IDENTIFYING FUNCTIONAL-GROUPS FOR RESPONSE TO DISTURBANCE IN AN ABANDONED PASTURE

In an abandoned pasture in Brittany, we compared artificial small-scal e disturbances to natural disturbances by wild boar and undisturbed ve getation. We developed a multivariate statistical approach which analy ses how species biological attributes explain the response of communit y composition to disturbances. This technique. which reconciles the in ductive and deductive approaches for functional classifications, ident ifies groups of species with similar responses to disturbance and char acterizes their biological profiles. After 5 months of recolonization, artificial disturbances had a greater species richness than undisturb ed vegetation as a result of recruitment of new species without the ex clusion of pre-existing matrix species. Species morphology, described by canopy structure, canopy height and lateral spread, explained a lar ge part (16 %) of community response to disturbance. Regeneration stra tegies, described by life history, seed mass, dispersal agent, dormanc y and the existence of vegetative multiplication, explained a smaller part of community response to disturbance (8 %). Artificial disturbanc es were characterized by therophyte and compact rosettes with moderate ly dormant seeds, including a number of Asteraceae and other early suc cessional species. Natural disturbances were colonized by leafy guerri lla species without seed dormancy. Few species were tightly related to undisturbed vegetation and were essentially grasses with a phalanx ro sette morphology. The functional classification obtained is consistent with the classification of the community into fugitives, regenerators and persistors. These groups are structured according to Grubb's mode l for temperate grasslands, with regenerators and persistors in the ma trix and fugitives taking advantage of Zaps open by small-scale distur bances. The conjunction of functional diversity and species diversity within functional groups is the key to resilience to disturbance, an i mportant ecosystem function. (C) Elsevier, Paris.