MULTI-TAXA FUNCTIONAL AND TAXONOMIC DIVERSITY IN UK PLANTATION FORESTS

It is increasingly recognised that plantations play a role in supporting biodiversity and delivering many of the ecosystem functions of natural woodland. However, there are still gaps in our understanding of how different plantation tree species and development stages influence associated forest biota, and the implications of this for resilience to environmental change. In this collaborative study between Edge Hill University and Forest Research, we explored diversity responses of four different taxonomic groups (vascular plants, mosses, spiders and carabid beetles) in UK forest plantations of Scots pine, Sitka spruce and oak. We conducted our study in chronosequences of multiple stand developmental stages. We took a novel approach by exploring not only forest habitat influences on the number and diversity of species present, but also on species ‘functional traits’ (i.e. attributes of species, such as dispersal ability, that indirectly influence fitness via impacts on reproduction, growth and/or survival), and, ‘functional diversity’ (i.e. diversity of functional traits within a system). Further, we explored taxonomic group responses over the long term by resampling stands first surveyed in the mid-1990s.

We found evidence that the youngest (pre-thicket) and oldest (old growth) developmental stages in the forest harvest cycle harbour the highest levels of taxonomic and functional diversity under fast-growing, shade-bearing tree species such as Sitka spruce, which exerts a strong environmental filtering effect. Comparatively, more consistent light levels across growth stages in Scots pine result in almost no significant diversity response. Functional and species diversity responses were not identical; e.g. moss and spider functional diversity changed significantly with stand age, while taxonomic diversity did not. We detected long-term declines in diversity in all plantation forest types over 20 years, but not for all taxonomic groups. Vascular plant and moss diversity were mostly negatively affected over time, while only the composition of carabid communities changed significantly in all forest types. All forest types harboured species of conservation concern, although they were greatest in oak, followed by Scots pine, then Sitka spruce.