The seedling stage is generally the most important bottleneck for the successful regeneration of trees in forests. The traits of seedlings, particularly biomass allocation and root traits, are more easily quantified than the traits of adults. In this study, we tested the hypothesis that seedling traits vary and trade‐off tracking the changing environment during secondary succession. We measured the major morphological traits of 27 dominant species and the major environmental factors in a chronosequence (30‐yr‐old fallow, 60‐yr‐old fallow, and old growth forest) after shifting cultivation in a tropical lowland rain forest on Hainan Island, China. The 30‐yr‐old fallow had higher light and nutrient availability, and the older forests had higher soil water content. Redundancy analysis based on species abundance and environmental factors revealed groups of seedlings that dominate in different stages of succession. Seedlings in different stages of succession had different strategies of biomass allocation for harvesting resources that varied in availability. Species characteristic of younger forest had higher allocation to roots and higher specific leaf area, while species characteristic of older forest had higher allocation to leaves. Our study suggests that the variations and trade‐offs in the major functional traits of tree seedlings among successional classes may reflect changes in environmental conditions during succession.

Abstract Tree species were assembled into forest communities by various processes, and it was found that trees are spatially arranged in a community by the abiotic and biotic conditions within that community. Here, we explore the abiotic processes and biotic interactions in the spatial patterning of tree species across six old‐growth forest types in a tropical nature reserve. Four spatial point process models (the homogeneous Poisson process, inhomogeneous Poisson process, homogeneous Thomas process, and inhomogeneous Thomas process) were used to evaluate the potential contribution of the random processes, habitat heterogeneity, dispersal limitation, and the joint effects of dispersal and habitat heterogeneity to the formation of the spatial patterns of tree species. A combination of the null model and size–distance regression analysis was applied to assess the effect of competition and facilitation on the tree species assembly. We found that the homogeneous and inhomogeneous Thomas processes were the best models for describing the spatial patterns of more than 85% tree species across the six tropical forests. The combination of the null model and size–distance regression analysis showed that 37–44% of tree species were affected by competition and 9–24% of tree species were affected by facilitation across the six tropical forest types. Competition was the dominant form of species interactions in forests with mild abiotic conditions such as the tropical montane rain forest and tropical lowland rain forest. Meanwhile, facilitation was the most important biotic interaction in the abiotically harsh tropical montane dwarf forest on mountaintops. Our study suggests that dispersal limitation and the joint effects of dispersal and habitat heterogeneity were the dominant abiotic processes in controlling the spatial patterning of trees in tropical forests. Moreover, the relative importance of competition and facilitation in the assembly of the tree species varied among the forest types with different abiotic conditions.

Exploring the associations between vegetation and abiotic environments might increase our understanding of biodiversity formation mechanisms. Here, we explore variation in plant composition/diversity and their abiotic determinants across six vegetation types in a biodiversity hotspot of Hainan Island, China.

Species-abundance distribution (SAD) is an essential tool to explain the mechanism of diversity maintenance in ecological communities. Most of the studies on diversity maintenance in a specific forest dynamics plot just consider stems with a certain minimum size class to include into the tree community to be examined. However, the species in the juvenile stage are easily disturbed by a variety of factors; here, we define the minimum stem size to tag trees in a community as the community size (DBHmintag), which implies that the communities with different minimum diameter at breast height (DBH) sizes to tag trees are tree assemblages containing tree populations of different minimum DBH. We used data from 17 1-ha forest dynamics plots across six old-growth forest types in a tropical nature reserve to explore diversity maintenance mechanism by SAD curves (at three levels of DBHmintag) fitting to neutral model and niche preemption model. We found that the SADs of the two zonal vegetation types (tropical montane rain forest and tropical lowland rain forest) were best fitted by neutral model at each level of DBHmintag; meanwhile, the best fitted models for the four azonal vegetation types (tropical coniferous forest, tropical deciduous monsoon rain forest, tropical montane evergreen forest, and tropical montane dwarf forest) varied with DBHmintag levels, for communities with DBHmintag >= 1 cm and DBHmintag >= 5 cm, the fitting effect of neutral model was better than niche preemption model's for the forest dynamics plots in the four azonal vegetation types, and for communities with DBHmintag >= 10 cm, the four azonal vegetation types were all best fitted by the niche model. Our results suggest that species diversity maintenance mechanisms of the two zonal vegetation types derived from the neutral model increased the predictive accuracy at each level of DBHmintag, and meanwhile, the four azonal vegetation types derived from the neutral model increased the predictive accuracy at smaller community size; however, with the increase in DBHmintag, these communities derived from the niche theory model increased the predictive accuracy. Habitat heterogeneity might be the major constraints in determining the neutral or niche process for diversity maintenance of a specific forest community.

