Riparian Plant Communities Research Articles

Impacts of invasive alien species on riparian plant communities in South African savanna

Abstract Biological invasions are a threat to protected areas globally; however, the relative lack of studies quantifying the ecological impacts impairs informed decision-making. We selected three annual alien plants, widespread in the riparian habitats of the Kruger National Park, South Africa: Datura innoxia, Parthenium hysterophorus, and Xanthium strumarium, to examine their potential impacts on riparian plant communities. We identified 12–13 populations for each and placed a pair of invaded and uninvaded plots in each population. Species richness, Shannon diversity, and Pielou evenness were compared between the invaded and uninvaded plots using LMM models, and species composition was compared using ordination. The invaded vegetation showed lower species richness compared to the uninvaded, with the strongest effect observed for P. hysterophorus. The invaded plots also showed lower Shannon diversity and Pielou evenness due to the presence of alien dominants. For all three invaders, the invasion resulted in changes in the composition of native vegetation. Some native plants were more frequent and abundant in the invaded vegetation, possibly due to the habitats created in sandy river beds. The native species richness decreased with increasing invader cover, but the species richness of aliens accompanying the invasive dominants was not negatively affected by their cover. Our results confirmed the negative impact of invasive aliens on native plant diversity, with the most pronounced effect by Parthenium hysterophorus invasions.

重庆主城河岸带植物群落功能性状与土壤理化性质的关系

PDF HTML阅读 XML下载 导出引用 引用提醒 重庆主城河岸带植物群落功能性状与土壤理化性质的关系 DOI: 10.5846/stxb202202160368 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 重庆市科技兴林项目（2021-9）；西南大学生命科学学院科学基金项目（20212005406201）；宁夏回族自治区重点研发计划项目（2020BFG03006）；中央林业改革发展资金科技推广示范项目（渝林科推2020-2） The relationship between plant functional traits and soil physicochemical properties in the riparian zones of downtown Chongqing Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于功能性状视角开展植物群落与环境关系的研究有助于揭示植物的适应策略。然而，目前关于城市河岸带植物群落功能性状的研究较少。为此选取10项植物功能性状指标和14项土壤理化性质指标，探究重庆主城3种生境类型河岸带（自然型河岸带（NRZ）、农耕主导型河岸带（FRZ）和开发建设主导型河岸带（BRZ））植物群落功能性状与土壤因子特征及互作机制。结果表明：（1）与NRZ生境相比，FRZ生境中的土壤速效磷、速效钾和氧化还原电位和BRZ生境中的土壤含水量显著偏高（P<0.05）；FRZ和BRZ生境中的土壤pH值和全磷含量显著偏高，而土壤有机质、全钾和全氮含量显著偏低（P<0.05）。（2）与NRZ生境相比，FRZ生境中的比根长和比根表面积显著较高，茎干物质含量和叶干物质含量显著较低；BRZ生境中仅茎干物质含量显著较低（P<0.05）。（3）冗余分析结果表明，影响各生境类型河岸带植物群落功能性状的土壤因子不同，NRZ生境为土壤容重、含水量和硝态氮，FRZ生境为土壤铵态氮、全磷和有机质，BRZ生境则是土壤含水量、温度和速效磷。研究发现与自然状态相比，农业和建筑类型的人为干扰导致重庆主城河岸带生境发生改变，植物群落通过权衡功能性状组合的策略提高对生境变化的适应性。 Abstract:Studying the relationship between plants and the environment through plant functional traits is of help to reveal plants' adaptation strategies. At present, most researches on the relationship between plant functional traits and environmental factors have mainly focused on the terrestrial ecosystems. Very few similar studies have been carried out in the riparian ecosystems. Riparian vegetation is a prerequisite for riparian ecosystems to function properly, while maintaining healthy watercourse and landscape connectivity. Therefore, our study selected 10 plant functional trait indices and 14 soil physiochemical property indices to explore plant community functional traits, soil factor characteristics and interaction mechanisms of three habitat types (natural riparian zone (NRZ), farming riparian zone (FRZ) and building riparian zone (BRZ)) within the riparian zones of downtown Chongqing. The results showed that:(1) compared with the NRZ habitat, the soil available phosphorus, available potassium and redox potential in the FRZ habitat and the soil moisture in the BRZ habitat were significantly higher (P<0.05). The soil pH value and total phosphorus content were significantly higher in FRZ and BRZ habitats, while soil organic matter, total potassium and total nitrogen content were significantly lower (P<0.05). (2) In comparison to the NRZ habitats, the specific root length and specific root surface area in the FRZ habitats were significantly higher, and the stem dry matter content and leaf dry matter content were significantly lower. Only the stem dry matter content was significantly lower in the BRZ habitats (P<0.05). (3) The results of redundancy analysis showed that the soil factors which affected the functional traits of riparian plant communities in different habitat types were different. For the NRZ habitats, the influencing factors were soil bulk density, soil moisture and nitrate nitrogen. For the FRZ habitats, the influencing factors were soil ammonium nitrogen, total phosphorus and organic matter. For the BRZ habitats, the influencing factors were soil moisture, soil temperature, and available phosphorus. This study found that in comparison to the natural riparian state, the anthropogenic disturbance of agriculture and structural engineering related projects led to changes in the riparian habitats of downtown Chongqing, and that the plant community improved its adaptability to various habitats through trade-off combinations of functional traits. 参考文献 相似文献 引证文献

