Digestibility, digestion-inhibitors and nutrients of herbaceous foliage and green stems from an African montane flora and comparison with other tropical flora.

Abstract

A total of 21 kinds of mature leaves and 12 kinds of green stems from the herbaceous flora of an afro-montane forest have been analysed for moisture content, dry matter digestibility in pepsin and cellulase enzymes, total phenolics, condensed tannins, acid detergent fibre, protein, and the micronutrients phosphorus, potassium, calcium and magnesium. Leaves were found to be significantly more digestible than stems, to contain less fibre but more total phenolics, and to be richer in protein and all micronutrients except potassium. Condensed tannins were found in very few samples, in contrast to their widespread occurrence in foliage from tropical rain forests in Africa and India. An analysis of the correlates of digestibility suggested that in green stems this was largely controlled by fibre content: the overall relationship with all measures being very similar to that recorded previously for rain forest foliage. Rather surprisingly the leaves failed to exhibit a similar relationship and none of the measures taken correlated strongly with digestibility. Compared with foliage from rain forest trees the leaves analysed in this study were found to be more digestible, richer in phosphorus and deficient in both fibre and tannin-based digestion-inhibitors. The two types of foliage are compared as sources of food for herbivores and findings discussed in the light of prevailing hypotheses of plant anti-herbivore chemistry.