Above-and Belowground Carbon Allocation in Developing and Mature Lodgepole Pine Forests in Yellowstone National Park: A Progess Report

Abstract

It has been proposed that forests will act as a sink for -50% of the anthropogenic C02 projected to be released into the atmosphere by the year 2050 as global net primary productivity in forests increases (DeLucia et al. 1999). Coniferous forest ecosystems dominate a large portion of the Earth's land area, and fire plays an important role in the natural disturbance regime of these ecosystems (Archibald 1995). Quantifying the components of the carbon cycle during ecosystem recovery from fire is fundamental for determining how fire and changes in fire frequency alter regional and global carbon budgets (Auclair and Carter 1993, Houghton 1996, Burke et al. 1997). Clearly, if we are to model the effects of terrestrial ecosystems on global carbon budgets, we must develop a better understanding of the role that natural disturbance plays in the carbon dynamics of these systems. Processes that occur after fire may be more important for carbon cycling than the immediate return of carbon to the atmosphere through biomass oxidation (Auclair and Carter 1993). For example, primary productivity following fire is reduced or eliminated until new chlorophyll is synthesized in new leaf area. In addition, aboveground detrital inputs are greatly altered and formerly live roots become available for decomposition. Moreover, litter quality changes with the oxidation of fine fuels; soils and litter become warmer with the removal of overstory shading and a change in albedo; and soils become wetter because of essentially no post-fire transpiration and very little interception of rain and snow. These changes can increase decomposition and soil respiration (Burke et al. 1997), releasing as much as three times more carbon to the atmosphere as the amount released by the initial fire (Auclair and Carter 1993). Notably, carbon is assimilated by new plant growth in fire-adapted ecosystems, with perhaps little net effect on atmospheric C02 (Crutzen and Goldhammer 1993). In addition to large effects on carbon budgets at the stand scale, fire and landscape variables interact to produce a mosaic of different vegetation types (Anderson and Romme 1991, Turner et al: 1997a and b, Foster et al. 1998). The resulting spatial heterogeneity in tree density, herbaceous cover, and species composition in Yellowstone National Park (YNP) will influence primary production and carbon storage for many years. Therefore, to determine the long-term effects of fire on carbon release and storage following fire, information is needed on how processes differ among sites as a function of community structure and stand age. YNP is an ideal study area for this kind of research. Our objective is to answer two questions: 1) How does the relative abundance of trees, shrubs, and herbs influence above- and belowground carbon storage and flux values in young post-fire stands? 2) How do above- and belowground carbon storage and fluxes in young post-fire stands differ from those in nearby mature forests?