Assessing the functional vulnerability of woody plant communities within a large scale tropical rainforest dynamics plot.

Introduction: Tropical forests are characterized by intricate mosaics of species-rich and structurally complex forest communities. Evaluating the functional vulnerability of distinct community patches is of significant importance in establishing conservation priorities within tropical forests. However, previous assessments of functional vulnerability in tropical forests have often focused solely on isolated factors or individual disturbance events, with limited consideration for a broad spectrum of disturbances and the responses of diverse species. Methods: We assessed the functional vulnerability of woody plant communities in a 60-ha dynamic plot within a tropical montane rainforest by conducting in silico simulations of a wide range disturbances. These simulations combined plant functional traits and community properties, including the distribution of functional redundancy across the entire trait space, the distribution of abundance across species, and the relationship between species trait distinctiveness and species abundance. We also investigated the spatial distribution patterns of functional vulnerability and their scale effects, and employed a spatial autoregressive model to examine the relationships between both biotic and abiotic factors and functional vulnerability at different scales. Results: The functional vulnerability of tropical montane rainforest woody plant communities was generally high (the functional vulnerability of observed communities was very close to that of the most vulnerable virtual community, with a value of 72.41% on average at the 20m×20m quadrat scale), and they exhibited significant spatial heterogeneity. Functional vulnerability decreased with increasing spatial scale and the influence of both biotic and abiotic factors on functional vulnerability was regulated by spatial scale, with soil properties playing a dominant role. Discussion: Our study provides new specific insights into the comprehensive assessment of functional vulnerability in the tropical rainforest. We highlighted that functional vulnerabilities of woody plant communities and their sensitivity to environmental factors varied significantly within and across spatial scales in the tropical rainforest landscape. Preserving and maintaining the functionality of tropical ecosystems should take into consideration the variations in functional vulnerability among different plant communities and their sensitivity to environmental factors.

The puzzling ecology of African Marantaceae forests.

Marantaceae forests are tropical rainforests characterized by a continuous understory layer of perennial giant herbs and a near absence of tree regeneration. Although widespread in West-Central Africa, Marantaceae forests have rarely been considered in the international literature. Yet, they pose key challenges and opportunities for theoretical ecology that transcend the borders of the continent. Specifically, we ask in this review whether open Marantaceae forests and dense closed-canopy forests can be considered as one of the few documented examples of alternative stable states in tropical forests. First, we introduce the different ecological factors that have been posited to drive Marantaceae forests (climate, soil, historical and recent anthropogenic pressures, herbivores) and develop the different hypotheses that have been suggested to explain how Marantaceae forests establish in relation with other vegetation types (understory invasion, early succession after disturbance, and intermediate successional stage). Then, we review the underlying ecological mechanisms that can explain the stability of Marantaceae forests in the long term (tree recruitment inhibition, promotion of and resilience to fire, adaptive reproduction, maintenance by megaherbivores). Although some uncertainties remain and call for further empirical and theoretical research, we found converging evidence that Marantaceae forests are associated with an ecological succession that has been deflected or arrested. If verified, Marantaceae forests may provide a useful model to understand critical transitions in forest ecosystems, which is of particular relevance to achieve sustainable forest management and mitigate global climate change.

Corrigendum: Identifying hotspots of woody plant diversity and their relevance with home ranges of the critically endangered gibbon (Nomascus hainanus) across forest landscapes within a tropical nature reserve.

[This corrects the article DOI: 10.3389/fpls.2023.1283037.].

Magnifying the hotspot: descriptions of nine new species of many-plumed moths (Lepidoptera, Alucitidae), with an identification key to all species known from Cameroon.

