Abstract
Large trees have survived for a long time, and their complex crown structure serves as habitat for epiphytic plants. Canopy plants are not as well studied in the temperate zones as in the tropics, because many of them are accidental epiphytes, epiphytic individuals of normally terrestrial species. We hypothesized that the canopy can serve as a refuge for terrestrial species that have difficulty establishing on the ground (e.g., insufficient light, over-browsing), promoting and conserving forest species diversity. Terrestrial species may also vary in their ability to adapt to canopy growth conditions. Here, we investigated canopy vascular plants hosted on a large Cercidiphyllum japonicum tree in a temperate old-growth forest, Japan. The canopy plant community was diverse with 39 vascular plant species, including 31 accidental epiphytes and six threatened, obligate epiphytes. High numbers of canopy plant species, including most accidental epiphytes, were found where multiple, large reiterated trunks as well as on large horizontal branches. Canopy plants leaves exhibited higher water use efficiency and higher nitrogen concentration compared to plants on the ground, but were controlled by transpirational water loss rather than by investing in leaf nitrogen with increasing height. We found at least 14 species could escape over-browsing by establishing in the canopy and may function as seed-sources for future re-colonization on the ground. Our results show one large tree crown can be defined as a local hotspot for current and future plant species diversity in a temperate old-growth forest, reinforcing its ecological value for conservation purposes.
One large tree crown can be defined as a local hotspot for plant species diversity in a forest ecosystem: a case study in temperate old-growth forest
