Abstract
Net primary productivity (NPP) is the total amount of organic matter fixed by plants from the atmosphere through photosynthesis and is susceptible to the influences of climate change and human activities. In this study, we employed actual NPP (ANPP), potential NPP (PNPP), and human activity-induced NPP (HNPP) based on the Hurst exponent and statistical analysis to analyze the characteristics of vegetation productivity dynamics and to evaluate the effects of climate and human factors on vegetation productivity in Northeast China (NEC). The increasing trends in ANPP, PNPP, and HNPP accounted for 81.62%, 94.90%, and 89.63% of the total area, respectively, and ANPP in 68.64% of the total area will continue to increase in the future. Climate change played a leading role in vegetation productivity dynamics, which promoted an increase in ANPP in 71.55% of the area, and precipitation was the key climate factor affecting ANPP. The aggravation of human activities, such as increased livestock numbers and intensified agricultural activities, resulted in a decrease in ANPP in the western grasslands, northern Greater Khingan Mountains, and eastern Songnen Plain. In particular, human activities led to a decrease in ANPP in 53.84% of deciduous needleleaf forests. The impact of climate change and human activities varied significantly under different topography, and the percentage of the ANPP increase due to climate change decreased from 71.13% to 53.9% from plains to urgent slopes; however, the percentage of ANPP increase due to human activities increased from 3.44% to 21.74%, and the effect of human activities on the increase of ANPP was more obvious with increasing slope. At different altitudes, the difference in the effect of these two factors was not significant. The results are significant for understanding the factors influencing the vegetation productivity dynamics in NEC and can provide a reference for governments to implement projects to improve the ecosystem.
Highlights
Over the past few decades, global average temperatures have risen by approximately0.74 ◦ C, and heavy precipitation events will continue to increase in the future [1]
The results indicate that the actual NPP (ANPP) in 72.23% of Northeast China (NEC) will increase, and the ANPP of different vegetation types is dominated by a future increase
Our results showed that the region with an increase in ANPP caused by human activities was mainly distributed in the Changbai Mountains in the southern NEC area (Figure 6), where the slope is steep (Figure 1b)
Summary
Over the past few decades, global average temperatures have risen by approximately0.74 ◦ C, and heavy precipitation events will continue to increase in the future [1]. Global climate change has led to significant changes in vegetation respiration, photosynthesis, and the biosphere carbon cycle, which affect ecosystem productivity [2]. A series of human activities, such as the rapid growth of population and increased industrialization, Remote Sens. Evaluating the influences of climate and human factors on ecosystems has great significance for maintaining the sustainable development of ecosystems [5]. Vegetation is an important part of ecosystems; it plays a key role in regulating ecosystem carbon balance and has the characteristics of adapting to the surface environment and reflecting human activities [4,7]. Vegetation growth status and surface coverage have undergone dramatic changes in China, and climate and human factors are the main driving forces of vegetation change [8,9]. Because of the continuous development of remote sensing technology, large-area observations and remote sensing analyses of vegetation have become more effective and less costly than human observations [10], and it is easier to obtain remote sensing data to study dynamic trends in vegetation [11,12,13]
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