<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>32</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">MaryBeth Keifer</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Age structure and fire disturbance in the southern Sierra Nevada subalpine forest</style></title><secondary-title><style face="normal" font="default" size="100%">Biology</style></secondary-title></titles><dates><year><style  face="normal" font="default" size="100%">1991</style></year></dates><urls><web-urls><url><style face="normal" font="default" size="100%">http://ezproxy.library.arizona.edu/login?url=http://proquest.umi.com/pqdweb?did=747829851&amp;sid=7&amp;Fmt=2&amp;clientId=43922&amp;RQT=309&amp;VName=PQD</style></url></web-urls></urls><publisher><style face="normal" font="default" size="100%">University of Arizona</style></publisher><volume><style face="normal" font="default" size="100%">M.S.</style></volume><abstract><style face="normal" font="default" size="100%">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.</style></abstract></record></records></xml>