The studying findings were: from 1991 to 2000, the farming land decreased by 39,853 hm2, the proportion accounting for total land areas decreased from 24.09% to 18.18%; the forest land and pasture increased by 27,055 hm2 and 13,251 hm2 respectively, the proportion increased from 5.48% and 66.64% to 9.49% and 66.60% respectively;
Compared with native pasture, cultivation of annual pasture resulted in significant reductions of total organic C by 36% in 0~10 cm, 29% in 10~20 cm and 41% in 20~30 cm depths, whereas in perennial pastures total organic C decreased by 18% only in 0~10 cm depth.
Compared with natural grassland where vegetation cover was more than 80%,at 0-20 cm depth the soil sand particle content increased by 10.7% and 15.2%,soil weight per unit volume increased by 9.3% and 12.4%,and bulk density decreased by 10.4% and 13.9% in grasslands with moderate and severe degrees of desertification respectively and whose vegetation covers were less than 50% and 10% respectively.
In this thesis,the research methods and main content of underground biomass in grasslands in China were summarized,such as the underground biomass spatial distribution,seasonal dynamics,the ratio of underground and aboveground biomass,and the influencing factors.
2. at about the same slope (19～22°), the quantity of soil loss is farming land (2 312 t/km~2)>grass land removing from plough (981t/km~2)>closed slope(67t/km~2) >slope land with vegetation(19~24t/km~2);
The results showed that from spring to autumn in the fourth year,compare to oat,total nitrogen in 0-10 cm soil in perennial grass was 0.07% higher,0.11% higher in 10-20 cm and 0.09% higher in 20-30 cm.
Results showed,Through the general observation of phosphorus transport under different land use of purple soil, we calculate that the total P in surface water of upland, paddy fields, forest land and grass land is 0.42mg/L, 0.19mg/L, 0.08 mg/L, 0.10 mg/L respectively.
the minimum saturated hydraulic conductivity of the north Larix gmelini pure plantation is 1.22 mm/min,the saturated hydraulic conductivity of Larix principis-rupprechtii and Picea crassifolia mixed plantation is 0.17 mm/min which is the least in the forest land,grass land and farmland is respectively 0.11 mm/min and 0.09 mm/min.
The threshold wind velocity of a number of variables was studied in four different land-use types: farm land, forestland, wild grassland and a flood plain in the Yongding River sandy land in Beijing.
The following conclusions were drawn: 1) The order of decreasing threshold of wind speed for sand displacement and surface roughness were forestland, wild grassland, farm land, sparse wild grassland and flood plain.
3) The mechanical composition of sand particles consisted mainly of silver sand in the flood plain and sparse wild grassland, and of silver sand, particle silver sand and floury sand in other land-use types.
The whole study area was divided into the wetland zone, the ecotone and the arid grassland zone in terms of habitat characteristics and vegetation types.
The greatest evenness indices (E) were found in the arid grassland zones.
We concluded that the conversion project from croplands to forests and grasslands based on scientific principles is very important in the formation of carbon sinks for reducing greenhouse effects.
The relationship between species richness and productivity in four typical grasslands of northern China
In this paper, we examine the relationship between species richness and productivity in four typical grasslands of Northern China at different spatial scales.
For all classes of ecosystems, the proportion of underground phytomass averages 26.7% of the total amount, varying from 22.0% in forests to 57.1% in grasslands and brushwoods.
Other land-use/land-cover (LULC) classes have the following NPP densities (in areas covered with vegetation): grasslands and brushwoods, 278 g C/m2; forests, 224 g C/m2; and wetlands, 219 g C/m2per year.
The average annual biomass of fine roots in ryegrass was twice that of the mixed natural grass-forest land.
The total amount of natural grass roots was 4.4 times that of the ryegrass model.
The amounts of water-stable aggregates of natural grass-forest lands (TN model) were higher than those of managed grass-forest lands (TL model).
We conclude that the program of converting agricultural lands to forest-grass lands is an effective way in improving soil anti-erosion capability.
The 26 remaining spectral clusters were merged into six vegetation types using the Chinese vegetation taxonomy system: evergreen broad-leaved forest, coniferous forest, bamboo forest, shrub-grass, aquatic vegetation, and agricultural vegetation.