ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 93 Number 3
Top-down versus bottom-up ecological control in cacao,Theobroma cacao L. (216)
Theobroma cacao L. (Malvaceae sensu lato) is one of the most important agricultural tree crops in the tropics. However, little is known about whether T. cacao is controlled via top-down (herbivore) or bottom-up (resource limitation) processes in plantations and in natural forests. This question was investigated in this study by planting seedlings of T. cacao in plots of primary and secondary tropical wet forest in northeastern Costa Rica, with a simultaneous planting of the same variety of seedlings in an adjacent reconstructed plantation that had a thin overstory of high canopy shade trees. Leaf growth and leaf damage (herbivory) were measured in the cacao grown under the contrasting systems over a three-year period, with one to two censuses per year. Seedlings grown in plantations were observed to have significantly higher amounts of leaf damage than seedlings grown in secondary or primary forest. Nonetheless, plantation-grown cacao grew much faster, had more leaves, and had larger leaves than forest-grown individuals. Furthermore, plantation-grown cacao plants were the only ones to produce flowers and fruits, and they did so within three years. This study demonstrates that the growth and survival of T. cacao is likely controlled by resource limitation (bottom-up control) rather than herbivory (top-down control), and that individuals in high light plantations reach reproductive status even with high rates of herbivore pressure. These findings can inform the choice of efficient cocoa farming system and management strategies to be adopted by cacao farmers in Costa Rica and other cocoa producing countries.
Keywords: Agro-forestry, cacao, cocoa, Costa Rica, farming system, growth, herbivory, shade cover, survival Crops