Search

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.

We investigated the relative role of manager traits and decisions for explaining the impact of riparian restoration. To do this, we used the difference in vegetation between post-restoration and controls for 243 pairs of sites to create a success index. We then determined how much variability in success could be explained by physical variables that directly impact vegetation (environment and weed removal) versus human variables (characteristics of the people who managed those sites and their management decisions). More than 60% of the variability in vegetation change could be explained, with human variables increasing adjusted R-square values of physical-only models by an average of 47%. Restoration “success” was positively associated with an increase in the number of collaborators, the number of information sources used, and the relative priority of plant-related goals. Worse outcomes were associated with an increase in the number of roles the manager held, monitoring frequency, and with higher manager education level. These results point to the indirect impacts of the human element, and specifically supports recommendations to include multiple partners and set specific goals. To our knowledge, this is the first time the importance of human characteristics as drivers of restoration outcomes has been quantified.

International audience; Bioengineering techniques have been encouraged over "hard" civil engineering such as riprap for recovering naturalness on stabilized riverbanks, but their effectiveness in reproducing the plant species diversity and vegetation succession present on non-stabilized (natural) riverbanks has rarely been assessed. Here, we compared alpha and beta diversity and successional trajectories of plant communities along the vertical profile of natural (40 sites), bioengineered (51) and riprap (33) riverbanks, in 55 streams of the second- to seventh-order in the province of Quebec (eastern Canada). Richness of total, hydrochorous and native species was higher on natural riverbanks than on those stabilized by riprap techniques along all riverbank elevations (upper, middle and lower parts of the riverbank). Bioengineered sites showed intermediate values. Natural sites contributed most to beta diversity on the upper bank, riprap sites on the middle bank. Temporal changes in species richness were observed only on the upper and middle banks, with an increase on riprap sites and a decrease on bioengineered sites. Beta diversity was mainly stable through time. Plant composition on bioengineered sites converged to that on natural sites for all bioengineering techniques at all bank levels, whereas for ripraps it did so only on the lower bank. For all bioengineering techniques, plant succession was driven by increasing native and hydrochorous species at all bank levels. Bioengineering is an effective alternative to riprap on stabilized riverbanks that leads to plant diversity and succession that most resemble those on natural riverbanks.

Questions: Studies in functional biogeography have mostly focused on unmanaged ecosystems, and neglected testing how management intensity affects community-level response of plant traits to bioclimatic gradients. We hypothesize that trait–climate relationships for arable weeds spontaneously establishing in croplands subject to intensive management should differ from the relationships characterizing less intensively managed grassland ecosystems. Location: France. Methods: We computed community-weighted means (CWM) and variances (CWV) of 954 and 5,619 cropland and grassland plant assemblages, respectively, for three fundamental leaf traits (specific leaf area, SLA; leaf dry matter content, LDMC; leaf nitrogen content, LNC). Based on growing season length accounting for both temperature and soil water limitations (GSLtw), we compared trait–climate relationships between herbicide-free croplands and grasslands, and between herbicide-free and herbicide-sprayed cropland assemblages. The contribution of beta-diversity to the trait–climate relationships was then evaluated using multiple regression on distance matrices. Results: Distinct trait–climate relationships characterized herbicide-free cropland and grassland plant assemblages. CWM of all traits showed weaker relations with GSLtw in cropland relative to grassland assemblages. CWV of LDMC and LNC responded more sharply in croplands. Furthermore, no herbicide effect on trait–climate relationships was detected within cropland assemblages. These results seem to be explained by a greater taxonomic beta-diversity along the GSLtw gradient for grasslands. Conclusions: Specific trait–environment relationships characterize croplands, underlining that management intensity greatly affects trait–climate relationships for plant assemblages. Deciphering the interplay between land use intensification and climate is critical to accurately forecast functional vegetation changes in response to global changes, and hence to foster actions enhancing ecosystem resilience.

