The ‘salão’ vegetation of Southwestern Amazonia

This paper presents a first account of the salão vegetation of southwestern Amazonia, a frequent but poorly known formation and unusual in that it is a lowland moist tropical environment in which virtually all of the plant diversity is accounted for by herbs. The salões occur along canalized portions of the Purus and Juruá river basins, and their substrates consist of exposed parent materials that characterize much of this sector of Amazonia but are usually overlain by a relatively thin (<1 m) layer of soil. They are constantly moist seeps or ‘seepage banks,’ and the lower portions are seasonally submerged. Strata are recognizable in the vegetation, and the physiognomy and composition of each vegetation band of the salões is likely determined by the slope, the parent material, and (for lower bands) the duration of flooding. To date the salão flora has registered 66 species: 11 bryophytes, 12 ferns, and 43 angiosperms. Five of the bryophyte species, two ferns, and one grass, Arundinella berteroniana, are found in most if not all salões and can be considered indicators of this vegetation type, while most of the pteridophytes and other angiosperms occur more sporadically. None of the species is endemic to the formation and only four to the region; most are associated generally with the margins of rivers, lakes, and streams, often on rocky or sandy substrates. The floristic and conservation significance of this formation lie in its apparent affinities with montane regions, in the fact that 21 species and eight genera are recorded for the Acre flora only from the salões, and in its local value as a source of filtered potable water.