Tracking Sustainable Restoration in Agro-Pastoral Ecotone of Northwest China

Lixiao Yang,Chansheng He,Stéphanie Horion,Rasmus Fensholt

doi:10.3390/rs13245031

Abstract

Large-scale ecological restoration (ER) projects have been implemented in northwest China in recent decades as a means to prevent desertification and improve ecosystem services. However, previous studies have demonstrated adverse impacts in the form of widespread soil water deficit caused by intensive ER activities. Understanding the role of climate change and ER efforts in vegetation dynamics and soil moisture consumption is essential for sustainable ecosystem management. Here, we used the break for additive season and trend (BFAST) method to analyse spatial patterns in the normalized difference vegetation index (NDVI) variation over the agro-pastoral ecotone of northwest China (APENC) for 2000–2015. From the combined use of generalized additive modelling (GAM) and residual-trend analysis (RESTREND), we distinguished and quantified the effects of climate and human management on vegetation and soil water dynamics. Approximately 78% of the area showed vegetation variations representing a significant change in NDVI, of which more than 68% were categorized as abrupt changes. Large areas of the abrupt change type, interrupted increase and monotonic increase in NDVI were observed before 2006, and small areas of the change type of negative reversals were observed after 2012. Anthropogenic activity was found to be the major driving factor of variation in vegetation (contribution rate of 56%) and soil moisture (contribution rate of 78%). The vegetation expansion, which was mainly related to the large number of ER programs that started in 2000, was found to increase soil moisture depletion. By comparing areas where anthropogenic activities had a high contribution rate to vegetation increase and areas where soil moisture consumption was severely increased, we identify and discuss hotspot areas of soil moisture consumption caused by the ER programs. The current methodological workflow and results represent a novel foundation to inform and support water resource management and ecological-restoration-related policy making.

Highlights

Was the most frequent type of change in normalized difference vegetation index (NDVI), where NDVI was characterized by a period of increase interrupted by a break and followed by a second period of increase
We found a significant positive correlation between evaporative moisture (ER_ET) and dry contribution (DC) (R reached 0.7), which implies that our results estimated at the pixel-level reflect well the change in soil moisture caused by human management
This study provides a novel methodological framework to track non-sustainable restoration characterized by increased soil water deficits as result of large-scale ecological restoration (ER) projects

Summary

Introduction

Studies have shown that vegetation growth in response to ER has been effective in combatting land degradation and desertification [10], increasing biomass [11], promoting carbon sequestration [12], reducing soil loss [12,13] and enhancing the biodiversity in degraded ecosystems [14]. A number of recent studies have shown that ER activities in some cases may lead to high-water consumption by newly planted vegetation, thereby, resulting in enhanced soil water deficits and increased plant water stress [1,15,16,17,18,19,20]. In water limited areas, studies have shown that revegetation of degraded areas can cause severe depletion of soil water resources [15,16,17], defeating the purpose of ER by increasing the problems of land degradation

Methods

Results

Discussion

Conclusion