Heavy metals (Cd, Cu, Zn) in wood and wood-feeding insects and other invertebrates associated with decaying pine trees.

Abstract

The study of metal distribution in trees and wood-feeding species of invertebrates is of interest from the perspective of ecological risk assessment of metal pollution as well as of forest ecology in general. Wood-feeding invertebrates are important for the physical destruction and natural removal of dead trees in forests. By carrying with them a microbial complex of wood-decompos ing fungi, bacteria, protozoa, and yeasts, they contribute to the chemical process of wood decay (Ausmus 1977; Mamaev 1977). The dynamics of wood decomposition keep up energy flow and matter circulation in forest ecosystem, which are crucial in sustaining a high biodiversity in forests. At the same time, species of bark- and wood-boring beetles have been shown to accumulate heavy metals in their body tissues according to the degree of industrial pollution of the environment (Vogel 1986; Heliovaara et al. 1987; Rothz-Holzapfel & Funke 1990; Esenin 1990). As forest insects and other invertebrates function as food items for birds and mammals they are linked to the process of foodchain transfer of metals in contaminated environments. The present study investigates the use of xylobiont invertebrates as components of a multi-species indicator system for the monitoring of forest ecosystems under metal stress. The approach followed in this study is based on the principle that each stage of decomposition of tree trunks, as shown by changes in density, hardness and chemical composition of the wood, is associated with a particular assemblage of insects and other wood-feeding invertebrates (Schimitschek 1952,1953; Mamaev 1977). The study has been carried out in two pine forest areas in The Netherlands, with different levels of metal contamination. One area, situated near the township of Budel, has been polluted by past emissions from a nearby zinc smelter; the other, a less polluted site, was situated near the city of Arnhem at about 100 km north-east of Budel. Metal contamination levels of soil and fauna of the two areas have been described earlier (Ma et al.1991). Several of the species of bark- and wood-feeding insects mentioned in this paper are studied for the first time in ecotoxicologi cal research.