Hyperdiverse Tropical Forests Research Articles

Assessing variation in the effectiveness of IUCN protected area categorisation. What remotely sensed forest integrity and human modification reveals across the major tropical forest biomes

• We focused on evaluating the efficacy of forested protected areas (PAs) across the three main tropical biomes- Congo Basin, Tropical Andes, insular Malaysia and Indonesia. • PA efficacy was evaluated on the basis of ecoregional representation, human modification and forest integrity. • Representation of key ecoregions varied with 7%, 11% and 22% of named ecoregions being unprotected within each major region. • IUCN management categories play a minor role in influencing PA efficacy. • PA size was an important determinant of PA efficacy. One of the major threats facing protected areas (PAs) in hyper-diverse tropical forest ecosystems is human modification of their natural habitats. With a focus on forested PAs situated across three of the world’s major tropical regions, the Congo Basin, insular Indonesia Malaysia and the Tropical Andes. We analyse their representation of identified ecoregions and remote sensing data of human modification and forest integrity levels within PAs and used a generalized linear modelling approach to estimate the influences on these pressures, with a particular focus on IUCN management categorisation, PA size, and geographic location. Representation of key ecoregions varied with 7%, 11% and 22% of named ecoregions being unprotected within each major region. Overall, the IUCN management category allocation played a minor role in influencing the modification and forest integrity observed within PAs. Instead, PA size was the most important determinant of these variables across the different regions under consideration. This work provides further evidence to suggest that the assignment of PAs to IUCN categories in their current form is not interpreted consistently across different regions and does not correspond to the conservation benefits expected to be conferred by this categorisation.

Spatial pattern of functional genes abundance reveals the importance of PhoD gene harboring bacterial community for maintaining plant growth in the tropical forest of Southwestern China

The concept of microbial functional genes has added a new dimension to microbial ecology research by improving the model of microbial community-ecosystem functions relationship. However, our knowledge vis-à-vis fine-scale spatial distribution pattern of functional genes and their probable impact on plant community in the hyper-diverse tropical forest ecosystem is very limited. Here, we investigated the spatial pattern of functional genes abundance (NirK, AOA, AOB, and PhoD), identified key influencing factors, and distinguished the key functional group supporting the plant community in a tropical rainforest located in Xishuangbanna. In total, 200 soil samples and vegetation data of ~4800 individuals of plants across a 1 ha study area were collected. Our results detected higher spatial variability with a maximum magnitude of abundance for PhoD gene (4.53 × 107 copies) followed by NirK (2.71 × 106 copies), AOA (1.97 × 106 copies), and AOB (7.38 × 104 copies). A strong spatial dependence was observed for PhoD and NirK over the distance of 17 and 18 m, respectively. Interestingly, the N:P stoichiometry played a critical role in structuring the spatial pattern of the most abundant PhoD gene. The significant positive and negative relationship of PhoD with N:P ratio and available phosphorus, respectively, indicated that the P-limiting environment was a driving factor for recruitment of PhoD gene community. The structural equation modeling ascertained the direct positive impact of PhoD on plant biomass and high demand of available P by plants suggesting that the organic phosphorus mineralization process is essential to maintain plant productivity by re-establishing the availability of the most limiting P nutrient. Our preliminary study improves our understanding of how microbial functional genes-environment associations could be used for monitoring soil health and its overall impact on ecosystem multifunctionality. Finally, we intend to conduct the study at a large spatial scale for achieving a holistic view.

Topography consistently drives intra‐ and inter‐specific leaf trait variation within tree species complexes in a Neotropical forest

