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Abstract
Seed Fall and Seedling Recruitment in Mixed Conifer Forests of the Sierra Nevada
Jon E. Keeley* and Philip van Mantgem, U.S. Geological Survey, Sequoia-Kings Canyon Field Station, Three Rivers, CA 93271; *ph: (559) 565-3170; *email: jon_keeley@usgs.gov
Regeneration is likely a sensitive indicator of global change perhaps evident in patterns of cone initiation, seed production, and seedling recruitment. This, however, is complicated by limited understanding of how current conditions control these parameters.
Recruitment strategies are poorly understood because of marked limitations in the temporal and spatial scale of study. The Sierra Nevada Global Change Project can contribute significantly because of its long-term focus across a broad elevational range from 1500 to 3000 m in the southern and central Sierra Nevada. Analysis along this gradient shows that elevation is an important predictor of conifer seedling density best illustrated by a simple exponential decay model. Elevational effects are only weakly evident in firs but prominent in pines. Not surprisingly in these largely undisturbed forests white fir (Abies concolor) dominates the recruitment and ponderosa pine (Pinus ponderosa) is barely represented. Incense cedar (Calocedrus decurrens) and sugar pine (P. lambertiana) patterns are broadly similar to white fir. Evidence of successful understory recruitment and establishment in the understory by sugar pine suggests limited fire dependence in this pine species. Although white fir is capable of successful recruitment in the understory of undisturbed forests it also recruits heavily into burned sites, suggesting the often-used term "a fire-intolerant species" may be inappropriate.
