Although competition and facilitation both influence tree diversity1-5, their relative importance and variation with latitude remain poorly understood. Using data from 17 large forest plots, including around 2.7 million trees and over 5,400 species spanning 5° S to 47° N, we quantified the latitudinal trends of the relative importance of negative (competitive) and positive (facilitative) interactions among neighbouring tree species, accounting for three biotic and eight environmental factors. We examined whether the average neighbourhood species diversity around individuals of each focal species was larger or smaller than expected under null models. The results show that negative interspecific interactions prevailed across most plots. Near the equator, the relative proportions of species surrounded by a lower or higher than expected number of neighbours were roughly equal, but at higher latitudes, the proportions of species with a relatively higher number of neighbours declined, and those with fewer neighbours increased significantly. This latitudinal pattern can be attributed in part to reduced abundance of legumes, non-arbuscular mycorrhizal associations, and the weaker canopy nursing effect towards higher latitudes, but it was mediated by mean annual temperature. These findings reveal a previously unrecognized relative decline in facilitative interactions and increase in competitive interactions with latitude and suggest that rising temperatures could enhance facilitative effects and promote tree community diversity at higher latitudes.

Ecosystem services are rapidly degrading under anthropogenic pressure. Therefore, it is increasingly important to understand how ecosystem services flow, particularly at local scales, where people directly rely on nature for their livelihoods and well-being. Many ecosystem services are underpinned by ecological (e.g. frugivory) and socioecological (e.g. cultivation) interactions, connected as multiple stages of ecosystem service flow. We use a multilayer network, constructed with local ecological knowledge, to assess how ecosystem services flow in a subsistence farming community in Papua New Guinea. Our results highlight the relative importance of plant species in directly providing different ecosystem services (e.g. food, medicine, etc.), as well as their role in structuring ecosystem service flow. Specifically, we found that firewood services may be more vulnerable to future environmental or social changes, with a single species, Pometia pinnata, disproportionately supporting over 30% of firewood services to the local community. Furthermore, we found that the value of plants to local farmers is linked to their role in maintaining connectivity of ecosystem service flow, with more important (i.e., less replaceable) plants for providing specific services also being more important for cohesive ecosystem service flows. The results of our study can be used to understand how disturbances could impact the provision of ecosystem services to local communities, as well as key species and actors that can influence the flow of ecosystem services under different conservation or agricultural practices. We also critically assess our framework, providing key lessons learned to improve accuracy for future applications.Read the free for this article on the Journal blog.

Endemic species exemplify both the exceptional evolutionary value and extraordinary vulnerability of tropical island biodiversity. Conservationists often face the difficult task of balancing ecosystem stability with species-level protection. To reconcile these objectives of biodiversity management, it is essential to understand how endemic species contribute to ecosystem functioning. In this study, we assessed the taxonomic and functional diversity of birds along an elevational gradient on New Britain, the largest island of the Bismarck archipelago, and the role of endemic species in its rainforest ecosystems. We combined field surveys with abundance-weighed trait data to assess avian functional distinctiveness from the large neighbouring landmass of New Guinea. We found a non-linear decrease of bird diversity with elevation, measured by Shannon index. The proportion of endemic species increased with elevation, from 42 to 55% of total species richness. Compared to mainland New Guinea, New Britain assemblages shifted from invertebrate prey to other food sources, such as nectar or fruits. This shift was more prevalent in higher elevations than in the lowlands, and was facilitated equally by endemic and non-endemic species. Most omnivores and nectarivores were endemic, but frugivores and insectivores were more represented among non-endemics. Endemic birds dominated in the provision of pollination, but often adopted more generalist foraging strategies due to seasonal availability of fruits and nectar. In contrast, seed dispersal and insect control were more represented by non-endemics. Functional distinctiveness of New Britain birds may facilitate a different response to human-induced land use change compared to the New Guinean mainland. As only some ecosystem services are chiefly dependent on endemic species, conservation strategies should focus on preserving avian diversity regardless of endemic status.

