Fire disturbance regulates soil aggregate stability (AS) and water repellency (WR) by altering soil organic matter (SOM), thereby influencing soil and water conservation functions in ecologically fragile regions. However, the mechanisms underlying the dynamic responses of AS and WR to combined variations in fire intensities and land-use types remain unclear. This study investigated grassland, shrubland, and forestland to elucidate how fire disturbance affects soil AS and WR. By integrating field sampling, laboratory-controlled heating, Mantel tests, and partial least squares path modelling (PLS-PM), this study demonstrates that AS and WR exhibit non-linear responses to fire disturbance intensity. Under low fire disturbance (LFD), the proportion of water-stable aggregates >0.25 mm (R-0.25), mean weight diameter (MWD), geometric mean diameter (GMD) and water drop penetration time (WDPT) increased by 7.77%, 13.43%, 20.68%, and 11.59%, respectively, compared with no fire disturbance (NFD). In contrast, moderate fire disturbance (MFD) and high fire disturbance (HFD) weakened these responses. Under HFD, all three land-use types exhibited reduced AS, and WR remained <5 s, indicating hydrophilicity behavior. Land-use type also influenced variations in AS, WR, and SOM to fire disturbance. Under LFD, forestland showed the largest increase in WR, with WDPT increasing by 19.85% relative to NFD. In contrast, high-intensity burning, shrubland exhibited the greatest losses in both SOM and AS, Under HFD, SOM decreased by 96.75% compared with NFD, while GMD declined to 0.48 mm, corresponding to a 35.74% reduction relative to NFD. SOM was identified as the primary factor driving the dynamic variation in AS and WR. PLS-PM analysis revealed that SOM exerted strong positive effects on WR (path coefficients: 0.47-1.53; P < 0.05) and AS (0.52-1.15; P < 0.05). Mantel tests further confirmed that SOM, soil water content (SW), and pH exhibited the strongest explanatory power for AS and WR (r >= 0.4, P < 0.05). Overall, this study elucidates SOM-dominated changes in AS and WR under fire disturbance. These findings provide new insights into the combined effects of fire intensity and land-use type on soil properties and offer a scientific basis for post-fire soil restoration and soil and water conservation.

Wildfire fundamentally alters forest soil properties and vegetation dynamics through changes in ash deposition and post-fire precipitation, yet the coupled mechanisms governing soil–plant feedbacks remain unclear. We conducted a full-factorial pot experiment in the dry valleys of southwestern China, crossing four ash thicknesses with four precipitation levels and incorporating two contrasting plant functional types: the pioneer grass Digitaria sanguinalis (L.) Scop. and the drought-tolerant crop Fagopyrum tataricum (L.) Gaertn. We monitored soil respiration, near-surface soil moisture and temperature, and plant height throughout early growth. Structural equation modeling and response surface analysis revealed distinct regulatory mechanisms. D. sanguinalis exhibited a nutrient-driven, water-tolerant strategy in which ash and temperature dominated respiratory responses, supporting rapid growth under moderate ash layers. In contrast, F. tataricum followed an ash-facilitated, moisture-threshold strategy, where high ash combined with high precipitation suppressed respiration but maintained stable height. Across both species, a consistent negative association between respiration and plant height reflected a fundamental carbon allocation trade-off between metabolic expenditure and structural growth. Based on these findings, we propose a staged restoration model that leverages the contrasting functional strategies of pioneer and drought-tolerant species to accelerate ground cover formation and stabilize ecosystem functioning in fire-affected dry-valley forests. These results provide mechanistic insights and practical guidance for post-fire restoration and carbon management in fire-prone landscapes.

