to unique spectral or temporal characteristics of the target species. Additionally, HSMs including categorical classifications are rarely explicit about assumptions of habitat suitability related to land cover, which could lead to unintended exclusion of potential habitat due to current land use. Although we support the broader application of remote sensing in general, we caution developers of HSMs to be aware of introduced model bias. These biases are more likely to arise when remote sensing variables are added to models simply because they improve accuracy, rather than considering how they affect the model results and interpretation. When including land cover classifications as predictors, we recommend that modellers provide more explicit descriptions of how habitat is defined (e.g., is deforested land considered suitable for trees?). Further, we suggest that continuous remote sensing variables should only be included in habitat models if authors can demonstrate that their inclusion characterizes potential habitat rather than actual species distribution. Use of the term ‘habitat suitability model’ rather than ‘species distribution model’ could reduce confusion about modelling goals and improve communication between the remote sensing and ecological modelling communities.
... Present conditions have an expanding front of non-native grasses that will promote an increase of fuels and connectivity at the wildland-urban interface and the Desertscrub/Semi-desert Grassland ecotone in the coming years and couple decades (Figure by MRS). (Olsson et al., 2012a) and elevates fire risk at the WUI (Olsson et al., 2012b). Buffelgrass burns hotter than most other native and non-native grasses, reaching fire temperatures of 800-900 • C (McDonald and McPherson, 2013). ...
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Only a few decades ago, the Sonoran Desert of northwestern Mexico and southern Arizona was considered mostly fireproof, a case of not enough fine fuel to connect the dominant shrubs and cacti. This has changed with invasions by non-native, winter annual and summer-flower perennial grasses that are rapidly transforming fireproof desert into flammable grassland. Of particular concern is buffelgrass, Pennisetum ciliare, a fire-prone and invasive African perennial grass that has already converted millions of hectares across Sonora since the mid-1960s and has made quick headway in southern and central Arizona beginning in the 1980s. Near Tucson and Phoenix, AZ, buffelgrass invasion is proceeding exponentially, with population expansion (and the costs of mitigation) more than doubling every year. As this conversion progresses, there will be increased fire risks, lost tourist revenue, diminished property values, insurmountable setbacks to conservation efforts, and the threat of large ignition fronts in desert valleys routinely spreading into the mountains. Although somewhat belated, an integrated, multi-jurisdictional effort is being organized to reduce ecological and economic impacts. My presentation will summarize the history and context of buffelgrass introduction and invasion, the disconnect in attitudes and policies across state and international boundaries, ongoing management efforts, the role of science and responsibilities of scientists, accelerated spread with changing climate, and impacts to regional ecosystems and economies. This narrative may serve as a template for other semi-arid lands where buffelgrass and similar grasses have become invasive, including Australia, South America, and many islands in the Pacific Ocean (including Hawaii), Indian Ocean, and Caribbean Sea.
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Although buffel grass (Cenchrus ciliaris) invasions on several continents have significant ecological impacts, little information is available on its stage-specific interactions with native vegetation. In areas of North America’s Sonoran Desert highly impacted by buffel grass, perennial plants are particularly vulnerable during the recruitment stage. We studied the impact of buffel grass on the emergence and early survival of native perennials that germinate during monsoon season with a field experiment. We used a pot experiment to test whether proximity to buffel grass induced water stress in the seedlings of a locally dominant native tree, the foothills palo verde (Parkinsonia microphylla). Seedlings of native perennials emerged at nearly twice the rate, and survived longer, on field plots where mature buffel grass was removed, or had never invaded, than where buffel grass remained. The stable isotope signatures of carbon in palo verde seedlings grown in pots with buffel grass indicated higher stomatal closure consistent with greater water stress than in seedlings grown alone. A stage-structured model based on palo verde population dynamics illustrates that if only recruitment rates were affected by buffel grass, palo verde would likely remain on the landscape, though at reduced densities. However, the long-lived nature of perennials implies we have yet to observe the full impacts of the invasion. The model indicates the kinds of studies needed to fully predict the impact of buffel grass.
Article
Conservation lands face mounting threats of ecosystem transformation and loss of biodiversity from the invasion of fire-prone grasses. Managers must make difficult decisions to find efficient ways to expend limited resources across large and complex landscapes amidst substantial uncertainty regarding effective treatment strategies, climates, and invader-induced novel processes. Coupled empirical and process-based models can simulate the effects of management activities, quantify potential management costs and ecological impacts, while considering uncertainties associated with climate, spread rates, and wildfires lacking historical precedent. We developed a state-and-transition simulation model coupled with a fire behavior model to study impacts to native biodiversity and fire regimes in a national park invaded by a perennial grass. We evaluated resources required to meet management objectives, and efficient and effective spatial allocation of those resources. Management strategies and ecological scenarios strongly influenced the ability to minimize potential invasion impacts. Adding aerial precision spot spraying, which can target low cover levels in remote regions, may be enough to conserve the desert ecosystem from small scale transformation through invasive competition and from broad functional transformations through invasive-induced fire regime changes. Spot spraying may also be beneficial if wetter monsoonal conditions create faster invader growth rates when likelihoods of achieving management goals decreases even with unlimited resources. Given current park budgets with the addition of spot spraying, management goals may be achievable regardless of spatial prioritization. Our techniques could be applied to other situations to evaluate conservation goal feasibility and determine actions that would be most efficient in meeting those goals.
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Climate models predict that in the coming decades many arid regions will experience increasingly hot conditions and will be affected more frequently by drought. These regions are also experiencing rapid vegetation change, notably invasion by exotic grasses. Invasive grasses spread rapidly into native desert ecosystems due, in particular, to interannual variability in precipitation and periodic fires. The resultant destruction of non-fire adapted native shrub and grass communities and the inherent soil resource heterogeneity can yield invader-dominated grasslands. Moreover, recurrent droughts may cause widespread mortality of both invasive and native plants, as well as the loss of soil resources, rendering the trajectory of vegetated communities uncertain. Using the Biosphere 2 facility in the Sonoran Desert, we evaluated the viability of these hypothesized relationships by simulating combinations of drought and elevated temperature (+5°C) and assessing the ecophysiological and mortality responses of both a dominant invasive grass (Pennisetum ciliare or buffelgrass) and a dominant native grass (Heteropogan contortus or tanglehead). While both grasses survived protracted drought at ambient temperatures by inducing dormancy, drought under warmed conditions exceeded the tolerance limits of the native species, resulting in greater and more rapid mortality than the exhibited by the invasive. Thus, two major drivers of global environmental change, biological invasion and climate change, can be expected to synergistically accelerate ecosystem degradation unless large-scale interventions are enacted.
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Buffelgrass (Cenchrus ciliaris), an invasive perennial grass in arid regions of the US, has drastically modified natural ecosystems. Understanding the aboveground-belowground links between buffelgrass invasion and soil microbial communities will be critical for developing a comprehensive understanding of arid ecosystems and for deploying successful control strategies. In a randomized-block field experiment located in Tucson, Arizona (U.S.A.), we investigated the effects of buffelgrass removal via hand pulling and nitrogen addition (and their interaction) on soil microbial communities during an extreme drought (summer 2020). We found that experimental treatments did not significantly impact bacterial and archaeal community diversity and composition, while plant removal affected fungal community diversity and composition. In addition, the removal treatment increased the proportion of putative chitinolytic bacteria (genus Lysobacter) and decreased the proportion of putative fungal endophytes (genus Darksidea). Buffelgrass manual removal appeared to favor fungal endophyte death around and inside of leftover intact roots, which may result in an increase of chitinolytic bacteria thriving on the degradation of fungal cell walls. Overall, our results suggest that hand removal – which is a common type of buffelgrass control – can alter soil fungal communities and the proportion of certain microbial functional groups. Since these changes could subsequently affect native plants, more research is needed to develop a comprehensive understanding of the effect of buffelgrass control efforts on target plants as well as surrounding ecosystem dynamics. This article is protected by copyright. All rights reserved.