Patterns of co-occurrence of species are increasingly used to examine the contribution of biotic interactions to community assembly. We assessed patterns of co-occurrence at four scales, in two types of tropical cloud forests in Hainan Island, China (tropical montane evergreen forests, TMEF and tropical dwarf forests, TDF) that varied significantly in soil nutrients and temperature. We tested if the patterns of co-occurrence changed when we sorted species into classes by abundance and diameter at breast height (dbh). Co-occurrence differed by forest type and with plot size, with significant species aggregation observed across larger plots in TDF and patterns of species segregation observed in smaller plots in TMEF. Analyses of differential abundance and dbh classes also showed that smaller plots in TMEF tend to have negative co-occurrence patterns, but larger plots in TDF tend to show patterns of aggregation, suggesting competitive and facilitative interactions. This underscores the scale-dependence of the processes contributing to community assembly. Furthermore, it is consistent with predictions of the stress gradient hypothesis that facilitation will be most important in biological systems subject to abiotic stress, while competition will be more important in less abiotically stressful habitats. Our results clearly demonstrate that these two types of tropical cloud forest exhibit different co-occurrence patterns, and that these patterns are scale-dependent, though independent of plant abundance and size class.

Variations in community-level plant functional traits might indicate the adaptation strategies of vegetations under changing environment. Here, we assess the key factors in controlling functional community compositions across different forest types.

QuestionWe tested whether co-existing tree species in tropical dwarf forests were deterministically assembled along gradients of air temperature, relative humidity and light availability, according to two important functional traits, specific leaf area (SLA) and maximum species height (H-max).LocationTropical montane cloud forest, Bawangling Nature Reserve, Hainan Island, south China.MethodsNull model analyses were used in conjunction with trait and species composition data collected to test our hypotheses at four plot sizes (25m(2), 100m(2), 400m(2) and 900m(2)), addressing whether the consistent importance of variation in SLA and H-max extends to these unique forests, as well as theoretical predictions concerning how patterns change with plot size.ResultsLow SLA species were significantly over-represented within forest communities for the two largest plot sizes, and taller-growing tree species were over-represented across all four plot sizes. Plot-level analyses indicated that low SLA species were associated with lower temperatures.ConclusionsOur results show that tropical dwarf forests are deterministically assembled with respect to these two traits, and are consistent with other studies indicating that SLA responds to abiotic filters. Co-existing tree species were not significantly divergent for these two traits, indicating that variation in these two traits among trees does not contribute to niche differences (i.e. limiting similarity) and therefore co-existence within forest plots. Finally, our study demonstrates that patterns of community assembly change with plot size; however, trait convergence did not increase with plot size as previously predicted.

The seedling stage is generally the most important bottleneck for the successful regeneration of trees in forests. The traits of seedlings, particularly biomass allocation and root traits, are more easily quantified than the traits of adults. In this study, we tested the hypothesis that seedling traits vary and trade-off tracking the changing environment during secondary succession. We measured the major morphological traits of 27 dominant species and the major environmental factors in a chronosequence (30-yr-old fallow, 60-yr-old fallow, and old growth forest) after shifting cultivation in a tropical lowland rain forest on Hainan Island, China. The 30-yr-old fallow had higher light and nutrient availability, and the older forests had higher soil water content. Redundancy analysis based on species abundance and environmental factors revealed groups of seedlings that dominate in different stages of succession. Seedlings in different stages of succession had different strategies of biomass allocation for harvesting resources that varied in availability. Species characteristic of younger forest had higher allocation to roots and higher specific leaf area, while species characteristic of older forest had higher allocation to leaves. Our study suggests that the variations and trade-offs in the major functional traits of tree seedlings among successional classes may reflect changes in environmental conditions during succession.