International audience; *Questions Does urbanization promote biotic differentiation or homogenization of swamp plant communities? What is the contribution of natives and exotics to swamp response to urbanization?*Location Quebec City, Canada.*Methods Plant communities of 34 swamps located in low, moderately or highly urbanized landscapes were sampled, and species classified into three exclusive groups: native wetland, native upland and exotic plants. Urbanization's influence on the richness of each plant group was assessed using mixed models. Between-site compositional similarities were calculated to identify variations in beta diversity with urbanization level using tests for homogeneity in multivariate dispersion. Beta diversity was further partitioned into species replacement and richness difference for each plant group. Finally, the relationships of ten environmental variables representing soil water saturation and microtopography with plant assemblages were determined by redundancy analysis.*Results Although the richness of exotics increased with urbanization intensity, revealing increasing propagule pressure, it remained six to 27 times lower compared to the richness of natives, which remained stable with urbanization. On the other hand, beta diversity increased with urbanization, with higher dissimilarities in species composition between highly urbanized swamps than between low-urbanized ones. This pattern resulted from high species replacement among natives, while richness difference mainly contributed to exotic beta diversity. Changes in plant assemblages were mostly associated with bryophyte cover and soil drainage and red mottle size, suggesting that hydrological conditions likely acted as a strong driver of swamp plant community response to urbanization.*Conclusions Swamp plant communities experienced biotic differentiation with increasing urbanization. This differentiation pattern likely was linked to the unpredictable effect of urbanization on hydrological regimes, which promoted high native turnover while limiting exotic spread. Long-term monitoring is recommended to ensure that exotics do not outcompete natives through time. Designing sustainable cities requires a greater understanding of the multifaceted effect of urbanization on biodiversity.

Arable weeds are key organisms for biodiversity maintenance and ecosystem service provision in agroecosystems. Disentangling the drivers of weed diversity is critical to counteract the global decline of farmland biodiversity. Even if distinct scale-dependent processes were alternatively proposed, no general framework unifying the multi-scale drivers of weed dynamics has yet emerged. Here, we investigate the joint effects of field- and landscape-scale processes on weed assemblages in 444 arable fields. First, field margins sheltered greater weed diversity than field core, evidencing their role as biodiversity refugia. Second, community similarity between field core and margin decreased with the distance to margin, highlighting a major role of local dispersal. Third, weed diversity at field margins increased with organic field cover in the landscape, pointing out massive regional dispersal. Fourth, while both local and landscape dispersal explained up to 41% of field core weed diversity, crop type strongly modulated their strength, depicting an intense filtering effect by agricultural management. This study sheds new light on the complex multi-scale interactions shaping weed diversity, field margins playing a key role by strengthening regional dispersal and sustaining local dispersal. Land-sharing strategies improving habitat heterogeneity both locally and regionally should largely promote agroecosystem multifunctionality and sustainability.

International audience; Arable weeds are key organisms for biodiversity maintenance and ecosystem service provision in agroecosystems. Disentangling the drivers of weed diversity is critical to counteract the global decline of farmland biodiversity. Even if distinct scale-dependent processes were alternatively proposed, no general framework unifying the multi-scale drivers of weed dynamics has yet emerged. Here, we investigate the joint effects of field- and landscape-scale processes on weed assemblages in 444 arable fields. First, field margins sheltered greater weed diversity than field core, evidencing their role as biodiversity refugia. Second, community similarity between field core and margin decreased with the distance to margin, highlighting a major role of local dispersal. Third, weed diversity at field margins increased with organic field cover in the landscape, pointing out massive regional dispersal. Fourth, while both local and landscape dispersal explained up to 41% of field core weed diversity, crop type strongly modulated their strength, depicting an intense filtering effect by agricultural management. This study sheds new light on the complex multi-scale interactions shaping weed diversity, field margins playing a key role by strengthening regional dispersal and sustaining local dispersal. Land-sharing strategies improving habitat heterogeneity both locally and regionally should largely promote agroecosystem multifunctionality and sustainability.

