【目的】中国东北虎豹国家公园是东北地区重要的生态安全屏障,其植被对气候变化较为敏感,且易受人类活动影响。探究该地区植被时空变化及其成因,为园区生态环境科学管理提供依据。【方法】借助GEE(Google earth engine)云平台,基于2001—2020年生长季(4—10月)中分辨率成像光谱仪(MODIS) NDVI数据,辅以数字高程模型(DEM)数据、气象数据、土地利用数据和植被类型数据,采用Sen+Mann-Kendall趋势分析,揭示不同时间尺度下中国东北虎豹国家公园植被时空变化特征;考虑到不同植被类型对气候变化的时滞效应及差异,运用偏相关分析、改进的残差分析与相对作用分析法,量化植被对气候变化和人类活动的响应机制,厘清不同情景下气候变化和人类活动在植被演变过程中的相对作用。【结果】①时间上,20 a来园区生长季归一化植被指数(NDVI)呈速率为0.003 2/a的显著增长趋势(P<0.05),在生长季内的不同季节,NDVI均值依次为夏季>春季>秋季,NDVI增长速率依次为春季>秋季>夏季;空间上,2001—2020年NDVI变化趋势具有明显的季节和区域差异,但总体均为改善区域面积大于退化区域面积,且随生长季内季节循环变化,NDVI改善区域面积先减少后增加,NDVI主要变化趋势类型由明显改善向轻微改善转化。②不同时间尺度下园区NDVI对气候的响应空间异质性明显,但整体上NDVI与气温和降水均呈正相关,且NDVI对气温的响应均强于降水,其中春季和生长季NDVI与气温呈显著正相关的区域面积较大(P<0.05),分别占比83.558%、42.241%,各时间尺度下园区大多数区域NDVI与降水均呈不显著正相关(P≥0.05);不同植被类型NDVI对气温和降水的最大响应滞后期不同,除栽培植被和草甸外,其余植被类型对降水响应的滞后性均强于气温。③人类活动对园区NDVI的影响具有双重效应,其中正向促进与负向干扰NDVI变化的区域分别占比94.087%、5.913%,实施林业工程是NDVI增长的关键,而建设用地扩张是NDVI减少的重要原因。④园区NDVI变化主要受气候变化和人类活动共同驱动,但整体上气候变化对NDVI变化的相对作用均值为32.699%、人类活动的相对作用均值为67.301%,且在NDVI改善及退化区域,人类活动的相对作用均值均大于气候变化。【结论】2001—2020年中国东北虎豹国家公园植被状况总体向好发展,不同时间尺度下植被时空变化趋势存在显著差异。气温是各时间尺度下促进园区植被生长的主导气候因子,气候变化和人类活动对植被变化的影响区域异质性明显,但均以积极作用为主,其中人类活动对园区NDVI变化的贡献度相对更高。建议在园区未来的植被维护中,除提升植被对气候变化的适应能力外,还应更加注重生态修复措施的持续落实,遏制土地资源的过度开发。

【Objective】The northeastern China Tiger and Leopard National Park is an important ecological security barrier in the northeast China, due to sensitivity of the vegetation to climate change and anthropogenic activities. This study aimed to explore the spatiotemporal changes in the vegetation of the region to provide a scientific basis for ecological restoration and improvement in the park management system. 【Method】Based on normalized difference vegetation index(MODIS NDVI) data of the growing season (April to October) from 2001 to 2020, Sen+Mann-Kendall trend analysis along with data supplemented by the Google earth engine(GEE) cloud platform, DEM data, meteorological data, land use data, and vegetation type data were used to reveal the spatiotemporal change characteristics of vegetation in the northeast China Tiger and Leopard National Park at different time scales. This considered the time lag effect of different vegetation types on climate change and their differences, as well as partial correlation analysis. Additionally, improved residual and relative role analyses were conducted to quantify the response mechanisms of the vegetation to climate change and anthropogenic activities, and clarify the relative role of climate change and anthropogenic activities in the evolution of vegetation under different conditions.【Result】 (1) Temporally, the growing season NDVI of the park showed a significant increasing trend at a rate of 0.003 2/a in the past 20 a (P<0.05). In different growing seasons, the order of the mean value and rate of increase of NDVI was summer >spring >autumn and spring >autumn >summer, respectively. Spatially, the NDVI trend showed clear seasonal and regional differences from 2001 to 2020; however, the improved area was larger than the overall degraded area. Since the seasonal cycle changes occurred within the growing season, the NDVI improvement area first decreased and then increased, and the main NDVI trend shifted from ‘significant improvement’ to ‘slight improvement’. (2) The spatial heterogeneity of the NDVI of the park in response to climate at different time scales was clear; however, the NDVI was positively correlated with both air temperature and precipitation, and the response of the NDVI to air temperature was stronger than precipitation. The area with a significant positive correlation between the NDVI and air temperature was larger in spring and growing seasons (P<0.05), accounting for 83.558% and 42.241% respectively, while most areas of the park showed no significant positive correlation between the NDVI and precipitation at each time scale (P≥0.05). Different vegetation types had different time lags for the maximum response of the NDVI to air temperature and precipitation, except for cultivated vegetation and meadows, wherein the response lags of other vegetation types were stronger to precipitation than to air temperature. (3) The impact of anthropogenic activity on the NDVI of the park had dual effects, in which the areas that positively promoted and negatively disturbed the NDVI trend accounted for 94.087% and 5.913%, respectively. The implementation of forestry projects was key for increasing NDVI, while the expansion of construction land was the prime factor for increasing NDVI. (4) The NDVI trend of the park was driven by both climate change and anthropogenic activities, but the mean relative role of climate change and anthropogenic activities on the NDVI trend was 32.699% and 67.301%, respectively. The mean relative role of human activities was greater than that of climate change in both the NDVI improved and degraded areas.【Conclusion】 The vegetation status of the northeast China Tiger and Leopard National Park has been generally improved from 2001 to 2020, with significant differences in spatiotemporal trends of vegetation at different time scales. Air temperature was the dominant climatic factor that promoted vegetation growth in the park at each time scale, and the effects of climate change and anthropogenic activities on vegetation changes varied significantly in terms of geography. However, both were dominated by positive effects, with the contribution of anthropogenic activities to the NDVI changes of the park being relatively higher. It is suggested that in the future, in addition to the park vegetation maintenance, efforts should be made to improve the adaptability of vegetation to climate change, along with ensuring continuous implementation of ecological restoration measures and curbing overexploitation of land resources.