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Several governmental programs have been established throughout Canada to foster agriculture sustainability. As a best management practice, cover crops (CCs) limit soil erosion and prevent nutrient losses in agroecosystems. Yet, the variable effects of CCs on cash crop productivity previously reported may limit their large-scale adoption by farmers. To address this variability, we conducted an unweighted meta-analysis including 2274 observations from 86 field studies conducted under humid temperate climate to evaluate yield response to CCs for three annual cash crops. Overall, CCs increased corn and small grain cereal yields by 13% and 22% respectively, but did not affect soybean yield. Legume CCs alone or mixed with grasses provided the highest small grain cereal and corn yield increases compared with non-legume broadleaf and grass CCs. CC benefits increased with nitrogen (N) content in CC aboveground biomass but decreased when N fertilizer inputs applied to corn exceeded 60 kg N ha−1. Greater precipitation and N fertilizer inputs reduced the negative effect of grass CCs on corn yield, while benefits of legume CCs were highly resilient to precipitation variations. CC benefits on corn yield increased through time and at low soil organic matter content, especially at low N fertilizer inputs. These results evidence the complex interplay between cash crop productivity, CC management, and environmental factors — related to N inputs from CCs, changes in soil properties (e.g., increased organic matter, improved soil structure or microbial activity), or potential competition for water under drier conditions — which provide new perspectives to promote CC inclusion in cropping systems.

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.

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.

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.

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

What leads to classically recognized patterns of biodiversity remains an open and contested question. It remains unknown if observed patterns are generated by biological or non-biological mechanisms, or if we should expect the patterns to emerge in non-biological systems. Here, we employ analogies between GNU/Linux operating systems (distros), a non-biological system, and biodiversity, and we look for a number of well-established ecological and evolutionary patterns in the Linux universe. We demonstrate that patterns of the Linux universe generally match macroecological patterns. Particularly, Linux distro commonness and rarity follow a skewed distribution with a clear excess of rare distros, we observed a power law mean-variance scaling of temporal fluctuation, but there is only a weak relationship between niche breadth (number of software packages) and commonness. The diversity in the Linux universe also follows general macroevolutionary patterns: the number of phylogenetic lineages increases linearly through time, with clear per-species diversification and extinction slowdowns, something that has been indirectly estimated, but not directly observed in biology. Moreover, the composition of functional traits (software packages) exhibits significant phylogenetic signal. The emergence of macroecological patterns across Linux suggests that the patterns are produced independently of system identity, which points to the possibility of non-biological drivers of fundamental biodiversity patterns. At the same time, our study provides a step towards using Linux as a model system for exploring macroecological and macroevolutionary patterns.

a b s t r a c t Invasion of Typha latifolia L. into man-made pools in restored North American peatlands may represent a serious barrier to the establishment of a plant community typical of natural pool edges. As no classical method of population management appears applicable in the context of peatlands, our aim was to deter- mine the ability of three environmental factors to inhibit T. latifolia germination, namely peat type, shade level and moss cover. A split-plot experiment conducted in a growth chamber investigated the effects of three substrates (fibric peat, mesic peat and filter paper) and six shade levels (including total obscurity) on germination rates of T. latifolia. In a second, greenhouse experiment, the effect of three increments of moss cover (null, fragmented and full) growing on two peat types (fibric and mesic) was examined for six corresponding seedbeds. Our results show that peat type was the major factor affecting germination, as almost none occurred on fibric peat while germination rates reached 84% on mesic peat. However, germination on mesic peat decreased with increasing moss cover: the germination rate dropped from 36 ± 3% on bare peat to 1 ± 0% in full moss carpets. Germination of T. latifolia was initiated by very low light levels (as low as 6%) but was inhibited by total obscurity. The low pH of fibric peat as well as the modification of environmental factors (e.g. light or substrate access) by moss carpets appear to be factors explaining the results. Establishing a dense moss cover and digging pools to a depth that prevents the exposure of peat with a pH favorable to seed germination (above 4) might be efficient methods to reduce Typha latifolia invasions in restored peatland pools.

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.