The Niwot Ridge LTER employs a program of long- and short-term manipulative experiments and long-term monitoring to study biotic and ecosystem responses and feedbacks to interannual variation in climatic and atmospheric inputs. The 45-yr climate record shows that the alpine tundra at Niwot Ridge is experiencing increased amounts of precipitation; similar measurements of atmospheric nitrogen inputs begun in the early 1980's demonstrate increased atmospheric nitrogen deposition. Redistribution of snowpack by wind amplifies and attenuates these inputs across the alpine tundra and subalpine forest and meadows. Descriptive and manipulative studies designed to understand the consequences of these phenomena in terms of ecosystem structure, function and fluxes are proposed. Concurrently, questions on influence of treeline on nitrogen redistribution and ecosystem response, and test of hypotheses on controls of treeline are also presented.
Interpretation of biotic responses to changing inputs requires a hierarchical perspective that explicitly acknowledges the evolutionary history of the biota, the paleoecological record, and the current interactions among ecosystem components. The inclusion of the subalpine provides not only new ecosystem comparisons, but also generates a separate line of questions regarding the biotic and biogeochemical significance of ecotones. At treeline, vegetation structure appears to control snowpack rather than vice-versa, and therefore the consequences of enhanced snowpack and accompanying N deposition are under biotic as well topographic controls. In essence, the mesoscale snowpack model is overridden by a higher order constraint, the controls on treeline. The proposed research outlines a series of descriptive and manipulative studies to identify these controls.
Niwot Ridge is the only multidisciplinary, long-term alpine and subalpine study site on the continent. As such, the site is an essential benchmark for local, regional and national networks that measure ecological phenomena and biological response to human-induced changes in climate and atmospheric chemistry. Accordingly, emphasis is placed on documenting research and archiving data for current and future scientists. This research is a continuation of studies initiated in 1981, and is based upon research and databases begun in the 1950s. Continued support of this long-term research program will allow these investigators to build upon the significant research accomplishments in alpine ecosystems at Niwot Ridge.