Response-effect trait overlap and correlation in riparian plant communities suggests sensitivity of ecosystem functioning and services to environmental change

Environmental changes and biodiversity loss have emphasized the need to understand how communities affect ecosystem functioning and services. In riparian ecosystems, integrative, generalizable, broad-scale models of ecosystem functioning are still required to fulfill this need. However, few studies have explored the links between functional traits, ecosystem functions, and the services of riparian vegetation. Here we adapt the response-effect trait framework to link drivers, traits, ecosystem functions, and services in riparian ecosystems and assess ecosystem functioning sensitivity to environmental changes. The response-effect trait framework distinguishes between traits related to responses to the environment (response traits) and effects on ecosystem functioning (effect traits). The framework predicts that if response and effect traits are tightly linked, shifts in environmental drivers may alter communities' traits and ecosystem functioning.We adapted the response-effect trait framework for riparian plant communities and used it to assess the overlap between response and effect traits. We tested for correlation among traits identified in the framework and for community functional responses to climatic, topographic, soil, and land cover factors using riparian plant communities along a Temperate-Mediterranean climate gradient in North Portugal.We found a high overlap between response and effect traits, with seven out of thirteen traits identified as both response and effect. Additionally, we found trait linkages in four groups of positively correlated community mean traits. Precipitation and aridity were the most predictive drivers of community functional structure, and life form and leaf area were the most responsive traits.Overall, our findings suggest riparian plant communities are likely to propagate the effects of environmental changes to ecosystem functioning and services, affecting several regulation ecosystem services.This work highlights the sensitivity of riparian ecosystems to environmental changes and how it can affect ecosystem services. Similar functional approaches can be useful for adaptive ecosystem management to sustain biodiversity and ecosystem services.

GIS-based planning of buffer zones for protection of boreal streams and their riparian forests

Forested buffer zones with varying width have been suggested as the most promising approach for protecting boreal riparian biodiversity, reducing erosion, and minimizing nutrient leaching from managed forestry areas. Yet, less optimal fixed-width approach is still largely used, likely because of its simple design and implementation. We examined the efficiency of varying-width buffer zones based on depth-to-water (DTW) index in protecting stream riparian plant communities. We further compared the economic costs of DTW-based buffer to commonly used 5, 10 and 15 m fixed-width buffers. We also included an additional buffer based on a combination of DTW and erosion risk (Revised Universal Soil Loss Equation, RUSLE) into these comparisons to see the extent and cost of a buffer that should maximize the protection of the linked aquatic environment. Plant species richness increased with increasing soil moisture and species preferring moist conditions, nutrient-rich soils and high pH were clearly more abundant adjacent to stream in areas with high predicted soil moisture than in dry areas. Differences in species richness were paralleled by differences in community composition and higher beta diversity of plant communities in wet than in dry riparian areas. There were also several indicator species typical for moist and nutrient-rich soils for wet riparian areas. Riparian buffer zones based on DTW were on average larger than 15 m wide fixed-width buffers. However, the cost for DTW-based buffer was lower than for fixed-width buffer zones when the cost was normalized by area. Simulated selective cutting decreased the costs, but cutting possibilities were variable among streams and depended on the characteristics of forest stands. Our results thus suggest a high potential of DTW in predicting wet areas and variable-width buffer zones based on these areas in the protection of riparian biodiversity and stream ecosystems.

