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Stemflow chemistry in relation to tree size: A preliminary investigation of eleven urban park trees in British Columbia, Canada
Abstract
Given increased atmospheric loads in cities, quantification of stemflow chemistry is necessary for a holistic understanding of elemental cycling in urban ecosystems. Accordingly, the stemflow volume and associated solute fluxes (K⁺, Ca²⁺, Na⁺, Mg²⁺) were measured for eleven deciduous trees in a manicured park setting in Kamloops, British Columbia, Canada. Over nine rainfall events from late June to early September, 2013, larger trees [diameter at breast height (DBH) > 30 cm] were found to generally produce higher event stemflow volumes but lower funneling ratios than the smaller trees (DBH < 30 cm). The median flux-based enrichment ratio, which compares the solute concentration of stemflow to that of rainfall on a per unit trunk basal area, also tended to be greater for smaller trees than larger ones. Under all-tree and single-leader tree conditions, significant negative non-linear relationships between tree DBH and mean flux-based enrichment ratios were found for Ca²⁺, Na⁺, and Mg²⁺, but not for K⁺. These preliminary results indicate that urban trees can considerably enrich rainfall that is partitioned into stemflow, and that ion concentrations and enrichment ratios exhibit notably high interspecific variability. In this study, tree size and presence of single versus multiple leaders explained some of this heterogeneity; however, further study into those physical tree characteristics that affect stemflow volume and stemflow chemistry must be carried out if the impact and challenges of urban greening, nutrient cycling, and stormwater management initiatives are to be more fully understood.
... Thus, both stemflow and throughfall take part in nutrient dynamics, since they alter the chemistry of rainwater that flows down tree canopies and contribute to biogeochemical cycling by carrying nutrients into the soil. Zhang et al. (2016) and Schooling et al. (2017) have shown that throughfall and stemflow water cycles are key drivers of ecosystem processes, mainly of nutrient cycling. Su et al. (2019) argue that rainfall is one of the main chemical input sources in forest ecosystems; therefore, understanding nutrient cycling and hydrochemical fluxes of forest ecosystems is essential to manage their dynamics. ...
We evaluated band planting (BP) to assess its efficiency in the early restoring of ecological processes using a multi-criteria protocol known as Framework for the Evaluation of Natural Resource Management Systems Incorporating Sustainability Indicators (MESMIS) to obtain the ecological functionality consolidation index (EFCI). We sampled a 4.3 ha-1 plantation, aged 3 years, with BP, 1.5-m space between bands, 2-m space between seedlings, and a 3.5-m band of natural regeneration, ten areas with conventional planting (CP), aged 5 years, in the coverage and diversity models, and ten areas restored by natural regeneration (NR), aged 4 years. Sampling was carried out in 36 10 m x 10 m blocks, totaling 144 plots, 15 blocks for BP, 11 blocks for CP, and 10 blocks for NR. Species richness was similar between the areas; however, there was a significant difference between BP and the other areas (CP and NR) by the Dunn’s test (p < 0.05). The NR area had the highest diversity (H' = 3.03; J' = 0.76), followed by BP (H' = 2.56; J' = 0.62), and CP (H' = 2.0; J' = 0.48), whereas the BP area (4.348 ind.ha-1) had the highest density. The BP had the highest EFCI for diversity (0.100), control, and management (0.067) compared to NR, for diversity (0.022), and similar to CP in soil protection and nutrient cycling (0.047). BP was efficient in recovering early ecological processes under conditions similar to fragments in the initial stage of succession.
... Thus, both stemflow and throughfall take part in nutrient dynamics, since they alter the chemistry of rainwater that flows down tree canopies and contribute to biogeochemical cycling by carrying nutrients into the soil. Zhang et al. (2016) and Schooling et al. (2017) have shown that throughfall and stemflow water cycles are key drivers of ecosystem processes, mainly of nutrient cycling. Su et al. (2019) argue that rainfall is one of the main chemical input sources in forest ecosystems; therefore, understanding nutrient cycling and hydrochemical fluxes of forest ecosystems is essential to manage their dynamics. ...
The study systematically analyzes the literature in order to identify the main contributions of the trunk runoff study on the soil nutrient flux in recent years. The review included 47 articles published from 2015 to 2019. The aim of the present study is to correlate the main stemflow research subtopics that have contributed to chemical soil enrichment. Correlation analysis was performed in Iramuteq software with the aid of R software,
based on keywords in the selected articles. There has been an overall upward trend in research related to stemflow impact on soil nutrient flux, mainly in Asia, whose publications have significantly increased over the latest years. Based on the keyword co-occurrence map, “stemflow” and “throughfall” were the main used terms because they established strong correlation to other keywords, mainly to “concentration”,
“composition”, “biogeochemical cycle”, “nutrient cycling” and “dissolved organic matter”. These terms, in their turn, were correlated to and co�occurred with several other keywords, such as “soil”, “nitrogen”, “water chemistry”, “nutrient dynamics” and “cations”
... Reported solute concentrations fall within the range of those reported in previous stemflow literature Van Stan and Stubbins, 2018). The higher stemflow solute concentrations from rough-barked trees, like C. crenata and T. sieboldii, also agree with the highly enriched stemflow solutions observed from similarly rough barked tree species, like Quercus species Van Stan et al., 2017), Cyclobalanopsis species (Su et al., 2019), Fraxinus pennsylvanica (Schooling et al., 2017), Liriodendron tulipifera . Therefore, in combination with previous results, our study supports the conceptual model that bark structure may decrease bulk stemflow solute concentration by influencing both (a) the amount of materials captured by bark and (b) the amount of stemflow available to dilute those washed off (and exchanged) materials (Van Stan and . ...
Compared to leaves, bark is under-studied with regards to its role in the water cycle. This is an important knowledge gap as, unlike leaves, bark is ever-present in forest ecosystems and can represent a significant interface for water interaction. Bark is also porous, hygroscopic, present in litter layers from shedding, as well as on fallen woody debris, and performs a multitude of ecophysiological functions. Finally, considering the particulates, organisms, and leachable/washable solutes present on and in bark, many opportunities may exist for improving forest ecohydrological understanding through the research of bark-water interactions. Thus, this collection contains articles that highlight bark interactions with various hydrologic processes and related ecological processes.
... Reported solute concentrations fall within the range of those reported in previous stemflow literature (Parker, 1983;Levia and Germer, 2015;Van Stan and Stubbins, 2018). The higher stemflow solute concentrations from rough-barked trees, like C. crenata and T. sieboldii, also agree with the highly enriched stemflow solutions observed from similarly rough barked tree species, like Quercus species (Levia and Herwitz, 2005;Van Stan et al., 2017), Cyclobalanopsis species (Su et al., 2019), Fraxinus pennsylvanica (Schooling et al., 2017), Liriodendron tulipifera (Levia et al., 2011). Therefore, in combination with previous results, our study supports the conceptual model that bark structure may decrease bulk stemflow solute concentration by influencing both (a) the amount of materials captured by bark and (b) the amount of stemflow available to dilute those washed off (and exchanged) materials (Van Stan and Gordon, 2018). ...
