On the ecology of tree and bush dynamics in African savannahs


CALL: 2016

DOMAIN: SR - Environmental and Earth Sciences


LAST NAME: Zacharias



HOST INSTITUTION: University of Bonn

KEYWORDS: Age determination, age-size relationships, bush encroachment, rangeland management, tree-rings, wood anatomy

START: 2016-10-01

END: 2019-09-30


Submitted Abstract

Savannah ecosystems undergo dynamics, such as bush encroachment. Reconstruction of past bush dynamics is essential for the understanding of the causes of bush encroachment. We present a new method to enable accurate age estimation of savannah bush species based on simple bush size parameters (stem circumference, height, and canopy diameter), which, in combination with repeated aerial photography (reconstruction of canopy diamters) and stem circumference measurements itself, could be used for the reconstruction and mapping of past bush encroachment. In our research area near Kuruman, South African part of the Kalahari, wood samples were collected from the eight most dominant bush species: Vachellia erioloba, Vachellia haematoxylon, Vachellia hebeclada, Senegalia mellifera, Diospyros lycioides, Grewia flava, Tarchonanthus camphoratus and Terminalia sericea. Tree-rings were counted on 482 stem discs of a total of 285 bushes to derive accurate age estimations for each bush. Our results show that stem circumference is strongly related to bush age in all species. Age-stem circumference relationships allow for the precise reconstruction and mapping of bush encroachment in South African Savannahs on a broad to a fine scale. Using repeated aerial photography, reconstruction of canopy diameters and thus bush encroachment was not possible. Recent bush encroachment is likely regulated through infilling of canopy gaps by existing individuals, rather than through recruitment of new species. We assume South African savannahs to be understood as an ecosystem affected by pulsating bush patterns (encroachment and clear of shrubs) through space and time.

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