Vegetation patterns, plant distribution and life forms across the alpine zone in southern Tierra del Fuego, Argentina

The alpine zone is examined at meso- and microscales in southern Tierra del Fuego (54 degrees 49'S), where the full zone is expressed. Mesoscale patte rns were studied on opposing aspects, and microscale patterns were studied on a series of solifluction terraces, in a hanging valley overlooking the B eagle Channel. Plant cover and life form data were collected within 50-m al titudinal bands on north and south aspects and comprehensive plant lists we re compiled for each band. Topography and associated surface cover were rec orded on the terraces. Six alpine plant communities, in lower and upper flo ristic zones, were differentiated with multivariate analyses and significan tly related to five ecological factors. Equivalent communities were separat ed by approximately 185 m altitude on opposing aspects, which related to a soil temperature difference of approximately 3.0 degreesC. The richness (an d range) of 80 local vascular taxa (18.6% of the regional flora), decreased with increasing altitude (6.6 per 100 m); however, richness differed signi ficantly with aspect (north: 5.6, south: 7.5). Upper altitudinal limits (ap proximately 1250 m a.s.l.), were associated with a midsummer isotherm of ap proximately 1.7 degreesC. Chamaephytes and hemicryptophytes dominated throu ghout but the tall tussock form was conspicuously absent. Reasons for this are discussed in the context of the Nothofagus treeline, which conformed to a midsummer isotherm of only approximately 6.0 degreesC. Such patterns are at variance with those found in the oceanic subantarctic islands, other oc eanic perhumid temperate mountain regions and tropical high mountains. Howe ver, the microscale pattern of fines, pebbles, stones and rock across the a ctive solifluction terraces, with dense vegetation on their steep risers, h ad a clear affinity with that of other subantarctic regions. Inferences tha t alpine systems of the Southern Hemisphere are necessarily equivalent to t hose at similar northern latitudes are cautioned against. Likewise, such co mparisons within the Southern Hemisphere may also be invalid.