摘要：Interactions between forest health variables and mensurational characteristics in an uneven-aged eastern Sierra Nevada mixed conifer stand were examined. The stand was located in the Lake Tahoe Basin on a site featuring a coarsely textured granitic soil and numerous rock outcrops. Its composition was dominated by California white fir (Abies concolor var. lowiana [Gord.] Lemm.), with Jeffrey pine (Pinus jeffreyi Grev. & Balf.) and sugar pine (Pinus lambertiana Dougl.) less prominent and incense-cedar (Libocedrus decurrens Torr.) and mountain alder (Alnus tenuifolia Nutt.) the most minor constituents. The majority of saplings and seedlings were white fir. The stand exhibited no evidence that its development had been influenced by fire and, overall, it consisted of numerous small trees accruing little radial growth. Nearly one-quarter of all standing stems pole size or larger were dead, with mortality concentrated in white fir. Forestfloor fuel accumulations were excessive, and coarse debris was especially prominent. A fir engraver beetle (Scolytus ventralis LeConte) epidemic in white fir contrasted against apparent endemic population levels of the Jeffrey pine (Dendroctonus jeffreyi Hopkins) and red turpentine (Dendroctonus valens LeConte) beetles in Jeffrey pine and of the mountain pine beetle (Dendroctonus ponderosae Hopkins) in sugar pine. The severity of fir engraver attack on white fir was weakly related to overall tree size and to the proportion of composition consisting of this host species, while in Jeffrey pine and sugar pine, bark beetle attacks were strongly correlated with the individual proportions of these 2 hosts. Across all species, basal area explained a substantial proportion of the variation in overall attack severity. We found light infestations of true fir dwarf mistletoe (Arceuthobium abietinum Engelm. ex Munz f. sp. concoloris) in white fir and western dwarf mistletoe (Arceuthobium campylopodum Engelm.) in Jeffrey pine, plus an early stage of infection by the white pine blister rust (Cronartium ribicola J.C. Fischer) in sugar pine. Collectively, this case study characterized and quantified many of the conditions, symptoms, and causative agents inherent in a decadent mixed conifer stand in the eastern Sierra Nevada.
