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  1. Abstract

    Determining population demographic rates is fundamental to understanding differences in species’ life‐history strategies and their capacity to coexist. Calculating demographic rates, however, is challenging and requires long‐term, large‐scale censuses. Body size may serve as a simple predictor of demographic rate; can it act as a proxy for demographic rate when those data are unavailable? We tested the hypothesis that maximum body size predicts species' demographic rate using repeated censuses of the 77 most common liana species on the Barro Colorado Island, Panama (BCI) 50‐ha plot. We found that maximum stem diameter does predict species' population turnover and demography. We also found that lianas on BCI can grow to the enormous diameter of 635 mm, indicating that they can store large amounts of carbon and compete intensely with tropical canopy trees. This study is the first to show that maximum stem diameter can predict plant species' demographic rates and that lianas can attain extremely large diameters. Understanding liana demography is particularly timely because lianas are increasing rapidly in many tropical forests, yet their species‐level population dynamics remain chronically understudied. Determining per‐species maximum liana diameters in additional forests will enable systematic comparative analyses of liana demography and potential influence across forest types.

     
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  2. Lianas are structural parasites of trees that cause a reduction in tree growth and an increase in tree mortality. Thereby, lianas negatively impact forest carbon storage as evidenced by liana removal experiments. In this proof-of-concept study, we calibrated the Ecosystem Demography model (ED2) using 3 years of observations of net aboveground biomass (AGB) changes in control and removal plots of a liana removal experiment on Gigante Peninsula, Panama. After calibration, the model could accurately reproduce the observations of net biomass changes, the discrepancies between treatments, as well as the observed components of those changes (mortality, productivity, and growth). Simulations revealed that the long-term total (i.e., above- and belowground) carbon storage was enhanced in liana removal plots (+1.2 kg C m –2 after 3 years, +1.8 kg C m –2 after 10 years, as compared to the control plots). This difference was driven by a sharp increase in biomass of early successional trees and the slow decomposition of liana woody tissues in the removal plots. Moreover, liana removal significantly reduced the simulated heterotrophic respiration (−24%), which resulted in an average increase in net ecosystem productivity (NEP) from 0.009 to 0.075 kg C m –2 yr –1 for 10 years after liana removal. Based on the ED2 model outputs, lianas reduced gross and net primary productivity of trees by 40% and 53%, respectively, mainly through competition for light. Finally, model simulations suggested a profound impact of the liana removal on the soil carbon dynamics: the simulated metabolic litter carbon pool was systematically larger in control plots (+51% on average) as a result of higher mortality rates and faster leaf and root turnover rates. By overcoming the challenge of including lianas and depicting their effect on forest ecosystems, the calibrated version of the liana plant functional type (PFT) as incorporated in ED2 can predict the impact of liana removal at large-scale and its potential effect on long-term ecosystem carbon storage. 
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  3. Summary

    Lightning is an important agent of plant mortality and disturbance in forests. Lightning‐caused disturbance is highly variable in terms of its area of effect and disturbance severity (i.e. tree damage and death), but we do not know how this variation is influenced by forest structure and plant composition.

    We used a novel lightning detection system to quantify how lianas influenced the severity and spatial extent (i.e. area) of lightning disturbance using 78 lightning strikes in central Panama.

    The local density of lianas (measured as liana basal area) was positively associated with the number of trees killed and damaged by lightning, and patterns of plant damage indicated that this occurred because lianas facilitated more electrical connections from large to small trees. Liana presence, however, did not increase the area of the disturbance. Thus, lianas increased the severity of lightning disturbance by facilitating damage to additional trees without influencing the footprint of the disturbance.

    These findings indicate that lianas spread electricity to damage and kill understory trees that otherwise would survive a strike. As liana abundance increases in tropical forests, their negative effects on tree survival with respect to the severity of lightning‐related tree damage and death are likely to increase.

     
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  4. Abstract

    The well‐established pattern of forest thinning during succession predicts an increase in mean tree biomass with decreasing tree density. The forest thinning pattern is commonly assumed to be driven solely by tree‐tree competition. The presence of non‐tree competitors could alter thinning trajectories, thus altering the rate of forest succession and carbon uptake. We used a large‐scale liana removal experiment over 7 years in a 60‐ to 70‐year‐old Panamanian forest to test the hypothesis that lianas reduce the rate of forest thinning during succession. We found that lianas slowed forest thinning by reducing tree growth, not by altering tree recruitment or mortality. Without lianas, trees grew and presumably competed more, ultimately reducing tree density while increasing mean tree biomass. Our findings challenge the assumption that forest thinning is driven solely by tree‐tree interactions; instead, they demonstrate that competition from other growth forms, such as lianas, slow forest thinning and ultimately delay forest succession.

