Ancient trees are defined as trees over 100 years of age, often characterized by substantial girths, towering heights, extensive canopy cover, and unusual biomass structure (Blicharska and Mikusiński, 2014). They constitute precious natural resources nurtured by the fortuitous combination of geography, ecology, and human activities over time (Yan, 2023; Pan et al., 2025). Playing an important role in ecosystem functions, they altruistically offer a varied spectrum of microhabitats, shelters and foods to many companion plants and animals to enhance biodiversity conservation (Jim and Zhang, 2013; Nolan et al., 2020), including birds, mammals, insects, fungi and epiphytic plants (Lindenmayer, 2017).

Some trees serve as repositories of valuable genes from endangered species, making them critically important for species conservation and ecosystem continuity (Spooner and Shoard, 2016; Chi et al., 2020). Moreover, their root systems can enrich soil fertility and maintain soil structure and porosity to sustain infiltration, percolation, and plant-available water storage (Nolan et al., 2021). By enhancing soil stability, they improve soil and water conservation and suppress erosion. Their presence can create diverse abiotic and biotic microenvironments, which can increase habitat and species richness (Hubble et al., 2010; Li and Zhang, 2021). Their physiology and physiognomy can contribute effectively to carbon sequestration and microclimatic regulation (Jones et al., 2013).

The prominent doyens belong to a separate and special class of keystone plants, whose vicissitudes are intimately intertwined with adjoining human communities (Liu et al., 2022). Ancient trees offer serve as a living link to both historical and contemporary landscapes (Lindenmayer and Laurance, 2017). As persistent members of ecosystems, their life spans traverse multiple human generations, allowing for deep association with human and natural history, as well as related environmental changes (Andersson and Östlund, 2004; Lai et al., 2019). Some ancient trees embody or engender religious, spiritual, and cultural values for local communities, serving as a bridge between nature and culture, and essential connectors to collective memory and sense of place (Chen and Hua, 2015). For example, Cupressus funebris and Ginkgo biloba trees have been enlisted as the material expression and inheritance of time-honored customs and cultural beliefs (Liu et al., 2020; Hou et al., 2022).

Studying the species composition and spatial distribution patterns of ancient trees can be fruitfully accompanied by investigating the associated drivers and processes (Cannon et al., 2022). Ancient trees dwelling in different regions are influenced by different natural conditions and human interaction regimes (Pan et al., 2025). The existing population of ancient trees in a given locality is expected to express a unique collection of traits, including floristic profile, age structure, evolutionary progression, spatial patterns, and plant migration and adaptation to the environment (Jim, 2005; Lai et al., 2019).

However, over the past century, the distribution and abundance of ancient trees have been reduced by harmful biotic and abiotic changes (Stagoll et al., 2012; Le Roux et al., 2014). They include climate change, drought, excessive soil moisture, soil erosion, invasive exotic species, increased pest and disease attack, environmental destruction, wildfires, excessive deforestation, and economic development (Mahmouda et al., 2015; Gilhen-Baker et al., 2022). Such extensive degradation has progressively eliminated a significant proportion of ancient trees. The residual populations are confined to fragmented remnant patches, with collateral impacts on ecosystems and biodiversity (Piovesan et al., 2022). These deleterious changes have altered the species composition, abundance, and distribution patterns of ancient trees (Yao et al., 2024). For instance, the density of scattered ancient trees in China is positively correlated with human population density. In contrast, the density of clustered ancient trees is negatively influenced by human population density (Liu et al., 2019). Some ancient trees are less damaged in regions with more water availability and moderate temperatures (Venter et al., 2017).

Chongzuo, a Chinese city near the Vietnam border, features a karst-dominated and highly varied terrain with notable relative relief. Its complex geology and topography have created a fine mosaic of distinctive soil, moisture and microclimatic conditions to nurture and sustain rich plant resources (Zhang et al., 2013). The spatially differentiated natural conditions provide conditions for biotic diversification. Moreover, recent rapid urbanization has imposed intense human activities and environmental degradation, which has been compounded and exacerbated by climate change (Asanok et al., 2021). These impacts severely challenge the growth and survival of ancient trees in Chongzuo. However, the alarming loss of an irreversible and valuable resource base has not attracted in-depth research. The lack of scientific knowledge has hindered conservation efforts.

This study represents the first attempt to assess the condition and plight of ancient trees in Chongzuo. It assesses the species composition, distribution patterns, and conservation needs of ancient trees in Chongzuo. Our key research questions include: (1) What are the key traits (species composition, diversity, dimensions and age range) of ancient trees in the study area? (2) What are the distribution patterns of the trees? (3) What are the relationships amongst trees and environmental attributes, including altitudinal gradient? The findings could inform management decisions for ancient trees in tropical China and elsewhere facing similar remnant-tree conservation concerns.

