Livestock grazing exclusion and microhabitat variation affect invertebrates and litter decomposition rates in woodland remnants

Abstract

Most of the remaining grassy woodland in south-eastern Australia exists as remnants on private land in agricultural landscapes. These have been subjected to various forms of disturbance including exotic plant invasion and livestock grazing. Little is known about the invertebrate communities in these remnants, which could contribute greatly to the diversity and function of these ecosystems. We need to know what invertebrates are present and how they respond to different types of land management, such as livestock grazing, in order to conserve them. We aimed to determine firstly if the invertebrate community was more diverse and abundant and leaf litter decomposition rates faster in woodlands with livestock excluded. Secondly, we asked how important microhabitat variation is for the invertebrate community and decomposition rates, and finally if grazing exclusion influences these microhabitat variables and alters the vegetation condition. We addressed these aims through the use of leaf litter decomposition bags and pitfall trapping near three microhabitats: beside logs, under trees and in open habitat, considering woodland remnants still grazed by livestock and remnants where livestock grazing had been excluded. A vegetation condition assessment was also performed at each site. Grazed woodlands were subject to either a strategic or set stocked grazing. Sites with grazing removed had a greater abundance of beetles and the Opportunist ant functional group, a faster rate of litter decomposition, greater native plant richness, greater length of logs and a better vegetation condition score. The Dominant Dolichoderinae ant functional group were the only insects trapped more frequently in currently grazed sites. Total invertebrate abundance, beetle abundance and richness, Anonychomyrma abundance and the quantity of leaf litter was greatest under trees. In comparison ants were in higher abundance and richness in the open areas. Leaf litter decomposition rates were fastest near logs. Beetles and Generalised Myrmicinae ants were more active near two of the microhabitats in rotationally grazed sites in comparison to the set stocked. Excluding livestock from woodlands has benefits for components of the invertebrate community, vegetation condition and the important process of litter decomposition. Strategic grazing which includes substantial periods of rest could play a role in balancing the production and conservation needs of privately owned woodlands. Woodland remnants have a range of invertebrates that are dependent on mature trees or logs, such that a variety of microhabitats needs to be retained within remnant native vegetation in agricultural landscapes to maintain a diverse and abundant invertebrate community.