Study On Dust-retention Pattern And Its Influence Mechanism In Three Kinds Of Road Protection Forests In Beijing

Urban forest is able to adsorb and block airborne particles through their foliage and complex canopy structures.Road protection forest is an important part of urban forest,which has protective effect to particulate pollution mainly caused by road traffic.In this paper,three representative protection forests in Beijing were selected as the research object.Leaf dust-retention,dustfall to forest ground,and particular matter concentration in 3 forests were observed continuously and synchronously in a whole year.Temporal-spatial change and influence mechanism of dust-retention effect in 3 forests were systematically studied.Results showed that:1.Comparison of dust-retention ability among 3 forests.(1)Leaf scales dust-retention ability of 3 forests was Sabina chinensis forest> Ginkgo biloba forest> Pinus tabulaeformis forest.The dust-retention ability of Sabina chinensis forest and Pinus tabulaeformis forest in different seasons showed winter> spring> autumn> summer,while in Ginkgo biloba forest,spring and autumn approximately equal,summer was the lowest.Plant and forest scales ability of 3 forests was Pinus tabulaeformis forest > Sabina chinensis forest> Ginkgo biloba forest.(2)There was no significant difference between 3 forests in dustfall amount.in different seasons dustfall amount showed spring> winter> summer >autumn.(3)TSP and PM10 concentration showed spring> winter> summer >autumn,while PM2.5 and PM1 concentration showed winter was the highest,and no significant difference between spring,summer and autumn.(4)Seasonal change of leaf dust-retention,dustfall,TSP,and PM10 showed high correlation with each other,while low correlation with PM2.5 and PM1.(5)Both yearly and seasonal total dustfall amount were all higher than total canopy dust-retention amount.2.Temporal change of dust-retention of 3 forsts.(1)Sabina chinensis forest had higher stability of leaf dust-retention.Both growth rate and reduction rate of Ginkgo biloba forest was the highest.(2)Rangeability of leaf dust-retention showed winter was the lowest and other seasons were high.(3)Dustfall temporal change showed same trend in 3 forests.Rangeability of dustfall showed winter was the highest.(4)Leaf dust-retention and dustfall showed positive correlation,and the correlation was lower in winter and spring,higher in summer and autumn.3.Spatial distribution of dust retention in 3 forests.(1)Spatial distribution of leaf dust-retention,dustfall,TSP and PM10 showed similar characteristics and obvious correlation.Pinus tabulaeformis forest and Sabina chinensis forest showed single valley distribution while Ginkgo biloba forest showed dual valley distribution.(2)Spatial distribution of leaf dust-retention,dustfall,TSP and PM10 in different seasons all showed that Xiangshan road was higher in winter,while Wuhuan road was higher in spring,and no significant difference were found between two sides in summer and antumn.(3)There was difference in leaf dust-retention amount between north and south side of tree conopy in 3 forests.The side near road was obviously higher than beyond the road.From side to inner,the difference went lower.4.Effect of weather conditions on dust-retention of 3 forests.(1)Low rainfall showed promotion to dust-retention while high rainfall showed redution effect.The reduction effect of rainfall on 3 forests showed Ginkgo biloba forest > Pinus tabulaeformis forest > Sabina chinensis forest.(2)All grade wind speed showed promotion to leaf dust-retention and the most in Ginkgo biloba forest.Dustfall amout went higher along with wind speed.(3)High pollution weather and sauna weather all showed promotion effct to leaf dust-retention while reduction effect to dustfall.