UNDERSTANDING DRIVERS OF VEGETATION CHANGE IN DHOFAR, OMAN: A BIODIVERSE DRYLAND ECOSYSTEM

Dryland ecosystems are highly sensitive to changes in climate, where small shifts in precipitation can cause degradation of the vegetation. Over 1/3 of the Earth’s population relies on these ecosystems for food and water resources; however, recent data is insufficiently brief to constrain how hydrological mechanisms influence plant communities. Here, we use rock hyrax middens as a paleoecological archive in the arid, biodiverse region of Dhofar, Oman. This study uses leaf wax biomarkers and bulk isotope data to constrain local ecological and hydrological changes over the mid-Holocene to present. Bulk δ¹³C and δ¹⁵N values can be measured on fecal pellets within the middens. Leaf wax n-alkanes can be extracted and isolated from the hyraceum matrix, from which n-alkane stable carbon (δ¹³C_wax) can be measured. Bulk δ¹³C and δ¹³C_wax provide a record of changes in the relative abundance of C3 and C4 vegetation. Bulk δ¹⁵N data indicate changes in local moisture availability, where decreasing values typically reflect increasing moisture. These complementary signals, in tandem with a previously established pollen record, can be used to develop a more complete picture of hydrologic change and vegetation response. The samples for this project include 22 fossil midden samples and four modern samples from Wadi Dhahabun spanning the last 4,000 years. The pollen record demonstrates an increase in herbaceous taxa beginning ~1.6 kyr BP. However, preliminary δ¹³C_wax and bulk δ¹³C data have no trends in their values through time. Bulk δ¹⁵N values seem to counterintuitively suggest increasing water availability but may in fact demonstrate a unimodal relationship with moisture in hyperarid conditions. These trends would suggest that aridification over this interval was the main driver of vegetation change over the last 4kyr in Dhofar, but that dry-adapted C4 plants were common even prior to this transition.