人类活动和自然环境塑造古树的物种组成与分布格局—— 以重庆市为例

Human Activities and Natural Environments Shape the SpeciesComposition and Distribution Patterns of Heritage Trees: A CaseStudy of Chongqing City

关键词:  园林植物  古树  重庆市  物种组成  分布格局  影响因素

Key words:  landscape plant  heritage tree  Chongqing City  species composition  distribution pattern  influencing factor

摘要:

古树是人类聚居地区重要的生物和文化遗产，具有无可替代的生态系统服务。构建了一个包含重庆市域范围内完整古树信息的数据集。在此基础上， 分析了古树物种组成和分布特征，揭示了人类活动和自然环境对古树分布格局和物种组成的影响。结果表明，重庆市现存古树25 662株，分属69科151属283 种，常见树种包括黄葛树(Ficus virens )、柏木(Cupressus funebris )、枫香树(Liquidambar formosana )、银杏(Ginkgo biloba )和黄连木(Pistacia chinensis )。栽培古树以不到30%的物种数贡献了69.07%的古树个体，而自然古树是古树物种多样性的主体。此外，记录到24个IUCN评定的受威胁物种。这 些物种保存了2 199株古树，占古树总数的8.6%。古树分布具有明显的地理格局，其中栽培古树主要分布在主城都市区，自然古树主要分布在渝东南地区。随机 森林模型和回归分析表明，古树的分布格局主要受到人类活动、海拔等因素的影响。此外，不同区域古树物种组成具有较大的差异。总体上，人类活动强度高的 地区(较高的人类足迹指数)以栽培古树为主，而人类活动弱的地区(较高的少数民族人口比例、森林覆盖和海拔)保存了更多的自然古树

Abstract:

Heritage trees represent an indispensable biological and cultural asset within human-dominated landscapes, delivering a wide array of ecosystem services that are virtually irreplaceable. In this study, we constructed a comprehensive dataset containing complete information on heritage trees within the administrative area of Chongqing Municipality. Based on this dataset, we classified all heritage tree individuals into cultivated trees and naturally occurring trees according to the cultivation degree of each species: cultivated trees originate from trees that have been widely introduced and planted by humans, while naturally occurring trees originate from natural forests, are remnants of natural forests, and are rarely cultivated. We then analyzed the species composition and distribution characteristics of heritage trees, revealing the influences of human activities and natural environmental factors on their distribution patterns and species composition. Our inventory documented a total of 25,662 living heritage trees in Chongqing, representing 283 species, 151 genera, and 69 families. The most frequently encountered species included Ficus virens, Cupressus funebris, Liquidambar formosana, Ginkgo biloba , and Pistacia chinensis. Among these individuals, cultivated trees amounted to 17,726 specimens, encompassing 94 species, 72 genera, and 40 families-accounting for less than 30% of the total species richness yet contributing 69.07% of the total individual count. In contrast, naturally occurring trees comprised 7,936 individuals, belonging to 189 species, 106 genera, and 56 families, and thus constituted the primary repository of species diversity. In addition, we identified 24 species that are currently assessed as threatened on the IUCN Red List, including notable taxa such as Picea neoveitchii, Artocarpus nanchuanensis, Ginkgo biloba, and Taxus wallichiana. These threatened species collectively contributed 2,199 heritage trees, representing 8.6% of the total population. With respect to individual structural traits, the average age of all heritage trees was 180.26 ± 94.82 years, mean height 18.24 ± 6.65 m, mean diameter at breast height (DBH) 93.55 ± 47.48 cm, and mean crown width 12.52 ± 6.00 m. Statistically significant differences (p< 0.001) were detected between the two categories for all four traits: cultivated trees exhibited substantially lower age and height but significantly larger DBH and crown width compared to their naturally occurring counterparts, reflecting the contrasting selection and management regimes imposed by human cultivation versus natural succession. Geographically, the distribution of heritage trees displayed a pronounced spatial dichotomy. Cultivated trees were overwhelmingly concentrated in the main urban metropolitan area, where historical and contemporary human activities are most intensive, whereas naturally occurring trees were predominantly situated in the southeastern part of Chongqing, a region characterized by rugged topography and higher forest cover. To elucidate the drivers of these distributional patterns, we employed random forest modeling combined with multiple regression analyses. Our results revealed that both human activity indices and topo-climatic factors, particularly altitude, exerted dominant controls. Specifically, the total number of individuals and species richness of heritage trees, irrespective of type, were significantly and positively correlated with the proportion of ethnic minority population - a proxy for traditional landuse practices and lower anthropogenic disturbance. For cultivated trees, individual abundance was positively associated with per capita GDP and cultivated land coverage, but negatively related to mean altitude. Conversely, the abundance of naturally occurring trees showed the opposite relationships: negative correlations with per capita GDP and cultivated land area, and a positive correlation with mean elevation, underscoring their refuge status in less accessible, less developed areas. Furthermore, species compositional dissimilarity among different geographic units was considerable. We found that the proportion of ethnic minority population, mean altitude, mean annual temperature, and the human footprint index collectively exerted the strongest explanatory power in accounting for spatial turnover in species composition. In synthesis, areas with elevated human footprint indices - indicative of intensive anthropogenic modification - were overwhelmingly dominated by cultivated trees, while regions characterized by higher ethnic minority proportions, greater forest coverage, and higher elevations harbored a greater abundance and diversity of naturally occurring trees.