| Chinese fir (Cunninghamia lanceolata (lamb.) hook) has been cultured for more than 1000 years in China, which is the special and native and fast growing tree of southern subtropical region. In the past three decades, more than nine million hectares of Chinese fir plantations have been established in Southern China. However, major concerns have been raised about the sustainability of the plantations in terms of site productivity and soil nutrients. Since 1970s, a long term research project has been conducting to monitor the changes in structure, function and productivity of Chinese fir plantations at the Huitong Ecosystem Research Station, Central South University of Forestry and Technology, Hunan Province, China. Long term research of biomass was a key role in maintaining stand productivity and sustainable management of Chinese fir plantations.Here about 20 years of continuous data from the Huitiong research station was employed to compare standing biomass and net primary productivity (NPP) of the two successive rotations on the same sites, and to discuss the malter effect in biomass and productivity. The standing biomass and NPP were measured and compared from four different-aged stands (7,11,14 and 18 year-old) in two successive rotations on the same sites. The main results were as the follows:a) The characteristics of biomass distribution in organs. There was significant difference between the two rotations in biomass distribution in organs varing with stand age and rotations. Distribution of biomass in organs of the first rotation was main influence by site conditions, whileas it was not the same to the second rotation. The percentage of biomass in stem to the whole individual tree of the first rotation (abbreviation as R1) was on the increase with age from 7a to 18a, and on the decrease from 20 years old. Whileas the percentage of biomass in leaves to the whole individual tree was slowly decreased with age from 7a to 20a, maintaining the percentage of about 7 percent except the age of 7 year old. The percentage of biomass in bark to the whole individual tree kept at 8 percent during the fast growing stage and 12 percent during stem growing stage. In the second rotation (abbreviation as R2), the percentage of stem biomass to the total tree was on the increase during the period of 7a to 20a, with a slow decreasing with age. The percentage of leaf biomass to the total tree downtrended from 7a to 20a with a decreasing desendance. Biomass in root increased with age of 7a to 14a, and decreased with age of 14a to 20a. The extent in increase of tree bark biomass downtrended from 7a to 18 a, and began to decrease from 20a. Change in biomass of branches showed irregularity during the period from 7a to 20a. The difference in biomass between the two rotations reduced from the near to maturity stage.b) Biomass in the herbs was about amount of 0.75 to 6.929t hm-2, biomass in shrubs of 1.048 to 7.773 t hm-2 during the period of 1a to 5a, with regular distribution ranking as root > stem> leaves. The amount of litterfall was annual average of 1109.86 (±117.27) kg·hm-2 during the period from 1995 to 2007. The percentage of biomass in litterfall varied with organs, for the needle leaves of 54.39%～75.06%, for branchlets of 17.55%～31.52%, for fruit drops of 3.15%～13.5%, for scraps of 2.19%. Seasonal change in litterfall was observed irregularly with three peaks, the first occurred in February of 90.42 kg·hm-2, the second in June of 111.42 kg·hm-2, and the third in August of 108.84 kg·hm-2. Litterfall production (y) was significantly correlated with stand age (x), which can be quantitatively expressed by the regression equation:y=-10.06x2+361.1x-1747, R2=0.920, p< 0.001. There was also a conic relationship (p< 0.05) between the production of branches, leaves and fruits litterfall and forest age, while the relationships of scraps and forest age were not significant.c) The difference in stand biomass between the two rotations decreased with stand age. The stand biomass in the second rotation were reduced by 16.48%,16.94%,6.46%,1.19%, and 1.20% in 7,11,14,18 and 20 year-old stands, respectively when compared to the first rotation. The stand biomass was measured for R1 of 45.38 t·hm-2,108.73 t·hm-2,104.45 t·hm-2,146.70 t·hm-2 and 209.50 t·hm-2, for R2 of 37.90 t·hm-2,90.31 t·hm-2,97.18 t·hm-2, 144.96 t·hm-2, and 199.95 t·hm-2 in 7,11,14,18 and 20 year-old stands, respectively. There was only small difference in stand biomass between 18 year-old and 20 year-old stand, with amount of 1.74 t hm-2 and 9.55 t hm-2 for 18a and 20a, respectively. The percentage of difference to total stand biomass was 1.20% and less than 5.0% for 18a and 20a, respectively. The biomass in the second rotation varied with growth grade from grade I to gradeⅤ, and was less than biomass in the first rotation according to the same