Search

Understanding the forest evolution is vital to answering the reforestation potential in karst areas. Here, we present the first‐ever pollen record in karst depression sediment, combined with comprehensive dating methods (137Cs, 210Pbex, and 14C) and historical documents, to reveal plant change history in southwest Guangxi, a severe rocky‐desertification region. We inferred three stages of "virgin forest–deforestation–sparse tree planting" over the past three centuries. Before the 1780s, the barren mountains used to be a lush mixed broadleaf forest probably. However, maize cultivation, along with explosive population growth and migration, accelerated mountain reclamation and deforestation, leading to severe rocky desertification since the 1780s, featured by the co‐occurrence of Zea pollen appearance and Dicranopteris spore surge from 0.92% to 12.18%. Since the 1930s, sparse tree planting began, as Cupressaceae/Taxodiaceae pollen abruptly increased by 32%. Our study is significant in understanding the rocky desertification causes and guiding ecological restoration in the region. Plain Language Summary: Rocky desertification refers to the transformation of a karst area once covered with vegetation into rock‐baer landscapes. In southwest China, rocky desertification is the greatest ecological degradation problem. Although hundreds of billions were invested to carry out ecological restoration, it is uncertain whether the region has reforestation potential. Therefore, we attempted to use pollen record in a closed‐environment sediment (karst depression) in southwest China to reveal the plant changes in the past three centuries. Combined with isotopic methods, we found that before the 1780s, tree pollens were high, implying the site used to be a lush forest. However, since the 1780s, maize pollen occurred, coinciding with the pollen percentage surge of another species indicative of ecological degradation. We inferred that maize cultivation, along with explosive population growth and migration, accelerated mountain reclamation and deforestation, leading to severe rocky desertification there. Since the 1930s, cypress and cedar pollens were abruptly increased, indicating that sparse tree planting began. These results are vital to supporting rocky desertification control and reforestation sustainability in the region. Key Points: The first‐ever pollen record of a karst depression in southwest China is presentedThree stages of "virgin forest–deforestation–sparse tree planting" over the past three centuries were inferredMaize cultivation since the 1780s triggered severe rocky desertification in the region [ABSTRACT FROM AUTHOR]

With the implementation of large‐scale ecological restoration projects, Southwest China has become one of the fastest forest growth areas in the world in terms of vegetation cover and above‐ground biomass (AGB). It is expected to be a potential area for achieving the carbon neutrality target in China. Accurate estimation of forest AGB is becoming an increasingly urgent necessity for carbon neutrality and forest management. However, due to the complex geological background, there is significant uncertainty in estimating forest AGB in the southwestern region, which generally results in underestimating carbon sinks from forest restoration. To address the issue, we propose a method by incorporating forest age information and stack learning technique to estimate forest AGB. Based on remote sensing, forest inventory and in situ forest biomass data, three fundamental methods (Multiple regression, Random forest and Support vector machine) are employed and compared to build the AGB estimation model with vegetation indices, texture feature factors and forest age. Optimal basic models are further enhanced by integration learning to improve the estimation performance and then applied to the study area Guangxi to obtain regional AGB information of different forest types. The results show that: (1) forest age plays a vital role in reducing the uncertainty of AGB estimation. By incorporating forest age information, R2 of AGB estimation is improved by 0.07–0.27 and RMSE is decreased by 16.35%–47.47% for different forest types; (2) with R2 value >0.78, random forest model outperforms support vector machine and multiple linear regression models. Compared with the single optimal model, integration model by stack learning further enhances R2 of estimation by 0.02–0.03 and decreases RMSE by 5.20%–14.89%. (3) The total forest AGB in Guangxi is 988.17 Tg and the average forest AGB level is 73.30 t/ha. Natural broadleaf forest has the highest AGB level (86.75 t/ha), followed by natural coniferous forest (81.19 t/ha), planted coniferous forest (63.23 t/ha) and planted eucalyptus forest (49.71 t/ha). AGB level in karst areas is lower than that in non‐karst areas due to soil and water constraints. The majority of plantation forests in Guangxi is in the early and middle stages of forest succession, with the rapid growth of forest AGB, and has hence significant potential as carbon sinks. This study indicates that stack learning and incorporation of forest age could significantly decrease the uncertainty of forest AGB estimation. Our study helps to provide more accurate AGB information for karst ecological project management and regional carbon neutrality assessment. [ABSTRACT FROM AUTHOR]

