Doctoral Dissertation Research: Spatio-Temporal Dynamics of Woody Plant Encroachment in Semiarid Rangelands of Argentina: Changes in Carbon Stocks, Albedo, and Radiative Forcing

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This doctoral dissertation research project will analyze the consequences of woody plant encroachment on ecosystem carbon stocks and albedo changes at regional scale in the Western Pampas grasslands, Argentina. Land cover change dynamics alter ecosystem and climate functioning primarily through changes in matter cycles and energy fluxes. Woody plant encroachment in semiarid rangelands is a global process of land cover change driven primarily by changes in land use practices. The widespread increase in woody plant cover alters ecosystem distribution of carbon and other nutrients and influences the radiative balance due to the different reflective properties of grasses, soil and woody plants. Despite the fact that rangelands comprise almost 45% of the global land surface, our understanding of the process of encroachment is limited, in most cases, to fine resolution studies of the northern hemisphere. In this study a space-for-time substitution approach will be used to analyze changes in C stocks in the woody plant, grass, litter and soil organic carbon pools and changes in albedo along an encroachment gradient. Field measurements along this gradient will be scaled up with the use of sub-pixel woody plant cover estimates derived from moderate resolution satellite imaginary. To understand the temporal component of the process of encroachment, woody plant cover change dynamics will be analyzed between 1880, 1960 and 2009. Historical land surveys (1880) will be digitized and sampling and statistical procedures will be used to develop estimates of woody plant cover. Aerial photographs (1960) and high resolution panchromatic satellite images (2009) will be processed using spatial wavelets and texture analysis, and moderate resolution images (2010) using multi-date spectral mixture models, in order to assess the changes in woody plant cover over time. This project will be among the first to investigate spatio-temporal dynamics of woody plant encroachment and its consequences on C stock and albedo at a regional scale in the southern hemisphere. Results will be critical for more complete accounting of C and the radiative forcing associated with woody encroachment in semiarid rangelands across the globe. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.