|Rau, B -|
|Tausch, R -|
|Reiner, A -|
|Johnson, D -|
|Chambers, J -|
Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 2, 2011
Publication Date: July 20, 2011
Citation: Rau, B.M., Tausch, R., Reiner, A., Johnson, D.W., Chambers, J.C., Blank, R.R. 2011. Developing a model framework for predicting effects of woody expansion and fire on ecosystem carbon and nitrogen in a pinyon juniper woodland. Journal of Arid Environments. 76:97-104. Interpretive Summary: In the Great Basin, woodland expansion has potential to sequester carbon (C) into vegetation and soil. To assess this potential, data collected from a Joint Fire Sciences Program demonstration area was used to develop a Microsoft Excel-based budget for ecosystem C. On treeless sagebrush-steppe ecosystems, biomass accounts for 4.5 Mg ha-1 C, which is <10% of total ecosystem C. As tree cover increases to near closed canopy conditions, aboveground biomass may account for 62 Mg ha-1 C, which is nearly 53% of total ecosystem C. Changes in soil C were small when compared to biomass C. Fire has the potential to release most aboveground biomass C through combustion or microbial oxidation. Further work is necessary to quantify woody debris decomposition, and soil C upon woodland expansion and prescribed fire. At present, we cannot offer definitive proof that woodland expansion will sequester soil C given the uncertainty surrounding global climate change, exotic species invasion, and fire.
Technical Abstract: Sagebrush-steppe ecosystems are one of the most threatened ecosystems in North America due to woodland expansion, wildfire, and exotic annual grass invasion. Some scientists and policy makers have suggested that woodland expansion will lead to increased carbon (C) storage on the landscape. To assess this potential we used data collected from a Joint Fire Sciences Program demonstration area to develop a Microsoft Excel-based biomass, carbon, and nitrogen (N) spreadsheet model. The model uses input for tree cover, soil chemistry, soil physical properties, and vegetation chemistry to estimate biomass, carbon, and nitrogen accumulation on the landscape with woodland expansion. The model also estimates C and N losses associated with prescribed burning. On our study plots we estimate in treeless sagebrush-steppe ecosystems, biomass accounts for 4.5 Mg ha-1 C and 0.3 Mg ha-1 N this is <10% of total estimated ecosystem C and N to a soil depth of 53 cm, but as tree cover increases to near closed canopy conditions aboveground biomass may account for 62 Mg ha-1 C and 0.6 Mg ha-1 N which is nearly 53% of total estimated ecosystem C and 13% of total estimated ecosystem N to a soil depth of 53 cm. Prescribed burning removes aboveground biomass, C and N, but may increase soil C at areal tree cover below 26%. The model serves as a tool by which we are able to assess our understanding of the system and identify knowledge gaps, which exist for this ecosystem. We believe that further work is necessary to quantify herbaceous biomass, root biomass, woody debris decomposition, and soil C and N with woodland expansion and prescribed fire. It will also be necessary to appropriately scale these estimates from the plot to the landscape.