The pollination system of the genus Paphiopedilum has long been considered a typical example of deceptive pollination without offering any reward. However, this study reports for the first time the distinct pollinium-feeding behavior of the pollinator insect of Paphiopedilum appletonianum, whichi challenging the previous inherent understanding regarding the pollination systems of Paphiopedilum species. Changes in plant pollination systems partly reflect the degree of plant evolution. P. appletonianum is the only Paphiopedilum species wild distributed on Hainan Island. Due to island isolation, there is a highly possibility that P. appletonianum has undergone evolution during environmental adaptation, which urgently requires further research for verification.

IntroductionRelic plants are crucial components of biodiversity. Studying the interspecific relationships and stability of endangered relic plants at various structural levels within communities helps to understand their survival status and provides a scientific foundation for conserving unique germplasm resources and biodiversity.MethodsThis study aims to address the following scientific questions: How does species composition across different distribution areas influence interspecific relationships? Which plant species impact the survival of Chunia bucklandioides populations in these areas? Are there differences in community stability at various structural levels? Based on survey data from the mountainous communities of Chunia bucklandioides in the Jianfengling and Di’anshan sections of Hainan Tropical Rainforest National Park, this study uses the variance ratio method (VR), test statistics (W), chi-squared test (χ2), AC connectivity coefficient, percentage co-occurrence (PC) test, and an improved stability analysis method developed by M. Godron to analyze interspecific relationships and community stability at different structural levels.ResultsThe results show that: (1) The communities inhabited by Chunia bucklandioides have rich species composition, and there are significant differences in community structure between the Jianfengling area and the Diaoluoshan area. (2) In both distribution regions, positive interspecific associations dominate among species in different forest layers of the Chunia bucklandioides communities, with strong interspecific association in the arbor layer and weak interspecific association in the shrub layer and herb layer. (3) Different structural layers of the Chunia bucklandioides communities in both the Jianfengling area and the Diaoluoshan area are in an unstable state. In terms of stability, the performance of the two distribution regions is as follows: Diaoluoshan area community > Jianfengling area community; the order is reversed among different forest layers—for the Jianfengling area: arbor layer > shrub layer > herb layer; for the Diaoluoshan area: herb layer > shrub layer > arbor layer. (4) Mature individuals of Chunia bucklandioides occupy an absolute dominant position in the community, while juvenile individuals are under highly competitive pressure, leading to restricted population regeneration. DiscussionThis research provides valuable insights into the interspecific relationships, community stability, and succession dynamics of endangered Chunia bucklandioides populations, offering key scientific knowledge for their conservation and practical guidance for ecosystem restoration in tropical rainforests.

Although mountain vertical vegetation belts are key in revealing the response to climate change and the maintenance mechanism of biodiversity, traditional field surveys and remote sensing methods face significant limitations in the structurally complex tropical humid mountainous regions of Hainan Island. As bryophytes are good microclimate indicators and characteristic components of the structure of the tropical rainforest, they may be useful tools for the construction of a general scheme of the altitudinal zonation of tropical rainforests. We surveyed bryophyte communities across eight elevations and three vegetation types at LiMu Mountain, southern China. Bryophyte species alpha diversity increased significantly as elevation increased, while beta diversity showed the contrasting pattern. Bryophyte community composition differed significantly along elevation gradients and the distribution of vegetation types was clearly distinguished by three significantly different bryophyte assemblages with specific elevational range. Hierarchical partitioning revealed that microclimate outweighed topography in structuring communities, aligning with global patterns of bryophyte thermal sensitivity. Bryophytes are effective bioindicators for tropical rainforest elevational zonation, reflecting fine-scale environmental gradients. Their sensitivity to microclimate supports their utility in monitoring vegetation shifts under climate change, particularly in topographically complex regions.