The hydroclimate niche: A tool for predicting and managing riparian plant community responses to streamflow seasonality

AbstractHabitat suitability is a consequence of interacting environmental factors. In riparian ecosystems, suitable plant habitat is influenced by interactions between stream hydrology and climate, hereafter referred to as “hydroclimate”. We tested the hypothesis that hydroclimate variables would improve the fit of ecological niche models for a suite of riparian species using occurrence data from the western United States. We focus on the climate conditions (temperature, precipitation and vapor pressure deficit) during the months of lowest and highest streamflow as integrative hydroclimate metrics of resource and stress levels. We found that the inclusion of hydroclimate variables improved model fit for all species in the western USA dataset. We then tested the utility of the improved habitat suitability models by projecting them onto a regulated segment of the Colorado River to assess potential impacts of streamflow seasonality on vegetation metrics of management concern. Species frequency derived from independent survey data in the Colorado River segment was significantly higher for species with predicted suitable habitat than for species without predicted suitable habitat. Under different simulated hydrographs for the Colorado River, overall species richness was predicted to be greatest with peak streamflows during summer, and native‐to‐non‐native species ratios were predicted to be greatest with lowest streamflows in winter. Summer high flows were particularly associated with higher predicted habitat suitability for species that have increased in cover over recent decades (e.g., Pluchea sericea, Baccharis species). We conclude that hydroclimate covariates can be useful tools for predicting how riparian vegetation communities respond to changes in the seasonal timing of low and high streamflows.

Revisiting irrigation efficiency before restoring ancient irrigation canals in multi-functional, nature-based water systems

CONTEXTIn the Middle Ages, the Muslims introduced communal water management in the Iberian Peninsula. Some irrigation systems of medieval origin are still in operation in the mountainous areas of Southern Spain. Snowmelt runoff is diverted during spring from high-altitude streams into contoured recharge ditches that convey the water to areas of high infiltration (shallow aquifers). This regulates and delays discharge into the main river, from which downstream flow is diverted, during late spring and summer, to irrigation ditches that supply terraces and fields on river plains. The Busquístar irrigation ditch and its irrigation scheme comprise one of these ancient systems. OBJECTIVES1) To characterize the Busquístar system, its water source and regulation, its water users' association, its multi-functionality, and its quality as a nature-based solution for water security. 2) To review the irrigation efficiency concept applied to the restoration of ancient irrigation systems, taking into account their ecosystem services. METHODSi) Semi-structured interviews with stakeholders to evaluate irrigation system operation and perceptions of multi-functionality; ii) field surveys for description of the irrigation ditch and its riparian flora; iii) satellite imagery for quantifying riparian vegetation; iv) water balance for irrigation efficiency computation. RESULTS AND CONCLUSIONSCrop production is the main function of the Busquístar irrigation scheme but additional ecosystem services are creation of landscape and biodiversity. Eight riparian plant communities were distinguished along the irrigation ditch. The discharge measured at its head on 23 July and 3 September 2017 represented 14 and 50% of the mean river flow in July and September, respectively. The flow measured at the first bifurcation of the ditch was about half that at the head, revealing the proportion filtered along its 6470-m long conveyance reach. The remaining flow was then diverted to 4 branches along the 3140-m long distribution reach proportionally to the irrigable area in each branch. Return flows and irrigation efficiency were estimated for the two measuring dates considering riparian and crop evapotranspiration. The estimated efficiency was highly dependent on which water uses were considered beneficial and on the scale of analysis, field, entire system or watershed. SIGNIFICANCEThe study revealed the integrated approach behind the traditional water management in these ancient systems. The article proposes a review of the irrigation efficiency concept that allows reconciling the character of a nature-based solution with the current restoration of the system, responding to the needs of the emerging export horticulture in the area.