Technical Report
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The spread of the invasive and fire-adapted buffelgrass (Cenchrus ciliaris L.) threatens desert ecosystems by competing for resources, increasing fuel loads, and creating wildfire connectivity. The Rincon Mountain District of Saguaro National Park addressed this natural resource threat with the use of glyphosate-based herbicides (GBHs). In 2010, the Rincon Mountain District initiated an aerial restoration plan to control dense buffelgrass patches in remote areas and implemented a trial project to evaluate the effects of aerial restoration techniques that included the helicopter application of GBHs. In 2014, more than 250 acres of buffelgrass in the Rincon Mountain District were treated with the aerial application of GBHs. This widespread aerial application of GBHs continued through 2018, but the potential transport and effects to aquatic ecosystems were unknown. In 2015–18, the U.S. Geological Survey, in cooperation with the National Park Service, studied the occurrence, distribution, fate, and transport of glyphosate in surface water and sediments derived from areas that were treated during past and current aerial herbicide applications. Three watersheds, treated with different regimens of GBHs, were sampled for glyphosate and the primary metabolite of glyphosate, aminomethylphosphonic acid (AMPA), during various hydrologic flow conditions. Water and aquatic sediment were collected from three watersheds, each in a different stage of application during the U.S. Geological Survey study. The unnamed watershed above the Loma Verde Trailhead referred to by the National Park Service as “Loma Verde canyon” had received no aerial treatment since 2014, whereas the Box Canyon watershed was aerially treated every year beginning in 2014. The Madrona Canyon watershed was first sprayed in 2016 and aerial application continued once a year though the entirety of the study. In addition, terrestrial soil samples were sampled from areas sprayed to understand dissipation rates and herbicide transport via sediments washing away during rainfall runoff. The concentrations present in water and sediment samples were compared to ecological benchmarks and characterized within the context of the environmental conditions of the park setting. Of the 48 water samples collected and analyzed for glyphosate and AMPA, 10.4 percent and 14.6 percent were detected above the laboratory minimum detection limit, respectively. Mean water concentrations, calculated using specific statistical methods for non-detects, were equal to the laboratory minimum detection limit of 0.02 microgram per liter for samples collected in all the watersheds. In aquatic sediments, glyphosate and AMPA were detected in 10.7 and 25.0 percent of the samples, whereas 89.5 and 100 percent of the terrestrial soil samples had detections for glyphosate and AMPA, respectively. Mean aquatic sediment concentrations were 1.13 and 4.42 micrograms per kilogram (μg/kg) for glyphosate and AMPA, respectively. Mean terrestrial soil concentrations were orders of magnitude greater than water and aquatic sediment with concentrations of 678 μg/kg for AMPA and 1,240 μg/kg for glyphosate. Hours after glyphosate-based herbicide was applied, the concentrations of glyphosate and AMPA were present in terrestrial soil samples near or above the laboratory maximum detection limit of 5,000 μg/kg. The Box Canyon watershed was the most intensively treated watershed in terms of total land area treated, total amount of GBH applied, and number of years treated. The frequent and large volume of treatment resulted in the highest number of detections of glyphosate and AMPA in water (3 and 7 detections, respectively) and in aquatic sediment (2 and 6 detections, respectively) samples. In comparison, the other two watersheds had two or fewer detections for glyphosate and AMPA in water and aquatic sediment. Glyphosate detected in pools was associated with increased rainfall closer in time to the last herbicide treatment. Glyphosate and AMPA concentration ratios above one, along with stable-isotope and tritium results, indicated that runoff processes were the primary transport mechanism for the two compounds when found in streams and pools rather than subsurface recharge or deeper flow paths. One pool in a small tributary of Box Canyon consistently had detections of glyphosate and AMPA in aquatic sediments, but these frequent concentrations were likely related to the intensive application upstream, near the steep terrain above the head of the channel that supplies the downstream pool. Intense flows during summer rainfall events move treated sediments into this channel where vegetation and the incised bedrock banks of the pool retained those sediments and ultimately led to frequent detections of both compounds. Isotope results in most of the pools and tinajas indicated that the water source had residence time representative of recently recharged waters, on the order of years. No water concentrations exceeded published criteria for human health or aquatic life. Median and maximum glyphosate and AMPA water concentrations were lower than those reported in other national assessments, but maximum concentrations observed in individual runoff samples were higher than median concentrations measured in the national assessments. A similar finding was observed with aquatic sediment concentrations measured in the Rincon Mountain District. Results from the study were compared and assessed in the context of other studies examining GBHs and their effects on amphibians, fish, and macroinvertebrates. This comparison was used to generalize the potential risk to aquatic species similar to those species in the Rincon Mountain District. Concentrations of published effect levels were several orders of magnitude greater than the highest concentration detected in water at the Rincon Mountain District. Most published studies evaluate acute and chronic toxicity for glyphosate and GBHs, and these criteria may not be representative of environmental conditions in the Rincon Mountain District. The classic lethal dose studies conducted in a controlled laboratory setting may not be suitable for comparison to the longer, variable, low-dose exposure conditions in the pools and tinajas in the Rincon Mountain District. However, this study determined that the fate of GBHs transported from treated areas to potential aquatic habitat was highly variable in occurrence, timing, and concentrations. This variability in glyphosate concentrations was too high, and the potential exposure was determined to be far too complex to directly compare with the results from controlled studies. This study provides the first information collected on GBHs used to control invasive buffelgrass in a remote, mountainous, and semiarid setting. The information about the transport and fate of herbicide application near aquatic habitat will help to inform managers about the broader ecosystem implications and provide useful information to other agencies implementing buffelgrass remediation strategies near aquatic habitat.
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The southwestern United States experiences extreme hydroclimatic variability, including intense but localized monsoon thunderstorms, tropical storms, and winter storms, resulting in complex and variable patterns of precipitation over space and time. Official gauges associated with long‐term monitoring networks are sparsely distributed throughout the region and are unable to capture the spatial complexity and variability of these precipitation patterns. The RainLog program, a volunteer precipitation monitoring program, was started in southern Arizona in 2005 to leverage enthusiasm among non‐scientists around weather, water, and climate to address the gaps in official monitoring networks. An examination of the portion of the dataset that spans the Tucson Metropolitan Area illustrates the opportunities and challenges in using volunteer data to track precipitation. We compare near‐complete records to an official observation to highlight how the broader RainLog network supports characterizing hydroclimatic variability over the period of record. We also examine several case study events drawn from metrics of network variability that represent different forms of hydroclimatic extremes. We find that in most cases the RainLog network captures a range of precipitation values that were notably different than the single value recorded at the official observing site, adding substantial value in recording and reconstructing past extreme precipitation events. This work highlights how volunteer citizen science precipitation monitoring networks can provide critical data for tracking precipitation variability and changes, though are only one complementary piece of coherent, long‐term hydroclimatic monitoring. This article is protected by copyright. All rights reserved.
