Length of the first growth period in 2005 (Number of days)

By studying vegetation leafing phenology and its coupling with climate along the urban-rural gradient in Phoenix metropolitan region, USA, we elucidated the degree of urbanization-induced transformations of phenology and primary productivity. In this study we used time-series of Normalized Difference Vegetation Index (NDVI) from the Moderate Resolution Imaging Spectroradiometer (MODIS) and spatially interpolated rainfall. Our analyses were stratified by major land covers and dominant soil texture. We also assessed time scales at which NDVI responds most strongly to climatic factors. No distinctive patterns in phenology were found along the urban-rural gradient; however some important generalities were confirmed. Agricultural and urban developments introduce growth multimodality, which is not attributable to desert but customarily found in riparian ecosystems of the area. Despite the existence of summer flush of growth in the desert its signal is not detected by de-noised satellite data. Urban and agricultural vegetation is characterized by fast growth and senescence rates. While agriculture has the shortest growth length, most urban vegetation stays photosynthetically active for longer periods. Growth in the desert is controlled by precipitation accumulated for 2-5 months. Spatial patterns of NDVI are predicted by precipitation grids. Positive relationship between these two variables changes seasonally reaching the maximum near the peak of annual growth. Spring and summer NDVI grids are in better agreement with longer term accumulated precipitation, but the early autumn growth is correlated more with immediate rainfall. Spatial and temporal correlations of desert NDVI with temperature are negative confirming the role of temperature in stimulating water loss from the soil. Our results supported the hypothesis that coarse-textured soils limit evaporative losses of soil water and promote growth. Riparian NDVI are moderately positively correlated with temperature but only weakly with precipitation. NDVI dynamics in urban and agricultural land covers are completely unsynchronized with natural vegetation communities and decoupled with precipitation. They exhibit positive, yet low, correlation with temperature. Overall, urbanization adds a greater diversity of phenological patterns that are not determined by climatic variability. Instead, urban and agricultural vegetation dynamics is expected to be explained largely by socio-economic variables.本研究以美国凤凰城都会区城乡梯度带为研究区域，针对植被展叶物候及其与气候的耦合关系开展研究，阐明了城市化诱导的物候与初级生产力转变程度。本研究采用中分辨率成像光谱仪（Moderate Resolution Imaging Spectroradiometer, MODIS）获取的归一化差分植被指数（Normalized Difference Vegetation Index, NDVI）时间序列，以及空间插值得到的降水数据。分析过程按主要土地覆被类型与优势土壤质地进行分层，并评估了NDVI对气候因子响应最强的时间尺度。研究未在城乡梯度带中发现显著的物候格局，但验证了若干重要共性规律：农业与城市开发活动引入了生长多峰性，该特征并非荒漠生态系统固有，而是该区域河岸生态系统的常见特征；尽管荒漠生态系统存在夏季生长萌发期，但经去噪处理的卫星遥感数据未捕捉到该信号。城市与农业植被具有生长与衰老速率较快的特征，其中农业植被的生长季长度最短，而多数城市植被的光合活性持续时长更长。荒漠植被的生长受2-5个月累积降水量调控，其NDVI的空间格局可通过降水栅格数据预测，二者的正相关关系随季节动态变化，在年度植被生长峰值附近达到最强。春季与夏季的NDVI栅格数据与长期累积降水的吻合度更高，而初秋的植被生长则与即时降雨相关性更强。荒漠植被NDVI与温度的时空相关性为负，证实了温度通过促进土壤水分蒸发发挥的调控作用。本研究结果支持“粗质地土壤可限制土壤水分蒸发损失并促进植被生长”这一假说。河岸带NDVI与温度呈中度正相关，而与降水的相关性较弱。城市与农业覆被下的植被NDVI动态与自然植被群落完全不同步，且与降水解耦，仅与温度呈现微弱的正相关关系。总体而言，城市化增加了非气候变异主导的物候格局多样性，城市与农业植被的动态变化主要应由社会经济变量予以解释。