Effects of topography on the composition of trees and seedlings have been demonstrated in many tropical forests. Less attention has been paid to interannual changes in seedling establishment as a potential driver of the species composition. We explored the associations of neighbouring vegetation physiognomy and the abiotic environment (mainly topography) with the composition of tree seedlings. To reveal the shifts in habitat preferences through ontogeny, we compared the compositional response of tree composition to the same abiotic variables. Further, we evaluated interannual differences in seedling composition and composition of newly recruited seedlings. Seedling composition was monitored in 800 permanent quadrats within the 50 ha forest dynamics plot in the lowland tropical forest in Papua New Guinea for five consecutive years. Redundancy analyses were used to reveal the effects of abiotic and biotic factors on the composition of trees and seedlings. The ridge-valley position and the slope steepness were associated with the distribution of seedlings and even more so of trees. The effect of neighbouring vegetation physiognomy on seedlings was negligible. We found mostly concordant responses of established trees and their seedlings to the ridge-valley gradient, although some species exhibited preferential shifts during their ontogeny. The species composition of seedlings varied significantly over consecutive years. Topography appears to shape the species composition with varying strength depending on the species identity and through the ontogeny of individual trees. Strong interannual variation in the distribution and identity of newly recruited seedlings can contribute to the maintenance of local tree diversity.

An assessment of sensitivity to increasing temperature for thousands of insect species in mountainous terrain reveals a risk of insect biodiversity loss in tropical lowlands. An assessment of sensitivity to increasing temperature for thousands of insect species in mountainous terrain reveals a risk of insect biodiversity loss in tropical lowlands.

New Guinea is the largest tropical island and hosts a rich native astacofauna represented by numerous parastacid crayfish from the genus Cherax. Thus, the island is a so-called enigmatic hotspot of crayfish diversity. Many of these species are endemics and remain poorly studied. Although more than 30 species occur in the western part of the island, only Cherax papuanus (Holthuis, 1949) is currently the known crayfish species with an exclusive native range in the eastern half of the island. The only detailed information published about this crayfish is its formal description. The present study provides new morphological and, for the first time, genetic data based on specimens collected from Lake Kutubu, Papua New Guinea, in 1970, 1973, and 2023. Here is provided the most extensive examination to date in terms of population variability and refining some of the key morphological characteristics of the species. The findings presented are crucial for accurate species identification, which is important for future research, sustainable exploitation, management, and potential conservation measures.

ABSTRACT Climate change is increasing drought frequency and intensity in many tropical forests. It remains uncertain how the changing patterns of drought may impact the forests of New Guinea where rugged terrain provides contrasting wetness conditions. We examined mortality responses of 21,102 trees (DBH ≥ 1 cm) across 147 quadrats in a 50‐ha lowland forest plot during the 2015–2017 El Niño drought in Papua New Guinea, comparing mortality across three topographic positions (valley, slope, and ridge) during pre‐drought (2009–2015), drought (2015–2017), and post‐drought (2017–2019) periods. Small trees showed 2–4 times higher mortality than large trees, but both size classes responded proportionally similarly to drought (no size × drought interaction). Topographic effects varied significantly with the census period. Valley trees maintained the highest mortality during pre‐drought and drought periods (7.80% and 8.81% per year respectively for 1‐cm DBH trees) but recovered rapidly post‐drought (mortality declining to 4.91% per year). Ridge trees showed contrasting patterns, with mortality increasing from 4.66% to 7.07% per year and remaining elevated post‐drought. Critically, post‐drought mortality exceeded pre‐drought levels ( p < 0.01) while drought‐period mortality did not differ significantly from pre‐drought ( p = 0.081), indicating strongly lagged mortality responses. These results indicate that topographic position governs both immediate drought vulnerability and recovery trajectories, with ridge habitats showing persistent stress despite harboring drought‐adapted species. Our results highlight the distinct topographic responses and vulnerabilities of New Guinea's rainforests to drought.

Tropical ant species differ in their daily activity, yet it remains unclear whether diel foraging and species coexistence patterns differ between primary forests and environmentally altered, invasion-prone secondary forests. We placed baits on the forest floor and trunks in Papua New Guinea to assess ant foraging activity in primary and secondary forests during day and night. Using species-time networks, co-occurrence null models and generalized linear mixed-effects models (GLMMs), we tested for differences in diel community patterns across forest types and strata. Primary forests hosted more diurnal species and exhibited a significant diel foraging specialization. In contrast, secondary forests were less species-rich, dominated by invasive ants and showed a random diel foraging pattern, with a greater number of species active at night. Mean ant abundance per bait was twice as high during the day as at night in both forest types, but this increase was stratum-dependent and driven by different guilds: arboreal and terrestrial ants showed higher daytime abundances on trunks in primary forests, while semiarboreal ants did so across both strata in secondary forests. This effect diminished in secondary forests when only native species were considered. Species co-occurrence patterns, however, remained strongly negative across forest types and time periods. We conclude that forest disturbance and the spread of invasive species simultaneously disrupt diel activity patterns in ant communities. The persistence of negative co-occurrence across forests and diel periods indicates that these patterns are driven by environmental filtering rather than shifts in interspecific interactions.

