Longevity of leaves of a tropical tree, Theobroma cacao, grown under shading, in relation to position within the canopy and time of emergence

Abstract

To gain detailed information on the structure and dynamics of the foliage within a canopy, the longevity of leaves of cacao trees (Theobroma cacao L.) growing under normal commercial planting shade in Bahia State, Brazil, was determined relative to their position within the canopy and the time of leaf emergence.

In the experimental stand, the relative light intensity above the cacao canopy ranged between 30 and 100% of full daylight, and 4–10% at ground level. The mean leaf area index for the canopy, and the extinction coefficient of the foliage were 3·9 and 0·61, respectively.

The longevity of leaves of adult trees of cacao with closely packed crowns varied with their position within the canopy, and/or the irradiance received, and the time of emergence. In particular longevity decreased greatly with the height of the leaf from ground level. The mean longevity for the upper foliage (more than 220 cm above the ground) within the canopy was 181 d; the mean longevity of the lower leaves (0–150 cm above the ground) was about twice that of the upper leaves.

Approximately 23% of emergent leaves fell within 60 d of emergence, following infection (about 14% of loss) or as a result of wind damage (about 5% of loss). Thereafter, in mature and senescent leaves, leaf fall followed normal physiological changes.