1981-2015年神农架林区森林生态系统净初级生产力估算

湖北省神农架林区是全国唯一以林区命名的行政单位，拥有全球中纬度地区唯一一块保存完好的原始森林，量化其森林生态系统NPP（net primary productivity，净初级生产力）对县域生态系统评估工作十分重要.基于CEVSA2（carbon exchange between vegetation，soil and atmosphere 2）模型模拟1981-2015年神农架林区森林生态系统NPP，并利用中国生态系统研究网络神农架站观测数据和野外调查数据进行验证，进而分析其NPP时空变化特征及其主要环境影响因子.结果表明:①1981-2015年神农架林区森林生态系统年均NPP为628.27 g/m2（以C计），空间分布表现为中部较低、东部以及周边较高，具有明显的空间异质性.②1981-2015年神农架林区年均NPP的增长速率为2.58 g/（m2·a）（R2=0.65，P < 0.001）；运用Mann-Kendall突变检验法发现，1998年前后是NPP增长速率变化的突变点，虽然1998年前后两个时段NPP均呈上升趋势，但1999-2015年NPP增长率较1981-1998年下降了7.01%；从空间上来看，林区中部和北部NPP增长率4~6 g/（m2·a）]相对较高，南部和东部部分地区NPP呈下降趋势，其变化速率在-3~0 g/（m2·a）之间.③神农架林区NPP年际变化与年均温、总辐射年际变化均呈正相关，与年降水量年际变化呈负相关，其中年均温年际变化对NPP年际变化的解释率最高，为43%（P < 0.01）；在空间尺度上，林区森林生态系统约67.83%区域的NPP年际变化由年均温年际变化控制，主要分布在林区中部和东南部，可见年均温是该地区森林生态系统NPP的主要影响因素. 

Estimation and Analysis of Net Primary Productivity of Forest Ecosystems in Shennongjia Forestry District during 1981-2015

The Shennongjia Forestry District of Hubei Province has a well preserved primeval forest at the mid-latitude region in the world, and it is the only administrative unit named by forest in China. Quantifying the net primary productivity (NPP) of the forest ecosystems plays an important role in the county ecosystem assessment. Based on the CEVSA2 (carbon exchange between vegetation, soil and atmosphere 2) model, we simulated the NPP of forests during 1981-2015, and verified the model performance using the field survey data. Then we analyzed the spatio-temporal variations of NPP and its correlation with climate factors. The results showed that:(1) The average NPP was 628.27 g/m² during 1981-2015, and the spatial distribution had significant spatial heterogeneity, lower in the central part and higher in the surrounding and east area. (2) The mean increasing rate of NPP was 2.58 g/(m²·a) (R²=0.65, P<0.001) during 1981-2015, and the turning point was found around 1998 using Mann-Kendall method. The NPP showed an upward trend in both periods, but the increasing rate decreased by 7.01% in the latter period. (3) The increasing rate of the middle and northern areas was relatively high (4-6 g/(m²·a)), while the southwestern and eastern parts showed downward trends (-3-0 g/(m²·a)). The inter-annual variation of NPP had a positive correlation with temperature and global radiation, but a negative correlation with precipitation. The inter-annual variation of temperature has the highest explanatory rate of NPP, which is 43% (P<0.01). In the spatial scale, the inter-annual variation of NPP in about 67.83% of the study area, located in the central and southeastern parts, was controlled by temperature. We can see that temperature was the main environmental factor driving the spatial and temporal variations of the NPP in the Shennongjia Forestry District.