Zhu Likai, Southworth Jane, Meng Jijun
Department of Geography, University of Florida, 3141 Turlington Hall, P.O. Box 117315, Gainesville, FL, 32611, USA.
College of Urban and Environmental Sciences, Peking University, Beijing, 100871, China.
Int J Biometeorol. 2015 Oct;59(10):1373-84. doi: 10.1007/s00484-014-0947-9. Epub 2014 Dec 27.
Understanding spatial and temporal dynamics of land surface phenology (LSP) and its driving forces are critical for providing information relevant to short- and long-term decision making, particularly as it relates to climate response planning. With the third generation Global Inventory Monitoring and Modeling System (GIMMS3g) Normalized Difference Vegetation Index (NDVI) data and environmental data from multiple sources, we investigated the spatio-temporal changes in the start of the growing season (SOS) in southern African savannas from 1982 through 2010 and determined its linkage to environmental factors using spatial panel data models. Overall, the SOS occurs earlier in the north compared to the south. This relates in part to the differences in ecosystems, with northern areas representing high rainfall and dense tree cover (mainly tree savannas), whereas the south has lower rainfall and sparse tree cover (mainly bush and grass savannas). From 1982 to 2010, an advanced trend was observed predominantly in the tree savanna areas of the north, whereas a delayed trend was chiefly found in the floodplain of the north and bush/grass savannas of the south. Different environmental drivers were detected within tree- and grass-dominated savannas, with a critical division being represented by the 800 mm isohyet. Our results supported the importance of water as a driver in this water-limited system, specifically preseason soil moisture, in determining the SOS in these water-limited, grass-dominated savannas. In addition, the research pointed to other, often overlooked, effects of preseason maximum and minimum temperatures on the SOS across the entire region. Higher preseason maximum temperatures led to an advance of the SOS, whereas the opposite effects of preseason minimum temperature were observed. With the rapid increase in global change research, this work will prove helpful for managing savanna landscapes and key to predicting how projected climate changes will affect regional vegetation phenology and productivity.
了解陆地表面物候（LSP）的时空动态及其驱动力对于提供与短期和长期决策相关的信息至关重要，特别是在涉及气候响应规划方面。利用第三代全球库存监测与建模系统（GIMMS3g）归一化植被指数（NDVI）数据和来自多个来源的环境数据，我们研究了1982年至2010年南部非洲稀树草原生长季开始时间（SOS）的时空变化，并使用空间面板数据模型确定了其与环境因素的联系。总体而言，SOS在北部比南部出现得更早。这部分与生态系统的差异有关，北部地区降雨量大且树木茂密（主要是树木稀树草原），而南部降雨量较低且树木稀疏（主要是灌木丛和草本稀树草原）。从1982年到2010年，主要在北部的树木稀树草原地区观察到提前趋势，而延迟趋势主要出现在北部的洪泛区和南部的灌木丛/草本稀树草原。在以树木和草本为主的稀树草原中检测到不同的环境驱动因素，关键分界线以800毫米等雨量线为代表。我们的结果支持了水作为这个水资源有限系统中的驱动因素的重要性，特别是季前土壤湿度，它决定了这些水资源有限、以草本为主的稀树草原的SOS。此外，该研究指出了季前最高和最低温度对整个地区SOS的其他常常被忽视的影响。较高的季前最高温度导致SOS提前，而观察到季前最低温度有相反的影响。随着全球变化研究的迅速增加，这项工作将被证明有助于管理稀树草原景观，并且对于预测预计的气候变化将如何影响区域植被物候和生产力至关重要。
