Madhuca hainanensis is a rare, endemic tree species of Hainan Island, with considerable ecological and economic value. Its natural regeneration is severely limited by habitat fragmentation and environmental stress. To investigate its adaptive across environmental gradients, we established experimental plots in the Jianfengling area of Hainan Tropical Rainforest National Park, encompassing elevation (400–1000 m) and canopy closure (30%–90%) gradients. Sapling growth and health were monitored for one year, alongside measurements of soil physicochemical properties and leaf photosynthetic pigment content. The results indicate that elevation was the primary factor influencing growth, with saplings at lower elevations exhibiting higher increments in height, diameter, and crown spread. While canopy closure was not statistically significant, moderate openness (30%–50%) at low elevations favored growth, whereas high-elevation, heavily shaded conditions constrained development. Sapling health declined over time, particularly in high-elevation and high-canopy-closure plots, and the interaction between elevation and canopy closure amplified physiological stress. Redundancy analysis revealed that elevation and canopy closure jointly explained ~36%–38% of the variance in growth and health, with chlorophyll a, carotenoids, and soil available phosphorus also contributing to sapling performance. These findings indicate that M. hainanensis is highly sensitive to light and elevation-related environmental gradients, and that low-elevation sites with moderate canopy openness are optimal for restoration and cultivation. This study provides a scientific basis for in situ conservation, wild reintroduction, and management of this threatened endemic species.

In tropical regions, the establishment of large-scale exotic plantations has addressed the demand for timber resources but has also disrupted the structural stability of native vegetation and altered soil nutrient cycling, thereby impairing ecosystem functions. Identifying effective restoration strategies for these plantations is crucial for sustainable forest management and ecological security. This study examined Acacia mangium Willd., Cunninghamia lanceolata (Lamb.) Hook., and Pinus caribaea Morelet. plantations in Hainan Tropical Rainforest National Park under three treatments: plantation control, girdling, and natural secondary forest. Vegetation surveys and soil analyses were conducted to explore the relationships between community structure, soil physicochemical properties, and enzyme activities. Diversity indices, Pearson correlations, and redundancy analysis were used to assess plant–soil relationships. The results showed that girdling significantly accelerated succession in C. lanceolata and P. caribaea plantations, increased species diversity, and enhanced the dominance of native species. Shrub-layer diversity indices (H_shrub, D_shrub, E_shrub) were the main drivers of soil properties and enzyme activities, while tree-layer effects were weaker. Girdling regulated soil nutrients and biological activity primarily via changes in community structure. These findings highlight the importance of optimizing shrub-layer structure and enhancing diversity for tropical plantation restoration. Combining forest type conversion with moderate interventions can promote coordinated plant–soil development over time.

Rural settlements are significant carriers of rural production, living, and land use activities and are also significant subjects for researching regional socio-economic development and spatial structural changes. With regard to the unique topographical environment and transportation situation in the Qiongbei volcanic lava area, a settlement form with prominent topographical constraints and transportation orientation is created. This paper utilizes land use/land cover data from different periods, along with rural settlement expansion patch data, to quantitatively analyze the spatial patterns and expansion characteristics of rural settlements, as well as their influencing factors, from 1990 to 2025 using GIS spatial analysis, buffer gradient analysis (BGA), and multi-order adjacency index (MAI). The research results indicate the following: (1) The spatial pattern of rural settlement distribution in the study area is “peripheral agglomeration and core sparsity,” and the general expansion trend is “rapid in the early period and stable in the late period.” The settlement area expands from 37.21 km² in 1990 to 80.87 km² in 2025. (2) The evolutionary pattern of rural settlements in the study area changes from “core–peripheral extension” in the early period to a mixed “core stabilization and peripheral leapfrogging development” model in the later period. The new patches formed in the peripheral areas have obvious discrete features, such as varying land use patterns and differing population densities compared to the core areas. (3) The spatial correlation factors for rural settlement expansion in the study area exhibit stage differences and distinct spatial non-stationary characteristics. During the early period (1990–2008), with strict limitations imposed by the natural material environment, sunlight (interpretability of 0.367) and water systems (0.286) show significant spatial coherence, indicating the great adaptability of rural settlements to the material conditions of the landforms; during the later period (2008–2025), after the implementation of the rural revitalization strategy, the population density (0.135) and transport-related factors become the main spatial correlation factors. The GWR model also shows the percentage of positive and negative influences by influencing factors at each stage and their significant differences in space, proving that human activities break through in the limitations of natural topology in a discontinuous way. According to this research, “inefficient land use” should be understood in a dialectical manner in volcanic geomorphological areas, and spatial optimization should be achieved on the premise of respecting the physicality of volcanic landscapes and rural identity. The research conclusions have important guiding significance for the spatial resilience planning in tropical volcanic areas and traditional settlement culture preservation.

