Abstract
AbstractConductive sapwood (xylem) area (Ax) of all trees in a given forested area is the main factor contributing to spatial tree transpiration. One hundred ninety‐five trees of 9 species in the Kalahari region of Botswana were felled, stained, cut into discs, and measured to develop allometric equations predicting Ax from estimates of stem (As) and canopy (Ac) areas. Stem discs were also subjected to laboratory‐based computed tomography, which well detected wood density contrasts but was not diagnostic with regard to delineation of Ax. The staining experiment, along with the help of visual and computed tomography analysis, allowed the definition of 4, tree‐species categories of Ax, C1–C4. In C1 (Acacia erioloba, Terminalia sericea, and Burke Africana), the staining and visual delineation of Ax matched the natural color difference between sapwood and heartwood; in C2 (Dichrostachys cinerea and Ochna pulchra), sapwood was divided into external conductive and internal nonconductive annuli; in C3 (Acacia fleckii and Acacia luederitzii), sapwood had sharp staining boundary between external highly conductive and internal low‐conductive annuli; and in C4 (Lonchocarpus nelsii and Boscia albitrunca), stems had no heartwood. Per‐species 0‐intercept linear regression models, Ax = slope.As (slope = 0.392 ÷ 0.794; R2 = 96.7 ÷ 99.8%) and Ax = slope.Ac (slope = 1.477 ÷ 17.044; R2 = 82.1 ÷ 92.2%) yielded excellent to good predictive allometric equations. The first equation is suitable for Ax scaling of small‐size Kalahari areas, where the As of all trees can be estimated on the ground, whereas the second, as contribution to automated tree transpiration mapping of large‐size Kalahari areas, where the Ac of trees can be derived through remote sensing interpretation of high‐resolution images.
Highlights
The quantification of vegetation water use in semiarid climates, where trees make use of shallow and deep soil moisture and even groundwater reserves, is essential for determining water balances of open savannas and agricultural systems (Dye, Soko, & Poulter, 1996; Hultine, Williams, Burgess, & Keefer, 2003; Lubczynski, 2009)
This study is dedicated to the research of Ax of Kalahari trees, as support for future Kalahari tree transpiration mapping, following the method proposed by Reyes‐ Acosta and Lubczynski (2013)
The main novelties of this study is in the recognition of the four categories of the conductive sapwood patterns (C1–C4) and in development of reliable linear allometric equations Ax ~ As and Ax ~ Ac, for the nine abundant Kalahari tree species based on the assessment of 195 Kalahari, world's deepest root trees
Summary
The quantification of vegetation water use in semiarid climates, where trees make use of shallow and deep soil moisture and even groundwater reserves, is essential for determining water balances of open savannas and agricultural systems (Dye, Soko, & Poulter, 1996; Hultine, Williams, Burgess, & Keefer, 2003; Lubczynski, 2009). Successful in many studies, according to Pfautsch, Macfarlane, Ebdon, and Meder (2012), the staining of sapwood cores is not always accurate because of insufficient color contrast and because it is species dependent; they advised to cross‐validate the assessment accuracy by microscopy of light transmission to identify open vessels Another assessment approach is the resistance to penetration method (Rust, 1999), which uses a rotating needle inserted into the wood to detect the hardness difference between softer sapwood and harder heartwood. The main novelties of this study is in the recognition of the four categories of the conductive sapwood patterns (C1–C4) and in development of reliable (high R2) linear allometric equations Ax ~ As and Ax ~ Ac, for the nine abundant Kalahari tree species based on the assessment of 195 Kalahari, world's deepest root trees
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