Spatio-temporal changes in grassland fractional vegetation cover in Inner Mongolia from 2000 to 2020 and a future forecast

doi:10.11686/cyxb2022370

Abstract

Abstract:

Inner Mongolia is an important green ecological barrier in northern China， and grassland degradation in this region is of great concern. Fractional vegetation cover （FVC） is one of the most direct indicators of grassland ecological status. At present， it is still a challenge to build an accurate FVC estimation model for dynamic analysis of a large region over a long period of time. In this study， we used a large ground survey dataset， MODIS remote sensing data， and meteorological data from 2000 to 2020， and applied the random forest model for FVC partition modeling and prediction. The Sen+Mann-Kendall trend analysis method and Hurst index method were used to analyze the spatio-temporal changes in the FVC and its future trends. The main results were as follows： 1） The precision of each partition of the random forest model was better than that of the whole region， which effectively reduced the impact of spatial heterogeneity. 2） In Inner Mongolia， the grassland FVC generally showed a spatial pattern of being high in the east and low in the west， with obvious spatial differences. 3） In the past 21 years， the FVC of grassland in Inner Mongolia showed a fluctuating upward trend overall， the area of increased FVC was larger than the area of decreased FVC， and the magnitude of the extremely significant increase and significant increase was greater than that of the extremely significant decrease and significant decrease. 4） In the future， the grassland FVC in Inner Mongolia will generally improve. The area of FVC growth is larger than the area of FVC decrease， and the area with extremely significant growth and significant growth accounts for a high proportion （25.9%） of the total area. It is predicted that vegetation growth will develop well in the future.

Key words: Inner Mongolia grassland, fractional vegetation coverage, random forest model, spatio-temporal change, trend forecast

Hui-long ZHANG, Xiu-chun YANG, Dong YANG, Ang CHEN, Min ZHANG. Spatio-temporal changes in grassland fractional vegetation cover in Inner Mongolia from 2000 to 2020 and a future forecast[J]. Acta Prataculturae Sinica, 2023, 32(8): 1-13.

Figures/Tables 8

Fig.1 Grassland type distribution （a）， altitude distribution （b）， survey plots distribution （c） and grassland zoning map （d） in the study area

Table 1 Calculation formula of vegetation index

植被指数Vegetation index	计算公式Formula
归一化植被指数Normalized difference vegetation index （NDVI）	$N D V I = ρ N I R - ρ R e d ρ N I R + ρ R e d$
增强植被指数Enhanced vegetation index （EVI）	$E V I = 2.5 (ρ Ν Ι R - ρ R e d) ρ Ν Ι R + 6.0 ρ R e d - 7.5 ρ B l u e + 1$
差值环境植被指数Difference vegetation index （DVI）	$D V I = ρ N I R - ρ R e d$
比值植被指数Ratio vegetation index （RVI）	$R V I = ρ N I R ρ R e d$
土壤调节植被指数Soil adjusted vegetation index （SAVI）	$S A V I = (1 + L) (ρ N I R - ρ R e d) ρ N I R + ρ R e d + L$

Table 1 Calculation formula of vegetation index

植被指数Vegetation index	计算公式Formula
归一化植被指数Normalized difference vegetation index （NDVI）	$N D V I = ρ N I R - ρ R e d ρ N I R + ρ R e d$
增强植被指数Enhanced vegetation index （EVI）	$E V I = 2.5 (ρ Ν Ι R - ρ R e d) ρ Ν Ι R + 6.0 ρ R e d - 7.5 ρ B l u e + 1$
差值环境植被指数Difference vegetation index （DVI）	$D V I = ρ N I R - ρ R e d$
比值植被指数Ratio vegetation index （RVI）	$R V I = ρ N I R ρ R e d$
土壤调节植被指数Soil adjusted vegetation index （SAVI）	$S A V I = (1 + L) (ρ N I R - ρ R e d) ρ N I R + ρ R e d + L$

Fig.2 Correlation analysis and significance test results of explanatory variables

Table 2 Accuracy evaluation of training set and test set model

分区 Partition	训练集Training set			测试集Test set
分区 Partition	RMSE （%）	R²	MAE （%）	RMSE （%）	R²	MAE （%）
全区All partitions	7.3	0.9	5.6	15.2	0.6	11.8
东部分区Eastern partition	5.8	0.9	4.8	9.2	0.7	7.6
中部分区Central partition	5.8	0.9	4.4	10.5	0.7	8.6
西部分区Western partition	4.1	0.9	3.0	6.8	0.8	5.3

Fig.3 Spatial distribution of average grassland vegetation coverage in Inner Mongolia from 2000 to 2020

Fig.4 Spatial distribution of change rate of grassland vegetation coverage （a）， statistical results of change trend （b） and spatial distribution （c） and annual change of average vegetation coverage （d） in Inner Mongolia from 2000 to 2020

Fig.5 Spatial distribution （a） and segmentation statistical results （b） of Hurst index and future trend spatial distribution （c） and classification statistical results （d） of grassland vegetation coverage in Inner Mongolia during 2000-2020

Fig.6 Annual change of precipitation in the growing season and number of livestock of grassland in Inner Mongolia from 2000 to 2020

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