Research On The Growth Characteristics Of Shelterbelts And Soil Physical And Chemical Properties In Huajialing

Huajialing Shelterbelt, located at the Loess Hilly Region of East Gansu Province,is an important part of Three-North Protection Forest System in the central part ofGansu and plays an important role in the construction of the regional ecologicalbarrier system. The growth characteristics of shelterbelts, environmental adaptabilityand the changes of soil physical and chemical properties of Huajialing Shelterbeltwere analysed, according to the method of sample plot investigation, sampling andlaboratory routine analysis on the basis of theories of forest ecology and ecologicalengineering, to provide scientific basis for the selection of tree species and regulationof stand structure, and lay a theoretical foundation on promoting forest health andsustainable development of the shelterbelt. The conclusions are as follows:(1) The average DBH, average height and individual volume of the mean age of37.5years old poplar woods were10.35cm,6.10m and0.0212m3respectively, whichseemed to growth declination and forest loss overall; while the average DBH, averageheight and individual volume of the mean age of22a pure picea forest and20a purepine forest were8.10cm,5.31m,0.0195m3and11.80cm,7.90m,0.0475m3respectively. The growth state of young picea shelterbelt and pine shelterbelt had beenclose to the mature (overmature) shelterbelt, or even more.(2) The average DBH and average height of all kinds of stands in HuajialingShelterbelt showed negative correlation with the stand density. The growth conditionof picea and poplar mixed forest was better than pure poplar forest under the influenceof stand density, while the growth condition of pure picea forest and pure pine forestwere better than picea and pine mixed forest and picea and larix mixed forest.(3) The DBH growth of picea forest in Huajialing was more significant during10a～15a and25a～30a, while the tree height growth was more significant during20a～25a. The average height and DBH of picea forest were positively correlatedwith altitude, and the average DBH was significant positively correlated with altitude.It was more conductive to the growth of picea shelterbelt in shady environment.(4) The order of average soil bulk density of different forest types was purepoplar forest（1.45g/cm3）﹥pure pine forest（1.31g/cm3）﹥pure picea forest（1.28g/cm3）; the order of average non-capillary porosity was pure picea forest（4.08％）﹥pure pine forest（3.24％）﹥pure poplar forest（3.17％）; the order of saturation holding capacity of soil was pure picea forest（9711.97t/hm2）﹥pure pineforest（9628.55t/hm2）﹥pure poplar forest（8994.54t/hm2）. It showed that soilphysical properties of pure picea forest were obviously better than pure pine forestand pure poplar forest. The average capillary porosity of picea forest increased withthe increasing of the forest age, and the ventilation and the permeability of soil weregradually improved, meantime, the capacity of water conservation graduallyincreased.(5) The soil chemical properties of pure picea forest was better than pure pineforest and pure poplar forest; the soil available P and organic matter showed anfluctuating upward trend, and the soil total P decreased at first and then increased, andthe soil available and total N、K was fluctuating; with the increase of the forest age, allof the chemical index except available P and total K in different age of picea forestincreased by different degrees; the soil available N, total N, total P and organic matterincreased, decreased and then increased at last with the increase of altitude; thecontent of soil available N and organic matter in sunny slope was lower than that inshady slope and ridge top the content of soil available P, K, total N, P, K showed nosignificant change.