Hainan Island supports abundant tropical ancient Ficus trees owing to its distinctive hydrothermal conditions and long-term human–environment interactions, yet the environmental factors associated with their distributions and responses to future climate change remain insufficiently understood. This study focused on the ancient trees of four dominant Ficus species on Hainan Island—Ficus microcarpa, F. altissima, F. benjamina, and F. virens—using systematically surveyed occurrence records and 59 candidate variables representing climate, soil, topography, anthropogenic activity, and typhoon disturbance. Two parameter-optimized MaxEnt frameworks were developed. The Environmental Association Model (EAM) incorporated climatic, soil, topographic, anthropogenic, and typhoon-related variables to identify factors associated with the current distributions of these ancient trees, whereas the Natural-Environment Projection Model (NEPM) included climatic, soil, and topographic variables to estimate potential habitat suitability under current conditions and SSP126 and SSP585 scenarios for the 2050s and 2070s; only climatic variables were updated in future projections. Under the EAM framework, population density was the key variable associated with the modeled distributions of all four ancient-tree groups, accounting for 65.3%, 46.1%, 39.6%, and 26.3% of the model contribution for ancient F. microcarpa, F. altissima, F. benjamina, and F. virens, respectively. Climatic and soil variables showed species-specific effects; topographic variables contributed mainly to ancient F. altissima and F. virens, whereas typhoon impact intensity contributed only slightly to ancient F. benjamina. Under current climatic conditions, total suitable habitat ranged from 7771.31 to 10,489.97 km². Ancient F. microcarpa had the largest total suitable area, ancient F. benjamina the smallest, and ancient F. altissima the largest highly suitable area. Highly suitable habitats were concentrated mainly in northern and northwestern Hainan, with scattered central patches. Under future scenarios, the total and highly suitable habitats of ancient F. benjamina generally expanded, particularly under SSP585. In contrast, those of ancient F. microcarpa, F. altissima, and F. virens generally contracted, with substantial losses of highly suitable habitat; ancient F. virens faced the greatest habitat-loss risk. SSP585 intensified contraction for ancient F. microcarpa and F. virens, whereas ancient F. altissima showed more complex, scenario-dependent changes. Sensitivity analyses using alternative regularization settings supported these overall trends. These findings support conservation zoning, habitat restoration, germplasm preservation, and climate-adaptive management of ancient Ficus trees on Hainan Island.

Ecological stoichiometric ratios of soil provide insights into the interactions and limitations among elements. This study examined the nutrient characteristics K, N, and P stoichiometric ratios in the soils collected from three distinct shelter forests (Casuarina equisetifolia, secondary forest, and Cocos nucifera) in a tropical coastal region of Hainan Province, China. Significant differences were observed among forest types in terms of stoichiometric ratios and nutrient levels in soil (p < 0.05). This may be related to the high species diversity in secondary forests and the complex composition of litter. soil nutrient levels in the secondary forest were higher than those in C. equisetifolia and C. nucifera. The effects of soil nutrient factors on soil ecological stoichiometric ratios differed across shelterbelt types. Soil organic matter, total potassium, available potassium, and ammonium nitrogen content substantially influenced the N:P, K:P, and N:K ratios (Q² > 0.5). Soil TN content was highly significantly positively correlated with N:P, N:K, in C. equisetifolia and C. nucifera (p < 0.01), whereas in the secondary forest, it was highly significantly positively correlated with SOM and NH₄⁺-N (p < 0.01). These results reflecting the complexity of nutrient cycling as well as the interdependence and mutual regulation between vegetation and soil in coastal shelter forest ecosystems.