USDA Forest Service

Pacific Southwest Research Station
Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
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Research Topics Ecosystem Processes

Sierra Nevada Ecosystems

Response of Subalpine Conifers to 20th Century Climate Variability in the Sierra Nevada
Meadow invasion, snowfield colonization, and changes in growth, form, and genetic diversity--complex and threshold reactions to warming climates challenge current assumptions

Study Plan
Research Project Summary

The Research

Whitebark pine at upper treeline in the Sierra Nevada Using tree-ring methods, ecological plot evaluation, and genetic analysis, we are investigating multiple and independent indicators of vegetation response in subalpine conifers to 20th century climate change. To date we have studied annual internode growth in krummholz (stunted) whitebark pine (Pinus albicaulis); release of vertical branches in krummholz whitebark pine; invasion of whitebark and lodgepole (P. contorta) pines into retreating snowfields, and invasion of lodgepole pine into upper montane meadows.
We plan next to investigate patterns of stand expansion over elevational gradients, response to frost events, rate of stripbark formation, and crown release in diverse whitebark pine zones. We correlate these responses with regional climate parameters to identify individual tree, stand, and biome level responses to interannual, decadal (e.g., Pacific Decadal Oscillation), and century-long patterns. Responses have been strongly related to climate despite variability among sites in environmental and land-use histories, indicating non-linear, unique, and threshold effects.


blue arrrow Evaluate temporal responses in tree growth and stand dynamics of high-elevation pine forests during the past 200 years relative to interannual, decadal, and century long climate change.

blue arrrow Assess 20th century climate influences on subalpine vegetation relative to other natural and human-induced (livestock grazing, fire suppression) forces.


Application of Research Results

Subalpine forests are considered at high risk under current and future conditions of warming climates. This concern derives from an assumption that warming climates will force high-elevation vegetation ever higher where habitat diminishes in extent and finally off the tops of mountains. Research information is needed about their potential responses that are occurring already under changing climates of the 20th and early 21st centuries so that effective conservation measures may be taken. Our research indicates that subalpine forest response is far more complex than has been widely assumed, and threshold, disequilibrium, reversible, and interacting forces determine actual behavior. Conservation and management strategies must be built with reliable information about what how forests are responding at present.


map of the Sierra Nevada Ecoregion High central and eastern Sierra Nevada, between Mammoth Lakes and Bridgeport, CA.

Lead Scientists/Collaborators

1) Millar, C.I. 1) Delany, D.D. 1) Westfall, R.D. 2) King, J.C.

1) USDA Forest Service, PSW Research Station
Sierra Nevada Research Center
800 Buchanan St., Albany, CA 94706 USA
ph: 559-6300

2) Lone Pine Research, Bozeman, MT 59715

Publications and Reports
Last Modified: Aug 29, 2016 10:56:52 AM