growth grade.d) The stand productivity in the second rotation were reduced by 16.38%,17.29%, 6.96%, and 8.93% in 7,11,14, and 20 year-old stands, respectively when compared to the first rotation, with an exception of increase by 12.95% in 18 year-old stand. In all the stand age-classes, the stand productivity was main contributed by stem productivity, which indicats that the stem productivity was a key component of the whole stand productivity.e) The biomass was ranked as mountain foot> side-hill cut> middle hillside> middle bottomland> upper part of hillside for 7 year-old plantations, whileas vally type (33.6 kg per tree)> mountain foot (30.3 kg per tree)> hillside (16.4 kg per tree) for 11 year-old plantations. The productivity of 11 year-old plantations was sorted by vally type (9.89 t hm-2a-1)> mountain foot 2(8.35 t hm-2a-1)>mountain foot 1 (8.33 t hm-2a-1)> hillside (6.43 t hm-2a-1). The stand productivity at the valley and the pediment were 1.54 and 1.30 times higher than those at the hillside.f) Biological productivity of Chinese fir plantation was affected by different densities and management measures. Biomass increased with stand densities increasing which were from 1501～2000 individual hm-2 to 2001～2500 individual hm-2, and from 2501～3000 individual hm-2 to 3001～3500 individual hm-2. Stand biomass were decreased when the densities were from 2001～2500 individual hm-2 to 2501～3000 individual hm-2. Individual biomass of 11 a stands with 4 different densities was different in the same site type, in which individual tree biomass was the highest in the stand densities 3690 trees hm-2. The proportion of stem biomass were 61.08%,59.05%,55.10%, respectively, when the densities were 2750 individual hm-2,3120 individual hm-2,3550 individual hm-2 in 11a stands. And the proportion of stem biomass of 14a and 16a stands were decreased with decreasing densities. In similar stand densities, stand biomass in valley stand was higher than those in the pediments, stand biomass in slope type stand was lowest.The proportion of stem biomass to individual tree at 50% and 30% thinning treatments were close to the contrast, with values of 55.37%,54.82%,55.38%, respectively. The proportion of stem biomass in 16a stands were 62.21%,64.24%,65.03%, respectively, under 3 thinning treatments. Stem biomass of 11a stands under 50% and 30% thinning treatments were higher 130.11% and 89.25% to the control, and Stem biomass of 11a stands under 50% and 30% thinning treatments were higher 167.48% and 120.28% to the control.In the pediment site condition, individual biomass of 11a stands under 40%,30% and 20% thinning treatments were higher 122.27%,125.39% and 119.53% to the control, and individual biomass of 16a stands under 40%,30% and 20% thinning treatments were higher 145.39%,153.40% and142.23% to the control, respectively.In the pediment site condition, relative biomasses of 11a stands were increased as follows, 125.4 (30% thinning treatment)> 122.3%(40% thinning treatment)> 119.5%(20% thinning treatment)> 100.0%(the control). relative biomasses of 11a stands were increased as follows,153.4%(30% thinning treatment)> 145.4%(40% thinning treatment)>142.2%(20% thinning treatment)>100.0%(the control)The biomass of Chinese fir ecosystem was affected by different thinning treatments. In three site conditions, the stem biomass of all the stands were highest. In the mountain slope conditions, stem biomasses of 11a fir stands accounted for 54.99%-55.22% of the stand biomasses, root biomasses of 11a fir stands accounted for 22.51%-23.43% of the stand biomasses, this suggested that the proportion of stem and root biomasses of stand biomasses were no affected by different thinning treatments. However, in the valley conditions, stem and root biomasses of 11a fir stands accounted for 54.99%-55.22% and 23.82%-23.97% of the stand biomasses, respectively, and in the pediment conditions, stem and root biomasses of 11a fir stands accounted for 60.08%-64.54% and 19.89%-21.59% of the stand biomasses, respectively.In the fast-growth stages (11a stand), higher thinning treatments, such as 40% and 50%, caused to the decreasing of the tree layer biomass of the Chinese fir. In the mountain slope conditions, stand biomass of 16a stand were closed under 50% and 30% thinning treatments. In the valley conditions, stand biomass of 16a stand were closed under 40% and 20% thinning treatments. In the pediment conditions, stand biomass of 16a stands were diversity under different thinning treatments, the stand biomasses was lower than the control under 40% thinning treatments, the stand biomasses was 1.123 times and 1.168 times higher to the control, under 30% and 20% thinning treatments, respectively, which obviously indicated that the stand biomass were affected similarly by the 30% and 20% thinning treatments.
|
PDF Full Text Request