LB 39-332 - No evidence for leaf functional trait clustering in liana-tree interactions in a tropical forest of the Congo basin

As a structurally dependent life-form, lianas mostly rely on trees to gain access to the forest canopy. The interactions between lianas and trees can be affected by host tree characteristics. The objectives of this study were to assess (1) the association between liana load per host tree and host tree diameter, and (2) the association between liana colonization and tree functional types within the Yangambi forest reserve in central Congo basin. To address our objectives, we used generalized mixed models, and determined the effects of forest structure and species functional identities as determinants of liana-tree association in six 1-ha permanent plots subdivided into mixed and monodominant forests. We found that 18% of trees hosted at least one liana stem in mixed forest, and 27% in monodominant forest. Trees with larger diameters supported more lianas over their crowns and a higher total basal area of lianas than trees with smaller diameters in both forest types. The presence of lianas on trees was negatively associated with tree diameter increment in mixed forest. Tree wood density was positively associated with the number of lianas on trees in the mixed forests, and negatively associated with tree diameter increment in the monodominant forest. In both forest types, we however found no association of tree leaf functional traits with neither the presence or absence of lianas on trees, nor with the number of lianas on trees. We further showed that the functional identities (based on leaf traits) of lianas were not clustered within the functional identities of their host trees in both forest types. Overall these findings in the Yangambi reserve suggest that exposure time is a potentially important driver of liana infestation as larger tree individuals harbor relatively more lianas. Furthermore, the negative effect of lianas on trees in the central Congo basin might not vary with tree functional identities, but mainly with tree structural attributes. Lastly, liana infestation could potentially result in reduced tree growth with consequences on long-term carbon sequestration and storage.