This study confirms Mount Cameroon as an unprecedented hotspot for the diversity of many-plumed moths, with the discovery and description of nine new species: Alucitafako Ustjuzhanin & Kovtunovich, sp. nov., Alucitapyrczi Ustjuzhanin & Kovtunovich, sp. nov., Alucitasroczki Ustjuzhanin & Kovtunovich, sp. nov., Alucitapotockyi Ustjuzhanin & Kovtunovich, sp. nov., Alucitasedlaceki Ustjuzhanin & Kovtunovich, sp. nov., Alucitatonda Ustjuzhanin & Kovtunovich, sp. nov., Alucitaerzayi Ustjuzhanin & Kovtunovich, sp. nov., Alucitasokolovi Ustjuzhanin & Kovtunovich, sp. nov., and Alucitahirsuta Ustjuzhanin & Kovtunovich, sp. nov. Additionally, four additional species are reported from the Mount Cameroon area as new for the country: Alucitaagassizi, Alucitadohertyi, Alucitaplumigera, and Alucitarhaptica. Of the 89 Alucitidae known from the Afrotropics, the studied area hosts 36 species, most of which are endemic to the area. This unprecedented level of diversity and endemism within this lepidopteran family highlights Mount Cameroon's significance as a stronghold for specialised insect taxa. Efficient conservation efforts are necessary to protect these ecosystems and their associated unique microlepidopteran diversity.

Fate and Transport of Mercury through Waterflows in a Tropical Rainforest.

Knowledge gaps of mercury (Hg) biogeochemical processes in the tropical rainforest limit our understanding of the global Hg mass budget. In this study, we applied Hg stable isotope tracing techniques to quantitatively understand the Hg fate and transport during the waterflows in a tropical rainforest including open-field precipitation, throughfall, and runoff. Hg concentrations in throughfall are 1.5-2 times of the levels in open-field rainfall. However, Hg deposition contributed by throughfall and open-field rainfall is comparable due to the water interception by vegetative biomasses. Runoff from the forest shows nearly one order of magnitude lower Hg concentration than those in throughfall. In contrast to the positive Δ199Hg and Δ200Hg signatures in open-field rainfall, throughfall water exhibits nearly zero signals of Δ199Hg and Δ200Hg, while runoff shows negative Δ199Hg and Δ200Hg signals. Using a binary mixing model, Hg in throughfall and runoff is primarily derived from atmospheric Hg0 inputs, with average contributions of 65 ± 18 and 91 ± 6%, respectively. The combination of flux and isotopic modeling suggests that two-thirds of atmospheric Hg2+ input is intercepted by vegetative biomass, with the remaining atmospheric Hg2+ input captured by the forest floor. Overall, these findings shed light on simulation of Hg cycle in tropical forests.

Lipid concentration and composition in xylem sap of woody angiosperms from a tropical savanna and a seasonal rainforest.

Lipids may play an important role in preventing gas embolisms by coating nanobubbles in xylem sap. Few studies on xylem sap lipids have been reported for temperate plants, and it remain unclear whether sap lipids have adaptational significance in tropical plants. In this study, we quantify the lipid composition of xylem sap for angiosperm species from a tropical savanna (seven species) and a seasonal rainforest (five species) using mass spectrometry. We found that all twelve species studied contained lipids in their xylem sap, including galactolipids, phospholipids and triacylglycerol, with a total lipid concentration ranging from 0.09 to 0.26 nmol/L. There was no difference in lipid concentration or composition between plants from the two sites, and the lipid concentration was negatively related to species' open vessel volume. Furthermore, savanna species showed little variation in lipid composition between the dry and the rainy season. These results support the hypothesis that xylem sap lipids are derived from the cytoplasm of individual conduit cells, remain trapped inside individual conduits, and undergo few changes in composition over consecutive seasons. A xylem sap lipidomic data set, which includes 12 tropical tree species from this study and 11 temperate tree species from literature, revealed no phylogenetic signals in lipid composition for these species. This study fills a knowledge gap in the lipid content of xylem sap in tropical trees and provides additional support for their common distribution in xylem sap of woody angiosperms. It appears that xylem sap lipids have no adaptive significance.

Role of sacred groves in southwestern Nigeria in biodiversity conservation, biomass and carbon storage.