The endangered plant Hopea hainanensis serves as both an indicator and keystone species in tropical rainforests, and its survival status is influenced by the interspecific relationships among coexisting tree species within the community. To explore these relationships, species resource utilization patterns, and community succession dynamics within the endangered plant community, this study utilized survey data from the Hopea hainanensis community in the Bawangling and Jianfengling branches of the National Park of Hainan Tropical Rainforest. Various analytical methods were employed, including the Variance Ratio (VR) method, test statistic (W), χ2 test, Spearman’s rank correlation, and M. Godron’s stability analysis, to examine the interspecific associations among dominant tree species at different structural levels in the two regions and their effects on community stability. The results indicate that: (1) Hopea hainanensis is the dominant species in the medium tree layer in both study areas, while it functions as an associated species in other structural layers. (2) In communities where Hopea hainanensis is present in both Bawangling and Jianfengling, the dominant tree species across various structural layers generally show a non-significant positive association. (3) The results of the χ2 test and Spearman’s rank correlation test reveal that the interspecific associations across different structural layers of the Hopea hainanensis communities in both regions are predominantly non-significant. This suggests weak interspecific relationships and a high degree of species independence. The communities at different structural levels in both Bawangling and Jianfengling are in an unstable state, with ongoing dynamic adjustments to their internal tree species composition and structure. In terms of stability, the community stability across structural levels in these two regions follows the order: middle shrub layer > middle arbor layer > small arbor layer > large shrub layer. This study reveals the interspecific relationships, community succession status, and stability of dominant tree species at different structural levels in slope barrier communities across regions. These findings provide a theoretical basis for developing scientifically sound and reasonable protection strategies for slope barrier populations, as well as for the restoration and sustainable development of tropical rainforest vegetation.

This study developed an integrated approach for estimating tropical forest aboveground biomass (AGB) by combining UAV–LiDAR structural metrics and Sentinel-2B spectral data, optimized through successive projections algorithm (SPA) feature selection and random forest (RF) regression. Field surveys across three tropical forest sites in Hainan Province (49 plots) provided ground-truth AGB measurements, while UAV–LiDAR (1 m resolution) and Sentinel-2B (10 m) data were processed to extract 98 and 69 features, respectively. The results showed that LiDAR-derived elevation metrics (e.g., percentiles and kurtosis) correlated strongly with the AGB measurements (r = 0.652–0.751), outperforming Sentinel-2B vegetation indices (max r = 0.520). SPA–RF models with selected features significantly improved accuracy compared to full-feature RF, achieving R2 = 0.670 (LiDAR), 0.522 (Sentinel-2B), and 0.749 (coupled data), with the fusion model reducing errors by 46–54% in high-biomass areas. Despite Sentinel-2B’s spectral saturation limitations, its integration with LiDAR enhanced spatial heterogeneity representation, particularly in complex canopies. The 200-iteration randomized validation ensured a robust performance, with mean absolute relative errors of ≤0.071 for fused data. This study demonstrates that strategic multi-sensor fusion, coupled with SPA-optimized feature selection, significantly improves tropical AGB estimation accuracy, offering a scalable framework for carbon stock assessments in support of Reducing Emissions from Deforestation and Forest Degradation (REDD+) and climate mitigation initiatives.

Species and phylogenetic diversity play vital roles in sustaining the structure, function, and resilience of plant communities, particularly in tropical rainforests. However, the mechanisms according to which environmental filtering and competitive exclusion influence diversity across forest layers remain insufficiently understood. In this study, we investigated the species and phylogenetic diversity patterns in two representative tropical rainforest sites—Bawangling and Jianfengling—within Hainan Tropical Rainforest National Park, China, focusing on communities associated with the endangered species Hopea hainanensis. We employed a one-way ANOVA and Pearson’s correlation analyses to examine the distribution characteristics and interrelationships among diversity indices and used Mantel tests to assess the correlations with environmental variables. Our results revealed that the plant community in Jianfengling exhibited a significantly higher species richness at the family, genus, and species levels (a total of 288 plant species have been recorded, belonging to 82 families and 183 genera) compared to that in Bawangling (a total of 212 plant species, belonging to 75 families and 162 genera). H. hainanensis held the highest importance value in the middle tree layer across both sites (IV(BWL) = 12.44; IV(JFL) = 5.73), while dominant species varied notably among other forest layers, indicating strong habitat specificity. Diversity indices, including the Simpson index, the Shannon–Wiener index, and Pielou’s evenness, were significantly higher in the large shrub layer of Jianfengling, whereas Bawangling showed a relatively higher Shannon–Wiener index in the middle shrub layer. Phylogenetic diversity (PD) and the phylogenetic structure indices (NRI and NTI) displayed distinct vertical stratification patterns between sites. Furthermore, the PD in Bawangling’s large shrub layer was positively correlated with total phosphorus in the soil, while community evenness was influenced by soil organic carbon and total nitrogen. In Jianfengling, species richness was significantly associated with soil bulk density, altitude, and pH. These findings enhance our understanding of the ecological and evolutionary processes shaping biodiversity in tropical rainforests and highlight the importance of incorporating both species and phylogenetic metrics into the conservation strategies for endangered species such as Hopea hainanensis.