Bacteria, fungi, and protist are important in driving nutrient cycling. The microbiological mechanism underlying vegetation restoration during different temperature and precipitation gradients remains unclear. To determine the relationship between microbes and nutrients, we examined the changes in soil bacterial, fungal, and protist diversity and community composition under two different temperatures in a plantation forest and shrubland as well as reference cropland in a karst region. Bacterial and protist diversity in the warm and low‐altitude region of Guangxi (average temperature 20.9°C) was higher in cropland than in shrubland or plantation forest. By contrast, fungal richness was lower in cropland than in shrubland. A co‐occurrence network revealed higher numbers of correlated links among the bacterial, fungal, and protist taxa in the cool and high‐altitude region of Guizhou (average temperature 14.6°C) than in the warm and low‐altitude region of Guangxi. Stronger interactions were observed among microbial taxa under cropland than in vegetation restoration. The protist groups Cercozoa and Lobosa showed the highest numbers of links with the bacterial phyla Acidobacteria and Proteobacteria and with the fungal phylum Ascomycota. The numbers of Proteobacteria, Ascomycota, and Cercozoa were most correlated with soil nutrient levels of carbon, nitrogen, and phosphorus. Overall, microbial interactions were higher at low temperatures than at high temperatures, consequently intensifying the predation of bacteria and fungi by protists at a low‐temperature level. Furthermore, Proteobacteria, Ascomycota, and Cercozoa were the keystone taxa linked to nutrient availability; hence, effective monitoring of these dominant groups may be beneficial for increasing nutrient accumulation during vegetation restoration. [ABSTRACT FROM AUTHOR]

The responses of spatiotemporal variation of ecosystem service values (ESVs) to landscape pattern from 1985 to 2005 in a typical Karst area of the northwest Guangxi Zhuang Autonomous Region, China, were examined using remote sensing and geographic information system techniques in this paper. The total ecosystem service values declined significantly from 1985 to 1990, and then increased slowly from 1990 to 2005, almost equaled to the 1985 level. The ecosystem service values tended to decline from the west to the east and from mountainous regions to peak-cluster depression areas in 1985, 1990, 2000 and 2005 respectively. During the period from 1985 to 2005, the ecosystem service values have increased in the middle and eastern parts of the study area. Landscape pattern indices, such as total area, largest patch index, contagion, aggregative index, effective mesh and proportion of like adjacencies, are significantly correlated with ecosystem service values. This suggests that ecosystem service values tend to increase with the growth of patch area and patch connectivity. However, there are negative correlations between ecosystem service values and landscape pattern indices, such as division index and patch richness. It indicates that ecosystem service values decrease with patch fragmentation and patch size shrinkage. The ecosystem conditions in the typical Karst area have been improved because of the control measures of rocky desertification. It is important to protect key landscape types, such as woodland, shrub and grassland, and to increase patch size and connectivity to avoid further fragmentation. Furthermore, it is necessary to reduce disturbances to ensure the growth of ecosystem service values and to facilitate the sustainable development in this region. [ABSTRACT FROM AUTHOR]

ABSTRACT Reliable assessment of the spatial distribution of soil erosion is important for making land management decisions, but it has not been thoroughly evaluated in karst geo-environments. The objective of this study was to modify a physically based, spatially distributed erosion model, the revised Morgan, Morgan and Finney (RMMF) model, to estimate the superficial (as opposed to subsurface creep) soil erosion rates and their spatial patterns in a 1022 ha karst catchment in northwest Guangxi, China. Model parameters were calculated using local data in a raster geographic information system (GIS) framework. The cumulative runoff on each grid cell, as an input to the RMMF model for erosion computations, was computed using a combined flow algorithm that allowed for flow into multiple cells with a transfer grid considering infiltration and runoff seepage to the subsurface. The predicted spatial distributions of soil erosion rates were analyzed relative to land uses and slope zones. Results showed that the simulated effective runoff and annual soil erosion rates of hillslopes agreed well with the field observations and previous quantified redistribution rates with caesium-137 (137Cs). The estimated average effective runoff and annual erosion rate on hillslopes of the study catchment were 18 mm and 0.27 Mg ha−1 yr−1 during 2006-2007. Human disturbances played an important role in accelerating soil erosion rates with the average values ranged from 0.1 to 3.02 Mg ha−1 yr−1 for different land uses. The study indicated that the modified model was effective to predict superficial soil erosion rates in karst regions and the spatial distribution results could provide useful information for developing local soil and water conservation plans. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Geostatistical and statistical analyses were combined to examine the spatial distribution of soil water content under four vegetation types during the dry season, in the peak-cluster depression in the karst region in northwest Guangxi, southwest China. The soil water content significantly increased from farmland to plantation, secondary forest, and primary forest; whereas the variation coefficients, the sill ( C+ C), and total spatial variance increased, although the range decreased. The spatial distribution of soil water content in the different vegetation types had a high spatial autocorrelation. Different models produced a best fit for the semivariograms of the four vegetation types. Elevation and slope position were the primary factors influencing the spatial distribution of soil water content, with other key factors differing between the four vegetation types. Moreover, even though different specific factors influenced soil water content in the four vegetation types, the correlations and degrees of associations between the soil water content and these various factors differed. Therefore, the corresponding strategies for rational usage and management of water resources should be different for the four vegetation types in this region. [ABSTRACT FROM AUTHOR]

