Carabid communities on heather moorlands in northeast Scotland: The consequences of grazing pressure for community diversity

Abstract

This study investigates the effect of grazing on the structural development of Calluna and the composition of ground beetle (Coleoptera : Carabidae) communities on heather moorland in northeast Scotland. Carabid distribution across all sites was strongly influenced by soil organic content and Calluna height. These two variables were associated with particular species assemblages, while a group of species characteristic of open, sparsely vegetated sites was not consistently associated with any one environmental variable. On the ungrazed sites, the distribution of species was influenced by site wetness and Calluna development stage; Calluna stands on these sites differed significantly in height and in the proportionate weight of current year's growth. Heavy grazing levels impacted significantly on the biomass, height and shoot structure of Calluna and resulted in a significant change in the composition of the carabid community. Specifically, carabids associated with shady, vegetated ground were less abundant on the most heavily grazed sites, while species associated with open ground increased in number. Species characteristic of Calluna-dominated moor were particularly affected and carabid species richness was much reduced on the most heavily grazed sites.