Nonlinear Variations of Net Primary Productivity and Its Relationship with Climate and Vegetation Phenology, China

Jian Yang,Xin Zhang,Xi Yu,Zhao Luo

doi:10.3390/f8100361

Abstract

Net primary productivity (NPP) is an important component of the terrestrial carbon cycle. In this study, NPP was estimated based on two models and Moderate Resolution Imaging Spaectroradiometer (MODIS) data. The spatiotemporal patterns of NPP and the correlations with climate factors and vegetation phenology were then analyzed. Our results showed that NPP derived from MODIS performed well in China. Spatially, NPP decreased from the southeast toward the northwest. Temporally, NPP showed a nonlinear increasing trend at a national scale, but the magnitude became slow after 2004. At a regional scale, NPP in Northern China and the Tibetan Plateau showed a nonlinear increasing trend, while the NPP decreased in most areas of Southern China. The decreases in NPP were more than offset by the increases. At the biome level, all vegetation types displayed an increasing trend, except for shrub and evergreen broad forests (EBF). Moreover, a turning point year occurred for all vegetation types, except for EBF. Generally, climatic factors and Length of Season were all positively correlated with the NPP, while the relationships were much more diverse at a regional level. The direct effect of solar radiation on the NPP was larger (0.31) than precipitation (0.25) and temperature (0.07). Our results indicated that China could mitigate climate warming at a regional and/or global scale to some extent during the time period of 2001–2014.

Highlights

Net primary productivity (NPP) is the net amount of carbon accumulated by plants in a given period, and has been regarded as one of the main components of the carbon cycle [1]
The root mean square error (RMSE) and mean absolute error (MAE) deceased to 0.19 kg C m−2 a−1 and 0.14 kg C m−2 a−1, respectively for the Moderate Resolution Imaging Spaectroradiometer (MODIS) NPP data compared to 0.29 kg C m−2 a−1 and 0.23 kg C m−2 a−1 for the Miami model, as well as 0.31 kg C m−2 a−1 and 0.26 kg C m−2 a−1 for the Thornthwaite Memorial model, respectively
The results demonstrated that the NPP derived from MODIS had an improved performance of NPP

Summary

Introduction

Net primary productivity (NPP) is the net amount of carbon accumulated by plants in a given period, and has been regarded as one of the main components of the carbon cycle [1]. Due to a variety of direct and/or indirect anthropogenic activities (e.g., land clearing and conversion) and nature disturbances (e.g., fire, pests) as well as global and regional climate change, forested ecosystems have undergone substantial changes in cover and have increasingly shown declines in health over recent decades [2,3]. As a sensitive indicator of forest cover, function and health, NPP loss may affect the composition of the atmosphere, fresh water availability, biodiversity [4,5], and the ecological adjusting mechanism of energy supply and distribution [6]. Many studies have been undertaken on the spatiotemporal variation of NPP and its relationship with climate factors on global and regional scales using a range of approaches from observational [2,8,9] to a suite of remote sensing based methods [10,11]. Moderate Resolution Imaging Spaectroradiometer (MODIS) annual NPP products have been

Methods

Results

Discussion

Conclusion