Mapping dry-season tree transpiration of an oak woodland at the catchment scale, using object-attributes derived from satellite imagery and sap flow measurements

Integration of hydrogeophysics and remote sensing with coupled hydrological models

“…This indicates that once tree roots have access to groundwater, T g is then independent (or negligibly dependent) on water table fluctuation and that the trees can tap water interchangeably from any accessible reservoir in order to satisfy the transpiration requirements driven by the climatic conditions. This behavior reproduced well the results of experimental studies carried out in the same area (van der Tol, 2012;Reyes-Acosta and Lubczynski, 2013;Balugani et al, 2014) and is in agreement with other studies performed in other, similar open oak woodland ecosystems (David et al, 2004;Paço et al, 2009;Miller et al, 2010).…”

“…The La Mata catchment is a sub-catchment of the Sardón catchment (∼80 km 2 ) where extensive research on subsurface water fluxes at the catchment scale has been carried out (Lubczynski and Gurwin, 2005a;Lubczynski, 2009Lubczynski, , 2011Reyes-Acosta and Lubczynski, 2013;Balugani et al, 2014;Francés et al, 2014;Hassan et al, 2014). This catchment was selected because of a semi-arid, water-limited environment, negligible groundwater use, availability of monitoring data and shallow groundwater table (∼2 m depth) enhancing E g , T g and Exf g .…”

“…The fractional coverage areas were retrieved using the mapping of bare soil described in section 5.2.2.3 and the mapping of the tree canopies made by ReyesAcosta and Lubczynski (2013). The later was carried out for each tree species, using the same remote sensing technique and images as used for the soil classification.…”

Conductive sapwood area prediction from stem and canopy areas—allometric equations of Kalahari trees, Botswana

“…The majority of these methods estimate sap flow ( Q ) by measuring sap flux density ( J p ) across the conductive sapwood (xylem) area (Ax), where Q is a product of J p and Ax. In general, the per‐species J p variability among trees of different size and age is relatively modest or even low (Jaskierniak, Kuczera, Benyon, & Lucieer, ; Kumagai, Aoki, Shimizu, & Otsuki, ; Reyes‐Acosta & Lubczynski, , ). Therefore, spatial tree water uptake depends mainly on the conductive sapwood area of trees.…”

“…At the small scale of a plot (or stand), with a limited number of trees, the plot tree transpiration can be estimated by Ax and J p measurements of all trees. In large plots, where As of each stem can be estimated, the Ax can be scaled from limited amount of per‐species As and Ax measurements applying As ~ Ax allometric equations and applying per‐species J p estimated as the mean of different sizes or ages of trees if their variability is low or otherwise categorized as function of Ax (Reyes‐Acosta & Lubczynski, ). However, if the assessment of tree water use has to be done over large areas, for example, at the catchment scale with many trees of different tree species and different sizes, the direct measurement of As at each tree is impractical.…”