Study On Afforestation Density Of Excellent Clones Of Larix Spp.in Eastern Liaoning

Larch(Larix spp.)are excellent tree species in subalpine areas of north and south China.Nowadays,the afforestation technology for larch clone industry was extensive.Making further research on afforestation technology is of great significance to accelerate the cultivation of timber forest and meet our damand for timber.Four excellent larch clones were planted in Dagujia forest farm(Qingyuan,Liaoning),and three afforestation densities were designed,wich was marked as A(2m×3m),B(2m×2m)and C(2m×1.5m).Based on 10 years of continuous observation,the influences of afforestation densities on DBH,tree height,crown width,individual volume,stand volume,sand structure and start time of tending and intermediate cut were analyzed.The main research conclusions are as follows:(1)The effects of three different afforestation densities(A,B and C)on the stand growth of four clones were different.For each clone,the DBH,crown width and volume growth in different densities ranked as: density C > density A > density B during the 3-5 years old stage,while increased with density decreasing during the 7-11 years old stage.During the period of3-11 years old,the stand volume in density C was the largest for each clone.The effect of afforestation density on tree height growth was unobvious.The influences of density on DBH,crown width,individual volume and stand volume were increased with forest age.For each clone,at 11 years old,between high density and low density,the difference of average DBH was 2.11 cm,3.26 cm,2.14 cm,1.23 cm respectively;the difference of averge crown width was 0.79 m,0.91 m,0.58 m,0.16 m respectively;the difference of average individual volume was 0.0293m3,0.0484m3,0.0224m3,0.0162m3respectively;the difference of average volume per unit area was 16.19m3·hm-2,95.34m3·hm-2,53.9m3·hm-2,82.8 m3·hm-2.When the clones aged three to nine,tree hight of each clone in C treatment was the highest.When the clones aged 11,for both clone 1 and clone 2,tree hight in density A was the highest;for both clone 3and clone 4,tree hight in density C was the highest,but the tree hight increacment decreased.The growth characteristics of different clones were affected by genetic effects and showed different adaptability under different densities.(2)The effect of afforestation densities on the shape and quality index of larch clones were different.The tree trunk straightness of the four 12 a larch clones showed that the lower the afforestation density was,the higher the tree trunk straightness was;the smaller the density was,the smaller the tree trunk variation coefficient between individual plants was andthe more stable the stand was.Clone 1 had the largest trunk straightening degree,and the smallest variation coefficient of trunk straightening degree among individual plants.The best trunk straightening degree was under the afforestation density A.The tree trunk completeness of the four 12 a larch clones showed that the higher the afforestation density,the closer the tree trunk completeness to 1.0,the higher the density,the smaller the variation coefficient of tree trunk completeness,and the more stable the stand.The tree trunk completeness of clone4 was the one closest to 1.0,and the tree trunk completeness was the best under the afforestation density of high density C.when clones aged 3-11,the ratio of height to diameter of the four clones increased with forest age and density.The smaller the afforestation density was,the closer of ratio of height to diameter was to 1.0,the smaller the trunk sharpness was,the greater the completeness was and the more stable the stand was.(3)The effects of different afforestation densitis on the stand structures of larch clones were different.When clones aged three to seven,the variation coefficient of DBH in high-density C was the lowest.When clones aged nine to elenven,the variation coefficient of DBH in low-density A was the lowest.When clones aged three to seven,the variation coefficient of individual volume under high density C was the smallest,and it was the smallest under low density A when clones aged 11.Afforestation density had the strongest influence on the change coefficient of individual plant volume,followed by DBH,and had a relatively weak influence on the change coefficient of tree height.During the 7-11 years old stage,the change coefficient of tree height of each density stand is the smallest under the high density C,and the tree differentiation is the lowest.Moreover,the variation coefficients of DBH,individual volume and tree height decreased with forest age.The effects of different afforestation densities on the stand diameter grade and height grade structure of 11 years old larch clones were different.The individual rate in moderate and above diameter classes was increased with the density decrease.In three density treatments,the diameter class had the maximum individual rate was 14 cm,12cm and 12 cm respectively.The diameter structure of treatment A and B was approximately normal distribution,and the individual number in 12 cm and 14 cm diameter classed was more than50%.The individuals under density C centralized in smaller diameter classes.Among three density treatments,14 m height-class possessed the maximum individuals.(4)The initial thinnings of four larch clones were advanced with the increase of density,and the average DBH of the four clones decreased with forest age.The average growth amount of clons under different densities were different.The initial thinning of larch cloneswere determined according to the significant decrease in the averae growth amount.The initial thinning period of larch clones under density A was 5-,7-,9-and 5-year-old,respectively.The initial thinning of larch clones under density B was at 5-,7-,7-and9--year-old,respectively.The initial thinning period of larch clones underd density C was all at 5-year-old.