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DICKMAN, A., and COOK, S. 1989. Fire and fungus in a mountain hemlock forest. Can. J. Bot. 67: 2005-2016. Two mortality factors create large-scale pattern in forests of Tsuga mertensiana in subalpine central Oregon Cascade Mountains. Half of an 18 000 -ha study area has experienced stand-destroying fire during the last 500 years. These fires varied in size from 1 to 3200 ha. Individual Phellinus weirii infestations are smaller than most fires and collectively cover less total area, but they are more numerous and fine-grained in their dispersion. Postfire stands are colonized by Pinus contorta, which persists for 2 centuries before being replaced by mountain hemlock. In stands older than 200 years, Phellinus weirii becomes apparent as it spreads from centers and forms patches where it infects trees and alters the plant community. Fungal isolates were collected from 61 infestations; these were subjected to clonal analyses. Spatial dispersion of ramets and genets supports the inference that many infestations are sibling ramets of genets that have survived stand-destroying fire. The age distribution of genets yields the inference that infestations have been initiated or modified by basidiospore infection during the past 1300 years. Several genets are older than 1000 years. Fire has reduced the visible area of infestation of the fungus. It probably has done so by favoring less susceptible host species and by reducing the modal size of dead roots and logs. While repeated fire could reduce the level of fungal infestation, infestations may enhance the probability of stand-destroying fires. DICKMAN,A., et COOK, S. 1989. Fire and fungus in a mountain hemlock forest. Can. J. Bot. 67 : 2005-2016. Deux facteurs de mortalit6 crCent un pattern trbs Ctendu dans les forEts de Tsuga mertensiana des monts Cascades du Centre de 1'OrCgon. La moitiC d'une surface de 18 000 ha h 1'Ctude a subi une destruction par le feu au cours des 500 dernikres annCes. Ces feux variaient en Ctendue de 1 i 3200 ha. Des infestations individuelles de Phellinus weirii sont plus restreintes que la plupart des feux et leur surface totale regroupCe est moindre, mais ils sont plus nombreux et plus uniformes dans leur dispersion. Les aires forestibres aprbs-feu sont colonisCes par Pinus contorta qui persiste durant 2 sikcles avant d'ktre remplacC par la pruche de montagne. Dans les peuplements plus SgCs que 200 ans, Phellinus weirii devient apparent; il s'Ctend de rCgions centrales et forme des sites d'oh il infecte les arbres et altkre la communautC vkgttale. Des isolats fongiques furent prtlevCs de 61 infestations, puis sournis h des analyses clonales. La dispersion spatiale des individus d'un clone et de ceux provenant des semences ([> ambne h conclure que les infestations ont Ct C dCmarrCes ou modifiCes par l'infection de basidiospores au cou...

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In the Umpqua National Forest, Oregon, a 35-acre ponderosa pine (Pinus ponderosa Laws.) stand situated in the midst of a Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) forest is being invaded by Douglas-fir seedlings as a result of reduced fire frequency within the last 50 years. In earlier times frequent ground fires kept Douglas-fir at a minimum.