Biodiversity and interslope divergence of vascular plants caused by microclimatic differences at "Evolution Canyon", Lower Nahal Oren, Mount Carmel, Israel

Species diversity of plants was recorded in 1992 and 1993 at seven stations of the "Evolution Canyon" microsite. Higher solar radiation on the South-Facing Slope (SFS) causes warm, xeric savannoid formation versus temperate, cool, mesic, dense maquis on the North-Facing Slope (NFS), and riverine, segetal plant formations on the Valley Bottom (VB). In an area of 7000 m(2), we recorded 320 vascular plant species in 217 genera and 59 families. Plant cover varied from 35% (SFS) to 150% (NFS). Annuals predominated among all life forms (61.3% of all species). SFS and NFS varied in species content, sharing only 31-48% of species. Phytogeographical types varied among the two slopes and valley bottom. Inter- and intraslope species composition varied drastically due to differential microclimatic stresses, thereby demonstrating at a microscale natural selection in action.