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

Abstract

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.

Quaternary Vegetation Dynamics – The African Pollen Database

“…Hearths and settlement excavations from southern Oman and Yemen attest to wood harvesting, particularly taxa known for use as fodder, construction materials, or cooking fuel including Acacia, Terminalia, and Ziziphus. This evidence of fire and landscape modification is also visible in pollen and macrobotanical remains preserved in hyrax middens near archeological sites in Yemen (McCorriston et al 2002;Ivory et al, 2021). Further, following the initial decline in monsoon moisture around 6 ka, construction of simple check dams and irrigation features is observed along wadis in Oman and Yemen (Harrower 2008).…”

“…For example, in Wadi Sana, in the modern stony desert, occasional trees such as Maerua and Acacia are observed. In the mid-Holocene, in addition to higher pollen abundances of these common modern arboreal taxa, higher abundances of trees with tropical affinities only were found at the southernmost coast, such as Terminalia, Olea, and Dodonea viscosa were also an important part of the arboreal community (McCorriston et al 2002;Ivory et al, 2021). However, it is important to note, that as discussed above, much of southern as well as northern Arabia remained arid or semi-arid even at the peak in the monsoon, thus we suggest that these changes in vegetation composition are likely linked to the presence of increased surface water amidst persistent climatic aridity.…”

Vegetation dynamics in Dhofar, Oman, from the Late Holocene to present inferred from rock hyrax middens

“…Plant matter consumed by the hyraxes also passes through their digestive systems and is preserved in their dung (Scott et al, 2004;Scott and Woodborne, 2007;Gil-Romera et al, 2010;Chase et al, 2012). Stable carbon isotope analyses of fecal pellets and hyraceum reflect the input of C 3 and C 4 vegetation, and nitrogen isotope studies can reveal changes in relative moisture (Chase et al, 2012;Ivory et al, 2021). Middens can differ in thickness and the amount of hyraceum versus fecal pellets, and thus can have varying degrees of dietary bias and represent disparate temporal scales (Scott and Cooremans, 1992;Scott et al, 2004;Gil-Romera et al, 2006;Scott and Woodborne, 2007;Chase et al, 2009Chase et al, , 2012.…”

“…The temporal resolution of the Qunf Cave speleothem record was much higher than that of the middens, which were temporally averaged (Fleitmann et al, 2004(Fleitmann et al, , 2007Ivory et al, 2021). To help account for this, the 1σ range (68.3% probability) of the calibrated ages for the midden samples was used determine an age range over which to average the δ 18 O data from the speleothem record.…”

“…However, due to desiccation of most inland lakes by ~7 ka, evidence of vegetation change from sedimentary deposits in these areas after this time does not exist (Lézine et al, 2007). Pollen preserved in hyrax middens provides later records that suggest a semiarid woodland with tropical trees such as Terminalia at 5 ka at Wadi Sana, Yemen (Ivory et al, 2021). Little information exists about vegetation changes farther inland in Dhofar as aridification intensified from the mid-Holocene to the present.…”