Assessing Carbon and Nitrogen in a Central Nevada Pinyon Woodland with Tree Encroachment and Prescribed Fire

Date of Award

5-2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Watershed Sciences

First Advisor

Dale W. Johnson

Second Advisor

Jeanne C. Chambers

Third Advisor

Watkins W. Miller

Abstract

Long term climate change, land use history, woodland encroachment, exotic grass invasions, and altered fire regimes is dramatically influencing vegetation and biogeochemical cycles in the Great Basin, U.S. Currently there is a lack of data on carbon pools and fluxes within this region and the closely linked nitrogen cycle. Increasing concern toward global climate change may drive land management policy over the coming decades. It is therefore increasingly important to understand the current state of carbon (C) and nitrogen (N) pools, their trends, and the impact of land management on those pools. This research focuses on those goals by refining methods for estimating belowground C and N, and estimating whole ecosystem C and N associated with woodland encroachment into sagebrush (Artemesia tridentate spp.) ecosystems, and the effects of land management, particularly prescribed fire, on ecosystem C and N. We found that our use of a soil coring device to estimate belowground biomass and C and N gives similar estimates to those obtained from quantitative soil pits. However, the core device is more efficient in regards to sampling time and data processing. It is noted that belowground biomass may exceed 1/3 of total biomass in transitional woodlands, and that soil contains more than 80 % ecosystem C and 90 % ecosystem N at low tree cover. As tree cover increases, biomass and C accumulates rapidly on the landscape, and closed canopy woodlands may exceed 60 % of ecosystem C in aboveground biomass, but less than 15 % N. Prescribed burning at low tree cover releases some C and N to the atmosphere, but a portion is incorporated into soil pools. Burning at increasing tree cover results in more C and N lost to the atmosphere and less C and N incorporated into soils.

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