Document Type

Yellowstone National Park Report

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Primary productivity, the accumulation of nutrients, and other important ecosystem processes are largely dependent on the mineral soil organic matter that has developed during hundreds or thousands of years. In forest ecosystems, the decomposition of coarse woody debris, woody roots, twigs, leaves and micro-organisms is a primary source of this organic matter. Large quantities of coarse woody debris are typically produced following natural disturbances such as fires, pest/pathogen outbreaks, and windstorms, and make a significant contribution to the formation of soil organic matter (SOM). In contrast, timber harvesting often removes most of the coarse woody debris (CWD), which could result in a decrease in the quantity and a change in the quality of mineral soil organic matter. The 1988 fires in Yellowstone National Park continue to provide an excellent opportunity to study the effects of fires of various intensities on ecosystem processes. Ecosystems develop under conditions that are constantly changing, but which remain within some range of natural variability. At present, national forest managers are uncertain as to the quantity of CWD which should be left in a stand following timber harvest in order to maintain levels of SOM which are within the range of natural variability. Little empirical data exist which help characterize the range of natural variability with regard to CWD in lodgepole pine forests, and it is therefore difficult to assess current timber harvesting practices in terms of how much CWD should be left at each site. We began a pilot study in late summer 1995 to begin to address this deficiency. A larger study of broader scope is planned for an additional two to three years, beginning this year, in 1996. This research will attempt to measure specific processes which include the distribution, decomposition, combustion by natural fires, and removal of CWD. The specific objectives of our study are: i) compare the mass and distribution of coarse woody debris that remains following fires of varying intensities to that which remains following clearcutting in the Rocky Mountain Region; ii) estimate the amount of CWD that is combusted or converted to charcoal following fires of varying intensities in stands of varying stages of development; and iii) estimate the length of time necessary for every square meter of the forest soil to be affected by CWD under natural conditions.