Stemflow can be an important pathway for the drainage of precipitation and related solutes through tree canopies to forest soils. As stemflow must drain along bark surfaces, the effects of bark structure on stemflow chemical composition is merited. This study examines the relationship between stemflow chemistry and bark surface structure for six species of varying bark morphology (four deciduous broadleaf trees and two evergreen coniferous trees) at a montane and an urban site in Japan. Stemflow from smooth-barked species contained greater concentrations of solutes that appear to be rinsed from the stem surface (i.e., sea salt aerosols); while, rougher-barked tree species contained greater or less concentrations of solutes that appear to be leached (e.g., Ca ²⁺ ) or taken-up (e.g., inorganic N) by the bark, respectively. Site-specific atmospheric environments also influenced thee bark-stemflow chemistry relationships—where the greater elemental deposition in the urban plot generally resulted in greater stemflow chemistry than observed in the lower-deposition montane plot. Our results therefore suggest that the dynamics of dry deposition wash-off by stemflow, and the exchange of dissolved solutes between stemflow and the bark surface, are influenced by the surface structure of the bark and the site’s atmospheric environment. Therefore, the interactions between bark surface structure and its surrounding atmospheric environment are important factors in the stemflow-related elemental cycling between the tree and precipitation.
... Other factors may affect these processes, some of which, in this study, probably do not differ among the tree species since they are in the same stand (amount, intensity and duration of precipitation and abiotic stresses). However, others depend on their morphology, which will affect the initiation and rate of production for stemflow (Carlyle-Moses and Schooling, 2015;Rosier et al., 2016;Schooling et al., 2017;Su et al., 2019;Van Stan et al., 2016;Yang et al., 2019;Yuan et al., 2017), as well as the stemflow composition, justifying the significant difference between tree species. ...
Quantitative studies on the water and nutrient enrichment of throughfall and stemflow in the Cerrado are lacking, especially among tree species. This work tested the hypothesis that the chemistry of rainfall fractions is altered after passing through the canopy and that the chemistry of stemflow can substantially change among tree species. We compared the nutrient concentrations in rainfall, throughfall and stemflow, dry deposition and canopy exchange among eight Cerrado species in Brazil. Rainfall, throughfall and stemflow were monitored from April 2018 to March 2019. The following chemical factors were determined using a Metrohm liquid chromatograph ECO IC: Na 2+ , K + , Ca 2+ , Mg 2+ , Br − , Cl − , NO − 3 , SO 2− 4 and PO 3− 4. The enrichment ratio, depositions of rainfall, throughfall and stemflow and canopy budget of different nutrients were calculated for the stand and species. A comparison between the mean concentrations showed that most of the elements and compounds were relatively more concentrated in the throughfall and stemflow, except for Na 2+ and Ca 2+ , which were more concentrated in the rainfall (p<0.05). We noted that each species had a specific contribution to the stemflow nutrients. The different components and canopy geometry, as well as the bark morphology of the studied species, contributed varying proportions to the nutrient fluxes. The stemflow deposition of most nutrients was significantly higher in Xylopia aromatica. The highest nutrient input by stemflow was observed for K + , which ranged from 2.13 (A. peregrina) to 77.36 (X. aromatica) kg ha − 1 y − 1. A canopy budget model indicated that canopy exchange was often more dominant than dry deposition. Unlike the other nutrients, Cl − and PO 3− 4 were taken up by the canopy. Given the variation in the nutrient input, these results highlight the importance of investigating the individual contribution of the stemflow of each species in the Cerrado forest and provide a potential strategy for adapting the species to soil recovery.
... Duval (2019) utilized flux-based enrichment ratios for stemflow to characterize carbon and nitrogen fluxes and to identify related biogeochemical hotspots in a mixed cedar swamp in Southern Ontario, Canada. Excluding a study in which Schooling et al. (2017) identified variability in E P,B among isolated urban trees in British Columbia, Canada, the overwhelming majority of work utilizing E P,B has been limited to rural forests. This has created a paucity of knowledge with respect to stemflow solute fluxes within the urban forest. ...
Throughfall and stemflow serve as two important transport mechanisms for water and solutes in urban forests, though these fluxes are seldom quantified within cities. This study is the first to utilize two flux-based enrichment ratios for stemflow to characterize spatial patterns in water and solute distribution in urban forest fragments. Using event-based, in situ sampling, this study quantified stemflow enrichment for Quercus rubra (northern red oak) and Quercus alba (white oak) trees relative to open precipitation (EP,B) and throughfall (ET,B) per unit trunk basal area for dissolved Ca, K, Mg, Mn, NO3-N, and S. The study investigated variability in nutrient enrichment at the fragment, municipal, and regional scales. Among all solutes, observations for EP,B and ET,B for Q. rubra and Q. alba were generally lowest for Mg and highest for Mn and K. Significant intra-urban variability in stemflow enrichment was limited to EP,B of K and ET,B of Ca (p < 0.05), while trans-regional variability in stemflow enrichment consistently indicated higher EP,B and ET,B in more highly developed portions of the study region. At the fragment scale, EP,B and ET,B for Q. rubra was consistently higher than for Q. alba, with variability in these observations significant for all solutes. For example, interspecific variability in EP,B was greatest for K, where median values ranged from 2.8 ± 29.7 in Q. alba to 87.1 ± 97.1 in Q. rubra. While observations for ET,B were generally lower than those for EP,B, observations for Q. rubra also consistently exceeded those for Q. alba, with median values for K ranging from 1.5 ± 0.5 to 21.9 ± 3.1 for Q. alba and Q. rubra, respectively. Findings were likely driven by variability in biophysical characteristics between the two species (e.g., bark morphology). Further, findings indicate that species heterogeneity within the urban forest contributes to significant variability in nutrient (and possibly pollutant) transport and fate via throughfall and stemflow below the canopy, with subsequent impacts on urban forest biogeochemistry.
... In numerous studies, Ca, Mg, and K all display elevated concentrations in precipitation in urban areas as compared to rural areas and are elevated in stemflow and/or throughfall as compared to wet deposition (Takagi et al. 1997;Chiwa et al. 2003;Aikawa et al. 2006;Juknys et al. 2007;Michopoulos et al. 2007a;Michopoulos et al. 2007b;Quan et al. 2008, Schooling et al. 2017). In general, these studies have not suggested uptake of these base cations by the urban tree canopy, though Juknys et al. (2007) noted a reduction in Ca in throughfall as compared to wet deposition in a suburban forest. ...
Urban trees have diverse effects on hydrologic processes, influencing water quality within and downstream of the city. Urban trees, which include street trees, trees on private property, and those in urban forests, parks, and arboreta, intercept and modify precipitation before it reaches the ground. Urban canopies alter precipitation chemistry through interaction with atmospheric components such as ions and particles, uptake and leaching, and within-canopy production of materials. Due to numerous sources of nutrients and pollutants in urban areas, trees often act to concentrate chemical inputs to the urban ground surface, though this effect varies depending on such factors as urban form and tree species. Ultimately, the effect of the urban tree canopy on the urban hydrologic cycle is a complex topic with intertwined socio-ecological causes and effects. While the scientific community has been exploring this topic for the last 40 years, there is still much work to be done to describe the effects of the urban tree canopy on urban water quality and to use this understanding to maximize urban tree canopy benefits.