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Buffelgrass ( Pennisetum ciliare (L.) Link ) is a drought-tolerant invasive grass that is a threat to native biodiversity in the drylands of the Americas and Australia. Despite efforts from land managers to control P. ciliaris , management approaches tend to have mixed success, treatment results can be poorly communicated among entities, and there are few long-term controlled studies. In this literature review we synthesize data from both peer-reviewed and “grey” literature on the efficacy of management techniques to control P. ciliaris and the secondary impacts to native plant communities. Our search resulted in 42 unique sources, containing a total of 229 studies that we categorized into 10 treatment types, which included herbicide, seeding, manual removal, fire, grazing, biocontrol, fire + additional treatments, manual removal + additional treatments, herbicide + additional treatments, and herbicide + manual removal. We found treatments that utilized multiple techniques in tandem as well as follow-up treatments were the most effective at controlling P. ciliaris . Fewer than 1/3 of the studies reported impacts of management on native species and the most commonly studied treatment (herbicide, N = 130) showed detrimental impacts on native plant communities. However, the average time between treatment and outcome measurement was only 15 months; we suggest the need for more long-term studies of treatment efficacy as well as secondary impacts on the ecosystem. Lastly, we conducted a second literature review on P. ciliaris biology and traits for mechanisms that allows it to alter the invaded environment to facilitate a competitive advantage over native species. We found evidence of self-reinforcing feedbacks of invasion being generated by P. ciliaris through its interactions with water availability, nutrient cycling, and disturbance regimes. We developed a conceptual model of P. ciliaris based on these feedback loops and offer management considerations based on its invasion dynamics and biology.
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Radicinin is a phytotoxic fungal dihydropyranopyran-4,5-dione under evaluation for the development of a target-specific bioherbicide for invasive buffelgrass (Cenchrus ciliaris) control. It has already demonstrated high toxicity on host plants, low toxicity to native plants and no negative effects on zebrafish embryos. To continue these studies at the whole-plant level there is a need to obtain much larger quantities of radicinin, either by optimizing its large-scale production by fungal fermentation or through its total stereoselective synthesis. A rapid and sensitive HPLC method for quantification of radicinin in complex mixtures has been developed in order to evaluate its production by different Cochliobolus australiensis strains and in different cultural conditions. The analysis proved that radicinin is not produced by all the strains tested and its synthesis is strongly affected by cultural conditions. The HPLC method could be useful in selecting the best fungal source for the production of this promising potential bioherbicide.
Article
The fungal pathogen Cochliobolus australiensis isolated from infected leaves of the invasive weed buffelgrass (Pennisetum ciliare) was grown in vitro to evaluate its ability to produce phytotoxic metabolites that could potentially be used as natural herbicides against this weed. Two new tetrasubstituted 3-chromanonacrylic acids, named chloromonilinic acids C (1) and D (2), were isolated from the liquid cultures of C. australiensis, together with the known chloromonilinic acid B. Chloromonilinic acids C and D were characterized by spectroscopic and chemical methods as (E)-3-chloro-3-[(5-hydroxy-3-(1-hydroxy-2-methoxy-2-oxoethyl)-7-methyl-4-oxo-4H-chromen-2-yl)]acrylic acid and (Z)-3-chloro-3-[(5-hydroxy-3-(2-methoxy-2-oxoethyl)-7-methyl-4-oxo-4H-chromen-2-yl)]acrylic acid, respectively. The stereochemistry of chloromonilinic acids C and D was determined using a combination of spectroscopic and computational methods, including electronic circular dichroism. The fungus produced these compounds in two different liquid media together with cochliotoxin, radicinin, radicinol, and their 3-epimers. The radicinin-related compounds were also produced when the fungus was grown in wheat seed solid culture, but chloromonilinic acids were not found in the solid culture organic extract. All three chloromonilinic acids were toxic to buffelgrass in a seedling elongation bioassay, with significantly delayed germination and dramatically reduced radicle growth, especially at a concentration of 5 × 10–3 M.
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Pyricularia grisea has been identified as a foliar pathogen on buffelgrass (Cenchrus ciliaris) in North America and was studied as a potential source of phytotoxins for buffelgrass control. Two monosubstituted hex-4-ene-2,3-diols, named pyriculins A and B, were isolated from its culture filtrate organic extract together with (10S,11S)-(−)-epipyriculol, trans-3,4-dihydro-3,4,8-trihydroxy-1(2H)-napthalenone, and (4S)-(+)-isosclerone. Pyriculins A and B were characterized by spectroscopic (essentially nuclear magnetic resonance [NMR], High-resolution electrospray ionization mass spectrometry [HRESIMS]) and chemical methods such as (4E)-1-(4-hydroxy-1,3-dihydroisobenzofuran-1-yl)hex-4-ene-2,3-diols. The relative and absolute configuration of these compounds was determined by a combination of spectroscopic (NMR, electronic circular dichroism [ECD]) and computational tools. When bioassayed in a buffelgrass coleoptile and radicle elongation test, (10S,11S)-(−)-epipyriculol proved to be the most toxic compound. Seed germination was much reduced and slowed with respect to the control and radicles failed to elongate. All five compounds delayed germination, but only (10S,11S)-(−)-epipyriculol was able to prevent radicle development of buffelgrass seedlings. It had no effect on coleoptile elongation, while the other four compounds caused significantly increased coleoptile development relative to the control.
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Seed dispersal by caching rodents is a context-dependent mutualism in many systems. Plants benefit when seed remaining in shallow caches germinates before being eaten, often gaining protection from beetles and a favorable microsite in the process. Caching in highly unfavorable microsites, conversely, could undermine the dispersal benefit for the plant. Plant invasions could disrupt dispersal benefits of seed caching by attracting rodents to the protection of a dense invasive canopy which inhibits the establishment of native seedlings beneath it. To determine whether rodents disproportionately cache seed under the dense canopy of an invasive grass in southeastern Arizona, we used nontoxic fluorescent powder and ultraviolet light to locate caches of seed offered to rodents in the field. We fitted a general habitat-use model, which showed that disproportionate use of plant cover by caching rodents (principally Chaetodipus spp.) increased with moonlight. Across all moon phases, when rodents cached under plants, they cached under the invasive grass disproportionately to its relative cover. A greenhouse experiment showed that proximity to the invasive grass reduced the growth and survival of seedlings of a common native tree (Parkinsonia microphylla) whose seeds are dispersed by caching rodents. Biased dispersal of native seed to the base of an invasive grass could magnify the competitive effect of this grass on native plants, further reducing their recruitment and magnifying the effect of the invasion.
