Rainforest Tree Species Research Articles

The importance of wood density in determining the phenology of tree species in a coastal rain forest

AbstractThe phenology of tree species in tropical dry forests is related to a well‐characterized interaction between functional traits (e.g., wood density) and climatic seasonality (e.g., drought stress), but the existence of these relationships in tropical wet forests is largely unknown. For 12 months, we monitored the vegetative and reproductive phases of 281 individuals of 46 tree species in a coastal rain forest in Northeastern Brazil. We hypothesized that wood density and related tissue water storage would reliably distinguish phenological groups of trees, and that leaf shedding, flushing, and flowering in high wood density species would be closely related to rainfall, due to low tissue water storage capacity in these species. By contrast, we predicted leaf unfolding and flowering of low wood density species would depend exclusively on photoperiod. As predicted, wood density and saturated water content were inversely correlated, and species with either high or low wood density had distinct phenological patterns and levels of synchrony within species. Abiotic variables were not strongly associated with phenological events. Phenophases of leaf unfolding, flowering, and fruiting occurred earlier in low wood density species than in high wood density species, possibly indicating an adaptive strategy for preemptive resource capture.Abstract in Portuguese is available with online material.

Bombax ceiba is a Good Native Tree Species for Performing Reforestation to Restore Highly Degraded Tropical Forests in Hainan Island, China

Reforestation is an effective way to alleviate deforestation and its negative impacts on ecosystem services. It is widely recognized that the most key step for reforestation is using suitable native species, but selecting suitable native tree species is much more complex and challenging than the selection of non-native tree species that have been widely used for reforestation. Here, we quantify whether the native tree species (Bombax ceiba) can be suitable for performing reforestation to restore a 0.2 km2 highly degraded tropical monsoon forest in Baopoling Mountain (BPL), Sanya, China, due to 20 years of limestone mining for cement production. We found that stomatal closure helped Bombax ceiba develop higher drought stress tolerance than the most dominant native tree species (Bridelia tomentosa) in an undisturbed tropical rainforest in BPL, thereby better adapting well to drought stress in the dry season. These characteristics in turn facilitated it to have high survival rate (92% ± 4%) and fast growth rate, after three years of monoculture in BPL. Thus, Bombax ceiba is very suitable for performing reforestation to recover highly degraded tropical forests in Hainan Island, China.

Seed fates of four rainforest tree species in the fragmented forests of Anamalais in the southern Western Ghats, India

Seed predation is one of the key ecosystem processes governing the plant population and community structure in forests. Forest fragmentation and habitat loss have been shown to affect seed predation, leading to altered tree recruitment. However, the effects of fragmentation and habitat loss on seed predation are highly variable and context-specific, with limited information from South Asia. For four rainforest tree species in a production landscape of tea and coffee, we examined the influence of forest type (benchmark, N = 3, and fragmented, N = 5, forests) and seed size on the proportion of seeds, 1) predated by vertebrate seed predators, 2) predated by invertebrate seed predators, and 3) removed by vertebrate seed predators. The seed fates were tracked by placing the seeds in four 1 × 1 m plots under the canopy of the tree (N ≥ 11 individuals per tree species and 48 trees overall), and camera traps were placed under a subset of trees (N = 29, trap-nights = 712). Overall, we recorded nine species of seed predators, and that the seed predator species composition differed among the four tree species. However, there was no significant difference in either seed predator species composition or their visitations across the forest types. The seeds were more likely to be predated (on average 6% higher predation) by vertebrate seed predators in the fragments than in the benchmark forests. Medium-seeded species were more likely to be predated by vertebrate seed predators than large-seeded species (on average 41% higher predation). Invertebrate seed predation and seed removal by vertebrate seed predators had a weak relationship with forest type, with higher invertebrate seed predation in the fragments and higher seed removal in the benchmark forests. With altered seed dispersal patterns resulting from habitat fragmentation and habitat loss, differential seed predation can alter regeneration patterns, thereby influencing adult tree communities in fragmented forests.

