Forest composition, structure, and change in an old-growth mixed conifer forest in the northern Sierra Nevada.

We documented current forest conditions and 39 years of change in community composition and structure in an old-growth, mixed conifer forest in the northern Sierra Nevada. In 1996, we remeasured and mapped a 4-ha stand, originally established by F.S. Baker between 1954 and 1961. For trees greater than or equal to 9.5 cm dbh in 1996, total tree density was 721 stems/ha, and total basal area was 75.3 m(2)/ha. Pseudotsuga menziesii (Mirbel) France var. menziesii and Abies concolor (Gordon & Glend.) Lindley codominated the plot. A. concolor was the most abundant tree species, 420 stems/ha but P. menziesii had the highest basal area, 31.3 m(2)/ha. A retrospective analysis of trees greater than or equal to 24 cm in dbh showed that in the last 39 years, stand density increased 39% from 157 to 219 stems/ha, and stand basal area increased 15% from 57.9 to 66.7 m(2)/ha. These increases were due largely to the canopy recruitment of A. concolor (60% of new recruits) and the continued growth and low mortality (0.3%/yr) of P. menziesii. Overall stand mortality of trees originally measured by Baker was 0.6%/yr. Regeneration size classes were dominated (in order of frequency) by A. concolor, P. menziesii, and Calocedrus decurrens (Torrey) Florin. There was little regeneration of the less shade-tolerant pine species, Pinus lambertiana Douglas and Pinus ponderosa Laws.