THE RESPONSE OF 2 WOODY SPECIES TO THE CONDITIONS CREATED BY A SHIFTING ECOTONE IN AN ARID ECOSYSTEM

Vegetation stripes alternating with bare areas appear in some arid lands as a consequence of the redistribution of rainwater by sheet flow. The borders between stripes and bare areas are ecotones (one up-slope and one down-slope of each arc) between a very open scrub and a densely vegetated patch. For Prosopis glandulosa and Flourensia cernua, the distribution of seedlings and adults was recorded in transect belt perpendicular to the stripes. Seedlings of both species established in the up-slope ecotone, F. cernua almost exclusively and P. glandulosa with a marked preference. No seedlings of F. cernua were recorded >5 m away from the nearest adult whereas seedlings of P. glandulosa were recorded >30 m away from the nearest adult. Prosopis glandulosa was present in all the arcs and in the bare areas between arcs, whereas F. cernua was absent in the bare areas and in some of the arcs. Differences in cover values were found between zones and species but not between arcs. -from Authors