Evaluation On The Close-to-nature Thinning In The Pinus Tabulaeformis Palatation In Huanglong Mountain

With strong adaptability and stress resistance, Pinus tabulaeformis is one of the zonalityplanting species in Huanglongshan forest region on the Loess Plateau and play an importantrole in the local water and soil conservation and ecological protection. Consecutive samplingplot investigations for nine years were respectively conducted in the Pinus tabulaeformisplantation in Huanglong Mountain under close-to-natural management thinning15%(lightthinning),30%(medium thinning) and45%(heavy thinning). With the un-thinned plantationas the control, the changes of the stand growth, population regeneration and communitystability in the plantation were studied to find the influences of thinning intensity on Pinustabulaeformis plantation and then to evaluate the effects of thinning, so as to provide ascientific basis for the sustainable management of the local Pinus tabulaeformis plantation.The main results are as follows:1. Under the four thinning intensities, the growth of height, DBH, crown and individualvolume increased as the intensity increased. Except the height growth, there was significantinfluence between thinning intensities. Stand volume decreased as the thinning intensityincreased, but gap reduced with the passing of time. Thinning could raise the quantityproportion of large diameter grade wood in the plantation. In the environmental factors,canopy density was the most significantly related to the stand growth.2. The Pinus tabulaeformis plantation under the four thinning intensities all had fruitingability. The cones had a different quantity distribution in the different directions and in thedifferent vertical layers of crown, which respectively showed the order of sunny side﹥shadyside, middle﹥upper﹥lower. Under the four thinning intensities, with the increase of thinningintensity, the yield of the cones and seeds increased and there were significant influencebetween thinning intensities. The full seed rate decreased. Thinning had no significantinfluence on the cone size and the same as the seed viability and germination rate. But the fullseed size and the thousand seed weight increased as the thinning intensity increased. Thinningcould promote the survival rate of one-year-old seedlings, and the promotion action becamemore significant as the thinning intensity became larger. Thinning could promote the growthof seedlings. The average growth rate increased firstly then decreased with that in the mediumthinning plots the best.3. Thinning contribute to raising the regenerative potential of population; thinning reduced the volume of arbor, but could increase the biomass of shrub and the biomass of herb;Compared with the control, the species diversity and soil characteristics were improved in thethinning plots. Therefore, the forest communality stability evaluation of Pinus tabulaeformisplantation showed the order of the heavy thinning forest＞the medium thinning forest＞the light thinning forest＞the uncut forest.4. Close-to-natural management contributed to the cultivation of wood with high qualityand large diameter grade and also could promote the population regeneration. Afterclose-to-natural thinning, the forest communality stability got raised, which drove the stand todevelop towards a multiple layer and uneven-aged stand. Therefore, close-to-naturalmanagement is suitable to the management of Pinus tabulaeformis plantation in HuanglongMountain. In the four thinning intensities, the close-to-natural management thinning45%wasthe most conducive to the sustainable development of the local Pinus tabulaeformis plantation.To better promote the seedling regeneration, the suggestion was proposed that the shrubaround seedlings should be cleared.