Is canopy interception increased in semiarid tree plantations? Evidence from a field investigation in Tehran, Iran

From 30 January 2011 to 30 January 2012, we measured the rainfall interception (I) and canopy storage capacity (S) of individual trees of Pinus eldarica and Cupressus arizonica planted in the Chitgar Forest Park near Tehran, Iran. Gross rainfall (GR) in this semiarid region was measured using the mean of 6 plastic rain gauges placed in an open area adjacent to the trees. To measure throughfall (TF), 20 plastic rain gauges were installed beneath the crowns of 5 individual trees of each species. I was calculated as GR minus TF. S was estimated using indirect methods: the minimum, Gash and Morton, mean, and Pereira methods. The cumulative mean values of relative percentage of I (I:GR) for P. eldarica and C. arizonica trees averaged 44.2% and 34.4%, respectively. Significant negative relationships were observed between the percent of I:GR and GR for P. eldarica (R^2 = 0.63) and C. arizonica (R^2 = 0.67) trees. For P. eldarica, S was estimated to be 1.10 mm, 1.00 mm, 1.09 mm, and 1.05 mm using the minimum, Gash and Morton, mean, and Pereira methods, respectively. For C. arizonica, the corresponding values are 0.58 mm, 0.52 mm, 0.56 mm, and 0.55 mm. This study proposes that in this climate dominated by small storms, planting C. arizonica is preferable to planting P. eldarica. However, the differences in the transpiration of these species should be quantified. Our results also indicated that the I value in this semiarid climate was higher than that of a humid climate.