p.1 Tree Regeneration in Single-Tree Selection Gaps in the Mixed Conifer Forests of the Sierra Nevada

Abstract Localized loss of canopy by natural or anthropogenic forces creates canopy gaps, providing changes in environmental conditions and influencing species recruitment. While gap dynamics in Eastern deciduous forests and tropical rain forests are well studied, little is known about the effect of gaps in the Sierran mixed conifer forests. Silvicultural implementation of gaps by selective logging could be important for small land-owners by providing a method to create revenue while still maintaining a continuous canopy cover. This study looked at ~0.04 hectare gaps created by single-tree selection in two compartments at University of California Berkeley’s Blodgett Forest Research Station. Following creation of gaps, material was piled and burned to create an ash substrate in gap centres. Seedlings in the gaps and in the background of the stand were measured in one compartment a year after the harvest, and in the other compartment three years after harvest. Species, substrate, age, and location were recorded for each seedling. Gaps have higher densities of fir seedlings (Douglas-fir, Pseudotsuga menziesii, and white fir, Abies concolor) than pine (ponderosa pine, Pinus ponderosa, and sugar pine, Pinus lambertiana) or incense-cedar (Calocedrus decurrens) seedlings. Firs prefer areas with high amounts of bare mineral soil to those with high amounts of litter. There was no clear relationship between gap size and seedling density. This study shows no strong evidence that single-tree selection gaps of this size increase the regeneration of timber species in the Sierra Nevada mixed conifer forest