PhD Candidate, Griffith University
The presence of woody climbers is one of the main features that characterise and identifies rainforests. In some forest systems lianas contribute up to 40% of the above ground green leafy biomass. Such ubiquity and abundance in rainforests suggests a likely functional importance, particularly for herbivory – the fundamental way in which the products of primary production enter the wider food web. Much of our current understanding of insect herbivory in rainforests comes from the study of large canopy trees and saplings. However, inferences and conclusions about herbivory gathered from data on trees cannot simply be extended to lianas due to distinct contrasts in leaf traits between the two groups; most notably, structural, chemical, and phenological properties. Information is needed to quantify the contribution of each functional group, and the roles they play in supporting herbivory. As climatic conditions continue to favour the growth of lianas, understanding their role in ecosystem functioning is increasingly necessary and urgent.
During two consecutive years (May 2016 and 2017) leaves were collected from 36 lianas and 57 trees (29 of which hosted the sampled lianas) in a subtropical rainforest in Queensland, Australia. Herbivory damage from each individual was quantified from over 100+ leaves using the software package ImageJ, and leaf traits such as leaf toughness, total phenols, and elemental concentrations, were determined.
Preliminary results suggest variation in leaf chemistry, leaf structure and herbivory between trees and lianas; and between trees with lianas compared to trees without. Trees hosting lianas had lower levels of herbivory, as well as higher concentrations of leaf nitrogen than those without lianas. Analyses also indicated a lack of consistency among the variables influencing herbivory for each of the plant types. In trees, leaf toughness, phenol concentrations and phosphorus were correlated with herbivory, whereas in lianas no such correlations were evident.
Abstract: Lianas are an important growthform in tropical forests, and liana abundance and biomass may be increasing in some regions. Explanations for liana proliferation hinge upon physiological responses to changing resource conditions that would favour them over trees. Testing a chemical basis for such responses, we assessed 22 foliar traits in 778 lianas and 6496 trees at 48 tropical forest sites. Growthform differences in chemical allocation occurred on a leaf mass and area basis. Light capture-growth and maintenance-metabolism chemicals averaged 14.5 and 16.7% higher mass-based concentration in lianas than in trees globally, whereas structure and defence chemicals averaged 9.0% lower in lianas. Relative differences in chemical allocation by lianas and trees were mediated by climate with peak differences at about 2500 mm year(-1) and 25 °C. Differences in chemical traits suggest that liana expansion could be greatest in forests undergoing increased canopy-level irradiance via disturbance and climate change.
Pub.: 14 Jun '12, Pinned: 07 Aug '17
Abstract: The climbing habit is an evolutionary key innovation in plants because it is associated with enhanced clade diversification. We tested whether patterns of species divergence and variation of three ecophysiological traits that are fundamental for plant adaptation to light environments (maximum photosynthetic rate [A(max)], dark respiration rate [R(d)], and specific leaf area [SLA]) are consistent with this key innovation. Using data reported from four tropical forests and three temperate forests, we compared phylogenetic distance among species as well as the evolutionary rate, phylogenetic distance and phylogenetic signal of those traits in lianas and trees. Estimates of evolutionary rates showed that R(d) evolved faster in lianas, while SLA evolved faster in trees. The mean phylogenetic distance was 1.2 times greater among liana species than among tree species. Likewise, estimates of phylogenetic distance indicated that lianas were less related than by chance alone (phylogenetic evenness across 63 species), and trees were more related than expected by chance (phylogenetic clustering across 71 species). Lianas showed evenness for R(d), while trees showed phylogenetic clustering for this trait. In contrast, for SLA, lianas exhibited phylogenetic clustering and trees showed phylogenetic evenness. Lianas and trees showed patterns of ecophysiological trait variation among species that were independent of phylogenetic relatedness. We found support for the expected pattern of greater species divergence in lianas, but did not find consistent patterns regarding ecophysiological trait evolution and divergence. R(d) followed the species-level pattern, i.e., greater divergence/evolution in lianas compared to trees, while the opposite occurred for SLA and no pattern was detected for A(max). R(d) may have driven lianas' divergence across forest environments, and might contribute to diversification in climber clades.
Pub.: 11 Jun '14, Pinned: 07 Aug '17
Abstract: Recent studies indicate that lianas are increasing in size and abundance relative to trees in neotropical forests. As a result, forest dynamics and carbon balance may be altered through liana-induced suppression of tree growth and increases in tree mortality. Increasing atmospheric CO2 is hypothesized to be responsible for the increase in neotropical lianas, yet no study has directly compared the relative response of tropical lianas and trees to elevated CO2 . We explicitly tested whether tropical lianas had a larger response to elevated CO2 than co-occurring tropical trees and whether seasonal drought alters the response of either growth form. In two experiments conducted in central Panama, one spanning both wet and dry seasons and one restricted to the dry season, we grew liana (n = 12) and tree (n = 10) species in open-top growth chambers maintained at ambient or twice-ambient CO2 levels. Seedlings of eight individuals (four lianas, four trees) were grown in the ground in each chamber for at least 3 months during each season. We found that both liana and tree seedlings had a significant and positive response to elevated CO2 (in biomass, leaf area, leaf mass per area, and photosynthesis), but that the relative response to elevated CO2 for all variables was not significantly greater for lianas than trees regardless of the season. The lack of differences in the relative response between growth forms does not support the hypothesis that elevated CO2 is responsible for increasing liana size and abundance across the neotropics.
