Canopy transpiration of a semi arid Pinus canariensis forest at a treeline ecotone in two hydrologically contrasting years

Amsterdam

2015

S. 120-127

BandaufführungSonderdruck

191399

Given its importance, transpiration of forest canopies has been measured in a wide range of environ-ments. However, measurements in treeline ecosystems with Mediterranean climate are rare more soin semi arid climates. Therefore in the present study we investigate inter-annual variation in canopytranspiration (Ec) of a Pinus canariensis forest located on a treeline ecotone in Tenerife, Canary Islands,Spain, where the climate is typically semi arid Mediterranean. Meteorological conditions and sap flowwere continuously monitored during two consecutive years. In both years, atmospheric conditions weretypical for the study site. Nevertheless large differences were detected in precipitation (P) with a highinter-annual variability. Calendar year (January December) P was higher in 2008 than in 2009, whilein the corresponding hydrological year (October September), P was considerably lower in 2008 than in2009. Despite this difference in P between both years top soil water availability was almost exhaustedduring both summers. However, the effect of top soil drought, showing a visible seasonality on Ecwasonly clearly detected in 2008 with values down to 0.02 mm day-1during summer. During the summer2009, in contrast, Ecrates were up to 1.12 mm day-1showing that P. canariensis is able to tap water fromdeep soil layers when P of the previous wet period (October April) recharged these reserves. This pointsout the importance of evaluating sap flow studies in semi arid treelines with respect to hydrological yearP. Climate change models predict a reduction of more than 30% in precipitation. In our study the effectof only one hydrological dry year resulted in severe water stress. Thus, when winter rainfall is low fora number of years, chronic drought may have negative implications for tree and stand transpiration insemi arid treelines.©
Keywords: Canary Islands pine ; Climate change ; Drought ; Mediterranean climate ; Sap flow ; Tissue heat balance