Ulster University Logo

Ulster Institutional Repository

Browsing lawns? Responses of Acacia nigrescens to ungulate browsing in an African savanna

Biomedical Sciences Research Institute Computer Science Research Institute Environmental Sciences Research Institute Nanotechnology & Advanced Materials Research Institute

Fornara, D. A. and Du Toit, J. T. (2007) Browsing lawns? Responses of Acacia nigrescens to ungulate browsing in an African savanna. ECOLOGY, 88 (1). pp. 200-209. [Journal article]

[img]
Preview
PDF - Published Version
229Kb

Abstract

We measured browsing-induced responses of Acacia trees to investigate ``browsing lawns'' as an analogy to grazing lawns in a semiarid eutrophic African savanna. During the two-year field study, we measured plant tolerance, resistance, and phenological traits, while comparing variation in leaf nitrogen and specific leaf area ( SLA) across stands of Acacia nigrescens, Miller, that had experienced markedly different histories of attack from large herbivores. Trees in heavily browsed stands developed ( 1) tolerance traits such as high regrowth abilities in shoots and leaves, high annual branch growth rates, extensive tree branching and evidence of internal N translocation, and ( 2) resistance traits such as close thorn spacing. However, phenological ``escape'' responses were weak even in heavily browsed stands. Overall, browsing strongly affected plant morpho-functional traits and decreased both the number of trees carrying pods and the number of pods per tree in heavily browsed stands. Hence, there is experimental evidence that tolerance and resistance traits may occur simultaneously at heavily browsed sites, but this comes at the expense of reproductive success. Such tolerance and resistance traits may coexist if browsers trigger and maintain a positive feedback loop in which trees are continually investing in regrowth ( tolerance), and if the plant's physical defenses ( resistance) are not nutritionally costly and are long-lived. Our results confirm that chronic browsing by ungulates can maintain A. nigrescens trees in a hedged state that is analogous to a grazing lawn. Further research is needed to fully understand the long-term effects of chronic browsing on reproduction within such tree populations, as well as the overall effects on nutrient cycling at the ecosystem level.

Item Type:Journal article
Faculties and Schools:Faculty of Life and Health Sciences
Faculty of Life and Health Sciences > School of Environmental Sciences
Research Institutes and Groups:Environmental Sciences Research Institute
Environmental Sciences Research Institute > Terrestrial Ecology
ID Code:460
Deposited By:Dr Dario Fornara
Deposited On:22 Jan 2010 10:35
Last Modified:28 Mar 2012 15:51

Repository Staff Only: item control page