Modelling LEAF stomatal resistance for common REED, peach‐leaf willow and cottonwood riparian plant communities

AbstractAccounting for the impact of riparian plant communities on water balances is usually ignored due to the lack of data and information on water use of these plant communities. This is especially important for areas with limited water resources and in areas where water resources are shared between different users (agriculture, riparian zones, other ecosystems/agro‐ecosystems, municipalities, recreational, mining, agro‐ecology, etc.). Modelling stomatal resistance (rL) of riparian vegetation species is a complex process, but is also one of the limited processes to estimate evaporative losses for these plant communities for more inclusive, complete and robust water balance and hydrologic analyses for forecasting, planning, allocating and managing surface and groundwater resources and for hydrologic modelling. The objectives of this research were to (i) modify Jarvis‐type model for estimating rL for three riparian plant species [Common reed (Phragmites australis), Peach‐leaf willow (Salix amygdaloides) and Cottonwood (Populus sect. Aigeiros)], (ii) investigate the rL response to microclimate/environmental variables, and (iii) evaluate the photosynthetic photon flux density (PPFD) versus rL response curves for estimating hourly rL. A Jarvis‐type model was modified by re‐parametrization using porometer‐measured data collected via extensive field campaigns in 2009 and 2010. Flooding in 2010 impacted the phenology and physiology of all species with increased rL and impedance in growth due to oxygen stress. While R2 values were generally low for both years for all species, the response of rL to the same climate variables under the same environmental conditions exhibited substantial variations between the species. Overall, the response of rL to climatic variables was species‐specific, complex and varied with surface and atmospheric conditions. For all species, stronger relationships between rL versus air temperature and net shortwave radiation were observed. The Jarvis‐type model underestimated rL for all species and hence required independent re‐parameterization for each specie independently. The model performance after re‐parameterization improved substantially during both calibration and validation. Validation of the new modified Jarvis‐type model (NMJ‐model) resulted in good estimates of rL with root‐mean‐squared difference (RMSD) and R2 values of 31 s m−1 and 0.51 for Common reed; 56 s m−1 and 0.81 for Peach‐leaf willow; and 237 s m−1 and 0.51 for Cottonwood, respectively. Strong agreements were found between measured and re‐parameterized NMJ‐model‐estimated rL values for all three species in both years, but the relationships improved significantly in 2009 with no flooding. The NMJ‐model‐estimated rL values were within 10, 7 and 11% of the measured values for Common reed, Peach‐leaf willow and Cottonwood, respectively. rL values estimated using PPFD versus rL response curves developed for individual species were used to estimate hourly rL and the response curves were able to effectively track the trends and magnitudes of rL. With re‐parameterization, the NMJ‐models developed and tested for each riparian vegetation specie provide robust estimates of rL that can be used to quantify evaporative losses of these riparian plant communities for more complete local and regional water balance analyses by accounting for riparian vegetation water use.

The responses of riparian plant communities to environmental and spatial factors in the upper Han River basin, China

Exploring the relative roles of environmental and spatial factors in shaping community composition is crucial to gain insights into community assembly. At present, however, their roles in riparian plant communities remain to be fully elucidated. Here, we investigated the responses of taxonomic and functional trait compositions of riparian plant communities to environmental and spatial factors in the upper Han River basin, China. We aimed to (1) investigate the responses of both taxonomic composition and functional traits to anthropogenic disturbances and (2) compare the relative roles of environmental and spatial factors in affecting both taxonomic and functional trait compositions. Results showed that species diversity of riparian plant communities was highest under mild disturbance, and both types of riparian plant community composition were strongly influenced by anthropogenic activities. In addition, the riparian plant community compositions in the upper Han River basin were driven by both environmental and spatial factors. Compared to spatial factors, environmental filtering was more important in explaining species composition, while the opposite trend was observed for functional composition due to the high environmental heterogeneity of the 5 tributaries and the reproductive mode from riparian plants. Thus, for assessment and management of riparian vegetation, the taxonomic and functional characteristics of communities should be considered as they may respond to important drivers and anthropogenic disturbances differently.

