Summary 1.Trait-based approaches applied to community ecology have led to a considerable advance in understanding the effect of environmental filters on species assembly. Although plant traits are known to vary both between and within species, little is known about the role of intraspecific trait variability in the non-random assembly mechanisms controlling the coexistence of species, including habitat filtering and niche differentiation. 2. We investigate the role of intraspecific variability in three key functional traits -specific leaf area (SLA), leaf dry matter content (LDMC) and height -in structuring grassland communities distributed along a flooding gradient. We quantified the contribution of intraspecific variability relative to interspecific differences in the trait-gradient relationship, and we used a null model approach to detect patterns of habitat filtering and niche differentiation, with and without intraspecific variability. 3. Community mean SLA and height varied significantly along the flooding gradient and intraspecific variability accounted for 44% and 32%, respectively, of these trait-gradient relationships. LDMC did not vary along the gradient, with and without accounting for intraspecific variability. Our null model approach revealed significant patterns of habitat filtering and niche differentiation for SLA and height, but not for LDMC. More strikingly, considering intraspecific trait variability greatly increased the detection of habitat filtering and was necessary to detect niche differentiation processes. 4. Synthesis. Our study provides evidence for a strong role of intraspecific trait variability in community assembly. Our findings suggest that intraspecific trait variability promotes species coexistence, by enabling species to pass through both abiotic and biotic filters. We argue that community ecology would benefit from more attention to intraspecific variability.

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In France the alteration of species‐rich grasslands is due mainly to agriculture and civil engineering projects (roadways, dams, ski resorts, etc.). The restoration of such ecosystems has been tested in many regions and after many sorts of degradation. According to the level of initial degradation, different responses can be envisioned. Some variations are presented of a general model of restoration and rehabilitation: (1) rejuvenation of fallow land by grazing with rustic animal breeds in wetlands or chalk grasslands in south and northwestern France, (2) restoration by recovery of extensive agricultural management in intensive agricultural areas such as the Rhône or Meuse Valleys, and (3) rehabilitation by appropriate ecological engineering carried out in grasslands degraded by intensification, ski‐track, or civil engineering installations. Despite some positive results, these undertakings have not always had the expected effects and therefore should not provide alibis for the destruction of natural grasslands. In general, the success of such undertakings depends on the maintenance in the surrounding areas of protected seed source reservoirs and on the persistence of a diversified landscape pattern permitting connectivity between these seed sources and the restoration or rehabilitation sites.

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The paper presents a new index for assessing water trophy and organic pollution. It is based on only true aquatic macrophytes -being calculated on species score, coefficient of ecological amplitude and degree of cover. The method was tested in an acidic lowland river and an alkaline mountain river, and is shown to be validated by bio-indication scales based on macrophyte communities. The practical interest is discussed regarding the Water Framework Directive.

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