Vegetation dynamics in Cantabrian heathlands associated with improved pasture areas under single or mixed grazing by sheep and goats

Abstract

Vegetation dynamics in partially improved heather-gorse shrublands were studied in a 3-year field experiment under single or mixed grazing of sheep and goats. The experimental plots comprised untreated heathland, mechanically cleared heathland and converted heathland to grassland (perennial ryegrass-white clover improved pasture, covering 33–50% of the total plot area). In the heathland and mechanically cleared areas, the accumulation of shrubs in terms of cover, height and phytomass was more controlled by goats than by sheep, with intermediate values for mixed treatments. The differences were mainly restricted to the gorse ( Ulex gallii), while the type of flock did not significantly affect heather species ( Ericaceae). Herbaceous species, chiefly grasses, increased more under goat than under sheep or mixed grazing. In the absence of grazing, the amount of phytomass accounted for 22 834 kg DM/ha in the heathland areas, with 73% heaths, compared to 11 654, 6764 and 8994 kg DM/ha under sheep, goat and mixed grazing, respectively. In the cleared areas the accumulation of phytomass without grazing reached 18 508 kg/DM ha, with 46% gorse, compared to 11 696, 6530 and 6902 kg DM/ha under sheep, goat and mixed grazing respectively. In the improved pasture areas, the cover and height of the flowerstems of perennial ryegrass ( Lolium perenne) were significantly lower under goat than under sheep grazing. After senescence, the rejected stems lead to increased percentages of dead matter in the pastures grazed only by sheep. White clover ( Trifolium repens) increased more during the first grazing season under goat than under sheep grazing. In the subsequent years, it increased in all treatments without significant differences. As consequence of the different sward composition, the nutritive quality of available pasture was higher under goat than under mixed and sheep grazing. Goats reduce the accumulation of woody phytomass in the heather-gorse shrublands, and maintain a better forage quality in the converted shrubland to grassland, thus enhancing the animal performance.