气候变化背景下天目山落叶阔叶林乔木层1996—2017年动态研究

Dynamic study on tree layer of deciduous broad-leaved forest in Mount Tianmu from 1996 to 2017 under climate change

【目的】明确1996—2017年气候变化对天目山落叶阔叶林乔木层[胸径(DBH)≥10 cm的植株]的群落组成与结构、生物多样性和植物区系的影响。【方法】采用样地调查法对浙江天目山国家级自然保护区落叶阔叶林25个400 m2样地进行调查,使用2期(1996和2017年)调查数据和天目山1996—2017年气象数据,对落叶阔叶林乔木层动态进行分析。【结果】①乔木层树种生活型组成发生变化,常绿树种的株数占比从17.5%提高至35.5%,提高了102.9%,落叶树种的株数占比从82.5%下降至64.5%,下降了21.8%。群落外貌已悄然发生变化。②乔木层树种更替剧烈,整体退出4科6属8种,进入1科3属4种,退出和进入树种变幅达27.3%。稀有种和偶见种的退出和进入是引起乔木层物种数量变化的原因。③乔木层中不同树种的作用发生变化,重要值排前17位优势树种变幅为47.1%,其中,常绿树种交让木Daphniphyllum macropodum的重要值从第19位的1.88%增加到第3位的10.36%;常绿树种重要值占比从22.6%提高至36.3%。常绿树种在乔木层的作用正在不断增加。④乔木层α多样性稍有减少,各类指数降幅为−9.1%~−3.1%。常绿树种α多样性指数有所增加,变幅为−3.0%~51.8%。⑤植物区系趋于热带成分。科的热带成分占比从55.6%提高至58.3%;属的热带成分占比从25.0%提高至30.3%。⑥径级结构均呈倒“J”型,群落稳定;小径级常绿树种的株数提高了165.3%,中径级常绿树种的株数提高了45.5%,大径级无明显变化。1996年乔木层增长型树种有11种,稳定型树种有1种,衰退型树种有4种。2017年乔木层增长型树种有7种,稳定型树种有5种,衰退型树种没发生变化。短毛椴Tilia chingiana、青钱柳Cyclocarya paliurus、香槐Cladrastis wilsonii和色木槭Acer pictum退出增长型,进入稳定型。台湾松Pinus taiwanensis、细叶青冈Cyclobalanopsis shennongii、四照花Cornus kousa subsp.chinensis、交让木和天目槭Acer sinopurpurascens生长潜力增强。【结论】气候暖湿化背景下天目山落叶阔叶林乔木层动态变化非常显著,落叶阔叶林乔木层外貌已从落叶树种占据优势向常绿与落叶树种均衡状态演替,生物多样性稍有减少,植物区系趋向于热带成分。

[Objective]This study aims to investigate the effect of climate change from 1996 to 2017 on the community composition and structure,biodiversity,and flora of trees with diameter at breast height(DBH)≥10 cm in the deciduous broad-leaved forest layer of Mount Tianmu.[Method]A sample plot survey was conducted on 25 sample plots of 400 m2 of deciduous broad-leaved forest in the National Nature Reserve of Mount Tianmu,Zhejiang Province,China.Phase 2(1996 and 2017)survey data and meteorological data of Mount Tianmu from 1996 to 2017 were used to analyze the dynamics of the tree layer in a deciduous broadleaved forest.[Result](1)The composition of life form of tree species in the tree layer changed significantly.The proportion of evergreen tree species increased from 17.5%to 35.5%,an increase of 102.9%,and the proportion of deciduous tree species decreased from 82.5%to 64.5%,which decreased by 21.8%.(2)The tree species in the tree layer changed drastically,with an exit of 8 species in 6 genera of 4 families,and entry of 4 species in 3 genera of 1 family.The exit and entry tree species reached 27.3%.The exit and entry of rare and occasional species were the keys to the change in species number in the tree layer.(3)The role of evergreen tree species in the tree layer was increasing.The variation range of the top 17 dominant tree species in the important value was 47.1%.Among them,the important value of Daphniphyllum macropodum,an evergreen tree species,increased from 1.88%in the 19th place to 10.36%in the 3rd place.The proportion of important values of evergreen tree species increased from 22.6%to 36.3%.(4)Theαdiversity of the tree layer decreased slightly,and the decline in various indices ranged from−9.1%to−3.1%.Theαdiversity index of evergreen tree species increased,ranging from−3.0%to 51.8%.(5)The flora tended to be tropical.The proportion of tropical components in the family increased from 55.6%to 58.3%.The proportion of tropical elements in the genus increased from 25.0%to 30.3%.(6)The diameter class structure showed an inverted J type,and the community was stable.The number of small-diameter evergreen tree species increased by 165.3%,while the number of medium-diameter evergreen tree species increased by 45.5%.There was no significant change in the largediameter species.In 1996,there were 11 growth-type tree species,1 stable-type tree species,and 4 decliningtype tree species.In 2017,there were 7 growth-type tree species,and 5 stable-type tree species,and decliningtype tree species did not change.Tilia chingiana,Cyclocarya paliurus,Cladrastis wilsonii,and Acer pictum changed from growth-type to stable-type.The growth potential of Pinus taiwanensis,Cyclobalanopsis shennongii,Cornus kousa ssp.chinensis,Daphniphyllum macropodum and Acer sinopurpurascens increased.[Conclusion]Under climate warming and humidification,the dynamic change of the tree layer in the deciduous broad-leaved forest in Mount Tianmu is very significant.The appearance of the tree layer in the deciduous broad-leaved forest has transitioned from the dominance of deciduous tree species to the balanced state between evergreen and deciduous trees,with a slight decrease in biodiversity and a trend towards tropical elements in the flora.