Ecological distribution of terrestrial orchids in a south Brazilian Atlantic region

Terrestrial orchids comprise a taxonomically and ecologically varied group, ranging from tropical to subpolar regions and from wet marshy to dry sand‐dune environments. An ecological survey of these plants was performed in a natural region of Rio Grande do Sul, south Brazil, namely the northern coastal plain, between the abrupt slopes of the Serra Geral and the coastal line of the Atlantic Ocean (29°01′S to 30°00′S, 49°43′W to 50°16′W). The study area presents a humid subtropical climate of the Cfa type. Mean annual temperature and precipitation range from 17.5 to 20.0°C and from 1200 to 1700 mm, respectively. The occurrence of indigenous terrestrial orchid species was recorded for six major habitats or vegetation types: bogs and marshes, peat forests, rain forests, dune forests, Butia ‐palm stands and coastal sand‐dunes. The ecological range was defined for 39 species belonging to 23 genera, based on literature, herbarium revisions and extensive collecting along the studied area. Species richness ranged from nine species, in both coastal dunes and palm‐groves, to 17 species in peat forests. A negative correlation was observed between species richness and ecological range, showing a general tendency for terrestrial orchids to be confined to one or a few habitats. Multivariate analyses indicated light (herbaceous vs woody vegetation) as a primary ecological factor, and soil drainage (sandy vs peaty substrates) as a secondary factor controlling terrestrial orchid distribution.