Effects of Wood Hydraulic Properties on Water Use and Productivity of Tropical Rainforest Trees

The efficiency of the water transport system in trees sets physical limits to their productivity and water use. Although the coordination of carbon assimilation and hydraulic functions has long been documented, the mutual inter-relationships between wood anatomy, water use and productivity have not yet been jointly addressed in comprehensive field studies. Based on observational data from 99 Indonesian rainforest tree species from 37 families across 22 plots, we analyzed how wood anatomy and sap flux density relate to tree size and wood density, and tested their combined influence on aboveground biomass increment (ABI) and daily water use (DWU). Results from pairwise correlations were compared to the outcome of a structural equation model (SEM). Across species, we found a strong positive correlation between ABI and DWU. Wood hydraulic anatomy was more closely related to these indicators of plant performance than wood density. According to the SEM, the common effect of average tree size and sap flux density on the average stem increment and water use of a species was sufficient to fully explain the observed correlation between these variables. Notably, after controlling for average size, only a relatively small indirect effect of wood properties on stem increment and water use remained that was mediated by sap flux density, which was significantly higher for species with lighter and hydraulically more efficient wood. We conclude that wood hydraulic traits are mechanistically linked to water use and productivity via their influence on sap flow, but large parts of these commonly observed positive relationships can be attributed to confounding size effects.

Growth and phenotypic plasticity of two tropical tree species under low light availability

Abstract Aims Screening tree species in tropical rainforest according to their shade tolerance is important to efficiently manage the native trees of economic significance in secondary forest enrichment regimes. The objective of this study was to determine the whole-plant light compensation point (WPLCP) and compare the phenotypic plasticity in relation to growth and carbon allocation of Cariniana legalis and Gallesia integrifolia seedlings under low light availability. Methods Seedlings were cultivated for 77 days under conditions of five photosynthetically active radiation (PAR) (0.02, 1.1, 2.3, 4.5 and 5.9 mol photons m−2 day−1) in three replicates. Growth and carbon allocation variables were determined. Important Findings Growth rates of C. legalis were higher and lower than those of G. integrifolia under 1.1 and 5.9 mol photons m−2 day−1, respectively. The WPLCP differed significantly between the two species. In accordance with the criteria of the shade tolerance classification for these two tropical tree species, our results showed that C. legalis had lower WPLCP and phenotypic plasticity in terms of higher growth rates and greater shade tolerance than G. integrifolia. From a practical point of view, we demonstrated that the differential linkage between growth and changing PAR between the two species can become a useful tool for comparing and selecting tree species in forest enrichment projects.

Ground flora species richness and diversity in traditional forests of southwest, Nigeria

Diversity indices of tree species in tropical rainforest have been studied, but less effort has been devoted to the ground flora studies especially in sacred groves of tropical rainforest, Nigeria, as it plays a critical role in nutrient cycling and energy flow within the forest ecosystem. This study was carried out to determine the ground flora species diversity, richness and density in five traditional forests (Igbo-Ile, Igbo-Oba, Igbo-Olua, Igbo-Olodumare Igbo-Gbopo) of southwestern Nigeria. The ground flora enumeration of 5 x 10m was laid at the centre of 50 x 50m laid in each of the sacred grove. All plants with dbh < 10cm were identified and the frequency of occurrence recorded. In all the Sacred Groves, a total of 14064 plants/ha individual were recorded with 80 species distributed among 36 families. Igbo-Oba had highest diversity index of 3.21, followed by Igbo-Olodumare (2.80), Igbo-Ile (2.42). The least diversity index was recorded in Igbo-Gbopo (1.97). Among the 36 families, maximum species was recorded in Sterculiaceae (10), followed by Euphorbiaceae (5), Apocynaceae (4), Combretaceae (4) and Sapindaceae (4). Among the families with lowest frequencies (1) recorded are: Acanthaceae, Araceae, Rutaceae, Sapotaceae, Solanaceae. The study concludes that anthropogenic disturbances observed, e.g. farming, spiritual engagements etc. around Igbo-Olua and Igbo-Gbopo might have contributed to low diversity index compared to Igbo-Ile, Igbo-Oba and Igbo-Olodumare where high diversity index was recorded. It is recommended that to maintain high diversity index in the scared groves, buffer zones should be created around the sacred groves.
 Keywords: sacred grove, diversity, ground flora, herbaceous

Size dependent associations between tree diameter growth rates and functional traits in an Asian tropical seasonal rainforest.

