2000-2020年祁连山植被净初级生产力时空变化及其驱动因素

植被净初级生产力(NPP)是评价植被生长的重要参数,也是评估陆地生态系统质量与功能的重要指标。基于MODIS NPP、数字高程模型(DEM)、气象水文及人类活动数据,采用空间分析、趋势分析,分别从像元尺度和县域尺度识别了2000-2020年以来祁连山NPP时空变化特征,采用偏相关分析研究了NPP对年均温和年降水的响应,并借助地理探测器模型揭示了NPP变化的驱动因素,最后采用Hurst指数预测了NPP未来变化趋势。结果表明:2000-2020年祁连山平均NPP呈波动增加趋势,年均增加2.38 g C/m²,其中栽培植被和阔叶林增长最为明显。近20年,像元尺度上有75.37%的区域NPP增加,主要位于东南部;县域尺度上,古浪、平安、化隆和永登县NPP增速较快,而祁连、海西、德令哈和门源县增速较慢。祁连山NPP空间分布具有明显的集聚性,高值集聚区主要位于东南部,而低值集聚区主要位于西北部。年均温和降水量的增加均促进了NPP的增加,但不同区域NPP对气温和降水的响应有明显差异。降水量、饱和水气压差和蒸散发是NPP变化的主要驱动因子,驱动因子之间对植被NPP变化存在交互作用,分为双因子增强和非线性增强效应。未来祁连山NPP变化以增加非持续性为主,说明植被变化面临较大不确定性。研究结果有助于揭示全球气候变化背景下区域植被NPP对气候变化及人类活动的非线性响应机制,亦可为祁连山生态保护与可持续发展提供理论依据。

Spatiotemporal change and driving factors of net primary productivity in Qilian Mountains from 2000 to 2020

Net primary productivity (NPP) is an important parameter for evaluating ecosystem vegetation growth and a critical indicator for representing the quality and function of terrestrial ecosystems. This paper collected the MODIS NPP data, DEM, meteorological, hydrological, and human activity data to reveal the spatiotemporal dynamic characteristics and driving factors of NPP in the Qilian Mountains (QLM) during the last 20 years. Based on the pixel and county scales, we investigated the spatiotemporal variation of the NPP in the QLM by employing spatial analysis and trend analysis. Furthermore, we studied the response of NPP to the meteorological factors (i.e. annual average temperature and annual precipitation) by using partial correlation and regression analysis. The Geodetector model was employed to reveal the driving mechanism of the NPP change. At last, the Hurst index was introduced to predict the future change trend of NPP. The results indicated that there was a fluctuant increase trend of NPP in the QLM during 2000-2020 with a slope of 2.38 g C m^-2 a^-1, the rising degree of the cultivated vegetation and broad-leaved forest was larger compared with other vegetation types. In the past 20 years, 75.37% of the regional NPP increased in the pixel scale, which primarily located in the southeastern regions of the QLM. At the county level, the NPP growth rates of Gulang County, Ping''an County, Hualong County, and Yongdeng County were fast, while that of Qilian County, Haixi County, Delingha County, and Menyuan County were slow. The spatial distribution of NPP in the QLM has obviously spatial agglomeration characteristics. The high-value agglomeration area mainly located in the southeast regions of the QLM, while the low-value agglomeration area mainly situated in the northwest regions of the QLM. The increase in annual average temperature and precipitation promoted the increase of NPP, but the responses of NPP to temperature and precipitation were significantly diverse in different regions. Precipitation, saturated water vapor pressure deficit, and evapotranspiration were the main driving factors of NPP change, and there were interactions effects of driving factors on NPP change, which were two-factor enhancement and nonlinear enhancement effects, respectively. The changing trend of the NPP in the QLM will dominate by the increase with nonpersistent in the future, which indicates that vegetation development in the QLM will face greater uncertainty. The results can help to reveal the nonlinear response mechanism of vegetation NPP to climate change and human activities under the background of global climate change and provide scientific support for the ecological protection and sustainable development of the QLM.