Canopy transpiration of a Canary Islands pine forest

Canopy transpiration ( E c) of a 50-year old Pinus canariensis Chr. Sm. Ex DC. stand in Tenerife, Canary Islands was estimated continuously throughout 1 year from August 2000 to July 2001 by means of xylem sap flow measurements. Although there was pronounced seasonal trend in soil water availability and evaporative demand, E c did not show any clear seasonal trend and averaged 0.80 during the cold-wet and 0.82 mm day −1 during the warm-dry period. This is, because summer drought is often mitigated by a high relative humidity of the air and a high frequency of clouds due to the north-east trade winds. However, at a given solar radiation and vapour pressure deficit E c was significantly lower during the warm and dry season than at other times during the year. The annual total of E c was 252.3 mm, which is significantly below the values estimated for other Mediterranean forest ecosystems and thus shows a strong adaptation to low soil water availability during periods of great evaporative demand.