| Evergreen broad-leaved forest is a typical subtropical forest vegetation type,which is of great significance in maintaining forest biodiversity.Population regeneration is an important ecological process of forest resource reproduction.Evergreen broad-leaved trees,deciduous broad-leaved trees and coniferous trees usually show different ecological strategies in the process of population regeneration.The effects of forest competition and topographic factors on the regeneration of trees in evergreen broad-leaved forest are still unclear.We compared the two data on Guanshan Evergreen Broad-leaved Forest Monitoring Plot surveyed in 2015 and 2020 to understand the regeneration status of different life forms(evergreen broad-leaved tree,deciduous broad-leaved tree,coniferous tree).We also analyzed the effects of forest competition and topographic factors on death and generation of trees.The main results are as followlings:(1)The abundance of each life form tree in the plot decreased within 5 years.Deciduous broad-leaved trees decreased the most,with the value from 16450 to 11601(i.e.,404 plants per hectare);evergreen broad-leaved trees decreasing with the value from 39917 to 36040(i.e.,323 plants per hectare);coniferous trees trees decreasing with the value from 5742 to4099(i.e.,137 plants per hectare).Among the 13 main trees,the abundance of 11 species showed a downward trend,particularly Cunninghamia lanceolata decreasing from 5197 to4040;Phoebe bournei and Castanopsis carlesii increased by 27 and 25,respectively.(2)The diameter class structure of 8 evergreen broad-leaved trees(Machilus thunbergia,Castanopsis eyrei,Quercus myrsinifolia,Daphniphyllum oldhami,Castanopsis carlesii,Machilus leptophylla,Elaeocarpus duclouxii,Phoebe bournei)and deciduous broad-leaved trees(Alniphyllum fortune)did not change significantly within 5 years.The diameter class structure was negative exponential type indicating the population was stable.The diameter class structure of Pinus massoniana was positive exponential type indicating the population was declining.The diameter class structure of deciduous broad-leaved trees(Liquidambar formosana,Choerospondias axillaris)and coniferous trees(Cunninghamia lanceolata)changed from negative exponential type to normal distribution type,showing a trend of decline.(3)Evergreen broad-leaved trees had the largest number of dead individuals(7263)and supplementary individuals(3386),the mortality rate and complement rate were 4.02% and1.97%,respectively.Dead individuals and supplementary individuals of deciduous broadleaved trees were 5538 and 689,respectively.Coniferous trees had the least number of dead individuals(1437)and supplementary individuals(64),the mortality rate and complement rate were 6.09% and 0.31%,respectively.Deciduous broad-leaved trees had the highest change rate of population(-6.98%),Coniferous trees(-5.78%),evergreen broad-leaved trees had the least change rate of population(-2.04%).The number of dead individuals and the number of supplementary individuals decreasing with the increase of diameter class.(4)Species competition affects the population regeneration of each tree.The competition intensity of dead trees was higher than that of live trees in all diameter classes.Individuals with DBH ≥ 20 cm had the greatest difference in competition intensity.Their competition intensity of dead individuals was 70.57% higher than that of surviving individuals.The individuals with the smallest difference in competition intensity are those within 1～5 cm DBH.The competition intensity of dead individuals was 13.35% higher than that of surviving individuals.The mortality of Machilus thunbergii,Elaeocarpus duclouxii,and Choerospondias axillaris gradually decreasing with the increase of competition intensity,yet,the mortality of 10 tree species such as Castanopsis eyrei,Quercus myrsinifolia,Daphniphyllum oldhami was positively correlated with competition intensity(5)Topography is another key factor influencing population regeneration.It was found that altitude and slope were the main factors leading to the death of tree,with the explanation ratios being 39.26 % and 23.50 %,respectively.Multiple linear regression results showed that slope and convexity were negatively correlated with tree mortality,instead,altitude and aspect were positively correlated with mortality(P < 0.001).The recruitment rate of tree species was negatively correlated with altitude,slope,slope aspect and convexity(P < 0.001).In conclusion,the population structure of evergreen broad-leaved trees in evergreen broadleaved forest is relatively stable within 5 years,instead,the population structure of deciduous broad-leaved trees(except Alniphyllum fortunei)and coniferous trees shows a declining trend.The greater the intensity of competition of trees,the higher the mortality rate;Competition combind with topographic factors affecting the mortality and recruitment of trees.The results of our study have reference significance for the mechanism for the commutity succession and species regeneration of evergreen broad-leaved forest. |
