Abstract:

Aims: Ancient trees serve as vital carriers of natural environmental evolution and human history, playing a crucial role in maintaining biocultural diversity. However, how the urban-rural dual structure differentially shapes the retention mechanisms of ancient trees under rapid urbanization remains poorly understood. 

Methods: Focusing on Chongqing, a core distribution area of endemic seed plant genera in China, this study utilized occurrence data of 29,104 ancient trees and 18 environmental variables to comparatively analyze the spatial distribution patterns and driving mechanisms of ancient trees across urban and rural scales, by integrating spatial autocorrelation analysis, an interpretable XGBoost-SHAP machine learning approach, and the maximum entropy (MaxEnt) model. 

Results: (1) The ancient trees in Chongqing comprised 304 species, exhibiting a coexistence of a few dominant species and a high proportion of rare species (38.8% of species with < 3 individuals), with significant tropical-temperate transitional floristic characteristics. Urban and rural compositions differed significantly, with urban areas dominated by ornamental species and rural areas by zonal relict species. (2) The spatial distribution showed significant clustering, with Southeast and Northeast Chongqing forming composite hotspots of high diversity and rarity. (3) The retention mechanisms differed markedly between urban and rural areas: rural diversity is primarily driven by natural habitat filtering, exhibiting complex nonlinear threshold effects (e.g., land surface temperature < 21.79℃ favored retention), with micro-environmental factors significantly explaining the residual variance; conversely, urban distribution was predominantly shaped by socio-cultural factors. Historical parks and cultural heritage sites served as core spatial carriers (distance to urban parks contributed 43.2%), and different tree species showed specific responses to anthropogenic factors. 

Conclusion: This study reveals the dual retention mechanism of “natural filtering in rural areas and humanistic shaping in urban areas”, and constructs a three-dimensional precision conservation strategy framework integrating “urban-rural gradient, rarity level, and tree species type”. This provides a scientific reference for the synergistic conservation of regional ancient tree resources and biocultural diversity.

Key words: ancient tree resources, urban-rural dual structure, spatial distribution pattern, retention mechanism, conservation strategies, Chongqing