Local canopy disturbance as an explanation for long‐term increases in liana abundance

Abstract

Canopy disturbance explains liana abundance and distribution within tropical forests and thus may also explain the widespread pattern of increasing liana abundance; however, this hypothesis remains untested. We used a 10‐year study (2007–2017) of 117,100 rooted lianas in an old‐growth Panamanian forest to test whether local canopy disturbance explains increasing liana abundance. We found that liana density increased 29.2% and basal area 12.5%. The vast majority of these increases were associated with clonal stem proliferation following canopy disturbance, particularly in liana‐dense, low‐canopy gaps, which had far greater liana increases than did undisturbed forest. Lianas may be ecological niche constructors, arresting tree regeneration in gaps and thus creating a high‐light environment that favours sustained liana proliferation. Our findings demonstrate that liana abundance is increasing rapidly and their ability to proliferate via copious clonal stem production in canopy gaps explains much of their increase in this and possibly other tropical forests.

Lianas Significantly Reduce Tree Performance and Biomass Accumulation Across Tropical Forests: A Global Meta-Analysis

“…The reduction in productivity found in this model was mostly driven by the capacity of lianas to strongly compete for water and light (Meunier et al, 2021). Given that climate change may be accelerating tree mortality (Mcdowell et al, 2018), and that lianas increase in density and basal area in disturbed areas created by tree falls (Ledo et al, 2016;Schnitzer et al, 2021), it is necessary to include the detrimental effects that lianas exert on forest growth and biomass accretion we quantified in this meta-analysis in future vegetation models.…”

“…In other words, lianas likely have a stronger detrimental effect on trees in areas where they are more abundant, assuming that their effect on trees scales with their abundance. Given that there are now 16 studies indicating that liana density, productivity, and biomass are all increasing relative to trees in tropical forests (Pandian and Parthasarathy, 2016;Ceballos and Malizia, 2017;Hogan et al, 2017;Venegas-González et al, 2020;Schnitzer et al, 2021), it is paramount to determine the magnitude at which lianas reduce tree performance and forest biomass, and how these effects change along important environmental gradients.…”

Lianas decelerate tropical forest thinning during succession

“…Lianas themselves contributed very little to the carbon they displaced (Estrada‐Villegas, Hall, et al, 2020; van der Heijden et al, 2015; Lai et al, 2017). The relatively small contribution of lianas to forest‐level carbon results from their low stem volume (Schnitzer et al, 2012, 2021), slow accumulation of biomass (Letcher & Chazdon, 2009), and their greater allocation of above‐ground biomass to leaves than to the stem than similar‐sized trees, which lowers their capacity to store carbon (Chave et al, 2001; Gerwing & Farias, 2000; Putz, 1983).…”

“…However, high liana abundance in young forests (e.g. 40 years and younger) (Barry et al, 2015; Dewalt et al, 2000; Schnitzer et al, 2012, 2021) reduce tree growth and biomass accumulation (Estrada‐Villegas, Hall, et al, 2020). Therefore, the negative effects of lianas on tree‐tree competition and forest thinning may be particularly important in the early stages of forest succession, where lianas likely reduce the potential of secondary forests to sequester carbon (Poorter et al, 2016).…”

“…The contribution of lianas to forest structure and dynamics appears to be increasing in tropical forests (Schnitzer & Bongers, 2011), which may further slow tree thinning and, concomitantly, reduce forest biomass uptake. Multiple long‐term studies in the neotropics and one study in South India (Pandian & Parthasarathy, 2016) reported an increase in liana density and biomass in both absolute terms and relative to trees (Chave et al, 2008; Ingwell et al, 2010; Laurance et al, 2014; Phillips et al, 2002; Schnitzer et al, 2020, 2021; Wright et al, 2004). The increase in lianas relative to trees in tropical forests suggests a greater role of these non‐tree competitors in future forest succession and thinning.…”