Plant communities and their environmental drivers on an arid mountain, Gebel Elba, Egypt

Abstract

Aims: Gebel Elba is an arid mountain range supporting biological diversity that is incomparable to any other region of Egypt. This mountain has a vegetation structure and floristic community similar to the highlands of East Africa and the southwestern Arabian Peninsula. We aimed to provide the first classification of the vegetation units on Gebel Elba and identify the environmental factors controlling their distribution. Study area: Wadi Yahmib and its tributaries, which drain the north-western slopes of Gebel Elba, south-eastern Egypt. Methods: On the basis of 169 relevés, we used TWINSPAN to classify the perennial vegetation. We calculated separate GAMs for the deciduous and evergreen species to describe the patterns for each leaf strategy type with elevation. We used CCA to quantify the relationship between the perennial vegetation and the studied environmental factors. To estimate diversity and our sampling strategy, we used rarefaction curves for species richness. Results: We identified seven communities along the elevational gradient of Wadi Yahmib and its tributaries. We found that each community was restricted to a confined habitat depending on its drought resistance ability. Deciduous Vachellia woodland was the main vegetation type on Gebel Elba, while evergreen Olea woodland appeared in small fragments at higher elevations. We analysed the distribution patterns of deciduous and evergreen trees along the elevational gradient. We found a turnover at 500 m, indicating a potential ecotone between the Vachellia and Olea woodlands that was occupied by a Ficus community. CCA revealed the importance of altitude and soil quality in determining the vegetation structure of Gebel Elba. The species richness increased with elevation as a result of reduced stress and increased water availability at the upper wadis. Conclusions: This study identified seven vegetation units in the study area and showed the importance of orographic precipitation, soil quality and the complex topography in determining the habitats. Taxonomic reference: Boulos (2009); names updated according to POWO (2019). Abbreviations: CCA = Canonical Correspondence Analysis; GAM = Generalized Additive Model; TWINSPANTWINSPAN = Two Way Indicator Species Analysis.

Vegetation classification goes open access

“…Zeballos et al (2020) classify dry subtropical forests in the Espinal province, Argentina, using vegetation plots, and call for their urgent conservation. Abutaha et al (2020) describe the plant communities and their environmental drivers on Gebel Elba, Egypt. Finally, Zervas et al (2020) present a phytosociological survey of aquatic vegetation in the main freshwater lakes of Greece.…”

Abundance, distribution, and growth characteristics of three keystone Vachellia trees in Gebel Elba National Park, south-eastern Egypt

“…tortilis) community was the main vegetation type on Gebel Elba. This community type occurred commonly in the water channels of wadis and gravel terraces from low to mid elevations (130-383 m), and the species was a member of all of the other six communities in the study area 17 . In addition, Vachellia tortilis subsp.…”

“…(Fabaceae: Mimosoideae 8 ), which are broadly distributed around the world, are considered keystone species within the communities they reside. For example, they are considered keystone species in parts of Australia 9 , Pakistan 10 , the Kalahari Desert, Botswana 11 , Tunisia [12][13][14] , the Sinai Desert, Egypt 15,16 , and south-eastern Egypt 16,17 . As pointed out by Abdallah et al 12 , isolated trees in arid habitats, including Vachellia species., have several characteristics that contribute to their keystone status: (1) shade from their canopies prevents extreme temperature fluctuations, increases soil moisture levels, and provides shelter for wildlife, (2) they improve soil conditions through biological nitrogen fixation and litter fall by increasing soil nitrogen content, organic carbon, and water-holding capacity, (3) they increase plant and animal biodiversity as a consequence of characteristics one and two, (4) they provide a source of food for wildlife, and (5) they provide a source of fuel, fodder, and medicines for local people and their domesticated animals.…”

“…An analysis of the plant communities of wadi Yahmib and three of its tributaries, on the north-western slopes of Gebel Elba, revealed the presence of seven plant communities, with these communities being arrayed across an elevational (environmental) gradient 17 . The Vachellia tortilis subsp.…”

“…Within arid and semi-arid ecosystems across north Africa and the Arabian Peninsula, plant ecologists have focused their attention on describing the vegetation of wadis that drain to the Red Sea, with these studies focusing on keystone Vachellia species [12][13][14][15][16][17]22,23 . The present study aimed to contribute to this body of knowledge by determining the distribution, abundance, and describing the growth characteristics of three Vachellia tree taxa in wadi Khoda and wadi Rahaba, in Gebel Elba National Park, south-eastern Egypt.…”