Floristic composition, phylogenetic diversity, and community assembly identify the Lutou Experimental Forest as a model subtropical hub in the tropical-temperate transition zone

Abstract

Subtropical mountain ecosystems serve as dynamic interfaces between tropical and temperate biotas, hosting high biodiversity shaped by complex topography and stable historical climate. This study presents a comprehensive assessment of the Lutou Experimental Forest in the northern Mulianjiu Mountains of central subtropical China, an area situated at a key tropical–temperate transition zone. A total of 1209 seed plant species belonging to 149 families and 595 genera were documented, showing a balanced composition of woody and herbaceous taxa as well as a coexistence of evergreen and deciduous species, typical of transitional floras. Floristic analyses demonstrated nearly equal proportions of tropical and temperate elements, complemented by exceptionally high proportions of East Asian endemic genera (18.13%) and East Asia–North America disjunct genera (10.1%). Principal component analysis (PCA) positioned Lutou centrally within the national subtropical transitional cluster, reflecting its unique biogeographic bridging role. Environmental data indicated that high annual precipitation (~ 1900 mm), moderate annual temperature (15 °C), and a pronounced elevational gradient (124–1272 m) jointly drive strong microhabitat differentiation. Castanopsis eyrei evergreen broad-leaved forest was identified as the most mature and ecologically representative community type. Regional comparison across 16 subtropical mountain ranges in China revealed that the Mulianjiu Mountains harbor the highest narrow-endemic species richness and Weighted Endemism Index (WEI) density. We conclude that Lutou is a core floristic and evolutionary hub in the tropical–temperate transition, where climate stability, topographic heterogeneity, and ecological maturity converge to sustain both relictual persistence and ongoing evolutionary diversification.

Keywords

Castanopsis forest / Community structure / Ecotone dynamics / Lutou Experimental Forest / Phylogenetic diversity / Subtropical flora

References

[1] Azuma H, García-Franco JG, Rico-Gray V, Thien LB. Molecular phylogeny of the Magnoliaceae: the biogeography of tropical and temperate disjunctions. Am J Bot, 2001, 88(12): 2275-2285

[2] Cao K, Rao MD, Yu JP, Liu XJ, Mi XC, Chen JH. The phylogenetic signal of functional traits and their effects on community structure in an evergreen broad-leaved forest. Biodivers Sci, 2013, 21(5): 564-571 in Chinese

[3] Chen ML, Liu DY, Cui SQ, Liu XY. The diversity of seed plants in liugujian nature reserve and its conservation strategy. Bull Bot Res, 2007, 27(4): 484-493 in Chinese

[4] Ding Y, Zang RG, Letcher SG, Liu SR, He FL. Disturbance regime changes the trait distribution, phylogenetic structure and community assembly of tropical rain forests. Oikos, 2012, 121(8): 1263-1270

[5] Fang JY, Ling Z, Tang ZY. Patterns of woody plant species diversity along environmental gradients on Mt. Taibai, Qinling Mountains. Biodivers Sci, 2004, 12(1): 115-122

[6] Fang S, Yuan ZQ, Lin F, Ye J, Hao ZQ, Wang XG. Functional and phylogenetic structures of woody plants in broad-leaved Korean pine mixed forest in Changbai Mountains, Jilin. China Chin Sci Bull, 2014, 59(24): 2342-2348 in Chinese

[7] He CS, Liu R, Yang ZC, Yin QL, Jia SH, Luo YF, Hao ZQ. Species composition and community structure of warm temperate deciduous broadleaved forests in Huangguan of Qinling Mountains. China. J Appl Ecol, 2021, 32(8): 2737-2744

[8] Huang YT, Yao L, Ai XR, Lü SA, Yi DING, A, . Quantitative classification of the subtropical evergreen–deciduous broadleaved mixed forest and the deciduous and evergreen species composition structure across two national nature reserves in the southwest of Hubei. China. Chin J Plant Ecol, 2015, 39(10): 990-1002 in Chinese

[9] Jewitt D, Goodman PS, O’Connor TG, Witkowski ETF. Floristic composition in relation to environmental gradients across KwaZulu-Natal South Africa. Austral Ecol, 2015, 40(3): 287-299

[10] Jin L, Liu JJ, Xiao TW, Li QM, Lin LX, Shao XN, Ma CX, Li BH, Mi XC, Ren HB, Qiao XJ, Lian JY, Hao G, Ge XJ. Plastome-based phylogeny improves community phylogenetics of subtropical forests in China. Mol Ecol Resour, 2022, 22(1): 319-333

