Andean rolling mosses gather on stone pavements: Geoecology of Grimmia longirostris Hook. in a high periglacial paramo

摘要

Rolling mosses of Grimmia longirostris Hook. were studied in Paramo Piedras Blancas, a high Andean area in Venezuela, using a geoecological research framework focused on interactions between geomorphic, ecological, and soil processes. Spatial patterns of mosses were analyzed downslope from granitic outcrops on three slopes at 4445-4480 m elevation. Fragments from epilithic mosses on the apex outcrops were the source of other mosses. Distance of moss transport below rocks was measured at all sites; mosses on the gentlest (<= 4 degrees), 34 m-long, slope were censused along a belt transect on 17 contiguous quadrats; density of moss growth forms, stone size, percent of bare-soil cover, and surface soil properties were determined. Surface clast morphology and profile characteristics of a periglacial stone pavement at the slope base were also examined. Mosses on this site included four growth forms: epilithic mosses on outcrops; mobile, rolling moss balls; epilithic mosses on loose clasts; and unattached elongated mosses. Moss balls (density: <= 0.87 mosses/m(2)) lay on upper-transect plots over bare soils (<= 92% cover) disturbed by needle ice. Soils here contained similar to 43-51% fine grains (<= 0.063 mm) and 2.9-5.9% organic matter; this made them exceptionally prone to ice segregation and needle-ice formation. Lower-transect plots showed 78-100% stone cover-cobbles and blocks but little exposed soil; mosses attached to loose clasts were exceedingly abundant (<= 31/m(2)) on this section. Unattached elongated mosses, often resting along boundaries between adjacent stones, were also common (<= 5.5/m(2)). The basal stone pavement showed a shallow (<= 7 cm) rock veneer over a 24 cm-thick profile with exceptionally fine soil-up to 83.2% fine grains, <= 8. 6% organic matter.