Shift from soil chemical to physical filters in assembling riparian floristic communities along a flooding stress gradient

Understanding community assembly is a key issue in recognizing community succession and guiding the restoration of degraded ecosystems. Based on the stress-dominance hypothesis (SDH), along a gradient of increasing environmental stress, the relative importance of environmental filtering is supposed to be dominant but species interaction could be a minor process in assembling communities. However, this hypothesized model of the assembly-rule shift was equivocally supported by various studies. In this study, by examining riparian plant communities with the zonation distribution of species composition along a markedly contrast flooding-stress gradient, a general aim was to clarify whether assembly rules of the communities would be also sorted into the zonation pattern as expected by the SDH. Another aim was to identify how edaphic factors associate with the assembly processes. Firstly, we found that even under the distinct stress gradient, community assembly was not stratified into different rules as the SDH expected, but environmental filtering appeared as a dominant assembly process across the stress gradient. Secondly, although filtering holds as a dominant assembly rule, environmental filters were found different along the gradient. By disentangling the filters of edaphic attributes, we found that the filters significantly shifted from soil physical properties to chemical nutrients governing the filtering process along the gradient. This result revealed that, across the contrast gradient, the environmental deterministic process on assembly is so strong that the other assembly processes became weaker. By synthesizing our results, the SDH may not be applied even under the context of a contrast stress gradient, which suggests that environmental context may be a key in testing and applying the SDH. Finally, in guiding riparian restoration under strong stress, we suggest that soil physical structure rather than chemical nutrients shall be given a priority for consideration in rebuilding the degraded riparian communities.

Does large dam removal restore downstream riparian vegetation diversity? Testing predictions on the Elwha River, Washington, USA.

Large dams and their removal can profoundly affect riparian ecosystems by altering flow and sediment regimes, hydrochory, and landform dynamics, yet few studies have documented these effects on downstream plant communities. Ecological theory and empirical results suggest that by altering disturbance regimes, reducing hydrochory, and shifting communities to later successional stages, dams reduce downstream plant diversity. Dam removal could reverse these processes, but the release of large volumes of sediment could have unexpected, transient effects. Two large dams were removed on the Elwha River in Washington State, USA, from 2011 to 2014, representing an unprecedented opportunity to study large dam removal effects on riparian plant communities. Our research objectives were to determine: (1) whether the Elwha River dams were associated with lower downstream plant diversity and altered species composition across riparian landforms pre-dam removal, and (2) whether dam removal has begun to restore downstream diversity and composition. To address these objectives, we compared plant species richness and community composition in river segments above, below, and between the two dams. Plant communities were sampled twice before (2005 and 2010) and four times after (2013, 2014, 2016, and 2017) the start of dam removal, with 2013 and 2014 sampled while the upstream dam removal was ongoing. Prior to dam removal, native species richness was 41% lower below dams compared with the upstream segment; 6 years after dam removal began, it increased ~31% between the dams, whereas nonnative species richness and cover were not apparently affected by dams or their removal. Deposition caused by large volumes of released reservoir sediment had mixed effects on native species richness (increased on floodplains, decreased elsewhere) in the lowest river segment. Plant community composition was also different downstream from dams compared with the upstream reference, and has changed in downstream floodplains and bars since dam removal. In the long term, we expect that diversity will continue to increase in downstream river segments. Our results provide evidence that (1) large dams reduce downstream native plant diversity, (2) dam removal may restore it, and (3) given the natural dynamics of riparian vegetation, long-term, multiyear before-and-after monitoring is essential for understanding dam removal effects.

A Green New Balance: Interactions among riparian vegetation plant traits and morphodynamics in alluvial rivers

AbstractThe strength of interactions between plants and river processes is mediated by plant traits and fluvial conditions, including above‐ground biomass, stem density and flexibility, channel and bed‐material properties, and flow and sediment regimes. In many rivers, concurrent changes in (1) the composition of riparian vegetation communities as a result of exotic species invasion and (2) shifts in hydrology have altered physical and ecological conditions in a manner that has been mediated by feedbacks between vegetation and morphodynamic processes. We review how Tamarix, which has invaded many southwestern US waterways, and Populus species, woody pioneer trees that are native to the region, differentially affect hydraulics, sediment transport, and river morphology. We draw on flume, field, and modelling approaches spanning the individual seedling to river‐corridor scales. In a flume study, we found that differences in the crown morphology, stem density, and flexibility of Tamarix compared to Populus influenced near‐bed flow velocities in a manner that favoured aggradation associated with Tamarix. Similarly, at the patch and corridor scales, observations confirmed increased aggradation with increased vegetation density. Furthermore, long‐term channel adjustments were different for Tamarix‐ versus Populus‐dominated reaches, with faster and greater geomorphic adjustments for Tamarix. Collectively, our studies show how plant‐trait differences between Tamarix and Populus, from individual seedlings to larger spatial and temporal scales, influence the co‐adjustment of rivers and riparian plant communities. These findings provide a basis for predicting changes in alluvial riverine systems which we conceptualize as a Green New Balance model that considers how channels may adjust to changes in plant traits and community structure, in addition to alterations in flow and sediment supply. We offer suggestions regarding how the Green New Balance can be used in management and invasive species management.

