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

Although ecosystem management techniques are designed to enhance species di versity in managed forests, no comprehensive study has been conducted to ev aluate effects of such techniques on diversity and productivity of hypogeou s 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 app roximately 6-week intervals. Half of the stands served as controls, half we re assigned a variable density thinning (VDT) treatment. A VDT stand compri sed a mosaic of patches thinned to different densities of standing live tre es. To further evaluate the effect of harvesting impacts, this mosaic was d ivided into two thinning categories, lightly thinned and heavily thinned ar eas. Truffle standing crop varied greatly but generally was highest in spri ng with a smaller peak in the fall. At least some sporocarps were found yea r round, with winter having the lowest biomass and species richness. Overal l standing crop biomass (over all seasons) was significantly lower in VDT s tands compared with control stands. The abundance of Gautieria and Hysteran gium species was lower in thinned stands, while Melanogaster species divers ity and productivity were highest in these stands.