Saproxylic insect diversity of beech: limbs are richer than trunks

The ecological value of dead wood (coarse woody debris) is broadly acknowledged, but in most commercial forests in Central Europe dead wood amounts are still low. Dead trees are removed because they are thought to obstruct forest management and to be potential sources of outbreaks of pest species. Consequently, the saproxylic fauna is impoverished in many forests of Central Europe. In places where one cannot agree on leaving entire dead trees, dead limbs could be promoted instead. However, limbs are thought not to be an appropriate habitat for saproxylic insects. I tested the hypothesis that trunks of beech Fagus sylvatica (L.) host more saproxylic Diptera and Coleoptera than fallen dead limbs of beech by comparing observed and estimated species richness and diversity. In both insect groups, limbs hosted more species and had a higher diversity than trunks. More threatened saproxylic coleopteran species were reared from limbs than from trunks. Species overlap between trunks and limbs was 55.3% for Diptera and 82.6% for Coleoptera. Hence, a considerable proportion of saproxylic insect species would benefit if at least dead limbs were allowed to accumulate in commercial forests. (C) 2001 Elsevier Science B.V. All rights reserved.