Article
By altering ecosystem structure and function, invasions by nonnative plants have the potential to alter the quantity and quality of habitat for animals. We examined effects of buffelgrass (Pennisetum ciliare), a nonnative grass that is increasing in distribution markedly throughout the southwestern United States and northern Mexico, on demographic characteristics and condition of Sonoran desert tortoises (Gopherus morafkai). In 2010 and 2011, we established 50 4-ha plots that spanned the gradient of buffelgrass cover in areas with environmental features characteristic of high-quality habitat for tortoises in southern Arizona. We surveyed each plot four times per year to characterize density, population structure, and condition of tortoises. We detected tortoises on 45 of 50 plots (90 %) and ≥1 tortoise during 114 of 200 surveys (57 %). We used a hierarchical model to estimate density of tortoises while accounting for imperfect detection rates. Density of tortoises averaged 0.35 individuals/ha (SE = 0.04) and did not vary appreciably with the amount of buffelgrass cover; similarly, age and sex structure of tortoise populations did not vary with buffelgrass cover. Condition of adult tortoises, however, averaged 10 % lower in areas where cover of buffelgrass was high (>15 %) relative to areas where buffelgrass was absent or cover was low (
Article
Ecological conditions following removal of exotic plants are a key part of comprehensive environmental management strategies to combat exotic plant invasions. We examined ecological conditions following removal of the management-priority buffelgrass (Pennisetum ciliare) in Saguaro National Park of the North American Sonoran Desert. We assessed soil, vegetation, and soil seed banks on seven buffelgrass site types: five different frequencies of buffelgrass herbicide plus hand removal treatments (ranging from 5 years of annual treatment to a single year of treatment), untreated sites, and non-invaded sites, with three replicates for each of the seven site types. The 22 measured soil properties (e.g., pH) differed little among sites. Regarding vegetation, buffelgrass cover was low (≤1 % median cover), or absent, across all treated sites but was high (10-70 %) in untreated sites. Native vegetation cover, diversity, and composition were indistinguishable across site types. Species composition was dominated by native species (>93 % relative cover) across all sites except untreated buffelgrass sites. Most (38 species, 93 %) of the 41 species detected in soil seed banks were native, and native seed density did not differ significantly across sites. Results suggest that: (1) buffelgrass cover was minimal across treated sites; (2) aside from high buffelgrass cover in untreated sites, ecological conditions were largely indistinguishable across sites; (3) soil seed banks harbored ≥12 species that were frequent in the aboveground vegetation; and (4) native species dominated post-treatment vegetation composition, and removing buffelgrass did not result in replacement by other exotic species.
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Using U.S. Forest Service fire occurrence records, we found that during the 29-year period 1955 to 1983, 1611 fires burned a total of 41,447 ha in the 391,000-ha desert portion of Tonto National Forest, Arizona (TNF). Lightning-caused fires, though fewer in number, burned approximately twice the area of fires set by people. Fires were numerous from May through August, but area burned was greater during June than all other months combined. Using average annual hectares burned and subtracting areas of overlap between fires, we estimated that 294 years were required for all parts of the TNF desert to burn. Ignoring overlap, estimated time required for an area of equal size to the TNF desert to burn is 274 years. Increasing fire occurrence during the 29-year period studied might be due to wetter-than-normal winters toward the end of the period, fuel provided by exotic annual plants, improved fire detection and reporting, and ignition by people.
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AimThe dynamics of spread of some representatives of Oenothera, a genus of New World origin and alien to Europe, was analysed.LocationDistribution data from six European countries., i.e. Austria, Czech Republic, Hungary, Portugal, Serbia and UK were used.Methods Floristic records covering the last 200 years were collated and the cumulative number of localities was plotted against time. A correction of the number of localities, taking into account the intensity of floristic research in particular countries, was applied based on the total number of available herbarium specimens to make comparisons of the rate of spread in particular countries possible.ResultsIn total, 35 alien taxa of the genus have been reported from the countries considered, the majority of which has only a limited distribution. So far 1800 records of Oenothera species have been reported from the six countries analysed since 1780, with O. biennis, O. erythrosepala, O. salicifolia, O. stricta, O. cambrica, O. rubricaulis, and O. chicaginensis having more than 50 localities. There is a highly significant negative correlation between the total number of localities in Europe and the year of the first introduction. Marked differences were found in the taxonomical pattern of invasion in particular countries.Main conclusionsMultivariate analyses have shown that in Europe, there are two distinct groups of species of North and South American origin, respectively, whose invasion is determined by climatic conditions, namely temperature and precipitation. The South American group is represented by perennial and annual species preferring oceanic climate (e.g. O. rosea, O. stricta), while the North American group consists of biennial representatives (O. biennis and others) better adapted to inland conditions with lower mean temperature and more balanced monthly precipitations. In addition, there is a transitional group of species, including namely O. erythrosepala and O. fallax, preferring regions with sufficient rainfall and higher temperatures. The relatively hot climate of Balkan Peninsula seems to prevent invasion by Oenothera representatives. Pattern of invasion of particular taxa corresponds well to the climatic conditions in the regions of their natural distribution.
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Popular pastoral species, Buffel grass (Cenchrus ciliaris) is receiving long overdue attention as an invasive weed that poses serious threats to biodiversity conservation worldwide. Most research focuses on the species as forage plant and is largely published in agricultural and grey literature. Meanwhile, there is a dearth of information about the species ecology in natural landscapes despite strong evidence from field workers and managers that the species is an aggressive invader and threat to biodiversity in many environments. We present a comprehensive review of the ecology, distribution and biodiversity impacts of Buffel grass when behaving as an invasive species. Foundations are laid for research into localised habitat requirements of the species that will aid in the management of Buffel grass invasions now and into the future.
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Using a combination of replicated microcosm experiments, simple nonlinear modelling and model fitting we show that unexpected levels of variability can be detected and described in the dynamics of plant disease. Temporal development of damping-off disease of radish seedlings caused by an economically important plant pathogen, Rhizoctonia solani, is quantified, with and without the addition of an antagonistic fungus, Trichoderma viride. The biological control agent reduces the average amount of disease but also greatly enhances the variability among replicates. The results are shown to be consistent with predictions from a nonlinear model that exhibits dynamically generated variability in which small differences in the initiation of infection associated with the antagonist are later amplified as the pathogen spreads from plant to plant. The effect of dynamically generated variability is mediated by the interruption of transient disease progress curves for separate replicates by an exponential decrease in susceptibility of the host over time. The decay term essentially 'freezes' the dynamics of the transient behaviour so that the solutions for different replicates settle on asymptotes that depend on initial conditions and parameter values. The effect is further magnified by nonlinear terms in the infection force in the models. A generalization of the Lyapunov exponent is introduced to quantify the amplification. The observed behaviour has profound consequences for the design and interpretation of ecological experiments, and can also account for the notorious failure of many biological control strategies through the creation of `hot spots', created by the amplification of plant to plant infection, where the control by the antagonist is locally unsuccessful.
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Protected area managers often face uncertainty when managing invasive plants at the landscape scale. Crested wheatgrass, a popular forage crop in the Great Plains since the 1930s, is an aggressive invader of native grassland and a problem for land managers in protected areas where seeded roadsides and abandoned fields encroach into the native mixed-grass prairie. Given limited resources, land managers need to determine the best strategy for reducing the cover of crested wheatgrass. However, there is a high degree of uncertainty associated with the dynamics of crested wheatgrass spread and control. To compare alternative management strategies for crested wheatgrass in the face of uncertainty, we conducted a decision analysis based on information from Grasslands National Park. Our analysis involves the use of a spatially explicit model that incorporates alternative management strategies and hypotheses about crested wheatgrass spread and control dynamics. Using a decision tree and assigning probabilities to our alternative hypotheses, we calculated the expected outcome of each management alternative and ranked these alternatives. Because the probabilities assigned to alternative hypotheses are also uncertain, we conducted a sensitivity analysis of the full probability space. Our results show that under current funding levels it is always best to prioritize the early detection and control of new infestations. Monitoring the effectiveness of control is paramount to long-term success, emphasising the need for adaptive approaches to invasive plant management. This type of decision analysis approach could be applied to other invasive plants where there is a need to find management strategies that are robust to uncertainty in the current understanding of how these plants are best managed.
