Effects of Farmland Shelterbelts in Controlling Wind and Sand in Sandy Land of Yanchi

Field observation on effects of typical farmland shelterbelts in controlling wind and sand in the sandy land of Yanchi in Ningxia revealed that the shelterbelt of Caragana microphylla shrubberies provided shelter over the woodlot per se and 0-3H(H stands for height) at the leeway edge of the forest,with a limited effective range in the leeway;that the wind speeds at both windward side and leeward side of the shelterbelt of Salix psammophila were greater than the threshold velocity(4.53 m·s^-1)of sand rising,so the shelterbelt gave little protection of the farmland;and that the fragmentary shelterbelt of Ulmus pumila,was unable to play its wind-breaking role.Sands accumulated on the leeway side of the latter two shelterbelts,indicating that they could not effectively prevent aeolian sands from coming into the farmland,while sands arrested inside the belts of Caragana microphylla,showing its effectiveness in controlling aeolian sands.