Species co-occurrence of lianas
Generally, lianas were assembled randomly on their hosts in most of the forest sites, suggesting that chance events rather than edge disturbance, determined liana distribution on trees. Thus, we argue that the liana communities might have been assembled on trees by stochastic processes including host characteristics. Our finding is consistent with that reported in a semi-deciduous forest in Brazil (Zulqarnain et al., 2016). Contrary to the above, liana species in edge site of Asenanyo Forest Reserve showed positive species co-occurrence on their hosts. Since this network was organised into modules, the positive co-occurrence trend could have existed within the modules. Thus, in the modules, liana species resorted to positive or facilitative interactions (McGarvey & Veech, 2018), that might have arisen deterministically. At forest edges, there is usually an elevated level of light coupled with dry conditions, and trellis availability, all of which can work together to enhance liana proliferation (Campbell et al., 2018). It appears that as these resources are increased at edge, lianas tend to share rather than compete for them, resulting in their positive co-occurrence on the host trees. The liana species aggregation on trees could have also arisen by facilitation, where increasing liana abundance at edge site would cause new liana individuals to use already established stems to climb trees (Pérez-Salicrup & Sork, 2001).
CONCLUSION
The findings of the study revealed considerable edge effects on liana diversity and abundance in the two moist semi-deciduous forests. Despite the enhanced diversity and abundance in edge site of each forest, the patterns of liana-tree network structure of edge site were similar to those in interior and deep-interior sites. All the networks in the two forests were less connected and non-nested, but modular and specialised. Lianas were mostly randomly distributed on host trees in all the forest sites except edge site in the Suhuma Forest Reserve. Topologically, the majority of liana and tree species were peripherals (i.e., specialist), but a few species tended to be generalists, acting as connectors, module hubs and network hubs. The role of most of the species did not change from one site to another, even though the topological role of a few species changed from one site to another. Overall, our study shows that liana community structure was more susceptible to forest edge than liana-tree network structure. The findings of our study corroborate previous studies, and also present unique findings related to liana-tree network structure. Our findings which enhance our understanding of liana-tree interactions, have conservation implications relating to stability and robustness of the networks. Finally, the findings of the present study can potentially contribute to a robust edge theory development.