IntroductionEndangered plants are crucial for ecosystem stability, influencing forest community structure. However, commercial logging and the expansion of economic forests have led to tropical forest habitat degradation and fragmentation.MethodsTo assess the community structure and stability of Heritiera parvifolia, an endangered plant, in the Diaoluo Mountain zone of National Park of Hainan Tropical Rainforest in China, a field study was conducted across 20 plots. The analysis utilized species diversity indices, principal component analysis, ward clustering, linear regression, and one-factor analysis of variance.ResultsThe results showed high species richness in the community, with 78 families, 196 genera, and 302 species. Dominant families include Rubiaceae, Euphorbiaceae, and Lauraceae. The species richness, Shannon index, and Simpson index for the arbor and shrub layers were significantly higher than those of the herbaceous layer (P < 0.001), while the Pielou index was also higher (P < 0.01). Cluster analysis indicated that plots with less human disturbance (Group I) had greater stability than those with more disturbance (Group II). The stability index positively correlated with stand density, proportion of mature trees, average diameter at breast height and average tree height of dominant trees (P < 0.05), all of which were key factors in community stability. Stability was also significantly influenced by altitude and slope aspect, with significant differences observed between altitudes of 200–299 m and 400–499 m (P < 0.05), and between southeast slopes and other aspects (P < 0.05).DiscussionThis study highlights the factors affecting the stability of H. parvifolia communities, providing insights for conservation, biodiversity protection, and rainforest restoration.

Based on the List of National Key Protected Wild Plants and related data in 2021,combined with field investigation,the List of National Key Protected Wild Plants in Hainan Province was integrated,and its composition and floristic characteristics were analyzed.The results were as follows:(1)Among the national key protected wild plants,the original Cycas changjiangensis,C.hainanensis,C.lingshuigensis and C.taiwaniana were incorporated into C.taiwaniana;compared with the List of National Key Protected Wild Plants in 1999,the original Semiliquidambar cathayensis and Amphicarpaea linearis were removed from the protection level,and Bretschneidera sinensis was degraded from Category I protection to the Category Ⅱ protection.A total of 127 species of national key protected wild plants were added,and a total of 173 species(including varieties)with the addition of original,belonging to 53 families and 83 genera,including 8 species of national Category I protected wild plants.There were 165 species of national Category Ⅱprotected wild plants and 32 endemic species in Hainan Province,which belonged to four groups.Among them,the angiosperm species were the most abundant,with 129 species.(2)Based on years of field investigation information and the results of this survey,C.rumphii,C.shanyagensis,Alsophila costularis and Paphiopedilum purpuratum had not been investigated.(3)The life forms of 173 protected plants were divided into five types,mainly phanerophytes(115 species),followed by hemicryptophytes(34 species)and geocryptophytes(22 species),and chamaephytes and cushion plant were the least(1 species).(4)At the family level,Orchidaceae had the largest number of species,including 47 species(27.17％).At the genus level,Dendrobium had the largest number of species,including 21 species(12.14％).(5)The floristic elements were complex and had obvious tropical characteristics.The families were mainly distributed in the pantropics and its variants.The genera were mainly distributed in tropical Asia and its variants.In summary,the tropical nature and unique phenomena of national key protected wild plants in Hainan Province are obvious,and there are many new protected species.Therefore,background investigation and dynamic monitoring should be carried out continuously,law enforcement should be strengthened,human factors of interference and destroy should be reduced,and in-situ and ex-situ protection measures should be taken to strengthen protection and management.

Due to the intensive use of land and global warming, the response of species within the plant community to environmental changes and the developmental trend of the community have attracted global attention. Affected by human disturbance and rising sea levels, mangrove forests are undergoing a significant reduction in plant density. Due to unfavorable factors such as increased salinity and prolonged flooding time accompanying rising sea levels, it is difficult to predict how the growth and physiological processes of different mangrove individuals will respond to these factors and what impact these responses will bring to the development of mangrove plant communities. In this study, we simulated rising sea levels by controlling light intensity, seawater salinity, and flooding time, and studied the physiological and ecological response mechanisms of six representative mangrove species on Hainan Island, China, to rising sea levels with the goal to predict the development of mangrove plant communities in this region. The results showed that tree species distributed at high tidal levels were more susceptible to rising sea levels than those growing at medium and low tidal levels. Due to the rise in sea level, increasing flooding time, and high salinity stress, mangroves would naturally migrate inland. However, due to human disturbance that resulted in shoreline hardening, the mangrove retreat space is inadequate as their distribution area gradually becomes smaller and disappears. If measures are not taken to restore the natural environment of the offshore coast and allow mangroves to advance and retreat freely, global warming and rising sea levels will affect in particular the mangrove species growing at high tidal levels, such as Excoecaria agallocha, Lumnitzera littorea, Lumnitzera racemosa, Bruguiera sexangula, and Ceriops tagal.

