| Chinese pine(Pinus tabuliformis)is a unique tree species in China.It is a representative forest species in North China.Chinese pine forest has many ecological functions such as water conservation,carbon sequestration and oxygen release.This study to analyze the diversity and heterogeneity of community structure and the characteristics of undergrowth regeneration and functional traits of dominant species was conducted on different forest ages of Chinese pine forest in Liaoheyuan,Hebei Province.In addition,the influence of biotic and abiotic variables on biomass and productivity were quantitatively assessed using redundancy analysis,stepwise regression and structural equation model with the aim of providing theoretical support for the stable and sustainable management for natural forest.The results are as follows:(1)In Chinese pine community,114 species,belonging to 44 families and 89 genera,were investigated.The ground bud plants accounted for the largest proportion,which reflected a typical vegetation type in temperate climate in study area.The shrub layer and herb layer had higher diversity index and species richness,which increased with forest age.The vertical structure of the community was obvious.The proportion of trees in the upper forest layer and the proportion of large diameter trees increased with the increase of stand age.The increasing forest age caused the diameter distribution to vary from inverted "J" to positive "J".The competition index and Gini coefficient decreased as stand age increases,whereas the opposite pattern was observed in the DBH evenness index.The Simpson index,Shannon index and variation coefficient of DBH of 60 a were significantly higher than those in other stand ages.The stand openness and gap fraction were larger in 60 a than in other stand ages.According to the observation of seed rain,soil seed bank and seedlings for three consecutive years,the secondary forest of P.tabuliformis were in good natural regeneration.The number of seed rains and soil seed bank were higher in 30 a and 70 a than other stand ages.The seed germination rate was positively related to the number of seed rain.The mortality rate of annual seedlings was high.The method of entropy was used to evaluate the regeneration and results showed that the regeneration index in 50 a was higher than that of other stand ages.The stepwise regression analysis showed that Simpson index of DBH and soil moisture content were the main influencing factors for regeneration.(2)The leaf and branchlet characters of Chinese pine showed a decreasing trend as stand age increases in the specific leaf area of new leaves,whereas the dry matter content,leaf area,and leaf phosphorus content of old leaves,the specific density and the total carbon content of branchlet increased as stand age increases.The characteristics of new and old leaves of Chinese pine were significantly different across stand ages.The specific leaf area,total nitrogen and total phosphorus content of new leaves were significantly higher than those of old leaves,while the dry matter content and total carbon content of leaves were significantly lower than those of old leaves.At the species level,the thickness and total carbon content of P.tabulaeformis were higher,while specific leaf area was lower than those of other species.On the level of functional group,the thickness,dry matter content and total carbon content of leaves can be ranked in decreasing order as follows:tree layer > shrub layer > herb layer,whereas the leaf area,specific leaf area,total phosphorus and total nitrogen showed the opposite pattern in different layers.(3)The biomass and productivity of P.tabuliformis stands of different ages were analyzed.The results showed that the total biomass of 60 a was significantly higher than that of other stand ages.The biomass of tree layer accounted for the largest proportion(>90%)of the total biomass,followed by litter layer,shrub layer and herb layer.In the tree layer,the biomass of 60 a was the largest,while the productivity of 50 a was the largest among the different stand ages.The biomass per unit area of shrub layer and herb layer showed an increasing trend with the increase of stand age with peak in 60 a.The total biomass of litter layer peaked in 60 a forest,with an average of 22.63 t/ha.Structural equation model analysis showed that forest structure(Gini coefficient and structural diversity)and leaf functional properties(leaf area and nitrogen content)were significant factors of biomass and productivity.Biomass was significantly negatively correlated with Gini coefficient,and positively correlated with DBH Shannon index,while productivity was mainly affected by functional traits.The results showed that the competition index and Gini index decreased with increasing of stand age,whereas the structure diversity index increased as stand age increase.The species diversity,structure diversity and biomass peaked in 60 a.Structural diversity has a significant impact on biomass accumulation,while new leaf area and leaf nitrogen content had a significant impact on productivity.Therefore,maintaining DBH diversity can promote biomass accumulation.In the protection and management of Chinese pine forest,measures to optimize forest structure at different growth stages can be taken to promote natural regeneration and productivity. |
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