Understanding how tropical rainforest trees may respond to the precipitation extremes predicted in future climate change scenarios is paramount for their conservation and management. Tree species ...clearly differ in drought susceptibility, suggesting that variable water transport strategies exist. Using a multi-disciplinary approach, we examined the hydraulic variability in trees in a lowland tropical rainforest in north-eastern Australia. We studied eight tree species representing broad plant functional groups (one palm and seven eudicot mature-phase, and early-successional trees). We characterised the species' hydraulic system through maximum rates of volumetric sap flow and velocities using the heat ratio method, and measured rates of tree growth and several stem, vessel, and leaf traits. Sap flow measures exhibited limited variability across species, although early-successional species and palms had high mean sap velocities relative to most mature-phase species. Stem, vessel, and leaf traits were poor predictors of sap flow measures. However, these traits exhibited different associations in multivariate analysis, revealing gradients in some traits across species and alternative hydraulic strategies in others. Trait differences across and within tree functional groups reflect variation in water transport and drought resistance strategies. These varying strategies will help in our understanding of changing species distributions under predicted drought scenarios.
Traditional fishing communities are strongholds of ethnobiological knowledge but establishing to what degree they harbor cultural consensus about different aspects of this knowledge has been a ...challenge in many ethnobiological studies.
We conducted an ethnobiological study in an artisanal fishing community in northeast Brazil, where we interviewed 91 community members (49 men and 42 women) with different type of activities (fishers and non-fishers), in order to obtain free lists and salience indices of the fish they know. To establish whether there is cultural consensus in their traditional knowledge on fish, we engaged a smaller subset of 45 participants in triad tasks where they chose the most different fish out of 30 triads. We used the similarity matrices generated from the task results to detect if there is cultural consensus in the way fish were classified by them.
The findings show how large is the community's knowledge of fish, with 197 ethnospecies registered, of which 33 species were detected as salient or important to the community. In general, men cited more fish than women. We also found that there was no cultural consensus in the ways fish were classified.
Both free-listing and triad task methods revealed little cultural consensus in the way knowledge is structured and how fish were classified by community members. Our results suggest that it is prudent not to make assumptions that a given local community has a single cultural consensus model in classifying the organisms in their environment.
Abstract Tropical forest and savanna biomes are pivotal in the functioning of the Earth system. Both are biodiverse and under increasing threat due to land clearing and anthropogenic climate change, ...and play important roles in the global carbon cycle, through maintenance of a large carbon pool in tropical forests, and exchange in savannas through extensive landscape fires. Reliable mapping of tropical forest and savanna is essential to understand how the current distribution of these vegetation types is controlled by climate land clearing and fire. Using Google Maps satellite imagery, we manually classified 24 239 random points as forest, savanna, or anthropogenic landscapes within the tropics and applied this novel dataset to defining the climatic zone where forest and savanna exist as alternative states. Because fire and climate are correlated, we developed separate geospatial models to rank the importance of climate, topography, and human influence on vegetation present. This modeling confirmed that those areas with more fires had lower probabilities of tropical forest, that forest was most likely in areas with high mean annual rainfall with little seasonal variation in precipitation, and that anthropogenic factors disrupt this environmental predictability. We also identified areas where tropical forest and savanna both co-occur, but these were relatively uncommon. These relationships suggest that future drier climates projected under anthropogenic climate change, combined with clearing and burning that have reduced tropical forest extent to a subset of its theoretical distribution, will lead to irreversible loss of tropical forests. Our modeling provides global mapping that can be used track further changes to distribution of tropical forests.
Ecological theory differentiates rainforest and open vegetation in many regions as functionally divergent alternative stable states with transitional (ecotonal) vegetation between the two forming ...transient unstable states. This transitional vegetation is of considerable significance, not only as a test case for theories of vegetation dynamics, but also because this type of vegetation is of major economic importance, and is home to a suite of species of conservation significance, including the world's tallest flowering plants. We therefore created predictions of patterns in plant functional traits that would test the alternative stable states model of these systems. We measured functional traits of 128 trees and shrubs across tropical and temperate rainforest - open vegetation transitions in Australia, with giant eucalypt forests situated between these vegetation types. We analysed a set of functional traits: leaf carbon isotopes, leaf area, leaf mass per area, leaf slenderness, wood density, maximum height and bark thickness, using univariate and multivariate methods. For most traits, giant eucalypt forest was similar to rainforest, while rainforest, particularly tropical rainforest, was significantly different from the open vegetation. In multivariate analyses, tropical and temperate rainforest diverged functionally, and both segregated from open vegetation. Furthermore, the giant eucalypt forests overlapped in function with their respective rainforests. The two types of giant eucalypt forests also exhibited greater overall functional similarity to each other than to any of the open vegetation types. We conclude that tropical and temperate giant eucalypt forests are ecologically and functionally convergent. The lack of clear functional differentiation from rainforest suggests that giant eucalypt forests are unstable states within the basin of attraction of rainforest. Our results have important implications for giant eucalypt forest management.