[11] Kikuchi S, Osone Y. Subspecies divergence and pronounced phylogenetic incongruence in the East-Asia-endemic shrub Magnolia sieboldii. Ann Bot, 2021, 127(1): 75-90

[12] Kuo CC, Liu YC, Su Y, Liu HY, Lin CT. Responses of Alpine summit vegetation under climate change in the transition zone between subtropical and tropical humid environment. Sci Rep, 2022, 12: 13352

[13] Lan J, Zhang X, Zhu J, Wei X, Chen B, Liu JF, Zheng SQ, He ZS. Environmental heterogeneity determines beta diversity and species turnover for woody plants along an elevation gradient in subtropical forests of China. For Res, 2023, 3: 26-26

[14] Lang F, Ye GF, Huang YX, Gao W, Lin J, Huang SD, Jiang H. Carbon storage and fraction of natural Castanopsis eyrei forest in the Wuyi Mountains. J Subtrop Resour Environ, 2012, 7(4): 71-77 in Chinese

[15] Legendre P, Gallagher ED. Ecologically meaningful transformations for ordination of species data. Oecologia, 2001, 129(2): 271-280

[16] Li L, Wen ZF, Wei SG, Lian JY, Ye WH. Functional diversity and its influencing factors in a subtropical forest community in China. Forests, 2022, 13(7): 966

[17] Li PK, Geng ZH, Wang XY, Zhang PP, Zhang J, Ding SY, Fu Q. Phylogenetic and functional structure of wood communities among different disturbance regimes in a temperate mountain forest. Forests, 2022, 13(6): 896

[18] Li RH, Zhu SD, Lian JY, Zhang H, Liu H, Ye WH, Ye Q. Functional traits are good predictors of tree species abundance across 101 subtropical forest species in China. Front Plant Sci, 2021, 12: 541577

[19] Li XF, Pei KQ, Kéry M, Niklaus PA, Schmid B. Decomposing functional trait associations in a Chinese subtropical forest. PLoS ONE, 2017, 12(4): e0175727

[20] Lin GJ, Huang ZL, Zhu L, Ouyang XJ. Beta diversity of forest community on Dinghushan. Acta Ecol Sin, 2010, 30: 4875-4880 in Chinese

[21] Liu L, Hao ZZ, Liu YY, Wei XX, Cun YZ, Wang XQ. Phylogeography of Pinus armandii and its relatives: heterogeneous contributions of geography and climate changes to the genetic differentiation and diversification of Chinese white pines. PLoS ONE, 2014, 9(1): e85920

[22] Liu WZ, Xie JG, Zhou H, Kong HH, Hao G, Fritsch PW, Gong W. Population dynamics linked to glacial cycles in Cercis chuniana F. P. Metcalf (Fabaceae) endemic to the montane regions of subtropical China. Evol Appl, 2021, 14(11): 2647-2663

[23] Lu ZJ, Bao DC, Guo YL, Lu JM, Wang QG, He D, Zhang KH, Xu YZ, Liu HB, Meng HJ, Huang HD, Wei XZ, Liao JX, Qiao XJ, Jiang MX, Gu ZR, Liao CL. Community composition and structure of Badagongshan (BDGS) forest dynamic plot in a mid-subtropical mountain evergreen and deciduous broad-leaved mixed forest. Cent China Plant Sci J, 2013, 31(4): 336

[24] Qiu YX, Fu CX, Comes HP. Plant molecular phylogeography in China and adjacent regions: tracing the genetic imprints of Quaternary climate and environmental change in the world’s most diverse temperate flora. Mol Phylogenet Evol, 2011, 59(1): 225-244

[25] Rezende VL, Eisenlohr PV, Vibrans AC, de Oliveira-Filho AT. Humidity, low temperature extremes, and space influence floristic variation across an insightful gradient in the Subtropical Atlantic Forest. Plant Ecol, 2015, 216(6): 759-774

[26] Shang KK, Song K, Da LJ. Ecology of relict tertiary deciduous trees in subtropical China. Vegetation structure and function at multiple spatial, temporal and conceptual scales, 2016, Cham, Springer : 149-167

[27] Shen YF, Cheng YL, Li KQ, Li HG. Integrating phylogeographic analysis and geospatial methods to infer historical dispersal routes and glacial refugia of Liriodendron chinense. Forests, 2019, 10(7): 565

[28] Tang CQ, Ohsawa M. Zonal transition of evergreen, deciduous, and coniferous forests along the altitudinal gradient on a humid subtropical mountain, Mt. Emei, Sichuan, China. Plant Ecol, 1997, 133(1): 63-78

