有关陆地生态系统的研究表明，近一半地球表面已经受到了人类活动不可逆转的影响(Vitousek et al., 1997)。每年人类消耗植被通过光合作用生产的干物质的量达10-55%左右(Vitousek et al., 1986; Rojstaczer et al., 2001)。DeFries 等(1999)估计，在过去的两个世纪，由于土地覆盖类型的变化，全球生态系统的潜在光合作用能力已经下降了5%。近年来从们开始关注城市化所带来的环境影响(McDonnell et al., 1997)。从生态学角度来看，城市化必然导致土地利用方式的变化，从而对生态系统产生很大影响，主要表现在改变其结构与组成，因而影响生态系统的过程与功能(Alberti, 2005)。

植被净第一性生产力(Net primary productivity, NPP)是植被通过光合作用将光能转化为化学能的量，是地球上包括人类在内的异养生物的主要食物来源(Imhoff et al., 2004)。定量研究城市化对植被净第一性生产力(NPP)、净生态系统生产力(NEP)以及净生物圈生产力(NBP)的影响是地球系统科学及全球变化研究的重要内容之一(Postel et al., 1996)。NPP影响大气的组成(Pimm and Raven, 2000)、淡水资源供给(Sala et al., 2000)、生物多样性(DeFries et al., 1999; Field, 2001)以及能量供给与分布的生态调节机制(Houghton et al., 1999)。因此NPP是气候与环境变化的一个重要指标因子(Schimel et al., 1995)。研究城市化对NPP的影响对于了解生态系统结构与功能的变化，预测未来全球碳循环趋势具有重要指示作用。

地表过程与资源生态国家重点实验室于德永等人选 取我国快速城市化的典型地区－深圳市，研究了1999-2005年深圳市土地利用变化情况及其对城市生态系统NPP的影响。结果表明：1999-2005 年，深圳市20.21%的土地利用/覆盖情况发生了变化，NPP损失了321.51 Gg C (1 Gg = 10⁹ g)。深圳市NPP的变化主要是由于人类活动的干扰，尤其是由于城市扩展蚕食森林、农田造成的。根据植被光合作用反应方程式，植被每吸收1.62g CO₂，制造1g干物质，同时释放出1.2g O₂。1999-2005年，深圳市生态系统损失了321.51 Gg C，相当于减少吸收520.85 Gg CO₂，少释放385.81 Gg O₂。1g干物质含有的热量相当于0.00067g标准煤，因此深圳市七年间损失的NPP，相当于损失了2.15×10⁶标准煤。另外也削弱了生态系统对自然灾害的调节能力，近年来，随着植被的大量被破坏，洪水灾害的发生频率增加。

本文的实际意义在于：城市化进程中要尽量避免或 减少对自然生态系统的影响，同时在城市生态环境建设中不仅仅要关注城市绿地覆盖率，更应该注重提高绿地质量即生产力，这对于提高城市生态系统的服务功能及 城市环境质量，创建宜居城市尤为重要。值得幸运的是近年来深圳市已经认识到这些问题，正在通过基本生态控制线、水系蓝线规划以及其它综合措施加强生态环境 的保护、建设与恢复。

 

 

China has made great economic achievements since the Reform and Opening policy implementation. Shenzhen as the representative city has experienced rapid urbanization and population growth. Urbanization strongly changes the nature of the land surface and has a large influence on the regional ecosystems. In the process of urbanization, fertile cropland and original forest are often destroyed. It is important to regularly monitor the effect of urbanization on the natural environment so as to allow us to control the encroachment to a reasonable extent. Net primary productivity (NPP) is an important productivity indicator of the ecosystem. We obtained land covers from Landsat TM images to quantify urbanization of Shenzhen between 1999 and 2005. We used the Moderate Resolution Imaging Spectroradiometer (MODIS-based) Normalized Difference Vegetation Index (NDVI) data, Landsat-based land cover map, meteorological data and other field data to drive the CASA productivity model and obtain net primary productivity for the study area. Finally, we estimated the effect of urban sprawl on regional NPP. The study on Landsat-based land cover maps indicated that a move towards urban is the most significant landscape change in Shenzhen City and urbanization has irreversibly transformed about 20.21% of Shenzhen’s surface during 1999-2005. NPP loss mainly resulted from urbanization during 1999-2005 and totaled to 321.51 Gg of carbon, an average annual reduction of 45.93 Gg of carbon. For every square km of Shenzhen area, NPP was on average reduced by 0.0017 Gg of carbon during 1999-2005. The loss of NPP is equivalent to a reduction in absorption of 520.85 Gg CO₂ and release of 385.81 Gg O₂, so urbanization has a large influence on the regional net primary productivity.

Figure. The difference of urban area (a) and NPP (b) for Shenzhen between 1999 and 2005

 

Agricultural and Forest Meteorology, 2009, 149, 2054–2060.doi:10.1016/j.agrformet.2009.07.012.