Contributions of natural and human factors to increases in vegetation productivity in China

Jingfeng Xiao,Li Zhang,Yu Zhou

doi:10.1890/es14-00394.1

Abstract

Increasing trends in vegetation productivity have been identified for the last three decades for many regions in the northern hemisphere including China. Multiple natural and human factors are possibly responsible for the increases in vegetation productivity, while their relative contributions remain unclear. Here we analyzed the long‐term trends in vegetation productivity in China using the satellite‐derived normalized difference vegetation index (NDVI) and assessed the relationships of NDVI with a suite of natural (air temperature, precipitation, photosynthetically active radiation (PAR), atmospheric carbon dioxide (CO2) concentrations, and nitrogen (N) deposition) and human (afforestation and improved agricultural management practices) factors. Overall, China exhibited an increasing trend in vegetation productivity with an increase of 2.7%. At the provincial scale, eleven provinces exhibited significant increases in vegetation productivity, and the majority of these provinces are located within the northern half of the country. At the national scale, annual air temperature was most closely related to NDVI and explained 36.8% of the variance in NDVI, followed by afforestation (25.5%) and crop yield (15.8%). Altogether, temperature, total forest plantation area, and crop yield explained 78.1% of the variance in vegetation productivity at the national scale, while precipitation, PAR, atmospheric CO2 concentrations, and N deposition made no significant contribution to the increases in vegetation productivity. At the provincial scale, each factor explained a part of the variance in NDVI for some provinces, and the increases in NDVI for many provinces could be attributed to the combined effects of multiple factors. Crop yield and PAR were correlated with NDVI for more provinces than were other factors, indicating that both elevated crop yield resulting from improved agricultural management practices and increasing diffuse radiation were more important than other factors in increasing vegetation productivity at the provincial scale. The relative effects of the natural and human factors on vegetation productivity varied with spatial scale. The true contributions of multiple factors can be obscured by the correlation among these variables, and it is essential to examine the contribution of each factor while controlling for other factors. Future changes in climate and human activities will likely have larger influences on vegetation productivity in China.

Highlights

Many studies on vegetation dynamics are based on the normalized difference vegetation index (NDVI) derived from the advanced very high resolution radiometer (AVHRR) instrument onboard the National Oceanic and Atmospheric Administration (NOAA) satellites
Our results showed that forest plantations were partly responsible for the increases in vegetation productivity inferred from NDVI
Our results show that each factor explained a part of the variance in NDVI for some provinces, and the dynamics of NDVI for some provinces could be attributed to the combined effects of three or more factors

Summary

Introduction

Numerous studies have examined the dynamics of vegetation productivity over the last two to three decades at regional to global scales (Zhou et al 2001, Ichii et al 2002, Xiao and Moody 2004a, 2005, Beck and Goetz 2011, Xiao et al 2013a). Many studies on vegetation dynamics are based on the normalized difference vegetation index (NDVI) derived from the advanced very high resolution radiometer (AVHRR) instrument onboard the National Oceanic and Atmospheric Administration (NOAA) satellites These studies used NDVI as a proxy for vegetation productivity and identified increasing trends in vegetation productivity in many parts of the world, including Eurasia (Jeyaseelan et al 2007), North America (Beck and Goetz 2011), and Australia (Donohue et al 2009) as well as globally (Ichii et al 2002, Xiao and Moody 2005, de Jong et al 2012). Other approaches such as ecosystem models have shown increased vegetation productivity in many regions (Hicke et al 2002, Cao et al 2003, Nemani et al 2003), many of which were in agreement with with the increasing trends of vegetation productivity inferred from NDVI (Hickler et al 2005)

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Conclusion