Amazonian Tree Species Research Articles

High extinction risk of the endemic tree flora in a hyper‐diverse region of the Amazon

Societal Impact StatementThe rapid global loss of biodiversity, especially in the Neotropics, underscores the need to understand how deforestation impacts endemic plant species' extinction risk and conservation status. Due to limited ranges and habitat specialization, endemics are particularly vulnerable. Our study reveals that around 14% and 47% of Ecuadorian Amazon endemic trees are Critically Endangered and Endangered, respectively, with 41% facing high extinction risk. Traits like life‐form, fruit size, and height relate to extinction vulnerability. These findings highlight the factors driving Amazonian tree flora endangerment, providing crucial insights for conservation efforts of this fundamental component of Amazon hyper‐diverse forests.Summary Comprehensive analyses of the global conservation statuses of endemic tree species are scarce, especially for species‐rich forests. Endemic trees arguably suffer a higher extinction risk than other plant species due to their restricted geographic range and habitat specialization. Here, we present an updated assessment of the conservation status and extinction risk estimates for the endemic tree flora of the Ecuadorian Amazon, a darkspot of biodiversity. We combined an extensively verified taxonomic database of Amazon tree species abundance and occurrence with the most updated data of deforestation for this region. We found that approximately one sixth of the Ecuadorian Amazon endemic tree flora is Critically Endangered. A few clades, including Myrtaceae, Elaeocarpaceae, Fabaceae s.l., and Lauraceae, harbor one third of the Critically Endangered endemic tree species. According to our analysis, the extinction risk for endemic trees is associated not only with extrinsic factors such as deforestation but also with their ecology. Life‐form, fruit size, and maximum height are significantly related to extinction risk. Thus, endemic understory and canopy trees with small fruits are more prone to suffer extinction than emergent tree species. We argue that assessment programs should also include biological trait information in addition to geographic ranges and habitat specialization for the establishment of effective conservation strategies of this hyper‐diverse region of the Amazon.

Lipid profiles and DNA barcoding markers reveal the genetic delimitation between species of the Carapa genus native from the Amazon

Authentic identification of Amazonian tree species is important for conservation and their sustainable exploitation. This work aimed to characterize the inter- and intraspecific divergence in two taxonomic units of the genus Carapa using the lipidomic profile of the seed oils, analyzed by gas chromatography-mass spectrometry (GC-MS) and DNA barcoding molecular markers to identify and discriminate differences between Carapa species. Seeds and leaves of 53 individuals were collected and morphologically grouped into Carapa guianensis and Carapa vasquezii. The oils extracted from seeds were esterified, and their lipidomic profiles were analyzed. Two chloroplast genome regions (psbA-trnH and rbcL) were amplified for genetic diversity analyses and the barcoding-gap test. The lipidomic profile allowed the identification of 40 substances present in the C. guianensis and C. vasquezii oils, with 20 shared among the species independent of the region of collection, two occurring only in the oil of C. guianensis from Acre, four in samples of C. guianensis and C. vasquezii from Amazonas, and 16 substances occurring only in samples of C. vasquezii oil. C. vasquezii presented a greater diversity of terpenoids. The genome regions made it possible to obtain 16 distinct haplotypes for the two species (C. guianensis and C. vasquezii), 999 conserved sites, and 32 polymorphic sites. The species presented significant molecular divergence (FST=0.87), and the rbcL region was considered promising for barcode studies at levels ranging from 0.1 to 0.2% of genetic distance. The results suggest that the two species morphologically identified C. guianensis and C. vasquezii constitute genetically divergent biological groups.

