| China’s forestry is gradually shifting from an extensive development mode primarily based on expanding forest area,to an intensive development mode focused on enhancing the quality of forests.Strengthening forest management,improving forest quality and efficiency,and fully realizing the multifunctional benefits have become necessary requirements for ecological civilization and modern forestry development.Matsu pine(Pinus massoniana)is one of the main timber and afforestation species in China.It plays an important role in maintaining ecological balance,preventing soil erosion,and promoting ecological and economic benefits.However,due to its inherent characteristics and poor management,the productivity of Matsu pine plantations may decline and be susceptible to pests and diseases.Therefore,adjusting the forest structure,enhancing the stability of the forest stand,and maximizing the multifunctional benefits are of great significance for the sustainable development of Matsu pine plantations.Interference thinning is a fine-scale near-natural forest management technology,which has an important role in improving forest stand structure and quality.In this study,different thinning intensities(35%,45%,55%)were applied in replicated stands and a control stand to explore the effects of interference thinning on the forest structure and multifunctionality of Matsu pine plantations,based on field investigation and indoor analysis.The main research findings are as follows:(1)Compared with the control,45% and 55% thinning significantly increased the breast diameter and annual average growth of retained trees(P<0.05),while the breast diameter and annual average growth of the retained trees in the 35% thinning plot showed an increasing trend(P>0.05).The three thinning intensities had no significant effect on the annual average height growth of retained trees(P>0.05).(2)Thinning between trees effectively improved the diameter structure of the stand,and the Weibull and Normal distribution functions were the optimal diameter distribution functions,with an acceptance rate of over 90.0%(P>0.05).The impact of thinning between trees on the height distribution of the stand was not significant(P<0.05).(3)The V-shaped diagram analysis showed that the number of adjacent trees to the center tree of the basic spatial structure unit of the Masson pine stand ranged from 3 to 10,with 8 possible values.The combination of 1 center tree and 5-7 adjacent trees accounted for more than 70.0%.When the thinning intensity was 45%,the average value of adjacent trees’ numbers was the smallest,at 5.95 trees.(4)Thinning between trees reduced the degree of stand competition.The average competition index of the three thinning intensities(35%,45%,and 55%)decreased by 38%,49%,and 64%,respectively,while the average aggregation degree decreased by 27%,44%,and 55%,respectively.Thinning between trees also improved the light transmission conditions of the stand,and the average openness of the thinned plots increased by 25%,36%,and 32%,respectively.However,the growth space of the stand after thinning was still insufficient(overall less than 0.3),possibly due to the short monitoring time.(5)Compared with the control,thinning between trees showed a decreasing trend in soil bulk density(P>0.05).The soil bulk density of the stands thinned by 35%,45%,and 55%were 0.14 g/cm3,0.14 g/cm3,and 0.06 g/cm3 lower than the control stand,respectively.The maximum water holding capacity of the soil showed an increasing trend(P>0.05),and the stands thinned by the three intensities had a maximum water holding capacity of 25.56 g/kg,48.80 g/kg,and 56.19 g/kg higher than the control stand,respectively.(6)Compared with the control,the Shannon-Wiener diversity index,Simpson diversity index,and richness of the stands thinned by 35% and 45% showed an increasing trend(P>0.05),while those of the stand thinned by 55% showed a decreasing trend(P>0.05).The evenness index was ranked in descending order as 45% thinning,55% thinning,35%thinning,and control.(7)Compared with the control,thinning between trees showed an increasing trend in the individual volume and biomass of the retained trees(P>0.05).However,the total biomass of the stand decreased with increasing thinning intensity(P<0.05),and the biomass of the stands thinned by the three intensities decreased by 8.20%,16.44%,and 36.94%,respectively.In summary,thinning between trees with intensities of 35% and 45% can increase the mean annual growth of diameter and volume of retained trees.After thinning,the diameter distribution of the stand improved significantly,and the Weibull and Normal distribution functions can reflect the diameter distribution status intuitively.The stand’s basic spatial structure unit composition is best when the thinning intensity is 45%.Thinning between trees reduced the degree of competition within the stand,increased the light transmittance,improved the dominance of trees,optimized the spatial distribution pattern of retained trees,reduced spatial compression between trees and tended to achieve a more even distribution of trees.After thinning,soil structure and the diversity of understory plant species improved,and the individual biomass of retained trees increased,but the total biomass of the stand decreased with increasing thinning intensity.In conclusion,thinning between trees with a45% density intensity has the best multifunctional improvement effect on the structure of the Masson pine plantation in this region. |
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