NOAA/WDS Paleoclimatology - North fire data from Rock Creek - IMPD USROC002

There have been few fire history studies of eastern Sierra Nevada forests in California, USA, where a steep elevation gradient, rain shadow conditions, and forest stand isolation may produce different fire regimes than those found on the range's western slope. We investigated historic fire regimes and potential climate influences on four forest types ranging in elevation from 1700 m to 3200 m on the Sierra Nevada's eastern slope and the White Mountains' western slope. Sample areas (approximately 15 ha to 45 ha) had mean site fire return intervals ranging from 4.8 yr to 16.9 yr across ten Jeffrey pine (Pinus jeffreyi Balf.) sites, and 13.4 yr to 45.7 yr across four high elevation lodgepole (P. contorta Douglas ex Louden), foxtail (P. balfouriana Balf.) and bristlecone (P. longaeva D.K. Bailey) pine sites. At most sites (13 of 14), >50 % of fire events occurred in late or dormant season wood. Twentieth century fire return intervals increased at some sites, while other sites continued to record frequent fire events into the 1950s. Years where two or more sites recorded fire events on two or more trees were correlated with drought conditions forecast by the Palmer Drought Severity Index (PDSI) in our sample locations at and north of Mammoth Lakes. The lower Sierra Nevada crest due west of these locations may connect weather patterns with western slope conditions more than at our southern eastside sample sites, which were not significantly correlated with PDSI. Our results suggest eastern Sierra Nevada Jeffrey pine forests have similar seasonality and fire return intervals as some western slope forests, but site fire history can be influenced by stand isolation, historical use, and local rain shadow conditions.

美国加利福尼亚州内华达山脉东部林区的火灾历史研究相对匮乏。该区域兼具陡峭的海拔梯度、雨影效应与林分隔离特征，其火灾制度（fire regime）可能与山脉西坡存在显著差异。本研究针对内华达山脉东坡与怀特山脉西坡海拔1700米至3200米的4种森林类型，探究其历史火灾制度及潜在气候影响因子。本次研究的样地面积约为15公顷至45公顷：在10个杰弗里松（Pinus jeffreyi Balf.）样地中，单样地平均火灾轮回期为4.8年至16.9年；在4个高海拔的扭叶松（P. contorta Douglas ex Louden）、狐尾松（P. balfouriana Balf.）以及大盆地狐尾松（P. longaeva D.K. Bailey）样地中，该数值区间为13.4年至45.7年。在14个样地中的13个样地内，超50%的火灾事件发生于生长季末期或休眠季。部分样地的20世纪火灾轮回期有所延长，而其余样地直至20世纪50年代仍频繁发生火灾。在猛犸湖及以北的样地中，存在2个及以上样地、2株及以上林木记录到火灾事件的年份，与由帕尔默干旱严重度指数（Palmer Drought Severity Index, PDSI）测算得到的干旱状况存在相关性。相较于本研究的南部东侧样地，上述样地以西的内华达山脉低矮山脊更易将天气格局与西坡环境相联系；而南部东侧样地与PDSI并无显著相关性。本研究结果表明，内华达山脉东部的杰弗里松林，其火灾发生季节与火灾轮回期与部分西坡森林较为相似，但林分的火灾历史可受到林分隔离、历史人类活动以及局地雨影效应的共同影响。