Spruce-Fir Forest at Its Southern Distribution in the Rocky Mountains, New Mexico

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Abstract
Nine stands of spruce-fir near Sierra Blanca Peak (3050-3350 m) in S New Mexico [USA] are described. They vary from young, fire-initiated to old-growth stands, but belong to the same association of Abies lasiocarpa/Senecio sanguisorboides, Ribes wolfii phase. Tree structure, ground flora and soil characteristics are given for each stand. At its southernmost distributional limit in the Rocky Mountains, this forest differs in striking ways from disjunct spruce-fir forests to the N. Jaccard''s community coefficient (J) and Sorenson''s K index of similarity were employed to indicate floristic similarities. Comparisons with 8 other spruce-fir types yielded a range from 0-14% similarity. There is no apparent trend in diversity of understory cover from young to old stands. The distribution of relative cover suggests a lognormal curve with a high number (38) of rare and infrequent species present. The nutrient-poor soils are found in the shrub thicket and young-growth stands while nutrient-rich soils appear in old-growth stand types. Adjoining Festuca thurberi communities seem to be unfavorable environments for forest advancement under present climatic conditions.