Major Forest Changes in Subtropical China since the LastIce Age

Article Major Forest Changes in Subtropical China since Last Ice Age Qiuchi Wan 1, Xiao Zhang 1, *, Yaze Zhang 1, Yuanfu Yue 2, Kangyou Huang 1, Rachid Cheddadi 3 and Zhuo Zheng 1,4 1 Guangdong Key Lab Geodynamics and Geohazards, School Earth Sciences and Engineering, Sun Yat-sen University, Zhuhai 519082, China; wanqch@mail3.sysu.edu.cn (Q.W.); zhangyz6@mail2.sysu.edu.cn (Y.Z.); hkangy@mail.sysu.edu.cn (K.H.); eeszzhuo@mail.sysu.edu.cn (Z.Z.) 2 Guangxi Laboratory on Study Coral Reef in South China Sea, Coral Reef Research Center China, School Marine Sciences, Guangxi University, Nanning 530004, China; yuanfu.yue@gxu.edu.cn 3 Institute Evolutionary Sciences, University Montpellier, CNRS, IRD, EPHE, 34000 Montpellier, France; rachid.cheddadi@umontpellier.fr 4 Sourn Marine Science and Engineering Guangdong Laboratory, Zhuhai 519082, China * Correspondence: zhangx636@mail.sysu.edu.cn Citation: Wan, Q.; Zhang, X.; Zhang, Y.; Yue, Y.; Huang, K.; Cheddadi, R.; Zheng, Z. Major Forest Changes in Subtropical China since Last Ice Age. Forests 2021, 12, 1314. https:// doi.org/10.3390/f12101314 Academic Editor: Juan A. Blanco Abstract: In subtropical zone sourn China, re was a considerable conversion forests from deciduous to evergreen broadleaf in early Holocene. However, exact timing this vegetation change and its relationship to climate are still unclear. We examined a high-resolution pollen record collected in mid-subtropical zone and n performed a correlation with regional data to reconstruct history forest ecosystems since last deglaciation. Our data show that expansion evergreen plant component already occurred at low elevations during last deglaciation. The subtropical mountain landscape was not recolonized by evergreen forests until mid-holocene at about 8.1 ka BP. Based on fossil pollen reconstruction and climate model simulation, we conclude that primary increase in evergreen components subtropical ecosystems was triggered by postglacial temperature increase, and that a complete conversion from deciduous to evergreen forest ecosystems did not occur until Holocene winter temperatures and seasonal temperature contrast reached a threshold suitable for growth and persistence evergreen tree species. Keywords: deglaciation; Holocene; pollen analysis; species distribution model; subtropical China; winter temperature Received: 27 August 2021 Accepted: 22 September 2021 Published: 26 September 2021 Publisher s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: 2021 by authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under terms and conditions Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1. Introduction Evergreen broadleaved forests (EBLFs) are now dominant biome in subtropical zone in east China with abundant endemic plant species and high biodiversity [1]. The EBLF extends from about 22 23 N to Yangtze River at 31 33 N [2,3]. During Last Glacial Maximum (LGM), subtropical China was covered by temperate deciduous (TEDE) and cool mixed (COMX) forests in a cooler climate [4,5]. Reconstructed LGM biomes suggest that tropical forests were absent from mainland sourn China, or ir range was reduced to very limited areas [6]. EBLF and warm mixed forest had retreated to tropical latitudes [7]. Therefore, it is likely that EBLF was restricted to sournmost part China, between 6 and 8 N south its present range [6 8]. However, exactly when and how EBLF recolonized subtropical regions since last deglaciation is poorly known [5,9]. Moreover, climatic interpretation forest conversion remains controversial. Although long-term global warming since last deglaciation is generally considered to be main cause forest changes and shifts in zonal vegetation boundaries [10,11], some have claimed that summer rainfall might have played a dominant role [10]. The mechanism low latitude vegetation response to global Forests 2021, 12, 1314. https://doi.org/10.3390/f12101314 https://www.mdpi.com/journal/forests

Forests 2021, 12, 1314 2 10 climate change driven by ice sheet mass and/or insolation is also debated [12,13]. In this study, we examine a high-resolution pollen record SZY peat bog in mid-subtropical zone. This pollen record allowed us to reconstruct timing conversion from LGM deciduous biome to now dominant EBLF. Climate thresholds for EBLFs were derived from its modern distribution using a species distribution model and past climate variables from transient climate simulations. A reconstruction biome turnover and climate data helped us identify key driving climate variables and effects postglacial global warming on EBLF s recolonization evergreen ecosystems in subtropical China. 