Time Series of Landsat Imagery Shows Vegetation Recovery in Two Fragile Karst Watersheds in Southwest China from 1988 to 2016

Jing Geng,Yang Yu,Qing Ying,Xiao-Peng Song,Shiguang Xu,Zheng Niu,Haifeng Tian,Maggi Kelly,Lei Wang,Li Wang,Xiaoyue Wang,Jianhua Cao,Jie Pei,Ni Huang

doi:10.3390/rs11172044

Abstract

Since the implementation of China’s afforestation and conservation projects during recent decades, an increasing number of studies have reported greening trends in the karst regions of southwest China using coarse-resolution satellite imagery, but small-scale changes in the heterogenous landscapes remain largely unknown. Focusing on two typical karst regions in the Nandong and Xiaojiang watersheds in Yunnan province, we processed 2,497 Landsat scenes from 1988 to 2016 using the Google Earth Engine cloud platform and analyzed vegetation trends and associated drivers. We found that both watersheds experienced significant increasing trends in annual fractional vegetation cover, at a rate of 0.0027 year−1 and 0.0020 year−1, respectively. Notably, the greening trends have been intensifying during the conservation period (2001–2016) even under unfavorable climate conditions. Human-induced ecological engineering was the primary factor for the increased greenness. Moreover, vegetation change responded differently to variations in topographic gradients and lithological types. Relatively more vegetation recovery was found in regions with moderate slopes and elevation, and pure limestone, limestone and dolomite interbedded layer as well as impure carbonate rocks than non-karst rocks. Partial correlation analysis of vegetation trends and temperature and precipitation trends suggested that climate change played a minor role in vegetation recovery. Our findings contribute to an improved understanding of the mechanisms behind vegetation changes in karst areas and may provide scientific supports for local afforestation and conservation policies.

Highlights

As a fundamental component of global terrestrial ecosystems, vegetation plays a critical role in global material and energy cycles [1], and has considerable impacts on regulating global carbon balance, mitigating atmospheric CO2 concentration, and maintaining global climate stability [2]
While no trends detected for residuals suggest insignificant human impacts on vegetation changes. We found that both watersheds exhibited a significant increasing trend in annual fractional vegetation cover during the period 1988–2016
Residual analysis and partial correlation indicated that human-induced ecological engineering rather than climate change was the primary driver of the vegetation variations

Summary

Introduction

As a fundamental component of global terrestrial ecosystems, vegetation plays a critical role in global material and energy cycles [1], and has considerable impacts on regulating global carbon balance, mitigating atmospheric CO2 concentration, and maintaining global climate stability [2]. The response of vegetation to global change has attracted extensive attention in the science community over the past decades [3]. Zhu et al [4] revealed a greening trend in Earth’s terrestrial vegetation using three long-term remotely sensed datasets coupled with ten ecosystem models. Piao et al [6] comprehensively detected and attributed the vegetation greening trend in China during the past three decades based on three different remotely sensed Leaf Area Index (LAI) data sets and five different process-based ecosystem models. Song et al [10] analyzed the trends in vegetation change and its relationships with climate change and human activities on the Qinghai-Tibet Plateau from 2000 to 2016 using a growing season integrated enhanced vegetation index (GSIEVI)

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