Sacred groves are remnants of primary forests with rich biological diversity, protected by indigenous communities. Their role in carbon sequestration and provision of other ecosystem services is being recognized. We investigated four sacred groves (Idanre Hills, Igbo-Olodumare, Ogun-Onire, and Osun-Osogbo) in southwestern Nigeria for biodiversity conservation, biomass production, and carbon storage. A total of 32 temporary sample plots of 800 m2 each were laid across all the sacred groves. Within each plot, all trees with dbh greater or equal to 10 cm were identified, and their diameters and heights measured. Saplings and seedlings were assessed within 100 m2 and 25 m2 sub-plots, respectively. Non-destructive methods were employed in estimating volume, biomass production, and carbon storage. Shannon-Wiener diversity index, Margalef index, and tree species richness in the four groves ranged from 2.63-3.55, 5.64-10.02, and 41-85, respectively, and differed significantly. The four groves were sanctuaries for many indigenous tree species of immense social, religious, ecological, and socio-economic importance. The high densities of seedling and sapling, together with the inverted-J tree diameter distributions, are indications of active regeneration and healthy ecosystem. Mean volume was high (range 244.99 to 343.08 m3 ha-1). The biomass (range 87.8 to 231.85 t ha-1) and carbon stock (range 43.9 to 115.9 t ha-1) of the groves revealed their potentials for climate change mitigation through atmospheric CO2 sequestration. Thus, besides being an effective biodiversity conservation method, sacred groves are important carbon sink. This calls for further conservation of sacred groves to serve as long-term carbon storage mechanism.

Identifying hotspots of woody plant diversity and their relevance with home ranges of the critically endangered gibbon (Nomascus hainanus) across forest landscapes within a tropical nature reserve.

Introduction: To achieve effective conservation objectives, it is crucial to map biodiversity patterns and hotspots while considering multiple influencing factors. However, focusing solely on biodiversity hotspots is inadequate for species conservation on a landscape scale. This emphasizes the importance of integrating hotspots with the home ranges of species to identify priority conservation areas. Methods: Compiling the vegetation data with environmental and anthropogenic disturbance data collected from kilometer-grid plots in Bawangling Nature Reserve, Hainan, China, we analyzed the spatial distribution of plant diversity (species richness and Shannon-Wiener index), as well as the main drivers affecting these patterns. We also investigated the spatial distribution of hotspots using a threshold approach and compared them with the home ranges of the flagship species, Hainan gibbon (Nomascus hainanus). Result: Climate and soil are predominant drivers shaping the spatial pattern of plant diversity in Bawangling Nature Reserve, surpassing the influence of anthropogenic disturbance and topographic factors. Both diversity indices exhibit a generally similar pattern with exceptions in surrounding areas of Futouling and Elongling. The hotspots identified by the Shannon-Wiener index showed a higher spatial overlap with the home ranges of Hainan gibbon compared to the species richness hotspots. The recently established Hainan gibbon Group E in 2019, located 8 km away from the original Futouling habitat, does not coincide with identified hotspots. Discussion: Our findings indicate that the hotspots of plant diversity within the habitat of Hainan gibbon Group E are relatively limited, emphasizing the necessity of giving precedence to its conservation. Integrating hotspots with the home ranges of critically endangered species offers decision-makers valuable information to establish rational conservation networks in the context of changing environments, as well as a reference for habitat restoration of species.

Diversity and conservation of mammals in indigenous territories of southern Mexico: proposal for an "Archipelago Reserve".

Southern Mexico's tropical forests are home to the country's highest richness of mammal species; La Chinantla region is situated within this area, its name from the indigenous group residing in the area and holding territorial ownership, namely the Chinantecos. In La Chinantla, there are no Protected Areas; instead, there are Areas Destined Voluntarily for Conservation (ADVC) and "Voluntary Conservation Areas" (VCA), that are managed by local inhabitants through social consensus. These ADVC may function as an archipelago reserve, which represents regional diversity, including the social context, through complementarity. To verify its biodiversity, we analyzed the richness, composition, distribution, and conservation of wild mammals in the region. Records were obtained from four sources-primary data collection, databases, scientific literature, and community monitoring-and were organized into four zones based on altitudinal and vegetation gradients. We compared the diversity between zones for three categories of mammals: small (<100 gr.), bats, and medium and large (>100 gr.). 134 species were identified comprising 11 orders, 26 families and 86 genera. The zone with highest elevation presented the greatest species richness for the assemblage of mammals and terrestrial mammals, while the zone with the lowest elevation had the highest richness of bats. For each mammal category, the zone with the most species also registered the highest number of exclusive species. For the assemblage of mammals and for medium and large mammals, the similarity index was highest between the two intermediate zones, while for small mammals and bats, the greatest similarity occurred between the areas of higher altitude. The study region was found to have the second highest richness of mammals in Mexico. Finally, we suggest that the conservation proposals by indigenous people could function as a set of "islands" that promote the conservation of biodiversity, possibly as an Archipelago Reserve.

