Disentangling above‐ and below‐ground competition between lianas and trees in a tropical forest

Abstract

Summary: Light is thought to be the most limiting resource in tropical forests, and thus above‐ground competition is commonly accepted as the mechanism that structures these communities. In many tropical forests, trees compete not only with other trees, but also with lianas, which compete aggressively for below‐ground resources and thus may limit tree growth and regeneration. Using a replicated experiment, we tested the relative strengths of above‐ and below‐ground competition from lianas on tree saplings in a disturbed forest in Côte d’Ivoire with a heterogeneous canopy and relatively high light penetration. We planted seedlings of three tree species and subjected them to below‐ground competition with lianas (BGC), above‐ and below‐ground competition with lianas (ABGC), or a liana‐free control treatment. After 2 years, we harvested the saplings and compared the amount of above‐ground biomass and its relative allocation among the three experimental treatments and different tree species. Lianas competed intensely with saplings in this tropical forest, substantially limiting sapling growth. Saplings grown in the ABGC and BGC treatments had only 18.5% and 16.8% of the above‐ground dry biomass of those grown in the liana‐free control treatment. Sapling biomass did not differ significantly among the ABGC and BGC treatments, suggesting that below‐ground competition was the driving force behind liana vs. tree competition in this forest. Above‐ground competition with lianas, however, did affect the allocation of biomass in saplings, resulting in shorter, thicker stems and a poorly developed crown. Collectively, our findings suggest that below‐ground competition with lianas plays a substantial role in limiting the growth of saplings in disturbed and secondary tropical forests, and above‐ground effects may be due to a combination of above‐ground competition and mechanical stress. Disentangling above‐ and below‐ground competition between lianas and trees is critical for a comprehensive understanding of the dynamics of naturally regenerating tropical forests, as well as formulating successful management plans for sustainable timber harvest.