The Teakettle Experiment1

A critical question in the Sierra Nevada concerns how to use disturbance effectively to restore forest ecosystems after nearly a century of fire suppression. With increases in stem densities and ladder fuels, many forests require a combination of stand thinning and controlled burning to mimic natural fire intensity. In spite of their widespread use, the different effects of fire and thinning on fundamental ecological processes have never been studied in mixed-conifer forests of the Sierra Nevada. The Teakettle Ecosystem Experiment is designed to compare these effects in an old-growth, experimental forest by applying fire and thinning manipulations in a factorial design. By using integrated sampling methods, coordinated studies will follow vegetation, soil, microclimate, invertebrate, and tree response variables before and after treatments on replicated plots. These five component studies will provide a core understanding of changes in ecosystem allocations of energy, water, and nutrients among plants and first-order consumers. Responses of these baseline processes should provide important metrics of fundamental changes in ecosystem conditions throughout higher trophic levels. This experiment can provide an important contrast of how the type and intensity of disturbance affect forest functions and succession. A fundamental question concerning forest management in the Sierra Nevada of California involves the degree to which selective timber harvesting mimics the ecological effects of the natural fire-disturbance regime. If thinning differs from burning, what ecosystem functions and processes are being altered, what are the consequences of these changes, and how might the effects be mitigated? In the Sierra Nevada, fire historically has been the disturbance dynamic driving forest ecosystem structure, function, and composition. If forest management is to conserve biodiversity and maintain ecosystem functions, the effects of silvicultural treatments should approximate the disturbance regime by which the flora and fauna of the Sierra have evolved. In the summary section of critical findings, the report from the recent Sierra Nevada Ecosystem Project (SNEP 1996, summary p. 4-5) emphasized that this essential information was absent: Although silvicultural treatments can mimic the effects of fire on structural patterns of woody vegetation, virtually no data exist on the ability to mimic ecological functions of natural fire. Silvicultural treatments can create patterns of woody vegetation that appear similar to those that fire would create, but the consequence for nutrient cycling, hydrology, seed scarification, nonwoody vegetation response, plant diversity, disease and insect infestation, and genetic diversity are mostly unknown. Accordingly, the Teakettle Ecosystem Experiment has been designed to compare the impacts of fire and timber harvest on key ecosystem functions in old-growth, mixed-conifer forest of the Sierra Nevada. 1 An abbreviated version of this paper was presented at the Symposium on the Kings River Sustainable Forest Ecosystems Project: Progress and Current Status, January 26, 1998, Clovis, California. 2 Research Ecologist, Pacific Southwest Research Station, USDA Forest Service, 2081 E. Sierra Ave., Fresno, CA 93710. USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 47