Geographical distribution and habitat characterization of Poa schizantha (Poaceae), a narrow endemic of the coastal sand dunes of the southern Pampas, Argentina

摘要

Poa schizantha is a dioecious, psammophilous grass endemic to Atlantic coastal dunes in Argentina. We quantified the distribution area of this rare endemic species and characterized its habitat in the southern Pampas region. Convex hull and alpha-hull methods were used to estimate and map its overall geographical range. Ecological characterization was based on location, environmental variables, floristic composition and vegetation cover. In total, 117 quadrats were sampled in spring. The convex hull (7553 ha) was split, after excluding discontinuities, into two polygons: area 1 (968 ha; a novel area for the species) and area 2 (449 ha) separated by 36 km, indicating two geographically distinct population groups. In active coastal dune fields, P. schizantha occurs mainly in interdune slacks, associated with herbaceous, short, grassland-type vegetation and moist sandy soils with low vegetation cover, suggesting high habitat specificity. Based on TWINSPAN classification and ordination analysis, P. schizantha is related to two main vegetation groups with 100% constancy and c. 30% relative importance: subgroups E (dominated by pioneer dune species) and F (associated with hygrophilous and ubiquitous species). Given the extent of occurrence (restricted to < 100 km(2)) and the severely fragmented habitat condition, we propose the species be categorized as Critically Endangered, following IUCN criteria. Actions aimed towards the survival of this species must prioritize population monitoring and conservation of its dune habitat.