THE EFFECTS OF FOREST DISTURBANCE ON DIVERSITY OF TROPICAL SOIL NEMATODES

We provide the first account of the effects of forest disturbance on s pecies richness of nematodes in tropical forest soils, from 24 sites a long gradients of disturbance and regeneration in the Mbalmayo Forest Reserve, Cameroon. Species richness was very high. Samples of 200 nema todes from individual soil cores contained a maximum of 89 and an aver age of 61 species; in total we recorded 431 species and approximately 194 genera. The model of Siemann et al. (1996), predicting that specie s richness scales as the number of individuals I-0.5, underestimates n ematode diversity 4-6 fold in these samples. Over 90% of specimens can not be assigned to known species. Although nematode species richness d eclined with forest disturbance, statistically significant effects wer e detectable only under the most extreme conditions (active slash-and- burn agriculture and complete mechanical forest clearance) and even he re remained at 40% of the richness of near primary sites. Impacts on t rophic structure were also small, and there were no significant change s in the maturity index (MI) (Bongers 1990) with disturbance (mean MI across all treatments was very high, at 3.58). In the light of this st udy, the problems of completing reliable all-taxon inventories in trop ical forests are briefly discussed.