Zhang Yang-zhen

Dynamics of saline-alkali land and its ecological regionalization in western Songnen Plain, China

As the important reserve land resources for food production, saline-alkali land should play a significant role to ensure the national food security in the context of global food crisis. The western Songnen Plain is one of main distribution regions of saline-alkali land in China, with great potential in agricultural development. In this study, the extent, transformation, spatial distribution and temporal change of saline-alkali land in the western Songnen Plain during 1954–2005 were investigated by using remote sensing and GIS spatial analysis methods. Saline-alkali land change was detected from a temporal series of topographic maps in 1954, satellite images of Landsat MSS in 1976, Landsat TM/ETM in 1988, 2000 and 2005 through artificial visual interpretation. The results indicated a significant expansion in saline-alkali land area and aggravation in salinization. The area of saline-alkali land had increased from 401.48×103 ha in 1954 to 1 097.45×103 ha in 2005. While the ratio of light, moderate and serious salinized land areas changed from 6.72:2.92:1.00 to 1.25:1.06:1.00 in the study period. Grassland, cropland, swampland and water body were the major land use and land cover types from which saline-alkali land transformed. And the secondary salinization occured mainly in Da’an City, Tongyu County, Changling County, Daqing City, Dorbod Mongolian Autonomous County and Zhaoyuan County. Finally, seven large ecoregions and 14 corresponding sub-ecoregions were delineated out based on spatio-temopral dynamic characteristics of saline-alkali land and geo-relational environmental attributes. According to the results, measures of amelioration and ways of development of saline-alkali land in the western Songnen Plain were put forward.

The driving forces of land use/cover change in the upstream area of the Nenjiang River

Based on the Landsat 5 and Landsat 7 TM images, the land use/cover change was detected in the upstream area of the Nenjiang River between 1995 and 2000. With the spatial analysis techniques of GIS, the maps of land use degree and its change within this period were produced. To identify the causes of changes, elevation and slope were regarded as the main natural influencing factors and were transformed from coverage format to grid format within GIS. The Thiesson polygon method was used to the spatial allocation of socio-economic factors including human population, live-stock numbers, mechanizing power of farming and the nearest distance from the changed pixel to the trunk stream and to main settlements, thereby the spatial relationship between land use degree change and socio-economic factor variation was analyzed. According to results of the spatial correlation, the determinants of changes in land use/cover, i. e. elevation, slope, population density change, livestock increase were extracted quantitatively in this area. At last, the spatial multi-linear regression model of land use degree change was developed as follows: Δ La=11.037−4.512* elevation-0.298* slope+0.292* Δ population+2.596* Δlivestock.

The mire in northeast of China

The northeast region is one of the principal mire distribution regions in China. According to the process of peat formation and accumulation, middle geomorphology type controlling water source supplement and the plant cover, 2 types, 10 subtypes and 27 mire bodies are divided. The mire area decreases gradually from north to south. There is more peat mire in the mountain and there is mainly gley mire without peat in the plain. The paper also explains the mire types in the principal mire distribution region and the utilization of mire in the fields of agriculture, forest, animal husbandry. The mire is a wetland ecosystem. It can reserve a lot of water, adjust rivers, humidify air. Thereby, attention must be paid to protecting ecological balance in the process of reclaiming mire and the mire protection.The northeast region is one of the principal mire distribution regions in China. According to the process of peat formation and accumulation, middle geomorphology type controlling water source supplement and the plant cover, 2 types, 10 subtypes and 27 mire bodies are divided. The mire area decreases gradually from north to south. There is more peat mire in the mountain and there is mainly gley mire without peat in the plain. The paper also explains the mire types in the principal mire distribution region and the utilization of mire in the fields of agriculture, forest, animal husbandry. The mire is a wetland ecosystem. It can reserve a lot of water, adjust rivers, humidify air. Thereby, attention must be paid to protecting ecological balance in the process of reclaiming mire and the mire protection.