Ancient trees are keystone components of landscapes, and studying their diversity is critical for achieving long-term conservation (Hartel et al., 2018; Miklín et al., 2018; Xie et al., 2024). Our results showed that Chongzuo has abundant ancient tree resources distributed across the region (Table 2; Figures 2, 3). These resources are closely linked to the high plant diversity of Southwest China (López-Pujol et al., 2011). The diverse flora and associated ecosystem functions supported by this regional richness are key to ensuring the long-term survival and natural regeneration of ancient trees (Lindenmayer et al., 2012).

In addition to these biotic underpinnings, the complex terrain and suitable climate in Chongzuo are key factors sustaining the abundant ancient tree resources. The diverse landforms of the region, including karst landscapes, hills, and plains, create a distinct mosaic of varied habitats for ancient tree species with varying needs. The heterogeneous terrains, rich in microhabitats with varying elevation, slope gradient, soil thickness and quality, plant-available water, and microclimate allow diverse plant species to selectively utilize the assorted sites (Guo et al., 2013). The natural setting provides a complex collection of relatively small and isolated habitat silos, allowing for independent evolutionary development and the accumulation of species endowment. The inherently high beta landscape diversity offers the precursor for high floristic beta diversity. This spatial multiplicity of habitats underpins evolutionary processes among vegetation species, which in turn supports diverse forest community structures and rich ancient tree species compositions (Du et al., 2017).

Moreover, the rugged karst topography, notoriously difficult to navigate, serves as a natural physical barrier to reduce the anthropogenic pressures of agricultural and urban expansion, thereby fostering in situ conservation of ancient tree populations (Guo et al., 2017). Having adapted to these harsh karst conditions over time, a proportion of Chongzuo’s ancient trees reveals not only the uniqueness of their habitat but also the profound interplay between natural selection and ecological adaptation. Furthermore, the subtropical humid monsoon climate in the region provides ample sunshine and rainfall throughout the year, fostering a favorable environment that enhances the vitality and resilience of ancient trees in conjunction with the broader biotic community (Woodruff, 2010; Wang et al., 2020).

Beyond nature’s inheritance, folk cultures and religious beliefs play a crucial role in maintaining ancient trees in pristine condition (Huang et al., 2020; Yan, 2023). The mountainous border region is predominantly inhabited by ethnic minorities, including the Zhuang, Yao, and Miao peoples, who have preserved traditions of nature worship and spiritual reverence toward ancient trees. For instance, species such as F. altissima, Liquidambar formosana, and Pistacia chinensis are venerated as sacred trees. Residents conduct ritual observances on specific dates, praying to these trees for divine protection and blessing. Through cultural preservation and intergenerational transmission, these traditions have been institutionalized as binding village regulations and customary agreements (Huang et al., 2025), ensuring effective conservation of ancient trees.

There are significant differences in the number of ancient trees among different families and genera, with 54 plant species belonging to single families and genera, exhibiting relatively small populations (Table 2; Figure 3). In contrast, a small number of species is strongly represented. This pattern indicates that Chongzuo maintains high species richness in ancient tree resources. However, the population is dominated by a small cohort of common species, accompanied by a large number of uncommon to rare and solitary species. Other studies confirm that when plant communities contain many taxa from a single genus, this composition generates distinctive diversity patterns within regional vegetation (Huang et al., 2025).

Several biotic and anthropogenic factors may explain these observed disparities in tree abundance. Species that occur in greater numbers are generally well-adapted to the local climate and have been culturally valued, which has facilitated their preferential as ancient trees. Moreover, most of these abundant species are long-lived trees. In contrast, shrubs and other short-lived woody plants are less likely to reach ancient status due to biological constraints, resulting in fewer preserved individuals (Yang et al., 2024).

Ancient trees embrace natural and cultural qualities, making them a unique biological group (Nolan et al., 2021; Fröhlich et al., 2024). The number of ancient trees decreased considerably with increasing tree age, height, DBH, and crown width (Figures 4, 5); this pattern is reflected by the fact that 95.33% of individuals belong to the tier-3 age group (Figure 4) and is likely driven by a combination of environmental and physiological factors. The terrain of Chongzuo is predominantly characterized by karst landforms, which give rise to a distinctive habitat marked by fragmented terrain, sparsely and unevenly distributed soils, a weak water retention capacity, and a low threshold for resisting external disturbance (Liu et al., 2021; Hu et al., 2023). Such chronic stresses inherently limit the growth and sustainability of ancient species. Concurrently, tree aging leads to physiological senescence, reducing stress resistance and increasing susceptibility to pathogens and natural disasters, thereby shortening their lifespans (Wang et al., 2020; Clark et al., 2019).

