Canopy transpiration of a Canary Islands pine forest

Canopy transpiration (Ec) 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, Ec 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 Ec was significantly lower during the warm and dry season than at other times during the year. The annual total of Ec 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.