Community Research and Development Information Service - CORDIS

Coarse Woody Debris (CDW) and plant/fungal biodiversity

An important feature of natural forests is that they possess high amounts of coarse woody debris (CWD) in all stages of decay and also a high proportion of old, living trees with dead parts. These different CWD types provide important habitats for a diversity of organisms, including fungi, bryophytes, lichens, invertebrates, amphibians, cavity nesting birds and small mammals. The importance of dead wood for forest biodiversity and ecosystem function is well studied from the boreal zone in temperate region, but the knowledge of this topic is much scarcer from temperate broad-leaved forests.

It is however estimated that artificial stand structure and disturbance regimes have reduced the availability of CDW considerably (up to 90-98%). The objectives of the research were to:

- To identify the importance of beech dead wood as a habitat for bryophyte and fungi biodiversity in different countries (as they are principal agents of wood decay in terrestrial habitats and hence they open up the wood resource for most other organisms living in dead wood);

- Produce an ecological succession model for plant and fungal community development on decaying beech dead wood, including the effect of tree related factors (tree size, tree type, and light conditions) for species composition;

- Build a species-specific probability matrix based on decay stages, tree size and geographical regions, to provide input for research on scenario analysis to model landscape scale effects of CWD on biodiversity.

Altogether 19 forest reserves were selected for this study: 2 in Slovenia, 2 in Hungary, 8 in The Netherlands, 5 in Denmark, and 2 sites from Belgium joined in on a voluntary basis. The criteria for site selection were the following: a) beech should be dominant and b) the sites should represent, as far as possible, the best natural reference of beech forests for the region.

Dead beech trees were selected using three criteria: decay stage, size (DBH), and degree of soil contact. Different decay stages and size (DBH) categories were as evenly distributed among the approximately 200 selected trees per country as possible. For all investigated organism groups' presence/absence (binary) data were recorded from the trees. Bryophytes and vascular plants occurring on the selected trees were recorded in each country in summer and autumn 2001. Fungal sporocarps (occurring strictly on dead wood) of selected taxa were recorded on three occasions (spring, late summer, autumn) at each site in the period of 2000-2001.

The inventory included the log, the uprooting part of the log, the snag (if present), and the major branches of the crown (if present). The whole dataset contains 161 bryophyte, 170 vascular and 457 fungi species. The main scientific conclusions are the following:

- For the species composition of fungi, decay stage was the most important factor at the European scale, while the decay stages had a regional effect on the species composition of bryophytes.

- The species pool of fungi was much larger and with higher proportion of rare species than that of bryophytes and vascular plants.

- The diversity of the investigated organism groups was high in Slovenia and Hungary, while the forest remnants in Atlantic region were impoverished in dead wood living species, especially for bryophytes. In Denmark there is a potential for restoration of saproxylic fungi in the region.

- For the diversity of both organism groups, management induced factors (continuity of dead wood in time, presence of all decay stages, presence of large trees) were more important than climatic factors, although low air humidity can limit the presence of epixylic bryophytes.

- The presence of large dead trees is a key factor for maintaining the diversity of dead wood dwelling bryophytes and fungi communities, because several species that have become rare and endangered in Europe depend on large dead trees.

For end-users (forest managers and conservation managers) the main messages of this research are:

- For the maintenance of the biodiversity of saproxylic organisms it is important to conserve near-natural reserves, where dead wood continuity is long, all decay stages and large trees are present. These sites contain the source populations of saproxylic species in a region, from where they can colonize dead trees of managed forests.

- Very important to leave a certain amount of dead wood also in managed forest e.g. trees of low commercial values thinned small trees, broken branches etc.

- For saproxylic diversity, the presence of large trees, different decay stages and the continuity of dead wood are essential.

- Heterogeneity of dead wood increase saproxylic biodiversity, i.e. the presence of different size categories (large trees, small trees, broken branches), decay stages, dead wood types (snags, logs, branches, uprooted parts).

Related information

Reported by

Alterra - Green World Research
PO Pox 47
6700 AA Wageningen
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