Many studies focus on the relationships between plant functional traits and tree growth performances. However, little is known about the ontogenetic shifts of the relationships between functional traits and tree growth. This study examined associations between stem and leaf functional traits and growth rates and their ontogenetic shifts across 20 tropical tree species in a tropical seasonal rainforest in Xishuangbanna, south-west China. For each species, physiological active branches of individual trees belonged to three size classes (i.e. small, diameter at breast height (DBH) 5-10 cm; middle, DBH 10-20 cm; big, DBH >20 cm) were sampled respectively. We measured 18 morphological and structural traits, which characterised plant hydraulic properties or leaf economic spectrum. Associations between diameter growth rates and functional traits were analysed across three size classes. Our results revealed that diameter growth rates of big-sized trees were mainly related to traits related to plant hydraulic efficiency (i.e. theoretical hydraulic conductivity (Ktheo) and leaf vein density (Dvein)), which suggests that the growth of large trees is limited mainly by their xylem water transport capacity. For middle-sized trees, growth rates were significantly related to traits representing leaf economic spectrum (i.e. specific leaf area (SLA), individual leaf mass (ILM), palisade thickness (PT) and spongy thickness (SP)). Diameter growth rates of small-sized trees were not correlated with hydraulic or leaf economic traits. Thus, the associations between tree growth rates and functional traits are size dependent. Our results suggest ontogenetic shift of functional traits which could potential contribute to different growth response to climate change.

Detecting Growth Phase Shifts Based on Leaf Trait Variation of a Canopy Dipterocarp Tree Species (Parashorea chinensis)

Canopy species need to shift their adaptive strategy to acclimate to very different light environments as they grow from seedlings in the understory to adult trees in the canopy. However, research on how to quantitively detect ecological strategy shifts in plant ontogeny is scarce. In this study, we hypothesize that changes in light and tree height levels induce transitions in ecological strategies, and growth phases representing different adaptive strategies can be classified by leaf trait variation. We examined variations in leaf morphological and physiological traits across a vertical ambient light (represented by the transmittance of diffuse light, %TRANS) and tree height gradient in Parashorea chinensis, a large canopy tree species in tropical seasonal rainforest in Southwestern China. Multivariate regression trees (MRTs) were used to detect the split points in light and height gradients and classify ontogenetic phases. Linear piecewise regression and quadratic regression were used to detect the transition point in leaf trait responses to environmental variation and explain the shifts in growth phases and adaptive strategies. Five growth phases of P. chinensis were identified based on MRT results: (i) the vulnerable phase, with tree height at less than 8.3 m; (ii) the suppressed phase, with tree height between 8.3 and 14.9 m; (iii) the growth release phase, with tree height between 14.9 and 24.3 m; (iv) the canopy phase, with tree height between 24.3 and 60.9 m; and (v) the emergent phase, with tree height above 60.9 m. The suppressed phase and canopy phase represent “stress-tolerant” and “competitive” strategies, respectively. Light conditions drive the shift from the “stress-tolerant” to the “competitive” strategy. These findings help us to better understand the regeneration mechanisms of canopy species in forests.

Linking drought-induced xylem embolism resistance to wood anatomical traits in Neotropical trees.

Drought-induced xylem embolism is considered to be one of the main factors driving mortality in woody plants worldwide. Although several structure-functional mechanisms have been tested to understand the anatomical determinants of embolism resistance, there is a need to study this topic by integrating anatomical data for many species. We combined optical, laser, and transmission electron microscopy to investigate vessel diameter, vessel grouping, and pit membrane ultrastructure for 26 tropical rainforest tree species across three major clades (magnoliids, rosiids, and asteriids). We then related these anatomical observations to previously published data on drought-induced embolism resistance, with phylogenetic analyses. Vessel diameter, vessel grouping, and pit membrane ultrastructure were all predictive of xylem embolism resistance, but with weak predictive power. While pit membrane thickness was a predictive trait when vestured pits were taken into account, the pit membrane diameter-to-thickness ratio suggests a strong importance of the deflection resistance of the pit membrane. However, phylogenetic analyses weakly support adaptive coevolution. Our results emphasize the functional significance of pit membranes for air-seeding in tropical rainforest trees, highlighting also the need to study their mechanical properties due to the link between embolism resistance and pit membrane diameter-to-thickness ratio. Finding support for adaptive coevolution also remains challenging.

Phylogenomic approaches reveal how climate shapes patterns of genetic diversity in an African rain forest tree species.

