Vegetation Greenness Dynamics in the Western Greater Khingan Range of Northeast China Based on Dendrochronology.

Abstract

Simple SummaryThis study reconstructed 193 years of vegetation greenness dynamics in the study area based on the chronology of the tree rings of Pinus sylvestris var. mongolica Litv. in the western Greater Khingan Range, and analyzed the vegetation greenness dynamics pattern accordingly. After the 1950s, it was found that the scale and intensity of extreme changes in the vegetation greenness dynamics increased significantly, and the frequency of occurrence also increased significantly. The study also found that climate (precipitation) is the most important factor influencing the change of vegetation greenness dynamics in the western Greater Khingan Range; the influence of human activities is also important and rapid, and the degree of influence has gradually increased in recent years. Finally, the influence of human activities on the vegetation greenness dynamics was ranked in terms of importance, as follows: livestock > afforestation > population > farmland.Understanding the vegetation greenness dynamics in the forest–steppe transition zone is essential for ecosystem management, and in order to study ecological changes in the region. This study provides a valuable record of the vegetation greenness dynamics in the western Greater Khingan Range over the past 193 years (1826–2018) based on tree-ring data represented by the normalized difference vegetation index (NDVI). The reconstructed vegetation greenness dynamics record contains a total of 32 years of high vegetation greenness and 37 years of low vegetation greenness, together occupying 35.8% of the entire reconstructed period (193 years). Climate (precipitation) is the main influence on the vegetation greenness dynamics at this site, but human activities have also had a significant impact over the last few decades. The magnitude, frequency, and duration of extreme changes in vegetation greenness dynamics have increased significantly, with progressively shorter intervals. Analyses targeting human behavior have shown that the density of livestock, agricultural land area, and total population have gradually increased, encroaching on forests and grasslands and reducing the inter-annual variability. After 2002, the government implemented projects to return farmland to its original ecosystems, and for the implementation of new land management practices (which are more ecologically related); as such, the vegetation conditions began to improve. These findings will help us to understand the relationship between climate change and inter- and intra- annual dynamics in northeastern China, and to better understand the impact of human activities on vegetation greenness dynamics.