Research On The Influence Of Vegetation Canopy And Litter On Snow Distribution And Soil Freeze-thaw Process

Freeze-thaw erosion is serious in spring thaw period in the Northeast China. Vegetation canopy and litter play an important role in the change of snow distribution, soil hydrothermal conditions, freeze-thaw process, and freeze-thaw erosion. A large number of studies have been carried out on the effects of vegetation and crop residues on the snow distribution and soil freeze-thaw process. However, there was no study on the snow and soil freeze-thaw process from the different vegetation types community and individual scales, and the soil temperature and freeze-thaw process under the litter cover was rarely reported too.In this study the different vegetation types of Tree Shrub Grass and Farmland in Quanhe watershed, the vegetation community with different vegetation coverage and plants density in Shenyang Agricultural university Nursery Garden, and the plants with different canopy morphology in Shenyang Agricultural university Botanical Garden were chosen to observation the snow and soil thawing, study the influence of vegetation canopy on snow distribution and soil thawing from the different vegetation types community and individual scales. By the simulation experiments of undisturbed litter cover taken from Quanhe watershed, study the influence of litter cover on soil temperature and freeze-thaw process. Draw the following conclusions:(1) Influence of vegetation on the snow distributionThe difference of snow distribution in different vegetation types was significant, the average snow depth was decline in the order of Farmland, Shrub, Broadleaved deciduous forest, Evergreen coniferous forest and Grassland. The semi variance analysis results show that the total spatial heterogeneity of snow distribution was decline in the order of Farmland, Shrub, Grassland, Broadleaved deciduous forest and Evergreen coniferous forest. At the community scale, the vegetation coverage is the main factor influence the snow distribution. With the vegetation coverage decrease, snow increased. For the plants the average snow depth was decline in the order of Flat topped deciduous tree(Eucommia ulmoides Oliver), Spherical deciduous shrub(Amygdalus triloba), Cylindrical evergreen tree(Sabina chinensis) and Pyramid evergreen tree (Picea wilsonii Mast) in the first snowfall. The average snow depth of plants in the Northwest was greater than that in the Southeast generally. The snow depth from plants root to crown edge of Amygdalus triloba、Picea wilsonii Mast and Sabina chinensis was increasing while the Eucommia ulmoides Oliver was change a lot in the observation period.(2) Influence of vegetation on soil thawingThe difference of soil thawing in different vegetation types was significant, the average soil thawing depth was decline in the order of Grassland, Shrub, Farmland, Broadleaved deciduous forest and Evergreen coniferous forest. The semi variance analysis results show that the total spatial heterogeneity of soil thawing depth was decline in the order of Shrub, Grassland, Broadleaved deciduous forest, Evergreen coniferous forest and Farmland. At the community scale, litter thickness had a significant negative correlation with the soil thawing depth, and the vegetation coverage is the main influence factor on soil thawing too, with the increase of vegetation coverage, soil thawing depth decreased. For the plants the average soil thawing depth was decline in the order of Flat topped deciduous tree (Eucommia ulmoides Oliver), Spherical deciduous shrub (Amygdalus triloba), Pyramid evergreen tree (Picea wilsonii Mast) and Cylindrical evergreen tree (Sabina chinensis). The average thawing depth of soil on the east side was the largest in the thawing begin period while in the thawing late period the Southwest was greater than the Northeast generally. The average soil thawing depth from plants root to canopy edge was increasing.(3) Influence of undisturbed litter on soil temperature and freeze-thaw processLitter cover could extended the soil freezing duration of monitored layers, especially in the freezing begin period, and the thicker the litter, the more complete the structure, the more obvious of extension effect. But the effect on soil thawing process of monitored layer was different due to the different composition and thickness of the litter during the thawing period.The effect of litter cover on soil temperature had two sides, which kept soil warm in the freezing begin period and the complete freeze period, while insulated the heat in the thawing period. The litter cover could restrain the fluctuation of soil temperature, the difference coefficient of soil temperature under different litter cover was decline in the order of CK,4 cm undisturbed litter collected from Pinus tabulaeformis forest,8 cm undisturbed litter collected from Quercus mongolica forest,8 cm undisturbed litter collected from Pinus tabulaeformis forest. The thicker the litter and with un-decomposition layer half decomposition layer and complete-decomposition humus layer same time, the better the effect of regulating the soil temperature which above 30 cm. While only 20 cm above the soil temperature regulation effect is better, when there was only un-decomposition layer and half-decomposition layer.