Aims Understanding processes underlying spatial distribution of tree species is fundamental to the study of spe-cies coexistence and diversity.Our objective was to determine the spatial structure and identify the processes that may generate spatial patterns of trees in a tropical lowland rain forest community on Hainan Island of South China.Methods Based on four models of point pattern analysis (homogenous Poisson process,inhomogenous Poisson process,homogenous Thomas process and inhomogenous Thomas process),we evaluated the potential contribu-tion of habitat heterogeneity and dispersal limitation to the formation of spatial patterns of tree species in two 1-hm2 stem-mapped forest dynamic plots.The relative importance of each process was assessed at six different spatial scales ( 2 m,2-5 m,5-10 m,10-15 m,15-20 m and 20-25 m).Important findings All stems combined revealed a strong aggregation at short distance (≤2 m),and the degree of aggregation decreased with increasing distance.Among the four models simulating tree distribution and pat-terning,the homogeneous Thomas process was the best-fit model.This result suggested that spatial patterns of tree species in tropical lowland rain forest might be formed by dispersal limitation.The homogeneous Poisson process that models the effect of spatial complete randomness was the second-best model.The inhomogeneous Thomas process and inhomogeneous Poisson process were equally important to forming spatial patterns of trees;they simulated the joint effects of habitat associations and dispersal limitation and modeled heterogeneity,respec-tively.The proportion of best-fit models differed across different scales.The dispersal limitation was a most im-portant mechanism in spatial patterning of tree species at most scales,while complete randomness process was second in importance.The joint effects of habitat associations and dispersal limitation mainly influenced tree dis-tribution at small scales (0-5 m).However,habitat heterogeneity only affected the distribution at larger scales (15-25 m).

Competition and facilitation between tree individuals are two kinds of non-random processes influencing the structure and functioning of forest communities, but how these two plant-plant interactions change along gradient of resources or environments remains very much a matter of debate. We developed a null model to test the size-distance regression, and assessed the effects of competition and facilitation (including interspecific interactions, intraspecific interactions and overall species interactions) on each adult tree species assemblage [diameter at breast height (dbh) ≥5 cm] across two types of tropical cloud forest with different environmental and resource regimes. The null model test revealed that 17% to 27% tree species had positive dbh-distance correlations while 11% to 19% tree species showed negative dbh-distance correlations within these two forest types, indicating that both competition and facilitation processes existed during the community assembly. The importance of competition for heterospecific species, and the intensity of competition for both heterospecific and overall species increased from high to low resources for all the shared species spanning the two forests. The importance of facilitation for conspecific and overall species, as well as that the intensity of facilitation for both heterospecific and conspecific species increased with increasing low air temperature stress for all the shared species spanning the two forests. Our results show that both competition and facilitation processes simultaneously affect parts of species assemblage in the tropical cloud forests. Moreover, the fact that nearly 50% species assemblage is not detected with our approaches suggest that tree species in these tropical forest systems are assembled with multiple ecological processes, and that there is a need to explore the processes other than the two biotic interactions in further researches.

Aims A major challenge in studies of tropical forest successional dynamics is to reveal the relative importance of deterministic versus stochastic processes affecting species composition, spatial distributions and their rates of change. Here, we tested succession trajectory of tropical secondary forests follow equilibrium or non-equilibrium dynamics by evaluating community reassembly for tropical lowland rainforest recovery on the abandoned shifting cultivation lands on Hainan Island of south China. Methods We explored species composition and dominance of different size classes (seedlings, saplings and adult trees) of communities along a chronosequence of secondary forest plots ranging from 15 to 60 years since abandonment after shifting cultivation. We included two old-growth forest plots for comparison. Important findings Both species diversity for the three size classes and the species similarity index among size classes in old-growth forests were significantly higher than in secondary forests. However, the proportion of dominant species in old-growth community was lower than that of secondary forests. Species similarity between secondary forests and old-growth forests increased with forest recovery, supporting the view of equilibrium succession dynamics. In each recovery stage, the number of individuals, species richness and abundance-based coverage estimator of seedlings were lower than those of both saplings and adult trees. Moreover, the species composition of seedlings in secondary forests differed significantly from that of both saplings and adult trees, suggesting that seedling recruitment might be an unpredictable process. Our results highlighted that the community assembly processes during secondary forest recovery are driven simultaneously by stochastic and deterministic processes.

With TWINSPAN classification and DCA ordination,the secondary forests of Zhayun Twonship in the interior mountainous area of Hainan were classified into 7 community types,including Form.Cyclobalanopsis kerrii+Albiza odoratissima+Diospyros strigosa,Form.Liquidambar formosana+Garcinia oblongifolia+Litsea variabilis,Form.Cratoxylum cochinchinense+Psychotria rubra+Vatica mangachapoi,Form.Schefflera octophylla+Schima saperba+Lithocarpus fenestratus,Form.Neolitsea oblongifolia+Cyclobalanopsis insularis,Form.Castanopsis fissa,Form.Xanthophyllum hainanense+Dasymaschalon trichophorum+Radermachera frondosa.The first axis of DCA expressed the formations' spatial distribution and the gradient of temperature,while the second one depicted unconspicuous environmental information.

