Session Information
| Session | Poster Session | | Date | Monday (2008-04-07) | | Time | 5:00 PM - 7:00 PM | | Room | Grand Terrace |
Presentation Information
| Presenter | Shelley Crausbay | | Title | Tropical cloud forest ecotone characteristics vary along a secondary climate gradient | | Affiliation | University of Wisconsin, Department of Botany | | Authors | Shelley Crausbay, Sara Hotchkiss | | Keywords | Climate change, Cloud forest, Ecotone, Hawaii, Treeline | | Presentation Type | Poster | Abstract:
Twentieth-century climate change has modified ecosystem structure and function broadly, but most strongly in the polar and temperate Northern Hemisphere. By AD 2100, however, pronounced climate and ecosystem change will likely span the globe. The biodiverse tropics, for example, are projected to warm by 1-4ºC. Oceanic warming in the central and eastern equatorial Pacific will displace current regional precipitation patterns eastward. Tropical climate change is already evident. Glaciers are melting, precipitation is declining, temperatures are increasing, ENSO (El Niño/Southern Oscillation) frequency is increasing, and many other aspects of atmospheric circulation are changing. Tropical ecosystems will likely vary in their sensitivity to climate change, depending on their proximity to system-specific thresholds. Tropical montane cloud forests – which are rich in endemic species and provide the vital ecosystem service of water capture and storage – are particularly vulnerable. The unique and extreme cloud forest microclimate varies abruptly in space, and therefore the upper limit of the cloud forest ends sharply in a forestline ecotone. Such climatically controlled ecotones will likely be the first ecosystem properties to respond to 21st century climate change.
The cloud forest ecotone on Haleakala volcano in the Hawaiian Islands is a highly tractable, taxonomically simple system for our research on tropical ecosystem sensitivity to climate change. Several high-latitude Northern Hemisphere studies document greater sensitivity (faster response time) or different direction of treeline ecotone response to climate change – based on position along a secondary climate gradient. In Hawai‘i the treeline ecotone is coincident with a strong elevational climate gradient, maintained by the Trade Wind Inversion, and a secondary precipitation gradient runs east to west along the ecotone boundary. In this research, we ask whether ecotone characteristics (vegetation species assemblage, community characteristics, and structure) vary with landscape position along the secondary climate gradient. Further, we use multivariate techniques to assess whether the relationship between community patterns and environmental variables (climate, fire, substrate age, slope, and aspect) varies with landscape position. Vegetation composition and structure provide evidence of a sharp ecotone at each landscape position, but ecotone characteristics (elevation of the ecotone, indicator species, degree of community composition difference across the ecotone, and structural patterns) differ in the most arid landscape position. These patterns are largely related to climate, rather than other environmental variables. Spatial variability in ecotone characteristics will have implications for the rate and direction of response to 21st century climate change along the ecotone boundary. |
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