林冠附生植物生态学研究进展

林冠附生植物及其枯死存留物是构成山地湿性森林生态系统中生物区系、结构和功能的重要组分。由于在林冠攀爬技术上的限制,过去对林冠附生植物在生态系统结构和功能过程中的作用未能引起足够的重视。近20年来,随着对林冠生物多样性及其在生态系统功能过程影响的认识和研究技术上的提高,对林冠附生生物的研究已逐步从个体水平转移到系统水平上。有关林冠附生植物多样性、生物量及其生态学效应已成为近年来国际上新兴研究领域——“林冠学”的研究热点之一。许多研究表明,林冠附生植物在生态系统水平上的交互作用比它们的解剖、形态和生理特征更为重要。国外大量的研究结果表明,林冠是一个适合于许多生物种类生存的场所,其数量比想象的更为丰富。在全球范围内估计有29 500余种附生植物,其中维管束附生植物的种类高达24 000种,约占总维管束植物种类的10%。林冠附生物的生物量在世界各地森林中存在较大的差异,其范围在105~44 000 kg·hm^-2之间,其中在一些热带和温带天然老龄林中林冠附生物的生物量超过了宿主林木的叶生物量。林冠附生植物还具有较大的叶面积指数(LAI)。林冠附生物丰富的物种组成、较高的生物量、独特的生理形态特征以及它们分布于森林与大气相互作用的关键界面,使得它们在生态系统物种多样性形成及其维持机制、养分和水分循环、指示环境质量等方面具有重要的作用。林冠附生植物及其枯死残留物具有较强的能力吸收雨水和空气中的营养物质,在林冠层中形成一个潮湿的环境促进氮固定,林冠附生植物群落还能为生存于林冠的其它生物(如鸟类、哺乳动物、两栖动物、爬行动物和昆虫等)提供食物和栖息场所。林冠附生植物的生长发育与分布格局除与宿主有关外,还受到环境因素(气候、地形、微生境条件等)和人为干扰的影响。由于世界各地森林类型多样和环境条件各异,目前国际上有关附生物的研究仍十分活跃,建立了林冠研究网络,研究不同类型森林中附生植物及其枯死残留物的动态及其与群落特征、环境因子的数量关系,探讨、交流和发展有效的标准测量方法和技术是该领域研究的主要内容。国内对林冠附生植物生态学的研究刚刚起步,有待于今后加强该领域的研究。

ADVANCES IN ECOLOGICAL STUDIES ON EPIPHYTES IN FOREST CANOPIES

Canopy-dwelling epiphytes and their associated dead organic matter are important floristic, structural and functional components in montane moist forests. Because of the difficulties related to access, the biodiversity and ecosystem-level functional attributes of epiphytes have received little attention in forests. With an increase in our understanding of epiphytic biodiversity and their roles in ecosystem-level interactions, combined with improved access to the forest canopy, studies on epiphytic organisms in forest canopies have progressed from the individual level to the ecosystem level. Biodiversity and biomass of epiphytes and their functional roles at the ecosystem-level are becoming a hot topic of recent study. Recent work in tree canopies in a variety of forest types, however, has pointed out that the role of epiphytes in ecosystem-level interactions are more important than previously thought due to their anatomical, morphological, and physiological characteristics. Considerable research conducted worldwide has shown that the forest canopy is a favorable habitat supporting a much richer epiphytic flora than previously thought. It was estimated that there are 29 500 epiphytic species, including 24 000 vascular epiphytes that account for 10% of the total vascular species in the world. There are large differences in the epiphytic biomass of forests worldwide ranging from 105-44 000 kg·hm^-2. The biomass of epiphytic material of forest canopies was greater than the leaf biomass of host trees in some old growth forests. Epiphytes have a tremendous leaf area index (LAI). Epiphytes play an important role in biodiversity, water and nutrient cycling in forest ecosystems, and are sensitive indicators of environment change, due to rich species, high biomass and special morphological traits and their position at the forest-atmosphere interface. The epiphyte community also provides a source of food and habitat for a variety of birds, mammals, amphibians, reptiles, and insects.