2. Regional Setting Study core SZY (119.034 E, 26.777 N; 1007 m) was collected from a mountain peat bog in Jiufeng Mountains, Fujian Province, souastern China (Figure 1). The summits nearby mountains are between 1300 and 1600 m. The area is located in sourn part mid-subtropical zone, which is strongly influenced by East Asian Summer Monsoon (EASM). The local mean annual temperature is about 16 C, and mean January temperature and daily minimum are 6 7 C and 4 C, respectively, at about 1000 m elevation. The average altitude constant is about 0.59 C/100 m. Annual precipitation varies between 1700 and 1900 mm, with most precipitation falling between late March and July. Evergreen broadleaved forest is main vegetation type, which can be divided into following five communities: coniferous/broadleaved mixed forest, warm coniferous forest, evergreen broadleaved forest, bamboo forest and shrubland. In regions below 1000 m altitude, re are few natural forests left due to heavy human impact. Dominant arboreal plants at genus level in local natural or secondary forests mountains are Pinus, Castanopsis, Cyclobalanopsis, Cunninghamia, Altingia, Cryptomeria, Cinnamomum, Forests 2021, 12, x FOR PEER REVIEW Machilus, Schima and Eleocarpus. The common shrub taxa include Eurya, Neolitsea, Lindera, Ardisia, Rhododendron, Prunus, etc. The temperate deciduous and conifer elements, such as Fagus, Quercus, Carpinus, Acer, Tsuga, Rhododendron, Symplocos, are generally found at higher altitudes 1200 m. Figure Figure 1. Location 1. Location study core study SZY. core SZY. 3. Materials and Methods 3.1. Coring, Sampling and Chronology

Forests 2021, 12, 1314 3 10 3. Materials and Methods 3.1. Coring, Sampling and Chronology The SZY core was taken in 2011 using a Russian Corer. In this study, upper 273 cm peat core (425 cm in total) was investigated. The uppermost sediment (0 32 cm) consists marsh clay with abundant plant debris and high water content. The main part core below 32 cm consists homogeneous brown-black peat and dark clay. For upper 273 cm core, a total 180 samples (including 132 previously published [5] and 48 newly added) were taken at 1 2 cm intervals, corresponding to a temporal resolution about 80 years between samples. The age-depth model was constructed using radiocarbon dating with accelerator mass spectrometry (AMS 14 C). Details radiocarbon samples can be referred to [5]. Based on calibrated age, interval extends to 15,000 cal yr BP at 274 cm. The depth-age plot [5] shows a higher sedimentation rate during Holocene (2.2 cm/100 yr) and a lower rate during last deglaciation (0.83 cm/100 yr). 3.2. Pollen Analysis The pollen preparation method basically followed traditional laboratory treatment techniques [14] with some improvements such as use hydrluoric acid. Each sample was weighed to 2 3 g sediment, and one tablet trace Lycopodium spores (27,637 per tablet) was used for calculation pollen concentration (grains/g). The main treatment procedure included hydrochloric acid (10%) to remove carbonates, hydrluoric acid (40%) to remove silicates and potassium hydroxide to remove organic matter. The palynomorphs were separated from mineral sediment using standard heavy liquid flotation techniques [15]. In general, more than 400 pollen grains were counted, and pollen percentage calculation was based on sum total pollen excluding aquatic taxa and all spores. 3.3. Biomization In order to better illustrate temporal vegetation changes, pollen taxa were grouped as plant functional types (PFTs). Based on which, biomes were reconstructed by applying biomization technique. We basically applied existing schemes plant functional types (PFTs) previously used for China [7], except for exclusion PFTs from high latitude arctic and boreal zones, and some moderate modifications to fit regional biomes. In this study, only following six biomes occurring in study area were reconstructed: subtropical evergreen broadleaved forest (EBLF), tropical rain forest (TRFO), temperate deciduous broadleaved forest (TEDE), cold mixed forest (CLMX), cool mixed forest (COMX) and alpine shrub and meadow (ALPM). We named biome subtropical (warm-temperate) evergreen broadleaved forest as EBLF, which is approximately same with warm evergreen and mixed forest (WAMF) used in [7] and adopted biome ALPM proposed by [4] to identify subtropical mountain vegetation. 3.4. Species Distribution Modelling By associating modern presence data and climate data, species distribution model (SDM) [16] predicts climatic envelope study species or vegetation type and projects it to different time periods to obtain potential distributions. Using this method, potential distributions EBLF at time slices LGM and present were predicted. The presence data EBLF was extracted from a digitalized vegetation map (Supplementary Figure S1). To avoid sampling bias, we divided distribution range presence data into several 1 1 grids, and randomly picked up only one point from each grid to obtain a filtered subset presence data (n = 129) using GridSample function R dismo package. Seven key parameters among 19 bioclimatic variables representative climate conditions from WorldClim database were used for model calibration (Supplementary Table S1). For LGM climate conditions, we relied on results estimated using an Earth System Model, MIROC-ESM [17]. The distribution EBLF at each time slice was finally predicted using one most popular SDM methods, maximum entropy algorithm

