Empirical Evidence for Impacts of Internal Migration on Vegetation Dynamics in China from 1982 to 2000.

Conghe Song,Jackson W Lord,Jingfeng Xiao,Liming Zhou

doi:10.3390/s8085069

Abstract

Migration is one of the major socio-economic characteristics of China since the country adopted the policy of economic reform in late 1970s. Many studies have been dedicated to understand why and how people move, and the consequences of their welfare. The purpose of this study is to investigate the environmental impacts of the large scale movement of population in China. We analyzed the trend in the Normalized Difference Vegetation Index (NDVI) from the Advanced Very High Resolution Radiometer (AVHRR) along with China migration data from the 1 percent national survey during 1982-1987, the 4th national census during 1985-1990 and the 5th national census during1995∼2000. We found that the internal migration in China has a statistically significant negative impact on vegetation growth at the provincial scale from 1982 to 2000 even though the overall vegetation abundance increased in China. The impact from migration (R2=0.47, P=0.0001) on vegetation dynamics is the second strongest as among the factors considered, including changes in annual mean air temperature (R2=0.50, P=0.0001) and annual total precipitation (R2=0.30, P=0.0049) and gross domestic production (R2= 0.25, P=0.0102). The negative statistical relationship between the rate of increase in total migration and the change in vegetation abundance is stronger (R2=0.56, P=0.0000) after controlling for the effects of changes in temperature and precipitation. In-migration dominates the impacts of migration on vegetation dynamics. Therefore, it is important for policy makers in China to take the impacts of migration on vegetation growth into account while making policies aiming at sustainable human-environment relations.

Highlights

Since the adoption of the policy of economic reform in China in late 1970s, a large amount of concealed surplus labor force in the old communal system in the rural area was released (Zhao, 1999; Lu et al, 2005)
Migrant workers often take low-skill labor intensive manufacturing jobs in the cities, more in-migrants are indicative of industrial expansion, which is usually associated with urban sprawl and causes dramatic decrease in Normalized Difference Vegetation Index (NDVI)
A greater deal of urban expansion is associated with in-migration than intra-provincial migration, leading to stronger negative impact on vegetation growth for in-migration compared with intra-provincial migration

Summary

Introduction

Since the adoption of the policy of economic reform in China in late 1970s, a large amount of concealed surplus labor force in the old communal system in the rural area was released (Zhao, 1999; Lu et al, 2005). Current literature on migration in China primarily focused on why and how migrants move from place to place, and the consequences of their welfare (Zhao, 1999; Liang, 2001; Liang and Ma, 2004; Fan, 2005a). The enormous exodus of people from rural areas allows regrowth of vegetation and reduces deforestation; on the other hand, huge rural-to-urban migration provided an almost unlimited labor force for construction and the expansion of manufacturing industry, causing rapid urban sprawl and loss of vegetation (Heilig, 1997). Urban area in China increased percent from 1990 to 2000 based on satellite observations (Liu et al, 2005). Several other recent studies found increased vegetation activity in China

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