Functional Trait Diversity Shapes the Biomass in the Dam-Induced Riparian Zone

The construction of dams has caused a serious decline in riparian ecosystem functioning and associated services. It is crucial to assess the response of riparian plant communities to flooding stress for their conservation. Functional traits composition, functional diversity, and species diversity are commonly used to investigate the effect of abiotic stress on ecosystem functioning and services (i.e., biomass). Yet, how the functional traits respond to the flooding stress along a dam-induced riparian habitat remains unclear, and how biodiversity affects biomass still exists controversy. Accordingly, this study investigated the response strategies of functional traits subjected to the flooding stress and its correlation with aboveground biomass (AGB) in the water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR). We found that leaf traits and root traits showed a significant response to elevation, whereas they demonstrated different distribution patterns. Leaf traits showed acquisitive-conservative-acquisitive resource strategies along the flooding stress, while root traits shifted from species conservative resource to acquisitive resource strategies. AGB was found to be positively related to the community weighted mean (CWM) trait values for leaf dry matter content (LDMC) and negatively related to specific leaf area (SLA), but the AGB showed no relationship with the root traits. AGB accumulated greatly in the intermediate species diversity, and we also found a significant relationship between functional diversity and biomass within threshold values. Additionally, Rao’s exerted the most significant influence on the biomass, suggesting that the functional diversity index is a better indicator of biomass variation. The results obtained only partly supported the “mass ratio hypothesis” in leaf traits and mainly supported the “niche complementarity hypothesis”, which suggested that these two theories are not mutually exclusive at the early stage of vegetation community succession with an unstable community structure in dam-regulated riparian zones.

Shifts from native to non-native riparian plant communities analyzed using hierarchical phytosociological data

Shifts from native to non-native riparian plant communities analyzed using hierarchical phytosociological data

Dam-induced difference of invasive plant species distribution along the riparian habitats

Riparian ecosystem is structurally unstable due to the frequent disturbances from water fluctuation. Moreover, dams on large rivers tend to trigger fundamental changes of the composition and structure of riparian plant communities, which provides high odds for invasive species to colonize. Yet, how the invasive species distribute along a dam-induced riparian habitat, and how the native species resist to plant invasion are still puzzles. In this study, we investigated spatial distribution of invasive floral species and its correlation with the distance from dam and the dam-triggered flooding stresses, as well as the resistance of native species to plant invasion in the water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) along the Yangtze River. By our investigation, a total of 43 alien plant species belonging to 14 families and 34 genera were found, including 20 existed and 23 newly discovered alien species recorded. Most of the new invasive species are annual herbs of the Asteraceae family. At the current successional stage, the new invasive species had not yet fully occupied the habitats of the existed invasive species. Longitudinally, number and coverages of the new invasive species showed an opposite distribution pattern to the existed invasive species, but vertically they demonstrated similar pattern. Currently, the new dominant invasive species are mainly concentrated at the intermediate elevation of WLFZ in the middle section of the reservoir, whereas the existed dominant invasive species have proliferated across the whole WLFZ. Additionally, native species showed a weak resistance to plant invasion, and water fluctuation along the elevation exerted the most significant influence on plant invasion. The results indicated that, after a decade of riparian community succession, the invasiveness of alien species remain persisted. The potential penetration site of the invasion may locate at the intermediate section along the vertical and longitudinal dimension.

The role of plant functional traits and diversity in soil carbon dynamics within riparian agroforests.

