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University of Twente (2015)

Tree - water interactions at varying spatio temporal scales in a water limited environment.

Reyes-Acosta, J.L.

Titre : Tree - water interactions at varying spatio temporal scales in a water limited environment.

Auteur : Reyes-Acosta, J.L. (Jeisson Leonard)

Etablissement de soutenance : University of Twente

Grade : Doctor University of Twente 2015

Final conclusions
This PhD study manages to prove that reliable estimation of transpiration at various spatio-temporal scales can be achieved through adequate use of sap flow measurement and the upscaling of transpiration from remotely sensed imagery. More importantly, however, it shows that detailed measurement of these can provide critical information about the vegetation processes influencing the hydrological systems in very dry conditions. As regards adequate sap flow measuring techniques, we concluded that the TDP method is susceptible to NTGs, especially at low flows, but that the CHD method successfully corrected the TDP signal and resulted in generally more accurate sap flux density estimates than other cyclic power methods. Exploring optimised field sap flow measurements revealed a novel set of physiological traits and flow dynamics that must be addressed to properly account for water flow in Q.i. and Q.p. , and to achieve this, an optimal approach is to combine the strengths of complementary methods such as TDP, CHD and HFD. The remote sensing upscaling approach proved to be a very efficient way of extrapolating the sap flow measurements, and this exercise allowed us to identify how both species importantly influence the hy-drological systems by using very specific strategies. On the one hand, Q.p. takes advantage of its proximity to riverbanks to intensely uptake water, whereas Q.i. relies more on its sturdiness and conservative uptake of water sources as it is normally further away from the riverbanks. These strategies both have very specific emerging spatial patterns, easily observed in tree transpiration maps. The considerable importance of employing isotopic tracing measurements and a modelling framework was clearly shown by the revealed insights. It was determined that in an area facing dry-conditions but with shallow groundwater - as in Sardón- vegetation with a long root system (as in the case of oak trees), will uptake water mostly from the ground- water very early in the season. Although groundwater consumption (e.g. T g ) will decrease towards the end of the dry season, it will still be highly relevant at that time. Such behaviour is more typical of riparian species (i.e. plant habitats and communities along the river margins and banks) than of standard woodlands and, consequently, hydrological modelling should be adjusted to reflect such dynamics. Finally, exploring the scaling up of water contributions further con- firmed the contrasting water uptake strategies of Q.i. and Q.p. to survive the summer drought. Moreover, such strategies were also reflected in the spatio-temporal patterns of stand transpiration components from the groundwater and from the unsaturated zone. Such observations are of great value for future guidelines for the management of water resources in Mediterranean areas by thinning or growing more vegetation where necessary.

Version intégrale (ITC)

Page publiée le 9 février 2018