Jim C Y
Department of Geography, The University of Hong Kong, Pokfulam Road, Hong Kong.
Environ Monit Assess. 2005 Mar;102(1-3):285-308. doi: 10.1007/s10661-005-6028-0.
Outstanding historical trees embedded in cities constitute pertinent environmental assets, yet they are widely threatened in third-world cities. Inadequate understanding of this valuable natural-cum-cultural heritage hinders proper conservation. A case study of Guangzhou in south China evaluated floristic composition, age profile and biomass structure of historical trees, assessed their performance in major habitats (institutional, park and roadside), and established a prognosis for future growth and management. The 348 historical trees examined belonged to only 25 species, vis-à-vis 254 trees in the entire urban forest, dominated by five species and native members. Roadside had more trees, followed by institutional and park, with merely the most common four species shared by all habitats. The limited commonality reflected tree-performance differentiation by habitats exerting selection pressure on species. The institutional growth-regime was more conducive to nurturing high-caliber specimens, whereas park is less capable. Individual species achievement by habitats, derived from tree-count ranking and relative-abundance indices, could inform species choice and tree conservation. Few trees exceeded 300 years of age in the millennium-old city, echoing a history of intense tree-city conflicts. Potential life-span, trunk and crown diameters indicated ample opportunities for further expansion of biomass and landscape impacts, which would be straitjacketed by the tightening urban fabric.
城市中留存的古树是重要的环境资产，但在第三世界城市中却受到广泛威胁。对这一兼具自然与文化价值的遗产认识不足，阻碍了其妥善保护。以中国南方的广州为例，研究评估了古树的植物组成、树龄结构和生物量结构，评估了它们在主要栖息地（机构、公园和路边）的生长情况，并对未来的生长和管理进行了预测。所考察的348棵古树仅属于25个物种，而整个城市森林中有254棵树，以五个物种和本地树种为主。路边的树更多，其次是机构和公园，所有栖息地仅共有最常见的四个物种。这种有限的共性反映了不同栖息地对树木表现的差异，对物种施加了选择压力。机构的生长环境更有利于培育高质量的标本，而公园则能力较弱。根据树木数量排名和相对丰度指数得出的不同栖息地单个物种的表现，可为物种选择和树木保护提供参考。在这座千年古城中，很少有树超过300年树龄, 这反映了城市与树木之间长期存在的冲突历史。潜在寿命、树干和树冠直径表明，生物量和景观影响有进一步扩大的充足机会，但城市空间的收紧将限制这一点。
