SPATIAL-DISTRIBUTION OF ECTOMYCORRHIZAL MATS IN CONIFEROUS FORESTS OFTHE PACIFIC-NORTHWEST, USA

Ectomycorrhizal mats in forest soils have a wide global distribution a nd have been noted as potentially important elements in forest soil nu trient cycling. To elucidate the relationship between ectomycorrhizal mats and their environment, we undertook field studies and spatial ana lyses of mat distributions at different spatial scales. We used two ex perimental approaches to study mat-forming ectomycorrhizal fungi in co niferous forests of the Pacific Northwest in the United States. In the first approach, ectomycorrhizal mats and other forest door features w ere mapped in 2 x 10 m plots and digitized into a geographical informa tion system (GIS) for spatial pattern analysis. In order to examine la rger-scale phenomena, a second approach involving other sites was take n; soil cores were taken along 30-m transects, and distance to the clo sest living potential host tree was calculated for each core. Mat patt erns were studied at two scales: (1) within-stand level (i.e. variabil ity attributed to distribution of other mat species, forest floor attr ibutes, and understory vegetation); and (2) stand level (i.e. variabil ity expressed along a successional gradient). Mat distribution was inf luenced by: (1) the proximity of one mat to another; (2) the distance from the mat to the closest living tree; (3) the density of living tre es in a stand; and (4) the successional stage of the stand. Although G IS analysis indicated that mats of different morphologies did not phys ically overlap, there was a tendency for clustering of mats. No appare nt correlations were observed between forest floor features and mats l ocated within the 2 x 10 m grids. On the scale of tens of meters, mats decreased with distance from the closest potential host tree. Spatial patterns of mat distributions in harvested sites suggest that these m ats may persist at least 2 years after their host trees have been cut. For Gautieria mats, total mat area, size, and frequency differed with stand age. This study has demonstrated the importance of both spatial scaling and forest stand age when the natural distribution of mycorrh izal fungi is examined. Results suggest the need for mat research dire cted at higher-order scales (e.g. stand and watershed) that will provi de accurate information for managing forests to ensure their survival and normal function.