Vegetation and Soil Restoration Process by Grazing Control at Desertified Sandy Grassland in Semi-arid Regions of Northeast China

27 Mar Vegetation and Soil Restoration Process by Grazing Control at Desertified Sandy Grassland in Semi-arid Regions of Northeast China

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Abstract

過放牧による砂漠化が問題となっている中国内蒙古自治区奈曼を事例として, 禁牧年数の異なる砂地草原での調査をもとに, 植生及び土壌の変化を地形条件との関連で把握したうえで, 放牧管理による植生・土壌回復プロセスの立地間差異について検討した。本研究の結果, 植生分布およびその動態は, 地形条件と関連した土壌特性あるいは水分条件の差異に規定されることが示唆された。植生および土壌の回復速度も地形条件によって異なり, 砂丘下部や平沙地では禁牧後速やかに回復へ向かうのに対し, 砂丘中～ 上部では, 20年程度の期間を要することがわかった。以上の結果に基づき, 地形タイプごとに持続的土地利用のあり方について検討した。

English Abstract

The process of vegetation and soil restoration by grazing control was studied at desertified sandy grassland in semi-arid regions of northeast Chi . The 128 quadrats (1m×1m) were situated along the transects set on sand dunes and flat sandy lands differing in the duration of grazing control, and the surveys of vegetation, soil property and topography were conduced. TWINSPAN was performed for all samples to classify the floristic data. Canonical Correspondence A lysis (CCA) was also applied for the samples of sand dunes to explore the relation between vegetation restoration and environmental variables including soil property and topography.
The samples were classified into two types by the first division of TWINSPAN which reflects not duration of grazing control but topography. This result suggested that soil property including texture, organic matter, nitrogen, and moisture condition related to topography were the important factors that determine vegetation distribution and successio l patterns. The result of CCA revealed that on sand dunes the process of vegetation restoration corresponded with that of soil restoration, and also varied with micro topography such as the position of dune slopes. The duration of grazing control required for the restoration was also different depending on topography. On flat sandy land and lower part of sand dune where surface soil still remained, vegetation would recover quickly by grazing control, while it would take about 20 years on the middle and upper part of dunes.
Those results suggested that the ecological evaluation of a carrying capacity at each land unit, e. g. landform unit, should be needed to maintain a sustai ble land use at a sandy grassland in semi-arid regions.