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

本博士论文研究项目将分析木本植物入侵对生态系统碳储量的影响，以及阿根廷西部潘帕斯草原在区域尺度上的碳储量变化。土地覆被变化动态主要通过物质循环和能量通量的变化改变生态系统和气候功能。半干旱牧场的木本植物入侵是一个全球性的土地覆盖变化过程，主要由土地利用方式的变化驱动。由于草、土壤和木本植物的反射特性不同，木本植物覆盖的广泛增加改变了生态系统中碳和其他养分的分布，并影响了辐射平衡。尽管牧场几乎占全球陆地面积的45%，但在大多数情况下，我们对侵蚀过程的了解仅限于对北方半球的精细分辨率研究。在这项研究中，将使用空间时间替代的方法来分析的变化，在木本植物，草，凋落物和土壤有机碳库和变化的碳储量沿沿着侵蚀梯度。将利用从中等分辨率卫星假想图中得出的亚像素木本植物覆盖估计数，扩大沿着这一梯度的实地测量。要了解的时间组成部分的过程中的侵蚀，木本植物覆盖变化动态将分析1880年，1960年和2009年之间。历史土地调查（1880年）将数字化，抽样和统计程序将用于制定木本植物覆盖的估计。将使用空间小波和纹理分析处理航空照片（1960年）和高分辨率全色卫星图像（2009年），并使用多日期光谱混合模型处理中分辨率图像（2010年），以评估木本植物覆盖随时间的变化。这一项目将是第一个调查木本植物入侵的时空动态及其对南半球区域范围内C类种群和热带雨林的影响的项目之一。结果将是至关重要的，更完整的核算碳和辐射强迫与树木入侵在半干旱牧场在整个地球仪。 作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立的研究生涯。

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.