Responses of a Sierran Mixed Conifer Understory Plant Community toOver Story Thinning, Slash Mastication, and Prescribed Fire RestorationTreatments

Abstract

Thinning implemented with a cut-to-length harvesting system coupled with on-site slash mastication and redistribution and followed by prescribed under burning were assessed for their impacts on the shrub understory and natural regeneration in an uneven-aged Sierra Nevada mixed conifer stand. Initial suppression of the cover and weight of huckleberry oak, the most prevalent ground cover species, by the combined thinning and mastication operations and those of prostrate ceanothus by the under burn were followed by a pronounced resurgence in abundance for both species in burned stand portions, particularly where thinning had preceded the fire. White fir was most prevalent initially among species represented in the seedling size class of natural regeneration and became predominant thereafter while this species dominated the sapling class throughout the study. White fir seedling establishment was enhanced where the mechanized operations were excluded, and especially so where fire was as well, and such was also the case for incense-cedar initially but its seedling abundance declined precipitously as the study progressed. White fir saplings were most numerous in the unthinned stand subunit but the under burn proved lethal to many of them therein. Jeffrey and sugar pine were little represented among seedlings and absent altogether among saplings.