Humid Tropical Forests Research Articles

Cropland expansion, intensification, and reduction in Mato Grosso state, Brazil, between the crop years 2000/01 to 2017/18

Growing populations require increased food production through increasing yields and expanding land use. Thus, agricultural production has a dialectical relationship with natural resource conservation. South America has been the recent site of both intensification and areal expansion of crop production. The presented study investigates the dynamics of land use and land cover (LULC) in Mato Grosso state at two-year intervals for an 18-year period consisting of the 2000/01 and 2017/18 crop years. We used a stratified sampling approach and visual interpretation of satellite image time series data to obtain estimates of LULC extent and dynamics, including area of cropland expansion, intensification, and reduction. Cropland dynamics exhibited an overall increase in both extent and intensification. The cropland use area in Mato Grosso increased from 38,324 km2 (±5618 km2) in 2000/01 to 97,394 km2 (±9938 km2) in 2017/2018. For the Cerrado tropical woodland biome portion of Mato Grosso, the expansion of cropland areas was related to soy and corn prices. For the humid tropical forest biome of Amazonia, soy production and deforestation were found to not be directly correlated. The intensification in Mato Grosso was increased from 8142 km2 (±1.39%) in the period from 2008/09 to 2010/11, to 30,487 km2 (±2.56%) in the period from 2010/11 to 2012/13. Overall dynamics reflect public and private conservation policies, soy market, climate and technology factors that spur or inhibit increased production of commodity crops. The end result reflects Brazil's increasing role as a global commodity crop producer.

A global evaluation of the effectiveness of voluntary REDD+ projects at reducing deforestation and degradation in the moist tropics.

Reducing emissions from deforestation and forest degradation (REDD+) projects aim to contribute to climate change mitigation by protecting and enhancing carbon stocks in tropical forests, but there have been no systematic global evaluations of their impact. We used a new data set for tropical humid forests and a standardized evaluation approach (based on pixel matching) to quantify the performance of a representative sample of 40 voluntary REDD+ projects in 9 countries certified under the Verified Carbon Standard (VCS). In the first 5 years of implementation, deforestation within project areas was reduced by 47% (95% confidence interval [CI]: 24-68) compared with matched counterfactual pixels, and degradation rates were 58% lower (95% CI: 49-63). Reductions were small in absolute terms but greater in sites located in high-deforestation settings and did not appear to be substantially undermined by leakage activities in forested areas within 10km of project boundaries. At the 26th Conference of the Parties of the United Nations Framework Convention on Climate Change, the international community renewed its commitment to tackling tropical deforestation as a nature-based solution to climate change. Our results indicate that incentivizing forest conservation through voluntary site-based projects can slow tropical deforestation and highlight the particular importance of prioritizing financing for areas at greater risk of deforestation.

THE SEQUENCE OF AMAZON PREHISTORY: A METHODOLOGY FOR ETHICAL SCIENCE

This article is about my research on the prehistory of the mainstream lower Amazon in Brazil and problems in research ethics there. The "New Archaeology", my dissertation in the Orinoco, Venezuela, and my museum job led me rethink the human occupation of the tropical forest. I was influenced by 19th century naturalists' research on Amazon archaeology. They recognized an occupation that began thousands of years ago with hunters who made projectile points and monumental rock art and early fishing villagers with pottery and culminated by the time of the European conquest in populous civilizations with mounds and elaborately decorated pottery vessels and figures. But in the mid-twentieth-century, "scientific" archaeologists decided that the sequence had been short and derivative, impeded by the hot, humid tropical forest. They ignored the early cultures and attributed Amazonian cultures to intrusions from the Andes. When radiometric dating contradicted their chronology, they suppressed the problematic dates and when other North Americans came to do research they tried to prevent their excavation permits and criticized them with false statements about their own teams' results. Thus, they involved Brazilian proteges in unethical practices and prevented their rediscovery of the sequence of the 19th century naturalists.