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A gridline survey for exotic plant species was undertaken in 1983 and repeated in 2005 at the Desert Laboratory, a 352-ha natural area just west of downtown Tucson, Arizona, USA. Coordinate data gathered during the surveys were used to plot distributions, determine frequencies (number of coordinate locations), and assess percent change. Fifty-two exotic species were encountered in all, 34 in the first survey, 44 in the second. The proportion of ornamental exotics doubled over time, reaching 50% in 2005. Casual, naturalized, and invasive exotics comprised 44%, 40%, and 15% of species found during the surveys. Minimum residence time increased significantly from casual to naturalized to invasive species, suggesting that the longer a species was present, the more likely it was to surmount barriers to naturalization and invasion. In both 1983 and 2005, casual, naturalized, and invasive species differed in mean frequency by an order of magnitude, with casual species having the lowest frequencies and invasive species the highest. Between surveys, frequency of 18 species decreased; most other species increased in frequency. The recent surge in ornamental exotics, combined with temporal trends in invasiveness, indicates that the proportion of invasive species in the flora will increase with time.
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Ecological responses to climatic variability in the Southwest include regionally synchronized fires, insect outbreaks, and pulses in tree demography (births and deaths). Multicentury, tree-ring reconstructions of drought, disturbance history, and tree demography reveal climatic effects across scales, from annual to decadal, and from local (�102 km2) to mesoscale (104–106 km2). Climate–disturbance relations are more variable and complex than previously assumed. During the past three centuries, mesoscale outbreaks of the western spruce budworm (Choristoneura occidentalis) were associated with wet, not dry episodes, contrary to conventional wisdom. Regional fires occur during extreme droughts but, in some ecosystems, antecedent wet conditions play a secondary role by regulating accumulation of fuels. Interdecadal changes in fire–climate associations parallel other evidence for shifts in the frequency or amplitude of the Southern Oscillation (SO) during the past three centuries. High interannual, fire–climate correlations (r � 0.7 to 0.9) during specific decades (i.e., circa 1740–80 and 1830– 60) reflect periods of high amplitude in the SO and rapid switching from extreme wet to dry years in the Southwest, thereby entraining fire occurrence across the region. Weak correlations from 1780 to 1830 correspond with a decrease in SO frequency or amplitude inferred from independent tree-ring width, ice core, and coral isotope reconstructions.
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Clearing of natural vegetation for pastures and the deliberate introduction of African grasses constitute significant threats to the biological diversity of the tropics, subtropics, and warm temperate regions of the Americas. African grasses have escaped from cultivated pastures and revegetated rangeland sites and invaded natural areas at alarming rates. Invaded ecosystems tend to be biotically impoverished and differ markedly from adjacent non-invaded areas in structure and function. Effects of pasture creation and invasion by African grasses on ecosystem processes (transformation and flux of energy and matter) are primarily related to loss of woody species and changes in the fire regime. However, the ecophysiological attributes of the African grasses (e.g. high biomass allocation to leaves, high growth rate, and high leaf-level gas exchange rates) also have important consequences. Here we describe the extent of pasture creation with African grasses and their invasive spread in the New World and review ecological effects of these land-cover changes. We highlight a number of comparative ecophysiological studies within the context of mechanisms responsible for invasion by African grasses and resulting ecosystem change.
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Bufflelgrass (Pennisetum ciliare syn. Cenchrus ciliaris) is an African grass that has been widely introduced in subtropical arid regions of the world to improve rangelands for cattle production. However, it can have a negative effect on the diversity of native plant communities. Buffelgrass was introduced to Sonora, Mexico in the 1970s as a means to bolster the cattle industry. “Desmonte,” the process by which native desert vegetation is removed in preparation for buffelgrass seeding, alters the land surface such that buffelgrass plots are easily detectable from aerial and Landsat satellite images. We estimated the extent of conversion to buffelgrass in a 1,850,000 ha area centered on Hermosillo, from MSS and TM images from 1973, 1983, 1990 and 2000. We then compared the relative above-ground productivity of buffelgrass to native vegetation using Normalized Difference Vegetation Index values (NDVI) from Landsat and Moderate Resolution Imaging Spectrometer (MODIS) satellite sensor systems. Buffelgrass pastures have increased from just 7700 ha in 1973 to over 140,000 ha in 2000. Buffelgrass pastures now cover 8% of the land surface in the study area. Buffelgrass pastures have lower net primary productivity, estimated by MODIS NDVI values, than unconverted desert land. The desmonte process removes trees and shrubs, while the buffelgrass plantings are often sparse, leading to an apparent net loss in net primary production from land conversion. We recommend that the desmonte process be discontinued until its efficacy and safety for native ecosystems can be established, and that a comprehensive plan for preserving biodiversity while accomodating economic development be established for this region of the Sonoran Desert in Mexico.
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1 The invasion of habitats by non-native plant and animal species is a global phenomenon with potentially grave consequences for ecological, economic, and social systems. Unfortunately, to date, the study of invasions has been primarily anecdotal and resistant to generalization. 2 Here, we use insights from experiments and from long-term monitoring studies of vegetation to propose a new theory in which fluctuation in resource availability is identified as the key factor controlling invasibility, the susceptibility of an environment to invasion by non-resident species. The theory is mechanistic and quantitative in nature leading to a variety of testable predictions. 3 We conclude that the elusive nature of the invasion process arises from the fact that it depends upon conditions of resource enrichment or release that have a variety of causes but which occur only intermittently and, to result in invasion, must coincide with availability of invading propagules.
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Proliferation of woody plants in grasslands and savannas since the 1800s has been widely documented. In the southwestern United States, increased abundance of honey mesquite (Prosopis glandulosa var. glandulosa) has been attributed to heavy grazing by livestock. Here, we test the hypothesis that P. glandulosa invasion of grasslands requires, first, reductions in herbaceous biomass and density such as those that accompany livestock grazing and, second, episodes of high soil moisture availability. No combination of grass density (nonmanipulated or reduced 50%) or defoliation (none, moderate, heavy) significantly affected P. glandulosa seedling emergence within a watering regime (natural and supplemented) at our field site in semiarid southern Texas. Seedling emergence on plots receiving only natural rainfall was high (42%), despite the fact that precipitation was substantially below normal. Supplemental watering, to generate moisture levels approximating years of unusually high annual rainfall, increased emergence to 59%. Seedling survival after 2 yr was high (62-77%) and statistically comparable across the density, defoliation, and watering treatments. Net photosynthesis (An) of 1-yr-old seedlings was enhanced by supplemental watering, but reductions in grass density or biomass had little effect on seedling An or xylem water potential. Height, aboveground biomass, and leaf area were comparable among 1- and 2-yr-old seedings across all density, defoliation, and watering combinations. High seedling emergence and survival on unwatered plots, even during a "drought year," suggests that Prosopis recruitment is not contingent upon unusual or episodic rainfall. Reductions in biomass and density of herbaceous vegetation had no influence on seedling emergence, growth, or survival, suggesting that Prosopis invasion is minimally influenced by grass competition. Historic grazing at this site appears to have altered herbaceous composition and reduced above- and belowground biomass production below the threshold level required for competitive exclusion of woody vegetation. Such data suggest that rates and patterns of seed dispersal may be the primary determinants of P. glandulosa encroachment on present-day landscapes in semiarid regions. Minimizing livestock dispersal of seed (in the case of leguminous shrubs) and maintenance of an effective fire regime (through production of fine fuels) may be crucial for sustaining herbaceous composition and production in grazed systems prone to invasion by unpalatable woody plants.