Hainan island in south China harbours vast areas of virgin forests, with rich biodiversity and is included in the globally important Indo-Burma biodiversity hotspot. In 2018, a national park covering an area of 4269 km 2 of the island was proposed to conserve its rainforest ecosystem integrity and authenticity. In this study, using an integrated valuation of ecosystem services and tradeoffs (InVEST) model, a revised universal soil loss equation (RUSLE), a net primary productivity transformation formula, and the maximum entropy (MaxEnt) model, we quantified five ecosystem services, i.e. water conservation, soil retention, carbon storage, oxygen release and biodiversity maintenance. The data of five ecosystem services was recorded in the year 2000, 2010 and 2019, for seven regions of the national park including Mt. Jianfeng (JFL), Mt. Bawang (BWL), Mt. Diaoluo (DLS), Mt. Limu (LMS), Mt. Yingge (YGL), Mt. Wuzhi (WZS), and Maorui Forest Farm (MR). Then, we determined the importance of each of the ecosystem services for each region. Finally, we determined conservation priority sites of every regions respectively for each ecosystem service by comparing conservation efficiencies with the help of ordered weighted averaging. We found that total and mean amounts of five ecosystem services in the national park had declined in 2010 but increased in 2019, indicating the establishment of the national park effectively improved ecosystem services. Over 65 % areas of the national park exhibited dominant ecosystem services of water conservation, carbon storage and oxygen release. Soil retention was relatively uniform in seven regions, whereas the water conservation was concentrated in the eastern part of the national park, i.e. YGL, LMS, WZS and DLS. Carbon storage and oxygen release were highest at the central part of the national park including WZS, DLS, YGL, BWL, and MR, while biodiversity maintenance was the top ecosystem service for WZS, DLS, BWL and MR. Conservation priorities were assigned to natural forests in high -altitude areas in WZS, DLS, YGL, BWL, and MR, mostly in central parts of the national park. These results revealed the spatiotemporal pattern of ecosystem services and conservation priorities. It is helpful to facilitate precise management of this newly established national park. The innovative approach identifies key ecosystem services and their trade-offs to pinpoint conservation areas, offering valuable insights for the management of other national parks and protected areas.

Revealing the impact of forest succession processes on changes in plant diversity is crucial for understanding the mechanisms that maintain plant diversity across various succession stages. While previous research has predominantly focused on the influence of environmental factors or management strategies on plant diversity within rubber plantation understories, there is a scarcity of studies examining the effects of forest succession processes on plant diversity. This study focuses on the plant diversity of the understory herbaceous layer within the rubber forest of the Yinggeling area, located in National Park of Hainan Tropical Rainforest. It employs a spatial analysis approach, rather than a temporal one, to examine the characteristics of the understory herbaceous community. The findings revealed that (1) The understory of Yinggeling rubber plantations harbors 175 plant species from 149 genera and 75 families, with Gramineae and Rubiaceae representing 46.45% of total species. And the dominant families are Rubiaceae, Gramineae, and Moraceae, with Ficus and Pteris being the dominant genera. (2) The dominant species vary with succession duration, with Tetrastigma pachyphyllum dominating in 0-year succession, Paspalum conjugatum in 3-year succession, and Microstegium fasciculatum in 7-year succession. (3) Diversity indices such as the Shannon-Wiener index, Simpson index, and Pielou index peak at 7 years of natural succession, while the species richness is highest at 3 years. (4) The similarity coefficient between understory herbaceous plant communities in rubber plantations undergoing 0 and 3 years of natural succession is highest 0.56, indicating a significant similarity, while similarity is lowest between 0 and 7 years of succession. This research shows that natural restoration helps increase species diversity in the understory herb layer of rubber forests. Succession leads to changes in the dominant families, genera, and species of the herbaceous layer. This change can be attributed to the intraspecific competition and ecological competition that occur during the succession process, leading to changes in biological and resource allocation.

