Identification of key factors and construction of a rapid diagnostic indicator system for evaluation of grassland degradation in Hulun Buir meadow grasslands

doi:10.17521/cjpe.2024.0152

Abstract

Abstract:

Aims China harbors extensive grassland resources, yet nearly 70% of these grasslands are afflicted by varying degrees of degradation under the combined pressure of climate change and human activities. Pinpointing the pivotal factors driving grassland degradation and establishing a rapid diagnostic system is imperative for precise condition assessments.

Methods This study was conducted in the Hulun Buir meadow steppe of Nei Mongol. The selected sites were categorized into four degradation levels: non-degraded, lightly degraded, moderately degraded, and heavily degraded. Vegetation and soil indicators were collected. Leveraging the random forests algorithm, degradation indicators were screened and weighted, with efforts made to reconcile ecosystem service priorities between the government and pastoralists.

Important findings This study identified ten key factors characterizing degradation, including aboveground biomass, proportion of high-quality forage, community height, litter biomass, species richness, leaf dry matter content, leaf thickness, soil density, soil water content and soil inorganic water content. These indicators encapsulate diverse ecosystem services, including forage supply, erosion control, biodiversity conservation, vegetation resilience, and water and nutrient regulation. Using non-degraded sites as a benchmark, a degradation index (DI) for the meadow steppes of Nei Mongol was developed, accompanied by delineated DI thresholds for different degradation levels. This study provides foundational data to support judicious selection of indicators for both national and regional standards.

Key words: grassland degradation, ecosystem services, random forests algorithm, degradation indicator

XU Meng-Zhen, LU Zheng-Kuan, TAN Xing-Ru, WANG Yan-Bing, SU Tian-Cheng, DOU Shan-De, PAN Qing-Min, CHEN Shi-Ping. Identification of key factors and construction of a rapid diagnostic indicator system for evaluation of grassland degradation in Hulun Buir meadow grasslands[J]. Chin J Plant Ecol, 2025, 49(1): 42-58.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2024.0152

https://www.plant-ecology.com/EN/Y2025/V49/I1/42

Figures/Tables 10

Table 1 Description of research site in the Hulun Buir meadow degradation steppe

序列 Sequence	群落类型 Community type	经度 Longitude (E)	纬度 Latitude (N)	海拔 Altitude (m)
1	狼针草群落 Stipa baicalensis community	120.12°	49.35°	672
2	狼针草群落 Stipa baicalensis community	119.67°	48.49°	756
3	羊草群落 Leymus chinensis community	119.39°	50.17°	528
4	羊草群落 Leymus chinensis community	120.05°	49.33°	630
5	羊草群落 Leymus chinensis community	120.03°	49.37°	637
6	羊草群落 Leymus chinensis community	120.15°	49.44°	687
7	线叶菊群落 Filifolium sibiricum community	120.73°	49.68°	867
8	线叶菊群落 Filifolium sibiricum community	119.35°	50.62°	592
9	线叶菊群落 Filifolium sibiricum community	120.03°	49.52°	817

