Human landscape modification and expansion of tropical woodland in southern Arabia during the mid-Holocene from rock hyrax middens

Aim: Dryland ecosystems, such as those in southern Arabia, are particularly vulnerable to climate and land-use change. Aridification and human subsistence changes at the end of the Holocene Humid Period at 6–4 ka have been used as an iconic example for evaluating such impacts to resilience of arid systems. Although records of ancient environments can provide critical insight into the biotic and abiotic mechanisms that alter ecosystems, traditional archives, such as lake deposits, are not common in southern Arabia after 6 ka; thus, we must use alternative archives. Location: Yemen. Taxon: Plants; Rock Hyrax (Procavia capensis). Methods: We use fossil pollen and stable isotopes (δ¹⁵N; δ¹³C) of rock hyrax (P. capensis) middens from Wadi Sana, Yemen, to look at changes in ecosystem structure and function across this key transition from 6 ka to the present. A total of 17 middens were radiocarbon-dated and stable isotopes were measured. Of these, pollen was extracted from hyraceum of 14 middens and identified using a light microscope. Fossil pollen assemblages were then compared to existing modern pollen samples from throughout Arabia. Results: During the mid-Holocene from at least 6 to 4.7 ka, the pollen flora reflects a landscape with abundant tropical trees. These included foundational woody taxa, such as Terminalia and Boswellia sacra (frankincense), which had a strong positive influence on local hydrology and the economy, respectively. Increased charcoal abundances also suggest that wildfire occurred periodically. Main conclusions: Connections with archaeological evidence suggest a strong link between human management and the presence of Terminalia woodland during the mid-Holocene. These may have promoted increased groundwater storage and ponding as regional rainfall was decreasing. The mid-Holocene expansion of Boswellia sacra (frankincense) may have helped support resin trade that became a critical export from the region. Fires were more common than today, suggesting semi-arid but continuous vegetation cover across what is now bare ground. Finally, after 1 ka, increased sedge abundances at the expense of grasses and trees suggest the development of desert conditions.