DESERT PLANT-COMMUNITIES IN HUMAN-MADE PATCHES - IMPLICATIONS FOR MANAGEMENT

We measured productivity and diversity of annual plant communities in human-made pits and mounds (20 x 30 x 100 cm) in the Northern Negev of Israel. We differentiated the species according to propagule size, dispersal mode, and geographical distribution in Israel. Our results in 28 experimental units containing a pit, a mound, and a portion of the undisturbed surrounding ''matrix'' showed that species richness, total plant density, and biomass yield were higher in the pits and mounds than in the matrix. Soil moisture at 0-15 cm depth was higher in the pits, but lower in the mounds relative to the matrix. Species with larger propagules (> 5 mm) became more abundant, and those with tiny seeds (< 1 mm) became less abundant, in the human-made patches relative to the undisturbed matrix. Wind-dispersed species and those with secondary dispersal by runoff were denser in pits and mounds, while short-distance rain dispersers were more abundant in the matrix. ''Edge'' species, occurring in the study site at the edge of their geographical distribution in Israel, increased more in density, species richness, and biomass than general ''core'' species, for which the study site is in the center of their distribution. The annual plant community responded to changes in three environmental factors: (1) microtopographic structure from flat surface to mounds or pits, which function as traps for seeds; (2) soil surface texture from densely packed to loose soil in pits and mounds, which provide suitable sites for larger propagules; (3) soil moisture availability, increasing in the pits but decreasing in the mounds relative to the matrix. The relevance of the study was discussed in relation to (1) combating desertification, (2) sustainable arid land use, and (3) species conservation.