Belowground ecological interactions in mixed-species forest plantations

Belowground competitive and complementary interactions define productivity and sustainability of mixed-species plantations to a large extent, but have received relatively little attention in the scientific literature. Belowground competitive ability is correlated with such traits as root length density, surface area and root plasticity. Competition for light can be asymmetrical with larger plants disproportionately shading smaller ones, but competition for soil resources is more symmetric. Niche separation and reduced competition belowground are commonly observed as the mechanisms that lead to coexistence of species in mixed-species plantations. Chemical interference through allelopathy may play a role in controlling the productivity of some mixed-species plantations. This paper reviews some of the well-known ecological principles by drawing examples from both temperate and tropical mixed-species plantations. We conclude that our ability to design successful mixed-species systems is constrained by limited information on belowground competitive and complementary interactions. Future research priorities that will help us expand our knowledgebase are identified.