Tropical forests shelter the highest species diversity worldwide, although genus diversity is lower than expected. In the species‐rich genera, species complexes are composed of closely‐related species that share large amounts of genetic variation. Despite the key role of species complexes in diversification, evolution and functioning of ecological communities, little is known on why species complexes arise and how they are maintained in Neotropical forests. Examining how individual phenotypes vary along environmental gradients, within and among closely‐related species within species complexes, can reveal processes allowing species coexistence within species complexes. We examined leaf functional trait variation with topography in a hyperdiverse tropical forest of the Guiana Shield. We collected leaf functional traits from 766 trees belonging to five species in two species complexes in permanent plots encompassing a diversity of topographic positions. We tested the role of topography on leaf functional trait variation with a hierarchical Bayesian model, controlling for individual tree diameter effect. We show that, mirroring what has been previously observed among species and communities, individual leaf traits covary from acquisitive to conservative strategy within species. Moreover, decreasing wetness from bottomlands to plateaus was associated with a shift of leaf traits from an acquisitive to a conservative strategy both across and within closely‐related species. Our results suggest that intraspecific trait variability widens species’ niches and converges at species’ margins where niches overlap, potentially implying local neutral processes. Intraspecific trait variability favors local adaptation and divergence of closely‐related species within species complexes. It is potentially maintained through interspecific sharing of genetic variation through hybridization.

Small vertebrates are key elements in the frugivory networks of a hyperdiverse tropical forest

The local, global or functional extinction of species or populations of animals, known as defaunation, can erode important ecological services in tropical forests. Many mutualistic interactions, such as seed dispersal of large seeded plants, can be lost in large continuous forests due to the rarity of large-bodied mammalian frugivores. Most of studies that try to elucidate the effects of defaunation on seed dispersal focused on primates or birds, and we lack a detailed understanding on the interactions between ground-dwelling fauna and fleshy fruits. Using camera traps in forest areas with different degrees of defaunation, we described the organization of frugivory networks involving birds, mammals and plants. We recorded 375 frugivory interactions between 21 frugivores and 150 fruiting trees of 30 species of fleshy fruit plants in six sites in continuous Atlantic forest of Brazil. We found that small frugivores—particularly small rodents and birds—were responsible for 72% of the events of frugivory. Large frugivores, such as tapirs and peccaries, were responsible for less than 21% of frugivory events. Our results indicate that the interactions between flesh fruiting plants and frugivores are dominated by small frugivores, an indication of a functional loss of large frugivores in this endangered biome.

Soil Fungal Community Characteristics and Mycelial Production Across a Disturbance Gradient in Lowland Dipterocarp Rainforest in Borneo

The rainforests of Southeast Asia are a global biodiversity hotspot under increasing pressure from human activity. Selective logging and forest conversion to oil palm plantation has major implications for biogeochemical cycling and carbon storage that are underpinned by plant-soil interactions. Soil fungi are key regulators of carbon and mineral nutrient flows between above- and below-ground organisms, yet understanding of fungal community-productivity relationships in hyper-diverse tropical forests is lacking. Recent studies suggest sensitivity of soil fungal communities to land-use change, although impacts on fungal productivity remain largely unresolved. To address this gap, we installed hyphal in-growth bags for 6 months in old-growth (OG) and selectively logged (SL) forest and oil palm plantation (OP) in Bornean lowland rainforest. Mycelial (actively foraging) fungal communities were characterized by ITS amplicon sequencing, and mycelial production estimated by measurement of fungal hyphae. Mycelial fungal community compositions were similar in OG and SL forest, whereas OP had significantly different communities of saprotrophic, mycorrhizal, and pathogenic fungi. In particular, total mycorrhizal and ectomycorrhizal fungal relative abundances, total mycorrhizal richness and mycelial production was reduced. However, due to restricted sampling replication in OP, effects associated with site could not be excluded. In forest plots (OG & SL), we further explored the broader drivers of mycelial fungal communities using tree community, structure and productivity data, and soil and environmental properties. Forest mycelial community dissimilarities were related to soil and vegetation characteristics, while mycelial production was broadly independent of these as well as fungal community attributes. An increase in arbuscular mycorrhizal relative abundance was also found with selective logging, which may have implications for carbon storage capacity in these forests, while an apparent retention of mycorrhizal mycelium in SL forest may act as a reservoir of inoculum that could aid forest restoration. Our results show that conversion of rainforest to oil palm plantation has significant consequences for fungal diversity-productivity relationships with implications for nutrient and carbon dynamics and restoration over large spatial scales.

