Studies On Stand Density Effect And Timber Grade Structure Of Cunninghamia Lanceolata Plantations

The question, stand density controlling, is one of the most key technologies that need to settle immediately in forest management. In this paper, the time series data from 28-year-old Cunninghamia lanceolata test forest in Dagang mountant Jingxi Province without artificial interference (5 initial planting density levels) and 27-year-old plantation with thinning treatment (4 different selection cutting levels) was analyzed. Base on the forest measurement factor according to distribution of diameter class, this paper systematically study the density effect and the dynamic changes rules of timber assortment structure for Cunninghamia lanceolata. The results are listed as following:1. The self thinning intensity increased with stand age and primary planting density increasing. The larger planting density was, the younger forest occurred self thinning was. When stand age are 28 years, in the plots A₂(2m×3m), B₂(2m×1.5m), C₂(2m×1m), D₂ (1m×1.5m)and E₂(1m×1m) with the same 14 site index class, the total self thinning intensity were 1.0%,5.5%,25.7%, 37.0%, 63.7%, respectively,the E3(1m×1m) plot, 85.0%, was the largest. In the plots A₁, A₃, B₁ and B₃ with the same 16 site index class, the self thinning intensity respectively reached 13.0%,7.0%,16.0% and 46.0%。2. In the plots with the same site index class and age, the stand average DBH, individual volume and crown width were decreasing with the initial density increasing; the stand basal area, gross volume, stand volume, ratio of height to diameter and clear bole height were increasing with the growth of forest age dominant height, whereas volume were increasing with the growth of the initial density. The stand dominate height of A₂, B₂, C₂, D₂ and E₂ plots with 14 site index class had no obvious difference, the study shows that the difference of dominant height mainly determined by site index class not stand density; The difference in plots except B₂ and C₂ was significant, which suggested that density had an effect on stand dominate height in the excessive thin or dense stand. The Cunninghamia lanceolata grow fast and need more nutrient, Under the condition of density being smaller, the unit area stand obtain more nutrient, which promote the growth of tree height, at the same time the average DBH of the sparse stands was larger, then the stand average height from it was larger, too. Contrarily, when the initial density was larger, the unit area stand obtained less nutrient and the stands had more overstock wood, the stand average height was lower. When the plots with the same initial density and site index class, the larger site index was, the larger values of all forest measured factors were.3.The thinning can't effectively promote the growth of stand average height, gross volume and the growth of the total basal area, but can promote the growth of stand living trees average DBH, individual volume and the growth of single basal area, and these indices increase with the increasing of the thinning intensity. The total basal area of stand living trees weren't significant except light thinning and control difference, the difference of other thinning treatments were up to significance level, and there was the trend that decreasing with the increasing of the thinning intensity. In plots with thinning treatment, the single basal area of stand was more than control, but the reserved trees were less than control after thinning, the growth of single basal area can't compensate the decreasing the total basal area because of decreasing the number of trees in a short time;the small density stand increased the total basal area at the growth speed of single basal area with the increasing of forest age, big density stand increased the total basal area by the larger number of trees per hectare, finally the basal area of each stand density were approached to uniform.4.The diameter class, in which the most trees and volume of stand diameter class located move to the higher diameter class with the stand age increasing. When at the same forest age, the low-density stands own higher extent and faster speed than high-density stands. With the same initial density, the higher site index class and approaching to diameter class were, the faster speed was. The stand diameter class of different thinning level and the most distribution rate of volume approached to high diameter class with increasing thinning intensity. With the same thinning intensity, the higher site index class results in the larger extent and the faster speed.5.The distribution of tree number of wood sorts (%) and volume (%) in stands depended on wood sorts, the percentage of tree number and volume of moderate and big diameter woods increased with stand age. growth increasing