College of Urban and Environmental Sciences, Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing, China.
National Engineering Laboratory of Forest Ecology and Applied Technology for Southern China and College of Biological Science and Technology, Central South University of Forest and Technology, Changsha, China.
Glob Chang Biol. 2018 Sep;24(9):4084-4094. doi: 10.1111/gcb.14317. Epub 2018 Jun 3.
Cities are natural laboratories for studying vegetation responses to global environmental changes because of their climate, atmospheric, and biogeochemical conditions. However, few holistic studies have been conducted on the impact of urbanization on vegetation growth. We decomposed the overall impacts of urbanization on vegetation growth into direct (replacement of original land surfaces by impervious built-up) and indirect (urban environments) components, using a conceptual framework and remotely sensed data for 377 metropolitan statistical areas (MSAs) in the conterminous United States (CONUS) in 2001, 2006, and 2011. Results showed that urban pixels are often greener than expected given the amount of paved surface they contain. The vegetation growth enhancement due to indirect effects occurred in 88.4%, 90.8%, and 92.9% of urban bins in 2001, 2006, and 2011, respectively. By defining offset value as the ratio of the absolute indirect and direct impact, we obtained that growth enhancement due to indirect effects compensated for about 29.2%, 29.5%, and 31.0% of the reduced productivity due to loss of vegetated surface area on average in 2001, 2006, and 2011, respectively. Vegetation growth responses to urbanization showed little temporal variation but large regional differences with higher offset value in the western CONUS than in the eastern CONUS. Our study highlights the prevalence of vegetation growth enhancement in urban environments and the necessity of differentiating various impacts of urbanization on vegetation growth, and calls for tailored field experiments to understand the relative contributions of various driving forces to vegetation growth and predict vegetation responses to future global change using cities as harbingers.
城市因其气候、大气和生物地球化学条件，成为研究植被对全球环境变化响应的天然实验室。然而，很少有综合研究关注城市化对植被生长的影响。我们使用概念框架和 2001 年、2006 年和 2011 年美国本土 377 个大都市区（MSAs）的遥感数据，将城市化对植被生长的总体影响分解为直接（原始土地表面被不透水建成区取代）和间接（城市环境）成分。结果表明，与所含铺面面积相比，城市像素通常更绿。间接效应导致的植被生长增强分别发生在 2001 年、2006 年和 2011 年 88.4%、90.8%和 92.9%的城市箱中。通过将偏移值定义为间接和直接影响的绝对值之比，我们发现，间接效应导致的生长增强平均补偿了 2001 年、2006 年和 2011 年因植被表面面积损失导致生产力降低的 29.2%、29.5%和 31.0%左右。城市化对植被生长的响应表现出很小的时间变化，但具有很大的区域差异，美国本土西部的偏移值高于东部。我们的研究强调了城市环境中植被生长增强的普遍性，以及区分城市化对植被生长的各种影响的必要性，并呼吁进行有针对性的实地实验，以了解各种驱动因素对植被生长的相对贡献，并利用城市作为先兆预测植被对未来全球变化的响应。
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