Islands in the desert: environmental distribution modelling of endemic flora reveals the extent of Pleistocene tropical relict vegetation in southern Arabia

Abstract

Background and Aims Southern Arabia is a global biodiversity hotspot with a high proportion of endemic desert-adapted plants. Here we examine evidence for a Pleistocene climate refugium in the southern Central Desert of Oman, and its role in driving biogeographical patterns of endemism. Methods Distribution data for seven narrow-range endemic plants were collected systematically across 195 quadrats, together with incidental and historic records. Important environmental variables relevant to arid coastal areas, including night-time fog and cloud cover, were developed for the study area. Environmental niche models using presence/absence data were built and tuned for each species, and spatial overlap was examined. Key Results A region of the Jiddat Al Arkad reported independent high model suitability for all species. Examination of environmental data across southern Oman indicates that the Jiddat Al Arkad displays a regionally unique climate with higher intra-annual stability, due in part to the influence of the southern monsoon. Despite this, the relative importance of environmental variables was highly differentiated among species, suggesting that characteristic variables such as coastal fog are not major cross-species predictors at this scale. Conclusions The co-occurrence of a high number of endemic study species within a narrow monsoon-influenced region is indicative of a refugium with low climate change velocity. Combined with climate analysis, our findings provide strong evidence for a southern Arabian Pleistocene refugium in Oman’s Central Desert. We suggest that this refugium has acted as an isolated temperate and mesic island in the desert, resulting in the evolution of these narrow-range endemic flora. Based on the composition of species, this system may represent the northernmost remnant of a continuous belt of mesic vegetation formerly ranging from Africa to Asia, with close links to the flora of East Africa. This has significant implications for future conservation of endemic plants in an arid biodiversity hotspot.

Interplay between topography, fog and vegetation in the central South Arabian mountains revealed using a novel Landsat fog detection technique

“…Another more recent method uses spectral, spatial and microphysical properties of fog from Meteosat 8 data (Cermak and Bendix 2008). These methods have been used to describe fog-vegetation relationships, such as in Oman's central desert (Borrell et al 2019) and elsewhere (Cereceda et al 2008;Cermak 2012;Obregon et al 2014;Lehnert et al 2018). However, one drawback of these methods is that fog distributions are mapped at a low resolution, of no less than 1.1 km (AVHRR imagery).…”

Distribution, reproductive potential and conservation assessment of the rare and endemic Dionysia mira in the Hajar Mountains, Sultanate of Oman

“…Here we combine separate, unpublished studies conducted by researchers from the City University of Applied Sciences, Bremen, Germany (2005), Sultan Qaboos University, Oman (2006), Patzelt (2004) and Oman Botanic Garden (2017-2019.…”

“…The vegetation of the northern mountains has strong affinities with the Irano-Turanian flora of central and southern Iran, in particular the Zagros Mountains and suggests a Pleistocene migration of Irano-Turanian elements into Arabia. Refugia for moisture-demanding vegetation in southern Arabia were provided during the late Tertiary and early Quaternary by a strong enhancement of the seasonal Indian Ocean monsoon (Mandaville 1984, Jolly et al 2009); central Oman experienced similar mesic conditions during the Pleistocene (Borrell et al 2019); the mountains of northern Oman thus had a moister climate. During the Pleistocene period low sea-levels resulted in the drying up of much of the Arabian Gulf allowing floristic elements from Iran and SW Pakistan to migrate into Arabia.…”