Multispectral canopy reflectance improves spatial distribution models of Amazonian understory species

Species distribution models are required for the research and management of biodiversity in the hyperdiverse tropical forests, but reliable and ecologically relevant digital environmental data layers are not always available. We here assess the usefulness of multispectral canopy reflectance (Landsat) relative to climate data in modelling understory plant species distributions in tropical rainforests. We used a large dataset of quantitative fern and lycophyte species inventories across lowland Amazonia as the basis for species distribution modelling (SDM). As predictors, we used CHELSA climatic variables and canopy reflectance values from a recent basin‐wide composite of Landsat TM/ETM+ images both separately and in combination. We also investigated how species accumulate over sites when environmental distances were expressed in terms of climatic or surface reflectance variables. When species accumulation curves were constructed such that differences in Landsat reflectance among the selected plots were maximised, species accumulated faster than when climatic differences were maximised or plots were selected in a random order. Sixty‐nine species were sufficiently frequent for species distribution modelling. For most of them, adequate SDMs were obtained whether the models were based on CHELSA data only, Landsat data only or both combined. Model performance was not influenced by species’ prevalence or abundance. Adding Landsat‐based environmental data layers overall improved the discriminatory capacity of SDMs compared to climate‐only models, especially for soil specialist species. Our results show that canopy surface reflectance obtained by multispectral sensors can provide studies of tropical ecology, as exemplified by SDMs, much higher thematic (taxonomic) detail than is generally assumed. Furthermore, multispectral datasets complement the traditionally used climatic layers in analyses requiring information on environmental site conditions. We demonstrate the utility of freely available, global remote sensing data for biogeographical studies that can aid conservation planning and biodiversity management.

Conservation of Tropical Forests in the Anthropocene.

If current trends continue, the tropical forests of the Anthropocene will be much smaller, simpler, steeper and emptier than they are today. They will be more diminished in size and heavily fragmented (especially in lowland wet forests), have reduced structural and species complexity, be increasingly restricted to steeper, less accessible areas, and be missing many heavily hunted species. These changes, in turn, will greatly reduce the quality and quantity of ecosystem services that tropical forests can provide. Driving these changes will be continued clearance for farming and monoculture forest plantations, unsustainable selective logging, overhunting, and, increasingly, climate change. Concerted action by local and indigenous communities, environmental groups, governments, and corporations can reverse these trends and, if successful, provide future generations with a tropical forest estate that includes a network of primary forest reserves robustly defended from threats, recovering logged and secondary forests, and resilient community forests managed for the needs of local people. Realizing this better future for tropical forests and people will require formalisation of land tenure for local and indigenous communities, better-enforced environmental laws, the widescale roll-out of payments for ecosystem service schemes, and sustainable intensification of under-yielding farmland, as well as global-scale societal changes, including reduced consumerism, meat consumption, fossil fuel reliance, and population growth. But the time to act is now, while the opportunity remains to protect a semblance of intact, hyperdiverse tropical forests.

Bioacoustic monitoring reveals shifts in breeding songbird populations and singing behaviour with selective logging in tropical forests

Abstract Selective logging is the primary cause of tropical forest degradation and is rapidly expanding worldwide. While the impacts of logging on species diversity and distributions are well understood, little is known about the effects of logging on animal behaviours central to individual fitness and population persistence. The song rate of breeding songbirds is a behavioural trait that is often positively associated with male density and used by conspecific females as an indicator of territory and male quality. Thus, contrasting logging‐induced adjustments in song rates of individual birds with population shifts may illuminate potential mechanisms underlying population distributions. We present a novel application of bioacoustic monitoring, integrating counts of individuals, songs and duets from single automated recording units (ARUs) with N‐mixture models, to estimate shifts in population parameters (occupancy, abundance) and singing behaviours (per‐capita song rates, per‐pair duet rates) of 32 Bornean songbird species with logging. We tested hypotheses on the relationships between adjustments in behavioural and population parameters with logging, and further tested the extent to which species traits predicted behavioural and population shifts. Adjustments to singing behaviour in 59 and 53% of species (57% of duetting species) were concordant with differences in occupancy and abundance respectively, such that species showing reduced populations with logging also produced fewer songs per‐capita, and vice versa. Species known to prefer undisturbed habitats and large‐bodied species showed the most negative effects of logging on singing behaviour and population distributions. Species known to exploit degraded habitats exhibited the opposite pattern. Subdued singing in logged forests by species of conservation concern suggests limited competition between territorial males in small populations and may also signal low‐quality territories. Synthesis and applications. We demonstrate that bioacoustic monitoring can be used to not only estimate important population parameters of occupancy and abundance across a diverse tropical songbird community, but also enables quantification of behaviours considered relevant to individual fitness, yet unobtainable with conventional methods (e.g. point counts). Bioacoustics provides a viable approach to reliable automated large‐scale monitoring of hyperdiverse tropical forest systems under logging operations and other land‐use pressures.