speed increased with declination in initial planting density and raise in site index; the proportion of moderate and big diameter woods at the age of 28 in density A plots with 16 site index class was the highest, the big diameter woods was 11.5% and 14.2%, respectively, moderate diameter woods was 56% and 74.8%. At different thinning intensity, the tree number(%)and volume(%)of big diameter woods increased with stand age; the growth rate increased with site index and thinning intensity. The tree number(%)and volume(%)of big diameter woods in density A district with 18 site index class was significantly higher than those in density D plots with 16 site index class and density B plots with 14 site index class, and all thinning plots were remarkably higher than control district; At the age of 20, the tree number (%) in all thinning plots were 58.3%,34.9%,36.0% and 22.4%, the volume (%) were 81.5%,60.6%,66.3% and 50.0%, respectively.6. The gross wood yield of stands increased with stand age, and increase with initial planting density increasing at the same stand age, and increased with the site index increasing when the initial density was same. However, the contribution percentage of wood yield of living trees to gross wood yield decreased with stand density when site index were same. The contribution percentage of wood yield of dead standing trees to gross wood yield increased with stand density and site index; in the plots A₂, B₂, C₂, D₂, E₂ with the same 14 site index class, the percentage of wood yield of living trees in gross wood yield were 99.6%, 98.3%, 91.8%, 88.7% and 69.4%, while proportion of dead standing trees were 0.4%, 1.7%, 8.2%, 11.3% and 30.6%, respectively at the stand age of 28. In the terms of gross wood yield of stands of thinning, there was an apparent difference between control and districts of thinning, but no such difference between control and intensive, moderate districts of thinning, outturn rate of living trees increased with stand age, outturn rate of living trees in districts of thinning was higher than control at the same age, and indicated that the increase in gross wood yield of stands could not be improved by thinning, but promoting outturn rate of living trees. At the stand of 20, the outturn rate of living trees in district A of 18 site index class, intensive thinning> slight thinning > moderate thinning>control, were 78.1%, 76.7%, 77.1% and 76.3%, respectively ; At the stand of 25, the outturn rate of living trees in district B of 14site index class, intensive thinning> moderate thinning> slight thinning>control, were 76.4%, 75.2%, 74.5% and 74.0%, respectively7.The outturn rate of dimension lumber of living trees (big, moderate and small diameter woods) decreased with stand density and increased with site index; At the stand age of 28, the outturn rates of big diameter woods in plot A and B with 16 site index class were higher, A₁>A₃>B₃>B₁,were 16.8%,13.2%,9.0% and 5.5%,respectively, the wood yield per hectare were 69.399m³, 57.694m³, 31.587m³ and 27.069m³; the outturn rates of moderate diameter woods was A₁>A₃>B₃>B₁,were 53.5%, 47.3%, 32.1% and 31.9%,respectively, the wood yield per hectare were 234.014m³, 195.555m³, 157.177m³ and 111.941m³, respectively; In contrary to big and moderate diameter woods, the outturn rates of small diameter woods was A₃131,were 12.1%, 14.8%, 36.1% and 38.3%,respectively, the wood yield per hectare were 52.970m³, 61.137m³, 126.733m³ and 187.427m³, respectively; at the stand age of 28, the outturn rate and wood yield of big diameter woods in density A and B with 16 site index class were low, could not meet the standards of big diameter woods, but the outturn rate and wood yield of moderate diameter woods in stands with density A accounted for a dominant proportion, and appropriating to cultivate moderate diameter woods.8.Under different thinning intensity, the total wood yield rate of dimension lumber of living trees increased with thinning intensity and site index; at the stand age of 27, outturn rates of big diameter woods,in 16 site index class and the plot D with moderate thinning treatment were larger,moderate thinning>intensive thinning >control> slight thinning, were 19.0%, 17.1%, 2.2% and 1.8%,respectively, wood yield of big diameter woods per hectare were 56.376m³, 44.239m³, 6.832m³ and 6.325m³; outturn rates of moderate diameter woods was control> intensive thinning>moderate thinning> slight thinning, were 47.3%, 42.3%, 41.6% and 24.2%,respectively, wood yield of big diameter woods per hectare were 146.928m³, 123.783m³, 105.196m³ and 85.408m³; outturn rates of small diameter woods was slight thinning>control>intensive thinning>moderate thinning, were 17.8%, 18.8%, 25.9% and 48.4%,respectively, wood yield of big diameter woods per hectare were 52.837m³, 47.121m³, 80.561m³ and 171.099m³.