Driving Factors of Recent Vegetation Changes in Hexi Region, Northwest China Based on a New Classification Framework

Ju Wang,Yaowen Xie,Kunming Guo,Xiaoyun Wang

doi:10.3390/rs12111758

Abstract

Since other factors (soil properties, topography, etc.) under natural conditions are relatively invariant over one or two decades, climate variables (precipitation and temperature) and human activities are the two fundamental factors driving vegetation changes in global or large-scale areas. However, the combined effects of either single climatic factor and human activities on vegetation changes and the role of human activities itself in a specific region has not been fully discussed. In this study, the Hexi region, a typical dryland consisting of three inland river basins in northwest China was selected as a case area. A new classification framework combining Pearson correlation analysis and residual trend approach was proposed to assess their individual and conjoint contributions of climate variables and human activities in areas of significant vegetation changes. Our results indicated that most of vegetation covered areas in the Hexi region experienced significant changes during the period 2001−2017, and vegetation improvements were widespread except the interior of oases; significant changes in vegetation caused by human activities, precipitation, the interactions of precipitation and human activities, temperature, the interactions of temperature and human activities, the interactions of temperature and precipitation, and the interactions of the three factors accounted for 50.46%, 16.39%, 19.90%, 4.33%, 2.32%, 2.11%, and 4.49% of the total change areas, respectively. Generally, the influence of temperature was relatively weaker than that of precipitation, and the contributions of the interactions of climate variables and human activities on vegetation changes were greater than that of climate contributions alone. Moreover, the results of various investigations, according to the trends and the time of vegetation changes, indicate that decreasing trends of the normalized difference vegetation index (NDVI) in the Hexi region were chiefly attributed to the adjustments of agricultural planting structure while the comprehensive treatment programs implemented in river basins supported a large proportion of vegetation improvements.

Highlights

The remarkable change in processes of vegetation in the world, or in different regions of the world over the past decades, have been proved by modern remote sensing [1,2,3,4]
Simple correlation analysis, e.g., Pearson could reveal the relationship between two variables [7,8,9,10]; partial correlation coefficient of each climate factor calculated by controlling other factors, represents the relationship between vegetation changes and the specific climate factor [11,12,13,14,15,16,17]; and multiple correlation analysis is applied to interpret the response of vegetation growth to variations of multiple climate factors [18,19]
In the Hexi region, 88.72% of vegetation covered areas experienced significant changes during 2001−2017, among which 92.32% were positive while 7.67% were negative (Figure 4)

Summary

Introduction

The remarkable change in processes of vegetation in the world, or in different regions of the world over the past decades, have been proved by modern remote sensing [1,2,3,4]. The significant changes in vegetation were mainly attributed to the ease of climate constraints and various human activities for survival and development. Both the two types of driving factors may work individually or simultaneously and the relative role of climate variables and human activities in vegetation changes varies significantly from region to region. Temperature and precipitation are two main climate factors affecting vegetation activities and the inter-annual changes of vegetation in arid and semi-arid regions are more sensitive to the fluctuations of precipitation [8,22,23,24,25]

Objectives

Results

Discussion

Conclusion