Differential copper toxicity in Amazon tree species explained by seed germination and initial seedling growth

Differential copper toxicity in Amazon tree species explained by seed germination and initial seedling growth

Ecosystem type affects how Amazonian tree species invest in stem and twig wood

Abstract Wood density (WD) is a key functional trait for its importance in tree performance and in biomass calculations of forests. Yet, the variation of WD among different woody tree parts, how this varies across ecosystems, and how this influences estimates of forest carbon stocks remains little understood, particularly for diverse tropical forests such as the Amazon. We assembled a dataset on stem and twig wood density from 119 tree species in three different Amazonian ecosystem types that differ considerably in soil nutrition and flooding: non‐flooded forest (Terra Firme), white‐water floodplain forest (Várzea) and black‐water floodplain forest (Igapó) to investigate (i) variation of stem and twig wood density across ecosystems, (ii) the relationships between stem and twig wood density and how these relationships vary across ecosystems. Wood density varied substantially across ecosystems. Várzea species showed lower mean WD for stems compared to Terra firme, while Igapó species showed higher WD for twigs compared to the other ecosystems. Twig and stem wood density were positively related (R2adj = 0.47) with similarly increasing rates across ecosystems, although average WD values differed between Terra firme and Igapó. For any given twig density, stem density tends to be lower in floodplain environments but higher in Terra firme, a habitat‐specific pattern of wood density variation within trees that may emerge from differences in the function of stem and twig wood for growth and survival in ecologically differentiated environments. Our results show how ecosystem has strong impacts on how trees allocate resources to different woody tissues, suggesting contrasting ecological strategies linked to ecosystem constraints. Our results suggest that greater consideration of the variation of WD within trees and how these changes across ecosystems might lead to more accurate estimates of above‐ground biomass in Amazonia. Read the free Plain Language Summary for this article on the Journal blog.

Tree species occurring in Amazonian wetland forests consistently show broader range sizes and niche breadths than trees in upland forests.

Generally, species with broad niches also show large range sizes. We investigated the relationship between hydrological niche breadth and geographic range size for Amazonian tree species seeking to understand the role of habitat specialization to Amazonian wetlands and upland forests on the current distribution of tree species. We obtained 571,092 valid occurrence points from GBIF and SpeciesLink to estimate the range size and the niche breadth of 76% of all known Amazonian tree species (5150 tree species). Hydrological niche breadth was measured on different unidimensional axes defined by (1) total annual precipitation; (2) precipitation seasonality; (3) actual evapotranspiration; and (4) water table depth. Geographic range sizes were estimated using alpha-hull adjustments. General linear models were used to relate niche breadth to range size while contrasting tree species occurring and not occurring in wetlands. The hydrological niche breadth of Amazonian tree species varied mostly along the water table depth axis. The average range size for an Amazonian tree species was 751,000 km2 (median of 154,000 km2 and standard deviation of 1,550,000 km2). Niche breadth-range size relationships for Amazonian tree species were positive for all models, and the explanatory power of the models improved when including whether a species occurred in wetlands or in terrestrial uplands. Wetland species had steeper positive slopes for the niche breadth-range size relationship, and consistently larger range sizes for a given niche breadth. Amazonian tree species varied strongly in hydrological niche breadth and range size, but most species had narrow niche breadths and range sizes. Our results suggest that the South American riverscape may have been acting as a corridor for species dispersal in the Neotropical lowlands.

Differential photosynthetic plasticity of Amazonian tree species in response to light environments.

To investigate how and to what extent there are differences in the photosynthetic plasticity of trees in response to different light environments, six species from three successional groups (late successional, mid-successional, and pioneers) were exposed to three different light environments [deep shade - DS (5% full sunlight - FS), moderate shade - MS (35% FS) and full sunlight - FS]. Maximum net photosynthesis (Amax), leaf N partitioning, stomatal, mesophile, and biochemical limitations (SL, ML, and BL, respectively), carboxylation velocity (Vcmax), and electron transport (Jmax) rates, and the state of photosynthetic induction (IS) were evaluated. Higher values of Amax, Vcmax, and Jmax in FS were observed for pioneer species, which invested the largest amount of leaf N in Rubisco. The lower IS for pioneer species reveals its reduced ability to take advantage of sunflecks. In general, the main photosynthetic limitations are diffusive, with SL and ML having equal importance under FS, and ML decreasing along with irradiance. The leaf traits, which are more determinant of the photosynthetic process, respond independently in relation to the successional group, especially with low light availability. An effective partitioning of leaf N between photosynthetic and structural components played a crucial role in the acclimation process and determined the increase or decrease of photosynthesis in response to the light conditions.