... Although the basal area does not necessarily equate with the area of stemflow water infiltration, if soils have associated surface hydraulic conductivities that are relatively high, the area of infiltration is limited to a relatively small area around the base of the tree (Schwärzel et al. 2012;Carlyle-Moses et al. 2018). Thus, urban trees with high , and surface soil hydraulic conductivities favourable to infiltration could be important self-irrigators, delivering both relatively high volumes of water and nutrients (Abas et al. 1992;Schooling et al. 2017; see also Chapter 18 of this volume). If, however, soils are compacted or the area around the base is insufficiently large to accommodate the stemflow input, this understory precipitation component has the potential to add to stormwater flow ( Fig. 17.2). ...
Impervious surfaces in urban areas generate substantial volumes of polluted surface runoff, resulting in flooding and degradation of waterway ecosystems. Urban trees can help to mitigate the adverse effects of runoff by restoring key hydrological processes, including canopy interception, throughfall, stemflow, and transpiration. Understanding how trees contribute to these processes can guide tree species selection and the design of green infrastructure elements. Climate, specifically the distribution of precipitation and evaporative demand, will ultimately determine the extent to which trees contribute to each process. In general, canopy interception, throughfall, stemflow, and transpiration will be greater where the rainfall distribution is dominated by smaller events separated by longer inter-event periods with higher evaporative demand. However, in any given climate, different tree species, and more importantly the traits which define them, can significantly alter their role in the urban hydrological cycle. For example, species with large, dense canopies (high leaf area) are likely to show greater canopy interception loss, resulting in lower throughfall and stemflow and reduced surface runoff. Additionally, larger trees with high leaf area can potentially transpire a significant amount of captured runoff when combined with stormwater control measures. However, selecting species to maximise retention and detention of runoff must do so without compromising other highly valued ecosystem services provided by trees. This chapter reviews the studies which contribute to our current understanding of how different species contribute to hydrological processes in the built environment. We discuss how this understanding has been integrated into urban hydrological models as well as opportunities for future studies to continue their development.
... The stemflow enrichment of small-diameter trees tended to be higher than that of large-diameter trees. This was similar to the result found by Schooling et al. [38] for urban park trees in British Columbia, Canada, reporting smaller trees (<20 cm DBH) had larger flux-based enrichment ratios than larger trees. These findings indicate that small-diameter trees contribute more stemflow base cations to stand stemflow per hectare, and they also promote a more favorable condition for the growth of small-diameter trees when competing with large-diameter trees. ...
Base cation transfer from stemflow is an important process for nutrient transfer and plays a key role in maintaining the balance of soil nutrient pools. To research the differences of stemflow chemistry in mixed plantations, we conducted a continuous field experiment in the rainy zone of Western China from December 2016 to November 2017. Three representative mixed plantations, including a conifer–broadleaved mixed plantation, a deciduous broadleaved mixed plantation and a multispecies mixed plantation, were selected to investigate the concentration and flux characteristics of K+, Na+, Ca2+ and Mg2+ in stemflow. The results showed that: (1) the K+, Na+, Ca2+ and Mg2+ fluxes ranged from 1.75 to 2.44 kg ha−1 year−1, 0.14 to 0.24 kg ha−1 year−1, 1.25 to 2.11 kg ha−1 year−1, and 0.40 to 0.60 kg ha−1 year−1 in these mixed plantations during the one-year observation, and the annual or seasonal (i.e., rainy or dry season) base cation fluxes in the stemflow varied slightly with the plantation types; (2) broadleaved trees had a higher average stemflow base cation contribution rate and flux-based enrichment ratio than coniferous trees, and the enrichment ratios showed a decreasing tendency with increasing trunk diameter; (3) the stemflow base cation concentration was higher in the dry season, while flux was observed to be higher in the rainy season. These results suggested that increasing the proportion of broadleaved species in mixed plantations might improve soil nutrient content and benefit material cycling in subtropical forest ecosystems.
... To provide a better understanding of the effect of tree size on stemflow DOM. Considering the earlier work has indicated that there are significant negative non-linear relationships between tree size and mean flux-based enrichment ratio for Ca 2+ , Na 2+ and Mg 2+ (Schooling et al., 2016). We hypothesize that: (1) the effects of tree size on the stemflow volume, stemflow percentage, and funneling ratio (FR) are different under the different rainfall intensities and (2) the stemflow DOM flux and flux-based DOM enrichment ratios are related to tree size. ...
Numerous studies have examined the variability of stemflow across different tree species under different meteorological conditions. However, studies have rarely considered stemflow associated with individual rainfall events and stemflow DOM flux. Therefore, we collected stemflow data from >100 individual rainfall events across four diameter size classes (20-30 cm, 30-40 cm, 40-50 cm, and DBH > 50 cm) of Castanopsis cuspidata in an evergreen forest (35° 26′ N, 136° 47E). The main objectives were to evaluate the stemflow hydrology and DOM flux characteristics in relation to tree size and different rainfall intensities based on a large dataset of individual rainfall events. In line with previous studies, the mean stemflow volumes and percentages of larger trees were higher than those of smaller trees; smaller trees have a higher funneling ratio than larger trees at both tree-scale (FR t) and stand-scale (FR s), which means that smaller trees are more effective in funneling water to their base. However, tree size significantly affects the stemflow volume and percentage only when the rainfall intensity is below 15 mm h −1. Tree size had a limited effect on the stemflow DOM concentration and stemflow DOM yield at a monthly scale. However, stemflow DOM flux and the flux-based DOM enrichment ratio were affected profoundly by tree size. Similar to the funneling ratio, small trees had a higher flux-based DOM enrichment ratio and supplied more DOM per unit trunk basal area. Thus, in addition to tree species, we suggest that tree size is also an important factor influencing the heterogeneity of the spatial patterns of the soil solution chemistry near the tree trunks.
... For certain forests and/or tree species within these environments, as well as various isolated trees in savanna, semi-arid, and urban areas, stemflow can be an important hydrological and biogeochemical input (Xiao et al., 2000;Levia and Germer, 2015;Carlyle-Moses et al., 2018), while for other forests and trees it may play a limiting role (Price et al., 1997;Carlyle-Moses et al., 2014;Van Stan and Gordon, 2018). As a consequence of the varying ecohydrological role of stemflow in different environments, which tree/forest characteristics and meteorological factors govern the volumetric importance, initiation, flow rate, and chemical composition of stemflow has garnered increased research attention (Van Stan et al., 2014;Schooling et al., 2017;Cayuela et al., 2018). Additionally, much has yet to be learned concerning the impact stemflow -or the lack thereof-and its spatial and temporal characteristics have on hydrological processes, including soil drying-rewetting cycles, preferential and subsurface flows, perched water-table development, groundwater recharge, and by-pass flows contributing to storm runoff (Levia et al., 2011a,b;Levia and Germer, 2015;Carlyle-Moses et al., 2018;Van Stan and Gordon, 2018), and on biogeochemical cycling (Michalzik et al, 2016;Siegert et al., 2017;Stubbins et al., 2017;Van Stan and Gordon, 2018). ...