Forests 2021, 12, 1314 4 10 (Maxent) within R dismo package with default settings based on filtered presence data and climate data. The resulting habitat suitability, value which ranges from 0 (unsuitable) to 1, was used to indicate potential distribution EBLF. By comparing predicted distribution model for present time and known distribution EBLF, model was validated with a threshold-independent measure area under receiver operating characteristic curve (AUC). The highest value 1 (0 being lowest) represents a complete match between modeled distribution and known distribution. 3.5. Transient Data Analysis TRACE21 is first state---art transient simulation global climate change over last 21 ka at T31 spatial resolution [18]. Two climatic variables including mean winter (December February) temperatures (corresponding to bioclimatic variable 11 in WorldClim) and temperature seasonality (July January) were used for comparison. We first extracted temperature values grid where SZY is located, and n uniformly correct simulated values by substituting in bias caused by altitudinal lapse-rate modern climate observation in study site. 4. Results The high resolution and well dated record SZY shows that vegetation last 15,000 years passed through four main phases characterized by four distinct pollen zones (Figure 2). During last deglaciation between 15 and 11.5 ka BP, regional vegetation was dominated by cold-tolerant deciduous forest. The constituent deciduous taxa are Fagus, Quercus, Alnus, Betula, Corylus, Carpinus and ors. Evergreen taxa such as Cyclobalanopsis and Castanopsis were also present in this pollen zone, but percentages are generally lower than subsequent Holocene values. Conifers such as Tsuga and Abies and Forests 2021, 12, x FOR PEER REVIEW shrub Rhododendron (Ericaceae) were more abundant during time interval earlier 5 than 11 11.5 ka BP. Herbaceous taxa including Artemisia and Poaceae fluctuated and sometimes reached 5% (Figure 2). Figure Figure 2. 2. Pollen Pollen diagram diagram selected selected taxa taxa from from SZY SZY record record last 15,000 last 15,000 years. years. All relative All relative abundances abundances were calculated based on total pollen sum. were calculated based on total pollen sum. During Holocene, at least three zones pollen assemblage can be identified. The lower zone is from 11.5 to 8.2 ka BP when Pinus and Taxodiaceae (possibly Chinese watercypress Glyptostrobus) and wetland sedge increased rapidly. Alnus was also relatively abundant, species which may belong to wetland environment taxon in region (i.e., A. trabeculosa). The middle zone dated to 8.1 0.8 ka BP corresponds to pollen

Forests 2021, 12, 1314 5 10 During Holocene, at least three zones pollen assemblage can be identified. The lower zone is from 11.5 to 8.2 ka BP when Pinus and Taxodiaceae (possibly Chinese water-cypress Glyptostrobus) and wetland sedge increased rapidly. Alnus was also relatively abundant, species which may belong to wetland environment taxon in region (i.e., A. trabeculosa). The middle zone dated to 8.1 0.8 ka BP corresponds to pollen assemblages marked by evergreen broadleaved taxa mainly including Cyclobalanopsis, Castanopsis and Altingia. The wetland sedge pollen Cyperaceae was extremely abundant in lower part this zone, which was followed by an increase in Poaceae and fern spores. The upper most zone corresponding to last ~0.8 ka BP shows an abrupt increase in Poaceae, Artemisia, Dicranopteris and Pinus, which are considered as pollen taxa associated with human activities [19]. The total non-arboreal pollen percentage is up to 52% in uppermost part record. The biome reconstruction result shows a strong dominance temperate deciduous broadleaved forest (TEDE) between 15 and 11.5 ka BP, and biome with second highest score was cool mixed forest (COMX). An obvious decrease in all biomes except alpine shrub and meadow (ALPM) happened at around 11.5 12.5 ka BP. During transition from early to mid-holocene (ca. 11.5 8.2 ka BP), re was a gradual increase in subtropical (warm-temperate) evergreen broadleaved mixed forest (EBLF), although its scores were still lower than those TEDE. The onset