Vegetation-climate interactions in Dhofar, Oman from the mid-Holocene to present

Abstract:

Dhofar, Oman is a unique region that while arid is highly biodiverse, and arid regions such as this are especially at risk from climate and land use change. These drivers of environmental change are poorly understood, however the paleoecological record can offer a critical perspective. Rock hyrax (Procavia capensis) middens host a variety of paleoenvironmental indicators and preserve fossil pollen. Pollen grains are diagnostic of a plant taxon and identifying the types of pollen present as a midden was deposited allows for the reconstruction of ancient plant communities. Discrete samples of different ages, from the same area, can be assessed for changes in the vegetation community through time. Here I present pollen data of 24 samples from Wadi Dhahabun, located in the Dhofar Nejd (desert), that have radiocarbon dates spanning the last 3500 years. Although today the geographical extent of monsoonal rainfall is limited to the coastal plain and escarpment regions, the Dhofar region was characterized by moister conditions during the mid-Holocene, when a stronger Indian monsoon extended further inland. Through time the monsoon weakened, and the Nejd became more arid. The pollen data from the midden samples reveal Terminalia (formerly Anogeissus), which now resides on the escarpment within monsoonal cloud forests, existed in the desert region during the mid-Holocene until approximately 150 years ago. A turnover in arboreal taxa occurs in this time frame: Ficus and members of the Combretaceae family decrease from 3500 BP to present, while Ziziphus and Acacia begin to increase in abundance beginning around 1600 BP. These trees dominate the landscape today. Herbaceous taxa such as grass (Poaceae), Heliotropium and Kohautia, also increase in abundance from 1600 BP to present. The turnover in arboreal taxa coupled with the overall decline in trees and increase in herbs indicates a change in vegetation composition forced by the weakening Indian monsoon. Studying past climate-vegetation dynamics in Dhofar, especially under increasing aridity, can lend itself to our understanding of how this region may respond to projected climate conditions due to anthropogenic warming.