Forest structure determines the abundance and distribution of large lianas in Gabon

Abstract

Aim Lianas are an important component of forest structure in the tropics, accounting for up to 45% of total stems. Mounting evidence that tropical forests are undergoing structural changes, with a growing abundance of lianas reducing forest carbon storage potential, imparts a sense of urgency to study the drivers that control liana abundance and biomass, particularly in Africa where data come from a few, small-scale studies.Location Gabon, Africa.Methods In the first countrywide study of lianas, we implemented the most ambitious, large-scale forest inventory in tropical Africa to date, quantifying the density, basal area and biomass of large lianas (10 cm in diameter) using a systematic, random design of 104 plots located across Gabon. Additionally, we examined the relative importance of environmental variables (mean annual precipitation, mean annual temperature, seasonality, soil nitrogen, soil fertility), disturbance (effect of gaps, forest type) and forest structure (large tree biomass) in driving macroscale variation in the abundance of large lianas.Results In total, we surveyed 1354 large lianas, and found the density, basal area and biomass of large lianas in Gabon to be comparable to that in other tropical forests. The success of large lianas was positively related to soil N, but most strongly correlated with forest structure, particularly large tree biomass. The strength of the association between large lianas and large trees increased with tree size class.Main conclusions Forest structure and the availability of large trees may be more important predictors of the abundance and distribution of large lianas in African tropical forests than environmental variables and disturbance. Changing environmental conditions are likely to have little direct effect on large lianas, but climate change, defaunation and land-use activities that diminish forest structure and reduce the number of large trees could have strong indirect effects on large lianas in Central African forests.

Old growth Afrotropical forests critical for maintaining forest carbon

“…Loss of the largest trees drastically changes forest structure and diameter distributions; thus understanding the relative importance of large trees to AGC in different forest types could help characterize forest degradation, which accounts for a large fraction of carbon loss world‐wide (Pan et al., 2013). Large tree biomass in Gabon is also correlated with high densities of coarse woody debris (Carlson, Koerner, Medjibe, White, & Poulsen, 2017) and large liana biomass (Poulsen et al., 2017); thus, the loss of large trees could affect multiple pools of carbon.…”

“…Large trees dominate intact tropical ecosystems, bolstering global biodiversity and carbon storage (Lewis, Edwards, & Galbraith, 2015; Sullivan et al., 2017). Rising above the canopy, they modulate the understorey microclimate and provide habitat and resources for animals, invertebrates, and plants like epiphytes and lianas (Poulsen et al., 2017), while storing a large fraction of forest carbon (Bastin et al., 2015; Stegen et al., 2011; ter Steege et al., 2013). The world's tallest and densest forests are temperate rain forests, but tropical forests are the most widespread, accounting for two‐thirds of all terrestrial biomass (Pan, Birdsey, Phillips, & Jackson, 2013).…”

Can terrestrial laser scanners (TLSs) and hemispherical photographs predict tropical dry forest succession with liana abundance?

“…We argue here that the first step in the development of such models is to have a clear understanding of how lianas affect ecosystem structure and composition, which in turn will affect tree mortality, recruitment, and carbon storage above ground and below ground (Poulsen et al, 2016;Schnitzer et al, 2014). Furthermore, lianas, because of their impact on the 3-D structure of a given forest space, may have the ability to change faunal diversity (e.g.…”

Afrotropical Tree Communities May Have Distinct Responses to Forecasted Climate Change

“…In this study, we employ tree census data from Gabon's National Resource Inventory-a national network of tree plots for estimating forest biomass and carbon stocks ( Figure 13) (Carlson et al 2017;Poulsen et al 2017;Wade et al 2019). Gabon is the second most forested country in the world, with a forest cover of 87%, a deforestation rate near zero (Sannier et al 2014), and one of the highest densities of carbon in Central Africa (Saatchi et al 2011 assigned, if possible, into an "early-successional" or "late-successional" class based on growth form, available trait data, and habitat class (Whitmore 1989;Raich and Khoon 1990;Finegan 1996;Davies and Semui 2006;Chazdon et al 2010;Hardwick and Elliott 2016).…”