Using biological traits to assess how urbanization filters plant species of small woodlands

Question: Which biological traits (persistence, regeneration, dispersion traits and resource requirements) may explain the distribution of woodland flora along an urban-rural gradient? Location: The study was carried out in three medium-sized conurbations of north-western France: Angers, Nantes and Rennes. Methods: We sampled the vegetation of 36 small woodlands of about 1.5 ha composed of nonplanted vegetation along an urban-rural gradient. We characterized the position of woodlands along the urban-rural gradient by examining adjacent land cover. By using an ordination analysis (RLQ), we analysed which traits out of -23 tested were related to the contrasted distribution of species along the urban-rural gradient. Results: Species that are more likely to be found in urban woodlands than rural woodlands have different persistence traits (higher specific leaf area , more often rosette or semi-rosette form, less underground vegetative multiplication), resource requirements (affinity for base-rich and fertile soils) and regeneration traits (short life-span). Dispersion traits were not related to the distribution of species along the urban-rural gradient. Conclusions: Our approach identifies traits that can help to determine the vulnerability of forest species as a result of the environmental changes that follow urbanization. Limiting the influence of the urban environment on habitat quality (particularly disturbance and soil enrichment) is likely to be of major importance in maintaining the plant biodiversity in woodlands.