A novel fossil-species of Meliolinites Selkirk (fossil Meliolaceae) and its life cycle stages associated with an angiosperm fossil leaf from the Siwalik (Mio-Pliocene) of Bhutan sub-Himalaya

Here, we report the in-situ occurrence of a new fossil-species of Meliolinites (fossil Meliolaceae), Meliolinites bhutanensis sp. nov. on the cuticle fragments of a compressed angiosperm dicot leaf recovered from the middle Siwalik (Formation II: latest Miocene to Pliocene) of Bhutan, eastern Himalaya. This unique foliicolous new fossil fungal species features well-preserved mycelia consisting of superficial, brown to dark brown, septate, thick-walled, branching hyphae with bi-cellular appressoria, unicellular phialides, and a characteristic long, slightly curved hyphal seta. The web-like, brown to dark brown fungal colonies also include globose to sub-globose, dark brown ascomata, and oblong to broadly cylindrical, 5-celled, 4-septate, brown to dark brown, mature ascospores. As almost all features of different stages in the life cycle (ascospores, mature germinating ascospores, superficial lateral hyphae, hyphal seta, hyphopodia, mycelial colony, and ascomata) of this new fossil-species are found, we have proposed the first time a possible life cycle of fossil-species of Meliolaceae. The in-situ evidence of M. bhutanensis on the host leaf cuticle indicates the possible existence of a host-ectoparasite relationship in Bhutan sub-Himalaya's ancient warm and humid tropical evergreen forest during the deposition. So, M. bhutanensis might have thrived generally under warm and humid climate conditions for its growth and development in the Mio-Pliocene time, which is in conformity with our recently published quantitative climatic data by CLAMP (Climate Leaf Analysis Multivariate Program) analysis.

Tropical forests as drivers of lake carbon burial

A significant proportion of carbon (C) captured by terrestrial primary production is buried in lacustrine ecosystems, which have been substantially affected by anthropogenic activities globally. However, there is a scarcity of sedimentary organic carbon (OC) accumulation information for lakes surrounded by highly productive rainforests at warm tropical latitudes, or in response to land cover and climate change. Here, we combine new data from intensive campaigns spanning 13 lakes across remote Amazonian regions with a broad literature compilation, to produce the first spatially-weighted global analysis of recent OC burial in lakes (over ~50-100-years) that integrates both biome type and forest cover. We find that humid tropical forest lake sediments are a disproportionately important global OC sink of 7.4 Tg C yr−1 with implications for climate change. Further, we demonstrate that temperature and forest conservation are key factors in maintaining massive organic carbon pools in tropical lacustrine sediments.

Prescribed burning in Pinus cubensis-dominated tropical natural forests: a myco-friendly fire-prevention tool

Aim of study: To evaluate the effects of two different prescribed burning strategies on ectomycorrhizal (ECM) fungal species in Pinus cubensis-dominated natural forest.
 Area of study: Yateras Silvicultural Base Business Unit, Guantánamo, Cuba.
 Material and methods: In June 2015, six plots (20 × 50 m) were subjected to forward or back burning. Nine interval samplings (performed 1 week before and up to 120 days after prescribed burning) were undertaken to determine the total number of sporocarps and to evaluate the effect of fire on the soil.
 Main results: Eight ECM species were collected from the study plots. Suillus sp. and Amanita muscaria started fruiting 15 and 60 days after the fire, respectively. Boletus sp., Suillus brevipes, Suillus decipiens, Suillus sp., Amanita muscaria, Lactarius semisanguifluus, Scleroderma stellatum and Pisolithus arhizus were found before and after prescribed burning. Sporocarp numbers showed an increasing trend after fire and significantly recovered 75 days after forward or back burning and were significantly higher 120 days after forward burning compared to unburned plots. The ECM fungal community in the heading fire and the backfire plots did not differ significantly. However, non-metric multidimensional scaling confirmed that ECM composition differed over time. According to a Mantel test, the sampling time after prescribed burning accounted for 64% of the variation in ECM composition, followed by edaphic factors (26%) such as organic matter and Na.
 Research highlights: This preliminary study suggests that low-intensity prescribed burning does not have a negative effect on ECM fungal dynamics in humid tropical forests.