Soil phosphorus (P) in sloping croplands of mountainous areas is highly susceptible to migration and loss through erosion, posing a major challenge to sustainable agriculture development. Although soil and water conservation measures can mitigate P loss, their interception effects differ greatly. Enclosure walls (EWs), a traditional ethnic soil and water conservation practice in Southwest China, were examined to determine their effectiveness in reducing P loss and the mechanisms underlying P redistribution. The research was conducted in the Anning River Basin, where soil samples were collected from different slope positions (upper and lower slope positions) and depths (0-10 cm, 10-20 cm and 20-40 cm). Total phosphorus (Pt), organic phosphorus (Po) and inorganic phosphorus (Pi), along with key soil properties, were assessed to explore the relationship between terrain and phosphorus migration, and to identify the main driving factors. The results showed that in sloping croplands with EWs, soil Pt, Po, and Pi exhibited significant differences between slope positions, with consistently higher concentrations at the lower slope position. In the 0-10, 10-20, and 20-40 cm soil layers, Pt increased by 45.28 %, 64.10 %, and 69.70 %; Po by 35.71 %, 33.33 %, and 30.43 %; and Pi by 56 %, 120 %, and 188.89 %, respectively. In contrast, the control plots without EWs (CK) showed no significant slope position differences, with smaller increases in Pt (12.5 %, 13.79 %, and 29.55 %), Po (-11.11 %, 0.66 %, and 20.69 %), and Pi (37.93 %, 36.36 %, and 46.67 %). The sloping croplands with EWs and CK showed the highest P content in the surface layer at the upper slope position, but at the lower slope position, only sloping croplands with EWs maintained this pattern, while CK displayed no clear depth gradient and even exhibited the lowest Po content in the surface layer. Slope and slope length were significantly correlated with phosphorus content. Soil chemical properties were identified as the dominated drivers of P migration, with TN explaining 32.39 % of Pt variation, SOC: TN explaining 32.64 % of Po, and SOC: TN explaining 24.96 % of Pi. In contrast, individual environmental factors contributed less than 15 % to the explained variance. EWs significantly reduced the risk of P loss through physical interception, and C-N coupling mechanisms controlled the spatial differentiation of P. These findings provide scientific support for promoting low-cost P-control strategies and indigenous soil and water conservation technologies in the sloping croplands of Southwest China.

Global warming has significantly increased the frequency and scale of wildfires. However, the effects of fire residues on soil CO₂ emissions and the germination of pioneer species in burned areas have been insufficiently studied. Understanding these impacts is crucial for post-fire ecosystem recovery. This study examined the effects of wildfire ash from Liangshan Yi Autonomous Prefecture, China, on the germination of Digitaria sanguinalis (L.) Scop and soil respiration (Rs). Within the applied ash gradient (0.00, 0.58, 1.16, 1.73 kg m−2), final germination of Digitaria sanguinalis was not significantly affected by ash, whereas precipitation exerted the dominant control. In contrast, early seedling growth showed a significant ash × precipitation interaction: under normal to moderately wet conditions, intermediate ash loading (≈0.58 and 1.16 kg m−2) promoted plant height, but this effect disappeared under the driest or wettest scenarios. Across all precipitation regimes, Rs increased with ash loading and showed an early rise, a mid-term peak, and a later stabilization or decline as ash-derived substrates were depleted. Rs was strongly related to 5 cm soil temperature, whereas, no significant monotonic association between Rs and 5 cm soil moisture was detected within the moisture conditions maintained by the precipitation treatments, suggesting that temperature explained more of the short-term variability in Rs. The temperature sensitivity (Q10) of Rs also increased with ash addition, with values of 1.30, 1.82, 2.18, and 2.34 for the four ash treatments. Wildfire ash within a realistic post-fire range did not significantly inhibit the germination of the pioneer grass D. sanguinalis, which was mainly controlled by precipitation, but moderate ash loading (0.58, 1.16 kg m−2) supported early seedling growth under adequate moisture. At the same time, ash inputs enhanced Rs and increased its apparent temperature sensitivity, with Rs being predominantly driven by soil temperature and with moisture effects not emerging as a detectable monotonic trend within the experimental moisture window. These findings suggest that, in water-limited dry-valley ecosystems, complete removal of surface ash to avoid potential germination inhibition is unnecessary; instead, management should prioritize maintaining soil moisture while allowing moderate ash to remain on the surface to support early post-fire recovery and to improve the representation of ash effects in soil respiration models for fire-affected forests.

