Seedling recruitment in mountain grassland restoration: Effects of soil preparation and grazing

Abstract

Abstract Questions Seedling recruitment is a key step in any seed‐based ecological restoration project. There is a controversial discussion (a) whether soil preparation is required to reduce competition of pre‐existing vegetation, or whether vegetation cover facilitate seedling recruitment, and (b) whether grazing should be excluded in initial stages of grassland restoration to protect seedlings, because grazing exclusion may also favour competitive ruderal species. We set up a combined soil preparation and grazing experiment to evaluate the effect of both factors on seedling recruitment of seeds transferred from a species‐rich donor site. Location Upper Durance valley, Hautes‐Alpes, France. Methods The experiment was set up using a full factorial split‐plot design with five replicate sites. The treatments included soil preparation (harrowed or not) and grazing (excluded or not). Seeds were transferred using plant material brushed in a non‐degraded reference grassland. The individuals of all occurring species were counted on the restoration sites, and the survival and reproduction of two focal species, Bromopsis erecta and Rhinanthus alectorolophus, were recorded for three months. Results Soil preparation by harrowing reduced the density of spontaneously emerging species and increased the seedling density of species transferred from the donor site. Grazing had only a weak negative effect on the recruitment of transferred species. The main effect of both treatments on seedling survival was not significant, but a significant interaction indicated that the grazing effect depended on soil preparation, with a negative effect of grazing only in non‐harrowed plots. Conclusions The reduction of competition by soil preparation before seed addition of brush material had a positive effect on the seedling recruitment of transferred species and can thus clearly be recommended in our study system. The weak negative effect of grazing may not always justify fencing costs.