Effects Of Pruning On The Growth Of A Young Plantation Of Pinus Massoniana And Its Environment Within The Forest

Masson pine(Pinus massoniana)is the timber species and afforestation pioneer tree species occupying the largest area of coniferous forests in our country.It has excellent characteristics such as fast growth,high yield,cold tolerance and barren tolerance,strong adaptability,and high degree of comprehensive utilization.Pruning is an important way of forest management.Through scientifically removing the branches of the lower layer of trees,it can reduce the number of tree knots,increase the utilization of forest nutrients,enhance the solar radiation flux under the forest,promote the growth of understory plants,regulate the soil environment,and stabilize the forest ecosystem,promote the high-quality growth of forest trees,and improve the quality and profit of wood.In order to understand the impact mechanism of pruning on the morphology of the masson pine and its internal environment,this study selected 7-year-old masson pine young plantation to carry out pruning experiments with three treatments: retaining three vessels,retaining four vessels,and no pruning.After pruning,measure indicators such as diameter at breast height,tree height,tree volume per plant,stem shape,forest light environment,understory vegetation,and soil physical and chemical properties to reveal the response mechanism of masson pine plantation morphology and forest environment to pruning,and provides scientific basis and theoretical guidance to cultivate high-quality large-diameter timber masson pine forests.The main results are as follows:1.The response of masson pine growth and stem shape to different pruning intensitiesPruning promoted the growth of diameter at breast height and tree height and the accumulation of standing timber volume per plant in some levels.The promotion range increased with the increase of the pruning intensity.Among them,retaining 3 round branches had the most obvious promotion effect on the height growth of masson pine.Compared with no pruning,it increased by 9.47%.Different pruning intensities had different effects on the stem shape indexes(under-branch height,crown length,crown length ratio,height-to-diameter ratio,breast height shape index)of masson pine,and pruning treatments had lower net growth under the branches and breast height shape index compared with non-pruning,but the growth rate of crown length and crown length was significantly improved,and the growth of breast height shape was slightly increased.Generally,pruning promotes the formation of high-quality stems,and it was the best to retain three-vessel branches.2.Effects of different pruning intensities on canopy structure and light environment of masson pineThe influence of different pruning intensities in the same season on the gap fraction,opening degree,direct fixed-point factor,indirect fixed-point factor,total fixed-point factor,direct radiation under the canopy,indirect radiation under the canopy,and total radiation under the canopy in the order of strength and weakness were: reserved 3vertex>retain 4 vertex>no pruning,the leaf area index is: retain 3vessels<retain 4 vessels<no pruning,except for indirect radiation under the canopy in autumn,all treatments had statistical significance(P<0.05);For example,in the autumn,the total radiation under the crown with 3 and 4 vessels was significantly increased by 67.59% and28.52% compared with no pruning.With the changes in spring,summer and autumn,the gap score,opening degree,direct fixed-point factor,indirect fixed-point factor,total fixed-point factor,direct radiation under the canopy,indirect radiation under the canopy,and total radiation of the same pruning intensity showed a downward trend,and the leaf area index was an upward trend.There were obvious seasonal changes in the retention of three-vessel branches and the retention of four-vessel branches,and the variation in retaining three-vessel branches was the largest.There was a significant difference between spring without pruning and summer and autumn.3.Effects of different pruning intensities on undergrowth of masson pine forestThe species of masson pine understory plants increased with the increase of pruning intensity and changes in spring,summer and autumn.The important value of different species had different trends.For example,the important value of the dominant tree species,white oak,in autumn was 0.938,0.998,1.087,respectively,in 3 vessels,4vessels and no pruning.Different pruning intensity of masson pine understory vegetation species richness,species Simpson index,species Shannon Wiener index,and species Pielou evenness index were all expressed as follows: retain 3 vessels > retain 4 vessels> no pruning,retain 3 vessels had a significant difference with unpruned(P<0.05);the community similarity coefficient decreased with increasing pruning intensity.The species diversity of understory vegetation of Pinus massoniana with and without pruning was complicated with changes in spring,summer and autumn.4.Effects of different pruning intensities on soil environment of masson pinePruning had greater impacst on the physical properties of soil than non-pruning.With the increase of pruning intensity,soil water content and soil bulk density gradually decreased,maximum water holding capacity,capillary water holding capacity,minimum water holding capacity,capillary porosity,non-capillary porosity and total porosity gradually increased.The effect of pruning on soil nutrients was complex.The soil nutrients of the masson pine forest after pruning were slightly improved compared with the unpruned forest,and it was better to retain 3 vertebral branches;the soil organic matter,total nutrients and available nutrients nitrogen,phosphorus and potassium content change with the seasons in different trends.Except for the obvious seasonal difference in available phosphorus,the seasonal difference in other nutrients was not obvious.In summary,pruning improves the stability of the ecosystem in the masson pine forest,is conducive to the growth of masson pine and the production of fine dry wood,and then promotes the formation of masson pine unjointed large-diameter timber,and the effect of retaining 3 vertebral branches is better.