The influence of stand structure on spider species and guild diversity in plantations of contrasting tree species

Abstract

Forests are understood to have a major role in supporting life through habitat provision but they also provide multiple ecosystem services such as timber, recreation, climate change mitigation and soil and water protection. Having recognised that the way we use our forests damages them and is not sustainable in the long-term, Sustainable Forest Management principles were formulated to guide foresters to manage more resilient forests.

An increasing proportion of the world’s forests are plantation (105 million hectares gained between 1990 and 2015) and there is a growing reliance on these rather than natural woodlands to deliver multiple ecosystem services across many countries. Plantations are increasingly recognised as having a potential role in supporting biodiversity. To understand how plantation forests can be used and managed sustainably in to the future requires a better understanding of the influence of changes in stand structure on biodiversity across different forest types.

Spiders play important functional roles in terrestrial ecosystems. As generalist predators, they help to maintain balance of food webs and control pest species but are also themselves a food source for other species. Despite this, our understanding of the impact of commercial plantation management on spider functional and taxonomic diversity in common commercial plantation types is limited.

This study determined ground-active spider assemblages in Sitka spruce and Scots pine plantation forests using a taxonomic and functional guild approach. The metrics were related to key drivers of change in forests, most notable stand structure across a clearfell forest harvesting cycle, and including long-term retention stands. 32 stands were located across the UK in clusters matched for site history, elevation and soil conditions. Spiders were sampled continuously from May to September in 2016 and 2017 using pitfall traps. Typically measured metrics of stand structure were recorded (canopy cover, stand density and diameter of trees).

Spider assemblages and functional guilds were affected by stand structure, with basal area a key parameter. Further, the impact of stand structure on spiders differed between tree species. Thresholds for structural parameters were determined, after which there were significant changes in assemblages. The results are discussed in the context of forest management and spider community resilience in commercial plantations.