| Pinus koraiensis is a valuable timber species in northeast China,and there is a large area of Pinus koraiensis plantation in northeast China,so it can be one of the main goals of large-diameter timber cultivation in plantations in Northeast China.In this study,137 fixed sample plots and more than 2,500 Pinus koraiensis open growing trees in different age and different stand densities of Pinus koraiensis plantations in 14 regions of Northeast China were used as research objects,through the analysis of stand density influence to stand base growth index,the Canopy indicators and stem form index,and to study the large-diameter timber directional cultivating control standards of Pinus koraiensis plantation were studied in Northeast China.The main conclusions are as follows:(1)According to the comprehensive analysis of the basic growth control index,stem form control index and Canopy indicators of stands,the optimal stand density of the existing plantation stands in 20a,40a,60a and 70a was 1050 plants/ha,640 plants/ha,370 plants/ha and 310 plants/ha respectively.Under the optimal stand density,the average DBH of 20a,40a,60a and 70a plantations should be controlled at about 13 cm,23.5 cm,32.5 cm and 37 cm respectively,the Individual volume was controlled at about 0.05 m3,0.35 m3,0.8 m3,and 1-1.3 m3,the stand volume was about 56 m3/ha,200 m3/ha,300 m3/ha,400 m3/ha,the large-diameter timber volume at 170 m3/ha,200 m2/ha,350 m3/ha and large-diameter volume did not consider in age of 20a.The stand density had little effect on the stem form,and the height-diameter ratio of all plantations was about 0.5-0.7.At the age of 20a,the crown length rate was about 0.9,and the crown length rate of other forest ages was between 0.5 and 0.6.The average crown width at 20a,40a,60a and 70a was about 4 m,5 m,7 m and 7 m respectively.(2)Based on the analysis and comparison of regional differences of control indexes of large-diameter timber,the average crown width and crown diameter ratio were finally selected as the basic control indexes.According to the state of free growth of Pinus koraiensis,the crown growth of Pinus koraiensis was not unlimited.At 100a,crown width basically stoped growing and hovered around 10 m.Crown diameter ratio decreased with the growth of forest age,when the forest age was about 15a,the crown diameter ratio reached about 41.0,and when the forest age reached 120a,it basically remained around 12.And based on the models of forest age,crown width,crown diameter ratio and tree height in the free growth state,the growth prediction table in the ideal state of Pinus koraiensis plantation was developed,and the optimal density control of the existing stands was carried out according to the current situation of the existing Pinus koraiensis plantation,and the growth prediction table after the optimized density of the existing Pinus koraiensis plantation was also obtained.(3)In the existing conventional cultivation of Pinus koraiensis forest,the directional cultivation of Pinus koraiensis large-diameter timber by changing the stand density is an effective way to alleviate the shortage of wood and improve the yield of large-diameter timber.In this study,the method of storing large-diameter timber and improving the evaluation by 20%can provide some technical guidance for the cultivation of large diameter timber in the current conventional cultivation mode.For example,the conventional cultivation mode of 40a Pinus koraiensis plantation was generally between 800?900 plants/ha,the average DBH of 800?900 plants/ha was used as the basis to distinguish large-diameter timber.When the stand density was 640 plants/ha,the average large-diameter timber improvement rate reached about 18%,and the improvement rate of large-diameter timber in some sample plots reached 23-28%.There was no significant difference in the relationship between the volume and stand density of 60a large-diameter timber,which may be caused by the different management foundation in the early stage of some sample plots.However,when the density was 370 plants/ha in some areas,the large-diameter timber accumulation was the highest,and the improvement rate of large-diameter timber in some sample plots was about 19.1%.At 70a,310 plants/ha was larger than 500 plants/ha,the improvement rate of diameter material was about 33%.(4)In the directional cultivation system of large-diameter timber in the plantation of Pinus koraiensis the initial planting density of afforestation should be 2500 plants/ha or 3300 plants/ha.Crown width of 15a Pinus koraiensis should be controlled between 2.8-4.2 m,crown diameter ratio between 32.6-38.7,and average DBH between 8.5-10.7 cm.At this time,thinning should be carried out around 14-15a to ensure the normal growth of Pinus koraiensis,and the retained density should be about 1000-1180 plants/ha.The final thinning time could be selected as about 80a,the crown width of 80a should be controlled between 7.6-8.8 m,the crown diameter ratio should be about 16.4-18.1,the average DBH should be 42.2-55.5 cm,and the reserved density should be about 170-260 plants/ha.For less frequent thinning,the first thinning was the same as the above,the second thinning was between 20-25a and the retained density was about 460-640 plants/ha,and the third thinning was around 45-50a and the retained density was 170-260 plants/ha.In summary,this study analyzes the growth status of Pinus koraiensis under different forest ages and densities,and developes a technical index system for directional cultivation of Pinus koraiensis large-diameter timber according to the average crown width and crown diameter ratio,which will provides certain guidance for the cultivation and thinning of Pinus koraiensis plantation with different forest ages and operating objectives and the determination of growth status. |
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