Ecological distribution of terrestrial orchids in a south Brazilian Atlantic region

Abstract

F. S. Rocha (rocha1403@yahoo.com.br), Programa de Po´s-Graduac ¸a˜o em Botaˆnica, Univ. Federal do Rio Grande do Sul, Av. Bento Goncalves9500, BR ˆ91.501-970, Porto Alegre, RS, Brasil. J. L. Waechter, Depto de Botanica, Univ. Federal do Rio Grande do Sul, Av. BentoGonc¸alves 9500, BR 91.501-970, Porto Alegre, RS, Brasil.Terrestrial orchids comprise a taxonomically and ecologically varied group, ranging from tropical to subpolar regions andfrom wet marshy to dry sand-dune environments. An ecological survey of these plants was performed in a natural regionof Rio Grande do Sul, south Brazil, namely the northern coastal plain, between the abrupt slopes of the Serra Geral andthe coastal line of the Atlantic Ocean (29801?Sto30800?S, 49843?Wto50816?W). The study area presents a humidsubtropical climate of the Cfa type. Mean annual temperature and precipitation range from 17.5 to 20.08C and from1200 to 1700 mm, respectively. The occurrence of indigenous terrestrial orchid species was recorded for six majorhabitats 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 revisionsand 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 indicatedlight (herbaceous vs woody vegetation) as a primary ecological factor, and soil drainage (sandy vs peaty substrates) as asecondary factor controlling terrestrial orchid distribution.