Structural Variation and Dynamics of Lodgepole Pine Forests in Lassen Volcanic National Park, California

Abstract

Diameter structure, age/diameter regressions, and stem dispersion patterns reveal spatial variability in lodgepole pine (Pinus contorla) forest structure and dynamics in Lassen Volcanic National Park, California (LVNP). Spatial variability in this early successional species within the LVNP landscape is linked with environmental influences (especially effects of cold-air drainage and substrate fertility), biotic interactions (relative success of more tolerant colonists on the site), and disturbance regimes (contrasts in the scale and timing of canopy openings among sites). Upland sites dominated by lodgepole pine are limited to locales altered by recent geologic activity or by chronic disturbance. Diameter and age structures on these sites conform to a negative exponential distribution with abundant regeneration. Toe-slope sites exhibit replacement of lodgepole pine (with a unimodal diameter and age form) by red fir (Abies magnifica) (with a negative exponential form). Lowland sites in LVNP exhibit both unimodal and negative exponential stand structures for lodgepole pine. Stand destroying disturbances followed by rapid canopy development promote unimodal structures, whereas localized disturbances coupled with gradual canopy closure promote negative exponential structures. These findings underscore the importance of interactions among environment, biota, and disturbance patterns in fostering landscape-scale variability in population structures of early successional plant species.