In this investigation we analyzed the spatiotemporal variation of ecosystem service values (ESVs) and its correlation with numerous environmental factors (EFs) for the karst region of Northwest Guangxi, China, from 1985 to 2005 using remote sensing, geographic information systems (GIS) and statistical techniques. The results indicate that historically ESVs for this karst region decreased from 1985 (109.652 billion Yuan) to 1990 (88.789 billion Yuan) and then increased at the turn of the twenty-first century. However, the ESVs in both 2000 (103.384 billion Yuan) and 2005 (106.257 billion Yuan) never achieved the level recorded in 1985. The total of nutrient cycling, organic production and gas regulation combined were 72.69, 64.57, 70.18 and 72.10% of ESVs in 1985, 1990, 2000 and 2005, respectively. In contrast, the ESVs of water conservation, soil reservation, recreation and culture were determined to be relatively low contributing only 17.44, 23.82, 19.26 and 24.76% of total ESVs, respectively, during these four years. With regards to the spatial distribution of ESVs, larger values were recorded in the west and smaller ones recorded in the east. The most significant factors that were deemed to influence ESVs are annual rainfall, per capita cropland, slope and vegetation coverage. Annual rainfall and slope exert a negative force, whereas per capita cropland and vegetation coverage exert a positive force on ESVs. The results of the study would suggest that ecosystem conditions of this important karst region have been improved as the result of the implementation of rocky desertification control policies. [ABSTRACT FROM AUTHOR]

Karst rocky desertification is a progressive process of land degradation in karst regions in which soil is severely, or completely, eroded. This process may be caused by natural factors, such as geological structure, and population pressure leading to poor ecosystem health and lagging economic development. Karst rocky desertification is therefore a significant obstacle to sustainable development in southwest China. We applied a radial basis function network model to assess the risk of karst rocky desertification in northwest Guangxi, a typical karst region located in southwest China. Factors known to influence karst rocky desertification were evaluated using remote sensing and geographic information systems techniques to classify the 23 counties in the study area from low to extreme risk of karst rocky desertification. Counties with extreme or strong karst rocky desertification risk (43.48%, nearly half of the study area) were clustered in the north, central and southeast portions of the study area. Counties with low karst rocky desertification (30.43%) were located in the west, northeast and southwest of the study area. The spatial distribution of karst rocky desertification was moderately correlated to population density. [ABSTRACT FROM AUTHOR]

Vegetation and soil have spatial distributions at different scales, while the spatial distribution of soil microorganisms and factors driving their distribution are still unclear. We aimed to reveal the spatial pattern of microbial functional diversity and to identify its drivers in forest soils at a regional scale. Here, we performed an investigation of microbes across several forest types covering an area of 236,700 km2 in Guangxi, southwest China. We examined a total of 185 samples for soil microbial functional diversity using Biolog EcoPlates. The soil microbial functional diversity had strong spatial heterogeneity across the Guangxi region. The distribution of microorganisms in forest soils was mainly determined by total nitrogen, available N, and C:N ratio, and stand age. We found that coniferous forests, especially pine forest, exhibited lower functional diversity, but the reverse was true for deciduous broadleaf forest/mixed evergreen and deciduous broadleaf forest. Our findings suggested that a heterogeneous distribution of microbial functional diversity in forest soils is related to forest types in Guangxi, China. In conclusion, high soil microbial functional diversity is favored in subtropical forests with looser soil structure, lower soil C:N ratio, greater total soil nitrogen and available nitrogen concentration, and broad-leaved tree species. [ABSTRACT FROM AUTHOR]

