Document: LOR-3-34-82

Climate variation and the dynamics of altitudinal treelines in the southern Andes

DANIELS, L.D.* and T.T.VEBLEN

University of Colorado, Boulder CO 80309 USA ¹

Abstract:
This research examines the impacts of climate variation on altitudinal treelines in the southern Andes. We have analyzed forest structure and recent tree establishment at 26 treeline sites within three study areas in Chile and Argentina at ca. 40S. Within areas, study sites were evenly distributed on north- and south-aspect slopes. Trees were measured in 5m-wide transects extending from the erect forest, 10m below timberline, to treeline. Nothofagus pumilio, N. antarctica formed treeline in Argentina; Chilean treelines also included N. betuloides. Maximum treeline elevations were 1295 miles above sea level in Chile and 1525 miles above sea level in Argentina. Treeline ecotones varied in length from five to 140 m. The majority of Nothofagus pumilio seedlings (height <130cm) were growing in the forest or within 10m of timberline. Seedlings were most abundant on sites with north aspects in Chile, and were virtually absent from north-aspects at the eastern study area in Argentina. A sample of 1200 seedlings (height <130cm) revealed ages from one to >70 years. Frequency distributions of age were multi-modal with single years accounting for up to 30% of observations for each study area. Superposed epoch analyses showed statistically significant relationships between seedling abundance and moisture availability and precipitation during the growing season. These results indicate the importance of moisture availability, rather than temperature, for tree seedling establishment at altitudinal treeline in Chile, where precipitation is high, and in the drier climate of Argentina.

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This abstract is being presented at: 11:45 AM in session:
Oral Session #43: Plant Community Responses to Climate Change.