Introduction The vegetation at the Sichuan-Tibet Interface (STI) in China serves as a core element in maintaining the ecological barrier function of the Qinghai-Tibet Plateau, playing a crucial role in safeguarding the ecological service functions of Southwest China.Methods Based on normalized difference vegetation index (NDVI) data in August between 2001 and 2023, this study investigates the spatiotemporal variations in vegetation coverage during the peak growth period across adjacent administrative boundaries (STI-Tibet and STI-Sichuan), analyzes the time-lag effects of major climatic factors on it with Pearson's correlation, and explores the driving factors by dream optimization algorithm-random forest model and Optimal parameter geographic detector.Results The research has found that the average NDVI value in STI regions was between 0.6 and 0.8 with a growth rate of 0.009 per decade, and 68.41% of areas showed higher mean NDVI from 2012-2023 compared to 2001-2011. STI-Sichuan displays higher proportions of both medium-low and high vegetation coverage and lower proportions of middle-high vegetation coverage compared to STI-Tibet, but STI-Sichuan showed higher proportions of non-significant increase, significant increase, and extremely significant increase compared to STI-Tibet. The NDVI shift in STI-Sichuan occurred approximately 2 years earlier than in STI-Tibet, with greater magnitude and coverage. NDVI response lags to growing-season temperature, precipitation, and solar radiation are 2 months, 1 month, and immediate, respectively. Elevation significantly impacts NDVI across both regions; however, temperature exerts greater influence in STI-Sichuan, while precipitation predominantly affects STI-Tibet. Dual-factor interactions generally enhance explanatory power, reflected by increased q-values.Discussion These findings provide valuable insights for transboundary vegetation management and conservation. Further research could encompass a broader range of ecological elements, and formulate targeted ecological restoration strategies.

Strategic hub in Panxi Economic Zone, the Anning River Basin faces fragile ecology and significant land governance issues. This study uses the "Production-Living-Ecological Space" (PLES) theory to assess how land use transformation affects ecosystem service value (ESV) and sustainable development. It draws on 1985-2023 land-use data, statistical yearbooks, the modified equivalent factor method, Geo-information TuPu, improved cross-sensitivity analysis (CICS) and optimal parameter geographic detector. the findings: (1) E-P land expanded by 255,893.21 hectares, with a dynamic degree of 29.05%; (2) E-P land supplies > 90% of total ESV (67% from regulating services). Since 2005, ESV dropped 326 M yuan overall, with E-P land declining 766 M yuan. Hotspots are in high-altitude areas; cold spots, in plains; (3) ecosystem services are most sensitive to E-P land conversions, with conversions between P-E land and other types generally lowering ESV; (4) 500 × 500 m Anning River Basin data show that population density influences ecosystem services (q = 0.602) in univariate analysis, with bivariate interactions boosting explanatory power. Findings reveal complex links between land use, ecosystem services, and socio-economic factors in the Anning River Basin, emphasizing the need to consider multiple factors in land management and ecological protection.

