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.