Table 2 Ecosystem services and their corresponding indicators

类型 Type	生态系统服务 Ecosystem service	指标名称 Indicator name
调节 Regulating	水分调节 Water regulation	土壤密度 Soil density
		土壤含水量 Soil water content
		田间持水能力 Field water holding capacity
	气候调节 Climate regulation	地下生物量 Belowground biomass
		植物群落碳含量 Plant community carbon content
		叶片碳含量 Leaf carbon content
	土壤肥力的维持 Maintenance of soil fertility	pH
		土壤有机碳含量 Soil organic carbon content
		土壤全氮含量 Soil total nitrogen content
		土壤全磷含量 Soil total phosphorus content
		土壤无机氮含量 Soil inorganic nitrogen content
		土壤速效磷含量 Soil available phosphorus content
	土壤侵蚀控制 Soil erosion control	群落高度 Community height
		植株高度 Plant height
		凋落物生物量 Litter biomass
		植被覆盖度 Vegetation cover
供应 Provisioning	牧草供应能力 Forage supply capability	地上生物量 Aboveground biomass
	牧草品质 Forage quality	优质牧草比例 High quality forage ratio
		植物群落氮含量 Plant community nitrogen content
		植物群落磷含量 Plant community phosphorus content
		叶片氮含量 Leaf nitrogen content
		叶片磷含量 Leaf phosphorus content
支持 Supporting	多样性保护 Diversity conservation	香农-维纳多样性 Shannon-Wiener diversity
		物种丰富度 Species richness
		β多样性 β diversity
	植被抗逆能力 Vegetation resilience	叶片厚度 Leaf thickness
	植被抗逆能力 Vegetation resilience	叶干物质含量 Leaf dry matter content
	植被光合能力 Vegetation photosynthetic ability	比叶面积 Specific leaf area
		叶茎比 Leaf to stem ratio
		叶绿素含量 Chlorophyll content

Table 3 Reference values, importance weights, and corresponding categories, services, and stakeholder weights for indicators of degradation in the Hulun Buir meadow steppe

类型 Type	生态系统服务 Ecosystem service	利益群体权重 Interest group weight	指标分类 Indicator category	指标名称 Indicator name	重要性权重 Importance weight	参考值 (平均值±标准差) Reference value (mean ± SD)
调节 Regulating	侵蚀控制 Erosion control	0.20	植被群落结构 Vegetation community structure	群落高度 CH (cm)	0.8	50.84 ± 15.26
	侵蚀控制 Erosion control	0.20	植被群落结构 Vegetation community structure	凋落物生物量 Litter (g·m^-2)	0.7	188.00 ± 116.27
	水分养分调节 Water and nutrient regulation	0.10	土壤特征 Soil characteristics	土壤密度 SD (g·cm^-3)	-0.1	1.00 ± 0.11
				土壤含水量 SWC (%)	0.1	28.62 ± 10.26
				土壤无机氮含量 SIN (mg·kg^-1)	0.1	4.99 ± 2.35
供给 Provisioning	牧草供应 Forage supply	0.40	牧草生产 Forage production	地上生物量 AGB (g·m^-2)	0.7	336.05 ± 82.34
供给 Provisioning	牧草供应 Forage supply	0.40	牧草生产 Forage production	优质牧草比例 HR (%)	0.1	44.25 ± 21.60
支持 Supporting	多样性保护 Diversity protection	0.15	生物多样性 Biodiversity	物种丰富度 SR	0.2	23.00 ± 7.77
	植被抗逆 Vegetation resilience	0.15	植物功能性状 Plant functional traits	叶片厚度 LT (mm)	0.4	0.26 ± 0.06
	植被抗逆 Vegetation resilience	0.15	植物功能性状 Plant functional traits	叶干物质含量 LDMC (%)	0.1	37.91 ± 2.87

Fig. 1 Process diagram for identifying degradation indicators and constructing a rapid diagnostic indicator system for meadow steppe degradation. ACC cv, cross-validation accuracy; ACC test, test set accuracy; AGB, aboveground biomass; AP, soil available phosphorus content; BGB, belowground biomass; CH, community height; Chl, chlorophyll content; FC, field water holding capacity; H, height; H′, Shannon-Wiener diversity index; HR, high quality forage ratio; LC, leaf carbon content; LDMC, leaf dry matter content; Litter, litter biomass; LN, leaf nitrogen content; LP, leaf phosphorus content; LS ratio, leaf to stem ratio; LT, leaf thickness; PC, plant community carbon content; PN, plant community nitrogen content; PP, plant community phosphorus content; SD, soil density; SIN, soil inorganic nitrogen content; SR, species richness; SOC, soil organic carbon content; SWC, soil water content; TN, soil total nitrogen content; TP, soil total phosphorus content; VC, vegetation cover.

