TY - THES T1 - Age structure and fire disturbance in the southern Sierra Nevada subalpine forest T2 - Biology Y1 - 1991 A1 - MaryBeth Keifer AB - I used age structure to examine the role of fire disturbance and climate on the population dynamics of the subalpine forest in the southern Sierra Nevada. I cored trees on ten 0.1 ha plots (3300-3400 m elevation) that varied in species composition, from single-species foxtail pine (Pinus balfouriana) or lodgepole pine (Pinus contorta, var. murrayana), to mixed-species stands of both pines. Crossdating was used to produce accurate dates of tree recruitment and fire events. Age structure varied by plot species composition: lodgepole pine recruitment pattern is pulsed, sometimes forming single-cohort patches in response to fire; foxtail pine plots have a more steady pattern of recruitment; mixed-species plots show an intermediate recruitment pattern. Fire may maintain a species composition mosaic in the subalpine forest. Foxtail pine regeneration may increase in areas opened by fire, although not immediately following fire. Low-intensity fire may spread over areas larger than previously reported under certain conditions in the subalpine zone. In addition, unusually frequent, extreme, and/or extended periods of drought may severely limit subalpine tree regeneration. Growing season frost events and grazing before 1900 may also have affected trees establishing in the subalpine zone. JF - Biology PB - University of Arizona VL - M.S. UR - http://ezproxy.library.arizona.edu/login?url=http://proquest.umi.com/pqdweb?did=747829851&sid=7&Fmt=2&clientId=43922&RQT=309&VName=PQD ER -