Summary
Understanding the anatomical basis of plant water transport in forest ecosystems is crucial for contextualizing community‐level adaptations to drought, especially in life‐form‐rich tropical ...forests. To provide this context, we explored wood functional anatomy traits related to plant hydraulic architecture across different plant functional groups in a lowland tropical rain forest.
We measured wood traits in 90 species from six functional groups (mature‐phase, understorey and pioneer trees; understorey and pioneer shrubs; vines) and related these traits to intrinsic water‐use efficiency (WUEi) as a measure of physiological performance. We also examined vessel size distribution patterns across groups to determine trade‐offs in theoretical hydraulic safety vs. efficiency.
Some plant functional groups exhibited significant differences in vessel parameters and WUEi. Vessel diameters in vines and pioneer trees were two‐ to threefold greater on average than in understorey trees and shrubs. Contrastingly, vessels in understorey trees and shrubs fell within the smaller size classes, suggesting greater safety mechanisms. In addition to these trends, large vessel dimensions were important predictors of WUEi among the functional groups.
We conclude that wood functional anatomy profiles varied across plant functional groups in a tropical rain forest. These groups can therefore serve as a framework for further investigations on structure–function relationships and a sound basis for modelling species responses to drought.
A lay summary is available for this article.
Lay Summary
Litsea Lam. is an ecological and economic important genus of the “core Lauraceae” group in the Lauraceae. The few studies to date on the comparative chloroplast genomics and phylogenomics of Litsea ...have been conducted as part of other studies on the Lauraceae. Here, we sequenced the whole chloroplast genome sequence of Litsea auriculata, an endangered tree endemic to eastern China, and compared this with previously published chloroplast genome sequences of 11 other Litsea species. The chloroplast genomes of the 12 Litsea species ranged from 152,132 (L. szemaois) to 154,011 bp (L. garrettii) and exhibited a typical quadripartite structure with conserved genome arrangement and content, with length variations in the inverted repeat regions (IRs). No codon usage preferences were detected within the 30 codons used in the chloroplast genomes, indicating a conserved evolution model for the genus. Ten intergenic spacers (psbE–petL, trnH–psbA, petA–psbJ, ndhF–rpl32, ycf4–cemA, rpl32–trnL, ndhG–ndhI, psbC–trnS, trnE–trnT, and psbM–trnD) and five protein coding genes (ndhD, matK, ccsA, ycf1, and ndhF) were identified as divergence hotspot regions and DNA barcodes of Litsea species. In total, 876 chloroplast microsatellites were located within the 12 chloroplast genomes. Phylogenetic analyses conducted using the 51 additional complete chloroplast genomes of “core Lauraceae” species demonstrated that the 12 Litsea species grouped into four sub-clades within the Laurus-Neolitsea clade, and that Litsea is polyphyletic and closely related to the genera Lindera and Laurus. Our phylogeny strongly supported the monophyly of the following three clades (Laurus–Neolitsea, Cinnamomum–Ocotea, and Machilus–Persea) among the above investigated “core Lauraceae” species. Overall, our study highlighted the taxonomic utility of chloroplast genomes in Litsea, and the genetic markers identified here will facilitate future studies on the evolution, conservation, population genetics, and phylogeography of L. auriculata and other Litsea species.
Although rain forest is characterized as pyrophobic, pyrophilic giant eucalypts grow as rain forest emergents in both temperate and tropical Australia. In temperate Australia, such eucalypts depend ...on extensive, infrequent fires to produce conditions suitable for seedling growth. Little is known, however, about constraints on seedlings of tropical giant eucalypts. We tested whether seedlings of Eucalyptus grandis experience edaphic constraints similar to their temperate counterparts. We hypothesized that phosphorous addition would alleviate edaphic constraints. We grew seedlings in a factorial experiment combining fumigation (to simulate nutrient release and soil pasteurization by fire), soil type (E. grandis forest versus rain forest soil) and phosphorus addition as factors. We found that phosphorus was the principal factor limiting E. grandis seedling survival and growth in rain forest soil, and that fumigation enhanced survival of seedlings in both E. grandis forest and rain forest soil. We conclude that similar to edaphic constraints on temperate giant eucalypts, mineral nutrient and biotic attributes of a tropical rain forest soil may hamper E. grandis seedling establishment. In rain forest soil, E. grandis seedlings benefited from conditions akin to a fire-generated ashbed (i.e., an "ashbed effect").