Aim: We test the hypothesis that wind dispersal is more common among emergent tree species given that being tall increases the likelihood of effective seed dispersal. Location: Americas, Africa and the Asia-Pacific. Time period: 1970-2020. Major taxa studied: Gymnosperms and Angiosperms. Methods: We used a dataset consisting of tree inventories from 2821 plots across three biogeographic regions (Americas, Africa and Asia- Pacific), including dry and wet forests, to determine the maximum height and dispersal strategy of 5314 tree species. A web search was used to determine whether species were wind-dispersed. We compared differences in tree species maximum height between biogeographic regions and examined the relationship between species maximum height and wind dispersal using logistic regression. We also tested whether emergent tree species, that is species with at least one individual taller than the 95% height percentile in one or more plots, were disproportionally wind dispersed in dry and wet forests within each biogeographic region. Results: Our dataset provides maximum height values for 5314 tree species, of which more than half (2914) had no record of this trait in existing global databases. We found that, on average, tree species in the Americas have lower maximum heights compared to those in Africa and the Asia Pacific. The probability of wind dispersal increased significantly with tree species maximum height and was significantly higher among emergent than non-emergent tree species in both dry and wet forests in all three biogeographic regions. Main conclusion: Wind dispersal is more prevalent in tall, emergent tree species than in non-emergent species and may thus be an important factor in the evolution of tree species maximum height. By providing the most comprehensive dataset so far of tree species maximum height and wind dispersal strategies, this study paves the way for advancing our understanding of the eco-evolutionary drivers of tree size.

In order to reveal the distribution and habitat characteristics of national key protected wild plants in Hainan Province,we studied the distribution characteristics and vegetation types of national key protected wild plants in Hainan Province by selecting national key protected wild plants,based on the 2021 edition of List of National Key Protected Wild Plants through the methods such as data reduction and field surveys.The results were as follows:(1)There were a total of 53 families,83 genera and 173 species of national key protected wild plants in Hainan Province,ranking fifth in the number of species and first in the density of species in China(based on the current data base of wild).(2)All 19 counties and municipalities in Hainan Province had national key protected wild plants,and the number of species in the central and the south of the cities/counties was much larger than that in the north,with the largest species richness in Changjiang Li Autonomous County(75 species),and the highest species density in Lingshui Li Autonomous County(0.604 5 ind.·km-2);the number of species of national key protected wild plants was distributed in nine gradients(with a gradient value of 200 m)from 0 m to 1 867 m above sea level,and there were a trend of slightly decreased-very rapidly increased-slowly decreased,with the highest number of species distributed in the elevation band.When 800 m ≤Altitude＜1 000 m and 1 000 m ≤ Altitude＜1 200 m,there was 81 national key protected wild plant species,while only 9 species in the segment 1 600 m ≤ Altitude＜1 867 m.(3)The habitats of national key protected wild plants in Hainan Province were complexed,relied on a total of 11 vegetation types,among which the lowland rainforest had the highest species richness(114 species),followed by mountain rainforest(105 species)and the semi-mangrove forest(1 species);and the most severely externally disturbed is freshwater wet grassland,followed by lowland rainforest,and the least is montane cloud forest.The results of the study provide the scientific reference for the conservation and utilization of national key protected wild plants in Hainan Province.