Diverse Xylaria in the Ecuadorian Amazon and their mode of wood degradation.

BACKGROUND: Xylaria is a diverse and ecologically important genus in the Ascomycota. This paper describes the xylariaceous fungi present in an Ecuadorian Amazon Rainforest and investigates the decay potential of selected Xylaria species. Fungi were collected at Yasuní National Park, Ecuador during two collection trips to a single hectare plot divided into a 10-m by 10-m grid, providing 121 collection points. All Xylaria fruiting bodies found within a 1.2-m radius of each grid point were collected. Dried fruiting bodies were used for culturing and the internal transcribed spacer region was sequenced to identify Xylaria samples to species level. Agar microcosms were used to assess the decay potential of three selected species, two unknown species referred to as Xylaria 1 and Xylaria 2 and Xylaria curta, on four different types of wood from trees growing in Ecuador including balsa (Ochroma pyramidale), melina (Gmelina arborea), saman (Samanea saman), and moral (Chlorophora tinctoria). ANOVA and post-hoc comparisons were used to test for differences in biomass lost between wood blocks inoculated with Xylaria and uninoculated control blocks. Scanning electron micrographs of transverse sections of each wood and assay fungus were used to assess the type of degradation present. RESULTS: 210 Xylaria collections were sequenced, with 106 collections belonging to 60 taxa that were unknown species, all with less than 97% match to NCBI reference sequences. Xylaria with sequence matches of 97% or greater included X. aff. comosa (28 isolates), X. cuneata (9 isolates) X. curta and X. oligotoma (7 isolates), and X. apiculta (6 isolates)., All Xylaria species tested were able to cause type 1 or type 2 soft rot degradation in the four wood types and significant biomass loss was observed compared to the uninoculated controls. Balsa and melina woods had the greatest amount of biomass loss, with as much as 60% and 25% lost, respectively, compared to the controls. CONCLUSIONS: Xylaria species were found in extraordinary abundance in the Ecuadorian rainforest studied. Our study demonstrated that the Xylaria species tested can cause a soft rot type of wood decay and with the significant amount of biomass loss that occurred within a short incubation time, it indicates these fungi likely play a significant role in nutrient cycling in the Amazonian rainforest.

Effects of plant diversity, soil microbial diversity, and network complexity on ecosystem multifunctionality in a tropical rainforest.

Introduction: Plant diversity and soil microbial diversity are important driving factors in sustaining ecosystem multifunctionality (EMF) in terrestrial ecosystems. However, little is known about the relative importance of plant diversity, soil microbial diversity, and soil microbial network complexity to EMF in tropical rainforests. Methods: This study took the tropical rainforest in Xishuangbanna, Yunnan Province, China as the research object, and quantified various ecosystem functions such as soil organic carbon stock, soil nutrient cycling, biomass production, and water regulation in the tropical rainforest to explore the relationship and effect of plant diversity, soil microbial diversity, soil microbial network complexity and EMF. Results: Our results exhibited that EMF decreased with increasing liana species richness, soil fungal diversity, and soil fungal network complexity, which followed a trend of initially increasing and then decreasing with soil bacterial diversity while increasing with soil bacterial network complexity. Soil microbial diversity and plant diversity primarily affected soil nutrient cycling. Additionally, liana species richness had a significant negative effect on soil organic carbon stocks. The random forest model suggested that liana species richness, soil bacterial network complexity, and soil fungal network complexity indicated more relative importance in sustaining EMF. The structural equation model revealed that soil bacterial network complexity and tree species richness displayed the significantly positive effects on EMF, while liana species richness significantly affected EMF via negative pathway. We also observed that soil microbial diversity indirectly affected EMF through soil microbial network complexity. Soil bulk density had a significant and negative effect on liana species richness, thus indirectly influencing EMF. Simultaneously, we further found that liana species richness was the main indicator of sustaining EMF in a tropical rainforest, while soil bacterial diversity was the primary driving factor. Discussion: Our findings provide new insight into the relationship between biodiversity and EMF in a tropical rainforest ecosystem and the relative contribution of plant and soil microibal diversity to ecosystem function with increasing global climate change.

