The water relations of young Olive trees in a Mediterranean winter: measurements of evaporation from leaves and water conduction in wood

We report measurements of evaporation rate, leaf resistance to evaporation and water conduction in the stems of young olive trees (Olea europea L.) growing in Messina, Italy, during the winter and early spring. We have measured what Zimmermann calls ‘leaf specific conductivity’ (LSC) of stem segments excised from olive trees. The LSC is a measure of the specific hydraulic conductivity of stem segments normalized per unit area of leaves supplied by the stem segment rather than per unit area of sapwood cross-sectional area. We find that the LSC's of primary stems were the largest followed in magnitude by the LSC's of secondary stems and tertiary stems. Under winter and early spring conditions the maximum evaporative flux from Coratina and Nocellara varieties of olive trees is about 2.6 x 10−5 kg 8−1 m−2. From this and the LSC measurements we calculate that the pressure gradients needed to maintain this rate of evaporation in the steady state is 65 kPa m−1 in primary stems, 170 kPa m−1 in secondary stems and 560 kPa m−1 in tertiary stems.