Study On Density Effect Of Phyllostachys Edulis Stands In Southern Anhui Province

Moso bamboo (Phyllostachys edulis) is the most important eco-economic bamboo species in subtropical region of China. It has not only relatively high economic value and social value, but also other important ecological functions. For now, as a key technology, density management is always used in P. edulis silviculture, because a reasonable density can express a vital function not only in improve productivity, but also in ecological function. It is important to study density effect from the aspect of sustainable management for P. edulis forest. Previously, the research of density was focus on the aspect of productivity, but with the continuous enhancement of the ecological requirements, more and more people took the balance of economic and ecological benefits as the new direction. In this research, four kinds of densities (D₁, D₂, D₃, D₄, represent the stand density of 1 200, 1 800, 2 400, 3 000 tree·hm-2 respectively) had been chosen at the southern Anhui province, and the characters of representativeness and environment condition were all contained in the samples. Through the study on different aspects of P. edulis forest, such as growth characteristics, soil quality, biomass, nutrient accumulation and distribution, and water conservation function, the mechanisms of forest density for productivity and ecological function were exposed, and the reasonable density was chosen as well. The aiming is to provide theoretical and technical guidance for P. edulis silvilcuture and sustainable management in the mountainous areas of southern Anhui province. The main results of this study are as follow:(1) There were no obvious differences in the grown factors under different densities, such as DBH, height, height under branch, crown width, basic diameter, wall thickness, number of internodes and branch, while significant difference was found in shooting, harmed and leaf area index (LAI) under all four stands. Sprouting rate and survival rate decrease with the increasing of stand density, but stand density had no significant influence on shooting mortality rate. The harmed rates of diseases, pests, freezing rain and snow were affected by stand density, the sequence of harmed rates were D₃ (16.67%)>D₄ (13.33%)>D₁ (10.19%)>D₂ (9.26%), therefore, the harmed rate can be reduced by density management of P. edulis forest. The sequence of LAI under different stands was D₄ (6.83)>D₃ (5.38)>D₂ (4.21)>D₁ (2.96). LAI=0.000588 N 0.9519 D 0.7136 can be used as LAI estimation models of P. edulis in the areas of southern Anhui province. The grown factors had various relationships between each other; furthermore, DBH and height had closer relationships than the other growth factors.(2) A weighted composite index method was used to make a comprehensive evaluation of soil quality of P. edulis forest with different density, and the order was D₁ (0.5086)>D₂ (0.5084)>D₃ (0.4943)>D₄ (0.4781). In the study area, soil condition is suitable for the growth of P. edulis, but there is a different between the N, P, K ratio in the soil and the N, P, K ratio needed for growth, and the content of P in soil is the main limiting factor for the growth of P. edulis. With the increasing of stand density, the overall activity of urease, invertase, protease, catalase and acid phosphatase in the soil showed that an increasing was found at the first beginning and then became stable under different density stands. The relationship among the soil enzymes were closely related to each other, as well as the relationship between soil enzymes and soil properties, so, the soil enzymes can be used as the indicators to evaluate soil quality.(3) Stand density had significant effect on biomass pattern of P. edulis forest. In the experimental area, the ecosystem biomass of P. edulis stands have been shown as D₄ (118.02 t·hm^-2)>D₃ (98.42 t·hm^-2)>D₂ (67.84 t·hm^-2)>D₁ (58.27 t·hm^-2). The max proportion of total biomass was the biomass of tree layer, which the range was D₄ (111.45 t·hm^-2)>D₃ (91.44 t·hm^-2)>D₂ (60.54 t·hm^-2)>D₁ (50.14 t·hm^-2). The biomass of undergrowth plant had less proportion of total biomass, the proportion of shrub ranged from 0.23 % to 4.60 %, the proportion of herb ranged from 0.25 % to 2.53 %. The biomass of shrub and herb had a significant negative correlation with stand density. The ratio of litter amount under various stands ranged from 5.08% to 7.40%. The litter amount order of P. edulis forest was D₄ (6.00 t·hm^-2)>D₃ (5.56 t·hm^-2)>D₂ (5.02 t·hm^-2)>D₁ (3.98 t·hm^-2). The stepwise multiple regression analysis showed that, the sequence of direct influence of biomass were stands density>soil organic matters>soil pH value>average DBH>soil bulk in P. edulis forest.(4) The nutrients accumulation and distribution had influence in some extent by stand density in different organic of bamboo body and different layer of bamboo forest eco-system. The arrangement order of total accumulation of nutrient under different stands was D₃ (54019.59 kg·hm^-2)>D₄ (46 676.53 kg·hm^-2)>D₂ (44 548.81 kg·hm^-2)>D₁ (25 650.10 kg·hm^-2), and the ratio of each element was potassium>nitrogen>phosphorus. Accumulation of different nutrient elements from soil had significant differences in P. edulis forest, and it was mainly enriched in nitrogen and phosphorus, but low in potassium. The nutrient contents of understory vegetation were higher than the tree layer, and the accumulation coefficients to nutrient element in soil decrease with the increasing of stand density.(5) Stand density had significant effect on water conservation of P. edulis forest. In the experimental area, the P. edulis stand with 1 200 tree·hm^-2 was the best stand which conserves water and soil. The arrangement order of the total water conservation of P. edulis stands was D₁ (722.20 t·hm^-2)>D₃ (720.71 t·hm^-2)>D₄ (655.96 t·hm^-2)> D₂ (616.04 t·hm^-2). The arrangement order of water-holding capacity of plant canopy layer of P. edulis stands was D₄ (7.93 t·hm^-2)>D₂ (6.34 t·hm^-2)>D₃ (6.33 t·hm^-2)>D₁ (5.30 t·hm^-2). With the increase of density, the water-holding capacity of branch and leaf of tree layer increase, while the water-holding capacity of undergrowth vegetation reduced. The maximal water holding capacities of litter layer was closely related to the litter amount, and the range was D₄ (20.70 t·hm^-2)>D₃ (17.71 t·hm^-2)>D₂ (17.04 t·hm^-2)>D₁ (13.56 t·hm^-2). The modified and maximal interception amount of litter increase with the increase of density, S = a In t+b and V = c t d were expressed in the relation between water holding capacity, water absorption rate and immerse time respectively. With the increase of density of P. edulis stands, the maximum water holding capacity of soil reduced, and the arrangement order was D₁>D₃>D₄>D₂. Model f = a t -n can simulate the process of soil water infiltration of P. edulis stands.(6) In the experimental area, 2 400 tree·hm^-2 was the reasonable management density of P. edulis forest. The order of productivity and main ecological function such as improve soil fertility, maintain the balance of ecosystem nutrient circulation and conserve water were different under different densities. A weighted composite index method was used to make a comprehensive evaluation of productivity, soil quality, nutrient accumulation and distribution, water conservation of P. edulis forest with different density. The comprehensive index of productivity and ecological function of P. edulis stands with different density were in the order of D₃ (0.4995)>D₂ (0.4803)>D1 (0.4662)>D₄ (0.2602). In southern Anhui province, P. edulis stand with 2 400 tree·hm^-2 not only bring about better economic benefit, but also improve soil fertility, maintain the balance of ecosystem nutrient circulation, conserve water, etc.