Long-Term Growth of Sierra Nevada Mixed Conifer in Response to Mechanized Thinning, Slash Mastication, and Prescribed Fire

Abstract

Thinning implemented with a cut-to-length system accompanied by on-site slash mastication and dispersal and followed by prescribed underburning were evaluated for their influences on individual tree and stand level growth in eastern Sierran mixed conifer. California white fir (Abies concolor var. lowiana [Gord.] Lemm.) dominated stand composition with Jeffrey pine (Pinus jeffreyi Grev. & Balf.) and sugar pine (Pinus lambertiana Dougl.) moderately represented while incense-cedar (Libocedrus decurrens Torr.) and California red fir (Abies magnifica A. Murr.) were exceedingly minor constituents. One decade after treatment, trees in the thinned stand subunit exhibited large height and DBH gains irrespective of fire treatment, responses attributable to the thinning protocol and to enhanced growth of residual stems, while minimal dimensional changes prevailed in the unthinned subunit. Diminished board feet and cubic volumes prevailed in the thinned subunit, and especially in its burned portion, through the end of the study, however, reflecting a reduction in stocking exacerbated by further loss caused by the underburn. Steep reductions in white fir volumes were responsible for the overall losses in the thinned and burned treatment combination. Jeffrey pine responded favorably to thinning but not to underburning, while sugar pine volume responses were unaffected by either treatment.