Can traits predict individual growth performance? A test in a hyperdiverse tropical forest.

Summary The functional trait approach has, as a central tenet, that plant traits are functional and shape individual performance, but this has rarely been tested in the field. Here, we tested the individual‐based trait approach in a hyperdiverse Amazonian tropical rainforest and evaluated intraspecific variation in trait values, plant strategies at the individual level, and whether traits are functional and predict individual performance.We evaluated > 1300 tree saplings belonging to > 383 species, measured 25 traits related to growth and defense, and evaluated the effects of environmental conditions, plant size, and traits on stem growth.A total of 44% of the trait variation was observed within species, indicating a strong potential for acclimation. Individuals showed two strategy spectra, related to tissue toughness and organ size vs leaf display. In this nutrient‐ and light‐limited forest, traits measured at the individual level were surprisingly poor predictors of individual growth performance because of convergence of traits and growth rates.Functional trait approaches based on individuals or species are conceptually fundamentally different: the species‐based approach focuses on the potential and the individual‐based approach on the realized traits and growth rates. Counterintuitively, the individual approach leads to a poor prediction of individual performance, although it provides a more realistic view on community dynamics.

Land use not litter quality is a stronger driver of decomposition in hyperdiverse tropical forest.

In hyperdiverse tropical forests, the key drivers of litter decomposition are poorly understood despite its crucial role in facilitating nutrient availability for plants and microbes. Selective logging is a pressing land use with potential for considerable impacts on plant–soil interactions, litter decomposition, and nutrient cycling. Here, in Borneo's tropical rainforests, we test the hypothesis that decomposition is driven by litter quality and that there is a significant “home‐field advantage,” that is positive interaction between local litter quality and land use. We determined mass loss of leaf litter, collected from selectively logged and old‐growth forest, in a fully factorial experimental design, using meshes that either allowed or precluded access by mesofauna. We measured leaf litter chemical composition before and after the experiment. Key soil chemical and biological properties and microclimatic conditions were measured as land‐use descriptors. We found that despite substantial differences in litter quality, the main driver of decomposition was land‐use type. Whilst inclusion of mesofauna accelerated decomposition, their effect was independent of land use and litter quality. Decomposition of all litters was slower in selectively logged forest than in old‐growth forest. However, there was significantly greater loss of nutrients from litter, especially phosphorus, in selectively logged forest. The analyses of several covariates detected minor microclimatic differences between land‐use types but no alterations in soil chemical properties or free‐living microbial composition. These results demonstrate that selective logging can significantly reduce litter decomposition in tropical rainforest with no evidence of a home‐field advantage. We show that loss of key limiting nutrients from litter (P & N) is greater in selectively logged forest. Overall, the findings hint at subtle differences in microclimate overriding litter quality that result in reduced decomposition rates in selectively logged forests and potentially affect biogeochemical nutrient cycling in the long term.

There's no place like home: seedling mortality contributes to the habitat specialisation of tree species across Amazonia.

