Plant ecological traits highlight the effects of landscape on riparian plant communities along an urban–rural gradient

• Published in: Ecological indicators 2016-02, Vol.61, p.568-576
• Main Authors: Schwoertzig, Eugénie, Poulin, Nicolas, Hardion, Laurent, Trémolières, Michèle
• Format: Article
• Language: English
• Subjects: Corridor; Life Sciences; Mixed effects models; Plant ecological groups; Riparian habitat; Urban biodiversity; Urban land use; Vegetal Biology
• ISSN: 1470-160X; 1872-7034
• DOI: 10.1016/j.ecolind.2015.10.008

•Traditional biodiversity indices are not enough to explain riparian plant distribution.•Community-level traits assess ecological continuity along a gradient of urbanization.•CWMi and Ri metrics complement one another to explain urban plant distribution.•Ecological types are mostly related to the features of the corridor.•Appearance of novel species is related to the surrounding matrix. Urban landscapes are characterized by an urban matrix often unfavorable for biodiversity, interspersed with remnant corridors such as riparian areas. Those are increasingly threatened by urban expansion and land use change worldwide. We investigated the effect of the two components, matrix versus corridor, by comparing the riparian plant diversity and the community-level ecological traits along an urbanization gradient. Species distribution was surveyed at a local-scale along an urban riparian corridor in Strasbourg, eastern France. Ninety plots were sampled along an urbanization gradient. Several plant metrics were measured using both plant richness (R) and mean ecological trait values of species weighted by their abundance (CWM). The surroundings of each plot were first described by selecting representative variables of matrix and corridor. Secondly, the distribution of plant species according to a given i ecological trait was analyzed in relation with different levels of urbanization. Using mixed effects models, we verified whether matrix or corridor variables best explain the distribution of traits. Three levels of urbanization were detected, termed urban, suburban and peri-urban, based on landscape composition. Neither the peri-urban nor the suburban level affected plant metrics. At the urban level, and whatever indicator value was considered, the CWMi metrics clearly decreased, whereas species richness Ri increased. The upstream distance to the nearest natural area and tree cover were the most influential variables on CWMi metrics, whereas Ri metrics were mainly driven by built component and landscape heterogeneity. Matrix variables were more important in explaining Ri metrics while corridor features affected CWMi metrics. These results highlight the preponderance of the corridor effect on plant ecological types and the importance of the matrix on the selection and/or the implantation of novel species. Thus, the urbanization gradient may operate simultaneously on the abundance of local species and impose the recruitment of new co-existing species. This study suggests