Why do some African thorn trees (Acacia spp.) have a flat-top: a grazer-plant mutualism hypothesis?

The quintessential African savanna tree is the flat-topped Acacia. However, the reason for the architecture occurring in sparse-canopied small-leafed tree species from well-lit, often mesic, environments is unclear. Brown (1960) suggested that it reduced feeding by the distinctly African herbivore, the giraffe.

Escaping recaptured herbivore and/or fire damage is crucial for palatable savanna trees such as acacias. The impact of fire depends on the fire intensity (mainly due to under-canopy dead grass biomass and weather conditions) and on woody plant height, as well as the plant's defence (e.g. bark thickness) and resprouting ability. The impact of herbivores also depends on plant height, as well as on the plant's defenses (e.g. spinescence). Below we show that flat-tops trade height for spread, and this is at a cost to the plant, because it reduces their likelihood of escaping fires or herbivores.

Publish DateMarch 27, 2018
Last UpdatedJanuary 27, 2021
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