Dispersal traits in the hyper-arid hot desert of the United Arab Emirates

Abstract

Background and aims – This study describes the dispersal traits of 302 species in five Afro-Arabian habitats from the hyper-arid hot desert of United Arabian Emirates (UAE).Methods – Diaspore size (diaspora length) was studied in relation to growth forms, dispersal modes, presence of structures for long distance dispersal, APG IV groups, phytogeography and dispersal phenology using ANOVA and Pearson χ2 test-statistical analyses.Results – Small diaspores were predominant (six orders of magnitude from 10-4 to 102). The major diaspores were found in Fabids phylogenetic APG IV group (1.80±0.41 cm) mainly trees and the minor in Commelinids (0.30±0.08 cm). The most dominant dispersal mode was semachory (43.7% of the total and 67.5% of the herbaceous species), followed by anemo-meteochory (28.8%) and barochory (23.8%). Semachores/barochores (67.5%) formed the largest groups from the Fabaceae, Poaceae, Boraginaceae, Brassicaceae and Amaranthaceae families. Savanna trees such as Acacia, Prosopis, Ziziphus sp. and Indigofera sp. produced large diaspores secondarily dispersed by vertebrates. Anemo-meteochoric species with small diaspores were predominantly semi-shrubs such as Haloxylon sp. Graminoids such as Stipa sp. and Stipagrostis sp., without structures for long-distance dispersal had diaspore appendages acted as “active drills” in soil cracks. Dryness (dry season) favours the efficient dispersion by the wind for the small shrub species with haired capsule (e.g. Aerva javanica), winged calyx (e.g. Astragalus squarrosus) or wings (e.g. Tribulus qatarensis). Most of the species studied (64.2%) dispersed in the dry season according to what was found in other arid region from the world. The longer dispersal phenology corresponded to Saharo-Arabian and Sudano-Decanian species which is related to the floristic richness of the study area. Species dispersal throughout the year indicates an important seed resource e.g. barochoric species with fleshy fruits or pods with nutrient structures (e.g. Senna italica and Indigofera sp.).Conclusions – In the hyper-arid hot desert of UAE, the dispersal spectra are close to those recorded in other arid environments but with particularities due to the presence of African floristic elements.