HR: 1340h
AN: U53A-0707    [Abstracts]
TI: High-Elevation Response of Conifers to Climate Change in the Sierra Nevada and Western Great Basin, USA: Treeline Elevation is Not the Primary Effect
AU: * Millar, C I
EM: cmillar@fs.fed.us
AF: USDA Forest Service, PSW Research Station, P.O. Box 245, Berkeley, CA 94701 United States
AU: Westfall, R D
EM: rwestfall@fs.fed.us
AF: USDA Forest Service, PSW Research Station, P.O. Box 245, Berkeley, CA 94701 United States
AU: King, J C
EM: lonepine@bigsky.net
AF: Lone Pine Research, 2604 Westridge Dr., Bozeman, MT 59715 United States
AU: Delany, D L
EM: ddelany@fs.fed.us
AF: USDA Forest Service, PSW Research Station, P.O. Box 245, Berkeley, CA 94701 United States
AU: Alden, H A
EM: HAA@scmre.si.edu
AF: Smithsonian Center for Materials Research and Education, 4210 Silver Hill Rd., Suitland, MD 20746 United States
AB: Traditionally change in alpine treeline elevation has been treated as the primary response by conifers to climate change, and considerable effort has gone into discriminating among complex climatic factors that determine a binary move (up or down slope). Four independent studies in the eastern Sierra Nevada (SN) and western Great Basin (GB), which assessed conifer response to historic climates at scales of decades to millennia, suggest that changes in slope, aspect, growth form, species composition, and forest structure are equally if not more important than changes in treeline elevation. (1) Over the past 3.5 millennia, limber pine (Pinus flexilis) alternately grew in sparse populations on highly restricted (NE-facing) sites in the Wassuk Range (GB) and sites in the SN during centuries of drought versus widespread on many slopes and aspects within similar elevation zones during favorable climate periods. (2) During the past millennium, the summit of Whitewing Mtn (near current local treeline, SN) has been alternately occupied by a mixed conifer forest (seven species), scattered, dwarfed pines (one species) and no trees, varying with distinct climate periods. (3) Treeline elevation of whitebark pine (P. albicaulis) in the Yosemite National Park region (SN) over the last millennium has remained stable, whereas climate periods are marked by changes in growth, growth form and forest density. (4) During the 20th century, type conversions from meadow to forest and from bare ground (former snowfields) to forest correspond to multi-decadal climate variability. These studies suggest that future global change may unfold as complex changes in slope, aspect, forest composition and structure rather than simple shifts in species and plant communities up or down slope.
DE: 1812 Drought
DE: 1851 Plant ecology
DE: 1620 Climate dynamics (3309)
SC: Union [U]
MN: 2004 AGU Fall Meeting