The causes and processes responsible for rocky desertification in karst areas of southern China

The karst region of southern China is a fragile ecological zone with widespread rocky desertification. This paper describes the rocky desertification occurring in this region in terms of both natural and anthropogenic factors. During geological time periods, the region’s changing environment governed the natural rocky desertification processes, whereas during historical and modern times, anthropogenic processes have been superimposed on these natural processes. Human activities have accelerated and exacerbated rocky desertification. The period from the beginning to the middle of the Qing dynasty was an important transitional period in which human activities began to exert a particularly strong influence on rocky desertification. Since then, the effect of anthropogenic factors has increasingly exceeded the effect of natural factors. The rocky desertification process in southern China’s karst region combines surface ecological processes (including vegetation degradation and loss, soil erosion, surface water loss, and bedrock solution) with a reduction of the land’s biological productivity, leading to degradation that produces rocky desert. Controlling rocky desertification requires comprehensive development of sustainable agriculture and economic development that provides employment alternatives to agriculture and thereby promotes the rehabilitation of rocky desertified land.

Spatial heterogeneity of soil water content in the reversion process of desertification in arid areas

Sandy soils in arid,rain-fed environments have low and limited water content,which is a principal factor limiting vegetation development,and a key constraint controlling the structure and functions of the ecological systems in arid areas.The spatial heterogeneity of soil water content is a major soil property,and a focus of soil science and hydrology.On the southern edge of the Tengger Desert,sample plots were selected from mobile sand dunes in desertified lands that had been enclosed for 5,15 and 25 years,respectively.This study explored the dynamic and spatial heterogeneity of soil water content in these different layers of soil that were also in the reversion process of desertification.The results showed that the soil water content of the mobile sand dunes was highest when in the initial stages of the reversion process of desertification,while the soil water content in the 0-20 cm,20-40 cm and 40-60 cm layers of soil was 1.769%,3.011%,and 2.967% respectively,presenting a restoring tendency after 25 years of enclosure.There were significant differences,as a whole,in the soil water content among different restoration stages and different soil layers,respectively.Changes in soil water content,in different soil layers,at different restoration stages,exhibited exponential or spherical patterns.The spatial distribution of soil water content exhibited a mosaic patch pattern with obvious spatial heterogeneity.The ratio of the heterogeneity of spatial autocorrelation to gross spatial heterogeneity was greater than 50%.The gross spatial heterogeneity of the 0-20 cm layer of soil improved gradually,while those of the 20-40 cm and 40-60 cm layers improved initially,then weakened in the reversion process of desertification.This study revealed that restoration with sand-binding vegetation reduced soil water content,and increased its spatial heterogeneity in arid areas.However,after 25 years of vegetation-soil system restoration,the soil water content started to increase and its spatial heterogeneity started to weaken.These results will further benefit the understanding of the ecological mechanism between soil water and sand-binding vegetation.

Desertification status mapping in MuttumaWatershed by using Random Forest Model

Potential of the Random Forest Model on mapping of different desertification processes was studied in Muttuma watershed of mid-Murrumbidgee river region of New South Wales,Australia.Desertification vulnerability index was developed using climate,terrain,vegetation,soil and land quality indices to identify environmentally sensitive areas for desertification.Random Forest Model(RFM)was used to predict the different desertification processes such as soil erosion,salinization and waterlogging in the watershed and the information needed to train classification algorithms was obtained from satellite imagery interpretation and ground truth data.Climatic factors(evaporation,rainfall,temperature),terrain factors(aspect,slope,slope length,steepness,and wetness index),soil properties(pH,organic carbon,clay and sand content)and vulnerability indices were used as an explanatory variable.Classification accuracy and kappa index were calculated for training and testing datasets.We recorded an overall accuracy rate of 87.7%and 72.1%for training and testing sites,respectively.We found larger discrepancies between overall accuracy rate and kappa index for testing datasets(72.2%and 27.5%,respectively)suggesting that all the classes are not predicted well.The prediction of soil erosion and no desertification process was good and poor for salinization and water-logging process.Overall,the results observed give a new idea of using the knowledge of desertification process in training areas that can be used to predict the desertification processes at unvisited areas.

The desertification and its rehabilitation inSongnen Sandy Land

Songnen Sandy Land lies in the eastern fringe of huge sandy belt of middle latitude inEurasia Continent Here is also the eastern fringe of desertification-prone land in China. Its specialconditions such as biology and climate, the history of evolution of sandy land and its location make itpossess features differing from other sandy lands in the country. This article systematitaly discussesthe regional featured such as the historical process, modern process, environmental factors ondesertification and the sandy land landscape and the degree of desertification, and raises some advicesfor rehabilitation and development in this area.

Desertification hazard zoning in Sistan Region, Iran

Desertification process as a great problem affects most of the countries in the world. This process has a high rate in arid and semiarid areas. Today, human societies are en- countering the desertification phenomenon as a serious problem which causes various ir- reparable damages to economic and social sectors. In order to assess desertification results in production of different regional models for their application in another region the indices should be re-investigated and adjusted to local conditions. Several models have been de- veloped for desertification evaluation. The present study, attempts to assess quantitatively the desertification process has in an area located at Sistan plain of Iran （Niatak region as a case study） by using Modified MEDALUS method. The obtained results indicated that of the whole studied region （comprising 4819.6 acres）, 2651.56 acres （55%） are located in medium de- sertification intensity class, 1269.48 acres （26.34%） are positioned in severe desertification intensity class, and 898.54 acres （18.64%） are placed in vary severe desertification intensity class.