Moths respond to key habitat structures in conifer plantations managed as irregular high forest

Conifer plantations need to deliver greater multi-functionality beyond the production of timber. This includes the support of biodiversity and associated ecosystem functioning. Forest managers are increasingly adopting novel, more sustainable forest management techniques such as irregular silviculture, a type of continuous cover forestry, to manage plantations, in response to climate change. This may confer benefits to important elements of woodland biodiversity such as moths, by creating plantations that have diverse vertical structure and a permanent canopy (called irregular high forest). In this study at two estates in south-west Britain we specifically tested whether moth species richness and abundance (at the guild and overall level) were associated with (1) surrounding land cover types and (2) habitat structures within stands undergoing transformation using irregular silviculture. A total of 268 species of 11,582 individuals were recorded. Moths responded to all four landscape cover types, negatively to arable and conifer woodland, positively for broadleaf woodland, and both positively and negatively for improved grassland. Moth richness and abundance had a positive association with basal area (albeit below standard even aged stocking rates with most plots around 40–45 m²ha) and a weak positive association with higher vertical structural complexity (indicated by a more developed understorey and sub-canopy layers). Moth abundance had a moderate positive association with broadleaf canopy where we recommend plantations should have at least 10–15 % broadleaf canopy cover. Moth richness and abundance were negatively associated to mean tree diameter and canopy openness. Many of these features are more prevalent in stands further progressed towards irregular high forest. We show how moth communities can be maintained via more sustainable forestry management techniques that increase overall habitat and structural complexity.