| Casuarina equisetifolia was originated from Australia and Vietnam and introduced in China in 1950s,has been showing a good adaptability and high productivity.It play an important role in wind break and sand fixation,ameliorating ecological environment and offering timber along the southeast coast of China.To some extent,it has become one of the irreplaceable plantations in protecting plantation,particularly on the wind gap site.The structure condition of coastal protection forest is the key factor which affects the Judeich protection potency,from November,2006 to March,2008,we study on the protective potency of the protection forest mainly made up by Casuarina equisetifolia and farmland shelterbelt behind that of chishan tree farm in dongshan county,Fujian province.Evaluating regional wind-break potency of farmland shelter forest network by studying on the structure characteristics of protective potency of different protection forest,investigating the effect to the protective potency of protective forest and ecological effects in the farmland protective forest network through studying on various structures composed of the following factors:transparence degree,tree species composition,forest levels,stands density,stands age,tree height,diameter at the breast height,width of shelterbelt,distances between shelterbelt,etc.Finding out quantitative evaluation methods of wind-break potency of casuarina protection forest by mathematical theory,determining the dominant factors of effecting protective potency of different structures of shelterbelt.Providing scientific and rational conclusions to the reasonable transformation and sustainable management of coastal protective forest.The results indicated that:1.The shelter belt of sparseness structure has a long protection distance and the strongest protective efficacy,the wind speed may fall to 16.4%of the open territory at 1 time of tree height after the forest belt,then the wind speed increases,but the increasing extent of the wind power is not high.And the windproof potency of the close structure and the ventilates structure is poor.2.The mixed forest of Casuarina equisetifolia and the pinus elliottii,thick pod lovesickness, Congo an ect.Is benefical to enhancing protection potency.And when the planter proportion of the beefwood and the thick pod lovesickness is 1:4 and for beefwood and the pinus elliottii proportion is 1:3,the shelter belt have a good windproof effect;In the thick pod lovesickness multiple coat forest of Casuarina equisetifolia and the pinus elliottii,the wind speed reduces 3.3%compared with which after the Casuarina equisetifolia monolayer forest's belt at a distances of 20 timea of tree height.3.The windproof ability drops when the age of Casuarina equisetifolia protective forest is more than 30 years,windproof potency 37 years old of Judeich is only 32.2%,decreasing 16.6% compared to 30 years old satnds,even lower than which are in the vegetal period,compared to the windproof potency of the forest at three years old,dicreased 4.4%.That indicated that:Casuarina equisetifolia protective forest of 37years old has already was at the decline stage.4.The forest belt width is one of the factors which composes forest belt structure,the observation of windproof potency of main forest belt widths at 0.5H,0.5～1H,the 1～2H indicated that.the lowest wind speed is about 45%at the 20H scope after three kinds of belt wide bands,and appears at 3H～4H after the belt When sparse degree and the growth condition are close to each other,the windproof potency decrease slightly after increasing the forest belt width.5.The height of forest belt affects the windproof potency of the forest belt,research on the average tree height is 6.2m,8.5m and the 11m stands indicated that the height of forest belt increases can enhance the windproof potency of the forest belt and the absolute value of protection distance of forest belt is proportional to the tree height,but the relative value doesn't have a significant change.6.The forest belt have different continuous windproof effect at the differences main forest belt distances.Research on the change of wind speed at 150×100m,200×150m and 80×150m of different specification's network of forest belts,discovered that main forest belt have a small distance have a good windproof effect.The protective potency at 150×100 and 80×150m network of forest belts is separately higher of 12.5 and 2.1 percentage points than 200×150m.7.Research on windproof potency in the same belt at different wind speed indicated that the wind speed increases,then the windproof potency of forest belt increases too,when wind speed increases to 10.6m/s from 4.5m/s,the average windproof potency increases to 55.1%%from 9.8%at the 20H scope after the belt.8.The coastal forest belt,the network of forest belts are very beneficial to the environmental enhancement,in winter seasons that may reduce pitch ground's even temperature equally 0.84 and 1.68℃at 0.5m～1.5m after the forest belt;and improve the relative humidity increases 2.4% equally,which can help the crops survive the winter,and the growth in the farmland network of forest belts,and prevents the freezing injury.9.Rearch onthe regional windproof effect of the farmland network of forest belts we found: the windproof effect has positive correlation to the height of forest belt,and has the inverse correlation to sparse degree and the supplementary forest belt length,the hejght of forest belt increases,the supplementary forest belt length reduces,sparse degree reduces,that can enhance the regional windproof effect of the network of forest belts.The height of forest belt have the biggest contribution rate to protective potency,secondly is the length of supplementary forest belt, sparse passing,then difference.10.Using the mathematical quantification method,the main influencing factors of windproof potency of forest belt in sequences as:Crown>tree height>tree diameter at breast height> landform type>density of stocking>height under branch>forest belt width.According to the principle of adjust measures to local conditions and the request of improve the protection effects of forsetbelt,designed the configuration scheme of management pattern of Casuarina equisetifolia trunk shelterbelt,configuration scheme of management pattern of Casuarinas equisetifolia shelterbelt on the lagging and configuration scheme of management pattern of farmland shelterbelt network,it can provide reference for planting of protection forest,application and popularization. |
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