武陵山区植被净第一性生产力的时空格局及其与地形因子的关系

本研究旨在探讨2001-2010年武陵山区植被净第一性生产力(NPP)的时空变化格局及其与主要地形因子间的关系。利用MODIS MOD17A3数据、地形数据,以及土地覆盖等数据,基于回归分析和分级统计等方法,开展了武陵山区植被NPP的时空变化格局及其与高程和坡度2个基本地形因子间关系的研究。结果表明：(1)10年间武陵山区植被年NPP的平均值为590.72 gC·m^-2·yr^-1,森林、灌草和农田的NPP平均值分别为596.79 gC·m^-2·yr^-1、586.98 gC·m^-2·yr^-1和563.31 gC·m^-2·yr^-1;(2)2001-2010年武陵山区植被NPP总量的平均值为98.90 TgC·yr^-1,波动范围为92.79 ~ 106.99 TgC·yr^-1,从NPP年际变化的空间分布来看,武陵山区植被NPP的变化趋势整体上呈北增南减的格局;(3)分别以30 m和3°为高程和坡度的分级级差时,发现武陵山区平均植被NPP随海拔和坡度的升高有明显的先增加后缓慢下降的趋势,但在海拔高于1500 m及坡度大于50°的地区,平均植被NPP出现了较大波动,然而,在波动中均有随海拔和坡度的增加而先上升后再下降的趋势;(4)在地理区间尺度上,200~1000 m的高程段以及5~25°的坡度段内植被NPP的平均值较高,500 m以上的高程区间平均植被NPP依次递减,但50°以上的坡度区间平均植被NPP反而有所增加,这在一定程度上反映了坡度高于某一临界值后坡面侵蚀强度又有所下降的趋势。

Spatio-temporal Pattern of NPP and Related Analyses with Terrain Factors in Wuling Mountainous Area

Based on MODIS NPP data, terrain data and land cover map, spatio-temporal pattern of the NPP in Wuling mountainous area during 2001-2010 and its relationship with the elevation and the slope were analyzed using regression analysis and classification statistics. Results showed that the average annual NPP of the study area from 2001 to 2010 was 590.72 gC·m^-2·yr^-1. The mean NPP of forest, shrub/grassland and cropland were 596.79 gC·m^-2·yr^-1, 586.98 gC·m^-2·yr^-1 and 563.31 gC·m^-2·yr^-1 respectively. During 2001-2010, the average annual total NPP of Wuling mountainous area was 98.90 TgC·yr^-1, ranging from 92.79 TgC·yr^-1 to 106.99 TgC·yr^-1. Besides, the spatial pattern of interannual variability of NPP in the north of our study area presented a significant increase trend, while in the south it indicated an opposite tendency. According to the relationships between the mean NPP and the elevation as well as the slope in the case of 30 m and 3° respectively, NPP increased with the altitude and slope first, then decreased slowly. But when the elevation went above 1500 m or the slope was greater than 50°, the mean NPP would present large fluctuations. However, as a whole, the mean NPP increased with the altitude and the slope first, then decreased again. Additionally, the mean NPP within the elevation range of 200~1000 m and the slope range of 5~25° were relatively high, but it decreased gradually from the range of 500 m and above, and had a trend of increase when the slope went greater than 50°, which reflected the erosion intensity was weakened when the slope was greater than a certain threshold.