The definition of &ldquo, arable weeds&rdquo, remains contentious. Although much attention has been devoted to specialized, segetal weeds, many taxa found in arable fields also commonly occur in other habitats. The extent to which adjacent habitats are favorable to the weed flora and act as potential sources of colonizers in arable fields remains unclear. In addition, weeds form assemblages with large spatiotemporal variability, so that many taxa in weed flora are rarely observed in plot-based surveys. We thus addressed the following questions: How often do weeds occur in other habitats than arable fields? How does including field edges extend the taxonomic and ecological diversity of weeds? How does the weed flora vary across surveys at different spatial and temporal scales? We built a comprehensive dataset of weed taxa in France by compiling weed flora, lists of specialized segetal weeds, and plot-based surveys in agricultural fields, with different spatial and temporal coverages. We informed life forms, biogeographical origins and conservation status of these weeds. We also defined a broader dataset of plants occupying open habitats in France and assessed habitat specialization of weeds and of other plant species absent from arable fields. Our results show that many arable weeds are frequently recorded in both arable fields and non-cultivated open habitats and are, on average, more generalist than species absent from arable fields. Surveys encompassing field edges included species also occurring in mesic grasslands and nitrophilous fringes, suggesting spill-over from surrounding habitats. A total of 71.5% of the French weed flora was not captured in plot-based surveys at regional and national scales, and many rare and declining taxa were of Mediterranean origin. This result underlines the importance of implementing conservation measures for specialist plant species that are particularly reliant on arable fields as a habitat, while also pointing out biotic homogenization of agricultural landscapes as a factor in the declining plant diversity of farmed landscapes. Our dataset provides a reference species pool for France, with associated ecological and biogeographical information.

International audience; Aim: The abundance–frequency relationship (AFR) is among the most-investigatedpatterns in biogeography, yet the relative contributions of niche-based processesrelated to ecological strategies, and of neutral processes related to spatial colonization–extinction dynamics, remains uncertain. Here, we tested the influences of ecologicalspecialization and functional traits on local abundance and regional frequency,to determine the contribution of niche-based processes.Location: France and the UK.Taxon: Vascular plants.Methods: We used two arable weed surveys covering 1,544 fields in Western Europe(France, UK), along with functional traits related to resource acquisition, resource requirements,flowering phenology and dispersal. We quantified specialization both toarable habitat and to individual crop types, and performed phylogenetic path analysesto test competing models accounting for direct and indirect relationships betweentraits, specialization, abundance and frequency. We performed the analysesfor all species in each country, as well as for a subset of the most abundant species.Results: Local abundance of weeds increased with their regional frequency, butthe relationship became negative or null when considering only the most abundantweeds. Specialization to arable habitat and to individual crop type either had a similaror opposite effect on regional frequency and local abundance explaining thesepositive and negative relationships, respectively. Regional frequency was not directlyexplained by any trait but indirectly by resource requirement traits conferring specializationto the arable habitat. Conversely, high local abundance was directly relatedto low seed mass, high SLA, early and short flowering.Main conclusions: Direct/indirect effects of functional traits on local abundance/regionalfrequency, respectively, supports a significant role of niche-based processes inAFR. Neutral spillover dynamics could further explain a direct linkage of abundanceand frequency. Similar causal paths and consistent influences of traits on specializationand abundance in the two studied regions suggest genericity of these findings.

