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在区域尺度上分析阿根廷潘帕斯西部草原木本植物入侵对生态系统碳储量和反照率的影响。土地覆盖动态变化主要通过物质循环和能量通量的变化来改变生态系统和气候功能。半干旱草原木本植物的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所驱动。木本植物覆盖的广泛增加改变了生态系统中碳和其他营养物质的分布，并由于草、土壤和木本植物不同的反射特性影响了辐射平衡。尽管牧地占全球陆地面积的近45%，但在大多数情况下，我们对侵蚀过程的理解是有限的，仅限于对北半球的精细分辨率研究。本研究将采用时空替代方法分析木本植物、禾草、凋落物和土壤有机碳库中碳储量的变化以及反照率沿侵蚀梯度的变化。沿着这一梯度进行的实地测量将使用由中分辨率卫星虚数得出的亚像素木本植物覆盖估计值进行放大。为了了解入侵过程的时间成分，本文将分析1880年、1960年和2009年的木本植物覆盖变化动态。历史土地调查（1880年）将被数字化，采样和统计程序将用于开发木本植物覆盖的估计。航空照片（1960年）和高分辨率全色卫星图像（2009年）将使用空间小波和纹理分析进行处理，中等分辨率图像（2010年）使用多日期光谱混合模型进行处理，以评估木本植物覆盖随时间的变化。该项目将是第一个在南半球区域尺度上研究木本植物入侵的时空动态及其对碳储量和反照率的影响的项目。研究结果对于更完整地计算全球半干旱草原上与森林侵蚀相关的碳和辐射强迫至关重要。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.