Patterns in the diversity and distribution of epiphytes and vines in a New Zealand forest
Abstract Plants that rely on other plants for support (i.e. epiphytes and vines) are common in many forest ecosystems. However, they are poorly understood relative to terrestrial plants, especially in the Southern Hemisphere. To help bridge this gap, we evaluated the diversity and distribution of vascular epiphytes and vines on seven common tree species in a conifer-broadleaf forest on New Zealand's North Island. Ground-based surveys of 274 host trees were used to test whether epiphyte and vine diversity increased with tree diameter, and whether diversity-diameter relationships differed among host tree species. Occurrence patterns of individual epiphyte and vine species were also assessed. We first evaluated the accuracy of ground-based inventories by comparing surveys of trees made from the ground to those made from a canopy walkway. On average, 1 in 10 species of epiphytes and vines were unseen from the ground. However, sampling accuracy did not differ among the three host tree species growing along the walkway, suggesting unbiased comparisons could be made between hosts. Results from ground-based surveys showed that species diversity of epiphytes and vines increased with host tree diameter. However, epiphytes showed stronger diversity-diameter relationships than vines. Epiphyte diversity increased markedly in four host species and less strongly in the remaining three host species. Conversely, vines showed weak diversity-diameter relationships in all host species. Occurrence patterns of individual species helped to explain diversity-diameter relationships. All common epiphyte species occurred more frequently on large trees, regardless of host species, but occurrence patterns in most vine species were unrelated to tree size. Rather, the vines often showed strong host 'preferences'. Overall results illustrate a rich diversity of distributional patterns in New Zealand's epiphytes and vines, and suggest that a similarly diverse set of ecological and evolutionary processes are responsible for them.