EBLF increase after obvious biome change at ca. 11.5 ka BP corresponds to cold Younger Dryas (YD), suggesting that EBLF s recolonization Forests 2021, 12, x FOR PEER REVIEW subtropical regions resumed and accelerated after YD termination. After 8.1 6 ka BP, 11 EBLF became dominant over TEDE, with several fluctuations abundance (e.g., at around 3.2 ka BP) until end Holocene (Figure 3). Figure 3. Reconstructed biomes last last 15 15 ka ka BP BP derived derived from from pollen pollen record record SZY SZY in souastereastern China. China. The principal The principal biomes biomes shown shown are subtropical are subtropical evergreen evergreen broadleaved broadleaved forest (EBLF), forest tropical (EBLF), in south- rain tropical forest rain (TRFO), forest temperate (TRFO), temperate deciduous broadleaved deciduous broadleaved forest (TEDE), forest cold (TEDE), mixed forest cold (CLMX), mixed forest cool (CLMX), cool mixed forest (COMX) and alpine shrub and meadow (ALPM). mixed forest (COMX) and alpine shrub and meadow (ALPM). The species distributionmodel modelwas wasused usedto topredict potential potential distributions distributions evergreen broadleaved broadleaved forest forest at at LGM LGM and and in in present present (Figure (Figure 4). The 4). The predicted predicted pre- evergreen present-day distribution distribution EBLF EBLF agrees agrees well well with with known known distribution distribution (AUC (AUC = 0.94), = 0.94), in- indicating that that modelis is reliablefor drawing furr conclusions. The simulated LGM distribution shows that EBLF migrated southward into norrn Indochina in western part but found potentially suitable conditions (in situ refugia) in central east (i.e., some large river basins between Wuyi and Xuefeng mountain ranges).

(CLMX), cool mixed forest (COMX) and alpine shrub and meadow (ALPM). The species distribution model was used to predict potential distributions evergreen broadleaved forest at LGM and in present (Figure 4). The predicted present-day distribution EBLF agrees well with known distribution (AUC = Forests 2021, 12, 1314 6 0.94), 10 indicating that model is reliable for drawing furr conclusions. The simulated LGM distribution shows that EBLF migrated southward into norrn Indochina in western part but found potentially suitable conditions (in situ refugia) in central east (i.e., some part but found potentially suitable conditions (in situ refugia) in central east (i.e., some large river basins between Wuyi and Xuefeng mountain ranges). large river basins between Wuyi and Xuefeng mountain ranges). Figure 4. Potential distribution evergreen broadleaved forest (EBLF) in sourn China simulated by Maxent. The quantile result critical climate thresholds for simulated present distribution is shown below. The suitability value ranges from 0 (unsuitable) to 1. The green to blue distribution ranges represent predicted most probable climatic-suitable habitats for EBLF. 5. Discussion 5.1. Substantial Forest Transformation during Holocene Our data show that vegetation in subtropical mountains around 1000 m elevation during last deglaciation was dominated by deciduous forest (TEDE) and conifers (COMX). The presence evergreen components might reflect a kind mixed forest in which deciduous trees predominated, but re were also a significant number evergreen taxa. It is also possible that some pollen evergreen plants was transported from lower altitudes by updraft wind, since evergreen forest belt in lower mountains was not very far from study area during last deglacial. However, considering small size our study site, we suppose that pollen assemblage our record largely reflects local vegetation composition [20]. The main transition from a deciduous to an evergreen biome occurred rapidly over a narrow time span at ca. 8.1 ka BP (Figure 3). However, this timing biome turnover raised controversy as pollen records from or latitudinal positions show different timing. In Taiwan Island, expansion subtropical (and/or warm temperate) evergreen forest took place much earlier at about 11.5 ka BP [4]. Fossil pollen data over eastern China show that timing vegetation change is not simultaneous, but rar follows a time-transgressive pattern from south (10.3 ka BP) to north (6 ka BP) [11]. Effectively, complete absence evergreen broadleaved forest during LGM in subtropical zone Chinese mainland inferred by previous biome reconstruction [6] is under debate as phylogeographic studies have suggested that species EBLF survived LGM locally in numerous norrn refugia [21]. Our pollen record shows that evergreen forest may have occupied lower altitude regions even during glacial periods, taking into consideration regional altitudinal air temperature lapse rate, which may have steepened during LGM [22].

