Study On Ecological Stability Of Sand-fixation Plantation Forest In Huangyangtan

The dissertation focuses on the sand-fixation forest ecosystem in Huangyangtan.Based on tree species, stand ages and distribution patterns,22sample stands (grasslands)were chose and investigated. In the light of the planting conditions and managementobjectives of sand-fixation forests, the ecological stability was determined.12factorsrelated to growth, resistance, as well as protection function of the stands were chose, andevaluation index system was established to assess the stability of sand-fixation forestecosystem in study area. Using subordinate function value method of fuzzy mathematics,combining with the factor weights, the stability degrees of different stand types wascomprehensively evaluated. Additionally, management measures and strategies to improvethe stand stability were presented after the analysis of the current situation of sand-fixationplantations. The results showed as follows:1. Biological stabilityBased on indicators related to species compostion, stand growth, species compostionof regeneration seedlings, grass cover and stand canopy closure, we analyzed the biologicalstability of the study stands. Results indicated: the biological stability of ten pure or mixedforest types including Caragana Korshinskii, Sabina vulgaris, Pinus sylvestnis var,Elaeagnus angustifolia, Platycladus orientalis, Ulmus pumila, Salix gordeivii, Populusbolleana Lauche and Amorpha fruticosa, reached middle or high level. the biologicalstability of stands including Populus simonii, Robinia pseudoacacia, Populussimonii×(Populus pyramidalis+Salix matsudana) showed middle level. However, grassstand with Artemisia halodendron and Astragalus adsurgens was under the condition oflow level of biological stability.2. Resistance stabilityThe dissertation showed that forest diseases and insect pests were not main disturbingfactors impacting ecosystem health of sand-fixation forest in Huangyangtan. There weretotal11stands and grasslands with high resistance stability, including Elaeagnusangustifolia, Pinus sylvestnis var. mongolica, Caragana Korshinskii, Platycladusorientalis, Amorpha fruticosa, Sabina vulgaris, Artemisia halodendron. These plotsdidn’t appear defoliation phenomenon or lower deciduous index during drought stress period. However, pure stands including Ulmus pumila and Salix gordeivii showed middleresistance stability as the indicators of severe defoliation phenomenon and light insectpests. Forest stands including populus and Robinia pseudoacacia presented the lowestresistance stability, because of higher deciduous index and occurrence of tree death underdifferent stress conditions.3. Function stabilityBased on indicators related to soil characteristic of sediment discharge, bulk density,porosity, soil water holding capacity and mechanical compostion, indicators related tochemical characteristic of N, P, K and organic matter, and indicators related to climateincluding temperature and moisture of forest, we analyzed the functional stability of thestudy stands. Results indicated: forests including mixed forest of Populus simonii andRobinia pseudoacacia, Ulmus pumila, Platycladus orientalis as well as CaraganaKorshinskii showed higher function stability. And forests including Populus simonii,Robinia pseudoacacia and Populus simonii×(Populus pyramidalis+Salix matsudana)showed lower functional stability.4. Based on the analysis results of biological, resistance and functional stability, thestability of sand-fixation plantation was integratedly evaluated by using the methods ofweighted mean and subordinate function. The highest stability of ten sample standspresented the order of Caragana Korshinskii> Pinus sylvestnis var>Sabinavulgaris>Caragana Korshinskii>mixed stand of Amorpha fruticosa and Sabinavulgaris>Platycladus orientalis>Platycladus orientalis>mixed stand of Amorphafruticosa and Pinus sylvestnis var>Ulmus pumila>Elaeagnus angustifolia. Four standsin middle stability level were mixes stand of Artemisia halodendron and Astragalusadsurgens, Ulmus pumila, Salix gordeivii, and Populus bolleana. And the lowest stabilityof stands showed the order of Populus simonii×(Populus pyramidalis+Salix matsudana),mixed forest of Populus simonii and Robinia pseudoacacia> mixed forest of Populussimonii and Prunus armeniaca>Populus simonii> Robinia pseudoacacia>Artemisiahalodendron> Stragalus adsurgens.