Invertebrate communities in hollowing trees

Background. In standing trees, most decay occurs in the heartwood (heart-rot). The rotted hearts of trees release nutrients for tree growth and provide habitat for assemblages of saproxylic bacteria and fungi, invertebrates and vertebrates. Some of the invertebrate species (e.g., the rare violet click beetle) are highly specialized on rotted wood of specific tree and/or wood decay fungal species. In addition, many of these taxa typically are attracted by specific stimuli, often emanating from volatile organic compounds (VOCs) released during the decay process. Given the susceptibility of veteran trees and the often-irreversible nature of their loss, the specialist fauna associated with heart-rot habitats is often endangered. Despite heart-rot having first been investigated almost 200 years ago our knowledge of the invertebrates dependent on this habitat is very limited. Understanding the requirements of the fauna and what makes these habitats attractive, is essential to develop strategies for effective conservation of such micro-ecosystems.

Project Aims and Methods. This project aims to define how heart-rot decay characteristics, succession and landscape context govern the composition and structure of fungal-invertebrate assemblages, including insects of high conservation value (e.g. the IUCN Red Listed violet click beetle, Limoniscus violaceus). By quantifying the presence and relative frequency of organisms, trophic links may be inferred to construct a food-web. This information will help guide conservation at sites where a generation gap exists between veteran trees with heart-rot and un-decayed trees, which will not undergo heart-rot for some time. The study builds on an earlier PhD project investigating fungal community composition in heart-rot and the potential for inducing heart-rot to increase its presence as a rare habitat. Using a combination of traditional taxonomic and culturing approaches, and more recently applied molecular (e.g. next generation sequencing) and chemical (e.g. GCMS) techniques, the invertebrate communities associated with beech tree (Fagus sylvatica) heart-rot will be quantified. Specifically, the project sets out to determine:
(i) the composition, and abundance and structure (e.g. network architecture) of the heart-rot invertebrate assemblages;
(ii) whether these communities vary according to location and characteristics of individual trees; and
(iii) the dependency of rare invertebrate species and community structure upon particular fungal species underpinning the food web.