| Close-to-nature transformation of 14-year-old pure Pinus massoniana and Cunninghamia lanceolata plantations were studied taking a series of harvest intensities and several hardwood species inter-planted into consideration under guide of close-to-nature forest management principles.The harvest intensities contained treatments I(80%),II(73%),III(66%)and IV(59%)for P.massaniana,I(69%),II(60%),III(51%)and IV(40%)for C.lanceolata,and no inter-planting and harvest as control.The five hardwood species inter-planted were Castanopsis fissa,C.hystrix,Manglietia glauca,Michelia hedyosperma and Erythrophleum fordii.The growth of remained trees and inter-planted saplings,under-story vegetation diversity and forest soils were investigated at fixed periods for nine years,so as to reveal dynamic changes of tree growth,under-story vegetation diversity and soil chemical properties,and their responses to harvest intensity,and to evaluate effectiveness of the close-to-nature transformation for pure coniferous plantations.The findings will provide evidences and technical supports for close-to-nature transformations of pure coniferous plantations,and thus facilitate evolution from pure coniferous plantations to close-to-nature forests with reasonable structure,strong ecological function,good landscape and high economic benefits.The main results were as follows:1.Thinning intensity had significant effects on tree growth of P.massoniana and C.lanceolata.Their mean annual growth rate of individual tree volume,DBH and crown area declined with decrease of thinning intensity,which was significantly higher than those of control(P <0.05),while stand volumes increased as thinning intensities decreased and were remarkably lower than that of control.However,thinning intensity had no significant effect on tree height(P?0.05).The dynamic response of crown was the most sensitive to thinning in P.massoniana plantations,the crown area increased rapidly and led to fast growth of DBH,and mean annual increases of tree height and height of crown base were relatively stable.As for C.lanceolata,crown diameter and DBH responded to thinning the most sensitively,and increased sharply,further led to rapid growth of individual tree volume.Under the same thinning intensity treatment in P.massoniana forest,the mean annual increment of crown area in the first 3 years after harvested was significantly higher than that of later stage;and the mean growth rate of DBH was the highest in the third to fifth year.While for Chinses fir,the mean annual increments of crown diameter,DBH and height of crown base were the highest within the first to third years after thinning,and those of individual tree volume,tree height and stand volume peaked in the third to fifth years after thinning.As compared in the same year,the individual tree volume and DBH showed the highest in treatment I for P.massoniana,while in treatment III for C.lanceolata;and height of crown base and stand volume showed the highest in control for both tree species.In the ninth year after thinning,stand volumes of treatments II,III and IV for P.massoniana and treatment III for C.lanceolata were not significantly different from that of the relevant controls.Taking individual tree volume and stand volume into consideration,thinning intensity of treatment II(300 trees remained per hectare)was optimal for P.massoniana,and treatment III(594 trees remained per hectare)for C.lanceolata.2.After three years of interplanting under P.massoniana and C.lanceolata plantations,DBH,tree height and crown width of the C.fissa,tree height and crown width of M.glauca and tree height of C.hystrix emerged a growth peak.In the fifth year of interplanting,DBH of C.hystrix,M.glauca and M.hedyosperma reached the highest growth rate.In the ninth year of interplanting,the increments of DBH,tree height and crown width of E.ferdii,tree height and crown width of M.hedyosperma as well as crown width of C.hystrix were the largest.In the viewpoint of the growth performance,the growth rate of above five tree species was as follows,C.fissa > C.hystrix > M.glauca > M.hedyosperma > E.ferdii.During the nine years after thinning,thinning intensity significantly influenced the growth of P.massoniana and the interplanted broadleaved tree species.The DBH,tree height and crown width of C.fissa and M.glauca as well as DBH and crown width of C.hystrix increased with increasing thinning intensity.However,as for M.hedyosperma,its DBH decreased with increasing thinning intensity.The DBH and crown width of E.ferdii as well as tree height and crown width of M.hedyosperma had no significant correlation with thinning intensity in the first seven years,and then decreased with decreasing thinning intensity.In conclusion,the optimal thinning intensities for M.hedyosperma interplanted under P.massoniana were 375 and 450 stems per hectare.For other four broad leaved tree species,the retained density should be 225 and 300 stems per hectare.The growth performance of broadleaved tree species under moderate thinning intensity was better than that of high and low thinning intensities,but no obvious trend was observed.The growth rate of M.hedyosperma was the lowest and the highest for C.fissa.The growth performance of C.fissa was better under treatment II(488 stems per hectare)that other three treatments.The best thinning intensity was 375 stems per hectare for E.ferdii,and 594 stems per hectare for C.hystrix,M.glauca and M.hedyosperma.3.The number of understory plant species increased significantly in the first year after harvest,while the diversity of understory vegetation decreased with time.The Simpson diversity index and Pielou evenness index of the shrub and herbs layers of P.massoniana were the highest in the the retained density of 300,375 and 225 plants hm-2 at 1,5 and 9 years after harvest,respectively.However,the number of species,Margalef richness index and Shannon-Wiener index are more stable with the increase of cutting intensity.The number of species,Margalef richness index and Shannon-Wiener diversity index of shrub layer and herbaceous layers of Cunning hamia showed an increasing trend with the increase of cutting density although there was only treatment I was significantly higher than that of control.At the 5 years after harvest,the diversity index of treatment I was not significantly different from that of the control,while the number of shrub and herbaceous species and Margalef richness index of the other three cutting treatments were significantly smaller than those of the control.Shannon-Wiener diversity index,Simpson diversity index and Pielou evenness index of herb layer of treatnebt IV were significantly higher than those of the control.At the 9 years after harvest,the Margalef richness index of shrub layer of four shredded treatments were significantly lower than that of the control.Moreover,the Margalef richness index,the Shannon-Wiener diversity index,Simpson diversity Sex index and Pielou evenness index were significantly higher than those of control.4.The cutting measurement significantly influenced the soil nutrient condition of P.massoniana and Cunning hamia forests.The soil organic matter and total nitrogen in the O layer increased significantly with time,while the soil fertility in the soil A and B layers did not change significantly.Overall,the total phosphorus and potassium were deficient seriously and the nutrient contents of soil O layer was higher than those of soil A,B layers.For the P.massoniana,the soil indexes,such as soil pH and organic matter in four thinning treatments decreased at first,and then increased with time.For the Cunning hamia,the available phosphorus and total potassium increased significantly over time,while the rest of the soil nutrient indicators changed little.Soil organic matter and total nitrogen content were significantly correlated with other soil nutrient contents,which indicated the soil fertility of P.massoniana and Cunning hamia forests.The soil fertility index of P.massoniana decreased first and then increased slowly with time.The higher the cutting intensity the lower soil fertility index.At 9 years after harvest,the soil fertility index of treatment IV(450 plants hm-2)and the control were Significantly higher than those of the remaining treatments.The soil fertility index of Cunning hamia was the highest in the contol.The soil fertility index of the treatments I(375 plants hm-2)and IV(732 plants hm-2)were significantly higher than those of the treatment II(488 plants hm-2)and III(594 strains hm-2).It is a long process to improve the soil nutrient status of pure coniferous forest by cutting and interplanting broad-leaved trees because the nutrient content of four thinning treatments has not yet reached the level of the control. |
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