Integrating Spatial Continuous Wavelet Transform and Normalized Difference Vegetation Index to Map the Agro-Pastoral Transitional Zone in Northern China

Yinan Han,Qi Mao,Zhiqiang Zhao,Jeroen Meersmans,Yanxu Liu,Jian Peng

doi:10.3390/rs10121928

Yinan Han, Qi Mao + Show 4 more

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https://doi.org/10.3390/rs10121928

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Abstract

The agro-pastoral transitional zone (APTZ) in Northern China is one of the most important ecological barriers of the world. The commonly-used method to identify the spatial distribution of ATPZ is to apply a threshold rule on climatic or land use indicators. This approach is highly subjective, and the quantity standards vary among the studies. In this study, we adopted the spatial continuous wavelet transform (SCWT) technique to detect the spatial fluctuation in normalized difference vegetation index (NDVI) sequences, and as such identify the APTZ. To carry out this analysis, the Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI 1-month data (MODND1M) covering the period 2006–2015 were used. Based on the spatial variation in NDVI, we identified two sub-regions within the APTZ. The temporal change of APTZ showed that although vegetation spatial pattern changed annually, certain areas appeared to be stable, while others showed higher sensitivity to environmental variance. Through correlation analysis between the dynamics of APTZ and precipitation, we found that the mean center of the APTZ moved toward the southeast during dry years and toward the northwest during humid years. By comparing the APTZ spatial pattern obtained in the present study with the outcome following the traditional approach based on mean annual precipitation data, it can be concluded that our study provides a reliable basis to advance the methodological framework to identify accurately transitional zones. The identification framework is of high importance to support decision-making in land use management in Northern China as well as other similar regions around the world.

Highlights

An ecological boundary is defined as a complex zone between two contrasting habitat patches [1]
Under the current influences of climate change and human disturbance, the ecosystems in an ecological boundary are more sensitive than those in the surrounding areas because the adaptation of species within these areas may be at their limit and the species may respond gravely when subjected to environmental change [4]
The current techniques for identifying the agro-pastoral transitional zone (APTZ) are largely dependent on the subjective judgment of experts; the accuracy of APTZ identification varies among studies

Summary

Introduction

An ecological boundary is defined as a complex zone between two contrasting habitat patches [1]. The landscape within and nearby an ecological boundary presents a remarkable discontinuity compared with the surrounding areas, which embody both landscape features and structures. This discontinuity is caused by large scale changes in environmental factors, which are a range of significant exogenous forces with either natural or anthropogenic characteristics [3]. An ecological boundary is known as an important object in ecological research, planning and management. Detecting the location of an ecological boundary and characterizing its spatial pattern provide an important basis for the further researches [5]

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