Floristic diversity and vegetation structure of Al-Dissah area northwestern Saudi Arabia

Abstract

This study was conducted on wadi Al-Dissah; a part of Jabal Qaraqir and its surrounding area in the Northwestern region of Saudi Arabia. Jabal Qaraqir in Saudi Arabia is the first site to be assessed for the Important Plant Area (IPA) programme in the Arabian Peninsula. This paper has the objective of determining the floristic composition, species diversity and the vegetation structure of the plant communities, including a breakdown of its different life forms and chorology of the recorded species. A total of 63 species belonging to 61 genera and 31 families were recorded. One family; Adiantaceae belongs to Pteridophyta, while the other 30 families are angiospermae. About 35% of the recorded species in the study area are belonging to four families: Asteraceae and Poaceae had the highest contribution (each had 9.5% of the total species followed by Boraginaceae and Fabaceae (7.9% each). The data also reflect the high taxonomic diversity in the study area. The life form spectrum of the recorded species showed the prevalence of theorphytes (49.2%) followed by chamaephytes (17.5%), phanerphytes (14.3%), geophytes (9.5%), while the least frequent life form class was hemicryptophytes (7.9%). The chorological analysis of the recorded species in the study area showed the predominance of biregional taxa (50.8%) over the other phytogeographical elements followed by the monoregional (25.4%). The present study findings showed that most species belonged to Saharo-Arabian – Sudanian (15.9%) followed by Sudanian elements (11.1%). Only one endemic species is recorded in the study area; Dolichorhynchus arabicus I.C.Hedge & KitTan (syn Douepea arabica). It is a rare threatened endemic plant species in Saudi Arabia. It was locally in Wadi Qaraqir. Other rare species were Ficus palmata which is a small tree with edible fruits, belonging to family Moraceae, and Parietaria umbricola which is an annual species belonging to family Urticaceae. Plant species of Al-Dissah area were checked with international IUCN list. Eight of the recorded species in the study area are globally threatened and incorporated into the IUCN Red List of Threatened Species Version 3.1: Cyperus laevigatus, Mentha longifolia, Nerium oleander, Phragmites australis, Tamarix nilotica, Typha domingensis, Chrozophora tinctoria, Adiantum capillus-veneris. All of them are included in the least concern category. Five plant communities were recognized in the study area. The highest plant diversity was reported in plant communities which occupy the wet wadi bed where the perennial stream flows together with the nearby areas between palm trees; Phragmites australis and Mentha longifolia communities. As floristic analyses are the prerequisites for conservation of plant species, therefore, it is critical to examine the current status of floristic and species diversity to provide appropriate guidelines for developing effective system of conservation and management. Information from this study may provide a valuable reference for appropriate conservation and management of the study area.