Abstract
The subtropical vegetation plays an important role in maintaining the structure and function of global ecosystems, and its contribution to the global carbon balance are receiving increasing attention. The fractional vegetation cover (FVC) as an important indicator for monitoring environment change, is widely used to analyze the spatiotemporal pattern of regional and even global vegetation. China is an important distribution area of subtropical vegetation. Therefore, we first used the dimidiate pixel model to extract the subtropical FVC of China during 2001–2018 based on MODIS land surface reflectance data, and then used the linear regression analysis and the variation coefficient to explore its spatiotemporal variations characteristics. Finally, the partial correlation analysis and the partial derivative model were used to analyze the influences and contributions of climate factors on FVC, respectively. The results showed that (1) the subtropical FVC had obvious spatiotemporal heterogeneity; the FVC high-coverage and medium-coverage zones were concentratedly and their combined area accounted for more than 70% of the total study area. (2) The interannual variation in the average subtropical FVC from 2001 to 2018 showed a significant growth trend. (3) In 76.28% of the study area, the regional FVC showed an increasing trend, and the remaining regional FVC showed a decreasing trend. However, the overall fluctuations in the FVC (increasing or decreasing) in the region were relatively stable. (4) The influences of climate factors to the FVC exhibited obvious spatial differences. More than half of all pixels exhibited the influence of the average annual minimum temperature and the annual precipitation had positive on FVC, while the average annual maximum temperature had negative on FVC. (5) The contributions of climate changes to FVC had obvious heterogeneity, and the average annual minimum temperature was the main contribution factor affecting the dynamic variations of FVC.
Highlights
The fractional vegetation cover (FVC) refers to the ratio of the vertical projection area of vegetation on the ground to the entire study area [1,2]; it is an important parameter reflecting the growth and distribution characteristics of surface vegetation [3] and an important basic data describing the condition of the ecosystem [4]
We found that the normalized difference vegetation index (NDVI) values of each year in the subtropical region approximately obeys the normal distribution
The areal ratios of the FVC high-coverage zone, medium-coverage zone, low-tomedium-coverage zone, low-coverage zone, and bare-land zone from 2001 to 2018 in the subtropical region are shown in Figure 3; combining Figure 3 with Figure 2 highlights that the temporal and spatial evolution characteristics of the FVC levels were significantly different, as follows: (1)
Summary
The fractional vegetation cover (FVC) refers to the ratio of the vertical projection area of vegetation (including leaves, stems and branches) on the ground to the entire study area [1,2]; it is an important parameter reflecting the growth and distribution characteristics of surface vegetation [3] and an important basic data describing the condition of the ecosystem [4]. Climate change has triggered a series of global-scale environmental problems, such as global warming, ecosystem degradation, and desertification, which have had a great impact on the growth, distribution, and succession patterns of vegetation [8,9,10] and are a major challenge to global sustainable development [11,12]. The total amount of net ecosystem productivity (NEP) in subtropical forests in the East Asian monsoon region is approximately 720 million tons of carbon per year, accounting for approximately 8% of the global NEP; this statistic challenges the traditional belief that temperate forests in Europe and America are the main carbon sink functional areas in the past [13,14,15]. Studying and analyzing the characteristics of the temporal and spatial dynamic variations in FVC in this subtropical region and exploring the correlations between FVC and climate factors are of great scientific significance for revealing the temporal and spatial evolution patterns of subtropical vegetation in China and evaluating the ability of vegetation to adapt and respond to climate change
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