Furthermore, climate change-induced high frequency of extreme climate events, such as prolonged droughts, heavy rainfall, and sudden temperature fluctuations, which in turn alters the spatial distribution and size of ancient tree populations (Lindenmayer et al., 2012). These changes pose a severe threat to fragmented karst habitats, as their lack of adequate ecological buffers to mitigate the impacts of extreme events, the adaptive capacity and migratory potential of ancient trees in response to climate change.

The composition of ancient trees is not only constrained by natural environmental factors, but also influenced by complex human activities and ethnic customs (Orłowski and Nowak, 2007). Our results indicate that the ancient trees in Chongzuo are dominated by C. drupifera, D. longan, E. tonkinense, and F. altissima, with trees counts exceeding 1000 each (Table 2; Table 4). C. drupifera dominates Chongzuo ancient tree populations due to its environmental adaptability and economic value. This species is primarily distributed in clusters and exhibits high ecological resilience. With a have high fat concentration, the seeds are extracted for use in cooking oil, chemical, food processing, and livestock feed industries (Zhang, 2008). This widespread use has led to extensive cultivation by local villagers. Furthermore, this nutrient-rich fruit will also be transported and stored by rodents after maturity, which will to some extent increase its distribution area (Xiao et al., 2015).

D. longan, as an edible fruit and traditional Chinese medicine, has a planting history of over 2000 years in China (Zhang et al., 2020). Longan pulp is rich in nutritional phytochemicals, including protein, carbohydrates, vitamin C, and polysaccharides, as well as polyphenols, which exhibit multiple biological activities such as antioxidant, immunomodulatory, and antitumor effects (Yang et al., 2011), making it a widely planted fruit tree in Chongzuo City.

E. tonkinense ranks third in abundance among ancient tree species in Chongzuo, a position attributable to its distinctive ecological traits. As a key constructive species in karst seasonal rainforests, it is recognized alongside Erythrophleum fordii and Garcinia paucinervis as the three important hardwood timber trees of Guangxi. The timber demonstrates significant economic value, particularly in crafting durable butcher blocks and furniture, driving its widespread cultivation (Xiang et al., 2013). Additionally, its small seeds possess membranous wings adapted for wind dispersal, enabling them to colonize germination-suitable microhabitats. This dispersal strategy helps to reduce mortality from high-density constraints around parent trees while expanding the species’ spatial distribution and population size.

There are significant spatial variations in the species richness and abundance of ancient tree resources across Chongzuo City, with Pingxiang possessing the highest species richness and abundance (Table 5; Figure 6). This is attributed to the presence of 8,937 ancient C. drupifera specimens within its territory gives Pingxiang an absolute quantitative advantage in ancient tree abundance, and this can be explained by the extensive cultivation history of this economic crop. Longzhou hosts the second-highest species richness and abundance of ancient trees in Chongzuo City (Table 5; Figure 6). This is partly attributable to the Guangxi Nonggang National Nature Reserve within its territory, which contains one of the world’s rarest, most structurally intact, and most representative northern tropical karst seasonal rainforests, and ranks as one of China’s 14 key biodiversity hotspots areas (Hu et al., 2023), which collectively explain the township’s exceptionally high biodiversity.

Jiangzhou and Tiandeng exhibit the lowest abundance of ancient trees in Chongzuo City (Table 5; Figure 6), a pattern attributable to interconnected factors including geomorphology, ecological conditions, land utilization patterns, and socioeconomic development. In Jiangzhou, karst features dominate the western sector, western sector while hills and small plains characterize the eastern and central regions. However, farmland has converted a significant portion of the natural vegetation, with sugarcane cultivation dominating the landscape (Wang et al., 2025). Moreover, as Chongzuo’s sole urban core, the township experiences accelerated urbanization. These combined pressures leave limited space or opportunity for preserving ancient trees. Tiandeng’s landscape is characterized by typical karst topography, with rocky surfaces covering 71% of its total area. The region is also facing severe rocky desertification, a process in which vegetation cover and fertile soil are lost, leaving behind barren, rocky surfaces (Guo et al., 2022). This landscape degradation severely damages the growth ability of trees and limits the population of ancient trees.

Among the nine tree habitats in Chongzuo, mountain (E), villages and farmlands (A), and parks, nature reserves, and scenic spots (B) had the highest numbers and species of ancient trees (Table 6). Especially the number of ancient trees in mountain (E) accounts for 59.57% of the total, indicating the crucial role of natural forest ecosystems in nurturing and protecting ancient trees. Mountains provide trees with more open, large, and natural conditions, which can allow ancient trees to flourish with enough room and a less stressful environment (Du et al., 2017). In addition, compared with the other seven habitats, ancient trees in business and commercial (D) and residential (G) habitats had a lower proportion of numbers and species (Table 6). This constraint may be related to their surfaces extensively sealed by buildings, roads and other paved areas, limited plantable space, confined greenery sites, and strong human disturbance.