Understanding the mechanisms generating species distributions remains a challenge, especially in hyperdiverse tropical forests. We evaluated the role of rainfall variation, soil gradients and herbivory on seedling mortality, and how variation in seedling performance along these gradients contributes to habitat specialisation. In a 4-year experiment, replicated at the two extremes of the Amazon basin, we reciprocally transplanted 4638 tree seedlings of 41 habitat-specialist species from seven phylogenetic lineages among the three most important forest habitats of lowland Amazonia. Rainfall variation, flooding and soil gradients strongly influenced seedling mortality, whereas herbivory had negligible impact. Seedling mortality varied strongly among habitats, consistent with predictions for habitat specialists in most lineages. This suggests that seedling performance is a primary determinant of the habitat associations of adult trees across Amazonia. It further suggests that tree diversity, currently mostly harboured in terra firme forests, may be strongly impacted by the predicted climate changes in Amazonia.

Seedling survival responses to conspecific density, soil nutrients, and irradiance vary with age in a tropical forest.

Understanding processes that promote species coexistence is integral to diversity maintenance. In hyperdiverse tropical forests, local conspecific density (LCD) and light are influential to woody seedling recruitment and soil nutrients are often limiting, yet the simultaneous effects of these factors on seedling survival across time remain unknown. We fit species- and age-specific models to census and resource data of seedlings of 68 woody species from a Costa Rican wet tropical forest. In decreasing order of prevalence, seedling survivorship was related to LCD, soil base cations, irradiance, nitrogen, and phosphorus. Species-specific responses to factors did not covary, providing evidence that species life history strategies have not converged to one continuum of high-surviving stress tolerant to low-surviving stress intolerant species. Survival responses to all factors varied over the average seedling's lifetime, indicating seedling requirements change with age and conclusions drawn about processes important to species coexistence depend on temporal resolution.

Diversity enhances carbon storage in tropical forests

AbstractAimTropical forests store 25% of global carbon and harbour 96% of the world's tree species, but it is not clear whether this high biodiversity matters for carbon storage. Few studies have teased apart the relative importance of forest attributes and environmental drivers for ecosystem functioning, and no such study exists for the tropics.LocationNeotropics.MethodsWe relate aboveground biomass (AGB) to forest attributes (diversity and structure) and environmental drivers (annual rainfall and soil fertility) using data from 144,000 trees, 2050 forest plots and 59 forest sites. The sites span the complete latitudinal and climatic gradients in the lowland Neotropics, with rainfall ranging from 750 to 4350 mm year−1. Relationships were analysed within forest sites at scales of 0.1 and 1 ha and across forest sites along large‐scale environmental gradients. We used a structural equation model to test the hypothesis that species richness, forest structural attributes and environmental drivers have independent, positive effects on AGB.ResultsAcross sites, AGB was most strongly driven by rainfall, followed by average tree stem diameter and rarefied species richness, which all had positive effects on AGB. Our indicator of soil fertility (cation exchange capacity) had a negligible effect on AGB, perhaps because we used a global soil database. Taxonomic forest attributes (i.e. species richness, rarefied richness and Shannon diversity) had the strongest relationships with AGB at small spatial scales, where an additional species can still make a difference in terms of niche complementarity, while structural forest attributes (i.e. tree density and tree size) had strong relationships with AGB at all spatial scales.Main conclusionsBiodiversity has an independent, positive effect on AGB and ecosystem functioning, not only in relatively simple temperate systems but also in structurally complex hyperdiverse tropical forests. Biodiversity conservation should therefore be a key component of the UN Reducing Emissions from Deforestation and Degradation strategy.

A joint individual-based model coupling growth and mortality reveals that tree vigor is a key component of tropical forest dynamics.