This study develops and evaluates a sensing system capable of measuring stemflow at high temporal resolutions. Leveraging affordable hobbyist grade electronics has allowed for the development of a system which is low-cost, easy to reproduce and adaptable. Eschewing classic stemflow measurement techniques, the system demonstrated herein utilizes a sensing payload which includes a wetness sensor and ultrasonic rangefinder. Combined, these sensors are capable of determining precise stemflow initiation and cessation times as well as capturing high temporal resolution stemflow volume measurements at 10 s intervals. A case study focusing on stemflow data collected by the sensing system from an isolated green ash (Fraxinus pennsylvanica Marshall) during a May 2016 rainfall event in Kamloops, British Columbia is used to evaluate the performance of the sensing system, demonstrating the accuracy of the collected data and the potential research questions that can be addressed by large scale deployment of the sensor system.
... Enrichment comparable to and exceeding levels for bacterial concentrations observed in this study has been reported for throughfall and stemflow solutes [Heartsill-Scalley et al., 2007;Zhang et al., 2016;Schooling et al., 2017]. In previous studies rainfall solutes have been attributed to leaf leaching (K + ) and dry deposition of sea salt aerosols (Na + and Cl -) [Staelens et al., 2007;André et al., 2008;Van Stan et al., 2012]. ...
Transport pathways of microbes between ecosystem spheres (atmosphere, phyllosphere, and pedosphere) represent major fluxes in nutrient cycles and have the potential to affect microbially-mediated biogeochemical processes. Novel data on bacterial fluxes from the phyllosphere to the pedosphere during rainfall via throughfall (rain dripping from/through the canopy) and stemflow (rain funneled down tree stems) are reported. Bacterial concentrations were quantified using flow cytometry and validated with quantitative Polymerase Chain Reaction (qPCR) assays in rainfall samples from an oak-cedar forest in coastal Georgia (Southeastern USA). Bacteria concentrations (cells mL-1) and storm-normalized fluxes (cells m-2 h-1, cells m-2 mm-1) were greater for cedar versus oak. Total bacterial flux was 1.5x1016 cells ha-1 year-1. These previously unexamined bacterial fluxes are interpreted in the context of major elemental pools and fluxes in forests, and could represent inoculum-level sources of bacteria (if alive), and organic matter and inorganic solute inputs (if lysed) to soils.
Forests provide important ecosystem services, several of them related to water. The interconnections between rainfall interception and the water cycle vary among the forest types. Tropical forests are one of the most relevant biodiversity shelters, with several endemic plant and animal species. These forests provide key ecohydrological services by directly acting on biogeochemical cycles and water supply. Understanding these interconnections is crucial for better planning forest conservation and reforestation initiatives, especially under climate change conditions. Therefore, a set of techniques and devices is required to monitor rainfall-forest interface processes in tropical forests as they are very complex ecosystems. In this chapter, we intend to assess rainfall-forest interface processes as well as some of the methods that have been used for quantifying rainfall interception in forests, contributing to the ecohydrological studies.
Key message
Tree bark structure and crown area, are the main biotic drivers, and maximum rainfall intensity and seasonality are the main abiotic drivers of carbon input via stemflow in a neotropical forest.
Abstract
Stemflow is an often-neglected concentrated water path in the forest, transports nutrients from the canopy along the main tree stem, through to the forest floor, thereby affecting the biogeochemical processes, and accelerating the nutrients redistribution in forest ecosystems. Here we assessed what are the effects of tree structural features (height, bark roughness, projected crown area), seasonality (wet and dry season, and previous dry period), and maximum rainfall intensity on stemflow total carbon enrichment ratios in a semi-deciduous tropical forest. The enrichment ratio allows quantifying the contribution of stemflow to delivery carbon to the forest soil. To evaluate the increase in total carbon concentration in the stemflow, we sampled and analyzed 61 rainfall events (gross rainfall, throughfall, and stemflow) and modeled the enrichment ratios using potential biotic and abiotic drivers through generalized linear models. The stemflow carbon enrichment ratios ranged from 1 to 30 relative to gross rainfall and from 0.8 to 11 relative to throughfall, which demonstrates the importance of forests on carbon cycle and to provide ecosystem services. The carbon concentration in stemflow was higher in the dry season; however, the greater rainfall amount in the wet season provided higher carbon inputs. Moreover, the carbon enrichment ratios were sensitive to variation on tree structural features and meteorological conditions, highlighting bark structure, crown area, maximum rainfall intensity, and season. Our findings demonstrate the role of the stemflow as a relevant source of total carbon input into tropical forests soils.
Question
Fine‐scale environmental heterogeneity supports floristic diversity in forest ecosystems by increasing the variety of niches available for specialist species. Although recognized in concept, the niche function of microsites has not been well documented. This study tests whether microsites at the base of large trees are physically or edaphically distinct from the forest floor in general, and whether forest herb composition responds to this form of heterogeneity.
Location
Long‐established deciduous forest in the unglaciated section of southeastern Ohio, USA.
Methods
We measured fourteen herb‐relevant environmental variables and censused the herb flora at the bases of large trees and in control plots away from trees.
Results
Moss cover, exposed root cover, and canopy openness were significantly greater at large‐tree bases than in control plots, while leaf litter cover was significantly lower at tree bases. Species richness and stem density were higher in tree‐base plots, and multivariate species composition differed significantly between tree bases and controls. Two species, Eurybia divaricata and Cardamine douglassii, were significantly more abundant at tree bases. Gradients of litter cover and root exposure accounted for the compositional difference between tree bases and controls. Coarse woody debris, moss cover, and soil root fraction accounted for differences orthogonal to the tree‐base/control axis indicating heterogeneity within tree‐base microsites.
Conclusions
Tree bases are physically distinct microsites which support diversity by providing niches to some forest herb species. Because availability of such microsites is linked to tree size, this aspect of community diversity appears to be controlled by stand development.
Over a large fraction of the global landsurface, precipitation interacts with standing vegetation or organic litter prior to reaching the mineral soil. This interaction has both benefits and costs for plants, and these arise over varying timescales from minutes or hours to years or decades. A two-way interaction emerges in which the precipitation-vegetation interactions can affect plant growth, which in turn may alter the nature of the physical processes responsible for the plant-precipitation interactions via changes in plant architecture. This chapter explores two important examples of these processes. These are canopy changes in the drop size characteristics of water reaching the mineral soil, and the occurrence of contact flow or ‘stemflow’. Both may result in important hydrologic and erosional outcomes in forests, shrublands, and croplands, some of which are beneficial to plants, and some potentially detrimental. In particular, the effect of vegetation canopies in creating throughfall drops that are larger than those of open-field rainfall may result in higher sub-canopy erosivity. Likewise, the rainwater funnelling action of vegetation canopies and the resulting focussed delivery of stemflow may result in overland flow and scour of the soil surface around the base of some plants. Many of the interactions of precipitation and vegetation are conditioned by the characteristics of the open-field rainfall incident upon plant canopies; the chapter therefore also presents an overview of some of the key attributes of rainfall as they relate to processes acting on, within, and beneath vegetation. In many cases, the most important attributes of rainfall relate to the timescales characteristic of rainfall events, including event duration, depth, and intensity. These, and the nature of the vegetation and soils, exhibit wide geographical variability. This leaves many significant challenges facing the development of a full understanding of the interactions of rainfall, vegetation, and soils.
