Peak-cluster Depression Research Articles

Spatio-temporal evolution of rocky desertification and its driving forces in karst areas of Northwestern Guangxi, China

Rocky desertification (RD) is a process of land degradation that often results in extensive soil erosion, bedrock exposure and considerable decrease of land productivity. The spatio-temporal evolution of RD not only reflects regional ecological environmental changes but also directly impacts regional economic and social development. The study area, Hechi, is a typical karst peak cluster depression area in southwest China. Remote sensing, geographic information systems (GIS) and statistical techniques were employed to examine the evolution, including the identification of driving forces, of karst RD in the Northwestern Guangxi. The results indicate that RD became most apparent between 1990 and 2005 when areas of various types of RD increased. Within the karst RD landscape, slight RD was identified as the matrix of the landscape while potential RD had the largest patch sizes. Extremely strong RD, with the simplest shape, was the most influenced by human activities. Overall the landscape evolved from fragmented to agglomerate within the 15-year timeframe. Land condition changes were categorized as five types; desertified, recovered, unchanged, worsened, and alleviated land. The largest turnover within the RD landscape was between slight and moderate RD. With regards to the driving forces all RD had been increasingly influenced by human activities (i.e., the stronger the RD, the stronger the intensity of human disturbances). Dominant impact factors of the RD landscape had shifted from town influence and bare rock land in 1990 to bare rock and grassland in 2005. Moreover, the impacts of stony soil, mountainous proportion and river density on RD increased over time, while that of others decreased. The significant factors included human activities, land use, soil types, environmental geology, and topography. However, only anthropogenic factors (human activities and land use) were reported as leading factors whereas the others acted simply as constraining factors.

The Heterogeneity and Its Influencing Factors of Soil Nutrients in Peak-Cluster Depression Areas of Karst Region

By selecting a typical peak-cluster depression area of karst region in Southwest China, we evaluated the effect of land use types and topographic factors on soil nutrients. Grid and line sampling methods were used to sample soil in depression and slope lands respectively, and classical statistical tools were applied to analyze the spatial variability character of soil organic carbon (SOC). total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available phosphorus (AP), available potassium (AK), pH, and C/N. It was found that land use type was the dominant factor that effected the spatial heterogeneity of SOC, TN, TP, TK, AN, and AP. The content of SOC, TN, and AN decreased with the increase of land use intensity. Due to high fertilizer input, TP and AP in tillage fields were higher than those in the other land use types. TK had no obvious change trend among various land use types. Topographic factors had a significant effect on SOC, TN, TP, AN, AP, AK, and pH. Habitat factor was the dominant factor that effected AK. Altitude factor was the dominant factor for pH. However, all of these factors had no significant effect on C/N. Tillage practice had important effect on soil nutrients loss and soil degradation in the fragile karst ecosystem, and the input of organic manure should be increased in this region.

Characteristics of Karst Ecosystems of Vietnam and Their Vulnerability to Human Impact

AbstractKarst in Vietnam covers an area of about 60,000 km2, i.e. 18 % of the surface of the country. The country has an annual average temperature of 24°C, an annual average rainfall of 2300 mm and a relative humidity of about 90%. Karst in Vietnam is typified by peak cluster‐depression landscapes ranging in elevation from 200 to over 2000 m. Tower and coastal karst landscapes also exit. Because of naturally favourable conditions, karst ecosystems are diverse and very rich. Higher plants (cormophytes) are abundant. They are represented by approximately 2000 species, 908 genera, 224 families, 86 orders and 7 phyla. They form a thick vegetation cover of evergreen tropical rainforest. Knowledge about lower plants is limited. The fauna is rich and diverse. Phyla such as Protozoa, Vermes, Mollusca and Arthropoda are yet ill known. Preliminary results show that the phylum Chordata is represented by 541 species from 80 families, 40 orders and 5 classes. There exist many precious and rare mammals, in particular some endemic species such as Trachypithecus poliocephalus, T. delacouri, Rhinopithecus avanculus, Rhinolophus rouxi, Seotoma dineties and Silurus cuephuongensis. The class Insecta has about 2000 species.The fast population growth, particularly in the mountainous areas of the country, triggers an increasing demand for land and therefore threatens the ecosystem. To obtain land for farming, people have cut, burned and destroyed natural forest cover; resulting in occurrence of hazards such as soil‐loss, water‐loss, flash floods, mud‐rock flows, rock‐falls, severe drought, water logging and changes of karstic aquifers etc. Poaching precious animals and illegal logging are increasing. In contrast to other natural systems, karst ecosystems cannot be reestablished once damaged. Living karst landscapes will become rocky desert ones without life. Conservation of karstic environmental systems in general and karstic ecosystems in particular should not be the sole vocation of scientists but also a duty and responsibility of authorities and people from all levels. A good example of a multidisciplinary approach to karst‐related problems is the implementation of the Vietnamese‐Belgian Karst Project (VBEKAP): “Rural development in the mountain karst area of NW Vietnam by sustainable water and land management and social learning: its conditions and facilitation”. The aim of this project is to improve living conditions of local people and sustained protection and management of the karst environment and ecosystem.