manages resources that are critically important to the nation's scientific community. Because the parks contain many areas that are relatively unaltered by human activity, and because there is commitment to their long-term protection, the parks are increasingly important to scientific investigations of larger environmental problems. The parks are invaluable for unraveling the mysteries of natural and human history, evolutionary adaptation, ecosystem dynamics, and other natural processes. They also serve as reservoirs of biotic diversity, as refuges for species threatened by human activity, and as valuable sources of baseline information for comparison with human-altered ecosystems.

One major challenge to the scientific community in general (and park managers as well) is to distinguish anthropogenic change from natural variation in biological and hydrological processes. For example, there is considerable year-to-year variation in the population of many animal species. Some is caused by natural events and cycles; in other cases the causes are attributable to anthropogenic changes in land uses that affect the availability of food and shelter and the quality of habitat. Research in relatively large park areas, where human impacts are less prevalent, provides scientists with some of the best opportunities to study natural variations and the effects of human activity.

The scientific value of park resources in the future is impossible to calculate. Only two decades ago, for instance, the processes that cause acid rain and diminishing stratospheric ozone were unknown. We cannot know what questions will demand attention two decades from now, but it is possible to make educated guesses given enough information. Research on the rates of primary production and decomposition of organic material, the numbers of key species and the general diversity of species, and soil conditions are all essential. Measurements of species over large areas (so natural spatial variation can be evaluated) and over long periods are needed to elucidate trends. Although all parks have been affected by human influences, some dramatically, measurements made where human effects are relatively minimal, such as in parks and other protected areas, serve as a control against which scientists can measure the effects of human



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