Ecophysiological studies on the water relations in a Pinus canariensis stand, Tenerife, Canary Islands

Abstract

Diurnal courses or sap flow denslly, changes in stem radius, needle level transpiration, and needle water potential were measured in 50-year old Pinus canariensis trees at a forest stand in 1650 m a .s.l. in Tenerlfe, Canary islands, Spain. A direct comparison of sap flow density estimated at the stem base and canopy transpiration measured at the needle level showed only small deviations in their diurnal courses. Needle water potentiaI and sl.em radius decreased from the onset of canopy transpiration, reeched in inimum values at noon, when sapflow was highest, and then continuously increased. Within the canopy however, gas exchange was highly variable among differently orientated twigs. Depending on the inclination of the sun a steep microclimatic gradient across the canopy affected apparent transpiration, leaf conductance and needle water potential. However, there were no significant differences in the amount of water transpired during a day between differently orientated twigs. Thus, our results suggest that sap flow sensors are a suitable tool for estimating canopy transpiration of pine trees in an environment where the crowns are often enveloped by rnist or fog, which is typically for pine forest at higher elevations in the western Canary islands.