Under the transformation from over-cultivation to ecological protection in China's karst, how human activities affect ecosystem services should be studied. This study combined satellite imagery and ecosystem models (Carnegie-Ames-Stanford Approach (CASA), Revised Universal Soil Loss Equation (RUSLE) and Integrated Valuation of Ecosystem Services and Trade-offs (InVEST)) to evaluate primary ecosystem services (net ecosystem productivity (NEP), soil conservation and water yield) in a typical karst region (Huanjiang County). The relationships between human activities and ecosystem services were also examined. NEP increased from 441.7 g C/m2/yr in 2005 to 582.19 g C/m2/yr in 2015. Soil conservation also increased from 4.7 ton/ha to 5.5 ton/ha. Vegetation recovery and the conversion of farmland to forest, driven largely by restoration programs, contributed to this change. A positive relationship between increases in NEP, soil conservation and rural-urban migration (r = 0.62 and 0.53, P < 0.01, respectively) indicated decreasing human dependence on land reclamation and naturally regenerated vegetation. However, declining water yield from 784.3 to 724.5 mm highlights the trade-off between carbon sequestration and water yield should be considered. Our study suggests that conservation is critical to vegetation recovery in this region and that easing human pressure on land will play an important role. [ABSTRACT FROM AUTHOR]

Exploring the effectiveness of the pilot project on comprehensive control of rock desertification since its launch by China's government is of great significance for regional sustainable development. Jointly affected by the karst surface-underground geological structure and human activities, the natural ecological environment is fragile in southwest Guangxi, with frequent droughts and floods, severe soil erosion and rock desertification. Consequently, the socio-economic development in this region is relatively lagging behind. With the support of national policies, southwest Guangxi has been comprehensively carrying out projects of controlling rocky desertification, promoting the control of rocky desertification and poverty alleviation in a coordinated manner. According to "Thirteenth Five-Year Plan for Comprehensive Control of Rocky Desertification in Karst Areas of Guangxi Zhuang Autonomous Region", southwest Guangxi is designated as an area for the control of cluster-peak depression, in which comprehensive control of rocky desertification has been carried out in terms of building ecological barriers, protecting biodiversity, and promoting the protection and the comprehensive utilization of water and soil resources. In order to further investigate the effectiveness of controlling rocky desertification in cluster-peak depression of southwest Guangxi, this study the physical exploration. Based on the correction of the data from the borehole, the parameter of geological radar, V, is taken to be 0.060 m•ns -1 which is applicable to the study area. The study results indicate that Biyun lake belongs to the oblique tectonic basin, where leakage points and underground river pipes are mainly developed close to the axis of the Babu compound oblique, along the lithological interface of three sections of greystone and the second section of the mudstone of Jialingjiang Group. The mudstone constitutes a water separating plate of the karst leakage zone. After lake water seeps along the zone, it flows northwest, and is discharged in the end at the outlet of the Babu underground river. In addition, the leakage of Biyun lake is mainly of the karst pipeline type. The karst leakage zone is located at the measuring point of 540 m, with a 40-meter- deep of karst pipeline; therefore, the leakage section is relatively narrow, and it is feasible to plug the leakage by grouting. The drilling test results confirm the reliability of the technical method used in karst areas, which is combined by hydrogeological investigation, tracer test and physical exploration, because this method can well determine the direction of the leakage channel and the location of the leakage zone, and thus providing guidance on the leakage control of lakes or reservoirs in karst areas. [ABSTRACT FROM AUTHOR]