Ecological succession is a complex community-wide process whose theoretical principles require further development. Here, we test the hypothesis that the succession of woody plants in tropical rainforests is determined by bottom-up plant competition, rendering top-down control by insect herbivores insignificant. Over 18 months of rainforest secondary succession, we removed insects and non-woody plants from replicate 5 & times; 5 m plots in a factorial experiment at 700 and 1700 m elevation in Papua New Guinea. At 700 m elevation, insect removal increased biomass, reduced diversity and altered the species composition of woody plants, while removal of non-woody plants increased both biomass and diversity of woody plants and altered their species composition. At 1700 m, the effect of insects on woody plant biomass and species composition disappeared while the effect of non-woody plants on woody plant biomass, diversity and species composition became stronger. The removal of insects did not increase the proportion of alien species in the woody vegetation as predicted by the enemy-release hypothesis. The increased disturbance caused by removing non-woody plants also did not promote alien plants. Synthesis. The importance of top-down insect herbivory decreased, while the importance of bottom-up plant competition with non-woody plant species increased with elevation, representing a gradient of increasing environmental stress in the succession of woody plants.

Tropical elevation gradients support highly diverse assemblages, but competing hypotheses suggest either peak species richness in lowland rainforests or at mid‐elevations. We investigated scolytine beetles—phloem, ambrosia and seed‐feeding beetles—along a tropical elevational gradient in Papua New Guinea. Highly standardised sampling from 200 to 3700 m above sea level (asl) identified areas of highest and lowest species richness, abundance and other biodiversity variables. Using passive flight intercept traps at eight elevations from 200 to 3500 m asl, we collected over 9600 specimens representing 215 species. Despite extensive sampling, species accumulation curves suggest that diversity was not fully exhausted. Scolytine species richness followed a unimodal distribution, peaking between 700 and 1200 m asl, supporting prior findings of highest diversity at low‐to‐mid elevations. Alternative models, such as a monotonous decrease from lowlands to higher elevations and a mid‐elevation maximum, showed lesser fit to our data. Abundance is greatest at the lowest sites, driven by a few extremely abundant species. The turnover rate—beta diversity between elevation steps—is greatest between the highest elevations. Among dominant tribes—Dryocoetini, Xyleborini and Cryphalini—species richness peaked between 700 and 2200 m asl. Taxon‐specific analyses revealed distinct patterns: Euwallacea spp. abundance uniformly declined with elevation, while other genera were driven by dominant species at different elevations. Coccotrypes and phloem‐feeding Cryphalus have undergone evolutionary radiations in New Guinea, with many species still undescribed. Species not yet known to science are most likely to be found at lower and middle elevations, where overall diversity is highest.

ABSTRACT Fruit traits have the potential to influence disperser communities and vice versa. Elevational gradients, where functional traits are known to change rapidly with distance, enable the study of these relationships at local scales. In this pilot study, we examine the trends in three fruit traits related to dispersal by frugivores: size, colour and presentation (i.e., location of displayed fruits on the trunk or on the branches) along a 200–2700 m asl rainforest elevation gradient in Papua New Guinea. We found fruit size to be lower at higher elevations. While specific fruit colours showed few significant elevational patterns, colours typically attributed to attracting avian dispersers were more prevalent at higher elevations. The proportion of ramiflorous species (bearing fruits from branches) increased with elevation. Finally, we use phylogenetic information to test the ‘dispersal syndromes’ hypothesis: that combinations of fruit traits have evolved in accordance with the preferences and sensory abilities of different frugivore guilds. All fruit traits except presentation showed little evidence of phylogenetic signal but we found fruits displaying colours attributed to attracting mammalian dispersers to be larger than ‘bird colour’ fruits. We found evidence for the correlated evolution of fruit size and colour, in support of the dispersal syndromes hypothesis. We encourage research at larger scales of time and space to further explore the relationships between fruit traits and frugivores, across elevational and other ecological gradients.

