Host-tree Selection by an Epiphytic Orchid, Epidendrum magnoliae Muhl. (Green Fly Orchid), in an Inland Hardwood Hammock in Georgia

We characterized the tree community of a mesic hardwood hammock in south-central Georgia as an oak-pine-hickory forest, with Liquidambar styraciflua (Sweetgum), , Magnolia grandiflora (Southern Magnolia), and Ilex opaca Ait. (American Holly) as subdominants. We surveyed this forest for colonies of the most northerly distributed epiphytic Orchid in the Western Hemisphere, Epidendrum magnoliae (Green Fly Orchid), and recorded the species and trunk diameter of 112 host trees (phorophytes) as well as the height and size of each Orchid colony. We calculated a selectivity index (SI) to compare phorophyte frequency with availability, based on a point-transect survey. Green Fly Orchid Occurred on 8 species of hardwood trees, but had a strong preference for Southern Magnolia as a host and a moderately strong preference for Quercus virginiana (Live Oak). Host trees were Much larger (presumably older) than the average of available trees, and that effect was strongest for the most preferred host. Orchid colonies also occupied significantly greater areas on individual Southern Magnolia than on other phorophytes. It is likely that old-growth Southern Magnolia and Live Oak trees are critical to the viability of this population of Green Fly Orchid, which is rare in inland forests in Georgia. In addition to being the most persistent epiphyte substrates in this environment, their broadleaf evergreen canopies-which would be especially true Of Southern Magnolia - may provide the most favorable microclimates in terms of shade, humidity, and frost protection.