Army ant middens - Home and nursery of a diverse beetle fauna.

Army ants provide nourishment to a large variety of animals. This includes birds that feed on animals flushed out by army ant raids, symbiotic arthropods that consume the ants' prey or their brood, and other arthropods that scavenge on army ant refuse deposits. The latter have not received much attention, and the few published studies lack detailed species identifications. Here we provide a first systematic inventory of the beetle fauna associated with refuse deposits of Eciton army ants, with a focus on Eciton burchellii. We collected 8364 adult beetles, 511 larvae, and 24 eggs from 34 deposits at La Selva Biological Station, Costa Rica. We used a combination of DNA barcoding and morphology to identify a subset of 436 specimens to species level. The samples included several new species, and we here formally describe two water scavenger beetles (Hydrophilidae). Refuse deposits harbored a diverse beetle fauna. The identified subset consisted of 91 beetle species from 12 families, with rove beetles being the most abundant and diverse visitors. Of the 85 species found with E. burchellii, 50 species were collected from only one or two refuse deposits. Conversely, seven species were found in 10 or more refuse deposits, indicating a certain level of habitat specialization. We matched adults and immatures for 22 beetle species via DNA barcodes, demonstrating that army ant middens also serve as a beetle nursery. The present survey highlights the significant ecological function of army ants as promoters of biodiversity and their status as keystone species in tropical rainforests.

Leveraging explainable machine learning models to assess forest health: A case study in Hainan, China.

Global forest area has declined over the past few years, forest quality has declined, and ecological and environmental events have increased with climate change and human activity. In the context of ecological civilization, forest health issues have received unprecedented attention. By improving forest health, forests can better perform their ecosystem service functions and promote green development. This study was carried out in the WuZhi Shan area of Hainan Tropical Rainforest National Park. We employed a decision tree algorithm, a machine learning technique, for our modeling due to its high accuracy and interpretability. The objective weighted method using criteria of importance through intercriteria correlation (CRITIC) was used to determine forest health classes based on survey and experimental data from 132 forest samples. The results showed that species diversity is the most important metric to measure forest health. An interpretable decision tree machine learning model was proposed to incorporate forest health indicators, providing up to 90% accuracy in the classification of forest health conditions. The model demonstrated a high degree of effectiveness, achieving an average precision of 90%, a recall of 67%, and an F1 score of 70.2% in predicting forest health. The interpretable decision tree classification results showed that breast height diameter is the most important variable in classifying the health status of both primary and secondary forests. This study highlights the importance of using interpretable machine learning methods for the decision-making process. Our work contributes to the scientific underpinnings of sustainable forest development and effective conservation planning.

Long-term ecological responses of a lowland dipterocarp forest to climate changes and nutrient availability.

Understanding the long-term impact of projected climate change on tropical rainforests is critical given their central role in the Earth's system. Palaeoecological records can provide a valuable perspective on this problem. Here, we examine the effects of past climatic changes on the dominant forest type of Southeast Asia - lowland dipterocarp forest. We use a range of proxies extracted from a 1400-yr-old lacustrine sedimentary sequence from north-eastern Philippines to determine long-term vegetation responses of lowland dipterocarp forest, including its dominant tree group dipterocarps, to changes in precipitation, fire and nutrient availability over time. Our results show a positive relationship between dipterocarp pollen accumulation rates (PARs) and leaf wax hydrogen isotope values, which suggests a negative effect of drier conditions on dipterocarp abundance. Furthermore, we find a positive relationship between dipterocarp PARs and the proxy for phosphorus availability, which suggests phosphorus controls the productivity of these keystone trees on longer time scales. Other pollen taxa show widely varying relationships with the abiotic factors, demonstrating a high diversity of plant functional responses. Our findings provide novel insights into lowland dipterocarp forest responses to changing climatic conditions in the past and highlight potential impacts of future climate change on this globally important ecosystem.

Unavoidable Extinctions in Ecosystems of Extreme Isolation.