One sixth of Amazonian tree diversity is dependent on river floodplains.

Amazonia's floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region's floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon's tree diversity and its function.

Thermal optima for seed germination of 30 tree species from Central Amazonia: a comparison of approaches and a new proposal

This study compared the seed germination of 30 tree species from Central Amazonia using a wide temperature range (5-40°C with 12 hours of light daily). Seeds were submitted to pre-germination treatments, whenever necessary, sown on vermiculite or germitest paper, and normal seedling development was assessed until stabilisation. With the same data set, seeds' optimal germination temperature (Topt ) was determined by comparing the following approaches: (i) 2-step, the temperature with the highest germination and the shortest time to seed population reach 50% of germination was chosen; (ii) the highest Germination Speed Index (GSI); (iii) using the formula developed by Olff and collaborators (Olff's approach); (iv) three species were evaluated with Covell's approach; and (v) new formulas for Topt calculation are proposed, based on germination success and five different variables of germination rate (Cipriani's approach). Comparing the results, Topt differed between 0.6-10.0°C. GSI and 2-step indicated generally higher values than Olff's formula. The minimum and maximum Topt differences between Cipriani's approaches were between 0.1-2.2°C. Our study showed that Toptshould be determined for each species as, even the 30 Amazonian tree species of the same habitat, Topt ranged between 22.5 and 32.5°C.

Understanding different dominance patterns in western Amazonian forests.

Dominance of neotropical tree communities by a few species is widely documented, but dominant trees show a variety of distributional patterns still poorly understood. Here, we used 503 forest inventory plots (93,719 individuals ≥2.5 cm diameter, 2609 species) to explore the relationships between local abundance, regional frequency and spatial aggregation of dominant species in four main habitat types in western Amazonia. Although the abundance-occupancy relationship is positive for the full dataset, we found that among dominant Amazonian tree species, there is a strong negative relationship between local abundance and regional frequency and/or spatial aggregation across habitat types. Our findings suggest an ecological trade-off whereby dominant species can be locally abundant (local dominants) or regionally widespread (widespread dominants), but rarely both (oligarchs). Given the importance of dominant species as drivers of diversity and ecosystem functioning, unravelling different dominance patterns is a research priority to direct conservation efforts in Amazonian forests.

Tropical forest lianas have greater non-structural carbohydrate concentrations in the stem xylem than trees.

Lianas (woody vines) are important components of tropical forests and are known to compete with host trees for resources, decrease tree growth and increase tree mortality. Given the observed increases in liana abundance in some forests and their impacts on forest function, an integrated understanding of carbon dynamics of lianas and liana-infested host trees is critical for improved prediction of tropical forest responses to climate change. Non-structural carbohydrates (NSC) are the main substrate for plant metabolism (e.g., growth, respiration), and have been implicated in enabling tree survival under environmental stress, but little is known of how they vary among life-forms or of how liana infestation impacts host tree NSC. We quantified stem total NSC (NSC) concentrations and its fractions (starch and soluble sugars) in trees without liana infestation, trees with more than 50% of the canopy covered by lianas, and the lianas infesting those trees. We hypothesized that i) liana infestation depletes NSC storage in host trees by reducing carbon assimilation due to competition for resources; ii) trees and lianas, which greatly differ in functional traits related to water transport and carbon uptake, would also have large differences in NSC storage, and that As water availability has a significant role in NSC dynamics of Amazonian tree species, we tested these hypotheses within a moist site in western Amazonia and a drier forest site in southern Amazonia. We did not find any difference in NSC, starch or soluble sugar concentrations between infested and non-infested trees, in either site. This result suggests that negative liana impact on trees may be mediated through mechanisms other than depletion of host tree NSC concentrations. We found lianas have higher stem NSC and starch than trees in both sites. The consistent differences in starch concentrations, a long term NSC reserve, between life forms across sites reflect differences in carbon gain and use of lianas and trees. Soluble sugar concentrations were higher in lianas than in trees in the moist site but indistinguishable between life forms in the dry site. The lack of difference in soluble sugars between trees and lianas in the dry site emphasize the importance of this NSC fraction for plant metabolism of plants occurring in water limited environments. Abstract in Portuguese and Spanish are available in the supplementary material.

