Thorn length and density on the latest year's growth were compared at three height (feeding) levels (<1m, >1m<2 m and >2 m) on individuals of Acacia karroo and Ziziphus mucronata in an area that was browsed by goats. Thorn length and density was greatest for branches within easiest reach of goats. However, there was no increase in thorn length or density on the latest year's growth of branches of A. karroo individuals protected from browsing. Thorns on distal ends of branches are relatively small and sparse and this is partly due to differences in internode length. Herbivores limit the extent of annual growth and this prevents development of small thorns characteristic of late season growth. Thus, browsed individuals which lack late season growth may have greater spinescence. This is only a passively induced response and is not due to the active production of larger thorns subsequent to browsing.
Journal articles from the Grassland Society of Southern Africa (GSSA) African Journal of Range and Forage Science as well as related articles and reports from throughout the southern African region.