High-gradient gullies, prevalent on steep slopes in mountainous regions, drive severe soil erosion and landscape degradation. To address the limitations of conventional single-source remote sensing approaches, this study developed an automated identification framework for high-gradient gullies by integrating high-precision unmanned aerial vehicle (UAV) photogrammetry data, including digital orthophoto maps (DOM) and digital elevation models (DEM). Focusing on arid valley gullies in Liangshan Yi Autonomous Prefecture, a critical yet understudied erosion hotspot, this study employed statistically rigorous screening via Spearman's rank correlation to identify pivotal topographic indicators, and fused these with spectral features, textural features, and geometric features. Leveraging object-based image analysis (OBIA) alongside three machine learning algorithms: K-nearest neighbor (KNN), support vector machine (SVM), and random forest (RF). The results show the superior performance of the RF model, achieving highest classification accuracy with minimal overfitting risk, validated by reducing out-of-bag (OOB) error analysis at 4.87 % and 1.27 %. Integration of topographic data enhanced average accuracy by 2.11 %, increased the average Kappa coefficient by 0.092, and raised the average Area Under the Curve (AUC) value by 0.062. Feature importance on the RF model and SHAP analysis reveals that key drivers of model performance included hill shade (HS), surface cutting depth (D), and surface curvature (Curvature), which collectively resolved edge ambiguities and shadow interference. This methodology advances highprecision gully mapping in complex terrains and provides a scalable framework to integrate UAV photogrammetry with geomorphic analytics, offering practical insights for regional soil conservation and disaster mitigation strategies.

The southern Tibetan Plateau has undergone accelerated warming that exceeds the global average, which has intensified surface hydrological processes. However, the mechanisms underlying drought effects on water-driven erosion under current climate change remain poorly understood. This paper aims to reveal the spatiotemporal changes in water-induced erosion in typical areas of the southern Tibetan Plateau using the Revised Universal Soil Loss Equation (RUSLE). Additionally, it seeks to identify the driving forces through the threshold segmentation method based on multi-timescale Standardized Precipitation Evapotranspiration Index (SPEI) data. The results showed that the average soil erosion in the study area from 2001 to 2019 was 46.90 t ha−1 a−1, with an overall significant decreasing trend (p < 0.05). Significant decreases were observed in 40.86

Most risk assessment and source apportionment studies of the heavy metals in the surface soils in China have focused primarily on East China, whereas studies focused on Northwest China, particularly regarding heavy metals in surface soils in the central and western areas, remain limited. In this study, surface soils in the central–western Ali region were investigated, and the concentrations of nine heavy metals were determined. Moreover, the distribution patterns and ecological risks of these heavy metals were elucidated via a combination of the geoaccumulation index, pollution load index (PLI), comprehensive potential ecological risk index (RI), and integrated X-ray diffraction (XRD)–multivariate statistical techniques. Additionally, the pollution characteristics and sources were analyzed. The results indicated the following: (1) The spatial distribution of heavy metal pollution is closely linked to the geological background, and high–pollution zones (e.g., Cr, Ni, Co, Cu, As, and Cd) conform well with the distributions of ultramafic rocks and iron/chromite ore beds. The geoaccumulation index revealed that Cd caused slight and moderate contamination at 29.1% and 5.5% of the sites, respectively, whereas As affected 14.6% of the sites. The pollution load index indicated moderate pollution in 20% of the sites, and the potential ecological risk index indicated that 41.8% of the sites posed moderate risks, which was largely driven by Cd (mean Eri = 43.1). The comprehensive ecological risk index (RI = 115) confirmed a moderate risk level overall. Principal component analysis revealed three primary sources: natural weathering (Cr–Ni–Co–Cu, 39.1%); a mixed source influenced by nonagricultural anthropogenic activities such as transport and regional deposition, combined with natural processes such as arid climate and alkaline soil conditions that influence Cd mobility (Cd–Mo–Pb, 20.8%); and industrial/mining activities (As–Sb, 14.2%). Mineralogical analyses further indicated that heavy metals are present via lattice substitution, adsorption, and precipitation. This study systematically clarifies the composite pollution pattern and sources of heavy metals in the alpine Ali region, supporting targeted contamination control.

