Effects of stocking density and breed of goats on vegetation and grasshopper occurrence in heathlands

Abstract

Adult grasshopper species richness and abundance were determined using sweep-net samplings during a 3-year study, in an incomplete design experiment based on the management of two goat breeds (Cashmere and Celtiberic) and two stocking densities (high and low) in the case of Cashmere breed. Shrub cover and plant canopy height decreased with increasing grazing pressure, leading to higher herbaceous plant cover compared to the low stocking density. Cashmere and Celtiberic goats induced different vegetation dynamics, with the latter causing a higher reduction of shrub cover and a higher increase of dead matter and herbaceous plant cover than Cashmere grazing. A significant grasshopper response to the vegetation alterations induced by grazing at local-scale was observed. The higher stocking densities increased total grasshopper density, but this was attained almost exclusively by one species, Stenobothrus stigmaticus. The other grasshopper species seemed to be favoured by the lower grazing intensity. Shrub and dead matter cover, total plant biomass and species richness were the most important plant variables explaining the responses of grasshoppers to the different grazing managements. The management of different grazing pressures could be recommended to diversify the ecological characteristics and thus the resources for grasshoppers in heathlands.