Restoration of agricultural riparian buffers with trees (agroforestry) provides an elegant solution to enhance carbon storage while also augmenting local biodiversity. Yet the scope and role of riparian plant community diversity in key soil dynamics remain unresolved. Operationalizing riparian age (young [<10 yr] and mature [>30 yr] since establishment] and forest stand type (coniferous and deciduous dominant) to capture the potential extent of plant diversity, we measured plant functional trait diversity and community weighted mean trait values, microbial composition, abiotic soil conditions, and rates of soil CO2 efflux (mg CO2 -C m-2 h-1 ). We used piecewise structural equation modeling (SEM) to further refine the role of biotic indices (leaf, root, and microbial characteristics), and abiotic factors (soil physio-chemical metrics) on soil C cycling processes in riparian systems. We found significantly lower rates of CO2 efflux (F=8.47; p<.01) over one growing season and higher total soil C (F=3.46; p=.03) in mature buffers compared with young buffers. Using SEM, we describe influences on soil C content (marginal r2 =61) and soil CO2 efflux (marginal r2 =53). Within young buffers, soil C content was significantly predicted by fungal/bacterial ratio and root length density, whereas in mature buffers, tree leaf characteristics were associated with soil C content. Soil CO2 efflux was predicted by soil moisture, soil carbon content, and herbaceous root characteristics. Evidently, leaf and root functional traits in combination with broad soil parameters significantly describe soil C dynamics in the field; however, significant pathways are not the same throughout the life cycle of a riparian agroforest.

Analysing the distance decay of community similarity in river networks using Bayesian methods

The distance decay of community similarity (DDCS) is a pattern that is widely observed in terrestrial and aquatic environments. Niche-based theories argue that species are sorted in space according to their ability to adapt to new environmental conditions. The ecological neutral theory argues that community similarity decays due to ecological drift. The continuum hypothesis provides an intermediate perspective between niche-based theories and the neutral theory, arguing that niche and neutral factors are at the opposite ends of a continuum that ranges from competitive to stochastic exclusion. We assessed the association between niche-based and neutral factors and changes in community similarity measured by Sorensen’s index in riparian plant communities. We assessed the importance of neutral processes using network distances and flow connection and of niche-based processes using Strahler order differences and precipitation differences. We used a hierarchical Bayesian approach to determine which perspective is best supported by the results. We used dataset composed of 338 vegetation censuses from eleven river basins in continental Portugal. We observed that changes in Sorensen indices were associated with network distance, flow connection, Strahler order difference and precipitation difference but to different degrees. The results suggest that community similarity changes are associated with environmental and neutral factors, supporting the continuum hypothesis.

Choked out: Battling invasive giant cane along the Rio Grande/Bravo Borderlands

AbstractAlong the U.S.‐Mexico border, an aggressive non‐native grass, giant cane (Arundo donax), grows in dense, nearly impenetrable stands along hundreds of kilometers of the Rio Grande/Bravo (RGB). Between 2008 and 2018, a diverse, multisector binational‐team repeatedly treated giant cane with prescribed fire and herbicide along 90 km of this binational river to restore aquatic and riparian habitat and native plant community composition. The large geographic scale, binational management response, treatment methods used, and development of a long‐term monitoring program to quantify treatment impacts on the RGB's riparian plant community underscore the unique aspects of this effort. Results of this decade‐long management experiment indicate that (i) the combination of a primary treatment of giant cane (using prescribed fire followed 4–6 weeks later by herbicide treatment of regrowth) and a secondary treatment (spot treatment of regrowth one or more years following primary treatment) was effective in reducing the extent and distribution of giant cane at relatively low cost, (ii) giant cane re‐establishment following treatment is often not rapid, nor dramatic; and (iii) as revealed by analysis of riparian vegetation monitoring data, eradication of dense stands of giant cane have fostered significant and long‐term reduction in giant cane cover and recovery of native woody riparian plant taxa. Important caveats to the long‐term viability of managing giant cane hinge on better understanding the consequences of herbicide use, securing funding to cover the cost of re‐treatment, and continuing river flow management focused on promoting the recovery of native riparian obligate plants over non‐natives.