The amount and patterning of precipitation beneath vegetation is determined by throughfall and stemflow. Throughfall is the portion of precipitation that falls through, or drips from, the canopy; whereas, stemflow is the portion that drains down the stem. This chapter briefly synthesises throughfall and stemflow methods, data and major drivers of variability from all studies returned from Web of Science that reported relative annual or seasonal throughfall and stemflow (% of precipitation across the canopy) to date: 644 observations spanning broad climate (boreal, temperate, Mediterranean, subtropical and tropical) and plant types (forests, shrublands, croplands and grasslands) around the globe. Relative throughfall was greatest for forests followed by shrubs > crops > grasses; whereas, relative stemflow was greatest for grasses followed by crops > shrubs > forests. This synthesis identified challenges to integrating net precipitation into large-scale (regional-to-global) hydrologic and climate processes and estimates, including: (1) under-sampling at sites; (2) lacking data for solid and mixed precipitation events’ throughfall and stemflow; (3) very few throughfall and stemflow observations for herbaceous vegetation (compared to woody plants) despite croplands and grasslands representing 11% and 27% of the land surface, respectively, as well as understory herbaceous vegetation being present in nearly all forests; and (4) the current focus on fine-scale drivers of highly localized patterns.
Partitioning of rainfall through a forest canopy into throughfall, stemflow, and canopy interception is a critical process in the water cycle, and the contact of precipitation with vegetated surfaces leads to increased delivery of solutes to the forest floor. This study investigates the rainfall partitioning over a growing season through a temperate, riparian, mixed coniferous‐deciduous cedar swamp, an ecosystem not well‐studied with respect to this process. Seasonal throughfall, stemflow, and interception was 69.2, 1.5, and 29.3 % of recorded above‐canopy precipitation, respectively. Event throughfall ranged from a low of 31.5 ±6.8 % for a small 0.8 mm event to a high of 82.9 ±2.4 % for a large 42.7 mm event. Rain fluxes of at least 8 mm were needed to generate stemflow from all instrumented trees. Most trees had funneling ratios < 1.0, with an exponential decrease in funneling ratio with increasing tree size. Despite this, stand‐scale funneling ratios averaged 2.81±1.73, indicating equivalent depth of water delivered across the swamp floor by stemflow was greater than incident precipitation. Throuhfall dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) averaged 26.60 ±2.96 and 2.02 ±0.16 mg L‐1, respectively, which were ~11 and 3 times above‐canopy rain levels. Stemflow DOC averaged 73.33 ±7.43 mg L‐1, 35‐times higher than precipitation, and TDN was 4.45 ±0.56 mg L‐1, 7.5‐times higher than rain. Stemflow DOC concentration was highest from Populus balsamifera, and TDN greatest from Thuja occidentalis trees. While total below‐canopy flux of TDN increased with increasing event size, DOC flux was greatest for events 20‐30 mm, suggesting a canopy storage threshold of DOC was readily diluted. In addition to documenting rainfall partitioning in a novel ecosystem, this study demonstrates the excess carbon and nitrogen delivered to riparian swamps, suggesting the assimilative capacity of these zones may be underestimated.
The growing recognition of trees’ value in urban environments is resulting in increased investment in “green infrastructure.” However, generalizations that deciduous canopies reduce stormwater are based largely on closed-canopy forests, highlighting the need for more detailed study of isolated urban trees. We systematically studied the effect of canopy traits on stemflow percent and funneling ratios for isolated deciduous trees in a semi-arid climate characterized by mostly small precipitation events. High stemflow production was generally associated with high branch angles (single- and multi-leader trees) small diameter-at-breast-height (single-leader trees), furrowed bark in single-leader trees for rain events ≥ 10 mm, and smooth bark in multi-leader trees for all except the lowest rain depth class. Higher numbers of leaders converging at the base were associated with high stemflow yields. Individual-tree stemflow percent and funneling ratio values were variable, even for similar rain depths, suggesting that meteorological factors play a role. Event maximum stemflow percent was 22.8 % (25.6 mm rain depth) for a columnar English oak and event maximum funneling ratio was 196.9 (5.6 mm) for a Riversii European beech. Our findings highlight the importance of infiltration capacity at the base of urban trees and of designing for the rainfall regime when integrating stormwater management with vegetation and soils in cities.
Tree canopy processes affect the volume and biogeochemistry of inputs to the hydrological cycle in cities. From June, 2012 to November, 2013, we studied stemflow production from 37 isolated deciduous park trees in a semi-arid climate dominated by small precipitation events. To clarify the effects of canopy traits on stemflow metrics, we analyzed branch angles, bark relief (one component of roughness), tree size, canopy and wood cover fraction, median leaf size, and branch and leader counts. High branch angles contributed to stemflow production in both single- and multi-leader trees. While bark relief was negatively correlated with stemflow rates in multi-leader trees, it was positively correlated with rates for single-leader trees, possibly reflecting the conducive role of linear furrows once bark of single-leader trees is saturated. The association between numerous leaders, low stemflow initiation thresholds, and high rates deserves further study. Among meteorological variables, rain depth was strongly correlated with stemflow yields; rainfall inclination angle and wind speed were positively correlated with yields while total intra-storm break duration and vapour pressure deficit were inversely related. For rain depths < 3 mm, greater stemflow was generally associated with leafless canopies. In support of integrated stormwater management, our results can inform climate-sensitive selection and siting of urban trees with traits that tend to either promote or minimize stemflow, depending on infiltration potential. This article is protected by copyright. All rights reserved.
A three-dimensional physically based stochastic model was developed to
describe canopy rainfall interception processes at desired spatial and
temporal resolutions. Such model development is important to understand
these processes because forest canopy interception may exceed 59% of
annual precipitation in old growth trees. The model describes the
interception process from a single leaf, to a branch segment, and then
up to the individual tree level. It takes into account rainfall,
meteorology, and canopy architecture factors as explicit variables. Leaf
and stem surface roughness, architecture, and geometric shape control
both leaf drip and stemflow. Model predictions were evaluated using
actual interception data collected for two mature open grown trees, a
9-year-old broadleaf deciduous pear tree (Pyrus calleryana "Bradford" or
Callery pear) and an 8-year-old broadleaf evergreen oak tree (Quercus
suber or cork oak). When simulating 18 rainfall events for the oak tree
and 16 rainfall events for the pear tree, the model over estimated
interception loss by 4.5% and 3.0%, respectively, while stemflow was
under estimated by 0.8% and 3.3%, and throughfall was under estimated by
3.7% for the oak tree and over estimated by 0.3% for the pear tree. A
model sensitivity analysis indicates that canopy surface storage
capacity had the greatest influence on interception, and interception
losses were sensitive to leaf and stem surface area indices. Among
rainfall factors, interception losses relative to gross precipitation
were most sensitive to rainfall amount. Rainfall incident angle had a
significant effect on total precipitation intercepting the projected
surface area. Stemflow was sensitive to stem segment and leaf zenith
angle distributions. Enhanced understanding of interception loss
dynamics should lead to improved urban forest ecosystem management.
