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

Abstract

Conductive 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.

Allometric relationships between sapwood area and shrub dimensions for six common Southern African savanna bush encroacher species: Universal or species‐specific?

“…This is not exclusive for the Etosha region. In the eastern Kalahari in Botswana, D. cinerea revealed the smallest slope of nine species (Lubczynski et al, 2017) with wider conduits or with more conduits in total. Such a sapwood composition at the expense of parenchyma is, however, more vulnerable to cavitation and embolism (Brodersen & McElrone, 2013), even if the same conductivity across the stem is reached compared to species exhibiting the allometric exponent of 2.33 of the WBE theory.…”

Use of remote sensing and long-term in-situ time-series data in an integrated hydrological model of the Central Kalahari Basin, Southern Africa

“…The topographic surface, is nowadays derived by RS techniques, applying for example interferometry (e.g. Noferini et al 2007;Wegmüller et al 2009), LiDAR (e.g. Liu et al 2005;Ma 2005) or analysis of stereoscopic images (e.g.…”

“…Considering the scarcity of fine spatial-resolution RS products, in the local scale IHMs, only tailor-made quantitative RS applications based on moderate, high-or very high-spatial resolution images can be utilized such as for example: (1) evapotranspiration mapping using Moderate Resolution Imaging Spectroradiometer (MODIS) with spatial resolution ranging from 0.5 to 1 km (Bastiaanssen et al 1998a, b;Su 2002) or at highresolution using Landsat 8 imagery with spatial resolution of 100 m (Senay et al 2016); (2) tree transpiration mapping using very high-resolution QuickBird or WorldView at 60-40 cm per pixel (Reyes-Acosta and Lubczynski 2013); (3) tree interception using QuickBird and WorldView at 60-40 cm per pixel (Hassan et al 2017); the aforementioned tree transpiration and tree interception mapping methods require tree-scaling functions, which for nine dominant Kalahari tree species are presented by Lubczynski et al (2017).…”

Dye tracer aided investigation of xylem water transport velocity distributions

“…(birch). More recently, the much less destructive thermometric methods (Marshall, 1958;Granier, 1985) became the dominant approach to investigate sap flux velocities and the role of dye tracers was mainly reduced to a supplementary mean to determine conducting sapwood areas (Dawson, 1998;McJannet et al, 2007;Lubczynski et al, 2017).…”