12B.6
Climate variability and ecosystem response at Long-Term Ecological Research sites
David Greenland., University of North Carolina, Chapel Hill, NC
Climate variability and ecosystem response was investigated at sites within the Long-Term Ecological Research (LTER) program. The study was guided by a set of questions designed to try to ensure a case of climate variability and ecosystem response is thoroughly considered and to suggest general principles. The first category of questions deals with the dynamics of climate variability and ecosystem response and assumes an underlying temporal sequence. The second category of questions deals with the nature and characteristics of climate variability and ecosystem response. The questions may be abbreviated as follows. What is the type of climate variability being considered? Are there any pre-existing conditions that will affect the impact of the climatic event or episode? Is the climate effect direct or does it go into a cascade? Is the primary ecological effect completed by the time of the next climatic event or episode (or part thereof) or not? Does the climatic event or episode or ecosystem response reverse back to some original state? Does the climatic event or episode or the ecological response have an identifiable upper or lower limit? If returning, do the values of the climatic or ecosystem variables return along their outward path? LTER investigators provided studies representing 14 different LTER sites and 4 different time scales representing seasonal to interannual, quasi-quintennial, decadal, and century to millennial. Most LTER sites show evidence on their landscape of some past climatic event or episode. For a climatic event or episode to be effective there must be some identifiable usually physiologically-related link to the flora and or fauna of the ecosystem. Some proportion of climate variability will not have an effect on the ecosystem. The response cascades may be short or long, intuitively obvious or not, and linear or non-linear or both. The nature of the cascade often depends on the complexity of the ecosystem. The LTER Network includes some fairly simple ecosystems such as McMurdo Dry Valleys in the Antarctic and some very complex ecosystems such as the Luquillo tropical rainforest in Puerto Rico. The study suggests there are two ways of viewing the topic. The first way views cascades or parts of cascades in the atmosphere and ecosystem acting as gateways, filters and catalysts to further ecosystem response. The second way suggests three broad classes of interaction between systems and climate namely: 1) the ecosystem buffers climate variability, 2) the ecosystem system simply responds to individual climate events and episodes that exceed some threshold for response, 3) the ecosystem gets into resonance with the climatic variability with positive and negative feedbacks that produce strong ecosystem response. Examples of ecosystem resonance to climatic variability are seen in the forest and grassland fire regime of the Sevilleta LTER site in New Mexico, the life histories of tabonuco forest in Puerto Rico in relation to the return period of category 4 or 5 hurricanes, and the reproduction of white spruce near the Bonanza Creek LTER site in interior Alaska.
Session 12B, Vegetation Response to Climate, Climate Variability, and Climate Change
Thursday, 31 October 2002, 1:30 PM-2:45 PM
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