Fig. 2 Changes in vegetation and soil indicators across various degradation levels of meadow steppe (mean ± SE). D0, no degradation; D1, slight degradation; D2, moderate degradation; D3, severe degradation. A-L represent indicators of vegetation community structure and diversity; M-U denote plant functional trait indicators; V-AD indicate soil characteristic indicators. Different lowercase letters indicate significant differences among different degrees of degradation (p < 0.05). AGB, aboveground biomass; AP, soil available phosphorus content; BGB, belowground biomass; CH, community height; Chl, chlorophyll content; FC, field water holding capacity; H, plant height; H′, Shannon-Wiener diversity; HR, high quality forage ratio; LC, leaf carbon content; LDMC, leaf dry matter content; Litter, litter biomass; LN, leaf nitrogen content; LP, leaf phosphorus content; LS ratio, leaf to stem ratio; LT, leaf thickness; PC, plant community carbon content; PN, plant community nitrogen content; PP, plant community phosphorus content; SD, soil density; SIN, soil inorganic nitrogen content; SOC, soil organic carbon content; SR, species richness; SWC, soil water content; TN, soil total nitrogen content; TP, soil total phosphorus content; VC, vegetation cover.

Fig. 3 Random forest method for screening degradation indicators, A, C, E, Importance ranking of vegetation structure and diversity indicators, plant functional traits, and soil indicators. B, D, F, Recursive feature elimination for selecting numbers of vegetation structure and diversity, plant functional traits, and soil indicators; red dots indicate optimal number of indicator. ACC cv, cross-validation accuracy; ACC test, test set accuracy. AGB, aboveground biomass; AP, soil available phosphorus content; BGB, belowground biomass; CH, community height; Chl, chlorophyll content; FC, field water holding capacity; H, plant height; H′, Shannon-Wiener diversity; HR, high quality forage ratio; LC, leaf carbon content; LDMC, leaf dry matter content; LN, leaf nitrogen content; LP, leaf phosphorus content; LS ratio, leaf to stem ratio; LT, leaf thickness; Litter, litter biomass; PC, plant community carbon content; PN, plant community nitrogen content; PP, plant community phosphorus content; SD, soil density; SIN, soil inorganic nitrogen content; SOC, soil organic carbon content; SR, species richness; SWC, soil water content; TN, soil total nitrogen content; TP, soil total phosphorus content; VC, vegetation cover.

Fig. 4 Selection of diagnostic indicators for meadow steppe degradation. A, Importance ranking of degradation indicators by random forest method. B, Number of indicators selected by recursive feature elimination. ACC cv, cross-validation accuracy; ACC test, test set accuracy. AGB, aboveground biomass; CH, community height; HR, high quality forage ratio; LDMC, leaf dry matter content; LT, leaf thickness; Litter, litter biomass; SD, soil density; SIN, soil inorganic nitrogen content; SR, species richness; SWC, soil water content.

Table 4 Differences in demand and weight assignment for grassland ecosystem services between stakeholder groups (government and herders)

功能类型 Function type	生态系统服务 Ecosystem service	政府 Government	牧民 Herdsman	平均 Average
调节 Regulating	侵蚀控制 Erosion control	0.35	0.05	0.20
调节 Regulating	水分养分调节 Water and nutrient regulation	0.15	0.05	0.10
供给 Provisioning	牧草供应 Forage supply	0.20	0.60	0.40
支持 Supporting	多样性保护 Diversity protection	0.20	0.10	0.15
支持 Supporting	植被抗逆 Vegetation resilience	0.10	0.20	0.15

Fig. 5 Degradation index (DI) of sample plots at different degradation levels in the study area. D0, no degradation; D1, slight degradation; D2, moderate degradation; D3, severe degradation.

Table 5 Grading of degradation assessment indicators in meadow grasslands

草甸草原退化等级 Degradation levels of meadow steppe	未退化 No degradation	轻度退化 Light degradation	中度退化 Moderate degradation	重度退化 Heavy degradation
指数范围 Index range	DI ≤ 0.35	0.35 < DI ≤ 0.55	0.55 < DI ≤ 0.75	DI > 0.75

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