Dam inundation simplifies the plant community composition

The construction of dams has caused riparian habitat degradation and ecosystem service loss globally. It is critical to assess the response of riparian plant communities to inundation gradients for their conservation. Recent evidence suggests that plant community assemblages are governed by flooding stress, soil nutrient availability, climate (environmental filtering) and dispersal, speciation, local extinction (dispersal filtering), but it remains unclear which dominates the riparian ecosystem regulated by a dam. Thus, this article aims to elucidate the relative importance of environmental and dispersal filtering to variations in plant communities to understand community assembly mechanisms in riparian ecosystems. Here we used plant community data related to four elevations in the riparian zone of the Three Gorges Dam Reservoir in China to show that species richness and diversity, community height, and the cover of total, annual, and exotic plant categories decreased, while the cover of perennial and native plant groups increased under higher flooding stress. Community composition varied substantially with elevation, and species composition tended to converge with increased inundation, characterized by flood-tolerant species. The community composition underwent stronger environmental filtering at low elevations and stronger dispersal filtering at high elevations, with stronger environmental filtering across riparian ecosystems. Therefore, we conclude that dam inundation drives community assemblages of riparian plants by the combined effects of environmental and dispersal filtering. Still, their relative contribution varies between elevations, and environmental filtering is more important in shaping community assembly. This study is the first to confirm that plant community assembly in the dam-regulated riparian area is determined by both niche-based and stochastic processes. Thus, we highlighted the importance of considering inundation intensity, propagule sources, and river connectivity when implementing restoration projects.

Invasive tree cover covaries with environmental factors to explain the functional composition of riparian plant communities.

Invasive species are a major cause of biodiversity loss worldwide, but their impact on communities and the mechanisms driving those impacts are varied and not well understood. This study employs functional diversity metrics and guilds-suites of species with similar traits-to assess the influence of an invasive tree (Tamarix spp.) on riparian plant communities in the southwestern United States. We asked: (1) What traits define riparian plant guilds in this system? (2) How do the abundances of guilds vary along gradients of Tamarix cover and abiotic conditions? (3) How does the functional diversity of the plant community respond to the gradients of Tamarix cover and abiotic conditions? We found nine distinct guilds primarily defined by reproductive strategy, as well as growth form,height, seed weight, specific leaf area, drought and anaerobic tolerance. Guild abundance varied along a covarying gradient of local and regional environmental factors and Tamarix cover. Guilds relying on sexual reproduction, in particular, those producing many light seeds over a long period of time were more strongly associated with drier sites and higher Tamarix cover. Tamarix itself appeared to facilitate more shade-tolerant species with higher specific leaf areas than would be expected in resource-poor environments. Additionally, we found a high degree of specialization (low functional diversity) in the wettest, most flood-prone, lowest Tamarix cover sites as well as in the driest, most stable, highest Tamarix cover sites. These guilds can be used to anticipate plant community response to restoration efforts and in selecting appropriate species for revegetation.

A near-range plant invasion homogenizes riparian vegetation but leads to more productive bird communities

AbstractBiological invasions are a leading driver of biodiversity loss and population declines worldwide. While much research has focused on understanding the effects of long-distance (e.g., cross-continental) invasion, the potential impacts of species that invade close to or within their native ranges are relatively understudied. We investigated the effects of the near-range introduction of a non-native plant, New Mexico locust (Robinia neomexicana), on riparian plant and bird communities in northwestern Colorado, USA. By surveying plant and bird communities and examining nest success and productivity in riparian forest with and without locust, we evaluated the following ecological responses to invasion: (1) tree and shrub richness and density; (2) bird species richness, occupancy, and abundance; and (3) avian reproductive success. Our results demonstrate biotic homogenization of the plant community with increasing intensity of locust invasion, yet we found little evidence for negative effects on avian habitat use or reproductive success. Instead, locust invasion showed a positive effect on nest productivity, with significantly higher brood sizes and numbers of young fledged for nests in invaded habitats compared to those where locust was absent. Because climate change is already leading to shifts in species distribution patterns, we suggest that understanding the ecological consequences of plant invasions that occur within or near historic ranges will advance the science and practice of invasive species biology in a changing world. Our findings of mostly neutral to positive effects of locust suggest that near-range plant invasions may not always negatively impact community structure.