Short Term Variability in a Long Term Context

Another aspect of short-term climatic variability and ecosystem response, partially and implicitly treated above, is the need to place these items into a longer term perspective. Boose points out the need for paleohurricane record studies as the next step in our understanding of the forest response to such storms. The hurricane study also shows how important preexisting conditions are, especially with regard to the passage of previous hurricanes and to human land-use patterns that may have been set decades to centuries previously. Kloeppel et al. note that the long-term importance of increasing our understanding of drought impacts on forest structure and function is central to anticipating the full impacts of suggested long-term climate change. The Arctic analysis demonstrates that the short-term climate variability and more or less direct response must be seen against a backdrop of steadily increasing temperatures at the decadal scale, as shown by borehole records. This situation foreshadows strong, nonlinear ecosystem responses if ground temperatures rise high enough to melt the permafrost. Gage's analysis uses long-term data to establish that the drought in 1988 was clearly different from other droughts that occurred during the 20-year period analyzed (1972-1991). The 1988 drought occurred in May and June, whereas in other years, significant periods of stress occurred later in the crop-growing season (July-August).

These comments end on an ominous note. Gage reminds us that the 1988 drought was a one-year drought compared to the multiyear "dust bowl" drought that occurred in the 1930s. During the past 60 years, a significant multiyear drought has not occurred in the North Central Region of the United States, and thus the probability of such a multiyear drought is high. The LTER program is well prepared to monitor and study the ecosystem responses to even more severe climatic events and episodes than those that occurred during the first two decades of the program.

References

Knapp, A. K., J. M. Briggs, J. M. Blair, and C. L. Turner. 1998. Patterns and controls of aboveground net primary production in tallgrass prairie. Pages 193-221 in Grassland dynamics: Long-Term Ecological Research in tallgrass prairie. New York: Oxford University Press.

Tilman, D., and J. A. Downing. 1994. Biodiversity and stability in grasslands. Nature 367: 363-365.

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Part II

The Quasi-Quintennial Timescale

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