Physical and chemical response of juvenile Acacia tortilis trees to browsing. Experimental evidence.

GOWDA, J.H.

FUNCTIONAL ECOLOGY

Año: 1997 vol. 11 p. 106 - 111

0269-8463

1. Changes in nutritional value and accessibility of leaves following browsing are important in the dynamics of plant-herbivore interactions because they influence the fitness of the plant attacked, and the future utilisation of it by the herbivore. 2. Hand pruning of Acacia tortilis, a spinescent tree common in savanna ecosystems of eastern Africa, resulted in  higher biomass of spines and new shoots in pruned trees than in unpruned controls. 3. Pruned trees allocated a higher proportion of shoot biomass to spines than unpruned ones, whereas the proportion of  leaf biomass in new shoots was slightly reduced. Because increases in spine biomass and density following pruning are coupled with an increase in shoot production, I conclude that higher production of spines is an inducible response of Acacia tortilis to pruning. 4. No significant changes in the concentration of total phenolics, condensed tannins or leaf nitrogen were induced by pruning. 5. Irrespective of treatment, high foliar concentrations of nitrogen were correlated with an increase in twig production for a given leaf biomass, and a reduction in the concentration of secondary substances in leaves. This relation may lead to a conflict between foraging efficiency and nutrition for browsers of A. tortilis.