Forests 2021, 12, 1314 7 10 Our simulated distribution evergreen forest shows a shrinkage evergreen forest distribution, which also persisted in nearby lowland areas as refugia such as basins between Wuyi and Xuefeng mountain ranges in souastern China. Such model simulations imply that local mountain evergreen forest experienced a complex migration upward from lowland during early to mid-holocene, agreeing well with refugia ory proposed by phylogeographic studies [21,23], although re may have also been some northward shift constituent evergreen species from south to north [21]. 5.2. Holocene Climatic Changes as a Cause Subtropical Forest Transformation The rapid EBLF/TEDE biome change at about 8.1 ka BP suggests that rate vegetation change increased as temperature increased and crossed a threshold that delineates climatic range two biomes. Mean minimum temperature and seasonal temperature contrast are commonly considered as effective climate indices for defining upper limit for evergreen broadleaved forest [24], as photosyntic efficiency leads to a reduction in evergreen broadleaved species [25]. From analysis Holocene climate changes in region (Figure 5), we furr confirm that seasonal temperature difference and/or coldest climate condition must be most important climatic factors controlling switch between evergreen/deciduous trees, and that it is much less related to change rainfall amount, because both moisture proxy from stalagmites [26] and simulated precipitation [27] show a maximum amount centered around 10 ka BP, which contradicts timing our pollen records. Forests 2021, 12, x FOR PEER REVIEW 8 11 Figure 5. Temperature and seasonal difference as key factors evergreen forest turnover during Holocene. Temperature indices indices including including brgdgt-based mean mean annual annual temperature temperature reconstruction [27], [27], TRACE21 TRACE21 [18] modeled [18] modeled winter winter temperature temperature (Twin) (Twin) and seasonal and seasonal mean mean temperature temperature dif- reconstructierence between July and January. The values two variables were revised from regional difference between July and January. The values two variables were revised from regional output according to local air temperature (SZY). output according to local air temperature (SZY). The The local local air air temperature temperature was was estimated estimated by by proxy proxy branched branched glycerol glycerol dialkyl dialkyl glycerol glycerol tetraer tetraer (brgdgt) (brgdgt) [28], [28], which which shows shows synchronous synchronous changes changes with with reconstructed reconstructed vegetation vegetation changes changes from from same same site site SZY. SZY. There There was was a rapid rapid increase increase in in mean annual temperature (MAT) from 13 to 16 C at about 8 ka BP. The temperature at about 16 C corresponds to most appropriate MAT range (14.5 18.5 C) for present evergreen forest based on simulated distribution (Figure 4). This suggests that a local forest change from a deciduous-dominated forest to an evergreen-dominated forest may have been triggered by temperature change up to threshold. Note also that

Forests 2021, 12, 1314 8 10 mean annual temperature (MAT) from 13 to 16 C at about 8 ka BP. The temperature at about 16 C corresponds to most appropriate MAT range (14.5 18.5 C) for present evergreen forest based on simulated distribution (Figure 4). This suggests that a local forest change from a deciduous-dominated forest to an evergreen-dominated forest may have been triggered by temperature change up to threshold. Note also that subsequent climate fluctuations after 8 ka BP to threshold MAT value about 14.5 C (e.g., at 3.2 ka BP) repeatedly caused a switch between evergreen/deciduous biomes. This furr supports significant role temperature threshold in biome turnover. The vegetation changes in studied pollen record are closely related to output TRACE21 climate model [18], e.g., trends in mean winter temperature (Twin) and seasonal temperature difference