Aims:Mangroves are woody plant communities that thrive in the intertidal zone of tropical and subtropical gulf estuaries,enduring periodic inundation by seawater.Understanding how mangrove plants adapt to this challenging environment and achieve multi-species separation and coexistence has been a focal point of research.Niche theory serves as an important framework for studying species coexistence within communities,with seedlings playing a crucial role in population renewal.The study aimed to construct a miniature mangrove community by selecting six widely distributed species found on Hainan Island and simulating different intertidal environments through manipulation of seawater salinity,flooding time,and light intensity. Methods:The net photosynthetic rate of these six species'seedlings was measured under various controlled conditions,while statistical analysis was conducted to examine niche width,overlap,and offset among the seedlings across three resource dimensions:seawater salinity,flooding time,and light intensity.This endeavor seeked to elucidate the mechanisms underlying the separation and coexistence of mangrove plants within the intertidal zone. Results:The results indicated that in terms of flooded water resources,the Avicennia marina(0.956)was the larger niche width and Ceriops tagal(0.906)was the smallest among the 6 seedlings.The niche overlaps were higher in Avicennia marina,Aegiceras corniculatum and Rhizophora stylosa,while they were higher in Kandelia obovata,Bruguiera sexangula and Ceriops tagal.The degree of niche separation reflected that among the species with a theoretical niche center of 12 h/d,Avicennia marina(0.698)exhibited a wider range of adaptation to flooding;whereas among the species with a theoretical niche center of 8 h/d,Kandelia obovata(0.185)showed a broader range of adaptation to flooding;and among the species with a theoretical niche center of 4 h/d,Bruguiera sexangula(0.115)demonstrated extensive adaptability to flooding.In terms of salinity resources,the Avicennia marina(0.987)exhibited the widest niche width,while Kandelia obovata(0.496)had the smallest niche width.The niche overlaps were high among Avicennia marina,Aegiceras corniculatum and Rhizophora stylosa;similarly,Bruguiera sexangula and Ceriops tagal showed significant overlap,whereas Kandelia obovata and other species displayed low levels of overlap.The degree of niche separation indicated that Avicennia marina(4.357)had a broader range of salinity adaptation in species with a theoretical niche center of 20,whereas Ceriops tagal(10.594)demonstrated greater adaptability to varying salinity levels in species with a theoretical niche center of 10.In terms of light resources,Ceriops tagal(0.995)had the widest niche width,while Avicennia marina(0.828)had the smallest niche width.The mangrove species exhibited higher levels of niche overlap.The degree of niche separation indicated that among species with a theoretical niche center of 100％light,Rhizophora stylosa(23.138)displayed a larger range of light adaptation,whereas among species with a theoretical niche center of 80％light,Ceriops tagal(12.522)showed a greater range of light adaptation. Conclusion:Combined with the niche analysis of flooding,salinity,and light resources,it is evident that the niche differentiation of each species in terms of flooding and salinity resources occurs relatively early and prominently.Each species occupies distinct ecological niches characterized by low overlap and weak competition for these resources,thereby achieving separation and coexistence in the intertidal zone.However,niche differentiation in light resources appears relatively delayed and inconspicuous.The majority of plants are sun plants exhibiting high niche overlap and strong competition for light.

Plantations left for natural succession play a significant role in Tropical Rainforest National Parks. Studying the succession and restoration of plantations is crucial for achieving a park’s authenticity and integrity, as well as for maximizing its ecological functions. However, the changes in vegetation and soil properties during the natural succession of these decommissioned plantations remain unclear. In this study, we examined rubber [(Hevea brasiliensis (Willd. Ex A. Juss.) Muell. Arg] plantations in the Yinggeling area of the National Park of Hainan Tropical Rainforest. We used community surveys, field sampling, and soil property analyses to investigate the species richness, diversity, and species composition of the aboveground plant communities during three succession periods of rubber plantations left for natural succession, including 0 years (ZY), 3 years (TY), and 7 years (SY). The soil pH, total organic carbon, total nitrogen, total phosphorus, available phosphorus, nitrate nitrogen, ammonium nitrogen, and total potassium contents in the three succession periods were analyzed. These results showed that there were 92 species of understory plants in the decommissioned rubber plantations, belonging to 72 genera in 39 families. The highest number of understory plant species was found in the plantations with 3 years of natural succession, totaling 66 species from 49 genera in 29 families. The number of families, genera, and species followed the pattern TY > SY > ZY. The Margalef richness index (F), Simpson index (D), and Shannon–Wiener index (H) of understory plants in the 0-year succession plantations were significantly lower than those in the 3-year and 7-year succession plantations. However, there was no significant difference in the Pielou (EH) index among the succession gradients. The soil pH, nitrate nitrogen (NO3--N), and available phosphorus (AP) in the 0-year succession plantations were significantly higher than those in the 3-year and 7-year succession plantations. There were no significant differences in soil total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), and ammonium nitrogen (NH4+-N) across the three succession gradients. The soil total potassium (TK) in the 3-year succession plantations was significantly higher than that in the 0-year and 7-year succession plantations. Soil available phosphorus and total phosphorus (TP) were positively correlated with the Margalef index, Simpson index, Shannon–Wiener index, and Pielou index. The recovery rate of understory vegetation in decommissioned rubber plantations was faster than that of the soil. This indicates that the construction of the National Park of Hainan Tropical Rainforest has significantly promoted the recovery of the number of plant species and plant species diversity that have been left from rubber plantation operations. These findings not only deepen our understanding of soil property changes during the vegetation succession of artificial forests, particularly rubber plantations, but they also hold significant implications for guiding tropical forest management and sustainable development.

