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The LTER sites (Table 1.1) are funded by the National Science Foundation (NSF) in 5 year renewable funding periods and overseen by a Central Coordinating Com­mittee consisting of all site principal investigators and normal NSF peer review procedures. One driving force behind studies at these sites was the desire to describe human-derived and natural perturbations acting over long time periods, e.g. air pollution, acidification, CO2• Studies at the sites are organized around five core themes which are 1) pattern and control of primary production; 2) spatial and temporal distribution of populations selected to represent trophic structure; 3) pattern and control of organic matte1· accumulation in surface layers and sediments; 5) patterns of inorganic input and movement through soils, groundwater and surface waters, and patterns and frequency of distur­bance to the research site.

There is a strong need to sample common parameters for comparison between LTER sites. Furthermore, climatological information is essential, either directly or indirectly, to investigations of the five core themes and the LTER program as a whole. In many cases records of climatic variables are the only truly 'long-term' records initiallv available at individual LTER sites. Climatological analyses are a beginning method for comparison across all LTER sites.