ABSTRACT Aim Avian functional diversity in montane systems has been scrutinised by researchers seeking to uncover deterministic processes driving community assembly. However, many tropical rainforests lack fully surveyed elevational gradients that could inform on functional ecology of avian assemblages. Here we expand global coverage of elevational trends in bird functional diversity to the third largest contiguous rainforest in the world. Location A 3500 m uninterrupted rainforest gradient in Papua New Guinea. Taxon Birds. Methods We conducted point‐count surveys of bird communities, sampling eight elevational sites from 200 m above sea level to the treeline at 3700 m. Functional diversity indices (functional richness, evenness, and divergence) were examined using Bayesian generalised additive models after standardising for bird species richness. Additionally, we analysed phylogenetic diversity and structure, and examined variation in individual functional traits, including feeding guild, morphology, and dispersal ability. Results Functional richness declined sharply from the lowlands to 1700 m above sea level, followed by a weak decrease towards the treeline. Functional evenness decreased monotonically with elevation, while functional divergence increased at low elevations and again near the treeline. Phylogenetic diversity exhibited a monotonic decline accompanied by increased phylogenetic clustering at higher elevations. The mid‐elevation collapse of functional richness was likely caused by trophic interactions. Reduced the availability of large fruits caused declines in frugivore body size and beak dimensions, while high abundance of invertebrates favoured functionally uniform insectivores. Near the treeline, bird communities displayed morphological shifts towards terrestrial lifestyles with reduced dispersal ability, suggesting environmental filtering by forest structure. Main Conclusions By examining trends in individual functional traits, we highlight the role of trophic interactions in shaping avian functional diversity in tropical montane systems. Similar research using robust trait data can deepen our understanding of ecosystem functions and guide conservation strategies for different functional groups of birds across tropical regions.

The SST-1M (webpage: https://sst-1m.space) is a Small-Sized Telescope (SST) designed to provide a cost-effective and high-performance solution for gamma-ray astrophysics, particularly for energies beyond a few TeV. The goal is to integrate this telescope into an array of similar instruments, leveraging its lightweight design, earthquake resistance, and established Davies-Cotton configuration. Additionally, its optical system is designed to function without a protective dome, allowing it to withstand the harsh atmospheric conditions typical of mountain environments above 2000 m a.s.l. The SST-1M utilizes a fully digitizing camera system based on silicon photomultipliers (SiPMs). This camera is capable of digitizing all signals from the UV-optical light detectors, allowing for the implementation of various triggers and data analysis methods. We detail the process of designing, prototyping, and validating this system, ensuring that it meets the stringent requirements for gamma-ray detection and performance. An SST-1M stereo system is currently operational and collecting data at the Ond & rcaron;ejov observatory in the Czech Republic, situated at 500 m a.s.l. Preliminary results from this system are promising. A forthcoming paper will provide a comprehensive analysis of the telescope's performance in detecting gamma rays and operating under real-world conditions.

Understanding the drivers of aboveground wood productivity (AWP) in tropical forests is crucial for explaining ecosystem functioning and predicting their responses to environmental change. While climatic water availability is a well-established driver, the role of soil nutrients and their interaction with other resources remains uncertain. We investigated how soil nutrients and light interactions shape AWP in lowland tropical forests using fine-scale soil and tree (≥ 1 cm DBH) data from 15 large forest plots. Canopy-exposed trees are nutrient-limited, with AWP increasing more with phosphorus (P) than with potassium (K), indicating P's greater role in plant growth and productivity. Conversely, understory AWP declined in fertile areas, likely due to intensified size-asymmetric competition. At the population level (mean across canopy layers), no relationship between soil nutrients and AWP emerged because contrasting responses among layers offset any overall association. Our results suggest that fine-scale heterogeneity and canopy stratification drive nutrient effects on tropical forest productivity.

