Biodiversity and interslope divergence of vascular plants caused by sharp microclimatic differences at "Evolution Canyon II", Lower Nahal Keziv, Upper Galilee, Israel

Species diversity of plants was recorded in 1999-2000 at seven stations of a microsite in Nahal Keziv, western Upper Galilee, designated as "Evolution Canyon II", and compared with that of "Evolution Canyon I", Lower Nahal Oren, Mount Carmel, situated 38 km southwest of Nahal Keziv. Higher solar radiation on the south-facing slope (SFS) causes warm, xeric garrigue and dry Mediterranean "savannoid" plant formation habitats, versus cool, mesic, dense "south-European" forest on the north-facing slope (NFS). Riverine and segetal plant communities are limited to the valley bottom (VB). In an area of 7000 m², we recorded 283 vascular plant species belonging to 200 genera and 56 families. Plant cover varied between 70%-90% (SFS) and 100% (NFS). Annuals are the predominant life form (54.7%). SFS and NFS vary in species composition, sharing only 11.6% of species. Phytogeographical types vary among the three habitats. Inter- and intraslope species composition varies remarkably due to differential microclimatic conditions, demonstrating the effect of climate on species diversity at a microscale. A comparison with Evolution Canyon I shows differences in the flora caused by the changing climate conditions, due to the more northerly location. The differences include: a change from Quercus calliprinos plant community on the NFS of Evolution Canyon I to Acer obtusifolium ssp. syriacus and Laurus nobilis plant communities on the NFS of Evolution Canyon II. Likewise, a significantly different species distribution was found between the slopes of both canyons.