Forest fragmentation drives liana community structure but not the patterns of liana–tree interaction network in two forest ecosystems in Ghana

Abstract

We assessed fragmentation impact on liana community structure and patterns of liana-tree interaction network structure, and edge effects on liana community structure in a rainforest and a moist semi-deciduous (MSD) forest in Ghana. In each forest, we randomly established 30 20 Â 20 m 2 plots at varied distances (0-20 m, 20-40 m, 40-60 m, 60-80 m, 80-100 m) from forest edge to interior in fragmented and intact sites. Lianas with diameter at 1.30 m from rooting base ≥1 cm and their host trees (diameter at breast height ≥ 5 cm) were identified and counted. Our findings revealed that fragmentation caused an increase in liana diversity in the rainforest, but not in the MSD. Fragmentation also resulted in shifts in species composition in both forests, and together with edge effects increased liana abundance in both forest ecosystems. Lianatree networks in the two forest ecosystems were less nested and connected, but more modular and specialized than their corresponding null models irrespective of fragmentation. Some species of lianas (rainforest fragment/ intact: 0.80/0.76%; MSD fragment/intact: 0.47/0.38%) and trees (rainforest fragment/intact: 0.65/0.35%; MSD fragment/intact: 0.54/0.36%) exhibited higher specialization than their null models. Topologically, most lianas in fragmented and intact sites of the forests played peripheral/specialist roles, whereas a few species exhibited structural importance in the form of connectors, network hubs and module hubs. The structural important species in fragmented sites did not also occur in intact sites, suggesting that fragmentation might have influenced topological roles of the species in fragmented sites.

Edge disturbance shapes liana diversity and abundance but not liana‐tree interaction network patterns in moist semi‐deciduous forests, Ghana

“…We found anti‐nested and modular structure in the three liana‐tree interaction networks in AFR. This trend has also been reported by Addo‐Fordjour and Afram ( 2021 ), and Addo‐Fordjour et al ( 2021 ), and to some extent by Magrach et al ( 2016 ) whose liana‐tree networks showed anti‐nested structure (see supplementary data in Magrach et al, 2016 ). Nevertheless, our results contrast with Sfair et al ( 2010 ), who recorded nested structure in three distinct vegetation formations in Brazil, and also differs from the networks of Sfair et al ( 2015 ), which did not show modularity.…”

“…Generally, our study adds to the number of studies that have demonstrated the existence of non‐nestedness and modularity in liana‐tree networks (e.g. Addo‐Fordjour & Afram, 2021 ; Addo‐Fordjour et al, 2021 ; Magrach et al, 2016 ).…”

“…For example, nestedness, a network pattern in which the interactions of less connected species form proper subsets of the interactions of more connected species (Bascompte et al, 2003 ; Landi et al, 2018 ; Ponisio et al, 2019 ), has been used to characterise the structure of liana‐tree networks. Different patterns of nestedness are reported in literature for liana‐tree networks including nested (Sfair et al, 2010 ) and non‐nested (Addo‐Fordjour & Afram, 2021 ; Addo‐Fordjour et al, 2016 , 2021 ; Blick & Burns, 2009 ; Magrach et al, 2016 ; Ofosu‐Bamfo et al, 2019 ) structures. Among the studies that did not find nested structure in liana‐tree networks, some reported anti‐nested structure which depicts non‐random assembly (Addo‐Fordjour & Afram, 2021 ; Addo‐Fordjour et al, 2021 ; Blick & Burns, 2009 ; Magrach et al, 2016 ), while others observed non‐significant nestedness that shows random assembly (Addo‐Fordjour et al, 2016 ; Ofosu‐Bamfo et al, 2019 ).…”

“…Different patterns of nestedness are reported in literature for liana‐tree networks including nested (Sfair et al, 2010 ) and non‐nested (Addo‐Fordjour & Afram, 2021 ; Addo‐Fordjour et al, 2016 , 2021 ; Blick & Burns, 2009 ; Magrach et al, 2016 ; Ofosu‐Bamfo et al, 2019 ) structures. Among the studies that did not find nested structure in liana‐tree networks, some reported anti‐nested structure which depicts non‐random assembly (Addo‐Fordjour & Afram, 2021 ; Addo‐Fordjour et al, 2021 ; Blick & Burns, 2009 ; Magrach et al, 2016 ), while others observed non‐significant nestedness that shows random assembly (Addo‐Fordjour et al, 2016 ; Ofosu‐Bamfo et al, 2019 ). Ecological networks can also be compartmentalised into modules whose members interact more among themselves (Carstensen et al, 2016 ).…”

“…The disturbance‐adapted nature of lianas makes them an ideal group of plants which can be used to test edge effects. Previous studies reported that edge effects enhanced liana diversity and abundance in some forests (Addo‐Fordjour et al, 2021 ; Campbell et al, 2018 ; Laurance et al, 2001 ; Ofosu‐Bamfo et al, 2019 ), but others did not detect changes in liana diversity in response to edge (Mohandass et al, 2014 ; Ofosu‐Bamfo et al, 2019 ). Several properties of forest edge such as edge size, edge type, and surrounding matrix type can mediate edge effects on plant community structure (Martino, 2015 ), and be responsible for the varied responses of community structure to edges in different forests.…”