Past human‐induced ecological legacies as a driver of modern Amazonian resilience

Abstract People have modified landscapes throughout the Holocene (the last c. 11,700 years) by modifying soils, burning forests, cultivating and domesticating plants, and directly and indirectly enriched and depleted plant abundances. These activities also took place in Amazonia, which is the largest contiguous piece of rainforest in the world, and for many decades was considered to have very little human impact until the modern era. The compositional shift caused by past human disturbances can alter forest traits, creating ecological legacies that may persist through time. As the lifespan of most Amazonian tree species is more than 200 years, forests that were modified over the last centuries to millennia are likely still in a mid‐successional state. Ecological legacies resulting from past human activity may also affect modern forest resilience to ongoing anthropogenic and climatic changes. Current estimates of resilience assume that forests are in equilibrium, and long‐term successional trajectories are not considered. We suggest that disturbance histories, generated through palaeoecological and archaeological surveys, should be paired with field‐based and remotely sensed estimates of forest resilience to recent drought events, to determine whether past human activities affect modern forest resilience. We have outlined how this can be accomplished in future research. Read the free Plain Language Summary for this article on the Journal blog.

MADERA: A standardized Pan-Amazonian dataset for tropical timber species.

We compiled and presented a dataset for all timber species reported in the Amazon region from all nine South American Amazonian countries. This was based on official information from every country, as well as from two substantial scientific references. We verified the standard taxonomic names from each individual source, using the Taxonomic Name Resolution Service (TNRS) and considered all Amazonian tree species with diameter at breast height (DBH) ≥10 cm. We also obtained estimates of the current population size for most species from a published approach based on data from 1900 tree inventory plots (1-ha each) distributed across the Amazon region and part from the Amazon Tree Diversity Network (ATDN). We then identified the hyperdominant timber species. In addition, we overlapped our timber species list with data for species that are used for commercial purposes, according to the International Tropical Timber Organization (ITTO), the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the International Union for Conservation of Nature (IUCN) taxa assessment and Red List categories. Finally, we also included IUCN Red List categories based on combined deforestation, and climate change scenarios for these species. Our final Amazonian timber species dataset contains 1112 unique species records, which belong to 337 genera and 72 families from the lowland Amazonian rainforest, with associated information related to population, conservation, and trade status of each species. The authors of this research expect that the information provided will be useful to strengthen the public forestry policies of the Amazon countries, inform ecological studies, as well for forest management purposes. The data are released under the Creative Commons Attribution 4.0 International license.

Basin-wide variation in tree hydraulic safety margins predicts the carbon balance of Amazon forests

Tropical forests face increasing climate risk1,2, yet our ability to predict their response to climate change is limited by poor understanding of their resistance to water stress. Although xylem embolism resistance thresholds (for example, varPsi 50) and hydraulic safety margins (for example, HSM50) are important predictors of drought-induced mortality risk3–5, little is known about how these vary across Earth’s largest tropical forest. Here, we present a pan-Amazon, fully standardized hydraulic traits dataset and use it to assess regional variation in drought sensitivity and hydraulic trait ability to predict species distributions and long-term forest biomass accumulation. Parameters varPsi 50 and HSM50 vary markedly across the Amazon and are related to average long-term rainfall characteristics. Both varPsi 50 and HSM50 influence the biogeographical distribution of Amazon tree species. However, HSM50 was the only significant predictor of observed decadal-scale changes in forest biomass. Old-growth forests with wide HSM50 are gaining more biomass than are low HSM50 forests. We propose that this may be associated with a growth–mortality trade-off whereby trees in forests consisting of fast-growing species take greater hydraulic risks and face greater mortality risk. Moreover, in regions of more pronounced climatic change, we find evidence that forests are losing biomass, suggesting that species in these regions may be operating beyond their hydraulic limits. Continued climate change is likely to further reduce HSM50 in the Amazon6,7, with strong implications for the Amazon carbon sink.

