Analysis of spatial and temporal variation in grassland vegetation cover in Xinjiang section of Tianshan Mountains and the driving factors from 2001 to 2020

doi:10.17521/cjpe.2023.0155

Abstract

Abstract:

Aims This study primarily aims to investigate the spatiotemporal evolution patterns of fractional vegetation cover (FVC) in the grasslands of Xinjiang section of Tianshan Mountains over the period 2001 to 2020. It seeks to elucidate the determinants of these patterns, emphasizing the influence of vegetation types, livestock farming practices, precipitation levels, and mean annual air temperature. Ultimately, the goal is to contribute important insights that will inform decisions concerning the sustainable management and ecological conservation of these grasslands.

Methods The investigation into the spatiotemporal evolution patterns of vegetation in Xinjiang section of Tianshan Mountains and the factors influencing these patterns leveraged MODIS NDVI remote sensing data spanning two decades. A suite of analytical techniques, including Senʼs Slope Estimator + Mann-Kendall trend analysis, coefficients of variation, and land-use dynamics assessments, were employed to analyze the spatiotemporal variations in grassland FVC.

Important findings The study revealed a general stability in FVC, with the multi-year average varying between 0.33 and 0.42. Notable FVC increases were observed in the northeastern and southwestern low-altitude areas of the range, comprising 3.14% of the analysis area. In contrast, significant FVC declines were predominantly in the Ili River Basin, representing 15.81% of the area studied. The dynamics of grassland FVC were primarily driven by vegetation types and the total value of livestock farming output, each influencing over 29.85% of the variation. When considering the interaction with precipitation and mean annual air temperature, the influence of these factors on FVC increased to above 48.70%. Furthermore, a positive association between FVC and both annual precipitation and average annual temperature was noted, with areas displaying a correlation to precipitation covering 80.84% of the total area, largely encircling the basins flanking Tianshan Mountains range. Meanwhile, a correlation with mean annual air temperature spanned 71.69% of the area, predominantly at higher elevations. These findings offer valuable reference data to support strategic planning for the sustainable use and protection of grassland ecosystems in the Tianshan Mountainous region.

Key words: fractional vegetation cover, climate change, grassland, spatial and temporal variation, Xinjiang section of Tianshan Mountains

CHEN Yi-Heng, Yusufujiang RUSULI, Abdureheman WUSIMAN. Analysis of spatial and temporal variation in grassland vegetation cover in Xinjiang section of Tianshan Mountains and the driving factors from 2001 to 2020[J]. Chin J Plant Ecol, 2024, 48(5): 561-576.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2023.0155

https://www.plant-ecology.com/EN/Y2024/V48/I5/561

Figures/Tables 15

Fig. 1 Average annual grassland fractional vegetation cover (FVC) in Xinjiang section of Tianshan Mountains (A), unmanned aerial vehicle (UAV) remote sensing image of Bosten Lake area (B), and UAV remote sensing image of river basins in the middle section of the northen slope of Tianshan Mountains side (C). ENT, river basins in the eastern section of the northern slope of Tianshan Mountains; MNT, river basins in the middle section of the northern slope of Tianshan Mountains.

Table 1 Natural and anthropogenic factors affecting grassland vegetation cover

类别 Category			空间分辨率 Spatial resolution	数据来源 Data sources
自然因素 Natural factor	X1	高程 Digital elevation model	30 m	https://www.gscloud.cn/
	X2	坡度 Slope	30 m	https://www.gscloud.cn/
	X3	坡向 Aspect	30 m	https://www.gscloud.cn/
	X4	地形 Topography	1 km	https://www.resdc.cn/
	X5	年降水量 Mean annual precipitation	1 km	http://www.geodata.cn/
	X6	年平均气温 Mean annual air temperature	1 km	http://www.geodata.cn/
	X7	土壤类型 Soil type	1 km	https://www.resdc.cn/
	X8	植被类型 Vegetation type	1 km	https://Ipdaac.usgs.gov/
	X9	土地利用 Land use and land cover change	30 m	http://www.geodata.cn/
人为因素 Human factor	X10	畜牧业生产总值 Gross livestock production	1 km	http://www.gisrs.cn/
	X11	家畜存栏数 Livestock stock	1 km	https://www.fao.org/
	X12	人口密度 Population density	1 km	https://landscan.ornl.gov/

Table 2 Factor relationships in interaction detection

判断准则 Judgement criteria	交互作用类型 Type of interaction
P(Xi∩Xj) < min[P(Xi), P(Xj)]	非线性减弱 Nonlinear weakening
min[P(Xi), P(Xj)] < P(Xi∩Xj) < max[P(Xi), P(Xj)]	线性减弱 linear weakening
P(Xi∩Xj) > max[P(Xi), P(Xj)]	线性增强 linear enhancement
P(Xi∩Xj) > P(Xi) + P(Xj)	独立 Independent
P(Xi∩Xj) = P(Xi) + P(Xj)	非线性增强 Nonlinear enhancement

Fig. 2 Accuracy inversion model validation diagram. FVC, fractional vegetation cover.

