Marginal effects on biodiversity, carbon sequestration and nutrient cycling of transitions from tropical forests to cacao farming systems

Abstract

Cacao (Theobroma cacao), a perennial crop predominantly cultivated as a multi-product and multi-strata agroforestry system, has been identified as one of an array of factors behind land use changes in the tropics. Concerns have also been raised about the gradual shift from traditional cacao growing systems under diverse and dense tree canopy to lower or no-shade cover, leading to further loss of direct and functional forest ecosystem values such as protective and regulatory environmental services. This paper surveys existing literature and focuses on changes to biodiversity, carbon sequestration and nutrient cycling conditions due to a transition from natural forests to traditional lower-density agroforestry and high-density hybrid monoculture cacao systems. We derive marginal effects on selected ecosystem functions expressed as a percentage unit change in corresponding ecosystem values from a natural forest baseline scenario. Data from 16 studies conducted in Africa and the Americas show a negative trend in marginal changes in above-and below-ground carbon sequestration potential for the two cacao farming systems. The extent of marginal losses in carbon storage was comparatively higher for the monoculture than cacao agroforestry system. A general trend denoting positive marginal changes has been reported for mean species richness in soil and litter and some essential chemical and physical soil properties (Calcium, Magnesium, sand and silt) of cacao agroforestry systems compared with a natural forest baseline. The balance between negative and positive changes show that traditional cacao agroforestry systems have greater potential for conservation of ecosystem services closer to a natural forest state than monocultures.