基于SPOT-VEGETATION数据的神农架林区1998-2013年植被覆盖度格局变化

基于1998-2013年的SPOT-VEGETATION归一化植被指数（normalized differential vegetation index，NDVI）数据，利用二分模型法、相关性分析和空间分析的方法，结合同期降水量和平均温度数据，估算了神农架林区及神农架国家级自然保护区的植被覆盖度，并分析了空间格局及植被覆盖度变化的影响因素。结果表明，1998-2013年间，神农架林区平均植被覆盖度为66.8%，年最大植被覆盖度为93.8%，保护区内最大植被覆盖度显著高于保护区外；林区植被覆盖度变化率为1.45%，保护区植被覆盖度变化率为2.26%，植被整体呈增加的趋势，保护区保护效果较好。温度、降水量、年最低气温、距道路和居民地距离的远近是影响植被覆盖度变化的重要因子，而海拔对植被覆盖度变化无影响。

Dynamics and analysis of vegetation fraction changes in Shennongjia Forest District during 1998 to 2013 by using SPOT-VEGETATION NDVI data

The fractional vegetation cover (FVC) is a very important parameter for describing forest vegetation dynamics and forest ecosystems. Among all the methods used for measuring FVC, the remote sensing method has its own advantages because of the vast spatiotemporal scale of satellite data. Shennongjia Forest District, considered as one of the well-preserved primary forest distribution areas in central China, has diverse species and forest resources. However, the forest was adversely influenced to a large extent by human activities in the 1970s and 1980s, because of the rapidly growing population and remarkable commercial logging. The anthropogenic disturbance has been mitigated and improved since a nature reserve was established, and related protecting policies were implemented. The protecting efficiency of the National Nature Reserve was determined by using a dimidiate model to measure the fractional vegetation cover over the Shennongjia Forest District from 1998 to 2013 by using the 1 km resolution, ten-day NDVI serial data of SPOT-VEGETATION. Yearly precipitation and average temperature in the same period, as well as elevation, distance to residential areas and main roads were included, and the main influencing factors were determined by conducting correlation analysis. The annual average FVC of the study area was 66.8%, whereas the annual maximum FVC was 93.8%, which was higher inside the reserve. During 1998-2013, FVC showed increasing tendencies both over the entire district and inside the reserve, and it increased by 1.45% and 2.26% for the Shennongjia Forest District and National Reserve, respectively. The National Reserve had a better protecting efficiency for forest vegetation. The correlation analysis for the main influencing factors showed that environmental factors, including yearly precipitation, average temperature, and extreme cold temperature, were positively correlated with FVC, whereas elevation did not show a significant correlation. The socioeconomic factors, including the distance to main roads and residential areas, had remarkable impacts on the changes of FVC. FVC near residential areas has increased owing to the urbanization and greening processes. FVC near roads showed both increasing and decreasing tendencies in space, because of the simultaneous construction of new roads and afforestation. This study revealed the changing tendency in Shennongjia Forest District and the National Reserve and indicated that both natural and socioeconomic factors had remarkable impacts on dynamics of fractional vegetation cover and forest ecosystems, which might provide detailed scientific basis for ecosystem management.