ENSO-RELATED PHENOMENA AT LONG-TERM ECOLOGICAL RESEARCH SITES

Abstract

I outline a framework for investigating and discussing climate variability and ecosystem response. The example of an El Niño-Southern Oscillation (ENSO) event is a relatively simple one for operationalizing this framework. I review some of the earlier findings related to El Niños and Long-Term Ecological Research (LTER) sites. Then I perform an analysis for the period 1957 to 1990 investigating the response of monthly mean temperature and monthly total precipitation standardized anomaly values to El Niño and La Niña events as indicated by the Southern Oscillation Index (SOI). Different LTER sites manifest strong, detectable, and weak or no climatic signals to El Niño and La Niña events. Some of the effects of the ENSO-related climate variability on selected ecosystems are discussed. A statistically significant climate signal at an LTER site does not necessarily mean there will be an ecologically significant response. El Niño signals in the temperature series at the Andrews Forest, Oregon, the Luquillo Rain Forest, Puerto Rico, and the Palmer, Antarctic (PAL), sites are found to be statistically the strongest. Of these, only the signal at the PAL site has an important ecological effect. Somewhat less statistically strong ENSO signals at the Northern Temperate Lakes, Wisconsin, and the Sevilleta, New Mexico, sites have important ecological effects. An analysis of the climatic response to the 1982/1983 “super El Niño” compared to more normal size warm events is equivocal. The results of the correlation analysis are discussed within the climate variability/ecosystem response framework previously outlined. The timing of the ENSO event and the identification of an ecosystem coupling mechanism are critical for this particular form of climate variability to have an effect. [Key words: Long-Term Ecological Research (LTER), ecosystem, El Niño-Southern Oscillation (ENSO), El Niño, La Niña, climate variability.]