Natural Regeneration And Density Regulation Of Mytilaria Laosensis Plantation

Mytilaria laosensis is an excellent timber species with wide suitable scope in southern subtropics area of China.It has certain natural regeneration potential,but current silviculture regime of the plantation was mainly the traditional clear-cutting silviculture regime with same-age.And wood products of the plantation were basically medium and small timber,the regeneration process of forest land was entirely artificial regeneration,which in cultivating seedling,control burning,soil preparing,potholing,afforestation,and so on.So this forest management mode had faced some problems,such as easy loss of soil and water on the surface,easy destruction of vegetation,regeneration cost increasing every year,single forest management goal,etc.,which was not conducive to giving full play with the natural regeneration potential and maintain the multiple ecological service functions of the plantation.To solve the above problems,the plantation in the subtropical area has been selected as the object in this study.Which have been research as the following aspect: the seed regeneration mechanism of the plantation,effects of cutting treatment and environmental factors on natural regeneration of the stand,effect of density control measures on growth of natural regeneration forest on the clear-cutting land of the plantation,effect of density regulation on growth of the plantation with middle age,and planning had been designed for silviculture regime with strip clear-cutting of the plantation.In this paper,space-time dynamic of seed rain was revealed in inner and outside the stand of the plantation,mechanism of seed regeneration was illuminated.Suitable harvest time,cutting bandwidth and tending time was discussed in the plantation with strip clear-cutting.Growth rules of the stand with different density regulation were proved.It serves as a theoretical basis for the design of strip clear-cutting under the multi-function management goal of the plantation.The main results of this study were as follows:(1)In the plantation that reached the mature age,which seed source of natural regeneration was sufficient,there was no limit with natural regeneration seed source.To seedrain of the plantation,the starting phase was from late September to October,the peak period was during the middle and late October to December,fading period was from late December to early January of the following year.Decreasing of seed rain and submerged seed density on the clear-cutting land of the reserve belt with the increasing distance of forest edge.Space distribution of the seed rain density and the submerged seed density on the clear-cutting land of the reserve belt were approximately exponential distribution,the farthest distance away from their spread was 25 m and 20 m respectively.Dynamics of seed rain and submerged seed ralative density values on the clear-cutting land of the reserve belt with the increasing distance of forest edge,which was simulated and forecasted better with the logarithmic function model basing on exponential function transformation.Activity reliability of fresh submerged seed was more than 80%,by the method of water separation.(2)Density and frequency of natural regeneration were extremely significantly effected by cutting and tending treatment(P<0.01).Light was the key factor affected the establishment of natural young trees in the stands.Based on seed dispersal period and natural regeneration characteristics of the plantation,natural regeneration of the cutting area could reach the standard of good grade(the regeneration density of sapling was more than 3 000 plants per hectare,and the regeneration frequency was more than 60%),by using clear-cutting,shelterwood cutting or strip cutting method.(3)Extract of letters of the plantation at a high concentration had a significant inhibitory effect on seed germination of the species(P<0.05).The physical and mechanical barrier of litter of the specie was the key factors,which hindered germination and seedling settlement.Seed of Mytilaria laosensis specie belongs to light neutral seed,and its germination rate was not obviously affected by light.(4)After 3.5 years with spacing,total growth and annual increment of average diameter at breast height(DBH),average tree height,and average single volume of the seed regeneration stands,were promoted very significantly(P<0.01)by thinning;and distribution,peak value and differentiation of stand diameter were obvious effected by stand density.Whereas,total growth of DBH,tree height,and single volume of dominant trees was not significantly affected(P >0.05).Before the 5th year,it was fast growth period for the stands with natural seed regeneration stands,so thinning was very important with radial growth of the stands.(5)After 3.5 years with sprouting thinning,total growth of the average DBH,average height,and average individual volume of coppice shoot in the stands were not significantly effected by stand density,but total growth of DBH and individual volume of dominant trees in the stands was affected by the density significantly(P<0.05).It was fast growth period for the radial and height growth of the stands before 5 years old,reasonable density and tending were extremely vital to the stands.Thinning measures within two sprouts in each stump could drastically increase the proportion of superior trees in the sprout forest.(6)In medium site of subtropical area,the radial slow-growing period occurred during the first 1-2 years,and the fast-growing stage occurred at 3-10 years of age,with attenuation starting at 14 years of age.Tree height exhibited distinct fast growing characteristics in the early stages of growth,spanning from the 2nd to the 6th year,and the annual increment of tree height took on a multimodality.The stock volume slow growth period of the medium trees and the dominant trees was in the first 6 years,giving way to a fast-growth period in the 8th year.After age of 14 years,the experimental form factor of the species tended to be stable.When the stem density fell into the range from 520 to 1 200 stems per hectare,the growth of tree height and the experimental form factor were not significantly affected by density regulation.The DBH growth and the stock volume growth of the mean trees were obviously affected by density regulation(P<0.05).The short-term DBH growth and stock volume growth of the dominant trees were also significantly affected by density regulation(P<0.05),but the influence was not significant in the long term.Density regulation can reduce diameter order differentiation and can increase the percentage of large diameter stems from the stands.(7)Based on natural regeneration mechanism and growth process characteristics of the species,the forest silviculture regime with strip clear-cuting of the plantation has been designed,which can provide a reference to the multi-functional,healthy,stable and efficient management of the plantation in subtropical region.