Diversity and productivity of hypogeous fungal sporocarps in a variably thinned Douglas-fir forest

Abstract

Although ecosystem management techniques are designed to enhance species diversity in managed forests, no comprehensive study has been conducted to evaluate effects of such techniques on diversity and productivity of hypogeous fungi (truffles). During this study, truffles were collected in a 55- to 65-year-old Douglas-fir forest from March 1993 through December 1995 at approximately 6-week intervals. Half of the stands served as controls, half were assigned a variable density thinning (VDT) treatment. A VDT stand comprised a mosaic of patches thinned to different densities of standing live trees. To further evaluate the effect of harvesting impacts, this mosaic was divided into two thinning categories, lightly thinned and heavily thinned areas. Truffle standing crop varied greatly but generally was highest in spring with a smaller peak in the fall. At least some sporocarps were found year round, with winter having the lowest biomass and species richness. Overall standing crop biomass (over all seasons) was significantly lower in VDT stands compared with control stands. The abundance of Gautieria and Hysterangium species was lower in thinned stands, while Melanogaster species diversity and productivity were highest in these stands.