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ALLOMETRIC RELATIONSHIPS BETWEEN SAPWOOD AREA AND SHRUB DIMENSIONS FOR 6 COMMON SOUTHERN AFRICAN SAVANNA BUSH ENCROACHER SPECIES: UNIVERSAL OR SPECIES-SPECIFIC?
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  • Roi Hendler,
  • Tim Herkenrath,
  • Rosemary Shikangalah,
  • Niels Blaum,
  • Katja Geissler
Roi Hendler
Universitat Potsdam Arbeitsgruppe Vegetationsokologie und Naturschutz
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Tim Herkenrath
Universitat Potsdam Arbeitsgruppe Vegetationsokologie und Naturschutz
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Rosemary Shikangalah
Namibia University of Science and Technology
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Niels Blaum
Universitat Potsdam Arbeitsgruppe Vegetationsokologie und Naturschutz
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Katja Geissler
Universitat Potsdam Arbeitsgruppe Vegetationsokologie und Naturschutz

Corresponding Author:kgeissle@uni-potsdam.de

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Abstract

Southern African savanna rangelands are facing a widespread degradation pattern called bush encroachment. This is associated with implications for various aspects of the water cycle and in particular canopy transpiration. At the individual-tree scale, it is estimated by scaling sap-flux density by sapwood area. However, the direct measurement of sapwood area is impracticable at landscape scale and general allometric equations of the West-Brown-Enquist (WBE) model relating sapwood area to primary size measures seem to fail for some species and climates. Therefore, we conducted intensive field measurements to establish species-specific allometric relationships between sapwood area and sizes (stem diameter, crown area) in six dominant shrub species involved in bush encroachment in Namibia ( Colophospermum mopane, Senegalia mellifera, Vachellia reficiens, Dichrostachys cinerea, Vachellia nebrownii, Catophractes alexandri). We found strong allometric relationships between sapwood area and stem diameter as well as between sapwood area and crown area for all six species. These relations are largely in line with the WBE theory but still provide estimates that are more accurate. Only in D. cinerea, the sapwood area was significantly smaller than predicted by the WBE theory, which might be caused by a larger need for stabilizing heartwood. Our results are useful to estimate water loss via transpiration at a large scale using remote sensing techniques and can promote our understanding of the ecohydrological conditions that drive species specific bush encroachment in savannas. This is particularly important in the light of climate change, which is considered to have major implications on ecohydrological processes in savannas.
23 Jun 2023Submitted to Ecohydrology
23 Jun 2023Submission Checks Completed
23 Jun 2023Assigned to Editor
26 Jun 2023Review(s) Completed, Editorial Evaluation Pending
06 Aug 2023Reviewer(s) Assigned
31 Aug 2023Editorial Decision: Revise Minor
27 Sep 20231st Revision Received
27 Sep 2023Submission Checks Completed
27 Sep 2023Assigned to Editor
27 Sep 2023Review(s) Completed, Editorial Evaluation Pending
13 Oct 2023Reviewer(s) Assigned