Applicability of Experimental Manipulations

Experimental manipulations of the environment have been a common way of exploring how tundra ecosystems and their components react to environmental changes. Such experiments have, indeed, given valuable information on environmental controls at various levels of resolution, although of necessity the information is limited by observation series over relatively short time spans. Hence, the time constraints of experimentation set a limit to the observations of long-term responses, which must be sought from other sources and by other means, such as modeling. This may lead to a risk of confounding short-term (years to decade), transient changes with long term processes, and careful consideration must be taken in extrapolations to longer time-scales and in parameterization of the models.

Experimental manipulations are, hence, most valuable for detection of short-term responses within ecosystems, but less useful for detection of larger scale processes and those acting over long time-spans, which structure the tundra landscape. For instance, we are not aware of any experiment in the Arctic, that has been conducted over a time-span long enough to detect changes in soil carbon pools or large-scale hydrological changes.

In spite of these shortcomings, a large part of our knowledge of processes in tundra ecosystems rests on results from manipulations undertaken during the last 20 years, mostly involving water or nutrient additions or changes of light and temperature within well-defined ecosystem types.

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