Abstract:

Aims：Ancient trees serve as vital carriers of natural environmental evolution and human history, and revealing their resource characteristics, spatial patterns, and retention mechanisms is of great significance for scientific conservation. Chongqing is located in the core distribution area of endemic genera of seed plants in China and harbors high plant diversity, yet systematic studies on its ancient tree resources remain insufficient. 

Methods：Based on data of 29,104 ancient trees in Chongqing, this study constructed a multi dimensional environmental factor system covering natural environment, socio economy, and historical culture. By integrating tree species diversity indices, spatial autocorrelation analysis, Spearman correlation analysis, and the MaxEnt model, we explored the distribution patterns and driving mechanisms of ancient trees at both rural and urban scales. 

Result：(1) The ancient trees in Chongqing belong to 73 families, 158 genera, and 304 species, exhibiting a coexistence of concentrated dominant species and a high proportion of rare species, with 38.82% of the species represented by fewer than three individuals. The floristic composition shows transitional characteristics between tropical and temperate zones. (2) The number of ancient trees, species diversity, and rarity level are significantly uneven in space, with obvious clustering in the southeastern and northeastern mountainous areas. There is a significant positive spatial correlation between diversity and tree age. (3) The diversity of ancient trees in rural areas is mainly driven by natural factors, showing a significant negative correlation with land surface temperature and positive correlations with precipitation, elevation, and terrain relief. The distribution of ancient trees in urban areas is primarily influenced by socio cultural factors, among which distance to urban parks, NDVI, and elevation are the core driving factors, with a cumulative contribution rate of 82.4%. Different tree species also show varying responses to these drivers. 

Conclusion: The ancient tree resources in Chongqing exhibit significant regional transition characteristics and local traits, and their retention mechanism reflects a differentiated pattern: natural filtering dominates in rural areas, whereas human activities shape the pattern in urban areas. Based on these findings, a three dimensional conservation strategy framework integrating urban rural gradient, rarity level, and tree species type was constructed, aiming to provide a theoretical basis and scientific reference for the precise conservation of ancient tree resources and the maintenance of cultural ecological diversity.

Key words: ancient tree resources, urban-rural dual structure, retention mechanism, XGBoost-SHAP, MaxEnt model, Chongqing