Future systems of extreme isolation, including initiatives in space exploration, may require the services of onboard ecosystems. Biosphere 2, which ran between 1991 and 1993, aspired to mimic the earthly ecosystem and assess the ability of humans and other species to survive in a fully enclosed space. In this study, the data for plant species survival in the tropical rainforest sector from the first 2-year mission were studied through the prism of the neutral theory of biodiversity (NTB), which predicts how closed communities develop and how they lose species due to random demographic effects. Biosphere-2 lost species faster than a neutral process would predict. The specific reasons have been well documented, but the integrated approach of NTB offers new insights. It predicts that a closed ecological community must lose species and there is a specific time frame for this. To test it properly, the operation time of Biosphere-2 should have been at least 30 times greater. The new insights that NTB brings to the story of Biosphere 2 could be important for microcosm studies in general. A similar analysis suggests that the operation and testing time of other simulated ecosystems should also be increased.

High vapour pressure deficit enhances turgor limitation of stem growth in an Asian tropical rainforest tree.

Tropical forests are experiencing increases in vapour pressure deficit (D), with possible negative impacts on tree growth. Tree-growth reduction due to rising D is commonly attributed to carbon limitation, thus overlooking the potentially important mechanism of D-induced impairment of wood formation due to an increase in turgor limitation. Here we calibrate a mechanistic tree-growth model to simulate turgor limitation of radial stem growth in mature Toona cilitata trees in an Asian tropical forest. Hourly sap flow and dendrometer measurements were collected to simulate turgor-driven growth during the growing season. Simulated seasonal patterns of radial stem growth matched well with growth observations. Growth mainly occurred at night and its pre-dawn build-up appeared to be limited under higher D. Across seasons, the night-time turgor pressure required for growth was negatively related to previous midday D, possibly due to a relatively high canopy conductance at high D, relative to stem rehydration. These findings provide the first evidence that tropical trees grow at night and that turgor pressure limits tree growth. We suggest including turgor limitation of tree stem growth in models also for tropical forest carbon dynamics, in particular, if these models simulate effects of warming and increased frequency of droughts.

Uncovering the dominant role of root metabolism in shaping rhizosphere metabolome under drought in tropical rainforest plants.

Plant-soil-microbe interactions are crucial for driving rhizosphere processes that contribute to metabolite turnover and nutrient cycling. With the increasing frequency and severity of water scarcity due to climate warming, understanding how plant-mediated processes, such as root exudation, influence soil organic matter turnover in the rhizosphere is essential. In this study, we used 16S rRNA gene amplicon sequencing, rhizosphere metabolomics, and position-specific 13C-pyruvate labeling to examine the effects of three different plant species (Piper auritum, Hibiscus rosa sinensis, and Clitoria fairchildiana) and their associated microbial communities on soil organic carbon turnover in the rhizosphere. Our findings indicate that in these tropical plants, the rhizosphere metabolome is primarily shaped by the response of roots to drought rather than direct shifts in the rhizosphere bacterial community composition. Specifically, the reduced exudation of plant roots had a notable effect on the metabolome of the rhizosphere of P. auritum, with less reliance on neighboring microbes. Contrary to P. auritum, H. rosa sinensis and C. fairchildiana experienced changes in their exudate composition during drought, causing alterations to the bacterial communities in the rhizosphere. This, in turn, had a collective impact on the rhizosphere's metabolome. Furthermore, the exclusion of phylogenetically distant microbes from the rhizosphere led to shifts in its metabolome. Additionally, C. fairchildiana appeared to be associated with only a subset of symbiotic bacteria under drought conditions. These results indicate that plant species-specific microbial interactions systematically change with the root metabolome. As roots respond to drought, their associated microbial communities adapt, potentially reinforcing the drought tolerance strategies of plant roots. These findings have significant implications for maintaining plant health and preference during drought stress and improving plant performance under climate change.

Flying squirrels, hidden treasures.

In the rain forests of Hainan, China, two species of squirrel create grooves on the surface of smooth nuts so that they can wedge them in the forks between branches.

Inner bark vs sapwood is the main driver of nitrogen and phosphorus allocation in stems and roots across three tropical woody plant communities.