It is well known that urban trees produce various types of benefits and costs. The computer tool i-Tree STRATUM helps quantify tree structure and function, as well as the value of some of these tree services in different municipalities. This study describes one of the first applications of STRATUM outside the U.S. Lisbon's street trees are dominated by Celtis australis L., Tilia spp., and Jacaranda mimosifolia D. Don, which together account for 40% of the 41,247 trees. These trees provide services valued at $8.4 million annually, while $1.9 million is spent in their maintenance. For every $1 invested in tree management, residents receive $4.48 in benefits. The value of energy savings ($6.20/tree), CO2 reduction ($0.33/tree) and air pollutant deposition ($5.40/tree) were comparable to several other U.S. cities. The large values associated with stormwater runoff reduction ($47.80/tree) and increased real estate value ($144.70/tree) were substantially greater than values obtained in U.S. cities. Unique aspects of Lisbon's urban morphology and improvement programs are partially responsible for these differences.
Urban forestry is an important green infrastructure strategy because healthy trees can intercept rainfall, reducing stormwater runoff and pollutant loading. Surface saturation storage capacity, defined as the thin film of water that must wet tree surfaces before flow begins, is the most important variable influencing rainfall interception processes. Surface storage capacity is known to vary widely among tree species, but it is little studied. This research measured surface storage capacities of 20 urban tree species in a rainfall simulator. The measurement system included a rainfall simulator, digital balance, digital camera, and computer. Eight samples were randomly collected from each tree species. Twelve rainfall intensities (3.5-139.5 mm h) were simulated. Leaf-on and leaf-off simulations were conducted for deciduous species. Stem and foliar surface areas were estimated using an image analysis method. Results indicated that surface storage capacities varied threefold among tree species, 0.59 mm for crape myrtle ( L.) and 1.81 mm for blue spruce ( Engelm.). The mean value across all species was 0.86 mm (0.11 mm SD). To illustrate application of the storage values, interception was simulated and compared across species for a 40-yr period with different rainfall intensities and durations. By quantifying the potential for different tree species to intercept rainfall under a variety of meteorological conditions, this study provides new knowledge that is fundamental to validating the cost-effectiveness of urban forestry as a green infrastructure strategy and designing functional plantings.
Biofiltration systems can be used to improve the quality of stormwater by treating runoff using plants grown in a moderately permeable soil. Most biofilters use herbaceous species, but in highly urbanized locations, such as streets, trees may be a more suitable vegetation. Biofilters that use urban woody vegetation are less studied. This experiment investigated the use of four street tree species [ Schauer, (R. Br.) Peter G. Wilson & J.T. Waterh., (Sm.) Colvill ex Sweet, and L.] and an unplanted control in model biofilters. All four tree species are used in urban landscapes in southern Australia and were chosen to investigate potential species differences in biofiltration systems. The trees were grown in mesocosms as a randomized block factorial design in soils with three saturated hydraulic conductivity rates (4, 95, and 170 mm h). The trees were regularly flooded with mains water (tap water) or artificial stormwater. Tree growth and nutrient removal performance of the systems were investigated over 13 mo. All four species grew well in all three soils, including one chosen for its low, and potentially growth-limiting, drainage rate. Tree growth increased significantly, except for , when flooded with stormwater. Unplanted controls were a source of nutrients; however, the presence of trees reduced oxidized nitrogen and filterable reactive phosphorus concentrations in leachate. There was little effect of species on the removal of nutrients from stormwater. Trees have the potential to be effective elements in urban biofiltration systems, but further field-level evaluation of these systems is required to fully assess this potential.
Many geoscientists now recognize stemflow as an important phenomenon which can exert considerable effects on the hydrology, biogeochemistry, and ecology of wooded ecosystems and shrublands. Despite the explosive growth of stemflow research, until this review there has been no comprehensive attempt to summarize and synthesize this literature since 2003. Topical areas of substantive new knowledge in stemflow research include: (1) the interrelationships among stemflow and meteorological conditions, especially within individual rain events; (2) the dynamic interplay between stemflow and canopy structure; (3) stemflow and the cycling of solutes and transport of particulate matter; (4) stemflow and its interactions with canopy fungi and corticolous lichens; and (5) stemflow-soil interactions. Each of these five topical areas of substantive new stemflow research are summarized and synthesized, with areas of future research opportunities discussed. In addition, we have reviewed the parameters which can be used to describe stemflow and critically evaluate their utility for different purposes. This review makes a call for scientists studying stemflow to utilize common metrics in an effort to increase the cross-site comparability of stemflow studies. Capitalizing on the insights of prior research, exciting research opportunities await hydrologists, biogeoscientists, and forest ecologists who will conduct studies to deepen our knowledge of stemflow which will enable a better and more accurate framing of stemflow in the larger context of watershed hydrology and biogeochemistry.
Overwhelming stormwater volumes, associated with deteriorating water quality and severe flooding in urbanizing cities, have become a great environmental and financial concern globally. Urban forests are capable of reducing the amount of stormwater runoff, in part, by regulating throughfall via canopy rainfall interception; however, the lack of stand-scale studies of urban throughfall hinders realistic estimates of the benefits of urban vegetation for stormwater regulation. Furthermore, urban forest characteristics that may be influencing rainfall interception are difficult to establish as these environments are extremely heterogeneous and managed, to a large extent, by private residents with varying landscape preferences. To quantify the amount of rainfall interception by vegetation in a residential urban forest we measured throughfall in Raleigh, NC, USA between July and November 2010. We analyzed 16 residential yards with varying vegetation structure to evaluate the relative importance of different descriptive measures of vegetation in influencing throughfall in an urban watershed. Throughfall comprised 78.1-88.9% of gross precipitation, indicating 9.1-21.4% rainfall interception. Canopy cover (p < 0.0001) and coniferous trees (p = 0.017) were the most influential vegetation variables explaining throughfall whereas variables such as leaf area index were not found significant in our models. Throughfall and vegetation characteristics varied significantly among yards (p < 0.0001), between front and back yards (p < 0.0001), and between rented and privately-owned yards (p = 0.001), suggesting a potentially significant role in stormwater regulation for urban residents.
Stemflow is an important subcanopy flux that delivers enriched rainfall to soils immediately surrounding a tree. Stemflow volume represents the quantity of this hydrologic flux while funneling ratio (FR) represents the efficiency with which individual trees scavenge water during rainfall events. Stemflow hydrology and storm meteorological characteristics were monitored from 2007 through 2012 to determine the interspecific differences in stemflow flux with a focus on FR efficiency. The objective of this study was to examine the influence of tree species and size on stemflow FR, determine how seasonality affects stemflow FR, and quantify the role of storm meteorological conditions on stemflow FR. The results presented in this paper build upon 2 years of previous hydrologic research from the Fair Hill, MD field site, which strengthen previous findings via larger storm sample size and highlight more complex stemflow hydrologic relationships than originally assumed. Specifically, this study has demonstrated (1) the efficiency with which smaller trees gain access to rainfall via higher FR than larger trees, (2) the FR variability of F. grandifolia induced by the species’ ease of generating stemflow under many storm conditions, and (3) the necessity of many years of hydrometeorological sampling to capture long-term rainfall characteristics and trends. The efficiency of smaller trees to preferentially funnel water to their tree base has implications for forests undergoing change. Forest disturbance and subsequent regrowth is dominated by smaller trees, but additional research is necessary to understand how saplings compete among one another to gain access to stemflow and how this may be influenced by changing climates and forest composition.
