Ecotone Dependent Recruitment of a Desert Shrub, Flourensia cernua, in Vegetation Stripes

Abstract

In tropical semi-arid areas, a local concentration of water on sheet wash surfaces allows the persistence of densely vegetated stripes parallel to the contour lines, alternating with almost bare soil stripes. The boundaries of the vegetated stripes are, upslope, a colonization ecotone, and, downslope, a regressive ecotone, thus inducing a slow upwards displacement. This formation, recently described in the Chihuahuan Desert (Mexico), is known from Africa and Australia. Flourensia cernua is a dominant shrub species of the stripes whose distribution suggests that its population dynamics is strongly dependent on the upslope ecotone. The spatial restrictions to recruitment were determined analyzing the location of seedlings, young individuals and adults, and the grass cover (Hilaria mutica), in 10 two-meter-wide belts perpendicular to 5 stripes (...)