Early dynamics of natural revegetation on roadcuts of the Salamanca province (CW Spain)

In order to reconcile conventional and emergent goals in restoration ecology, the knowledge of community assembly during succession at roadsides is crucial. With a chronosequence design, our study assesses the pathway and speed of vegetation succession on roadcuts under different specific site conditions, relating environmental factors to species cover by means of a combination of multivariate analyses and Huisman-Olff-Fresco (HOF) modeling. We want to ascertain to what extent environmental factors control primary colonization, establishment and early dynamics of vegetation on dry Mediterranean roadcuts. We found that changes in floristic composition during natural succession on roadcuts are mostly determined by the species-pool effect at different scales (landscape, regional, and local); particular site conditions of roadcuts (slope length, steepness) are also influential factors at a local scale. We also found a shift in the dispersal mode of plant species, from anemochory to zoochory, during succession on tertiary sediments and slates, and a tendency for life-form replacement, from pterophytes to hemicriptophytes, during succession on tertiary sediments. Competitive species are primarily circumscribed to tertiary sediments where succession is not so limited by environmental carrying capacity. Natural colonization is less active on granites, and hence succession is slower. Our results indicate that, in a relatively short time, vegetation communities spontaneously installed under roadcut's environmental harshness are rich in species whether an adjacent seed source is present in remnant patches of natural vegetation. In particular, surrounding woody vegetation favors zoochory dispersion and the early arrival of late-successional species.