A Study On Major Native Tree Species On Loess Plateau Of Northern Shaanxi Province

Loess Plateau of Northern Shaanxi,including mainly Yulin,Yanan,Tongchuan,lies in the middle reaches of Yellow River. Severe loss of soil and water hasits devastating effect on ecological environment of the area concerned. Nativeforest tree species, scattered in northern Shaanxi ,are major plant resource,for vegetation recovery and ecological improvement. Based on the data fromsample plots located in Fugu,Shenmu,Yuyang,Suide,Baota, Ganquan, Fuxianand Tongchuan, a floristical analysis and a result to arbors general surveyare given in the author；By setting up model and other methods, some biologicalcharacteristics of major native forest tree species were educed,such asphenology, growth, root distribution characteristics , meanwhile someindividual ecological characteristics,such as resistibility, adaptability,and characteristics of major nature forest were summed up and analyzed. Onthe basis of this research, several native trees are recommended,an appraiseto forest risk was made,otherwise the forest developing direction was pointedout. 1. According to the investigation and analyses,the xylophyta resourceof northern Shaanxi can be rudimentarily documented,and divided into 14 groupsto their usage, such as medical species, starch and candy species,and so on；A floristical documentation indicates that the native vegetation of Yulin sandarea is grassland, however only remains of them remain existed；sand plantshave taken up a leading position. Families'distribution types belong to northtemperate or cosmopolitan, which have an interlock characteristic betweensouthern grassland and northern forest. Xylophyta, especially tall and bigarbors resource are deficient. The loess area has rare vegetation andrelatively poor xylophyta resources though it is vast. The flora of majornative trees belong to North Temperate, E.Asia,E.Asia & N.Amer.disjuncted,Endemic to China and Pantropic. 2. According to analyzing distribution of growth index (high, DBH,closing), a common law was found,namely the short, thin, low storage andIII陕北黄土高原主要成林乔木树种的研究poor closing stands take up a leading position, northwards, the more obviousthis kind of advantage is, By analytic stem,and comparing all species growthcourses, and using Champan-Richards model, the characteristic of growthfactor for single arbor was got,meanwhile,fast-growing orders to high, DBH,stem volume were got too. The analysis of main native arbor in Baota district indicates that nativearbors in loess plateau have the same developing rhythm. Their positive growthperiod is in phase with the period (June - August) which has rich hot andmoisture Soil drilling and root digging method are applied for root distributioncharacters investigation in field work. According to the value of β,asequence(from deep to shallow) of 10 roots perpendicular distribution in thesame stand was deduced, i, e. Armeniaca sibirica, Quercus liaotungensis, Pyrusbetulaefolia, Pinus tabulaeformis,Populus simonii,Salix matsudana,Betulaplatyphylla, Populus davidiana,P. hopeiensis, Platycladus orientalis.Moreover the differences between deep－root arbors(represented by Pinustabulaeformis ) and shallow － root ones ( represented by Platycladusorientalis)in utilizing soil moisture. 3． By summarizing and comparing individual ecological characteristics,such as temperature, moisture, soil adaptability and shade－tolerance,etc.,the arbors were classified into barren-resistant species( Platycladusorientalis, Pinus tabulaeformis, Armeniaca sibirica, Betula platyphylla,Populus davidiana),hygrophilous species(Platycladus orientalis, Salixmatsudana , Pyrus betulaefolia, Ulms alba, Betula platyphylla, Pinustabulaeformis ), salina－resistant species(Platycladus orientalis, Salixmatsudana, Amygdalus , davidiana , Morus alba, Salix matsudana ) andacidophilous species ( Pinus tabulaeformis, Catalpa bungei, Populusdavidiana ). Results of enviro...