Spatial patterns in defoliation and the expression of clonal traits in grazed meadows

Abstract

Clonal plant species dominate meadow vegetation where grazing can generate spatial heterogeneity at different scales and can select for species that express particular sets of clonal traits. This in situ study aimed to characterize fine-grained spatial patterns of defoliation (<1 m) induced by contrasting cattle grazing intensities and to link these spatial patterns with the abundance of species-specific clonal traits. Using correlogams and synthetic spatio-temporal indices, the heterogeneity of vegetation height and leaf damage was monitored along a cattle grazing gradient. Species were identified and their clonal traits retrieved from the database CLO-PLA3. Under moderate grazing, fine-grained spatial patterns of defoliation were not stable over time. Defoliation was heterogeneous during the first months of the grazing season and then became homogeneous. Intensive grazing generated homogeneous defoliation, regardless of the date. In the study meadow, grazing gave rise to communities containing a greater abundance of annual species. However, clonal traits assumed to enable clonal fragments to benefit from heterogeneity do not seem advantageous. Increasing grazing intensity promoted species with clonal traits expected to minimize costs associated with clonality (aboveground clonal growth forms, short-distance lateral spread, and (or) short-lived connections). Ungrazed conditions favoured species with clonal traits associated with a high competitive ability.