Spatiotemporal Evolution and Quantitative Attribution of NDVI in the Lesser Khingan Mountains Considering Lag–Cumulative Effects

Abstract

Boreal forest ecosystems across mid-to-high latitudes in the Northern Hemisphere show strong responses to climate change. Vegetation growth is influenced by cumulative climatic effects with time lags, as well as human disturbances. This study selects the Lesser Khingan Mountains as the research area and uses MODIS NDVI data, meteorological records, and land use datasets covering 2001 to 2024. Trend analysis, stability and sustainability evaluation, optimal time window screening for multiple regression, partial correlation analysis, and ridge regression are adopted to examine the spatial and temporal patterns of NDVI changes. This research further explores how vegetation responds to hydrothermal conditions in terms of time-lag and cumulative effects and quantifies the respective contributions from climate and human activities. Results show that vegetation generally improved in the Lesser Khingan Mountains between 2001 and 2024. NDVI presents a spatial pattern of low values in the northwest and high values in the southeast, with an overall increasing rate of 0.0016∙year−1. A total of 92.35% of the study area shows positive vegetation trends. About 92.28% of the region maintains stable vegetation development trajectories. Nevertheless, valley areas in the northwest may shift from vegetation improvement to degradation. Vegetation has stronger temporal memory for precipitation compared with air temperature. The average lag period and cumulative duration for temperature are 0.68 months and 1.29 months, respectively. For precipitation, the average lag reaches 1.34 months, and its cumulative duration is 2.33 months. Distinct lag signatures were detected among different land-cover types. NDVI was significantly positively correlated with temperature over 77.11% of the area, while 63.00% of the region presented significant negative NDVI–precipitation correlations. The absolute contribution magnitudes of anthropogenic activities, temperature, and precipitation were 0.0012∙year−1, 0.0003∙year−1, and −0.0001∙year−1, respectively. This study highlights that incorporating lagged-cumulative climatic impacts substantially reduces attribution bias for vegetation dynamics in boreal forest regions. These findings can support local forest conservation and adaptive forest management under ongoing climate change.