     
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  5. Abstract

    The spatial habitat heterogeneity hypothesis posits that habitat complexity increases the abundance and diversity of species. In tropical forests, lianas add substantial habitat heterogeneity and complexity throughout the vertical forest profile, which may maintain animal abundance and diversity. The effects of lianas on tropical animal communities, however, remain poorly understood. We propose that lianas have a positive effect on animals by enhancing habitat complexity. Lianas may have a particularly strong influence on the forest bird community, providing nesting substrate, protection from predators, and nutrition (food). Understory insectivorous birds, which forage for insects that specialize on lianas, may particularly benefit. Alternatively, it is possible that lianas have a negative effect on forest birds by increasing predator abundances and providing arboreal predators with travel routes with easy access to bird nests. We tested the spatial habitat heterogeneity hypothesis on bird abundance and diversity by removing lianas, thus reducing forest complexity, using a large‐scale experimental approach in a lowland tropical forest in the Republic of Panama. We found that removing lianas decreased total bird abundance by 78.4% and diversity by 77.4% after 8 months, and by 40.0% and 51.7%, respectively, after 20 months. Insectivorous bird abundance and diversity 8 months after liana removal were 91.8% and 89.5% lower, respectively, indicating that lianas positively influence insectivorous birds. The effects of liana removal persisted longer for insectivorous birds than other birds, with 77.3% lower abundance and 76.2% lower diversity after 20 months. Liana removal also altered bird community composition, creating two distinct communities in the control and removal plots, with disproportionate effects on insectivores. Our findings demonstrate that lianas have a strong positive influence on the bird community, particularly for insectivorous birds in the forest understory. Lianas may maintain bird abundance and diversity by increasing habitat complexity, habitat heterogeneity, and resource availability.

     
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  6. Abstract

    Lianas reduce tree growth, reproduction, and survival in tropical forests. Liana competition can be particularly intense in isolated forest fragments, where liana densities are high, and thus, host tree infestation is common. Furthermore, lianas appear to grow particularly well during seasonal drought, when they may compete particularly intensely with trees. Few studies, however, have experimentally quantified the seasonal effects of liana competition on multiple tree species in tropical forests. We used a liana removal experiment in a forest fragment in southeastern Brazil to test whether the effects of lianas on tree growth vary with season and tree species identity. We conducted monthly diameter measurements using dendrometer bands on 88 individuals of five tree species for 24 months. We found that lianas had a stronger negative effect on some tree species during the wet season compared to the dry season. Furthermore, lianas significantly reduced the diameter growth of two tree species but had no effect on the other three tree species. The strong negative effect of lianas on some trees, particularly during the wet season, indicates that the effect of lianas on trees varies both seasonally and with tree species identity.

    Abstract in Portuguese is available with online material.

     
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  7. Abstract

    Lianas are prevalent in Neotropical forests, where liana‐tree competition can be intense, resulting in reduced tree growth and survival. The ability of lianas to grow relative to trees during the dry season suggests that liana‐tree competition is also strongest in the dry season. If correct, the predicted intensification of the drying trend over large areas of the tropics in the future may therefore intensify liana‐tree competition resulting in a reduced carbon sink function of tropical forests. However, no study has established whether the liana effect on tree carbon accumulation is indeed stronger in the dry than in the wet season.

    Using 6 years of data from a large‐scale liana removal experiment in Panama, we provide the first experimental test of whether liana effects on tree carbon accumulation differ between seasons. We monitored tree and liana diameter increments at the beginning of the dry and wet season each year to assess seasonal differences in forest‐level carbon accumulation between removal and control plots.

    We found that median liana carbon accumulation was consistently higher in the dry (0.52 Mg C ha−1year−1) than the wet season (0.36 Mg C ha−1year−1) and significantly so in three of the years. Lianas reduced forest‐level median tree carbon accumulation more severely in the wet (1.45 Mg C ha−1year−1) than the dry (1.05 Mg C ha−1year−1) season in all years. However, the relative effect of lianas was similar between the seasons, with lianas reducing forest‐level tree carbon accumulation by 46.9% in the dry and 48.5% in the wet season.

    Synthesis.Our results provide the first experimental demonstration that lianas do not have a stronger competitive effect on tree carbon accumulation during the dry season. Instead, lianas compete significantly with trees during both seasons, indicating a large negative effect of lianas on forest‐level tree biomass increment regardless of seasonal water stress. Longer dry seasons are unlikely to impact liana‐tree competition directly; however, the greater liana biomass increment during dry seasons may lead to further proliferation of liana biomass in tropical forests, with consequences for their ability to store and sequester carbon.

     
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