The karst area in Southwest China is an important region for the implementation of sustainable development strategies in China, as well as an area with extremely fragile ecological environment and concentrated distribution of rocky desertification. As a "National Pilot Zone for Sustainable Development" and "National Pilot Demonstration Zone for the Innovative Sustainable Development Agenda", Gongcheng Yao autonomous county of Guangxi is an important demonstration area for the coordinated development of karst landscape resource conservation and special ecological agriculture. Therefore, exploring the spatiotemporal evolution and the driving mechanism of rocky desertification in this area can provide an important scientific basis for the comprehensive management of rocky desertification, and the protection and restoration of karst ecosystem in China's pilot zones for sustainable development. Based on remote sensing images of Landsat series satellite from 2000, 2005, 2010, 2015, and 2021, this study extracted information on rocky desertification by the interpretation of human-computer interaction, and quantitatively analyzed the spatiotemporal evolution law of rocky desertification in Gongcheng county. Meanwhile, by combining data of carbonate rock and land use, this study revealed the inherent driving mechanisms of geological conditions and land use changes about the evolution of rocky desertification in Gongcheng county. The study results show that the rocky desertification in Gongcheng county experienced three stages: accelerated deterioration from 2000 to 2005, rapid improvement from 2005 to 2015 and slow deterioration from 2015 to 2021. The total area of rocky desertification ranged from 88.96--229.55 km2. From 2000 to 2005, the rocky desertification in Gongcheng county shifted from no rocky desertification to mild and intermediate rock desertification, and reversely, it showed improvement from 2005 to 2021. The rocky desertification presented a spatial pattern of development from north to south in Gongcheng county. Xiling town, Lianhua town and Ping'an town were the main areas where rocky desertification occurred, accounting for 55.47%--61.31% of the total rocky desertification area of the county. In 2005 and 2010, when the rocky desertification was relatively severe, it was mainly at a moderate level in Xiling town, while it was mainly at a mild level in other years. In addition, the rocky desertification of Gongcheng county mainly occurred in the limestone area, accounted for 71.42%--75.85% of the total rocky desertification area of this county. But the rocky desertification area in orchards and shrub land accounted for 35.92%--39.21% and 31.77%--31.86% of the county's total area, respectively. The study results indicate that there exist strong karstification, severe soil erosion/leakage, and insufficient materials and slow rates of soil forming due to the wide distribution of pure limestone in Gongcheng county. Besides, the long-term cultivation of single economic fruit forests such as peaches and plums in orchards has led to a decline in fruit tree quality, and a large number of fruit trees have been cut down in recent years, resulting in an exacerbation of rocky desertification. Therefore, the local authority in Gongcheng county should consider constructing three-dimensional ecological planting model in the karst areas such as Xiling town, Lianhua town and Ping'an town during the comprehensive treatment of rocky desertification, so as to promote the coordinated and sustainable development of ecological industry, rocky desertification control and social economy. [ABSTRACT FROM AUTHOR]

