International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.5, 229-239 http://ecoevopublisher.com/index.php/ijmec 23 0 are young, and later grow aerial roots that droop into the soil, eventually becoming independent large trees. Such plants are sometimes called strangling plants, but in a broad sense, they can be regarded as a special epiphytic life form (Sundue and Maraia, 2024). In addition, nomadic vines and others are also associated with epiphytic habits and are regarded as "structural parasitism", but their ecological strategies are different. This study will review the ecological roles of epiphytes in forest ecosystems, with a focus on their roles in maintaining forest diversity and participating in the material and energy cycles. The specific content is to explore the diversity and distribution pattern of epiphytes, discuss the ecological adaptation of epiphytes in terms of morphology and physiology, investigate the interaction between epiphytes and host trees, and summarize the functions of epiphytes in the ecosystem. This study aims to deepen the understanding of the ecological roles of epiphytes, emphasize their significant contributions to the ecological functions of forests, and provide references for the protection of epiphytes in the context of global change. 2 The Diversity and Distribution Pattern of Epiphytes 2.1 Distribution characteristics in tropical, subtropical and temperate forests Epiphytic plants are distributed in forests of different climate zones, but there are significant differences in their abundance and community characteristics. Tropical forests, especially moist lowland rainforests and cloud forests, are the regions with the highest diversity of epiphytes. In the mountain cloud forests of the neotropical region (Central and South America), epiphytic plants often account for more than half of the local plant species. Studies have pointed out that the species richness of tropical epiphytes often peaks at medium altitudes, where high humidity and frequent clouds and mists occur throughout the year, providing favorable habitats (Suissa et al., 2021). In contrast, the richness of epiphytes in subtropical forests is relatively low, but it is still considerable in humid monsoon evergreen broad-leaved forests and other environments. The subtropical mountain forests in Taiwan, China, southern Japan, etc. are rich in epiphytic orchids and ferns, mostly concentrated in the forest areas with high altitude and high humidity (Figure 1) (Hsu et al., 2024). Due to the relatively dry and cold climate in temperate forests, there are fewer epiphytic vascular plants, but there are still a large number of epiphytic mosses and lichens. Temperate rainforests (such as those along the northwestern coast of North America) are a special case: winters there are mild and rainy, with abundant epiphytic mosses and lichens that can cover tree trunks and branches, forming a thick "green carpet", accompanied by a small number of epiphytic angiosperms (Werner and Homeier, 2024). 2.2 Classification of major epiphytic plant groups and their life forms Epiphytic plants can be classified according to systematic classification or ecological life form. In terms of systematic classification, epiphytes cover multiple categories. Among angiosperms, Orchidaceae and Bromeliaceae are particularly representative. In addition, Araceae and Piperaceae also have a considerable number of epiphytic species. Among ferns, the Dipterophyllaceae and Pteridaceae families contain a large number of epiphytic ferns. Among mosses and algae, hanging lichens and mosses are the main body of epiphytic communities in temperate forests (Ceballos et al., 2025). In terms of ecological life forms, epiphytes can be classified into holo-epiphytes and hemi-epiphytes. All epiphytic plants remain unconnected to the soil throughout their lives, such as most epiphytic orchids and bromeliads. Semi-epiphytic plants, such as the aforementioned strangled plants, are epiphytic in the early stage and attached to the soil later (Sundue and Maraia, 2024). There are also some epiphytes (facultative epiphytes), which are usually terrestrial but can also epiphyte in suitable conditions, such as some ferns that can grow on the ground and climb tree trunks. According to the location and morphology of epiphytes, they can be further classified into trunk epiphytes (large epiphytes at the base of the main trunk, such as staghorn ferns and epiphytic iron horn ferns, which often attach to the base of the main trunk) and crown epiphytes (small species that inhabit the end of the tree crown, such as many tiny orchids and bromeliaceae air plants). There are also morphological categories such as the hanging type
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