Shade trees in cacao agroforestry systems: influence on roots and net primary production

• Applicant: Dr. Dietrich Hertel
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: from 2010 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 175291835

The presence of shade trees in agroforests is often assumed to negatively affect growth and yield of cacao plants through competitive water use. In contrast, results from a previous collaborating project suggest no such negative effects due to clear differences in vertical partitioning of soil water uptake among cacao and shade trees. Our earlier project indeed showed different vertical rooting patterns and a different soil drought response of shade and cacao trees. However, there are still few information about systematic differences in fine root biomass, vertical rooting pattern, and below-ground productivity of cacao and shade tree species under different soil moisture regimes. The proposed project intends to test the hypotheses that (1) the vertical segregation of the root systems of cacao and shade trees is more pronounced under low than under ample water supply, (2) both Gliricidia and native shade trees have deep root systems contributing to complementary soil water uptake, and (3) below-ground carbon partitioning into fine root biomass and turnover is higher in cacao agroforests at drier sites. The project shall compare cacao agroforests with no shade tress, Gliricidia shade trees, and native shade trees under contrasting rainfall. We will investigate standing fine root biomass, vertical root distribution and the occurrence of deep roots , and above- and below-ground productivity. The application of stable isotope (deuterium) techniques will help to clarify the importance of single deep roots for the trees water uptake. We will particularly cooperate with a project addressing ecohydrology of these stands.

• DFG Programme: Research Grants