CongoFlux – The First Eddy Covariance Flux Tower in the Congo Basin

The Congo basin is home to the second-largest tropical forest in the world. Therefore, it plays a crucial role in the regional water cycle, the global carbon cycle and the continental greenhouse gas balance. Yet very few field-based data on related processes exist. In the wake of global change, there is a need for a better understanding of the current and future response of the forest biome in this region. A new long-term effort has been set up to measure the exchange of greenhouse gasses between a humid lowland tropical forest in the Congo basin and the atmosphere via an eddy-covariance (EC) tower. Eddy-covariance research stations have been used for decades already in natural and man-made ecosystems around the globe, but the natural ecosystems of Central Africa remained a blind spot. The so-called “CongoFlux” research site has been installed right in the heart of the Congo Basin, at the Yangambi research center in DR Congo. This introductory paper presents an elaborated description of this new greenhouse gas research infrastructure; the first of its kind in the second-largest tropical forest on Earth.

Overview of Thaumatococcus Daniellii Plant, History, Uses, Benefits, and Characterization

Thaumatococcus daniellii (Benn.) Benth, known as “katempe” or “katemfe”. It grows in humid tropical forests and the coastal areas of West Africa, especially in Nigeria, Ghana, Central African Republic, Uganda, and Cote d'Ivoire. T. daniellii contains chemical compounds that have several uses in many fields and contain thaumatin protein, which plays an essential role in the food industry, used as a natural sweetener, and pharmaceutical industry. T. daniellii can play a significant role in economic growth in many countries in which it grows. This study summarises some crucial aspects of T. daniellii. As the study highlight, some of the chemical components are contained in the plant. In addition to the other medicinal benefits and applications used from T. daniellii. the study presented the importance of the plant in the production of thaumatin and highlighted the two types of this protein and the difference between them in the arrangement of amino acids.

Diversity of Endemic Ectomycorrhizae of Humid Forests of South Cameroon

The ecologically important below-ground ectomycorrhizal (ECM) biodiversity of tropical humid forests remain poorly known. Most ECM inventories have been based upon description and identification of fruitbodies with few work on ECM root tips of tropical tree species. Morpho-anatomical descriptions of root tips of 24 ECM Fabaceae/Detarioideae, Uapaca tree species, and Gnetum lianas were conducted in humid forest of South Cameroon. ECM forest clumps were the only resort sites for the more than 30 endemic ECM morphotypes, with apparently no host specificity. Distinguished by four colors – white, yellow, brown, and dark brown – and five textures – smooth, cottony, woolly, spiny and verrucose –, they differed from to the golden yellow coralloïdal Gnetum liana ECM with plectenchymatous mantle. Tree ECM were of monopodial-pinnate or -pyramidal types with external felt prosenchyma mantles shielded with abundant rhizomorphs, emanating hyphae and variously shaped cystida with clamp connections. These ECM fungal attributes may confer ECM associations with strong competitive abilities to strive at best on prevailing nutrient-poor acid soils and harsh conditions, thus better explaining tropical monodominance. Yet, much research is still needed to determine the role of below-ground ECM biodiversity on structure and functioning of tropical humid forests of the Congo basin.

TOWARDS A TREE COVER CHANGE EARLY WARNING SYSTEM BASED ON SENTINEL-1 DATA AND A NEURAL NETWORK ARCHITECTURE

Abstract. This study aimed at exploring the potential of neural networks composed of convolutional and Long Short-Term Memory (LSTM) layers to handle dense Sentinel-1 data time series to develop a tree cover loss Early Warning System (EWS). The study area was in the Madre de Dios region in Peru that hosts a humid tropical forest. The second objective of this study was to investigate the potential of large free open-source datasets such as those from the GLAD and Geobosques alerts to calibrate and validate the models. The study demonstrated the capacity of the tested NN models to improve the detection of tree cover loss compared to a classical random forest algorithm thanks to their capacity to handle explicitly both spatial and temporal data. The accuracies of the best model compare reasonably well with those from similar studies. However, the observed overestimation of the Cover-loss class in the output map can be mainly linked to the quality of the alert datasets used as input data. Avenues to overcome the identified limits of this preliminary study are presented. This work provides a solid knowledge basis on the potential of a NN-based EWS and opens potential avenues for further improvements.

