| The dynamics of biomass, nutrients storage and long term productivity of larch monoculture stands growing in Meng jiagang forest farm of Heilongjiang province, following continuing rotation cropping, were studied by incorporating rotation length, forest floor litter management, logging slash treatment and fertilization treatments. The work, employing Forest Ecosystem Management Model ( FORECAST, FORestry and Environmental Change ASsessmenT), focuses on the site degradation or potential site degradation. According to the preestimated results, the treatments of sustaining long-term productivity of larch were given.Based on the extensive data collection for the adaptation of the model FORECAST, the biomass growth model of components of individual larch tree was established and the biomass of monoculture larch plantation under various site qualities and with different initial spacing was estimated. The heterogeneous features of the distribution of litter, fine roots, and sunlight was estimated by employing the geostatistics, and the standing biomass of litters, fine root biomass, and light transmittance, as well as the production and turnover of fine roots of larch trees were calculated base on the estimation. By in situ survey and survey in stands with different age classes, the translocation of N, P, K in the foliage of larch, the N, P, K storage in litter and mineral soil, the N, P, K content and dynamics in fallen needles, twigs/branches, roots in different diameter classes were studied quantitively. The result is followed:1. The biomass of branch, total root, coarse root (>2cm), and bark were significantly interpreted by DBH; the biomass of dead bark, stemwood (with bark and no bark), small root (< 0.5 cm), medium root (0.5-2cm), needle were significantly interpreted by tree height; the biomass of living bark (phloem) was significantly interpreted by product of DBH and tree height (D~2H).The biomass of larch plantation of different site conditions and forest ages could be estimated by incorporating the individual tree biomass model and diameter distribution prediction model.2. The mass of larch litter fall in undecomposed, little decomposed, strong decomposed, and full-decomposed layers of 13-41a larch plantation were 4.0164-8.8970 t/hm~2, 3.9614-10.6206 t/hm~2, 0.5959-10.8017 t/hm~2, 1.9062- 21.2704 t/hm~2, respectively. The standing biomass of fine root in 0-10 cm, 10-20cm, 20-30cm, and 30-40cm soil layer of 13-41a larch plantation in June was 0.4748-1.5359 t/hm~2, 0.2776-0.8462 t/hm~2, 0.1348-1.4467 t/hm~2, 0.033-0.8898 t/hm~2, respectively. The annual production of fine root and turnover rate of fine root were 221.46-1907.94 g/m~2/a (mean value=904.09 g/m~2/a) and 0.53-1.46 (mean value= 1.16). The mean values of leaf area index and light index (transmittance) in larch plantation were 1.74-3.97 and 0.028-0.632.3. The nutrient in the senesced needle was partly translocated to the living tree, the translocation rates of N, P, and K in needles were 70.68%, 62.59%, 60.00%, respectively. The translocation amount was increased with forest age increased, translocation amount Were65.89-184.15 kg/hm2/a, 29.98-83.79 kg/hm2/a, 16.67-46.59 kg/hm2/a. The N, P, and K storages in litter had firstly increased then decreased trends with forest age, N, P, and K storages were 142.76-534.17 kg/hm2, 72.76-254.53 kg/hm2, and 35.03-134.96 kg/hm2, respectively. The biological decomposition coefficient (BDC) of N, P, and K in dead roots and fallen needles appeared the increasing trends with forest age, and was 0.7-1.5, 1.1-1.7, 1.0-3.5, and 0.9-1.3,1.1-1.7,1.0-1.3, respectively. The annually released amount of N, P, and K in dead roots and fallen needles was 5.41-36.5 kg/hm2, 2.86-25.77 kg/hm2, 3.1-15.73 kg/hm2 and 11.51-28.02 kg/hm2, 13.99-33.23 kg/hm2, 6.84-14.35 kg/hm2. The contents of N, P, and K in decomposing branch appeared the quadratic curve with time. After decomposing for one year of fallen branch which failed in last year, the contents of N, P, and K were 0.2756%, 0.0665%, 0.0586 %, and BDC werel.8229, 2.8812, 6.8379, respectively. In decomposing bark, N content appeared sigmoid curve with time, P and K contents appeared quadratic curve with time. After decomposing for one year, N, P, K contents in dark were 0.5177%,0.1953%, 0.1926%, and BDC were 0.6991,1.0681,1.2051.According to the results above, the FORECAST was calibrated. Based on the calibrated FORECAST, the ecological processes of larch plantation was simulated, and the effect of different management techniques was evaluated. The conclusion was below: 1) The ecological rotation of sustaining the long-term productivity under the general treatments should be more than 35 years; 2) The soil productivity of larch plantation using different felling cycles could be improved by reserving litter fall, and was especially obvious to the short felling circle; 3) The long-term productivity and nutrient storage of larch plantations experiencing different rotation length could be sustained by appropriate fertilization plan; 4) The treatment of keeping all logging slash could sustain long-term productivity of larch plantation using different felling cycle.
|
PDF Full Text Request