Study of spatio-temporal variation in fractional vegetation cover and its influencing factors in Xinjiang, China

doi:10.17521/cjpe.2022.0397

Abstract

Abstract:

Aims As the core area of the ecological security barrier in northwest China, Xinjiang has been highly concerned for the spatial variations in its ecological environment status and quality and their driving mechanisms.

Methods Based on the MODIS surface albedo data set (MOD09 A1) from 2003 to 2020, this study uses the advanced three-band gradient difference vegetation index (advanced TGDVI) to obtain the fractional vegetation cover (FVC), and uses multiple statistical methods, such as linear regression, partial correlation analysis, Tukey-test to analyze the spatio-temporal variation of FVC and to quantify the contribution of temperature, precipitation, and groundwater storage (GWS) to FVC in Xinjiang.

Important findings (1) In the past 18 years, the average FVC of Xinjiang has increased from 20.08% to 21.76%, showing an increasing trend as a whole, with a growth rate of 0.19%∙a^-1, and a rapid growth stage is found after 2008. Among them, cropland has the largest growth rate (0.66%∙a^-1), and sparse grassland has the slowest growth rate (0.11%∙a^-1). (2) Temperature is an important factor affecting FVC in the whole growing season in Xinjiang. The influence of temperature on FVC is mainly concentrated in spring and autumn, while precipitation and GWS are the main factors in summer. (3) In summer, GWS is the main factor affecting FVC of shrubland and cropland, precipitation has the greatest impact on FVC of grassland, and GWS has a greater impact on FVC of sparse grassland in summer. (4) With the hydrothermal conditions becoming wetter, the influence of temperature on FVC in Xinjiang gradually decreases, while the influence of precipitation increases. The influence of GWS on FVC increased from arid to semi-arid condition, and then it decreased from semi-arid to humid condition. The results of this study could provide theoretical foundation for ecological restoration and construction in Xinjiang, and have great significance for promoting the construction of ecological civilization and green sustainable development in Xinjiang.

Key words: fractional vegetation cover, advanced three-band gradient difference vegetation index, partial correlation analysis, spatio-temporal variation, arid land, Xinjiang

WU Han, BAI Jie, LI Jun-Li, Guli JIAPAER, BAO An-Ming. Study of spatio-temporal variation in fractional vegetation cover and its influencing factors in Xinjiang, China[J]. Chin J Plant Ecol, 2024, 48(1): 41-55.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2022.0397

https://www.plant-ecology.com/EN/Y2024/V48/I1/41

Figures/Tables 12

Table 1 Main land use types in Xinjiang and their main components

土地利用类型 Land use type	主要组成 Main components
林地 Forestland	常绿针叶林 Evergreen coniferous forest
	落叶阔叶林 Deciduous broadleaf forest
	落叶针叶林 Deciduous coniferous forest
	乔木园地 Tree orchard
	乔木绿地 Tree garden
	稀疏林 Sparse forest
灌丛 Shrubland	落叶阔叶灌木林 Deciduous broadleaf shrub forest
	常绿针叶灌木林 Evergreen coniferous shrub forest
	灌木园地 Shrub orchard
	灌木绿地 Shrub garden
	稀疏灌木林 Sparse shrub forest
草地 Grassland	草甸 Meadow
	草原 Steppe
	草本绿地 Lawn
稀疏草地 Sparse grassland	稀疏草地 Sparse grassland
耕地 Cropland	旱地 Dry farmland
耕地 Cropland	水田 Paddy field
水体 Waterbody	河流 River
	湖泊 Lake
	水库/坑塘 Reservoir/pond
	运河/水渠 Canal/channel
冰川 Glacier	冰川/永久积雪 Permanent ice/snow
人工地表 Built-up land	采矿场 Mining field
	工业用地 Industrial field
	交通用地 Transportation field
	居住地 Settlement
裸地 Bare land	裸土 Bare soil
	裸岩 Bare rock
	沙漠/沙地 Desert
	盐碱地 Salina

Fig. 1 Distribution of land-use in Xinjiang.

Fig. 2 Comparison of fractional vegetation cover between observed data and modelled data. RMSE, root mean square error.

Fig. 3 Spatio-temporal variation of fractional vegetation cover (FVC) in the vegetation covered area of Xinjiang from 2003 to 2020. Green pixels represent the increasing area of FVC, red pixels represent the decreasing area of FVC, and * represent the trend has passed the significance test of p < 0.05. NA, no vegetation covered area or area that fails the significance test.

Fig. 4 Fractional vegetation cover (FVC) variation of grassland (A), sparse grassland (B), shrubland (C) and cropland (D) in Xinjiang from 2003 to 2020.

Fig. 5 Partial correlation coefficient between fractional vegetation cover and temperature (A), precipitation (B) and groundwater storage (C) in the vegetation covered area of Xinjiang from 2003 to 2020. * represent the trend has passed the significance test of p < 0.05. NA, no vegetation covered area or area that fails the significance test.

Fig. 6 Spatial distribution and proportion of main influencing factors of fractional vegetation cover change in different periods of Xinjiang from 2003 to 2020. A, E, Growing season (Apr. to Oct.). B, F, Spring (Apr. to May). C, G, Summer (June to Aug.). D, H, Autumn (Sept. to Oct.). The colored area represents that the absolute value of partial correlation coefficient between one type of influencing factor and fractional vegetation cover is greater than 0.5. GWS, groundwater storage; MIX, no dominant influencing factor (that is, the absolute value of partial correlation coefficient is less than 0.5); NA, no vegetation covered area or area that fails the significance test; PRE, precipitation; TMP, temperature.

Fig. 7 Proportion of main influencing factors of changes in fractional vegetation cover of vegetation types in Xinjiang from 2003 to 2020. A, Growing season (Apr. to Oct.). B, Spring (Apr. to May). C, Summer (June to Aug.). D, Autumn (Sept. to Oct.). GWS, underground water reserves; MIX, no dominant impact factors; PRE, precipitation; TMP, temperature.

Fig. 8 Absolute mean value of partial correlation coefficient (R) between environmental factors and fractional vegetation cover (FVC) in spring, summer and autumn of Xinjiang from 2003 to 2020 (mean ± SD). A, Temperature (TMP). B, Precipitation (PRE). C, Groundwater storage (GWS). Different lowercase letters indicate significant differences between different land use types (p < 0.05).

Fig. 9 Relationship between mean annual precipitation and the influence of precipitation on fractional vegetation cover (FVC) of grassland (A), sparse grassland (B), shrubland (C) and cropland (D) in Xinjiang from 2003 to 2020. RFVC-PRE, the partial correlation coefficient between FVC and precipitation.

Fig. 10 Relationship between fractional vegetation cover (FVC) influencing factors of main vegetation types in Xinjiang and aridity index from 2003 to 2020 (mean ± SD). A, Temperature. B, Precipitation. C, Groundwater storage. RFVC-TMP, RFVC-PRE and RFVC-GWS represent the partial correlation coefficient between fractional vegetation cover and temperature, precipitation and groundwater storage, respectively. The black curve represents the fitting results of three vegetation types (grassland, shrubland, cropland), and the red curve represents the fitting results of four vegetation types (grassland, sparse grassland, shrubland, cropland).

Fig. 11 Trends of agricultural planting and management in Xinjiang from 2003 to 2019.

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