Research Topics Ecosystem Processes
About this Research:
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
Research Project Summary
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.
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.
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.
High central and eastern Sierra Nevada, between Mammoth Lakes and Bridgeport, CA.
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
2) Lone Pine Research, Bozeman, MT 59715
Publications and Reports
- Millar, C.I., Graumlich, L.J., King, J.C., Delany, D.L., and Westfall, R.D. 2004. Response of subalpine conifers in the Sierra Nevada, California, USA to twentieth-century warming and decadal climate variability. Arctic, Antarctic, and Alpine Research, 36(2):181-200.
- Millar, C.I., R. Neilson, D. Batchelet, R. Drapek, and J. Lenihan. In press. Climate change at multiple scales. Chapter 3 in Salwasser, H. and M. Cloughesy (eds). Forests, Carbon, and Climate Change. Oregon Forest Resources Institute Publication.
- Millar, C.I. and L.B. Brubaker. 2006. Climate change and paleoecology: New contexts for restoration ecology. Chapter 15 in M. Palmer, D. Falk, and J. Zedler (eds) Restoration Science. Island Press. pp315-340.
- Westfall, RD and Millar, CI. 2004. Genetic Consequences of Forest Population Dynamics Influenced by Historic Climatic Variability in the Western USA. Forest Ecology and Management. 197: 157-168.
- Poster: Millar, CI; Westfall, RD; Delany, DL; King, JC; and Alden, HA. 2004. Climate as an Ecosystem Architect; Responses of High-Elevation Conifers to Past Climate Variability.
- Poster: Millar, CI; Westfall, RD; Delany, DL; King, JC; and Alden, HA. 2004. High-Elevation Response of Conifers to Climate Change in the Sierra Nevada and Western Great Basin, USA: Treeline Elevation is Not the Primary Effect.