The rubber tree is an economically important tree planted in many tropical countries. While rubber planting has improved the livelihoods of growers, it has also resulted in soil degradation. However, systematic studies on assessment of soil health and its management in rubber plantations are limited. The present study explored whether intercropping of Michelia macclurei (an ornamental evergreen tree) in rubber plantation could help conserve soil health compared to traditional monoculture practice with randomised complete block design. The rubber tree density was the same in monoculture and intercropping, with the addition of Michelia macclurei in intercropping. The effects of soil properties and microbial communities was used to analyse two different planting patterns of rubber monoculture and rubber intercropping using soil sampling from field plots. The study investigated variation in soil physical structure, soil moisture, soil nutrients, soil microbes, and enzyme activities in two types of rubber plantations viz. a monoclonal plantation without intercrop (RM) and a plantation with Michelia macclurei as an intercrop (RAS). The results from above study showed an increase in soil organic carbon (SOC), total nitrogen (TN), ammonium nitrogen (AN), available phosphorus (AP), nitrate nitrogen (NN) and total potassium (TK) in plantation with intercrop as compared to monoclonal plantation without intercrop. When comparing the corresponding values of RM to RAS, bacteria and total microbial abundance of RAS increased on average by 75.51

To investigate the differences in soil hydrolytic enzyme activity and enzyme stoichiometry among different mangrove communities, as well as the driving factors behind these variations, we will explore their implications for nutrient limitations of soil microbes and the availability of soil nutrients. This study will focus on the Rhizophora stylosa communities (RS), Aegiceras corniculatum communities (AC), and RS-AC mixed communities (MF) within the Hainan Xinying Bay mangrove conservation area, using adjacent bare flats (BF) as a control group. We will analyse soil enzyme activity and physicochemical properties in at soil depths of 0–20 cm and 20–40 cm across different mangrove communities to uncover the synergistic changes between these variables. The results indicate the following. (1) Except for acid phosphatase (ACP), the enzyme activities and their stoichiometric ratios in different mangrove soil communities differ significantly. In the layer of soil 0~20 cm, β-glucosidase (BG) activity is markedly diminished in the MF community relative to the other communities. Conversely, the activities of β-1,4-N-acetylglucosaminidase (NAG) and leucine aminopeptidase (LAP) are the most elevated in MF. In the 20~40 cm soil layer, the activity of cellulase (CBH) was found to be highest in the MF community, while the activities of BG and NAG in MF were significantly lower than those in other communities. Overall, the activity of the five enzymes decreased with increasing soil depth. (2) The ratios of ln (BG + CBH)/ln (NAG + LAP) and ln (BG + CBH)/ln (ACP) in different soil layers indicated that MF was significantly lower than other communities; in the 0~20 cm soil layer, the ln (NAG + LAP)/ln (ACP) ratio was highest in MF and lowest in RS, while no significant differences were observed between BF and AC. In the 20~40 cm soil layer, no significant differences in ln (NAG + LAP)/ln (ACP) ratios were found among the different communities. (3) The vector angles of the soil enzymatic stoichiometry in the three different mangrove communities and light beaches are all less than 45°. (4) The soil enzyme C:N:P ratio, after logarithmic transformation, measures at 1:1.36:1.28, deviating from the global average (1:1:1). This, in combination with the enzymatic stoichiometry, suggests that nitrogen and phosphorus both constrain the soil microorganisms in this study region, with nitrogen constraining them more strongly. Redundancy analysis indicates that the soil TK content is a primary driver regulating soil enzyme activity and its stoichiometric ratios. From the perspective of accelerating nutrient cycling and alleviating nutrient limitation, this study found that increasing exogenous inputs of nitrogen and potassium can alleviate nitrogen and phosphorus limitation in the mangrove ecosystem of Xinying Bay. These findings provide a basic theoretical basis for restoring and maintaining a healthy tropical mangrove ecosystem.