The morphophysiological mechanisms of light-induced net primary production of Amazonian tree species

We investigated the morphophysiological mechanisms indicative of resource uses behind net primary production in seedlings of three valuable forest species of socio-economic value in the Amazon:mahogany (Swietenia macrophylla), Brazil nut (Bertholletia excelsa) and Laurel (Cordia alliodora). The hypotheses tested were: (i) the three species will grow better under mild to high light but with different magnitudes of response; and (ii) the three species will show different mechanisms to reach a better growth under mild to high light We measured biomass production and a set of morphophysiological leaf traits and calculated the relative growth rates (diameter and height) of seedlings subjected to low(0.9), moderate (11.3) and high (45.0 mol m-2 day-1) irradiance for 80 days. For all species, biomass and growth increase with irradiance and the magnitude of the effect were species-dependent. The changes in total biomass by irradiance varied 1.5-fold (B. excelsa) and twofold (S. macrophylla). Light-induced changes in biomass partitioning and morphophysiological traits varied among species. S. macrophylla and C. alliodora significantly increased root/aboveground mass ratio (R/A) under high irradiance. Gas exchange increased with irradiance for C. alliodora and B. excelsa. The non-structural carbohydrates of C. alliodora and S. macrophylla were greater in high (total soluble sugars) and moderate (starch) light environments. The traits associated with total biomass were starch, stomatal conductance and transpiration for B. excelsa; leaf area ratio, leaf area root mass ratio, total soluble sugars and starch for C. alliodora; and RIA, leaf area ratio, and leaf area root mass ratio for S. macrophylla. The species obtained a high total biomass under mild to high irradiance but following different morphophysiological mechanisms. We discussed the potential to use these mechanisms in silvicultural systems designed to supply the plants with intermediate to high levels of light, for example enrichment planting in secondary forests or reforestation on degraded areas.

Parallel evolution and cryptic diversification in a common and widespread Amazonian tree, Protium subserratum.

The lowland Amazon rainforest houses some of the greatest tree diversity on Earth. While the vast majority of these species are rare, a small number are common and widespread and thus considered to play a disproportionate role in many of the global ecosystem services provided by the Amazon. However, the extent to which dominant Amazonian tree species actually include multiple clades, each on their own unique evolutionary trajectory, is unknown. Here we investigate the extent to which lineage divergence may be occurring within Protium subserratum (Burseraceae), a common and widespread tree species that is monophyletic with populations exhibiting genotypic and phenotypic differences associated with soil and geography. Utilizing a combination of phylogenomic and population genomic methods with sampling from across the range, we found that P.subserratum contains at least eight distinct clades. Specialization onto white-sand soils has evolved independently at least twice within the species; however, phenotype is not correlated with soil type. Finally, cryptic diversity at the base of the Andes is associated with elevational shifts. Together these results lend support to the hypothesis that common and widespread Amazon tree species may not represent evolutionary cohesive units. Instead, these dominant species may more commonly represent species complexes, undergoing evolutionary transitions on a trajectory to become multiple range-restricted, specialist species.

Soil fertility and drought interact to determine large variations in wood production for a hyperdominant Amazonian tree species

IntroductionThe productivity of the Amazon Rainforest is related to climate and soil fertility. However, the degrees to which these interactions influence multiannual to decadal variations in tree diameter growth are still poorly explored.MethodsTo fill this gap, we used radiocarbon measurements to evaluate the variation in tree growth rates over the past decades in an important hyperdominant species, Eschweilera coriacea (Lecythidaceae), from six sites in the Brazilian Amazon that span a range of soil properties and climate.ResultsUsing linear mixed-effects models, we show that temporal variations in mean annual diameter increment evaluated over a specific time period reflect interactions between soil fertility and the drought index (SPEI-Standardized Precipitation and Evapotranspiration Index).DiscussionOur results indicate that the growth response of trees to drought is strongly dependent on soil conditions, a facet of forest productivity that is still underexplored, and which has great potential for improving predictions of future tropical tree growth in the face of projected climate change.

Long-term drought effects on the thermal sensitivity of Amazon forest trees.

