Temporal variability of climate at the US long-term ecological research (LTER) sites

Abstract

We examine the temporal climate variability of 18 Long-Term Ecological Research (LTER) sites in the United States including Puerto Rico and Antarctica. Annual and seasonal means of air temperature and totals of precipitation were collected from sites for the period 1957-1990 and, for some sites, for longer periods ranging up to a century. Fourteen of the sites show a positive trend in annual mean temperature during the 1957-1990 period, while 4 show a negative trend. Statistical evidence exists at some groups of sites for a step function in temperature and precipitation occurring in the 14 yr either side of 1976. Comparisons suggest that with respect to changes in time, the cli- mates of sites in the North Central part of the US tend to act in concert as one group while the climates of sites near the East Coast tend to act together as a separate group. The climates of the Antarctic sites also seem to act in a coherent manner. There is less coherence among the climates of other LTER sites. These patterns are shown in the variations of the detrended standardized 5 yr mov- ing averages of temperature and precipitation at the sites. The patterns are associated with variations in the values of teleconnective indices, particularly the North Atlantic Oscillation index for the North Central and East Coast LTER sites and the Pacific North American index for the Alaskan and Pacific Northwest group of LTER sites. The climates of some sites, such as those in the center of the country, show some evidence of 'cyclicity' but the record length is too short to make definitive statements about this. We review the variability of some ecological effects that have been documented at LTER sites as this variability relates to the described climate.