Nutrient allocation is central to understanding plant ecological strategies and forest roles in biogeochemical cycles. Thought to be mainly driven by environmental conditions, nutrient allocation to woody organs, especially to living tissues, is poorly understood. To examine the role of differences in living tissues (sapwood, SW, vs inner bark, IB), organs, ecological strategies, and environmental conditions in driving nutrient allocation and scaling in woody plants, we quantified nitrogen and phosphorus in main stems and coarse roots of 45 species from three tropical ecosystems with contrasting precipitation, fire regime, and soil nutrients. Nutrient concentration variation was mostly explained by differences between IB and SW, followed by differences between species and, in the case of phosphorus, soil nutrient availability. IB nutrient concentrations were four times those of SW, with root tissues having slightly higher concentrations than stem tissues. Scaling between IB and SW, and between stems and roots, was generally isometric. In cross-sections, IB contributed half of total nutrients in roots and a third in stems. Our results highlight the important role of IB and SW for nutrient storage, the coordination in nutrient allocation across tissues and organs, and the need to differentiate between IB and SW to understand plant nutrient allocation.

Flying squirrels use a mortise-tenon structure to fix nuts on understory twigs.

Squirrels of temperate zones commonly store nuts or seeds under leaf litter, in hollow logs, or even in holes in the ground; however, in the humid rainforests of Jianfengling in Hainan, South China, we show that some flying squirrels cache elliptical or oblate nuts by hanging them securely in vegetation. These small flying squirrels were identified as Hylopetes phayrei electilis (G. M. Allen, 1925) and Hylopetes alboniger (Hodgson, 1870), in video clips captured of their behavior around focal nuts. Squirrels chewed grooves encircling ellipsoid nuts or distributed on the bottoms of oblate nuts, and then used these grooves to fix nuts tightly between small twigs 0.1-0.6 cm in diameter that were connected at angles of 25-40°. The grooves carved on the nuts (concave structure) connected with Y-shaped twigs (convex structure) and thus firmly affixed the nuts to the plant in a way similar to a mortise-tenon joint used in architecture and carpentry. Cache sites were on small plants located 10-25 m away from the closest potentially nut-producing tree, a behavior that likely reduces the discovery and consumption of the nuts by other animals. The adaptive squirrel behavior that shapes and fits nuts between twigs seems to be directed at providing more secure storage that increases food supply during dry periods in a humid tropical rainforest. In addition to providing such benefits for the squirrels, we suggest that this behavior also impacts the distribution of tree species in the forest.

The rainy forests of South China are home to Cyclobalanopsis trees whose smooth, elliptical nuts are favoured by many animal species. While doing fieldwork in the Jianfengling nature reserve in the southern province of Hainan, China, researchers came across an unusual sight: many of these nuts had been wedged into the Y-shaped forks between diverging twigs. A closer inspection revealed that a carefully crafted groove on the surface of the nuts helped them to stay wedged and secured between the branches. Which creature was responsible for such a feat? To investigate, Xu et al. set up motion-triggered, infra-red cameras near some of the hoarding sites. They discovered that the culprits were Hylopetes phayrei electilis and Hylopetes alboniger, two small species of flying squirrel that tend to store Cyclobalanopsis nuts to prepare for the dry, cool season. The footage showed that the squirrels first chewed the nuts before inserting them tightly between the branches. In fact, this process appeared to require much care ­ and, potentially, cognitive involvement ­ with the squirrels testing and adjusting their grooves many times until a perfect fit was achieved. Caching sites were usually found 10 to 25 meters away from the nearest Cyclobalanopsis tree, which probably helps to protect the hoards from other animals on the hunt for nuts. Squirrels from temperate regions typically prepare for winter by hiding food in the ground, between logs or inside hollow trees; in humid, tropical forests, however, such caching sites may promote mould, decomposition or germination. In these conditions, securely hanging nuts between branches may prove to be a more suitable strategy. By choosing caching sites that are away from the mother tree, squirrels may also inadvertently help Cyclobalanopsis to expand their range, with forgotten nuts becoming dislodged and sprouting in new locations across the reserve. Overall, these findings shed new light on animal adaptation and cognition, as well as on the forces that help to shape forest ecology.