between July and January (STdif) from last deglaciation to Holocene (Figure 5). The modeled winter temperature in subtropical climate zone shows a gradual change from 2 to 5 C in early Holocene at 11.5 8.1 ka BP (more abrupt since 9 ka BP). Similarly, re was a gradual decrease in seasonal temperature difference at 11.5 8.1 ka BP from 24.5 to less than 23 C (Figure 5). Note that se values were corrected to altitude SZY record based on local average elevation lapse rate. These values at 8.1 ka BP agree very well with present-day range most suitable temperature for evergreen trees (Twin: 5.5 10.5 C, STdif: 14 23.5 C). They are also in broad agreement with meteorological data delineating modern evergreen broadleaved forest in subtropical mountains [24,25]. Therefore, re is no doubt that evergreen trees became dominant in forest when winter and seasonal rmal conditions reached ir thresholds. After YD at 11.5 ka BP, progressive winter warming and decreasing seasonality led to an increase in evergreen broadleaved elements in local forest, and subsequent onset Holocene optimum at ~8.1 ka BP forced general forest turnover. According to our record, we suggest that forest change from deciduous to evergreen composition was initiated after YD in subtropical region. The greatest extent EBLF in our study area corresponds to Holocene optimum, which begins at ~8 ka BP and shows a close relationship with increase in winter temperature and decrease in seasonal temperature difference to thresholds. Our data are consistent with winter climate dynamics influencing strength Asian summer monsoon [29]. This study provides an improved understanding ecologically sensitive region at interface between warm temperate and tropical bioclimatic zones. Ice sheet melting exerts an important influence on low latitude climate through associated changes in global sea level [30], and sea surface temperature Indo-Pacific warm pools shows a progressive warming since beginning Holocene [31]. The observed amplitude subtropical ecosystem changes during global climate warming over last postglacial period draws our attention to period when one extended biome with new species replaced anor. The biome turnover we identified occurred over a time span comparable to few decades ongoing global climate change. Thus, ongoing climate change will likely have a significant effect on ecosystems, especially upland species [32], although impact is expected to be less significant in upland areas than in lowland areas [33]. Many endemic species, e.g., Fagus, Cryptomeria, Tsuga, Pseudotsuga, Quercus, in subtropical Asia are near threatened, vulnerable, endangered or even critically endangered according to IUCN Red List [34]. These species are all fragmented and scattered within evergreen biome. Ongoing warming is likely to lead to ir extinction, resulting in a depletion biodiversity in Asian ecosystems, which deserve establishment new national parks and biosphere reserves. 6. Conclusions This study shows that both ecosystem composition and ir range have undergone major changes since last ice age, especially in last thousand years. The observed biome transformation in our study site appears to have taken place within a time span comparable to that ongoing climate warming, providing important knowledge to better

Forests 2021, 12, 1314 9 10 References understand ecosystem transformations and manage ir future changes. Many endemic evergreen tree species are now threatened with extinction, which also raises many questions regarding managing diversity in subtropical ecosystems. Supplementary Materials: The following are available online at https://www.mdpi.com/article/10.3390/f12101314/s1, Figure S1: The distribution presence points extracted from digitalized EBLF distribution used for predicting modern distribution EBLF, Table S1: Estimates relative contributions environmental variables to Maxent model. Author Contributions: Conceptualization, Q.W., X.Z. and Z.Z.; methodology, Q.W., X.Z., Y.Z., K.H. and Z.Z.; writing original draft