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.

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.

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.