The accumulation and decomposition of soil carbon pools directly influence the global terrestrial ecosystems' carbon balance. In contrast, the loss of soil organic carbon (SOC) and dissolved organic carbon (DOC) poses a serious threat to the sustainable management of sloping croplands. As a traditional agricultural landscape and distinctive soil and water conservation measure in the Yi ethnic minority region of Southwest China, Enclosure walls (EWs) exhibit an unclear capacity for carbon sequestration. This study uses the Anning River Basin as a case to elucidate the intercepting effects and driving mechanisms of EWs on SOC and DOC in sloping croplands. By combining field sampling with multivariate analysis methods such as Random Forest (RF) and partial least squares path modeling (PLS-PM), the results show that: SOC and DOC contents increase significantly downslope; compared to upslope position, SOC content in the surface layer (0-10 cm), middle layer (10-20 cm), and bottom layer (20-40 cm) of the soil at downslope position increased by 23.98 %, 65.07 %, and 127.9 %, respectively, while DOC content increased by 36.39 %, 84.21 %, and 111.54 %, respectively. Along the profile direction, SOC and DOC content decreased with increasing soil depth; however, at the downslope position, the presence of EWs resulted in no significant differences in SOC content across different soil layers. Additionally, we compared SOC and DOC content in sloping croplands with EWs and without EWs, thereby demonstrating the carbon sequestration effect of EWs. RF and PLS-PM identified the key drivers of SOC and DOC, including soil chemical indicators such as total nitrogen, alkaline hydrolysable nitrogen, C: N ratios, total phosphorus, and C: P ratios. EWs enhance the carbon sink potential of sloping croplands through the 'erosion interception-structural reconstruction-synergistic feedback' mechanism. This study provides a scientific basis for advancing soil and water conservation and carbon neutrality goals in mountainous areas.

Abstract: High-gradient gullies are common geomorphic features on steep slopes in mountainous regions, leading to significant soil erosion. This study developed an effective automatic identification method for high-gradient gullies using high-precision digital orthophoto maps (DOM) imagery and digital elevation model (DEM) data from unmanned aerial vehicle (UAV) photogrammetry. Focusing on typical gullies in arid valley regions of Liangshan Yi Autonomous Prefecture, we employed Spearman's rank correlation coefficient to screen for key core topographic indicators and deeply integrated topography and imagery data as features. Object-based analysis (OBA) and three machine learning methods (K-nearest neighbor (KNN), support vector machine (SVM), and random forest (RF)) were utilized to extract gullies. Results indicated that the RF model exhibited superior classification performance. Integration of topographic data enhanced average accuracy by 2.11%, increased the average Kappa coefficient by 0.092, and raised the average Area Under the Curve (AUC) value by 0.062. This demonstrates that fusing topographic data complements feature information from visible light imagery bands, optimizing gully extraction model performance. Specifically, hill shade (HS), surface cutting depth (D), and surface curvature (Curvature) were identified as influential factors. These findings improve high-gradient gully identification accuracy in mountainous regions and provide valuable data support for regional gully mapping and management.

Step pools are micro-geomorphology hosted in gullies which are closely related to the channel erosion rate and hydraulic characteristics of runoff. These features are widely developed in the Yuanmou dry-hot Valley area of the Central Yunnan Plateau, China. In this paper, the morphological characteristics of different types of step pools in the Yuanmou dry-hot Valley were analyzed using analysis of variance and cluster analyses. The results show that: (1) step pools can be divided into differential, bedrock, barrier, and sub-erosion step pools based on the environment of development; the bedrock and differential step pools develop on a large scale, while barrier and sub-erosion step pools develop on a small scale; (2) the width and depth of the step, the height of the step, the width of the pool, and the depth of the step of the differential type, bedrock type, and sub-erosion type step pools exhibited a significant positive correlation (P < 0.01); the height of the step and the depth of the pool of the barrier type step pools were significantly negatively correlated with the height of the step and the concave hole depth of the sub-erosion type (P < 0.01); (3) the differential type and undercurrent type step pools were seriously eroded. The study of the types and morphologies of gully step pools in the Yuanmou dry-hot Valley helps understand the formation and evolution mechanisms of erosion gullies and provides a scientific basis for monitoring and controlling soil erosion.

