| After a large-scale human disturbance,the area of primary forests has been continuously reduced and fragmented.After the implementation of natural forest protection projects and artificial afforestation,comprehensive enclosure has been implemented for nearly 20 years.As the plantation formed by artificial restoration mode and secondary forest formed by the natural restoration model are gradually evolved into the main body of china forest,how to evaluate the advantages and disadvantages of the artificial restoration and the natural restoration model is an urgent problem to be solved.In this paper,we studied the Chinese fir forest that was artificially restored for 42 years after clear cutting,the secondary forest that naturally recovered for 36 years after clear cutting,and the old-growth evergreen broad-leaved forest as the research objects in Jiulian Mountain.Based on the determination of community,species functional trait,topography and soil factors and the old-growth forest is used as the final vegetation restoration community,there are two restoration model,an artificial restoration model consisting of Chinese fir forest after clear cutting and old-growth forest and a naturally restored model consisting of a secondary forest after clear cutting and old-growth forest.The variations of different types of species and the community-level functional traits were explored in these forests.Moreover,the effects of environmental factors on variation pattern of community-level functional traits were clarified across these two restoration models.The main research results are as follows:(1)By the analysis of leaf nitrogen(N)and phosphorus(P)stoichiometric characteristics of different families,we found that the families with higher leaf nitrogen and phosphorus contents are Paulowniaceae and Staphyleaceae,while the lower families are Guttiferae and Tapisciaceae.However,N,P and the ratio of nitrogen and phosphorus(N/P)were often ranked in the middle for the subtropical dominant family.The analysis of leaf nitrogen and phosphorus stoichiometric characteristics of different genus levels revealed that the genus with higher leaf nitrogen and phosphorus content is Paulownia,while the lower family is Garcinia,and the variation of N for each family and genera was often greater than N and N/P.Regression analysis of leaf N and P stoichiometric characteristics across family and genera levels showed that family explained at least 30% of the variation in N and P stoichiometric variations,while family levels explained at least 45%.The effect of genera on N and P stoichiometric variations was always greater than the family level.Meanwhile,Chinese fir forest at family level explained the largest amount of N and P stoichiometric variations,while secondary forests often explained the largest amount of N and P stoichiometric variation at genus level.(2)By analyzing the differences in leaf N and P stoichiometric characteristics of different endangered species,we found that N and P of endangered and critically endangered species was often low,and N/P of vulnerable,endangered and critically endangered levels was often lower than the non-hazardous and near-hazard levels.By analyzing the difference in leaf N and P stoichiometric characteristics of different endemic species,we found that leaf N and P stoichiometric characteristics of endemic species was often smaller than that of non-endemic species.By analyzing the differences in leaf N and P stoichiometric characteristics of different leaf habits,we found that the leaf N and P stoichiometric characteristics of evergreen tree species was often smaller than that of deciduous tree species.By analyzing the differences in leaf N and P stoichiometric characteristics of different shade-tolerant species,it was found that leaf N and P stoichiometric characteristics of intolerant tree species was often greater than that of neutral and shade-tolerant species.Therefore,evergreen,shade-tolerant,endemic and endangered species have a smaller leaf N and P content,while deciduous,intolerant,non-endemic non-endangered species usually had a higher leaf N and P content.(3)By analyzing the differences of community-level functional traits in different forest types,the results showed that: Chinese fir forest had the highest endangered grade,deciduous tree species ratio and N/P,the lowest endemic species ratio,leaf N and P content;Secondary forest had the highest endemic species ratio,leaf N and P content,the lowest endangered grade and shade tolerance tree species ratio;Oldgrowth forest had the highest shade tolerance tree species ratio,the lowest deciduous tree species ratio and N/P.(4)There was a significant positive correlation between the endangered grade and the proportion of endemic species in Chinese fir forest,while there was no significant correlation between other forest stands;there was a significant positive correlation between the endangered grade and N/P in Chinese fir forest,but the opposite was true for old-growth forest;There was a significant negative correlation between the proportion of endemic species and N/P,but not in old-growth forest;the proportion of deciduous tree species in Chinese fir forest and secondary forest was significantly positively correlated with leaf N,but not in old-growth forest;There was a significant positive correlation between the proportion of shade-tolerant tree species and N/P in Chinese fir forest,while the opposite was true for secondary forest;Leaf N content was significantly positively correlated with leaf P content in these three forests;leaf N content had a significant positive correlation with N/P in Chinese fir forest and oldgrowth forest;There was a significant negative correlation between P content and N/P in secondary and old-growth forests.(5)Compared with the natural recovery model,more environmental factors in the artificial recovery model significantly affected the functional trait variation,and environmental factors also explained more functional trait variations;,Both slope and nitrate nitrogen significantly affected the variations of functional traits in the natural and artificial recovery models;the amount of variation of functional traits explained by the soil alone was equivalent in the two models,the terrain alone explained more variations of functional traits in the natural restoration model,and the interaction between soil and terrain played an important role in the artificial restoration model.(6)In the artificial restoration model,forest type significantly affected each index of functional traits,the range of explained variation of each functional trait was from22% to 88%,while in the natural restoration model,the forest type only affects the endangered level,endemic species ratio,leaf N and N/P,the range of explained variation was from 20% to 58%,without affecting the proportion of deciduous tree species,the proportion of shade-tolerant tree species and P content;Both endangered grade and leaf N content were affected by soil nitrogen content,endemic species ratio was only affected by nitrate nitrogen content,the ratio of deciduous tree species was affected by soil water holding capacity,and the leaf P content was affected by soil moisture content,leaf N/P was influenced by slope in two restoration models;the influence factors on the proportion of shade-tolerant tree species are different in the two restoration models. |
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