Characterising soil microbial communities in thinned and unthinned eucalyptus forest in southwestern Australia

Climate change stress in forested ecosystems globally has led to die-off events, and management actions are needed to help mitigate these pressures. Forest thinning has been proposed to reduce competition for moisture between trees, however, the effects of forest thinning on lesser-studied organisms, such as soil microbial communities, need quantification. Soil microbial communities are essential for processes such as nutrient cycling and can be used as indicators of below-ground health and as an overall proxy for biodiversity. This study examined soil microbial communities, and site and soil characteristics, directly at the base of trees and in inter-tree spaces in a paired thinned, and unthinned forest stand in the Northern Jarrah ( Eucalyptus marginata , Donn ex Sm) Forest, southwestern Australia, two years post-thinning. We found that the sampling location was more important to the soil microbial community than the thinning operation. We observed only subtle shifts in the relative abundances of bacterial and fungal families and functional groups, and no differences in richness and diversity indices between the thinned and unthinned plots. By examining short-term effects of forest thinning on the soil microbiome, this study contributes to our understanding of how below-ground biodiversity responds to disturbance, and also to a growing awareness that below-ground biodiversity should be included in impact assessments. It is crucial to understand soil microbial responses to forest management practices, because techniques such as thinning will be increasingly used in the future. • We investigated the short-term responses of soil microbial communities to forest thinning. • Soil samples were collected from thinned and unthinned areas, beneath trees and inter-tree spaces. • Sampling location influenced microbial communities more strongly than thinning. • Thinning treatment induced only subtle differences in diversity and functional groups. • Higher fungal diversity and bacterial richness and diversity in intertree samples.