Pool margins and wet depressions (hollows) contribute considerably to peatland biodiversity by sheltering specific plant assemblages. In peatlands restored after peat extraction, the typical communities associated with pools generally fail to re-establish if only the moss layer transfer technique is applied, a common approach on flat bare peatlands. To adapt peatland ecological restoration methods for recolonizing shallow wet fen habitats, this study investigates the response of plant communities re-establishing in wet depressions subjected to four revegetation strategies. In a restored fen (southeastern Quebec, Canada), 48 depressions were dug out and revegetated with 1) mosses, 2) Carex species, 3) Scirpus validus, or 4) through spontaneous colonization (control treatment without implanted species). After four growing seasons, plant community structure and composition were surveyed in and outside the revegetated area respectively to test whether reintroduced communities had a propensity to extend beyond the central wet depression. Restoration strategies strongly impacted plant communities. Moss-revegetated wet depressions had higher moss and vascular fen-specialist species richness and distinct species assemblages relative to other treatments. Carex treatment increased only vascular cover compared to control, while Scirpus validus treatment did not differ from control. The positive impact of moss transfer was local and limited to core revegetated areas, as transferred plant material did not colonize any further. Our results suggest that transferring moss in created wet depressions is an effective strategy to foster the recolonization of diverse and distinct plant assemblages, and thereby restore local fen biodiversity hotspots.

Spatial modeling has proven to be useful in understanding the drivers of plant populations in the field of ecology, but has yet to be applied to understanding variation in biocontrol impact. In this study, we employ multi-scale analysis (Moran’s Eigenvector Maps) to better understand the variation in tree canopy exposed to defoliation by a biocontrol beetle (Diorhabda spp.). The control of the exotic tree Tamarix in riparian areas has long been a priority for land managers and ecologists in the American southwest. Diorhabda spp. was introduced as a bio-control agent beginning in 2001 and has since become an inseparable part of Tamarix-dominated river systems in the southwest. Between 2013 and 2016 tamarisk dieback was assessed at 79 sites across Grand County, Utah, arguably the epicenter of Diorhabda impact in the U.S. Canopy cover of Tamarix was between 73 and 81% at these sites, with the percent that was live cover fluctuating by year with a minimum of 42%. Using a traditional general linear model, we found that readily and commonly measured environmental factors could explain only up to 26% of the variation in Tamarix live canopy each year. The number of defoliations was correlated with an increase rather than a decrease in percent live canopy, suggesting compensatory growth. Spatial structure alone explained 22–40% of variation. We found fine scale spatial structure at less than 10 km and broad scale spatial structure from 10 to 30 km. Combining both traditional and novel spatial statistical methods we increased that percentage to 43–63%, depending on year. These results suggest that scientists and land managers must look beyond commonly measured environmental variables to explain non-random biocontrol impact in this system. In particular, this study points to the potential for biotic interactions and variation in flood cycles for further exploration of the identified spatial structure.

Most studies assessing vegetation response following control of invasive Tamarix trees along southwestern U.S. rivers have been small in scale (e.g., river reach), or at a regional scale but with poor spatial-temporal replication, and most have not included testing the effects of a now widely used biological control. We monitored plant composition following Tamarix control along hydrologic, soil, and climatic gradients in 244 treated and 172 reference sites across six U.S. states. This represents the largest comprehensive assessment to date on the vegetation response to the four most common Tamarix control treatments. Biocontrol by a defoliating beetle (treatment 1) reduced the abundance of Tamarix less than active removal by mechanically using hand and chain-saws (2), heavy machinery (3) or burning (4). Tamarix abundance also decreased with lower temperatures, higher precipitation, and follow-up treatments for Tamarix resprouting. Native cover generally increased over time in active Tamarix removal sites, however, the increases observed were small and was not consistently increased by active revegetation. Overall, native cover was correlated to permanent stream flow, lower grazing pressure, lower soil salinity and temperatures, and higher precipitation. Species diversity also increased where Tamarix was removed. However, Tamarix treatments, especially those generating the highest disturbance (burning and heavy machinery), also often promoted secondary invasions of exotic forbs. The abundance of hydrophytic species was much lower in treated than in reference sites, suggesting that management of southwestern U.S. rivers has focused too much on weed control, overlooking restoration of fluvial processes that provide habitat for hydrophytic and floodplain vegetation. These results can help inform future management of Tamarix-infested rivers to restore hydrogeomorphic processes, increase native biodiversity and reduce abundance of noxious species.

