Study On The Change Of The Soil Moisture Content And Its Effect On The Vegetation In The Ulmus Pumila Umbrella Area

The distributing number and depth of the roots of Ulmus pumila and the vegetation in Ulmus pumila tree umbrella area was analyzed using soil excavation. The results were as follow: the distributing depth of the vegetation roots in the tree umbrella area was mainly from 0 to 45cm, and the depth of the concentrating roots was from 15 to 35cm depth, the vegetation roots were found a few under 60cm. The distributing depth of the tree roots was mainly from 60 to 105cm ,and the depth of the concentrating roots was from 75 to 105cmï¼›the tree roots were found a few from 120 to 200cm.The number of Ulmus pumila roots distributed mainly over the vertical projection area of the tree crown (0.5r plot and 1r plot), and the number of the outside area (1.5r plot and 2r plot)decreased with increasing distance from the treeï¼›r was the average radium of the tree crown (approximately for 5m)The results of the soil moisture content in the tree umbrella area were as follow: the average soil moisture content increased with increasing distance from the tree. The average soil moisture content in the vertical projection area of the tree crown (0.5r plot and 1r plot) was lower than the outside area (1.5r plot and 2r plot).Except the last ten days of June ,the average soil moisture content in 105~135cm depth was higher than the root layers(60~105cm depth) of the tree. On the last ten days of June and the last ten days of August, the average soil moisture content of the root layers of the vegetation is the highestï¼›on the first ten days of August and the last ten days of September, the average soil moisture content of the root layers of the vegetation is the lowest.The numerical characteristics of the vegetation in the tree umbrella area was analyzed using quantitative sampling belt. The results were as follow: the above-ground biomass increased with increasing distance from the treesï¼›the above - ground biomass was the lowest in the area near tree(0~2.5m), was the highest in 2r plot(7.5~10m),and was close between 1r plot (2.5~5m) and 1.5r plot (5~7.5m). The natural height of the vegetation in the area near tree was the lower than the outside areaï¼›the density and relative coverage of the vegetation were the highest in 1r spot(2.5~5m).