Climate, Rain Shadow, and Human-Use Influences on Fire Regimes in the Eastern Sierra Nevada, California, USA

Malcolm P North,Scott L Stephens,Kip M Van De Water,Brandon M Collins

doi:10.4996/fireecology.0503020

Abstract

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.

Highlights

Fire has strongly affected the structure, composition, and ecological processes of many western United States forests (Pyne 1982, Skinner and Chang 1996)
A C10 fire return interval could not be calculated from the bristlecone pine samples because only one fire event was recorded in the same year on two or more trees
Similarities included: 1) variation in fire return interval across forest types (Caprio and Swetnam 1995, Swetnam et al 2000); 2) greater proportion of scars occurring in latewood and dormant ring positions (Stephens and Collins 2004, Taylor and Beaty 2005, Moody et al 2006); and 3) average Jeffrey pine site fire return intervals within the range of those reported for western slope ponderosa pine (Caprio and Swetnam 1995, McKelvey et al 1996) and Tahoe Basin Jeffrey pine forests (Taylor 2004)

Summary

Introduction

Fire has strongly affected the structure, composition, and ecological processes of many western United States forests (Pyne 1982, Skinner and Chang 1996). Fire histories have been completed for the Tahoe Basin (Taylor 2004, Beatty and Taylor 2008) and forest types along the Sierra Nevada’s western slope including ponderosa pine Lawson) (Caprio and Swetnam 1995), mixed conifer (Kilgore and Taylor 1979, Stephens and Collins 2004, North et al 2005), red fir Forests of the eastern Sierra Nevada, those toward the southern portion of the range, are not as well researched (but see Stephens 2001, Vaillant and Stephens 2009). Managers often rely on fire histories from westside Sierra Nevada studies (Michelle Slaton, Inyo National Forest, personal communication)

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