Questions Plant community resilience largely depends on the secondary succession induced by species re-colonization from seed banks. Soil seed bank resilience is, however, poorly understood, especially in regularly disturbed habitats like riparian zones. Two questions were asked: what are the changes in species diversity experienced by riparian soil seed banks along successional trajectories, and to what extent do riparian soil seed banks promote vegetation resilience during secondary succession? Location Southeastern Quebec, Canada. Methods Soils were collected along five rivers in field edges and riverbanks of post-agricultural riparian zones with three contrasting successional stages (unplanted – planted with trees 15-17 years prior to sampling – natural riparian forests), and their seed bank composition determined with the seedling emergence method. Species richness in seed banks was assessed along successional trajectories for distinct ecological groups, using linear mixed models. The compositions of soil seed banks and standing vegetation (from botanical surveys) were compared based on NMDS and Indicator Species Analysis. Results Seed bank species richness decreased along successional trajectories. Tree-planted riparian zones were generally closer to unplanted riparian zones than to natural riparian forests, the latter being more species-rich for natives, trees, shrubs and zoochores, and species-poor for exotics, forbs and stress-tolerators. Likewise, seed bank species composition of unplanted and tree-planted riparian zones was similar but differed from those of natural riparian forests. Conversely, standing vegetation of tree-planted riparian zones was intermediate between early- and late-successional stages, at least at field edges. For the three successional stages, seed bank composition clearly differed from standing vegetation. Conclusions The high resilience of riparian plant communities appeared poorly related to the dynamics of their soil seed banks. This species shift between seed banks and standing vegetation during secondary succession is likely due to periodic flooding leading to the regular turnover of seeds. The resilience of riparian communities might thus be more influenced by spatial dispersal along rivers and across landscapes than by in situ temporal dispersal in soils. This article is protected by copyright. All rights reserved.

Although riparian zones provide numerous ecological services, they have been widely degraded by agricultural intensification. To recover water quality and restore other critical services, tree planting has been implemented in agricultural riparian buffer zones worldwide. However, intensive agricultural practices adjacent to tree plantations are likely to impede their establishment. In this study, we assessed the survival and size of trees planted in riparian buffer zones along a gradient of agriculture intensification. We studied 68 riparian buffer zones in two agricultural watersheds of southeastern Quebec (Canada) where trees had been planted 3⿿17 years prior to sampling. Tree survival and size (height, diameter and crown width) were measured and related to agricultural intensification, quantified as the frequency of annual crops in the agricultural field adjacent to riparian zones during the seven years prior to sampling. Tree survival decreased by 25% with increasing frequency of annual crops (P

[Departement_IRSTEA]Territoires [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmesChapter 1; International audience; The Green Revolution and the introduction of chemical fertilizers, synthetic pesticides and high yield crops had enabled to increase food production in the mid and late 20th. The benefits of this agricultural intensification have however reached their limits since yields are no longer increasing for many crops, negative externalities on the environment and human health are now recognized and economic inequality between farmers have increased. Agroecology has been proposed to secure food supply with fewer or lower negative environmental and social impacts than intensive agriculture. Agroecology principles are based on the recognition that biodiversity in agroecosystems can provide more than only food, fibre and timber. Hence, biodiversity and its associated functions, such as pollination, pest control, and mechanisms that maintain or improve soil fertility, may improve production efficiency and sustainability of agroecosystems. Although appealing, promoting ecological-based agricultural production is not straightforward since agroecosystems are socio-ecosystems with complex interactions between the ecological and social systems that act at different spatial and temporal scales. To be operational, agroecology thus requires understanding the relationships between biodiversity, functions and management, as well as to take into account the links between agriculture, ecology and the society. Here we review current knowledge on (i) the effect of landscape context on biodiversity and ecosystem functions and (ii) trophic and non-trophic interactions in ecological networks in agroecosystems. In particular, many insights have been made these two previous decades on (i) the interacting effects of management and landscape characteristics on biodiversity, (ii) the crucial role of plant diversity in delivering multiple services and (iii) the variety of ecological belowground mechanisms determining soil fertility in interaction with aboveground processes. However, we also pinpointed the absence of consensus on the effects of landscape heterogeneity on biodiversity and the need for a better mechanistic understanding of the effects of landscape and agricultural variables on farmland food webs and related services. We end by proposing new research avenues to fill knowledge gaps and implement agroecological principles within operational management strategies.