Altitude is the key factor affecting species diversity pattern. In order to explore the altitude distribution pattern of species diversity in tropical natural forest in Diaoluo Mountain, vegetation survey was conducted in six tropical natural forest plots from 245 to 1 130 m. The species diversity and community characteristics of tropical natural forest along the altitude of Diaoluo Mountain were analyzed from the aspects of species composition, species diversity, flora composition and leaf characteristics. The results were as follows: (1)With the increase of altitude, the temperature decreased, the humidity increased and the human disturbance decreased. The species composition of tropical natural forest in Diaoluo Mountain and the diversity indexes of Margalef, Shannon-Wiener, Simpson, and Pielou all showed a pattern of first increase and then decrease. The middle-altitude community had the most suitable hydrothermal conditions and moderate human disturbance, and the α species diversity was the highest. (2)With the increase of altitude, the proportion of important value (IV) of dominant species decreased first and then increased, and the dominant species had obvious replacement phenomenon. The middle altitude community showed the transition nature of lowland rain forest and mountain rain forest. (3) The Sørensen community similarity coefficient between communities was significantly negatively correlated with altitude difference (P<0.05). (4)The floristic composition was dominated by tropical elements and mainly distributed in tropical Asia (India-Malaysia). The proportion of tropical distribution was significantly negatively correlated with altitude (P<0.01), and the proportion of temperate distribution was significantly positively correlated with altitude (P<0.01). (5)The leaf characteristics showed the obvious indigenous characteristics in tropical regions mainly with mesophyll leaves, single leaves, leathery leaves and entire leaves. The proportion of microphyll leaves and single leaves was significantly positively correlated with altitude (P<0.01), while the proportion of leathery leaves and non-entire leaves was not significantly correlated with altitude (P>0.05). To sum up, the hydrothermal conditions and human disturbance degree of low altitude community in Diaoluo Mountain are quite different from those of high altitude community, which leads to the difference of species distribution and community characteristics, and reflects the characteristics of tropical plants adapting to their habitat conditions.

To understand the changes of community structure and diversity of natural forests in mountainous areas of central Hainan Island, two surveys were conducted in the montane rain forest in Wuzhishan, the lowland rain forest in Jianfengling, the montane rain forest in Diaoluoshan and the cloud forest in Bawangling from 2012 to 2020. A plot with a size of 1600 m~2 was set up for each forest type. The temporal variations of community structure, tree growth, tree mortality and species diversity in eight years were analyzed. The results showed that from 2012 to 2020:（1） DBH size-class and tree height class of the montane rain forest in Wuzhishan and the lowland rain forest in Jianfengling showed an inverted “J” shape. DBH size-class of the montane rain forest in Diaoluoshan and the cloud forest in Bawangling showed an inverted “J” shape, while tree height class showed a near “L” shape. The community structure became more complex over time.（2） Height growth rate of young trees was faster. With the increase of DBH, growth rate of tree height decreased and growth rate of DBH increased. The number of dead indivi-duals decreased with the increase of DBH. Young trees had a strong competition for resources, such as sunlight.（3） The change rates of population size of Pterospermum heterophyllum, Garcinia oblongifolia, Prismatomeris tetrandra and Symplocos hainanensis were higher than 5%, indicating rapidly changing populations. Pioneer species were gradually replaced by transitional species.（4） The average change rate of species diversity was +1.48%, +1.59%, +4.19%, and +12.26% in the montane rain forest in Wuzhishan, the lowland rain forest in Jianfengling, the montane rain forest in Diaoluoshan and the cloud forest in Bawangling, respectively. Most of the immigrating and exiting species were occasional species, which accounted for the changes of species diversity. Community succession of the damaged forests in the mountainous areas of central Hainan Island can be well restored, the structure complexity, species diversity and community stability of which can be effectively improved by effective enclosure.

The terrain of Hainan Island is high in the middle and surrounded by low terrain on all sides. From the central mountainous area to the eastern coastal plains, due to the difference of natural conditions and historical human interference, the composition of flora has changed. In this study, quadrant and line transect survey was carried out in Huishan Nature Reserve (in the middle and east of Hainan Island) to discover its composition. Then combined with the data of Wuzhishan Nature Reserve in the middle of Hainan Island (now part of the Tropical Rainforest National Park), Baishiling Nature Reserve in the eastern non-coastal area and Tongguling Nature Reserve in the northeastern coast, which investigated by our team, the flora composition characteristics were compared and analyzed. Try to explore the relationship between the change of flora composition and the secondary, area and altitude of the nature reserve. The results were as follows: (1) There were 1 893 species, 1 415 species, 634 species, and 913 wild seed plants in Wuzhishan, Huishan, Baishiling, and Tongguling nature reserves, the numbers of species in the two central nature reserves were significantly higher than that in the other two nature reserves. (2)Species similarities between nature reserves were significantly negatively correlated with differences in altitude and area (P<0.05). (3) Four nature reserves were dominated by tropical elements, but at the level of genera, Wuzhishan was dominated by tropical Asia, while others were dominated by pantropical distribution; at the level of species, distribution of tropical Asia was the most in the four nature reserves. In conclusion, from the central mountainous area to the eastern coastal plains, the more secondary, the lower the altitude, the fewer the habitat types, and the fewer the number of plant species; at the same time, at the level of genera and species, the tropical elements are increased, while temperate, endemic and relict elements are decreased.