The Genus Plagiochila (Dumort.) Dumort. (Marchantiophyta) in Madagascar

Plagiochila (Dumort.) Dumort. is one of the largest liverwort genera of Madagascar. A study of the rich Plagiochila holdings from Madagascar kept in the herbaria of Brussels, Eger and Paris leads to the recognition of 22 species, in six sections. One species, P. vandenberghenii Gradst., sp. nov., is new to science and P. bifaria (Sw.) Lindenb., P. macrostachya Lindenb. (synonym: P. granditexta Steph. syn. nov.) and P. simplex (Sw.) Lindenb., all three from the Neotropics, are recorded for the first time from Africa. Madagascar harbors about half of the African Plagiochilas and three species are endemic, P. fracta Pócs, P. sikorae Steph. and P. vandenberghenii Gradst., sp. nov. The high Plagiochila richness of Madagascar is explained by the large tracts on the island of humid tropical montane forest, being the preferred habitat of the genus. East African and Afro-American taxa prevail and four species, P. bifaria, P. macrostachya, P. simplex and P. stricta Lindenb., have a peri-Afro-American range being absent on the African mainland. A key to the Madagassan species of Plagiochila is provided and each species is described and illustrated, with data on types, synonyms, geographical distribution, habitat and differentiating characters.

Soil carbon and microbes in the warming tropics

Abstract Climate warming could destabilise the Earth's largest terrestrial store of reactive carbon (C), by accelerating the decomposition of soil organic matter. A third of that C store resides in the tropics. The potential for tropical soils to sequester C, or to act as an additional source of CO2, will depend on the balance of C inputs and outputs, mediated by the response of soil microbial communities and their activity to perturbation. We review the impact of warming on microbial communities and C storage in humid tropical forest soils over multiple time‐scales. Recent in situ experiments indicate high sensitivity of tropical forest soil C mineralisation to warming in the short term. However, whether this will translate into long‐term soil C decline remains unclear. At decadal time‐scales, high sensitivity of soil C mineralisation to warming is consistent with the correlation between the inter‐annual variation in the tropical land surface temperature and atmospheric CO2 growth rate, and with simulations using the Carnegie‐Ames‐Stanford Approach biosphere model. This observed sensitivity may further contribute to climatic change over millennial time‐scales, suggested by radiocarbon dating of organic matter in river basins showing a twofold acceleration in tropical soil C release during the late‐glacial warming period. However, counter to this evidence, long‐term stability of tropical soil C is suggested by observed steady‐state soil C turnover across temperature gradients with elevation, and by the presence of C in tropical soils that pre‐dates the Holocene Thermal Maximum and late‐glacial warming periods. To help reconcile these recent experimental findings and long‐term observations, we propose mechanisms to explain tropical soil C and microbial responses to warming across multiple time‐scales. Combined in situ experimental and monitoring approaches—large‐scale and cross‐site—are urgently needed to resolve the interplay of these mechanisms across spatial and temporal scales, to shape a better understanding of the relationship between soil microbes and C storage in tropical soils. Read the free Plain Language Summary for this article on the Journal blog.

