The term "coarse woody debris" (CWD) is used to denote the input of fallen trees and other woody matter into watercourses. CWD may consist of entire trees, root boles, trunks, logs, branches and other pieces of wood that can accumulate within river systems, either submerged or partially submerged in the water.
Invertebrates utilise CWD in various ways. The score provides details of 147 species that are considered to be particularly associated with CWD: by feeding directly on the wood (obligate xylophages, which have the strongest fidelity to this habitat), feeding on micro-organisms on and within the wood, such as fungi and bacteria (facultative xylophages), or by using other features of the wood such as substrates for oviposition, pupation or emergence, or micro-habitats created by the presence of the wood (non xylophages, having the weakest fidelity to the habitat).
A total of 15 obligate xylophages have been identified along with 3 possible obligate xylophages, 48 facultative xylophages, 33 probable xylophages and 30 non-xylophages. Further checking and tightening-up of the species within these categories is required. The fidelity classes are:
- Fidelity score a = obligate xylophages
- Fidelity score b = possible obligate xylophages
- Fidelity score c = facultative xylophages
- Fidelity score d = probable xylophages
- Fidelity score e = non xylophages
For more information see: Godfrey, A. (2003) A review of the invertebrate interest of coarse woody debris in England. English Nature Research Report 513.