Tree vigor is often used as a covariate when tree mortality is predicted from tree growth in tropical forest dynamic models, but it is rarely explicitly accounted for in a coherent modeling framework. We quantify tree vigor at the individual tree level, based on the difference between expected and observed growth. The available methods to join nonlinear tree growth and mortality processes are not commonly used by forest ecologists so that we develop an inference methodology based on an MCMC approach, allowing us to sample the parameters of the growth and mortality model according to their posterior distribution using the joint model likelihood. We apply our framework to a set of data on the 20-year dynamics of a forest in Paracou, French Guiana, taking advantage of functional trait-based growth and mortality models already developed independently. Our results showed that growth and mortality are intimately linked and that the vigor estimator is an essential predictor of mortality, highlighting that trees growing more than expected have a far lower probability of dying. Our joint model methodology is sufficiently generic to be used to join two longitudinal and punctual linked processes and thus may be applied to a wide range of growth and mortality models. In the context of global changes, such joint models are urgently needed in tropical forests to analyze, and then predict, the effects of the ongoing changes on the tree dynamics in hyperdiverse tropical forests.

Rainfall seasonality and pest pressure as determinants of tropical tree species' distributions

Drought and pests are primary abiotic and biotic factors proposed as selective filters acting on species distributions along rainfall gradients in tropical forests and may contribute importantly to species distributional limits, performance, and diversity gradients. Recent research demonstrates linkages between species distributions along rainfall gradients and physiological drought tolerance; corresponding experimental examinations of the contribution of pest pressure to distributional limits and potential interactions between drought and herbivory are limited. This study aims to quantitate differential performance and herbivory as a function of species range limits across a climatic and floristic transition in Southeast Asia. Khao Chong Botanical Garden, Thailand and Pasoh Forest Reserve, Malaysia straddle the Kangar-Pattani Line. A reciprocal transplantation across a seasonality gradient was established using two groups of species (“widespread” taxa whose distributions include seasonally dry forests and “aseasonal” taxa whose distributions are limited to aseasonal forests). Growth, biomass allocation, survival, and herbivory were monitored for 19 months. Systematic differences in performance were a function of species distribution in relation to rainfall seasonality. In aseasonal Pasoh, aseasonal species had both greater growth and survivorship than widespread species. These differences were not a function of differential herbivory as widespread and aseasonal species experienced similar damage in the aseasonal forest. In seasonally dry Khao Chong, widespread species showed higher survivorship than aseasonal species, but these differences were only apparent during drought. We link this differential performance to physiological mechanisms as well as differential tolerance of biotic pressure during drought stress. Systematic decreases in seedling survival in aseasonal taxa during drought corresponded with previously documented physiological differences and may be exacerbated by herbivore damage. These results have important implications for tropical diversity and community composition in light of predicted increases in the frequency and severity of drought in hyperdiverse tropical forests.

The relative importance of dispersal limitation and habitat preference in shaping spatial distribution of saplings in a tropical moist forest: a case study along a combination of hydromorphic and canopy disturbance gradients

• Introduction Various processes contribute to shaping the local assemblage of species in hyperdiverse tropical forest. The relative contribution of environmental factors and dispersal limitation in determining the spatial distribution of saplings at local scale is unclear.

Taxonomic scale-dependence of habitat niche partitioning and biotic neighbourhood on survival of tropical tree seedlings

In order to differentiate between mechanisms of species coexistence, we examined the relative importance of local biotic neighbourhood, abiotic habitat factors and species differences as factors influencing the survival of 2330 spatially mapped tropical tree seedlings of 15 species of Myristicaceae in two separate analyses in which individuals were identified first to species and then to genus. Using likelihood methods, we selected the most parsimonious candidate models as predictors of 3 year seedling survival in both sets of analyses. We found evidence for differential effects of abiotic niche and neighbourhood processes on individual survival between analyses at the genus and species levels. Niche partitioning (defined as an interaction of taxonomic identity and abiotic neighbourhood) was significant in analyses at the genus level, but did not differentiate among species in models of individual seedling survival. By contrast, conspecific and congeneric seedling and adult density were retained in the minimum adequate models of seedling survival at species and genus levels, respectively. We conclude that abiotic niche effects express differences in seedling survival among genera but not among species, and that, within genera, community and/or local variation in adult and seedling abundance drives variation in seedling survival. These data suggest that different mechanisms of coexistence among tropical tree taxa may function at different taxonomic or phylogenetic scales. This perspective helps to reconcile perceived differences of importance in the various non-mutually exclusive mechanisms of species coexistence in hyper-diverse tropical forests.