Avian biodiversity in tropical rainforests is threatened by increasing intensity of anthropogenic disturbances. Secondary forest birds can maintain ecosystem services that are otherwise lost with disappearing primary forests. However, the stability of these services can be impeded by area effects reducing bird diversity. We compared the effects of fragmentation on avian ecosystem functions in both primary and secondary forests. We performed point count surveys in both continuous rainforests, as well as isolated forest fragments in lowland Papua New Guinea. We combined taxonomic diversity with functional and phylogenetic indices and patterns of individual functional traits. Bird taxonomic diversity was lower in secondary forests and decreased considerably due to fragmentation. In contrast, functional diversity was not affected by fragmentation but increased in secondary forests. Phylogenetic diversity increased in all human‐modified forests. Decreases in taxonomic diversity stemmed from the loss of forest‐dependent birds. In contrast, decreases in functional and phylogenetic diversity were prevented by the introduction of open‐habitat species. This was demonstrated by shifts in trait composition, as bird phenotypes reliant on forest continuity became less prevalent. Specifically, we recorded a proportional decrease in insectivory and ground foraging, and an increase in nectarivory and dispersal ability. Increased dispersal ability was also observed in secondary forests, where it was associated with shifts towards frugivory and canopy foraging. Increases in phylogenetic diversity were likely amplified by high phylogenetic dispersion of introduced habitat generalists. Policy implications . We show that compensatory patterns of species introduction fail to account for the loss of ecosystem functions due to the decline of forest‐dependent birds. As such, conservation policies should be targeted towards species that share traits associated with disturbance sensitivity, such as insectivory, ground foraging and low dispersal ability. This could prevent biodiversity loss in poorly explored tropical landscapes in the early stages of large‐scale deforestation.

Aim: We address a critical gap in the elevational community ecology of tropical non-volant mammals in the Australian and Oceanian zoogeographic realms. Specifically, we document alpha and beta diversity, environmental predictors and community composition of individual clades in relation to their ecology and evolutionary history along an extensive elevational gradient, for the first time in this region. Location: Complete rainforest elevational gradient and subalpine zone of Mount Wilhelm (45-3700 masl), Papua New Guinea. Methods: We conducted extensive sampling using traps (> 21,800 trap-nights) and collaboration with indigenous hunters across nine localities at 500 m intervals along the gradient, from lowland rainforest to subalpine grassland. The marsupial and rodent species were identified using morphological and genetic data. The community variables were correlated with key environmental variables. Results: In total, we recorded 61 marsupial and rodent species. We reveal an unusual pattern for tropical mammals: species richness increased linearly with elevation within continuous forest, then declined sharply in the open subalpine habitat. This contrasts with the mid-elevation richness peak, evident in regional mammal fauna and also common along elevation gradients globally. Community composition was primarily associated with temperature, with a sharp faunal turnover at 1200 masl dividing the assemblages into distinct lowland and highland communities. Main Conclusions: The novel elevational pattern challenges prevailing models and underscores the importance of integrating multiple sampling techniques including collaboration with indigenous hunters, where possible, to accurately capture the full extent of community composition. We highlight the ecological and conservation values of examining complete elevational gradients in tropical ecosystems, as a single Mt. Wilhelm transect encompasses 80% of the regional diversity of non-volant mammals. We suggest that any long rainforest elevational gradient is likely a high conservation priority.

Muon counting is an effective strategy for discriminating between gamma and hadron-initiated air showers. However, their detection, which requires shielded detectors, is highly costly and almost impossible to implement in large ${\rm km^2}$ environmentally sensitive areas. This work shows that the gamma/hadron discriminators, based on the new $LCm$ variable and the number of muons, have equivalent proton rejection levels at the PeV energies. It is, therefore, possible to build, at an affordable cost, a large, high-performant, wide field-of-view gamma-ray observatory.

We present measurements of the atmospheric depth of the shower maximum X_{max}, inferred for the first time on an event-by-event level using the surface detector of the Pierre Auger Observatory. Using deep learning, we were able to extend measurements of the X_{max} distributions up to energies of 100 EeV (10^{20}  eV), not yet revealed by current measurements, providing new insights into the mass composition of cosmic rays at extreme energies. Gaining a 10-fold increase in statistics compared to the fluorescence detector data, we find evidence that the rate of change of the average X_{max} with the logarithm of energy features three breaks at 6.5±0.6(stat)±1(syst)  EeV, 11±2(stat)±1(syst)  EeV, and 31±5(stat)±3(syst)  EeV, in the vicinity to the three prominent features (ankle, instep, suppression) of the cosmic-ray flux. The energy evolution of the mean and standard deviation of the measured X_{max} distributions indicates that the mass composition becomes increasingly heavier and purer, thus being incompatible with a large fraction of light nuclei between 50 and 100 EeV.