Structural attributes estimation in a natural tropical forest fragment using very high-resolution imagery from unmanned aircraft systems

Structural attributes are fundamental biophysical parameters of forest, useful for ecological and environmental monitoring and planning. Canopy height is an important input for the estimation of several biophysical parameters as aboveground biomass and carbon stock, and can be related with forest degradation, deforestation, and emission reduction. Thus, an accurate canopy height estimation is a crucial issue in climate change studies and REDD+ initiatives. VHR imagery from unmanned aircraft systems has been studied as a low cost mean for canopy height estimation at local scales, but the accuracy in the estimation is a factor that determines its utility. We evaluated the ability of VHR imagery from unmanned aircraft systems to derive structural attributes, specifically tree-crown area and height, in a natural tropical forest fragment located in the foothills of the Andes Mountains, in the humid tropical forests of the region known as Biogeographic Chocó, South America. The region is one of the most biodiverse areas of the world and has a high level of endemism, but it is also at higher risk of natural-resource loss. We used a structure from motion approach to derive canopy height models of the forest fragment, and we applied mean-shift algorithms to identify single tree crowns. The accuracy assessment was performed using reference data derived from field campaigns and visually interpretation of VHR imagery. The estimated root-mean-square error of the population of vertical errors for the canopy height model was 3.6 m. The total accuracy for delineating tree crowns was 73.9%. We found that using VHR imagery, specific trees and canopy gaps can be identified and easily monitored, which is an important step in conservation programs. We also discuss the usefulness of these findings in the context of fragmented forests and the tradeoffs between the price of a LIDAR system and the accuracy of this approach.

How Well Do We Understand the Land‐Ocean‐Atmosphere Carbon Cycle?

AbstractFossil fuel combustion, land use change and other human activities have increased the atmospheric carbon dioxide (CO2) abundance by about 50% since the beginning of the industrial age. The atmospheric CO2 growth rates would have been much larger if natural sinks in the land biosphere and ocean had not removed over half of this anthropogenic CO2. As these CO2 emissions grew, uptake by the ocean increased in response to increases in atmospheric CO2 partial pressure (pCO2). On land, gross primary production also increased, but the dynamics of other key aspects of the land carbon cycle varied regionally. Over the past three decades, CO2 uptake by intact tropical humid forests declined, but these changes are offset by increased uptake across mid‐ and high‐latitudes. While there have been substantial improvements in our ability to study the carbon cycle, measurement and modeling gaps still limit our understanding of the processes driving its evolution. Continued ship‐based observations combined with expanded deployments of autonomous platforms are needed to quantify ocean‐atmosphere fluxes and interior ocean carbon storage on policy‐relevant spatial and temporal scales. There is also an urgent need for more comprehensive measurements of stocks, fluxes and atmospheric CO2 in humid tropical forests and across the Arctic and boreal regions, which are experiencing rapid change. Here, we review our understanding of the atmosphere, ocean, and land carbon cycles and their interactions, identify emerging measurement and modeling capabilities and gaps and the need for a sustainable, operational framework to ensure a scientific basis for carbon management.

Responses of tree growth and biomass production to nutrient addition in a semi-deciduous tropical forest in Africa.

Experimental evidence of nutrient limitations on primary productivity in Afrotropical forests is rare and globally underrepresented yet are crucial for understanding constraints to terrestrial carbon uptake. In an ecosystem-scale nutrient manipulation experiment, we assessed the early responses of tree growth rates among different tree sizes, taxonomic species, and at a community level in a humid tropical forest in Uganda. Following a full factorial design, we established 32 (eight treatments × four replicates) experimental plots of 40 × 40 m each. We added nitrogen (N), phosphorus (P), potassium (K), their combinations (NP, NK, PK, and NPK), and control at the rates of 125 kg N ha-1 year-1 , 50 kg P ha-1 year-1 and 50 kgK ha-1 year-1 , split into four equal applications, and measured stem growth of more than 15,000 trees with diameter at breast height (dbh) ≥1cm. After 2 years, the response of tree stem growth to nutrient additions was dependent on tree sizes, species and leaf habit but not community wide. First, tree stem growth increased under N additions, primarily among medium-sized trees (10-30 cm dbh), and in trees of Lasiodiscus mildbraedii in the second year of the experiment. Second, K limitation was evident in semi-deciduous trees, which increased stem growth by 46% in +K than -K treatments, following a strong, prolonged dry season during the first year of the experiment. This highlights the key role of K in stomatal regulation and maintenance of water balance in trees, particularly under water-stressed conditions. Third, the role of P in promoting tree growth and carbon accumulation rates in this forest on highly weathered soils was rather not pronounced; nonetheless, mortality among saplings (1-5cm dbh) was reduced by 30% in +P than in -P treatments. Although stem growth responses to nutrient interaction effects were positive or negative (likely depending on nutrient combinations and climate variability), our results underscore the fact that, in a highly diverse forest ecosystem, multiple nutrients and not one single nutrient regulate tree growth and aboveground carbon uptake due to varying nutrient requirements and acquisition strategies of different tree sizes, species, and leaf habits.

