Controlled, localized heating was applied to the trunks of young Aleppo pines (Pinushalepensis Mill.) during the winter. Three levels of burning were applied to the circumference of the trunks (zero, partial, or total), and the effects on tree physiology and growth were monitored during the 7 months following heating. Effects of the heat treatment on tree physiology were assessed by measuring predawn water potential, sap flux density, microvariations in trunk diameter, electrical resistance of the cambium, and gas exchanges from the needles (photosynthesis and stomatal conductance). Morphological response measurements included height and radial growth of the trees and morphological characteristics of the needles. The amount of chlorotic foliage was also measured. Aleppo pine was highly resistant to trunk injury, surviving when 80% of the trunk circumference was destroyed by fire. The behaviour of partially burnt pines was not significantly different from that of controls, for all variables studied. Trees whose trunks were totally burnt died from 1 to 5 months after treatment. Sap flux density of totally burnt trees was already significantly lower than that of other trees in the first week following the treatment. A decrease in net photosynthesis and stomatal conductance in the still surviving totally burnt trees was also recorded during the first measurements made in July. Treatment differences in predawn water potential, microvariations in trunk diameter, and electrical resistance of the cambium only appeared a few days before death of the totally burnt trees.
The dynamics of radial sap flux density reflects changes in stomatal conductance in response to soil and air water deficit