Herb assemblage dynamics over seven years in different cocoa production systems

Summary

Both agronomic practices and spatial position can determine the assemblage of herbaceous species. We assess the dynamics and the contribution of these two aspects over time to the herb assemblages of different cocoa production systems. Braun-Blanquet surveys were performed over seven years in a long-term trial in Bolivia to compare different cocoa production systems: successional agroforestry (SA) with no external inputs, organic agroforestry (OA) and organic monoculture (OM), both including a leguminous perennial cover crop, conventional agroforestry (CA) and conventional monoculture (CM), where agrochemicals were applied. Using general linear models and multivariate analysis we found that assemblages were mainly driven by spatial position only at the beginning. After this, a very dynamic selection process related to the different management practices took place, which became more stable over the years. We observed a decline in species in both the CA and OA systems, due to the loss of heliophilous species and the low number of new species established in them. The OM presented the most conservative pattern, with the lowest number of new species and species lost, due to the presence of the cover crop. Both the most intensively managed system (CM) and the most diverse and least intensive one (SA) had the highest number of new species recorded over time, which led to highly specialized assemblages, with worldwide distributed and herbicide resistant species in the first case and secondary forest species, in the second. We conclude that the promotion of organic management and agroforestry systems, especially highly divers and successional agroforestry sytems would favour herb assemblages with high conservation value and prevent the establishment of globally distributed species.