The continued functioning of tropical forests under climate change depends on their resilience to drought and heat. However, there is little understanding of how tropical forests will respond to combinations of these stresses, and no field studies to date have explicitly evaluated whether sustained drought alters sensitivity to temperature. We measured the temperature response of net photosynthesis, foliar respiration and the maximum quantum efficiency of photosystem II (Fv /Fm ) of eight hyper-dominant Amazonian tree species at the world's longest-running tropical forest drought experiment, to investigate the effect of drought on forest thermal sensitivity. Despite a 0.6°C-2°Cincrease in canopy air temperatures following long-term drought, no change in overall thermal sensitivity of net photosynthesis or respiration was observed. However, photosystem II tolerance to extreme-heat damage (T50 ) was reduced from 50.0 ± 0.3°C to 48.5 ± 0.3°Cunder drought. Our results suggest that long-term reductions in precipitation, as projected across much of Amazonia by climate models, are unlikely to greatly alter the response of tropical forests to rising mean temperatures but may increase the risk of leaf thermal damage during heatwaves.

The impact of species complexes on tree abundance patterns in Amazonia.

The impact of species complexes on tree abundance patterns in Amazonia.

Amazonian species evaluation using leaf-based spectroscopy data and dimensionality reduction approaches

Sampling trees in natural environment can be used in studies ranging from floristic composition and phytogeography to management and growth modelling, and accurate inventories are based on highly labor-intensive methods. Relying on hyperspectral approach, this study aimed to differentiate spectral libraries of four Amazon tree species. We first prepared the spectroradiometer data on representative bands on foliar biochemistry, followed by reflectance inflection difference and finally, we applied vegetation indices. Next, the discriminant analysis was reasoned on multivariate approach, were successfully discriminated the spectral curves related to each of evaluated tree species. By visual analysis, some regions of the electromagnetic spectrum with higher differentiation in reflectance responses can be seen, in portions of the visible spectrum (0.5–0.65 μm), near-infrared (0.913–1.25 μm) and short-wave infrared 2 (2.1–2.5 μm). There was a higher contribution in distinguishing between species based on specific RID (Reflectance Inflection Difference) heights, such as seen on specific representative bands, where RID approach reached 99.87% of data variability related to principal component 1 (PC1) and 99.72% for leaf structure-based bands in PC1. Principal component analysis applied to the vegetation indices brought satisfactory results, with PC1 highly related to the variability of the vegetation indices results (99.37%). Adopting this approach in hyperspectral data at the leaf level and well-defined classes results in good responses. We emphasize the importance of using combined vegetation indices, with greater contributions by indices developed for quantization or absorption of electromagnetic radiation by chlorophyll, which are based in the visible region. These results can improve further research by using remote sensing techniques, as create brand-new data for Amazonian tree species policymaking, conservation and research.

Exploring wood anatomy, density and chemistry profiles to understand the tree-ring formation in Amazonian tree species

Long-term analysis of tree growth using annual tree rings is increasingly in demand for tropical tree species. The basis of these studies has traditionally been the anatomical identification of the annual ring boundary. However, the structure of these annual rings has been sparsely explored for complementary physical and chemical wood traits. Here, we explore the relationships among wood density features and chemical elements (S, K, Ca, Mn) involved in the annual tree ring formation of 12 tropical tree species from non-flooded forest in the southern Amazon basin. Transverse wood sections were used for each species to determine: 1) macroscopic distinction (radial growth and wood density), 2) microscopic analyse of vessels, axial and ray parenchyma (anatomy) and 3) X-ray densitometry (physical) and X-ray fluorescence (chemical). For some species, the profiles of wood density, and Ca and Mn content showed intra- and inter-annual patterns that allowed to define and characterize the growth boundary of tree rings. Ca, K and S were mainly distributed in axial parenchyma cells, and around vessels, whereas, Mn was mainly distributed in fibres. Our results showed significant species-specific correlations between tree-ring width, density and concentrations of Ca, K and Mn. The anatomical characterization and the complementary information provided by the density and chemical profiles in some Amazonian species can represent a valuable proxy to improve the definition of annual ring-boundaries and improve the understanding of long-term growth and physiological patterns.