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The 'pulse-reserve' conceptual model--arguably one of the most-cited paradigms in aridland ecology--depicts a simple, direct relationship between rainfall, which triggers pulses of plant growth, and reserves of carbon and energy. While the heuristics of 'pulses', 'triggers' and 'reserves' are intuitive and thus appealing, the value of the paradigm is limited, both as a conceptual model of how pulsed water inputs are translated into primary production and as a framework for developing quantitative models. To overcome these limitations, we propose a revision of the pulse-reserve model that emphasizes the following: (1) what explicitly constitutes a biologically significant 'rainfall pulse', (2) how do rainfall pulses translate into usable 'soil moisture pulses', and (3) how are soil moisture pulses differentially utilized by various plant functional types (FTs) in terms of growth? We explore these questions using the patch arid lands simulation (PALS) model for sites in the Mojave, Sonoran, and Chihuahuan deserts of North America. Our analyses indicate that rainfall variability is best understood in terms of sequences of rainfall events that produce biologically-significant 'pulses' of soil moisture recharge, as opposed to individual rain events. In the desert regions investigated, biologically significant pulses of soil moisture occur in either winter (October-March) or summer (July-September), as determined by the period of activity of the plant FTs. Nevertheless, it is difficult to make generalizations regarding specific growth responses to moisture pulses, because of the strong effects of and interactions between precipitation, antecedent soil moisture, and plant FT responses, all of which vary among deserts and seasons. Our results further suggest that, in most soil types and in most seasons, there is little separation of soil water with depth. Thus, coexistence of plant FTs in a single patch as examined in this PALS study is likely to be fostered by factors that promote: (1) separation of water use over time (seasonal differences in growth), (2) relative differences in the utilization of water in the upper soil layers, or (3) separation in the responses of plant FTs as a function of preceding conditions, i.e., the physiological and morphological readiness of the plant for water-uptake and growth. Finally, the high seasonal and annual variability in soil water recharge and plant growth, which result from the complex interactions that occur as a result of rainfall variability, antecedent soil moisture conditions, nutrient availability, and plant FT composition and cover, call into question the use of simplified vegetation models in forecasting potential impacts of climate change in the arid zones in North America.
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Species invasions are a principal component of global change, causing large losses in biodiversity as well as economic damage. Invasion theory attempts to understand and predict invasion success and patterns of spread. However, there is no consensus regarding which species or community attributes enhance invader success or explain spread dynamics. Experimental and theoretical studies suggest that regulation of spread dynamics is possible; however, the conditions for its existence have not yet been empirically demonstrated. If invasion spread is a regulated process, the structure that accounts for this regulation will be a main determinant of invasion dynamics. Here we explore the existence of regulation underlying changes in the rate of new site colonization. We employ concepts and analytical tools from the study of abundance dynamics and show that spread dynamics are, in fact, regulated processes and that the regulation structure is notably consistent among invasions occurring in widely different contexts. We base our conclusions on the analysis of the spread dynamics of 30 species invasions, including birds, amphibians, fish, invertebrates, plants, and a virus, all of which exhibited similar regulation structures. In contrast to current beliefs that species invasions are idiosyncratic phenomena, here we provide evidence that general patterns do indeed exist. • conservation • invasion • population dynamics • range expansion • regulation
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Climate change may exacerbate invasions by making conditions more favorable to introduced species relative to native species. Here we used data obtained during a long-term biannual survey of the distribution of ant species in a 481-ha preserve in northern California to assess the influence of interannual variation in rainfall on the spread of invasive Argentine ants, Linepithema humile, and the displacement of native ant species. Since the survey began in 1993, Argentine ants have expanded their range into 74 new hectares. Many invaded hectares were later abandoned, so the range of Argentine ants increased in some years and decreased in others. Rainfall predicted both range expansion and interannual changes in the distribution of Argentine ants: high rainfall, particularly in summer months, promoted their spread in the summer. This suggests that an increase in rainfall will promote a wider distribution of Argentine ants and increase their spread into new areas in California. Surprisingly, the distribution of two native ant species also increased following high rainfall, but only in areas of the preserve that were invaded by L. humile. Rainfall did not have a negative impact on total native ant species richness in invaded areas. Instead, native ant species richness in invaded areas increased significantly over the 13 years of observation. This suggests that the impact of Argentine ants on naïve ant communities may be most severe early in the invasion process.
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Data on the spread of invasive weeds into arid western lands are used to evaluate the environmental and economic importance of controlling invasive weed infestations early. Variable rate and constant rate infestation expansion paths are estimated. The implications of variable vs. constant infestation growth rates for projecting both biophysical and economic effects are illustrated. The projections derived from both constant and variable growth rate expansion paths support the contention that it is expedient to control new infestations early.
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Around 1900 temperate and semidesert grassland productivity declined, soil erosion increased, and drought destabilized the livestock industry in the northern and southern hemispheres. As government leaders throughout the world began to recognize the importance of grassland productivity and soil conservation, a massive experiment began to evolve. Government and private individuals collected seed from every continent, and planted seed at experimental stations and ranches in their respective countries. Hundreds of individuals who conducted thousands of seeding trials observed that buffelgrass (Cenchrus ciliaris L.), weeping lovegrass [Eragrostis curvula (Schrad.) Nees], kleingrass (Panicum coloratum L.), and lovegrass (Eragrostis lehmanniana Nees) plants from seed collected in Africa were easier to establish and persisted longer than other grasses. Between 1930 and 1986 scientists in many countries evaluated the establishment and persistence of these grasses, but no attempt was made to synthesize the data base and determine the effects of climate and soil on plant establishment and persistence. Our objective was to: (1) determine the climatic and edaphic characteristics of areas where the seed of each grass was collected in Africa, and where each grass has been successfully established in both hemispheres, and (2) identify characteristics which influence long-term persistence. Where buffelgrass predominates and spreads, summer rainfall varies from 150 to 550 mm, winter rainfall is less than 400 mm, mean miminum winter temperatures rarely fall below 5° C, and soil texture is loamy. Weeping lovegrass can be established and plants persist when spring, summer, and fall rainfall varies from 400 to 1,000 mm on deep sandy soil and mean minimum winter temperatures rarely fall below -5° C. The invasion of adjacent nonplanted sites occurs only in Africa where growing season rainfall infrequently cycles between 750 and 1,000 mm and soils remain wet in mid-summer. Kleingrass can be established where mean maximum daily summer temperatures are above 30° C, mean minimum daily winter temperatures rarely fall below 0° C, summer growing season rainfall varies from 400 to 990 mm, and soils are clayey or silty. Kleingrass, like weeping lovegrass, spreads to nonplanted sites only in Africa where a mid-summer drought does not occur. Lehmann lovegrass predominates and spreads only in southern Africa, southeastern Arizona, and northern Mexico when summer rainfall in 30 to 40 days exceeds 150 mm, and soil textures are sandy or sandy loam.
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Batches of buffel grass seeds, which had been sown near Alice Springs, N.T. at the usual depth of about one inch, were recovered at increasing intervals. Germination percentages were compared with those of seeds stored in the laboratory for the same periods. At the time of sowing 30 per cent germination was obtained. This level was maintained in the soil for eight months, followed by, a sharp decline to 10 per cent which was maintained for another two years. Stored seed showed an increase to 94 per cent germination in the 8 to 18 month period. The implications are discussed in relation to seed dormancy.