Warming drives sustained plant phosphorus demand in a humid tropical forest.

Phosphorus (P) is often one of the most limiting nutrients in highly weathered soils of humid tropical forests and may regulate the responses of carbon (C) feedback to climate warming. However, the response of P to warming at the ecosystem level in tropical forests is not well understood because previous studies have not comprehensively assessed changes in multiple P processes associated with warming. Here, we detected changes in the ecosystem P cycle in response to a 7-year continuous warming experiment by translocating model plant-soil ecosystems across a 600-m elevation gradient, equivalent to a temperature change of 2.1°C. We found that warming increased plant P content (55.4%) and decreased foliar N:P. Increased plant P content was supplied by multiple processes, including enhanced plant P resorption (9.7%), soil P mineralization (15.5% decrease in moderately available organic P), and dissolution (6.8% decrease in iron-bound inorganic P), without changing litter P mineralization and leachate P. These findings suggest that warming sustained plant P demand by increasing the biological and geochemical controls of the plant-soil P-cycle, which has important implications for C fixation in P-deficient and highly productive tropical forests in future warmer climates.

Fast redox switches lead to rapid transformation of goethite in humid tropical soils: A Mössbauer spectroscopy study

AbstractHumid tropical forest soils experience frequent rainfall, which limits oxygen diffusion and creates redox heterogeneity in upland soils. In this study we gauged the effect of short‐term anoxic conditions on Fe mineralogy of relatively Fe‐ and C‐rich surface soils (C/Fe mole ratio ∼5) from a humid tropical forest in Puerto Rico. Soils subjected to 4‐d oxic/anoxic oscillation were characterized by selective chemical extractions, Mössbauer spectroscopy (MBS), and X‐ray diffraction. Chemical extraction data suggested that rapidly switching redox conditions had subtle effects on bulk Fe mineralogy. Mössbauer, on the other hand, indicated that (a) the soil Fe is a mixture of goethites of varying characteristics with minor contributions from ferrihydrite (<5%) and Fe(III)‐organic matter (OM) phases (∼10%), and (b) anoxic conditions rapidly transformed all forms of goethite to relatively stable Fe oxides. Such fast changes in goethite features could be due to rapid depletion and sorption of bio‐released structural Al or sorbed OM onto residual soil components. The rapid temporal changes in MBS parameters and corresponding pore water nominal oxidation state of C values suggest that Fe‐C transformations in these upland tropical soils are complex and intricately coupled. A comprehensive understanding of the fate of Fe, Al, and OM (Fe‐organic moieties) during redox switches and concurrent changes in pore water chemistry is critical for development of robust transport models in humid tropical soils, which are subject to episodic low‐redox events.

Paleoclimatic and paleoenvironmental changes in Amazonian lowlands over the last three millennia

The paleoclimatic and paleoenvironmental history of the Amazon basin over the last millennia and the behavior of the South American Monsoon System (SAMS) throughout the lowlands have not yet been thoroughly examined due to a lack of records from more central portions of the basin. Here we discuss these past changes based on new high-resolution δ18O and δ13C records from speleothems collected in the southwestern Amazon Basin, at the core region of the convective activity of the SAMS. We demonstrate that the δ18O from these new records is representative of SAMS variations and that this convective system provides distinct precipitation patterns over the basin. The SAMS was in a neutral phase with homogeneous precipitation between 1000 BCE and 300 CE, whereas drier conditions prevailed over the western side of the basin between 700 and 1200 CE and an east-west climatic dipole was established over the Amazon Basin after 1450 CE when wetter conditions prevailed over our study site. The speleothem δ13C record indicates an overall tendency toward a more humid tropical forest during the studied period, except for a drier period which correlates with the Medieval Climate Anomaly (MCA). The dynamics of pre-Columbian cultures from southwestern Amazonia seem to have been related to paleoclimatic and environmental changes reported for the region.

