基于CASA模型的广西植被NPP季节变化研究

植被净初级生产力（Net Primary Productivity，NPP）是判定陆地生态系统碳汇/源的关键要素，不仅直接代表了自然环境条件下植被群落的生产能力，还体现了陆地生态系统的质量水平。本文基于陆地生态系统碳汇模型（CASA模型），利用2019年中分辨率成像光谱仪（MODIS）归一化植被指数（NDVI）数据和其他气象数据，对月、季节、年尺度上的广西植被NPP的空间变化进行估算，分析其时空变化特征，并探讨不同植被类型、气象因子和地形地貌对其的影响。结果表明：2019年广西整体区域的植被NPP平均值为880.56 g C·m^-2·a^-1，植被NPP空间分布呈内陆中心向四周递增、东北部向西南部递增的特点。月植被NPP在时间序列上总体呈现正弦曲线的变化特征，1-8月的植被NPP呈上升趋势，在8月达到峰值，而且9月仍然维持较高值；之后至12月，植被NPP逐步下降。广西植被NPP的季节变化明显，冬季的植被NPP整体最低，区域差异性不突出；夏季的植被NPP整体最高，区域差异性突出。常绿阔叶和混交林分布面积广且其光能利用率较大，对广西植被NPP贡献较大。从月尺度上来看，月植被NPP与月累计降水量主要呈负相关关系，与月平均气温主要呈正相关关系；月平均气温与月植被NPP的偏相关性比月累计降水显著，月平均气温是广西月植被NPP的主要影响因子。在中海拔地区（700-1 300 m），植被NPP并不受喀斯特地质环境背景的影响，喀斯特地区和非喀斯特地区植被NPP相差不大且随着海拔高度的上升趋于稳定。在全球变化背景下，分析广西植被NPP的时空演变规律及其与环境要素之间的关系，可为广西生态环境监测与管理、生物多样性保护、生态服务评估等提供科学参考。

Study on the Seasonal Change of NPP of Guangxi Vegetation Based on CASA Model

Net Primary Productivity (NPP) of vegetation is a key element for determining carbon sinks/sources in terrestrial ecosystems, which not only directly represents the production capacity of vegetation communities under natural environmental conditions, but also reflects the quality level of terrestrial ecosystems.Based on the carbon sink model of terrestrial ecosystems (CASA model), this article used the Normalized Difference Vegetation Index (NDVI) data of Moderate Resolution Imaging Spectroradiometer (MODIS) and other meteorological data in 2019 to estimate the spatial changes of vegetation NPP in Guangxi on monthly, seasonal and annual scales, analyze its spatial and temporal variation characteristics, and discussed the influence of different vegetation types, meteorological factors and topography on it.The results showed that the average value of vegetation NPP in the whole region of Guangxi in 2019 was 880.56 g C·m^-2·a^-1, and the spatial distribution of vegetation NPP was characterized by increasing from the inland center to the surrounding area and from the northeast to the southwest.Monthly vegetation NPP generally showed the variation characteristics of sine curve in time series.The vegetation NPP showed an upward trend from January to August, peaked in August, and remained high in September.After that, the vegetation NPP gradually decreased until December.The seasonal variation of vegetation NPP in Guangxi was obvious.The vegetation NPP in winter was the lowest, and the regional difference was not prominent.The NPP of vegetation in summer was generally the highest, and the regional difference was prominent.Evergreen broad-leaved and mixed forests had a wide distribution area and a large utilization rate of light energy, which contributed greatly to vegetation NPP in Guangxi.From the monthly scale, the monthly vegetation NPP was negatively correlated with the monthly cumulative precipitation, and positively correlated with the monthly average temperature.The partial correlation between monthly average temperature and monthly vegetation NPP was more significant than that of monthly cumulative precipitation.Monthly average temperature was the main influencing factor of monthly vegetation NPP in Guangxi.In the middle altitude area (700-1 300 m), vegetation NPP is not affected by karst geological environment background.The vegetation NPP in the karst area and the non-karst area was not much different and tended to be stable with the increase of altitude.Under the background of global change, analyzing the spatial and temporal evolution of vegetation NPP in Guangxi and its relationship with environmental factors can provide scientific references for ecological environment monitoring and management, biodiversity conservation, and ecological service assessment in Guangxi.