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Red brome is a Mediterranean winter annual grass that has invaded south-western USA deserts. Unlike native annuals, it does not maintain a soil seed bank, but exhibits early and uniform germination. Above-average winter precipitation in these regions allows red brome to reach high density and biomass. These are time for concern, as large numbers of easily dispersed seeds increase the likelihood that it may spread into new areas. However, early and uniform germination can also lead to population crashes when drought precludes seed production. Winter droughts dramatically reduce densities of red brome, but provide opportunities for management of this exotic grass.
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1 The invasion of the wetlands of tropical Australia by the woody weed Mimosa pigra L. was examined at two scales: within a single wetland system on the Adelaide River flood plains, 70 km east of Darwin, and across the entire western coastal region of the Northern Territory. 2 Modelling indicated that, if wind dispersal alone were involved, the fastest rate of linear increase of a stand would be 18.3 m year-1. Actual rates of spread in the wetland system were found from aerial photographs to average 76 m year-1 or greater in five out of six years. This suggests that dispersal of seeds by flotation is central to the observed rapid expansion of the weed in the region's wetlands. 3 Skellam's ( 1 95 1 ) model for areal spread was an inadequate descriptor of the spread of this invading species within the wetland system, probably because it assumes normally distributed dispersal distances, whereas actual distances were log-normally distributed, and because of the irregular, elongate shape of the infestation, where the model assumes roughly circular infestations. 4 There was a close correlation (r = 0.94, P = 0.005) between the increase in the area colonized by the plant and the rainfall in the previous wet season, largely perhaps because of greater dispersal distances. The doubling time over the period of study averaged out at 1.2 years. 5 Across the region as a whole, the doubling time for numbers of infestations was much slower, being 6.7 years, probably because of the separation of the plant's major wetland habitats by eucalypt savannas that it can colonize less readily. There is no evidence to support the widespread popular perception that feral buffalo grazing suppressed the weed, nor that the removal of grazing pressure has resulted in an upsurge of the weed. 6 A graphical model is used to show that seed predators have little effect on the rate of spread of invasive plants until very high levels of predation are achieved, but that seed predators combined with folivores can slow the rate of spread considerably.
Article
SUMMARY (I) We evaluated through simulation the spatial growth of an invading terrestrial plant population and various strategies for its control. The initial population comprised a single large expanding focus but had the potential for the continual establishment of new foci. (2) We compared the area occupied through the establishment and expansion of these "satellite" foci to the area occupied by the initially large or main focus under varying regimens of repeated control, in which either the area of the main focus was reduced or some satellites were destroyed, or both. (3) Whether varying growth rates for the foci, rates of satellite establishment, the level of reduction of the main focus or the intensity of satellite detection and destruction, the overall effectiveness of control measures was greatly improved by destroying even 30% of the satellites. (4) These predictions contrast with much current practice in the control of alien plants, where large or otherwise conspicuous infestations are often treated at the expense of eradicating isolated populations while they still remain small. As supported by empirical precedents, consistent implementation of the general strategy suggested by our model should improve the control of alien plants.
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Aim The dynamics of spread of some representatives of Oenothera, a genus of New World origin and alien to Europe, was analysed.
Article
Aim Biological invasions facilitate ecosystem transformation by altering the structure and function, diversity, dominance and disturbance regimes. A classic case is the grass–fire cycle in which grass invasion increases the frequency, scale and/or intensity of wildfires and promotes the continued invasion of invasive grasses. Despite wide acceptance of the grass–fire cycle, questions linger about the relative roles that interspecific plant competition and fire play in ecosystem transformations. Location Sonoran Desert Arizona Upland of the Santa Catalina Mountains, Arizona, USA. Methods We measured species cover, density and saguaro (Carnegiea gigantea) size structure along gradients of Pennisetum ciliare invasion at 10 unburned/ungrazed P. ciliare patches. Regression models quantified differences in diversity, cover and density with respect to P. ciliare cover, and residence time and a Fisher’s exact test detected demographic changes in saguaro populations. Because P. ciliare may have initially invaded locations that were both more invasible and less diverse, we ran analyses with and without the plots in which initial infestations were located. Results Richness and diversity decreased with P. ciliare cover as did cover and density of most dominant species. Richness and diversity declined with increasing time since invasion, suggesting an ongoing transformation. The proportion of old-to-young Carnegiea gigantea was significantly lower in plots with dominant P. ciliare cover. Main conclusions Rich desert scrub (15–25 species per plot) was transformed into depauperate grassland (2–5 species per plot) within 20 years following P. ciliare invasion without changes to the fire regime. While the onset of a grass–fire cycle may drive ecosystem change in the later stages and larger scales of grass invasions of arid lands, competition by P. ciliare can drive small-scale transformations earlier in the invasion. Linking competition-induced transformation rates with spatially explicit models of spread may be necessary for predicting landscape-level impacts on ecosystem processes in advance of a grass–fire cycle.
Article
We review and synthesize recent developments in the study of the spread of invasive species, emphasizing both empirical and theoretical approaches. Recent theoretical work has shown that invasive species spread is a much more complex process than the classical models suggested, as long range dispersal events can have a large influence on the rate of range expansion through time. Empirical work goes even further, emphasizing the role of spatial heterogeneity, temporal variability, other species, and evolution. As in some of the classic work on spread, the study of range expansion of invasive species provides unique opportunities to use differences between theory and data to determine the important underlying processes that control spread rates.
Article
This paper interprets plant community dynamics within three major vegetation regions - the Sonoran desert, the Encinal and coniferous forest - which extend from 700 m to the summit (2 766 m) on the south slope of the Santa Catalina Mts., Arizona. On the bajada, Larrea tridentata and disturbed desert scrub communities have been degraded by overgrazing and Carnegiea gigantea reproduction is failing on many sites. In the Spinose, suffrutescent desert scrub on protected lower mountain slopes Carnegiea is reproducing but mature populations are periodically decimated by freezing temperatures. In the desert grassland, graminoids or Agave schottii dominate, the former favored by fire, the latter by fire protection. In the Encinal above 1 220 m an open oak woodland dominated by Quercus oblongifolia is transitional to the pine, oak woodland where fire and drought result in several community segregates. A relict Cupressus arizonica forest is restricted to certain canyons. Above the Encinal (2 100 m) a Pinus ponderosa-Q. hypoleucoides forest is replaced by a less xeric P. ponderosa forest. In the latter a dense pine understory develops with fire protection and savanna-like pine stands are favored by fire. At higher elevations a mature Pseudotsuga menziesii, Abies concolor forest dominates the north-facing slopes where fire plays a significant factor in its perpetuation. An even-aged subalpine Abies lasiocarpa stand on the north slope below the summit suggests post-fire origin. In the Pinaleno Mts. to the northeast, mixed conifer and spruce, fir forests complete the vegetation gradient typical of these southwest mountain ranges. Here fire and windthrows interact in maintaining a mosaic of pure or mixed even or uneven-aged stands. Although Shreve’s (1915) description of this mountain vegetation is still valid after more than half a century, the role of grazing and freezing at lower elevations and fire at higher elevations adds a new dimension to those factors operative in this series of relatively stable yet highly dynamic communities.
