基于垂直三分区的太行山区NDVI时空格局及其驱动因素

Spatial-temporal pattern and driving factors of vegetation NDVI in Taihang Mountain area based on three elevation partitions

  • 摘要: 气候变化背景下, 太行山区植被时空格局发生复杂变化, 对京津冀协同发展带来深远影响。本研究利用太行山区低山区(≤500 m)、中山区(500~1 500 m)和亚高山区(>1 500 m) 2000—2022年植被NDVI的遥感影像, 结合线性趋势分析、回归分析等方法, 解析了该区23年来全域及垂直三分区植被时空变化格局及驱动因素, 并采用结构方程模型分析了不同因子对NDVI时空变化的直接和间接影响。结果表明: 1)时间尺度上, 2000—2022年太行山区NDVI总体呈上升趋势, 平均年际变化率为0.005 8;海拔梯度上, 低山区、中山区和亚高山区NDVI均呈上升趋势, 平均年际变化率分别为0.004 1、0.006 6和0.005 7, 中山区NDVI升幅最大; 2)空间尺度上, 23年间太行山区NDVI分布空间异质性明显, 整体呈南高北低、中段高低值交叉分布的特征, NDVI呈增加趋势的面积占94%, 主要集中于中山区和亚高山区; 3)太行山区NDVI受气候因素影响显著, 其中低山区NDVI更易受气温的影响(相关系数为−0.233), 中山区和亚高山区更易受降水量的影响(相关系数为0.369和0.511); 地形因子中, 植被NDVI随坡度的增加而增加, 随海拔的上升先增加后减小; 人为因素中人口密度、人类足迹与植被NDVI变化均呈负相关, 亚高山区受人口密度和人类足迹的影响最小(相关系数分别为−0.036和−0.325); 4)SEM分析表明, 对太行山区全域、低山区、中山区和亚高山区NDVI综合影响最显著的因素分别为坡度(综合效应值为0.52)、人类足迹(−0.36)、坡度(0.58)和降水量(0.52)。此外, 各海拔分区中, 除亚高山区外, 植被NDVI均受人类足迹的直接影响最显著, 亚高山区植被NDVI受降水的直接影响最显著。海拔通过坡度、气温等因素对各海拔分区植被NDVI产生的间接影响最显著。研究结果对明晰气候变化背景下太行山区全域及垂直三分区植被动态变化情况具有重要意义, 为三分区制定针对性生态保护措施提供了理论依据。

     

    Abstract: Under the background of climate change, spatial-temporal pattern of vegetation in Taihang Mountain area has undergone complex changes, which has a far-reaching impact on the coordinated development of Beijing-Tianjin-Hebei region. Based on remote sensing images of vegetation NDVI from 2000 to 2022 in the hilly area (elevation ≤500 m), the middle mountain area (elevation 500~1 500 m), and the subalpine area (elevation >1 500 m) of the Taihang Mountain area, combined with methods such as linear trend analysis and regression analysis, we analyzed the spatial-temporal variation pattern of vegetation in the whole area and the three elevation partitions in the past 23 years and discussed the driving factors of vegetation change. The structural equation model was used to analyze the direct and indirect effects of different factors on the spatial-temporal variation of vegetation NDVI. The results showed that: On the time scale, the NDVI in Taihang Mountain area showed an overall upward trend from 2000 to 2022, with an average annual change rate of 0.005 8; while on the elevation gradient, the NDVI in hilly area, middle mountain area and subalpine area all showed an increasing trend, with average annual change rates of 0.004 1, 0.006 6, and 0.005 7 respectively, and NDVI in middle mountain area increased the most. On the spatial scale, the spatial distribution of NDVI in the Taihang Mountain area had an obvious heterogeneity in the past 23 years, with the overall characteristics of high NDVI in the south and low NDVI in the north, and the cross distribution of high and low NDVI in the middle section, and the vegetation NDVI in 94% of the whole mountain area had increased, primarily concentrated in the middle mountain area and subalpine area. The NDVI in Taihang Mountain area was significantly affected by climate factors, among which the NDVI in hilly area was more easily affected by temperature (correlation coefficient of −0.233), while in the middle mountain area and the subalpine area, NDVI was more affected by precipitation (correlation coefficient of 0.369 and 0.511). Among the topographic factors, NDVI increased with slope and initially increased then decreased with elevation. In terms of human factors, population density, human footprint, and vegetation NDVI variation were all negatively correlated, and the subalpine area was least affected by population density and human footprint (correlation coefficient of −0.036 and −0.325). SEM model analysis showed that the most significant factors affecting NDVI in the whole mountain area, hilly area, middle mountain area and subalpine area were slope (comprehensive effect value of 0.52), the human footprint (−0.36), slope (0.58) and precipitation (0.52) respectively. Additionally, across all elevation partitions, except for the subalpine area, vegetation NDVI is most directly influenced by human footprint. In the subalpine area, vegetation NDVI is most directly influenced by precipitation. Elevation exerts the most significant indirect effects on vegetation NDVI across elevation partitions through factors such as slope and temperature. The research results are of great significance to clarify the dynamic variation of vegetation in Taihang Mountain area and the three elevation partitions under the background of climate change, and provide theoretical basis for developing targeted ecological protection measures in the three elevation partitions.

     

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