Understanding how trees influence water movement in an urban landscape is important because in an ‘engineered xeriscape’ small changes in rainfall frequency or magnitude have significant implications to plant water availability and mortality at one extreme, and stormwater runoff and flooding at the other. This study relates direct measures of tree canopy interception and discusses their implication for catchment hydrology in different urban landscape contexts. We measured canopy throughfall and stemflow under two eucalypt tree species in an urban street setting over a continuous five month period. Eucalyptus nicholii has a dense canopy and rough bark, whereas Eucalyptus saligna has a less-dense canopy and smooth bark. E. nicholii, with the greater plant area index, intercepted more of the smaller rainfall events, such that 44% of annual rainfall was intercepted as compared to 29% for the less dense E. saligna canopy (2010). Stemflow was less in amount and frequency for the rough barked E. nicholii as compared to the smooth barked E. saligna. However, annual estimates of stemflow to the ground surface for even the smooth barked E. saligna would only offset approximately 10 mm of the 200 mm intercepted by its canopy (2010).
Tree canopy and bark characteristics should be considered when planting in pervious green space, or impervious streetscapes, because of their profound impact upon tree and surrounding water availability, soil water recharge or runoff. This study provides an evidence base for tree canopy impacts upon urban catchment hydrology, and suggests that rainfall and runoff reductions of up to 20% are quite possible in impervious streetscapes. Street tree canopies can function as a cost-effective compliment to water sensitive urban design for stormwater reduction benefits.
Stemflow leachate chemistry from a deciduous canopy tree species monitored during late winter and early spring precipitation events demonstrated significant chemical enrichment. By considering stemflow volume and chemical concentration in relation to the quantity that would be expected in a rain gage occupying an area equivalent to the trunk basal area, manganese was found to be enriched by a mean factor of 1450 and potassium by a mean factor of 580. The most pronounced enrichment was documented during a late winter rain-on-snow event characterized by temperature oscillations near the freezing point. During this event, manganese was enriched by a factor of 4400 and potassium by 1715. We conclude that mixed precipitation events with multiple freeze-melt cycles can generate significantly more leachate than spring rainfall events because of lower air temperatures and increased kinematic viscosity and surface tension of stemflow drainage. These physical properties lengthen the residence time of intercepted precipitation on the woody frame of the tree and promote its funneling from inclined branches. Stemflow represents a spatially localized and enriched point input that may affect tree vigor in early spring. The influence of localized aqueous chemical fluxes to the forest floor on forest biogeochemistry and ecophysiological functioning are discussed.
Meteorological influences on the variability of stemflow generation can affect the hydrology, ecology and soil chemistry of wooded ecosystems, yet the effects of directional wind-driven rainfall on differential stemflow production remain relatively un-researched. This study examines the correspondence of directional wind-driven inclined rainfall with stemflow generation in individual tree crowns utilizing multiple correspondence analysis (MCA) and intrastorm observations at 5min monitoring intervals. In general, preferential stemflow generation at Fair Hill was observed during episodes of inclined rainfall driven by wind from the east to north-northeast (33.76–101.25°). This was supported by MCAs which produced significant correspondences between stemflow production and periods of inclined wind-driven rainfall for nearly all monitored storm events. Intrastorm plots of stemflow production from dominant and subcanopy trees of each codominant species (Fagus grandifolia Ehrh. (American beech) and Liriodendron tulipifera L. (yellow poplar)) also verified this correspondence. Interspecific canopy characteristics of L. tulipifera and F. grandifolia affected crown position, canopy structural characteristics, and, thus, the canopy's response to inclined precipitation. The greater vertical canopy depth observed for F. grandifolia trees enabled them to more efficiently capture inclined rainfall for enhanced stemflow production; whereas, the greater horizontal surface area of L. tulipifera canopies enhanced their droplet capture efficiency and subsequent stemflow generation for periods of un-inclined rainfall. As inclined wind-driven rainfall occurred within a majority of rain events at this site, preferential stemflow production may be a significant process to consider when examining the spatial distribution of canopy-derived water fluxes to the forest floor of wooded catchments under similar meteorological conditions.
Stemflow has distinguishable effects on the hydrology and biogeochemistry of wooded ecosystems. Nonetheless, it is a relatively poorly understood hydrologic process. No known studies have investigated the temporal variability of stemflow volume at 5-min intervals in a beech-yellow poplar forest of eastern North America. The aim of this research is to compare the temporal variability of stemflow generation by Fagus grandifolia Ehrh. (American beech) and Liriodendron tulipifera L. (yellow poplar) in relation to tree species and size. Employing a dense network of tipping-bucket stemflow gages interfaced with a datalogger, a 5 min stemflow yield database was assembled and analyzed to better discern how stemflow production varies (temporally) with tree species and size. Results indicate that both tree species and size have detectable effects on the temporal variability of stemflow yield. Observational data, scientific analysis, and correspondence analysis reveals that stemflow yield: (1) is more similar within than between the two tree species with differences likely being attributable to differences in bark texture and water storage capacity; (2) tree size affects stemflow yield within species; (3) rain event characteristics affect stemflow yield; and (4) stemflow yield for particular trees and rain events is the result of a complex set of interactions among tree species, tree size, and meteorological conditions. These results suggest that the temporal variation in stemflow yield from co-occurring forest trees may play a significant role in subsurface drainage of wooded ecosystems during rain events.
Rainfall, throughfall and stemflow were monitored on an event basis in an undisturbed open tropical rainforest with a large number of palm trees located in the southwestern Amazon basin of Brazil. Stemflow samples were collected from 24 trees with a diameter at breast height (DBH) > 5 cm, as well as eight young and four full-grown babassu palms (Attalea speciosa Mart.) for 5 weeks during the peak of the wet season. We calculated rainfall, throughfall and stemflow concentrations and fluxes of , , , , , , , and and stemflow volume-weighted mean concentrations and fluxes for three size classes of broadleaf trees and three size classes of palms. The concentrations of most solutes were higher in stemflow than in rainfall and increased with increasing tree and palm size. Concentration enrichments from rainfall to stemflow and throughfall were particularly high (81-fold) for . Stemflow fluxes of and exceeded throughfall fluxes but stemflow fluxes of other solutes were less than throughfall fluxes. Stemflow solute fluxes to the forest soil were dominated by fluxes on babassu palms, which represented only 4% of total stem number and 10% of total basal area. For , stemflow contributed 51% of the total mass of nitrogen delivered to the forest floor (stemflow + throughfall) and represented more than a 2000-fold increase in flux compared what would have been delivered by rainfall alone on the equivalent area. Because these highly localized fluxes of both water and persist in time and space, they have the potential to affect patterns of soil moisture, microbial populations and other features of soil biogeochemistry conducive to the creation of hotspots for nitrogen leaching and denitrification, which could amount to an important fraction of total ecosystem fluxes. Because these hotspots occur over very small areas, they have likely gone undetected in previous studies and need to be considered as an important feature of the biogeochemistry of palm-rich tropical forest.
