Effect Of Thinning Intensity On The Architecture And Growth Of Quercus Variabilis Trees

In order to explore the effect of thinning intensity on the architecture and growth of Quercus variabilis, Quercus variabilis forests of Shangluo region in Qinling south slope under different thinning intensities(unthinned, reserve the canopy density of 0.6, 0.7 and 0.8) were taken as the research object, aboveground growth and stem-form, fine root of Quercus variabilis reserved trees, architecture and growth of 6 years old seedlings aboveground part and root after seven years of thinning were investigated and analyzed. The main conclusions were as follows:1. Thinning promoted the growth of Quercus variabilis trees. With the increase of thinning intensity, diameter at breast height, crown area, basal area at breast height and volume of single tree of Quercus variabilis were increased, showed the order of heavy thinning> moderate thinning > weak thinning > control. The annual average growth rate of tree diameter at breast height, tree height and crown area were showed the order of crown area annual average rate> DBH annual average rate and tree height annual average rate. But thinning reduced the basal area at breast height of forest stand and crowing stock. After thinning, the average tree straight degree increased, and got the highest in moderate and weak degrees thinning intensity, height-diameter ratio and height under living branch were decreased, the average branching ratio decreased at first then increased.2. Thinning significantly affected the Quercus variabilis forest soil nutrient, fine root morphology, fine root biomass and its vertical distribution. Thinning promoted the decomposition of soil organic matter and the release of available nutrients in the surface soil(0~20 cm), and improved the soil environment of Quercus variabilis forest. The promoting effect reached the largest when canopy density is 0.6. After tending thinning, fine root biomass and other main characteristic indexes of Quercus variabilis forest decreased, fine roots are mainly distributed in topsoil where the soil nutrient condition was good. The larger thinning intensity, the more decreased of fine root content in the deep soil(20~40 cm). Soil organic matter, available nitrogen, available phosphorus and available potassium and soil pH were positively correlated to fine root biomass and morphology index. Soil pH, available phosphorus and available potassium had significant effects on the fine root morphology and biomass, while available nitrogen had no significant impact on the fine root mass density.3. Thinning promoted the growth of diameter and height, and the biomass accumulation of branch, stem, and leaf of Quercus variabilis seedlings. The promoting effect reached the largest when the thinning intensity was maximum(crown density was 0.6). Seedlings under different thinning intensity forest could adjust the strategy for resource acquisition by the plasticity of branches and leaves. By elongating primary branch, increasing total leaf area, branch angle, and crown area, seedlings could increase canopy photosynthesis area to capture more photosynthetic available radiation as much as possible, and meet the needs of height growth and lateral growth, when un-thinned or thinning intensity was small. When thinning intensity increasing, by increasing the branching rate, leaf number and leaf area index, seedlings could obtain more light resource, meanwhile by reducing the branch angle and self-shadowing, could avoid damage from strong light radiation.4. Tending thinning had effect on underground root morphology and biomass accumulation of Quercus variabilis. After thinned by different intensity, by promoting the longitudinal and transverse elongation of root, increasing root surface area and volume, and adjusting lateral root branching rate, diameter, lateral root length, angle between lateral root and taproot, and interval between lateral root to adapt the environment, absorb more nutrients and water resources, and provide the needs of nutrients and support for aboveground part. With the increase of thinning intensity, dry matter allocated to the roots of Quercus variabilis increased gradually, and promoting effect of heavy thinning intensity(crown density was 0.6) on root system growth reached the largest.5. Subordinate function evaluation results showed that, after thinning, the growth and architecture of Quercus variabilis trees improved, and heavy thinning(crown density was 0.6) was best for cultivating high-quality Quercus variabilis trees.