广州市植被净初级生产力对土地覆被变化的时空响应特征

Spatio-Temporal Response of Vegetation NPP to Land Use/Land Cover Change in Guangzhou

植被净初级生产力(NPP)指单位面积和单位时间内转换并固定下来的碳量,是反映城市扩张和人类活动对生态系统影响的重要指标,探索巨型城市——广州在快速城市化时期的NPP动态及其影响具有重要意义。本文应用MODIS-1km NPP影像数据开展2001~2006年广州市净初级生产力的时空格局变化分析,及NPP对土地利用覆被变化响应特征的初步探究。结果表明广州市城区及近郊NPP主要分布在250~500 gC·m?2·a?1,山区NPP主要分布在500~750 gC·m?2·a?1,总体呈现出2001~2003以0.13平均速率增长,而后在2003~2006年以?0.75的平均速率下降的趋势。广州市不同地区NPP总量和土地利用覆被变化率分布均存在明显差异。通过对比土地利用覆被变化驱动的NPP转移强度比例,发现灌丛、木本草地和混交林等高NPP均值地类转为草地和农用地等低值NPP地类,是NPP下降的主要原因。这与城市扩张后通过复垦这些地类来保持农用地数量平衡的策略密切相关,各地类上NPP的变化清晰指示了生态系统对城市化及人类活动的响应。

Net primary productivity (NPP) is defined as the organic carbon accumulated by green plants photosynthesis in per area and time, and as a key ecological indicator reflecting the impacts of urbanization expansion and Human activities on the ecosystem. It is significant to explore NPP variations in a fast urbani- zation case of mega city, Guangzhou. This research applies MODIS-1km NPP data to analyze spatio-tempo- ral pattern variation of NPP and its response to the changes of land use/land cover (LULCC) in Guangzhou during the period of 2001-2006. NPP time-series data were obtained through the projection and pretreatment of MOD17A3, and spectral angle mapper (SAM) decision tree was applied to obtain 8 vegetation types, of which the classification accuracy was more than 80%. The results display that NPP varied with range of 250~ 500 gC·m?2·a?1 in the urban central areas and the suburb areas, and 500~750 gC·m?2·a?1 in mountainous re- gions. Moreover, NPP increased with ratio of 0.13 from 2001 to 2003, and decreased with an average change rate of ?0.75 per year from 2003 to 2006. There were distinct NPP variations and the land covers transfer among the central, suburb and exurb areas in Guangzhou. By contrasting NPP conversion intensity driven by LULCC, it was found that the land covers with high NPP value such as shrublands, woody savannas and mixed forest turn into land covers with low value such as grassland and croplands that mainly led to the loss of NPP. The case is related with the strategy of balancing the croplands through reclaiming these vegetation covers. Therefore, the NPP variation of different land use/land cover indicated the response of ecosystems to urbanization and human activities.