Strawberry guava (Psidium cattleianum) is a shade‐tolerant shrub or small tree invader in tropical and subtropical regions and is considered among the world's top 100 worst invasive species. Studies ...from affected regions report deleterious effects of strawberry guava invasion on native vegetation. Here we examine the life history demographics and environmental determinants of strawberry guava invasions to inform effective weed management in affected rainforest regions. We surveyed the vegetation of 8 mature rainforest and 33 successional sites at various stages of regeneration in the Australian Wet Tropics and found that strawberry guava invasion was largely restricted to successional forests. Strawberry guava exhibited high stem and seedling densities, represented approximately 8% of all individual stems recorded and 20% of all seedlings recorded. The species also had the highest basal area among all the non‐native woody species measured. We compared environmental and community level effects between strawberry guava‐invaded and non‐invaded sites, and modelled how the species basal area and recruitment patterns respond to these effects. Invaded sites differed from non‐invaded sites in several environmental features such as aspect, distance from intact forest blocks, as well as supported higher grass and herb stem densities. Our analysis showed that invasion is currently ongoing in secondary forests, and also that strawberry guava is able to establish and persist under closed canopies. If left unchecked, strawberry guava invasion will have deleterious consequences for native regenerating forest in the Australian Wet Tropics.
Abstract
Climate change scenarios predict increasing atmospheric CO2 concentrations (CO2), temperatures and droughts in tropical regions. Individually, the effects of these climate factors on plants ...are well established, whereas experiments on the interactive effects of a combination of factors are rare. Moreover, how these environmental factors will affect tree species along a wet to dry gradient (e.g., along tropical forest–savanna transitions) remains to be investigated. We hypothesized that under the simulated environmental conditions, plant growth, physiological performance and survivorship would vary in a manner consistent with the species’ positions of origin along this gradient. In a glasshouse experiment, we raised seedlings of three Eucalyptus species, each occurring naturally in a wet forest, savanna and forest–savanna ecotone, respectively. We evaluated the effect of drought, elevated temperature (4 °C above ambient glasshouse temperature of 22 °C) and elevated temperature in combination with elevated CO2 (400 ppm CO2 above ambient of 400 ppm), on seedling growth, survivorship and physiological responses (photosynthesis, stomatal conductance and water-use efficiency). Elevated temperature under ambient CO2 had little effect on growth, biomass and plant performance of well-watered seedlings, but hastened mortality in drought-affected seedlings, affecting the forest and ecotone more strongly than the savanna species. In contrast, elevated CO2 in combination with elevated temperatures delayed the appearance of drought stress symptoms and enhanced survivorship in drought-affected seedlings, with the savanna species surviving the longest, followed by the ecotone and forest species. Elevated CO2 in combination with elevated temperatures also enhanced growth and biomass and photosynthesis in well-watered seedlings of all species, but modified shoot:root biomass partitioning and stomatal conductance differentially across species. Our study highlights the need for a better understand of the interactive effects of elevated CO2, temperature and drought on plants and the potential to upscale these insights for understanding biome changes.
Increased drought is forecasted for tropical regions, with severe implications for the health and function of forest ecosystems. How mature forest trees will respond to water deficit is poorly known. ...We investigated wood anatomy and leaf traits in lowland tropical forest trees after 24 months of experimental rainfall exclusion. Sampling sun‐exposed young canopy branches from target species, we found species‐specific systematic variation in hydraulic‐related wood anatomy and leaf traits in response to drought stress. Relative to controls, drought‐affected individuals of different tree species variously exhibited trait measures consistent with increasing hydraulic safety. These included narrower or less vessels, reduced vessel groupings, lower theoretical water conductivities, less water storage tissue and more abundant fiber in their wood, and more occluded vessels. Drought‐affected individuals also had thinner leaves, and more negative pre‐dawn or mid‐day leaf water potentials. Future studies examining both wood and leaf hydraulic traits should improve the representation of plant hydraulics within terrestrial ecosystem and biosphere models, and help fine‐tune predictions of how future climate changes will affect tropical forests globally.
Understanding how tropical rainforest trees will respond to climate change is important given worrisome projection drought events in tropical regions. We found that mature tropical trees can modify their water transport mechanisms when exposed to drought, at least in the short term. These results allow us to highlight complexities for understanding plant responses to climate change.
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