Table 3 Area statistics of grassland fractional vegetation cover (FVC) from 2001 to 2020 in Xinjiang section of Tianshan Mountains

覆盖度等级 FVC class	面积 Area (×10⁴ km²)					百分比 Percentage (%)					土地利用动态度 LUCC dynamic (K, %)
覆盖度等级 FVC class	2001	2005	2010	2015	2020	2001	2005	2010	2015	2020	2001-2020
极低 Lowest	8.16	6.44	5.66	5.91	6.03	31.99	25.25	22.20	23.19	23.63	-1.31
较低 Lower	8.47	8.78	8.13	7.79	7.43	33.22	34.44	31.88	30.56	29.11	-0.61
中等 Medium	5.40	6.44	6.91	7.10	6.79	21.18	25.27	27.11	27.85	26.63	1.28
较高 Higher	3.11	3.44	4.45	4.51	5.09	12.20	13.50	17.48	17.67	19.95	3.17
极高 Highest	0.35	0.39	0.33	0.18	0.16	1.41	1.54	1.33	0.73	0.64	-2.69

Fig. 3 Spatial and temporal variation (A) and trend significance (B) of grassland fractional vegetation cover (FVC) in Xinjiang section of Tianshan Mountains. ENT, river basins in the eastern section of the northern slope of Tianshan Mountains; MNT, river basins in the middle section of the northern slope of Tianshan Mountains.

Fig. 4 Yearly trend of grassland fractional vegetation cover (FVC) of different classes in Xinjiang section of Tianshan Mountains from 2001 to 2020.

Table 4 Grassland fractional vegetation cover (FVC) variation coefficient classification in Xinjiang section of Tianshan Mountains

变异程度 Variation	面积 Area (×10⁴ km²)				百分比 Percentage (%)
变异程度 Variation	2001-2005	2006-2010	2011-2015	2016-2020	2001-2005	2006-2010	2011-2015	2016-2020
极不显著 Highly insignificant	4.47	5.29	5.18	5.07	27.36	32.40	31.71	31.09
不显著 Insignificant	5.47	5.39	5.58	4.58	33.53	33.00	34.20	28.08
适中 Intermediate	3.40	2.97	3.25	3.02	20.81	18.22	19.89	18.53
显著 Significant	1.44	1.32	1.25	1.63	8.84	8.10	7.64	9.97
极显著 Highly significant	1.54	1.35	1.07	2.01	9.46	8.29	6.56	12.33

Fig. 5 Spatial and temporal distribution of degrades of coefficients of variation of grassland fractional vegetation cover (FVC) in Xinjiang section of the Tianshan Mountains from 2001 to 2020. ENT, river basins in the eastern section of the northern slope of Tianshan Mountains; MNT, river basins in the middle section of the northern slope of Tianshan Mountains.

Fig. 6 Optimal discretization of the drivers of spatial variation in grassland fractional vegetation cover in Xinjiang section of the Tianshan Mountains.

Fig. 7 Detection of spatial differentiation factors of fractional vegetation cover of grasslands in Xinjiang section of Tianshan Mountains.

Fig. 8 Detection of spatial variation drivers of grassland fractional vegetation cover in the middle part of Xinjiang section of Tianshan Mountains. X1-X10, names of driving factors, see Table 1 for details. Circle size indicates interaction force magnitude, and the number in the circle indicates the impact value (q) of the interaction force.

Fig. 9 Annual variation of fractional vegetation cover (FVC) and mean annual air temperature (A) and mean annual precipitation (B) in Xinjiang section of Tianshan Mountains grasslands from 2001 to 2020.

Fig. 10 Multi-year averages of mean annual air temperature and annual precipitation (A, C) and rates of change of temperature and precipitation (B, D) in Xinjiang section of Tianshan Mountains from 2001 to 2020. ENT, river basins in the eastern section of the northern slope of Tianshan Mountains; MNT, river basins in the middle section of the northern slope of Tianshan Mountains.

Fig. 11 Correlation of fractional vegetation cover (FVC) with temperature (A) and precipitation (B) in the same period in Xinjiang section of the Tianshan Mountains grasslands from 2001 to 2020. ENT, river basins in the eastern section of the northern slope of Tianshan Mountains; MNT, river basins in the middle section of the northern slope of Tianshan Mountains.

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