Soil carbon, nitrogen and phosphorus are important factors of soil quality, which play important roles in increasing soil nutrient storage, improving soil fertility and promoting plant growth. A large number of studies have shown that returning cultivated land back to forest and grassland and converting land use patterns will lead to changes in soil nutrient status and stoichiometry. However, systematic studies on total and easy-to-use components of soil carbon, nitrogen, and phosphorus are relatively few in Pingguo karst area of Youjiang River Valley in central Guangxi. In this study, plots of three types of land use (the restored forest and grassland from cultivated land and cultivated land for sugarcane and maize) inside and near Pingguo National Field Observation and Research Station of Karst Ecosystem, Guangxi were taken as research objects, and 0-15 cm surface soil was sampled in March, 2021. The physical and chemical properties of soil, total and easy-to-use components of carbon, nitrogen and phosphorus and their relationships were analysed in order to better understand the effects of returning cultivated land back to forest and grassland and converting land utilization patterns on total and easy-to-use components of carbon, nitrogen and phosphorus of soil in karst areas. The results showed as follows: 1) Compared to cultivated land, the soil pH values of the restored forest and grassland from cultivated land increased significantly. The macro-aggregates of restored forest and grassland (42.82%, 57.11% respectively) were significantly higher than those of cultivated land for sugarcane (16.94%) and maize (5.49%), and their micro-aggregates (4.58%, 1.76% respectively) were significantly lower than those of cultivated land for sugarcane (12.42%) and maize (16.34%). Meanwhile, compared to cultivated land for sugarcane (103.39 mg⋅kg-1, 3.22 mg⋅kg-1) and that for maize (105.02 mg⋅kg-1, 3.07 mg⋅kg-1), available nitrogen of restored forest and grassland significantly increased to 156.55 and 166.49 mg⋅kg-1, respectively, while available phosphorus significantly decreased to 0.41 and 0.30 mg⋅kg-1, respectively. 2) Compared to cultivated land, the organic carbon, microbial biomass carbon and total nitrogen of soil in restored forest and grassland increased significantly. The values of soil organic carbon of restored forest and grassland (34.12 g⋅kg-1, 32.45 g⋅kg-1 respectively) were 1.98 and 1.88 times of cultivated land for sugarcane (17.26 g⋅kg-1), and 2.15 and 2.04 times of cultivated land for maize (15.89 g⋅kg-1), respectively. The values of microbial biomass carbon of soil in restored forest and grassland (985.35 mg⋅kg-1 1,110.04 mg⋅kg-1 respectively) were 2.71 and 3.05 times of cultivated land for sugarcane (364.07 mg⋅kg-1), and 3.14 and 3.54 times of cultivated land for maize (313.92 mg⋅kg-1), respectively. The values of total nitrogen of soil in restored forest and grassland (4.14 g⋅kg-1, 4.10 g⋅kg-1 Respectively) were 2.48 and 2.46 times of cultivated land for sugarcane (1.67 g⋅kg-1), and 2.19 and 2.16 times of cultivated land for maize (1.89 g⋅kg-1), respectively. The total value of phosphorus in restored grassland was the highest (1.04 g⋅kg-1), followed by that of cultivated land for maize (0.81 g⋅kg-1), and the values of dissolved phosphorus of cultivated land for sugarcane and maize were significantly higher than those of restored forest and grassland. The values of stoichiometry of carbon, nitrogen, and phosphorus, OC/TP, TN/TP of soil in restored forest were significantly higher than those of restored grassland and cultivated land, and the values of restored grassland and cultivated land did not show significant difference. 3) Soil bulk density, aggregate structure, pH value, available nitrogen and available phosphorus were significantly correlated with total and easy-to-use components of carbon, nitrogen and phosphorus of soil. Properly speaking, soil pH value, large macro-aggregates, and available nitrogen showed a significantly positive correlation with organic carbon, microbial biomass carbon, total nitrogen and microbial biomass nitrogen of soil, and a significantly negative correlation with dissolved phosphorus. Meanwhile, bulk density, micro-aggregates, and available phosphorus of soil showed a significantly negative correlation with organic carbon, microbial biomass carbon, total nitrogen and microbial biomass nitrogen of soil, and a significantly positive correlation with dissolved phosphorus. The results indicated that the measures of returning cultivated land back to forest and grassland and converting land use patterns significantly improved soil carbon, nitrogen and soil quality in karst areas. These two measures are important and effective ways to control rocky desertification and protect ecological environment in karst areas. [ABSTRACT FROM AUTHOR]

Abstract: Rock fragments (>5mm in diameter) at the soil surface and within the topsoil have a large effect on the intensity of various hydrologic and geomorphic processes. However, little information is available on the spatial distribution of rock fragments in subtropical regions. The objective of this paper was to investigate the relationship between the spatial distribution of rock fragments and landforms on two different steep karst hillslopes in northwest Guangxi, southwest China. On the first hillslope (a disintegrated landslide failure) with the presence of several large rock outcrops (>2m in height), the spatial distribution of rock fragment cover had no obvious relationship with topographic position except that the mean cover percentage of small rock fragments (5–20mm) decreased from bottom to top. On the second hillslope (an avalanche slope) without the presence of large rock outcrops, the mean total rock fragment cover (5–600mm) increased from bottom (5%) to top (21%) with decreasing variability and rock fragments with various sizes (5–20, 20–75, and 75–250mm) showed a similar increasing trend. The mean total rock fragment cover increased linearly with slope gradient on the second hillslope and tended to increase and then decrease with gradient but their relationship was not obvious on the first hillslope. This indicated that the spatial distribution of surface rock fragment cover had a close relationship with the presence of large rock outcrops and slope gradient. However, the median diameter (D50) of the surface rock fragments had an increase–decrease trend with slope gradient but there was no obvious relationship on both hillslopes with low overland flow. Therefore, the dominant factor for the spatial distribution of rock fragment cover and size at the soil surface might not be soil erosion by water, but slope gradient, vegetation and geomorphologic condition of the slope. The mean total volumetric rock fragment content (5–250mm) within the topsoil (10–20cm thick) increased linearly from bottom (16%) to top (39%) with slope gradient on the first hillslope, and had a logarithmic increase from bottom (10%) to top (27%) with gradient on the second hillslope. This suggested that rock fragment content within the topsoil was mostly controlled by slope gradient and topographic positions and had not a close relationship with the presence of large rock outcrops. [Copyright &y& Elsevier]