Aspects of the Ecology of Vascular Epiphytes in Colombian Cloud Forests, I. The Distribution of the Epiphytic Flora

Abstract

The diversity and abundance of vascular epiphytes is greater in the neotropics than in other tropical regions. Previous observations indicate that this difference is partially due to the presence of large areas of montane cloud forest in the neotropics. In this study the distribution of epiphytes was compared in two montane regions, the Sierra Nevada de Santa Marta and the Serrania de Macuira, both situated in northeastern Colombia. Our evidence shows, other factors being favorable, that the greatest abundance and diversity of vascular epiphytes are found in those montane regions where periods of cloud cover are most frequent, regular, and prolonged. Amount of rainfall is of little consequence to cloud-forest epiphytes; the greatest abundance of vascular epiphytes was found on the Serrania de Macuira, which experiences daily 14hour periods of cloud cover and negligible rainfall for 10 months of the year. La diversidad y abundancia de epifitas vasculares es mayor en los neotropicos que en otras regiones tropicales. Previas observaciones indican que esto es parcialmente debido a la presencia de grandes 'areas de bosques nublados montafiosos en los neotropicos. En este estudio, la distribucion de epifitas fue comparada en dos regiones montaniosas: la Sierra Nevada de Santa Marta y la Serrania de Macuira, situadas en el noreste de Colombia. Nuestra evidencia muestra, que dados otros factores favorables, la gran abundancia y diversidad de epifitas vasculares son encontradas en aquellas regiones montafiosas donde los periodos nublados son mas frecuentes, regulares, y prolongados. Ios niveles de Iluvia son de pequena consecuencia para las epifitas de bosques nublados; la mayor abundancia de epifitas vasculares fue encontrada en la Serrania de Macuira, la cual tiene diariamente un periodo de 14 horas nubladas, y lluvias insignificantes por 10 meses del aiio. THE RICHEST POPULATIONS of vascular epiphytes are found in the neotropical regions (Richards 1952), where Madison (1977) estimates that 15510 species have been recorded as epiphytes compared with 12560 species from the entire palaeotropics. Despite this numerical asymmetry, most of our knowledge concerning the ecology of vascular epiphytes has come from the palaeotropics. Detailed studies have been performed in both lowland and submontane forests in Micronesia (Hosokawa 1955), Asia (Went 1940), Nigeria (Sanford 1968, 1969), and Liberia (Johansson 1974 with a detailed bibliography). Other studies in Sarawak (Richards 1936), Nigeria (Richards 1939), the Australian subtropics (Burges and Johnston 1953), and elsewhere in the Old World (see Johansson 1974) have only briefly considered epiphytes as a component of a general vegetational analysis. Although the work of Schimper (1888) remains the most detailed ecological study of neotropical epiphytes, several important contributions have been made more recently (Davis and Richards 1933, Richards 1952, Grubb et al. 1963, Howard 1968). The results of a comparison of lowland (380 m) and montane (1780 m) forest in Ecuador (Grubb et al. 1963) support Richards' (1952) contention that montane habitats are more favorable for epiphytes than are lowland habitats. They found that the population density at 1780 m was nearly ten times higher than at 380 m and that species diversity was I 6 times greater. This result is, however, in direct contrast to the situation found by Johansson (1974) in Liberia, where the species diversity was greater at 500-700 m than at 1000-1300 m on Mt.