An investigation was taken on wild medical plants resources in Nangeng and Chaoba village which are Li minority in Baoting county,Hainan province.The investigation shows that there are 225 species(186families,83 genera) of vascular plant,including 6 species(6 families,6 genera) of fern,2 species(2 families,2 genera) of gymnosperm and 217 species(75 families,178 genera) of angiosperm.It contains 13 species of Hainan endemic species(Cycas hainanensis C.J.Chen、Cyclea hainanensis Merr.、Stephania hainanensis H.S.Lo et Y.Tsoong.、Firmiana hainanensis Kosterm.、Nephelium topengii(Merr.)H.S.、Dalbergia odorifera T.Chen etc.),7 species of national protected plants(Cyathea podophylla(Hook.) Cop.、Euphoria longan(Lour.)Steud.、L.chinensis Sonn.var.cuspontanea Hsue etc.),5 species of protective plants in Hainan province(Cratoxylon ligustrinum(Spach.)Bl.,Amesiodendron chinense(Merr.)Hu,Euphoria longan(Lour.)Steud.,Litchi chinensis Sonn.,Nephelium topengii(Merr.)H.S.etc.) and 15 species of folk medicines which are not recorded in documents or were not further studied before(Casearia membranacea Hance,Mukia javanica(Miq.) C.Jeffrey,Trichosanthes bracteata Voigt etc.).After analyzed the families and genera's characteristics of the medicinal plants resources of Li minority in Baoting county,the results show that those medical plant resources distribution is more centralized in families(Papilionaceae,Euphorbiaceae,Compositae,Zingiberaceae,Verbenaceae,Rutaceae,Saplandaceae,Umbelliffrae and Rubiaceae etc.) but is comparatively scattered in genera(only 30 genera have 2 and more than 2 species in 186 genera).

Vegetation characteristics and ecological niche features of the feeded plants in habitats of Macaque in Huoling Nature Reserve were studied by quadrat sampling method and route survey method The results showed a total of 69 species were recorded in the plot with an area of 2 000 m2,of which 20 species,accounting for 29.0% of total species number and 31.24% of total important value,respectively,were feeded by the Macaca mulatta.There were only 8 plants or 11.59% of total species number when the ecological niche breadth was higher than 1,while other plants were 88.41% when the niche breadth was lower than 1.Among the feeding plants,there were only 2 plants when the niche breadth was higher than 1,while there were other 18 plant when a niche breadth was lower than 1.And there were 5 species pairs when the overlapping value was higher than 0.5.This study indicated that current habitats for macaque were mostly tropical secondary deciduous monsoon forests,which had a larger living space for macaque feeded plants.Some suggestions for the reserve construction were raised from the aspect of protecting the macaque.

Big and small structural picture and survival curve were chosen to research the population dynamics of Pinus latteri.With methods including diffusion coefficient,Lloyd's mean crowding,patchiness index and Morisita's index,the distribution pattern was studied.The space pattern was analysed with Greig-Smith method,population structure and distribution patteren of P.latteri in Bawangling National Nature Reserve,Hainan Island were studied.The results showed that the population structure of P.latteri was a relativly stable type,however,the seedlings and saplings were scarce.The survival curve trended to be the type Deevey Ⅰ.The survival rate of young seedlings was low when dbh was under 2.5cm,while it began to increase during the saplings period,and reached the highest in the medium-sized population.However,the survival rate started to decline in the mature period,and the mortality rate was highest during the aged period.The population pattern was crowding type as a whole,the population pattern scale was between 100 square meters and 400 square meters.

Objective To analyze the constituents of the essential oil from Horsfieldia hainanensis Merr.MethodsThe volatile oil was obtained by steam distillation.The chemical constituents were separated and identified by gas chromatography-mass spectrometry(GC-MS).The relative contents were determined by area normalization.ResultsThe extraction rate of Horsfieldia hainanensis Merr.leaves was 0.11%.11 compounds were separated and identified,which accounted for 100% of the essential oil of the skins.The main chemical components of the essential oil were 3,7,11-trimethyl-,1,6,10-Dodecatrien-3-ol(46.03%),(-)-Globulol)(8.39%),adipic acid,dioctyl ester(7.03%),Ledol(7.00%),Copaene(5.86%),etc.ConclusionThe essential oil of leaf of Horsfieldia hainanensis Merr.is studied for the first time.It has provided scientific foundation for exploitation and utilization of Horsfieldia hainanensis Merr.