In semi-arid and arid areas, gully erosion is one of the most destructive forms of erosion and causes serious land degradation and resource destruction. Steepland gullies are widely distributed in the dry valleys of southwest China, and their formation is one of the main causes of soil erosion and the destruction of sloping farmland in the region. Previous research on the development of steepland gullies is limited, and further study is needed. In this study, 11 steepland gullies at various stages of development located in Guobu Village, Xide County, Liangshan, Sichuan Province, were selected for investigation using a digital elevation model (DEM) derived from unmanned aerial vehicle data as the primary data source. These data had a spatial resolution of 0.1 m. Fundamental parameters such as the gully length, width, depth, area, and volume were extracted from the remote sensing data. Other characteristic parameters, including the coefficient of main and tributary gullies, vertical gradient, gully elongation, and gully openness, were also investigated. The results indicate a significant linear positive correlation between the gully's degree of openness and elongation as the gully's length, width, and depth increase. Furthermore, the vertical gradient and coefficient of main and tributary gullies exhibit power-law relationships with these gully dimensions. The development of steepland gullies was divided into infancy, youth, maturity, and old age based on the use of the gully length as an ergodic indicator in space-for-time substitution. The morphological characteristics of these different stages were quantitatively analyzed, and a proposed mechanism for how the evolution of the gullies proceeds was developed. An empirical model of volume-length erosion was established to investigate the development process of steepland gullies in the dry valleys. It has been observed that the development law of steepland gullies is essentially consistent with the very active stage of typical gully formation, suggesting that steepland gully may represent the initial stage of gully development. The results show that these steepland gullies have their origin in high-intensity rainfall events that are accompanied by the formation of steps and drop water. The effects of gravity erosion and hydraulic erosion then cause the gullies to expand rapidly, forming gullies with a large head and a small tail before they gradually stabilize. The results of this study will help with the understanding of the formation and evolution of steepland gullies and will be of practical significance for the prevention of gully erosion and the protection of sloping farmland in the dry valley region of southwest China.

Climate change affects the geographical distribution of species. Predicting the future potential areas suitable for certain species is of great significance for understanding their distribution characteristics and exerting their value. Based on the data of 276 effective distribution points of Polygonum capitatum and 20 ecological factors, the maximum entropy (MaxEnt) model and the ArcGIS software were employed to predict the areas suitable for P. capitatum growth, and the main environmental factors affecting the geographical distribution of this species were explored. Under the current climatic conditions, the areas highly suitable for P. capitatum are mainly distributed in southwestern China, with a small number of sites in coastal areas and most sites in Guizhou Province. Under different climate scenarios, the suitable areas were reduced to varying degrees. The dominant environmental variables affecting the distribution of P. capitatum were precipitation in the driest month, annual precipitation, and elevation, with a cumulative contribution rate of 84.1%. Against the background of a changing climate, the areas suitable for P. capitatum in China will be widely distributed in the southwestern region, with Guizhou Province and Yunnan Province as the main distribution areas; some sites will also be distributed throughout the southwest of Tibet Autonomous Region, the south of Sichuan Province, the north of Guangxi Autonomous Region, and the coastal area of Fujian Province. Optimal conditions for P. capitatum include a dry month precipitation range of 13.4 to 207.3 mm, elevations from 460.3 to 7214.3 m, and annual precipitation between 810 and 1575 mm. Given these insights, we recommend enhanced conservation efforts in current prime habitats and exploring potential cultivation in newly identified suitable regions to ensure the species’ preservation and sustainable use.

