Edaphic distribution of some species of the fern genus Adiantum in western Amazonia

The distribution patterns of Adiantum species were inventoried at twelve noninundated rain Forest (tierra firme) sites in Amazonian Peru and Ecuador. Six species belonging to the genus were found, and four of these were abundant at some of the sites. At six of the sites none of the species was particularly abundant. Both the occurrence and the abundance of the species varied among sires with regard to soil texture and concentration of exchangeable bases and within sites with regard to topography. Adiantum tomentosum Klotzsch was restricted to loamy soils with intermediate to low content of extractable bases and was locally most abundant in the well drained parts of slopes and ridge tops. Adiantum terminatum Kunze ex Miq. and A. humile Kunze occurred at sites with intermediate to high content of extractable bases, but their relative abundances differed among and within sires, Adiantum pulverulentum L. was restricted to soils with relatively high base concentration. Ecological differences among the species obviously explained many of the differences in their distribution patterns at the local and regional scales, and may be important for the understanding of such patterns at biogeographical scales as well.