CANOPY ARCIllTECTURE OF SOME ECUADORIAN COCOA POPULATIONS WITH SPECIAL REFERENCE TO LIGHT PENETRATlON

SUMMARY The problems of investigating the light regirne in cocoa is discussed, lirst in general terms and lhen with particular referonce to the light climate of Ecuador. The qua!ity and quantity of light reaching a cocoa canopy is effected by lhe annual radiation regime on a climatic level and by ,hade trees at a local level; at bolh levels considerable practica! problems arisc. The penetration of Iighl through the canopy depends on physical characteristics of lhe cocoa trec. Results of investigalions into tive differenl cocoa varieties are presented in terms of leaf area index, leaf number and density per unit volume, fresh weightfdry weight relationships etc., and lighl extinction curves are examined under bright and dun condition •. There are marked differences in every canopy characteristic examined between the possibly indigenous "Nacional" variety and the introdueed varietie., Ihe local hybrid complex resulting from lhe crossing of these dislinct types being intermediate in a1mo.t every feature, but resembling the introdueed types more Ihan lhe "Nacional". The extreme vegetative vigour of sorne recent biclonal introductions results in exlremely dense canopie. which reduce Huctu· ations of air temperature and relative humidity within Ihe canopy compared to those outside Ihe cauopy. As these varieties were iutroduced from a country having much higher levels of radiation lhan Ecuador they do not appear to be well adapted to a low light regime to which must be added the effeclS of dense overhead shade often found in farmers cocoa.