[29] Tang ZY, Fang JY, Chi XL, Feng JM, Liu YN, Shen ZH, Wang XP, Wang ZH, Wu XP, Zheng CY, Gaston KJ. Patterns of plant beta-diversity along elevational and latitudinal gradients in mountain forests of China. Ecography, 2012, 35(12): 1083-1091

[30] Wang MN, Duan L, Qiao Q, Wang ZF, Zimmer EA, Li ZC, Chen HF. Phylogeography and conservation genetics of the rare and relict Bretschneidera sinensis (Akaniaceae). PLoS ONE, 2018, 13(1): e0189034

[31] Wang Y. Structure characteristics of Castanopsis eyrei forest community in Wuyishan Ecological Reserve. For Inventory Plan, 2011, 36(02): 43-46 in Chinese

[32] Wu LW, Yen SH, Lees DC, Lu CC, Yang PS, Hsu YF. Phylogeny and historical biogeography of Asian Pterourus Butterflies (Lepidoptera: Papilionidae): a case of intercontinental dispersal from North America to east Asia. PLoS ONE, 2015, 10(10): e0140933

[33] Wu M, Feroz SM, Hagihara A, Xue L, Huang ZL. Vertical stratification, floristic composition and woody species diversity in a subtropical evergreen broadleaf forest (Dinghushan Nature Reserve, South China). Tropics, 2010, 19(1): 9-19

[34] Wu YG, Xie ZJ, Wan ZM, Ji QQ, Yang JJ, Chen TW, Wu DH, Scheu S. Elevational changes in canopy Collembola community composition are primarily driven by species turnover on Changbai Mountain, northeastern China. Biodivers Conserv, 2023, 32(14): 4853-4872

[35] Xie L, Bao XX, Chen SF, Ding H, Fang YM. The effects of small geographical resolution and age on the phyllosphere microbial diversity ofCastanopsis eyreiin subtropical forest. Microbiol Spectr, 2025, 13(3): e02024-e12091

[36] Yan DY, Peng S, Lehtonen S, Chen JM, Li ZZ. Phylogeography and population genomics of the critically endangered aquatic plant Caldesia grandis in China. Glob Ecol Conserv, 2024, 55: e03235

[37] Yang AH, Zhong YD, Liu SJ, Liu LP, Liu TY, Li YQ, Yu FX. New insight into the phylogeographic pattern ofLiriodendron Chinense(Magnoliaceae) revealed by chloroplast DNA: east–west lineage split and genetic mixture within western subtropical China. PeerJ, 2019, 7: e6355

[38] Yang J, Lu MM, Cao M, Li J, Lin LX. Phylogenetic and functional alpha and beta diversity in mid-mountain humid evergreen broad-leaved forest. Chin Sci Bull, 2014, 59(24): 2349-2358 in Chinese

[39] Yang Q, Ding H, Fang YM, Chen X, Xu HG. Species composition and diversity of evergreen broad-leaved forest of Castanopsis eyrei in Daanyuan. J Anhui Agric Univ, 2014, 32(1): 16-20 in Chinese

[40] Zang SY. A project of sustainable utilization of forest resources supported by GIS. Chin Geogr Sci, 2000, 10(2): 188-192

[41] Zhan QH, Liao HH, Liang YL, Zhang Z, Le XG, Xiong Y, Cheng L, Ding WQ, Lu J, Zhou YD, Yang BY. Elevational patterns of orchid diversity in mid-subtropical mountain forests of Eastern China. Glob Ecol Conserv, 2025, 57: e03405

[42] Zhang JX, Swenson NG, Liu JM, Liu MT, Qiao XJ, Jiang MX. A phylogenetic and trait-based analysis of community assembly in a subtropical forest in Central China. Ecol Evol, 2020, 10(15): 8091-8104

[43] Zhao WY, Liu ZC, Wang L, Fan Q, Liu J, Liao WB. The endemism and relict property of spermatophyte flora of the Luoxiao Mountains. Biodivers Sci, 2020, 28(7): 854-866

[44] Zhou WB, Xiang QY, Wen J. Phylogenomics, biogeography, and evolution of morphology and ecological niche of the eastern Asian–eastern North American Nyssa (Nyssaceae). J Syst Evol, 2020, 58(5): 571-603

[45] Zhu H, Cao M, Hu HB. Geological history, flora, and vegetation of Xishuangbanna, southern Yunnan. China Biotropica, 2006, 38(3): 310-317

Funding

Hunan Forestry Science and Technology Innovation Project(XLK202455)

Hunan Provincial Department of Education Scientific Research Project(22B0274)

Changsha Science and Technology Project(kq2402253)

RIGHTS & PERMISSIONS

Northeast Forestry University