Abstract
Forest ecosystem plays a vital role in the global carbon cycle and maintaining climate stability. However, how net primary productivity (NPP) dynamics of different stand ages of forest respond to climatic change and residual (being other climate factors or human activities) still remain unclear. In this study, firstly, forests are divided into two categories based on their stand age: forests appeared before appeared before the research period (Fold), and forests appeared during the research period (Fnew). Secondly, we improved a quantitative method of basic partial derivatives to disentangle the relative contributions of climatic factors, other climate factors, and human activities to the NPP of Fold and Fnew. Then, different scenarios were simulated to identify the dominant drivers for forest restoration and degradation. In this study, we hypothesized the residual of Fold was other climate factors rather than human activities. Our results revealed that from 2000 to 2019, Fold and Fnew of NPP in Yangtze River Basin showed a significant increment trend and precipitation was the major positive contributor among all of the climatic factors. We found that, in Fold, climate change and other climate factors contributed 9.77% and 28.33%, respectively, in explaining NPP. This finding unsupported our initial hypothesis and implied that residuals should be human activities for Fold. Furthermore, we found that human activities dominate either restoration or degradation of Fnew. This result may be due to the attenuated human disturbances and strengthened forest management, such as ecological policies, forest tending, closing the land for reforestation, etc. Therefore, based on disentangling the two types of factors, we concluded that human activities govern the forest change, and imply that the environment-friendly forest managements may favorite to improving the forest NPP against the impacts of climate change. Thus, effective measures and policies are suggested implement in controlling forest degradation in facing climate change.
Highlights
The terrestrial ecosystem plays a vital role in sequestering carbon
net primary productivity (NPP) dynamic is the function of climate factors and other variables such as ecological projects, winds, natural disaster, etc.; the contribution of each factor to the interannual variation rate of NPP can be estimated for each pixel using Equation (2)
We employed NPP as an evaluation indicator for forest restoration and degradation, and a quantitative method of basic partial derivatives was improved by separating Fold and Fnew for the relative contributions of climate change and human activities to NPP variations in Yangtze River Basin (YRB)
Summary
The terrestrial ecosystem plays a vital role in sequestering carbon. As an important part of the terrestrial ecosystem, forests cover about 31% of the earth’s surface area (4.06 billion ha) [1], and they have irreplaceable values for their ability to manage biodiversity, store carbon, and provide other ecosystem services [2]. The residual trend method is to construct an NDVI-climate model, to predict NDVI which is considered undisturbed by human activities [12,16] This method is primarily applicable to these regions that precipitation is the main restrictive factor for vegetation growth such as arid and semi-arid climate zones [17]. There exists a knowledge gap to deal with residuals when we study the causes of forest changes Against this background, in this study, the quantitative method based on the partial derivative was applied to evaluate the relative contribution of climatic factors, other climate factors, and human activities to forest net primary productivity in the Yangtze River Basin (YRB).
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