Despite the fact that atmospheric deposition is widely accepted to be an important process in the biogeochemical cycling of wooded ecosystems, no single study is known that has examined stemflow chemistry in relation to atmospheric deposition across time scales, from within discrete events to season, to chronicle alterations in temporal patterns of stemflow chemistry. This research partitioned stemflow solute fluxes (K+, Na+, Mg2+, Ca2+, Cl−, NO3−, and SO42−) from two tree species of differing canopy form and bark morphology into their leaching and dry deposition washoff components using a modified Kazda (1990) integration model at the intra-storm scale to examine differences within and among discrete rain events. Median annual stemflow concentrations in yellow poplar (Liriodendron tulipifera L.) stemflow were higher than American beech (Fagus grandifolia Ehrh.) stemflow for all ions except NO3−. Beech median enrichment ratios were larger for all monitored ions than yellow poplar. All intra-storm stemflow ionic fluxes were initially high, exponentially decaying to a steady input, typically dominated by leaching contributions. With the exception of yellow poplar stemflow Cl− and NO3− fluxes and beech Na+ flux, all intra-storm mean ionic fluxes began with higher dry deposition percentages and transitioned to primarily leaching. Observations in the field implicate increased magnitude and rainfall intensity in the initiation of new stemflow flowpaths, evidenced by increased variability in the timing of stemflow ionic deposition and fluctuations in the proportion of washoff and leaching during some events. Beech stemflow fluxes were larger than yellow poplar for all ions during the leafed, leafless, and annual periods. Our results demonstrate: (1) the critical role of the initiation of new flowpaths and expansion and maturation of developed flowpaths on a tree’s surface to solute enrichment and transport to the forest floor as a canopy wets-up; and (2) the importance of temporal scale in providing important insights into some effects of stemflow on biogeochemical cycling.Highlights► First known study to examine/contrast within-event to season. ► Documents effects of new flowpaths on solute flux. ► Temporal scale affects stemflow chemistry. ► Tree species affects leaching/washoff proportions.
Leaching of nutrients from aboveground vegetative surfaces of canopy trees represents an important component of the intra-system nutrient cycle in forested ecosystems. The hypothesis tested is that there is no difference in winter stemflow leachate concentration or quantity among different storm types and meteorological conditions. Non-hierarchical cluster analysis demonstrated that there was an association between precipitation event type and chemical enrichment of stemflow drainage from the leafless crowns of deciduous canopy trees monitored over two successive winter seasons. Three clusters were derived on the basis of chemical enrichment. Stemflow was most enriched during snow-to-rain events. Rain and rain-to-snow events also enriched stemflow but to a lesser extent than snow-to-rain events. Snow, sleet, and rain shower events enriched stemflow the least. Stemflow from all precipitation events were chemically enriched compared to the incident bulk precipitation. The extent of chemical enrichment was inversely proportional to stemflow volume generated by canopy trees during discrete precipitation events. Other factors affecting the amount of winter stemflow leaching were precipitation type (influences interception efficiency) and intra-storm temperature regime. Stemflow from precipitation events of long duration and low intensity with air temperature oscillations around the freezing point was the most enriched because of the longer residence time of intercepted precipitation with the leafless crown. Because stemflow leachate quantities were found to differ among precipitation events as a function of meteorological conditions, it is possible that the winter biometeorology of deciduous forests could potentially impact tree vigor, forest stand productivity, and species composition of deciduous forests.
Redistribution of ground-level rainfall and interception loss by an isolated Quercus ilex tree were measured over 2 years in a Mediterranean oak savannah. Stemflow, meteorological variables and sap flow were also monitored. Rainfall at ground level was measured by a set of rain-gauges located in a radial layout centred on the tree trunk and extending beyond the crown limits. Interception loss was computed as the difference between the volume of rainwater that would reach the ground in the absence of the tree and the volume of water that actually fell on the ground sampling area (stemflow included). This procedure provided correct interception loss estimates, irrespective of rainfall inclination. Results have shown a clear non-random spatial distribution of ground-level rainfall, with rainwater concentrations upwind beneath the crown and rain-shadows downwind. Interception loss amounted to 22% of gross rainfall, per unit of crown-projected area. Stand interception loss, per unit of ground area, was only 8% of gross rainfall and 28% of tree evapotranspiration. These values reflect the low crown cover fraction of the stand (0·39) and the specific features of the Mediterranean rainfall regime (predominantly with few large storms). Nevertheless, it still is an important component of the water balance of these Mediterranean ecosystems. Copyright © 2005 John Wiley & Sons, Ltd.
Stemflow was monitored on event-basis in an undisturbed open tropical rainforest with a large number of palm trees located in the southwestern Amazon basin of Brazil. We estimated stemflow of 24 trees with a diameter at breast height (DBH) over 5 cm and of 16 juvenile and eight aborescent babassu palms (Orbignya phalerata Mart.). To obtain within-event stemflow variability we monitored stemflow of one additional aborescent babassu palm with a tipping-bucket rain gauge at 5-min intervals. Total stemflow of the forest accounted for 8.0 ± 1.8% (S.E.) of incident rainfall and reached the forest floor over an area corresponding to the total basal area that sums up to only 0.3% of the plot area. The most influential predictive variables for stemflow generation were DBH and rainfall amount. The stemflow parameter ‘funneling ratio’, which is normalized for DBH and rainfall amount, was particularly useful to highlight the relevance of small trees (DBH ⩽ 10 cm) for stemflow generation. Small trees and babassu palms had significantly higher funneling ratios than larger trees (median funneling ratios: 15–27 and 1–2, respectively). The maximum 5-min stemflow intensity (1232 mm h−1) was 15-fold that of rainfall. High funneling ratios of small trees and babassu palms suggest that high stemflow intensities are the rule rather than the exception. Therefore, we expect small trees and babassu palms to influence hydrologic processes as subsurface flow, saturation overland flow or groundwater recharge. Consequently, stemflow studies should include all DBH classes and species with exceptionally high funneling ratios. For modeling purposes, stemflow should be estimated and not just assumed if study sites have a large number of palms or of small trees.
pH and ion concentrations (Na(+), K(+), Mg(2+), Ca(2+), NO(-)(3)) in the stemflow of the evergreen broad-leaved tree, Ilex rotunda, planted in the median strip of a highway and nitrogen oxides concentration in the air in an urban site were compared with a suburban site in Fukuoka city, Japan. The annual average of the nitrogen oxides concentration in the air was higher and NO(-)(3) concentration in the stemflow at the urban site was higher or similar compared with the suburban site. However, the annual average of pH in the stemflow at the urban site was higher than at the suburban. The annual average cation concentrations in the stemflow at the urban site were higher than at the suburban except Na(+). In particular, K(+) and Ca(2+) were higher throughout the measurement period. Therefore, higher pH in the urban stemflow was probably due to neutralization by higher concentrations of K(+), Mg(2+) and Ca(2+).
Canadian Climate Normals, Station Name: Kamloops A* (available online)
Environment Canada, 2014. Canadian Climate Normals, Station Name: Kamloops
A* (available online).
The Humane City: Cities as If People Matter
- J R Short
Short, J.R., 1989. The Humane City: Cities as If People Matter. Basil Blackwell
Oxford.