preparation, Q.W., X.Z. and Z.Z.; writing review and editing, Q.W., X.Z., Y.Z., Y.Y., K.H., R.C. and Z.Z. All authors have read and agreed to published version manuscript. Funding: This research was funded by National Natural Science Foundation China (Grant Nos. 42072205, 41472143, 41902186, 42077414, 41630753, 41472143, 41661144003 and 41702182), Innovation Group Project Sourn Marine Science and Engineering Guangdong Laboratory (Zhuhai) (Grant No. 311020002), Project influence Quaternary glacial cycle on biodiversity in Nanling Mountains (Grant No. 2021GJGY001) and Guangxi scientific projects (No. 2018GXNSFAA281293). Data Availability Statement: Data is contained within article or supplementary material. Conflicts Interest: The authors declare no conflict interest. 1. Song, Y.-C.; Chen, X.-Y.; Wang, X.-H. Studies on evergreen broad-leaved forests china: A retrospect and prospect. J. East China Norm. Univ. 2005, 1, 1 8. 2. Wu, Z.Y. Vegetation China; Science Press: Beijing, China, 1980. 3. Fang, J.Y.; Wang, Z.H.; Tang, Z.Y. Atlas Woody Plants in China: Distribution and Climate; Higher Education Press: Beijing, China, 2011. 4. Lee, C.-Y.; Liew, P.-M. Late quaternary vegetation and climate changes inferred from a pollen record Dongyuan Lake in sourn Taiwan. Palaeogeogr. Palaeoclimatol. Palaeoecol. 2010, 287, 58 66. [CrossRef] 5. Yue, Y.; Zheng, Z.; Huang, K.; Chevalier, M.; Chase, B.M.; Carré, M.; Ledru, M.-P.; Cheddadi, R. A continuous record vegetation and climate change over past 50,000 years in Fujian province eastern subtropical China. Palaeogeogr. Palaeoclimatol. Palaeoecol. 2012, 365, 115 123. [CrossRef] 6. Ni, J.; Yu, G.; Harrison, S.P.; Prentice, I.C. Palaeovegetation in China during late quaternary: Biome reconstructions based on a global scheme plant functional types. Palaeogeogr. Palaeoclimatol. Palaeoecol. 2010, 289, 44 61. [CrossRef] 7. Yu, G.; Chen, X.; Ni, J.; Cheddadi, R.; Guiot, J.; Han, H.; Harrison, S.P.; Huang, C.; Ke, M.; Kong, Z.; et al. Palaeovegetation china a pollen data-based synsis for mid-holocene and last glacial maximum. J. Biogeogr. 2000, 27, 635 664. [CrossRef] 8. Zheng, Z.; Yuan, B.; Nicole, P.-M. Paleoenvironments in China during last glacial maximum and holocene optimum. Episodes 1998, 21, 152 158. 9. Ni, J.; Cao, X.; Jeltsch, F.; Herzschuh, U. Biome distribution over last 22,000yr in China. Palaeogeogr. Palaeoclimatol. Palaeoecol. 2014, 409, 33 47. [CrossRef] 10. Wang, X.; Yao, Y.-F.; Wortley, A.H.; Qiao, H.-J.; Blackmore, S.; Wang, Y.-F.; Li, C.-S. Vegetation responses to warming at younger dryas-holocene transition in hengduan mountains, southwestern china. Quat. Sci. Rev. 2018, 192, 236 248. [CrossRef] 11. Zhou, X.; Sun, L.; Zhan, T.; Huang, W.; Zhou, X.; Hao, Q.; Wang, Y.; He, X.; Zhao, C.; Zhang, J.; et al. Time-transgressive onset Holocene Optimum in East Asian monsoon region. Earth Planet. Sci. Lett. 2016, 456, 39 46. [CrossRef] 12. Liu, Z.; Zhu, J.; Rosenthal, Y.; Zhang, X.; Otto-Bliesner, B.L.; Timmermann, A.; Smith, R.S.; Lohmann, G.; Zheng, W.; Elison Timm, O. The holocene temperature conundrum. Proc. Natl. Acad. Sci. USA 2014, 111, E3501 E3505. [CrossRef] 13. Cheng, Y.; Liu, H.; Wang, H.; Hao, Q. Differentiated climate-driven Holocene biome migration in western and eastern China as mediated by topography. Earth-Sci. Rev. 2018, 182, 174 185. [CrossRef] 14. Faegri, K.; Iversen, J. Textbook Pollen Analysis; Wiley: New York, NY, USA, 1989. 15. Nakagawa, T. A trial density pollen fractionation from sediment core samples for purpose pollen ams dating: Evaluation and perspectives. Summ. Res. Using AMS Nagoya Univ. 1998, 9, 244 252. 16. Phillips, S.J.; Anderson, R.P.; Schapire, R.E. Maximum entropy modeling species geographic distributions. Ecol. Model. 2006, 190, 231 259. [CrossRef] 17. Hijmans, R.J.; Cameron, S.E.; Parra, J.L.; Jones, P.G.; Jarvis, A. Very high resolution interpolated climate surfaces for global land areas. Int. J. Climatol. 2005, 25, 1965 1978. [CrossRef]

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