ASSOCIATION OF ECTOMYCORRHIZAL MATS WITH PACIFIC YEW AND OTHER UNDERSTORY TREES IN CONIFEROUS FORESTS

This study was designed to determine whether ectomycorrhizal mats (ECM ) are more likely to be present in soils at the base of common underst ory trees than in soils distant from trees and to determine whether oc currence of ECM is related to tree size. Three understory trees were s tudied: Pacific yew (Taxus brevifolia Nutt.), western hemlock (Tsuga h eterophylla (Raf.)Sarg), and vine maple (Acer circinatum Pursh). The 1 2 sites studied represent a range of climatic conditions and managemen t histories. More than 2,900 plots were surveyed over 18 months. The i ncidence of ECM was higher at the base of all three species than in co ntrol plots. Incidence of mats was also positively correlated with tre e size. Saplings consistently had a lower incidence of ECM than did la rger trees.