Gully erosion is one of the most severe forms of land degradation and poses a serious threat to regional food security, biodiversity, and human survival. However, there are few methods for the quantitative evaluation of gully activity, and the relationships between gully activity and influencing factors require further in-depth study. This study takes the Sunshui River Basin, as a case study. Based on field investigation, unmanned aerial vehicle (UAV) photography and remote sensing images, 71 typical gullies were identified. The vegetation coverage (VC), slope and main-branch gully ratio (MBGR) were used as evaluation indicators, and the gully activity was calculated using the fuzzy mathematics membership degree and then evaluated quantitatively. The factors influencing different active gullies were also analyzed. The results showed that (1) the fuzzy comprehensive evaluation method can be used to identify gully activity. Different levels of gully activity were defined based on the gully activity index. The active indices of stable gullies ranged from 0-0.25, those of semiactive gullies ranged from 0.25-0.75, and those of active gullies ranged from 0.75-1. (2) The activity indices of the 71 gullies ranged from 0.054 to 0.999, with an average value of 0.656. There are 31 active gullies, and 31 semiactive gullies. A total of 87.32% of the gullies in the study area were in the early or middle stage of gully development. Gully erosion was intense, which is consistent with the serious reality of soil erosion. (3) Gully activity was affected by multiple factors. It was significantly positively correlated with topographic relief (TR) (r = 0.64, P<0.01) and surface curvature (SC) (r = 0.51, P<0.01), while it was significantly negatively correlated with land use type (LUT) (r = -0.5, P<0.01). Surface roughness (SR) (r = 0.2, P<0.01) was positively correlated with gully activity; but not significantly. There was no significant correlation between aspect (As) and gully activity. The results of this study are helpful for quantitatively determining the level of gully activity and understanding the development process and mechanism controlling gullies, providing a reference for research on related regions and geomorphologic information.

[目的]研究安宁河流域土地利用的时空演变、地形梯度分异特征及其转型的驱动因素,为区域土地利用规划及土地资源管理提供理论依据.[方法]选取海拔、坡度和地形起伏度3个地形特征,基于土地利用、自然环境和社会经济数据,借助CA-Mark-ov模型、PLUS模型和地形分布指数等方法,分析2000-2020年安宁河流域土地利用时空演变特征、驱动机制和地形梯度分异,并进行2030年未来情景模拟.[结果]2000-2020年,安宁河流域土地利用以林地和耕地为主,二者分别占61.74％和24.86％以上;其次为草地和建设用地,分别占8.40％和1.02％以上;水域和未利用地面积较少,占比均低于1.13％.2000-2020年林地和建设用地迅速增长,其余地类不同程度减少,耕地、林地和草地与其他地类转化强烈.2020-2030年建设用地和林地有缩减趋势,其余地类呈增长趋势.耕地、建设用地和水域集中在地形起伏较小的低中海拔河谷地带,林地、草地和未利用地集中于地形起伏较大的中高海拔山区.海拔、坡度和人口密度是影响耕地、林地和未利用地变化的主要驱动因素,GDP、距水域和高速公路距离为草地、水域和建设用地变化的主要驱动因素.[结论]安宁河流域土地利用转型深受自然环境和社会经济因素的影响,土地利用空间格局具有显著地形梯度差异,需秉承因地制宜原则,促进人地关系和谐发展.

The evolution process of ephemeral gully (EG) is a major content in the study of gully erosion and geomorphology. However, due to the short duration of EG existence, field-based continuous quantitative observation information is still lacking. The objective of this study was to characterize the morphological changes and evolution mechanisms of EG under natural conditions in the Dry-hot Valley. A representative EG was observed from 2016 to 2020 by using laser scanning. Results showed that after four years, the erosion area and erosion volume increased 4.5 and 17.3 times, respectively. The length, width, and depth of the main channel continuously increased over time but the growth rates decreased. During the four monitoring periods, the average growth rates of width were 0.12, 0.26, 0.33 and 0.06 m/year, respectively; the average growth rates of depth were 0.07, 0.08, 0.03 and 0.02 m/year, respectively; and the growth rates of length were 7.58, 1.78, 2.17 and 1.17 m/year, respectively. EG morphological parameters varied at different locations of the hillslope. The crosssection area increased gradually towards downslope, especially in the middle and lower parts of the channel. However, the width-depth ratio of EG decreased gradually from upper to lower parts of the hillslope, and the values were generally greater than 1.0. In addition, the variation of sinuosity, density and tortuosity complexity were influenced by both headward and lateral erosion, which increased and then decreased. The vertical gradient increased significantly and then tends to be stable. The results of this study are helpful to enrich current studies on the evolution process of ephemeral gully.

