Submitted to: Journal of Range Management
Publication Type: Abstract Only
Publication Acceptance Date: September 1, 1996
Publication Date: N/A
Technical Abstract: Little information is available regarding carbon exchange rates on western U.S. native rangelands. The Inter-mountain Sagebrush region encompasses about 130 million acres in Nevada and parts of Utah, Idaho, Oregon, Washington, and California. Our objective was to determine carbon exchange rate and net flux during the growing season on ungrazed native rangeland. We selected an Artemisia tridentata var. Wyomingensis site for the study. Understory species included Stipa thurberiana and Agropyron spicatum. We used two methods to estimate carbon (C) flux. Bowen-ratio energy balance was utilized to estimate net community C dynamics concurrently with individual plant measurements obtained using 1-m^3 closed chambers. Chambers were placed on permanent plots containing either grasses and forbs only, or grasses and forbs with sagebrush overstory. Within each plot, soil respiration was measured both under the canopy and within the interspace. Carbon exchange for both plant and soil chambers was estimate using a LICOR 6200 portable photosynthesis system. In April, minimum soil temperatures were about 1 degree C, and daily fluxes during mid-April varied between -1.5 and 1.8 g/m^2/d^1. Negative C fluxes are toward the surface. In May, flux rates were consistently toward the surface, with a daily average of about -4 g/m^2/d^1 net carbon uptake. Later, as soils dried, net daily flux was away from the surface, representing a net loss of soil and plant carbon. Based on this preliminary study, the period of carbon gain was short, being limited by soil temperature and water content.