Oak trees decline; a sign of climate variability impacts in the west of Iran

The Persian oak, Quercus brantii, trees in the Zagros region of Western Iran have been in decline since ۲۰۰۰. The decline is assumed to be highly connected with changes in meteorological parameters. Our objectives were to quantify the long-term trends in meteorological parameters and reference evapotranspiration (ET۰) in the Zagros region and estimate ecohydrological parameters highly affected by climate variability and related to rainfall interception (I) process (i.e., canopy storage capacity (S), the ratio of mean evaporation rate from the wet canopy to the mean rainfall intensity (E/R), and the free throughfall coefficient (p)). Long-term (۱۹۶۱-۲۰۱۰) changes in air temperature (T), precipitation (P), and wind speed (WS) were obtained from six synoptic meteorological stations located in the region. Throughfall (TF) was measured using the sixteen rain gauges randomly located underneath the crown of the five individual trees. P was measured using rain gauges fixed in an open space nearby to the oak trees .I was computed as the difference between P and TF. From ۲۰۰۰ to ۲۰۱۰, meteorological parameters and ET۰ changed slightly; T, WS, and ET۰ increased (+۰.۶ ˚C, +۰.۴ m.s-۱, +۰.۲۵ mm.day-۱, respectively), while P decreased (-۶۰ mm).When climate patterns between ۱۹۶۱-۲۰۱۰ were analyzed for ۶ synoptic weather stations, P significantly decreased significantly at one station, whereas T significantly increased at two stations and significantly decreased at another. I was estimated to be ۴۰% and ۲۵% within in-leaf and leaf-less periods, respectively. During the in-leaf period, the mean values of S, E/R, and p were roughly estimated to be ۱ mm, ۰.۲۲, and ۰.۲۳, respectively. Our results indicate that the Zagros region is getting warmer and oak trees will indisputably experience reduction in the available water because of increased evaporative loss.

Keywords:

Ecohydrological parameters , Evapotranspiration , Interception , Meteorological parameters , Oak trees decline