Study On The Effect Of Disturbance Intensity On Environmental Characteristics Of Chinese Fir Plantation In Huitong

The effect of disturbance on the forest ecosystem is one research focus of ecological study. Four thinning treatments (contrast,15% intensity of the lower thinning,30% intensity of the middle thinning and 50% intensity of the strong thinning) were designed in this experiment. The effects of different thinning treatments on the floristic diversity, aquatic environment, soil environment, litter, stand structure and carbon dynamics of 11 years Chinese fir plantation in Huitong, Hunan were studied. The main objective of this study was to enhance the productivity of Chinese fir plantation, the accurate data of the improvement of the Chinese fir plantation ecological functions, as well as provide the theoretical basis for optimizing Chinese fir plantation. The main findings are summarized as the following five aspects:(1) The effect of thinning on ecosystem of under-forest including microen-vironment, plant biodiversity and litterfall were also studied. The results revealed that the microenvironment of under-forest after thinning changed along with the season and time. The plant species quantity of under-forest also significantly increased compared with contrast. The plant of under-forest were mainly shrub and herbage, while less dungarunga. The biomass of under-forest was higher than contrast and increased with the increase of thinning intensity. The cover degree and Shannon-Wiener index of shrub and herbage both exhibited increasing trend as the thinning intensity increased. The biomass in unit area of un-decomposed layer and semi-decomposed layer of litterfall decreased with the increase of thinning intensity, while the biomass in unit area of decomposed layer increased (chapter 3).(2) Thinning can effectly decrease the harm of acid deposition and reduce the overland runoff. The acid deposition of Huitong Ecological Station was very serious. After thinning, the pH of overland runoff and subsurface runoff changed to normal value, which may be mainly attributed to the improvement of forest structure, and the vegetation layer under canopy, litterfall layer and soil would mitigate the process of acid deposition. Thinning can increase the overland runoff without downpour and extraordinary rainstorm. Under this research content, the effects of thinning on the decrease of overland runoff and the mitigation of acid deposition increased with the increase of thinning intensity (chapter 4).(3) Thinning significantly improved the properties of soil. The soil structure (porosity and volume-weight) were ameliorated, so that the vent ability and water permeability increased, correspondingly. As a result, the soil fertility was also enhanced. Thinning can also significantly increase the soil pH, which may increase the available content of nutrient element, that the soil fertility was enhanced sequentially. In addition, thinning can also increase the total content of nutrient, available content of nutrient element and soil organic matter content. Under the effect of thinning, catalase, urease and proteinase activity all increased at different extent. The effect of thinning on the soil enzymatic activities changed along with the seasons, and thinning had more obvious effects in summer and autumn. The effect of thinning on the soil properties were more obvious in shallow soil and 50% intensity of the middle thinning showed the best effect (chapter 5).(4) The results of the studies of thinning’s effect on the growth factor, biomass production, canopy density and leaf area index of Chinese fir plantation suggested that thinning treatments were in favour of the growth of Chinese fir. Thinning can increase the individual tree volume of Chinese fir, and the stand volume of different thinning treatments were following:15% intensity of the lower thinning> contrast> 50% intensity of the strong thinning> 30% intensity of the middle thinning. The tree branch and tree trunk of different thinning treatments were higher than contrast, and 15%intensity of the lower thinning showed the highest rate of tree branch and tree trunk biomass against total biomass (chapter 6).(5) Different thinning intensities exhibited various effects on the carbon storages of the arborous layer of Chinese fir plantation. Of which, the carbon storages of individual plant increased with the increase of thinning intensity, while the carbon storages of unit area decreased with the increase of thinning intensity. After thinning, the carbon storages of shrub and herbal layer significantly increased. In addition, thinning also increased the carbon storages of litter layers. The total carbon storages of soil showed increase trend along with the increase of thinning intensity. The respiratory rate of soil followed the order of:50% intensity of the strong thinning>15% intensity of the lower thinning> contrast> 30% intensity of the middle thinning. From April to December, the respiratory rate of soil changed with seasons and increased initially and decreased at later stage, which reached the highest in August (chapter 7).