Effects Of Thinning On The Growth Of Larix Olgensis Plantation

As a main interfere measure of plantation growth, thinning has important effects on forest development. The reasonable thinning is very significant in theory and practice to improve the nutation space of canopy and conditions of water and nutrition underground, to guarantee individual and colony development and to improve forest community biomass and productivity. The study of thinning effects on forest development will help not only to perfect the model system of planted forest growth and yield, but to take a reasonable thinning regime for optimal forest management as well.With Larix olgensis plantation as an example, this paper studied the effects of thinning on the increment of basal area, volume and biomass, and compared the fitness of thinning effect models. In addition, the paper analyzed and simulated growth process of stand basal area, volume and biomass under different initial planting density for Cunninghamia lanceolate, plantation.The analyses of the trend of basal area and volume growth of Larix olgensis plantation showed that the growth of basal area and volume of thinning and control plots increased with forest age. At initial stages the basal area and volume of thinning plots were less than those of control, but the annual average growth rate of thinning plots was more than that of control. That is to say, the growth speed of thinning plots was higher than that of control. With the increasing age and competition, basal area and volume of thinning plots were gradually approached to those of control. Crown Competition Factor (CCF) was adopted to describe the trend of basal growth. CCF of control kept relatively stable, but that of thinning plots firstly decreased, then increased with ages and graduallyapproached to that of control. For Cunninghamia lanceolata plantation with different initial planting density, annual average growth rate of basal area and volume of low-density stands was more than that of high density. It showed that the basal area and volume of low density gradually approached to those of high density.Models on thinning effects on basal growth prediction are the kernel of the model system of stand growth and yield prediction. Richards growth model and Schumacher growth model were used as the basal area growth model in establishing the basal growth prediction of Larynx lenses and Cunningham lancelet plantation in this study. The fitting result of Schumacher model was better than that of Richard when the number of trees per hectare or stand density index (SDI) was included in both models at the same time. Both models with stand density index (SDI) as an independent variable had better performance than those with the number of trees per hectare.As an index of evaluating potential site productivity, the volume per unit reflects the status and level of forest management. The paper selected Richards growth model, Schumacher growth model and SDI volume growth model to study the effects of thinning on volume growth. Different stand density indices were tested in these models. Schumacher model including age, site index and stand basal area was proved the best.Forest biomass is the basic quantitative feature of forest ecosystem, which indicates the complex relationship in material circulation and energy flow between forest and environment. Based on the results of compatible biomass models, the research calculated biomass of different parts aboveground of Larix olgensis plantation and compared individual biomass difference with different thinning intensity and initial planting density. Biomass of thinning stands was lessthan that of control at initial stages, but the annual averaged growth rate of biomass of thinning stands was more than control. Biomass of thinning stands approached to control with the increase of ages. In order to harvest more biomass of timber and branches, light thinning intensity was desirable. On the other hand, more leave biomass can be harvested in stands without thinning.