Pub.: 05 Dec '14, Pinned: 07 Aug '17
Abstract: Lianas are an important component of tropical forests, contributing up to 25% of the woody stems and 35% of woody species diversity. Lianas invest less in structural support but more in leaves compared to trees of similar biomass. These physiological and morphological differences suggest that lianas may interact with neighboring plants in ways that are different from similarly sized trees. However, the vast majority of past liana competition studies have failed to identify the unique competitive effects of lianas by controlling for the amount of biomass removed. We assessed liana competition in the forest understory over the course of 3 years by removing liana biomass and an equal amount of tree biomass in 40 plots at 10 sites in a secondary tropical moist forest in central Panama. We found that growth of understory trees and lianas, as well as planted seedlings, was limited due to competitive effects from both lianas and trees, though the competitive impacts varied by species, season, and size of neighbors. The removal of trees resulted in greater survival of planted seedlings compared to the removal of lianas, apparently related to a greater release from competition for light. In contrast, lianas had a species-specific negative effect on drought-tolerant Dipteryx oleifera seedlings during the dry season, potentially due to competition for water. We conclude that, at local scales, lianas and trees have unique and differential effects on understory dynamics, with lianas potentially competing more strongly during the dry season, and trees competing more strongly for light.
Pub.: 17 Dec '14, Pinned: 07 Aug '17
Abstract: Tropical forests store vast quantities of carbon, account for one-third of the carbon fixed by photosynthesis, and are a major sink in the global carbon cycle. Recent evidence suggests that competition between lianas (woody vines) and trees may reduce forest-wide carbon uptake; however, estimates of the impact of lianas on carbon dynamics of tropical forests are crucially lacking. Here we used a large-scale liana removal experiment and found that, at 3 y after liana removal, lianas reduced net above-ground carbon uptake (growth and recruitment minus mortality) by ∼76% per year, mostly by reducing tree growth. The loss of carbon uptake due to liana-induced mortality was four times greater in the control plots in which lianas were present, but high variation among plots prevented a significant difference among the treatments. Lianas altered how aboveground carbon was stored. In forests where lianas were present, the partitioning of forest aboveground net primary production was dominated by leaves (53.2%, compared with 39.2% in liana-free forests) at the expense of woody stems (from 28.9%, compared with 43.9%), resulting in a more rapid return of fixed carbon to the atmosphere. After 3 y of experimental liana removal, our results clearly demonstrate large differences in carbon cycling between forests with and without lianas. Combined with the recently reported increases in liana abundance, these results indicate that lianas are an important and increasing agent of change in the carbon dynamics of tropical forests.
Pub.: 16 Oct '15, Pinned: 07 Aug '17
Abstract: Ecological orthodoxy suggests that old-growth forests should be close to dynamic equilibrium, but this view has been challenged by recent findings that neotropical forests are accumulating carbon and biomass, possibly in response to the increasing atmospheric concentrations of carbon dioxide. However, it is unclear whether the recent increase in tree biomass has been accompanied by a shift in community composition. Such changes could reduce or enhance the carbon storage potential of old-growth forests in the long term. Here we show that non-fragmented Amazon forests are experiencing a concerted increase in the density, basal area and mean size of woody climbing plants (lianas). Over the last two decades of the twentieth century the dominance of large lianas relative to trees has increased by 1.7-4.6% a year. Lianas enhance tree mortality and suppress tree growth, so their rapid increase implies that the tropical terrestrial carbon sink may shut down sooner than current models suggest. Predictions of future tropical carbon fluxes will need to account for the changing composition and dynamics of supposedly undisturbed forests.
Pub.: 16 Aug '02, Pinned: 07 Aug '17
Abstract: Lianas are a principal physiognomic component of tropical and subtropical forests and are typically considered to be parasites of trees. In contrast, the substantial contribution of lianas to rainforest leaf litter production (up to 40%) suggests that they play important roles in nutrient cycles and may benefit their host trees. Lianas contribute disproportionately to total forest litter production at least partially because lianas invest relatively little in support structures and proportionately much more to leaf production when compared with trees. In contrast to tree leaves, liana leaves are higher in nutrient concentrations, relatively short-lived, and decompose more rapidly. In addition, the special life form of lianas allows them to grow vertically and horizontally in the forest and relocate nutrients, mainly towards their host trees, through the production of leaf litter. Consequently, lianas may contribute substantially to the high rainforest productivity, and the roles they play in liana/tree associations and rainforest dynamics needs to be re-evaluated.
Pub.: 02 Dec '11, Pinned: 07 Aug '17
Abstract: Inventories of trees and lianas were performed at a 13-year interval (1979–1992) in an evergreen forest in north-east Gabon. The number of trees decreased while their basal area and species richness increased. In contrast, both the richness and density of lianas decreased. Lianas with active climbing mechanisms were the main types to disappear.
Pub.: 01 Feb '01, Pinned: 07 Aug '17
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