Article
Although invasions by exotic plants have increased dramatically as human travel and commerce have increased, few have been comprehensively described. Understanding the patterns of invasive species spread over space and time will help guide management activities and policy. Tracing the earliest appearances of an exotic plant reveals likely sites of introduction, paving the way for genetic studies to quantify founder events and identify potential source populations. Red brome (Bromus madritensis subsp. rubens) is a Mediterranean winter annual grass that has invaded even relatively undisturbed areas of western North America, where it threatens native plant communities. This study used herbarium records and contemporary published accounts to trace the early introductions and subsequent spread of red brome in western North America. The results challenge the most frequently cited sources describing the early history of this grass and suggest three possible modes for early introductions: the California Gold Rush and Central Valley wheat, southern California shipping, and northern California sheep. Subsequent periods of most rapid spread into new areas, from 1930 to 1942, and of greatest spread into new regions, during the past 50 years, coincide with warm Pacific Decadal Oscillation regimes, which are linked to increased winter precipitation in the southwestern USA and northern Mexico. Global environmental change, including increased atmospheric CO2 levels and N deposition, may be contributing to the success of red brome, relative to native species.
Article
Through seeding and subsequent spread, Lehmann lovegrass Eragrostis lehmanniana Nees. has transformed the structure and function of at least 145 000 ha of semi-desert grassland in southern Arizona since its introduction in 1932. Our study of its spread on the Santa Rita Experimental Range since 1954 showed that by 1989 it was present on >85% of 75 relatively widely dispersed non-seeded permanent plots and accounted for >40% of all perennial grass plants on these plots. In addition, it represented >50% of the perennial grass plants on sites <16 years after colonization, livestock grazing was not necessary for its spread, and it can account for >90% of the grass biomass and produce 2–4 times more biomass annually than native grass vegetation. In the future, strong consideration of these plant composition changes, and the likely decrease in wildlife diversity and increase in fire frequencies accompanying Lehmann lovegrass dominance, should be made before seeding the species.
Article
The south African succulent Carpobrotus edulis has been invading native and non-native plant assemblages in California since its introduction in the early 1900s. Coastal grasssland, backdune, and coastal scrub differed in several factors that influenced invasion: soil disturbance, herbivory, and identity of competitors. Disturbance of the soil was required for establishment of Carpobrotus at the grassland site. Soil disturbance did not promote Carpobrotus establishment in the coastal scrub or backdune. Establishment in these sites was restricted by herbivory. The influence of neighboring vegetation on Carpobrotus establishment was site dependent. At the grassland site, Carpobrotus seedling survival was reduced by grasses, and the only surving seedlings were on gopher mounds. Growth of larger Carpobrotus, however, was unaffected by grasses. Proximity to shrubs, the dominant plant type at the backdune and coastal scrub sites, did not affect Carpobrotus seedling survival, but decreased root and shoot biomass of seedlings and cuttings. Invasion is expected to occur most rapidly at the grassland site. Although germination and early survival there depend on the occurrence of rodent disturbances, these occur frequently, and seedling recruitment in the grassland was observed. Once established, clonal growth is great and is not affected by herbivory or competition. At the dune site, even caged plants showed very poor growth, and invasion is expected to be slow due to harsh physical conditions that limit both survival and growth. -from Author
Article
Arid environments are characterized by limited and variable rainfall that supplies resources in pulses. Resource pulsing is a special form of environmental variation, and the general theory of coexistence in variable environments suggests specific mechanisms by which rainfall variability might contribute to the maintenance of high species diversity in arid ecosystems. In this review, we discuss physiological, morphological, and life-history traits that facilitate plant survival and growth in strongly water-limited variable environments, outlining how species differences in these traits may promote diversity. Our analysis emphasizes that the variability of pulsed environments does not reduce the importance of species interactions in structuring communities, but instead provides axes of ecological differentiation between species that facilitate their coexistence. Pulses of rainfall also influence higher trophic levels and entire food webs. Better understanding of how rainfall affects the diversity, species composition, and dynamics of arid environments can contribute to solving environmental problems stemming from land use and global climate change.
Article
Accidental introductions of nonindigenous invasive species impair ecosystems, increase the risk of native species extinctions, and cause substantial economic damages on a worldwide basis. Despite the magnitude of the problem, very little economic analysis has been focused on this topic to date. This manuscript develops an optimal control model of the management of a nonindigenous species stock following its introduction and establishment. We find that the influence of changes in ecological and human factors (such as the invader's intrinsic growth rate, carrying capacity, and the effectiveness of invasive species management technologies) on the optimal level of management are analytically (mathematically) ambiguous in sign and depend on the values of other parameters and variables. To estimate actual numerical solutions to the model and conduct sensitivity analyses, we construct a case study illustration based on invasive plant species on arid lands. The illustration shows that the optimal level of management effort is sensitive to biological and ecological factors (the stock's intrinsic rate of growth, the carrying capacity afforded the invasive species, and the form of the invader's growth function) that are species- and site-specific as well as uncertain given currently available scientific information. This highlights the need for better collaboration and information transfer between economists and scientists interested in this topic. Given that resources for addressing nonindigenous species threats typically are quite constrained, and complete eradication in a particular area is often technically infeasible, the model provides useful insight on optimal levels of ongoing management and how they may vary according to bioeconomic factors. Copyright Kluwer Academic Publishers 2002
Article
The history of the development of statistical hypothesis testing in time series analysis is reviewed briefly and it is pointed out that the hypothesis testing procedure is not adequately defined as the procedure for statistical model identification. The classical maximum likelihood estimation procedure is reviewed and a new estimate minimum information theoretical criterion (AIC) estimate (MAICE) which is designed for the purpose of statistical identification is introduced. When there are several competing models the MAICE is defined by the model and the maximum likelihood estimates of the parameters which give the minimum of AIC defined by AIC = (-2)log-(maximum likelihood) + 2(number of independently adjusted parameters within the model). MAICE provides a versatile procedure for statistical model identification which is free from the ambiguities inherent in the application of conventional hypothesis testing procedure. The practical utility of MAICE in time series analysis is demonstrated with some numerical examples.
Spread of Filago arvensis L
  • F Forcella
  • S Harvey
Forcella, F., Harvey, S., 1982. Spread of Filago arvensis L. (Compositae) in the United States. Madroño 29, 119e121.
Dynamically generated variability in plant-pathogen systems with biological control Rates of spread of an invading species: Mimosa pigra in Northern Australia
  • A Kleczkowski
  • D J Bailey
  • C A Gilligan
Kleczkowski, A., Bailey, D.J., Gilligan, C.A., 1996. Dynamically generated variability in plant-pathogen systems with biological control. Proceedings of the Royal Society of London: Biological Sciences 263, 777e783. Lonsdale, W.M., 1993. Rates of spread of an invading species: Mimosa pigra in Northern Australia. Journal of Ecology 81, 513e521.
Controlling the spread of plant invasions e the importance of Nascent Foci Vegetation of the Santa Catalina Mountains e community types and dynamics
  • M E Moody
  • R N Mack
Moody, M.E., Mack, R.N., 1988. Controlling the spread of plant invasions e the importance of Nascent Foci. Journal of Applied Ecology 25, 1009e1021. Niering, W.A., Lowe, C.H., 1984. Vegetation of the Santa Catalina Mountains e community types and dynamics. Vegetation 58, 3e28.
The Buffelgrass Strategic Plan. Arizona-Sonora Desert Museum
  • A Rogstad