Publication Date

5-2012

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Hydrologic Sciences

Department

Geosciences

Major Advisor

Shawn G. Benner

Second Advisor

Jennifer L. Pierce

Third Advisor

Marie-Anne deGraaf

Abstract

More than 20,000 km2 of sagebrush (Artemesia spp.) ecosystems within the Great Basin have been replaced, often following wildfire, by the nonnative winter annual cheatgrass (Bromus tectorum). At a field site in the central Snake River Plain of southern Idaho, the impact of this invasion on the soil carbon (C) reservoir has been evaluated and the potential soil C benefits of bunchgrass (Agropyron cristatum) seeding was assessed. Using a large soil C dataset (n = 850), differences in total organic carbon and root biomass were quantified in immediately-adjacent sagebrush, cheatgrass, and bunchgrass communities. Statistical significance was determined by employment of nonparametric analysis using bootstrap resampling and the two-population Kolmogrov-Smirnov test for statistical significance. Replacement of sagebrush by cheatgrass following fire has resulted in a 50% loss in below-ground carbon (56 to 29 Mg C ha-1, over a 27 yr period), with decreased root-C accounting for 20% of the total below-ground carbon loss. Bunchgrass seeding immediately following the fire reduced the amount of C lost to sagebrush degradation by 30% (31 vs. 40 Mg C ha-1). There is a positive relationship between above-ground biomass and below-ground soil carbon, however C loss is an order of magnitude greater in below-ground compared to above-ground C pools (27 vs. 3 Mg ha-1). Observed changes in soil structure, in particular the loss of large soil aggregates, and altered soil moisture conditions may contribute to the observed soil carbon loss. Extension of these results to the entire Great Basin, suggest the total below ground carbon loss with cheatgrass invasion is on the order of 60 Mt C and projected losses may exceed 2 Gt C. Conversely, treatment with bunchgrass or recovery of the original sagebrush may achieve similarly large carbon storage benefits.

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