Riparian Salicaceae are prolific producers of short-lived seeds that require very restrictive hydro-geomorphic conditions for establishment. It is generally assumed that if floods are able to create nursery sites timed with seed dispersal, recruitment will occur. Other spatial and temporal seed dispersal patterns besides the dispersal period have historically received little attention. However, seed dispersal patterns can be highly variable between regions, species and over the years. In this paper, we report the seed dispersal patterns of three dominant riparian Salicaceae trees in Europe: Populus alba, P. nigra and Salix alba to suggest possible trade-offs between seed dispersal patterns, germinability, longevity and establishment. Seed rain of the three species was monitored in 33 glue-coated traps for three months yearly from 2006 to 2008 in an 8-km stretch of the Middle Ebro River (N Spain), which has a pluvio-nival regime. P. alba dispersed seeds earlier during a shorter time period and with a fewer number of seed release pulses compared with P. nigra, and especially with S. alba. With overlapping seed dispersal periods, the two latter species occupy similar landform units but rarely compete with P. alba, usually at higher elevations, as shown in a previous study in the same study area. The three species had very high germinability immediately after release (>90%), but longevity in S. alba was eight times shorter than that of its two Populus counterparts. We suggest that S. alba has compensated its lower seed quality with a more spaced seed release in several pulses of similar magnitude. With similar seed dispersal patterns and germinability but a higher longevity, P. nigra had a much higher density of individuals than S. alba in the recruitment zones of the study area. We hope that our results may inform river managers about how to optimize river flows to promote sexual regeneration of these species. Copyright © 2015 John Wiley & Sons, Ltd.

The disruption of hydrological connectivity by human activities such as flood regulation or land-use changes strongly impacts riparian plant communities. However, landscape-scale processes have generally been neglected in riparian restoration projects as opposed to local conditions, even though such processes might largely influence community recovery. We surveyed plant composition of field edges and riverbanks in 51 riparian zones restored by tree planting (565 1-m2 plots) within two agricultural watersheds in southeastern Quebec, Canada. Once the effects of environmental variables (hydrology, soil, agriculture, landscape, restoration) were partialled out, three models of spatial autocorrelation based on Moran's eigenvector maps and asymmetric eigenvector maps were compared to quantify the pathways and direction of the spatial processes structuring riparian communities. The ecological mechanisms underlying predominant spatial processes were then assessed by regression trees linking species response to spatial gradients to seed and morphological traits. The structure of riparian communities was predominantly related to unidirectional spatial gradients from upstream to downstream along watercourses, which contributed more to species composition than bidirectional gradients along watercourses or overland. Plant traits selected by regression trees explained 22% of species response to unidirectional upstream-downstream gradients in field edges and 24% in riverbanks, and predominantly corresponded to seed traits rather than morphological traits of the adult plants. Our study showed that even in agriculturally open landscapes, water flow remains a major force structuring spatially riparian plant communities by filtering species according to their seed traits, thereby suggesting long-distance dispersal as a predominant process. Preserving hydrological connectivity at the watershed-scale and restoring riparian plant communities from upstream to downstream should be encouraged to improve the ecological integrity of rivers running through agricultural landscapes.