在对海南岛南端与北端沿海低山丘陵植物区系进行实地调查的基础上,对两个地区植物物种组成进行了比较研究。结果显示两地物种组成既有相似性也有差异性:琼南有种子植物876种,隶属于112科484属,植物区系以热带成分为主,兼有一定的温带成分和中国特有成分,且海南特有成分较高,具有一定的过渡性;琼北有种子植物934种,隶属于141科580属,植物区系以热带分布类型为主,同时有一定的温带成分,海南特有成分较高;两地植物区系的共同点是:均具有种类丰富、地理成分多样、优势成分明显、热带性质较强等。

OBJECTIVETo analyze the constituents of the essential oil from the bark of Horsfieldia hainanensis.METHODSThe volatile oil was obtained by steam distillation. The chemical constituents were separated and identified by gas chromatography-mass spectrometry (GC-MS). The relative contents were determined by area normalization.RESULTSThe extraction rate of the bark of Horsfieldia hainanensis was 0.14%. 32 compounds were separated and identified, which accounted for 98.62% of the essential oil. The main chemical components of the essential oil were Copaene (25.55%), Naphthalene, 1,2,3,5,6,8a-hexahydro-4,7-dimethyl-1-(1-methylethyl)-(11.14%), Hexanedioic acid, bis(2-ethylhexyl) ester (8.09%) , 9-Octadecenoic acid (7.04%), etc.CONCLUSIONIt has provided scientific foundation for exploitation and utilization of Horsfieldia hainanensis.

Antiaris toxicaria,an endangered tree species grew mainly around the natural villages in Haikou Aera.Our objectives were to explore the effects of human activity on the quantitative characteristics and distribution pattern of A.toxicaria population.We placed 6 sample plots in Haikou and studied the quantitative characteristics and distribution pattern of A.toxicaria population including size structure,static life table,survival curve,distribution pattern and its dynamics.The results showed that: ①The seed bourgeon rate was high,seedling was abundant,the young tree lacked,the single was abundant at the middle age,the single lacked at the old age.The spindle-shaped size class structure indicated that the populations of A.toxicaria were declining;②The mortality of size classes Ⅱ and Ⅲ was negative,indicating a shortage of size class Ⅱ and Ⅲ individuals.The peaks of mortality at size classes Ⅵ was caused for approaching the species' longevity;③Although its' seed survival rate was relatively high,its young tree survival rate was low,its survival curve was close to Deevey Ⅲ type;but without the artifical disturbance effect in the young tree period,the survivorship curves of A.toxicaria populations generally follow Deevey Ⅰ Type.It assumed convexity.The habitat of the Haikou was suitable for the growth of A.toxicaria;④The spatial distribution pattern tended to be clumped,which was accordant to most rare plant community;the artificial disturbance and natural environment affected its disturbance pattern,which made the community turn into the random distribution from assemble distribution,and then developed to the assemble distribution.

After species data and environmetal information were obtained based on vegetation surveys in Li minority region in Qichai,Hainan Island,a classification and ordination were made with PC-ORD software.After referring to the classification principles of"Chinese Vegetation",reviewing related research data such as"Guangdong Vegetation",and artificially adjusting quantitative classification results,the vegetation classification system of Qichai region was established.It includes three vegetation type groups,eight vegetation types,two formation groups and six formations.The six formations are discribed as Form.Bombax ceiba+Lannea coromandelica+Terminalia nigrovenulosa,Form.Pinus latteri,Form.Imperata arundinacea,Form.L.coromandelica+Kleinhovia hospital+B.ceiba,Form.Dacrydium pierrei+Syzygium araiocladum+Cyclobalanopsis bambusaefolia and Form.Vatica mangavhapoi+Ameslodendron chinense+Ficus altissima+Koilodepas hainanensis.The first axis of NMDS ordination expresses the gradients of soil moisture,while the second one depicts the height change of elevation.Therefore,plot arrangements in the axes are fitted with their practical distributions in the fields.The vegetation formation,distribution and change in the region may be related to its special climatic conditions and unique human activities of Li minority.