在城镇化推进和退耕还林还草等政策影响下,南充市土地利用结构发生显著改变,基于2000—2019年3个时期土地利用数据,运用价值当量因子和空间统计分析等方法,探索南充市土地利用与生态系统服务价值(ESV)的时空变化.结果表明:(1)耕地是南充市主要土地利用类型,占82％以上,2000—2019年耕地和灌木呈减少趋势,而林地、水域、草地和建设用地呈增长趋势,建设用地(109.44％)和水域(40.62％)增长最为显著.(2)2000—2019年南充市ESV总量先急速增长后小幅回落,净增加73.8亿元,增长率为22.89％,耕地ESV占38％以上;单项ESV以水文调节和土壤保持为主,两者占总ESV的44％以上;各县(市、区)ESV总量和单位面积ESV呈北高南低的特点.(3)2000—2019年3个时期ESV及其变化的Moran's I指数均大于0,具有显著自相关性;ESV高值区和低值区不断扩展,空间聚集性逐步增强;ESV减损区和变化冷点区集中于城镇建设区域,增益区和变化热点区集中于水域和林地覆盖区域.研究结果可为南充市国土规划和生态文明建设提供参考.

Fire is a common natural disturbance in forest ecosystems and plays an important role in subsequent vegetation patterns. Based on the spatial sequence method, adopted as an alternative to the time successional sequence method, we selected burned areas in different locations in the Anning River Basin, which encompasses typical dry valleys. Quadrat surveys and quantitative classification were used to identify and classify the vegetation and distribution pattern and to carry out environmental interpretation during the natural restoration process after a forest fire. The results showed the following: (1) in the early stage of natural recovery after a forest fire disturbance, the vegetation community could be divided into seven community types, and Quercus guyavaefolia H. Leveille (Qg) was the dominant species in the community; (2) the vegetation samples could be divided into five ecological types, and the classification and distribution pattern of community types in this region changed most notably with altitude; and (3) a detrended correspondence analysis could be used to accurately classify vegetation community types, while a detrended canonical correspondence analysis could reveal the relationships between species and environmental factors. This study provides a scientific basis for guiding the restoration of ecosystem structural stability and biodiversity in burned areas.

土地利用变化和生态系统服务价值一直是生态学研究的重点之一.本文基于 2000、2010 和 2020 年宜宾市遥感影像图,采用GIS制图和面积转移矩阵等方法分析了2000-2020 年宜宾市土地利用变化及其生态系统服务价值时空效应.结果表明:(1)近20 年来,宜宾市土地利用类型转换面积以耕地、林地和建设用地为主,建设用地面积增速呈现上升的趋势,2000-2010 年与2010-2020 年土地利用综合动态度分别为0.32%和0.31%;(2)生态系统服务价值在时间序列上呈现先降低后回升的趋势,总价值从 490.64×108 元增长到 491.24×108 元,其中林地、耕地和水域的贡献率最大;在空间分布上,单元格生态系统服务价值主要以中和较高等级区域为主,低等级区域主要集中于宜宾市主城区和南溪区(建设用地为主).(3)生态系统服务价值聚类分布具有显著正相关性,H-H聚类与H-L聚类的生态系统服务价值增值区域主要分布在耕地转为林地的区域,L-L聚类与L-H聚类的减值区域则主要分布在林地转为耕地与建设用地的区域.本研究通过直观清晰的展现土地利用与生态系统服务价值的时空变化,有助于揭示两种变化之间的关系,并为指导生态环境建设提供科学依据.