Structure and dynamics of whitebark pine forests in the South Warner Wilderness, northeastern California

I examined the structural characteristics and population dynamics of whitebark pine (Pinus albicaulis) across a 640 m elevational range in the Warner Mountains, northeastern California. I established permanent plots (8 x 50 m) at 90 m elevational intervals along six systematically located transects. Transects followed an east-west orientation, parallel to the slope. At each plot I inventoried physiographic conditions, stem density, basal area, height, and diameter, and I aged all single-stemmed individuals (1.4 m) and the largest sound stem of multi-stemmed clusters. I also noted whether each stem occurred individually or as part of a multi-stemmed cluster. Whitebark pine forest structure and dynamics vary with elevation. At low elevations whitebark pine began expanding downslope into sagebrush steppe habitat in the latter half of the 19th century. These stands are characterized by low stem density and basal area, and by relatively young, small trees. Forests at middle and high elevations exhibit age and size distributions typical of old, self-perpetuating stands. Other structural characteristics (density, basal area, and height) vary between middle and high elevation stands. Whitebark pine regeneration is occurring at all elevations, but sapling and seedling density are uniformly lower than that of tree density. No differences were detected at different elevations in either the percentage of clustered vs. unclustered stems, or in the number of stems within each cluster. Trees generally occur in clusters more often than saplings, and saplings generally occur in clusters more often than seedlings, suggesting that growth form (single stem vs. multistem) and cluster size may vary within an "individual" over time.