Seed dispersal by spider monkeys in logged and unlogged sites in the Calakmul tropical humid forest, Mexico / Dispersión de semillas por monos araña en sitios talados y no talados en el bosque húmedo tropical de Calakmul, México

Seed dispersal by animals can be negatively affected by selective logging, but effects such changes in critical food resource, quality of food resources and food availability on seed dispersal and seedling recruitment, remains poorly understood. We investigated how selective logging, impacts the quantity of seed dispersal, focusing on highly frugivorous primate Ateles geoffroyi yucatanensis in Calakmul, Mexico. We assessed whether seed dispersal by the spider monkey differs between a logged and an unlogged site in the Calakmul tropical humid forest, Mexico. We recorded seeds in monkey faeces, including those deposited in latrines under sleeping trees (aggregated seed dispersal) and those dispersed across the forest (scattered seed dispersal) during a 5-mo period. The use of sleeping tree was similar in both forest conditions, averaging (± SD) 4.5 ± 4.3 weeks. They deposited 15,853 seeds (1–35 mm in length) from 20 tree species under sleeping trees, but seed abundance was 2.2 times higher in unlogged forests. Scattered seed dispersal (997 seeds from nine species) followed the opposite pattern, with 2.3 times more seeds in logged forests. The number of seeds and species per faecal sample did not differ between forest types, averaging 9.4 ± 20.2 seeds from 1.0 ± 0.8 seed species. Most (95%) scatter-dispersed seeds were undamaged in both forest types. These findings suggest that primate quantity seed dispersal is not limited in logged forests, potentially contributing to the recovery of these managed forests.

Radial variations in wood functional traits in a rain forest from eastern Amazonia

Key messagePositive radial trends in WSG were common among light-demanding species, and were mainly explained by radial shift in fiber and parenchyma traits.Trees can modify their wood structure in response to changes in mechanical, hydraulic and storage demands during their life-cycles. Thus, examining radial variations in wood traits is important to expand our knowledge of tree functioning and species ecological strategies. Yet, several aspects of radial changes in wood functional traits are still poorly understood, especially in angiosperm trees from tropical humid forests. Here, we examined radial shifts in wood traits in trunks of tropical forest species and explored their potential ecological implications. We first examined radial variations in wood specific gravity (WSG). Then, we asked what anatomical traits drove radial variations in WSG, and whether WSG, vessel fraction and specific hydraulic conductivity vary independently from each other along the radius gradients. We measured WSG and eight wood anatomical traits, at different radial positions along the trunks, in 19 tree species with contrasting shade-tolerance from a lowland tropical forest in eastern Amazonia. Most species had significant radials shifts in WSG. Positive radial gradients in WSG (i.e., increments from pith to bark) were common among shade-intolerant species and were explained by different combinations of fiber and parenchyma traits, while negative radial shifts in WSG (e.g., decreases towards the bark) were present in shade-tolerants, but were generally weakly related to anatomical traits. We also found that, in general, WSG was unrelated to vessel fraction and specific hydraulic conductivity in any radial position. This study illustrates the contrasting radial variations in wood functional traits that occur in tree species from a humid lowland tropical forest. In particular, our results provide valuable insights into the anatomical traits driving WSG variations during tree development. These insights are important to expand our knowledge on tree ecological strategies by providing evidence on how wood allocation varies as trees grow, which in turn can be useful in studying trait-demography associations, and in estimating tree above-ground biomass.