Rainfall and dust interception potentials of oak trees and plantations in the Zagros region

The Persian oak, Quercus brantii trees and to a lesser extent, man-mad plantations in the Zagros region of western Iran have been in decline since 2000. The decline is assumed to be partially connected with invasions of dust and particulate materials created in neighboring countries. We measured rainfall interception (I) and quantified the amount and size of dust and particulate material (PM) deposited on leaves of Q. brantii as well as Pinus brutia and Cupressus arizonica man-made trees after rainfall (GR) leaching. Throughfall (TF) was measured using the sixteen rain gauges randomly located under the crown of individual species. GR was measured using rain gauges fixed in an open field nearby to the species and I was computed as the difference between GR and TF. Seven and three GR events and corresponding collected TF were centrifuged and dried out to measure the amount and size of intercepted PM by the species, respectively. Fifteen GR events occurred during the study period (cumulative GR: 128.9 mm). The mean ratio of I to GR equaled 35% for Q. brantii against 53% for P. brutia and 45% for C. arizonica. We found out that mean rainfall event (7.83 mm) during the measurement period was able to wash off PM content by 3.6, 6, and 6.8 mg per square meter of crown projected area (CPA) for Q. brantii, P. brutia, and C. arizonica, respectively. The ratio of PMs smaller than 5 µm was lower in TFs (mean: 15.4% for all species) compared to open field 27.2%. All species presented approximately the same potential for PM absorption. P. brutia and C. arizonica were capable of absorbing larger PMs compared to Q. brantii. The results showed that exotic species demonstrated satisfactory potentials in absorbing particulate material nevertheless their higher interception capacity should be considered while they are recommended for afforestation in the semi-arid climate of the Zagros region.