Our analysis revealed distinct correlations between socio-environmental factors and ancient tree species richness (Figure 7). A positive correlation was observed with land area, built-up area, GDP, population density, and farmland area. This relationship can be attributed to the selective preservation of diverse species driven by cultural and economic development activities (Mahmouda et al., 2015). They include the preservation of natural habitats or the creation of artificial habitats that provide suitable ecological niches (Beninde et al., 2015), as well as moderate disturbance that suppresses competitive dominance (Cannon et al., 2022), all of which can collectively promote species richness.

In contrast, forest coverage was negatively correlated with species richness. This pattern arises primarily in areas with high forest coverage, where habitats are predominantly composed of a few dominant species (Mori et al., 2017). Additionally, minimal human disturbance in these regions does not furnish the conditions or generate the need for introducing diverse ancient tree species (Hou et al., 2022). Meanwhile, natural ecological succession tends to allow a limited number of dominant species to progressively monopolize resources (Jucker et al., 2014), thereby suppressing and even displacing other ancient tree species and ultimately reducing overall species richness.

The abundance of ancient trees shows a positive correlation with forest coverage (Figure 7), which is attributable to the stable and undisturbed habitats provided by densely forested areas that support the completion of their full life cycle (Lindenmayer et al., 2012). Conversely, the negative correlation with land area, built-up area, GDP, population density, and farmland area (Figure 7) is due to the associated intensive human activities. Through direct clearing, land development, habitat destruction, and environmental pollution, these human actions systematically threaten the survival and persistence of ancient trees (Grimm et al., 2008).

Altitude can bring considerable climatic changes that affect plant growth, development, and metabolism, thereby shaping the growth of ancient trees (Pinto-Junior et al., 2020; Vetaas and Grytnes, 2002). Our results showed that elevation negatively correlated with the species richness and abundance of ancient trees (Figures 8a, b), indicating that high altitude significantly limits their distribution. In Chongzuo, habitat heterogeneity intensifies with altitude, characterized by stronger sunlight, reduced soil moisture, thinner soil layers, stronger wind, and increased rock exposure, thereby constraining the adaptability of ancient trees (Chen et al., 2015). The shifts in distribution, structure and species diversity of ancient trees from low to high elevations reflect their adaptation to progressively drier and harsher conditions, highlighting their capacity to exploit karst microhabitats and optimize survival strategies under environmental stress (Wang et al., 2025).

Our results reveal that ancient trees in Chongzuo are characterized by high species richness yet uneven population distribution, featuring the coexistence of numerous rare and solitary species alongside a small cohort of dominant species. Furthermore, their survival and regeneration are closely intertwined with regional environmental factors (e.g., karst terrain, climate conditions) and socioeconomic activities (e.g., human disturbance, cultural preservation practices), which jointly shape their current distribution patterns and population dynamics. Consequently, targeted spatial planning and the integration of habitat and socioeconomic considerations are imperative for formulating effective conservation strategies to ensure their long-term survival (Lindenmayer and Laurance, 2017).

To more effectively conserve ancient tree resources, we propose the following targeted and differentiated protection measures: implement special conservation initiatives for national key protected species and solitary tree species, including formulating exclusive conservation plans and establishing germplasm banks to enhance their long-term survival capacity; strengthen systematic maintenance and rejuvenation of middle-aged ancient trees while maintaining the ecological balance of dominant tree populations (Pan et al., 2025); adopt differentiated regional conservation strategies, designate key areas as core reserves, and construct ecological corridors to connect fragmented habitats; meanwhile, optimize urban and agricultural planning to mitigate the disturbances of human activities and environmental pressures on ancient tree habitats (Gilhen-Baker et al., 2022). In addition, a comprehensive dynamic monitoring system should be established to track the real-time growth status of ancient trees, providing scientific support for adaptive conservation management and thus facilitating the harmonious coexistence of human development and natural heritage.

Our results showed that Chongzuo City support an abundance of ancient tree resources, yet exhibits significant spatial variations in species composition and tree abundance. This spatial heterogeneity stems from the combined effects of natural and anthropogenic factors. Future investigations could integrate habitat, soil, climate, land use, and local cultures to explore the spatial distribution patterns of ancient trees across macro- and micro-scales. Such a multiscale analysis will enable identification of conservation hotspots and inform targeted protection strategies based on comprehensive assessments of tree health status and local geomorphological characteristics.