Optimization of dry‐season sap flow measurements in an oak semi‐arid open woodland in Spain

Abstract

In sap flow studies, there is no method complying with high efficiency and versatility of sap flow measurements. To improve that, we propose combining two methods: (1) thermal dissipation probe (TDP) known to be efficient and cost effective and (2) heat field deformation (HFD) known to be versatile. For that purpose, we used a step-wise TDP sap flux density (J p ) optimization method consisting of (1) natural temperature gradient (NTG) correction applying the cyclic heat dissipation (CHD) method, (2) night flow ΔT max correction using HFD data as reference and (3) radial-azimuthal correction using HFD as reference. We applied this optimization method on Quercus ilex (Q.i.) and Quercus pyrenaica (Q.p.) trees in a Spanish semi-arid open woodland during dry season. The NTG correction resulted in substantial reduction of J p as compared with standard TDP. The subsequent ΔT max night flow correction resulted in the increase of NTG-corrected J p and good agreement with the outermost 2 cm of HFD measurements for both species. The final radialazimuthal adjustment of TDP J p resulted not only, in a good agreement with HFD J p , but also provided novel ecohydrological insights such as: (1) evidence of continuous night flow in all Q.p. trees and some Q.i. trees, (2) exponential reduction of J p with sapwood depth for both species, (3) significantly larger J p in the outermost 1 cm of sapwood for Q.p. than for Q.i. and (4) high azimuthal J p variability for both species. The presented study offers efficient and versatile method of tree sap flow measurements that contributed to a better understanding of water-related dynamics of Q.i. and Q.p. under water-stress conditions.

Sap flow in response to rainfall pulses for two shrub species in the semiarid Chinese Loess Plateau

“…The response of sap flow is related not only to the physiological characteristics, but also to environmental variables (Gao et al, 2011;Liu et al, 2012;Reyes-Acosta and Lubczynski, 2014). The sap flow response of these two shrubs to greater evaporative demand was shown to exhibit low R 2 values with increasing Q o and D z (Fig.…”

Tree Water Dynamics in a Semi-Arid, Pinus brutia Forest

“…Sap flow instruments are widely used for the estimation of whole-plant water use and transpiration [3][4][5]. The accuracy of sap flow measurements and the upscaling of these to the whole-plant water use relies on the knowledge of species-specific physiological characteristics, as well as on information of radial and circumferential patterns of sap velocity [6][7][8].…”

“…The spatial configuration of the sapwood affects tree hydraulic properties and environmental adaptation [10]. The relationship between sap flux density and sapwood depths can be linear [6,11], exponential [4], or variable, depending on temporal or environmental changes [12,13]. Loustau et al [14] found that the variability of sap flux density of Pinus pinaster species, with a deep rooting system enabling it to grow in areas with a mean annual rainfall as low as 350 mm [43,44].…”

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

“…The distribution of conductive sapwood in stems, as disclosed by cut and dye method (Figure 2), has critical implication for eventual sap flux density (J p ) measurements in Kalahari trees, as J p varies radially, typically from large in the outer rings, to smaller in inner rings, towards heartwood (Granier et al, 1994;Nadezhdina, Čermák, & Ceulemans, 2002;Phillips, Oren, & Zimmermann, 1996;Reyes-Acosta & Lubczynski, 2014;Wullschleger & King, 2000). Therefore, if, for example, a measured section of J p probe is substantially shorter than the conductive sapwood depth, such J p measurement is prone to overestimation.…”

“…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.…”