C04_P06

AMS radiocarbon investigation of the African baobabs from the semi-arid cloud forest of Wadi Hinna, Dhofar, Oman

Patrut A^1,2, Molnar M³, Patrut R¹, Rakosy L⁴, Brown J⁵, Varga T⁶, Ratiu I^1,2

¹Babes-Bolyai University, Faculty of Chemistry and Chemical Engineering, Cluj-Napoca, Romania, ²Babes-Bolyai University, Raluca Ripan Institute for Research in Chemistry, Cluj-Napoca, Romania, ³Interact Centre,Institute for Nuclear Research, Debrecen, Hungary, ⁴Babes-Bolyai University, Faculty of Biology and Geology, , Cluj-Napoca, Romania, ⁵Qatar University, College of Arts and Sciences, Doha, Qatar, ⁶University of Debrecen, Doctoral School of Physics, , Debrecen, Hungary

Wadi Hinna is a small semi-arid valley (3 km2) at the edge of the Dhofar Mountains (17º03' N, 54º36' E, altitude 300-360 m) and at 20 km from the coastal plain, in southern Oman. Wadi Hinna hosts a unique water-limited cloud forest of African baobabs (Adansonia digitata).

The precipitation (annual rainfall 130 mm) falls during the rainy season (mid-June to mid-September), when moist air from the Indian Ocean, i.e., the southwest monsoon, encounters the mountains, leading to clouds and dense fog. The rainfall is significantly supplemented by horizontal precipitation, namely cloud water interception within the canopy of trees.

Over 120 baobabs grow on a slope among huge stones of sedimentary rocks. We dated by AMS radiocarbon wood samples from the largest baobabs. We found that they exhibit, with one exception, ages of several hundreds of years. The exception is the Big tree of Wadi Hinna, which is by far the biggest and oldest baobab. The oldest part of the Big tree started growing more than 1000 years ago.

The African baobab typically exhibits well-defined growth rings, which correspond in many cases to one rainy season. Nevertheless, age modeling of baobab rings demonstrated that ring-growth anomalies occur more frequent than for other tree species. For the old baobabs of Wadi Hinna, we found that the ring frequency varies between 0.43 and 0.78 rings/year. The large number of missing rings is due to the semi-arid climate.

The research was funded by the Romanian Ministry of Research CNCS-UEFISCDI under grant PN-III-P4-ID-PCE-201620-2567, No. 145/2021.