The world's second largest expanse of tropical rainforest is in Central Africa, and it harbours enormous species diversity. Population genetic studies have consistently revealed significant structure across Central African rainforest plants. In particular, previous studies have repeatedly demonstrated a north-south genetic discontinuity around the equatorial line, in a continuous expanse of rainforest where a climatic inversion is documented. Here, we took a phylogeographic approach by sequencing 351 nuclear markers in 112 individuals across the distribution of the African rainforest tree species Annickia affinis (Annonaceae). We showed for the first time that the north-south divide is the result of a single, major colonization event across the climatic inversion from an ancestral population located in Gabon. We suggested that differences in ecological niche of populations located on either side of this inversion may have contributed to this phylogenetic discontinuity. We found evidence for inland dispersal, predominantly in northern areas, and variable demographic histories among genetic clusters, indicating that populations responded differently to past climate change. We show how newly developed genomic tools can provide invaluable insights into our understanding of tropical rainforest evolutionary dynamics.

The Progressive Spread of the Vascular Wilt Like Pathogen of Calophyllum Detected in Ranomafana National Park, Madagascar.

Pathogens are threatening crops worldwide, but little attention has been given to the threat to tree species in undisturbed rainforest. This communication reports the first case of a tree die off caused by a “wilt” in Madagascar. In 2016 while monitoring monthly tree phenology of Ranomafana National Park (RNP), the Centre ValBio research station observed that many Calophyllum adult trees had brown wilted leaves. There are three species of Calophyllum in this rainforest, C. paniculatum, C. drouhardii, and C. milvum, and all three have contracted this pathogen. Our goal was to document the spead of this suspected wilt in Calophyllum trees and determine if site, elevation and DBH had an influence on tree mortality. In 2019 we conducted an inventory of all Calophyllum trees in RNP and 42% of the observed trees were dead. The species with the highest mortality was C. paniculatum, with 53% of trees dead, followed by C. milvum with 18%, and C. drouhardii with only 2% of surveyed trees dead. Bark beetle traces were observed in all dead Calophyllum trees. Tree death caused by this suspected fungal pathogen has spread across a major river in the area and has been found at mid and high elevations. Our results show that C. paniculatum trees with a larger DBH have a higher mortality risk. Our report highlights the importance of fighting invasive pathogens that threaten protected ecosystems.

Vulnerability and hydraulic segmentations at the stem-leaf transition: coordination across Neotropical trees.

Hydraulic segmentation at the stem-leaf transition predicts higher hydraulic resistance in leaves than in stems. Vulnerability segmentation, however, predicts lower embolism resistance in leaves. Both mechanisms should theoretically favour runaway embolism in leaves to preserve expensive organs such as stems, and should be tested for any potential coordination. We investigated the theoretical leaf-specific conductivity based on an anatomical approach to quantify the degree of hydraulic segmentation across 21 tropical rainforest tree species. Xylem resistance to embolism in stems (flow-centrifugation technique) and leaves (optical visualization method) was quantified to assess vulnerability segmentation. We found a pervasive hydraulic segmentation across species, but with a strong variability in the degree of segmentation. Despite a clear continuum in the degree of vulnerability segmentation, eight species showed a positive vulnerability segmentation (leaves less resistant to embolism than stems), whereas the remaining species studied exhibited a negative or no vulnerability segmentation. The degree of vulnerability segmentation was positively related to the degree of hydraulic segmentation, such that segmented species promote both mechanisms to hydraulically decouple leaf xylem from stem xylem. To what extent hydraulic and vulnerability segmentation determine drought resistance requires further integration of the leaf-stem transition at the whole-plant level, including both xylem and outer xylem tissue.

Forest cover and fruit crop size differentially influence frugivory of select rainforest tree species in Western Ghats, India

AbstractForest fragmentation and habitat loss are major disruptors of plant–frugivore interactions, affecting seed dispersal and altering recruitment patterns of the dependent tree species. In a heterogeneous production landscape (primarily tea and coffee plantations) in the southern Western Ghats, India, we examined effects of surrounding forest cover and fruit crop size on frugivory of four rainforest bird‐dispersed tree species (N = 131 trees, ≥30 trees per species, observed for 623 hr). Frugivore composition differed among the four tree species with the large‐seeded Canarium strictum and Myristica dactyloides being exclusively dependent on large‐bodied avian frugivores, whereas medium‐seeded Persea macrantha and Heynea trijuga were predominantly visited by small‐bodied and large‐bodied avian frugivores, respectively. Using the seed‐dispersal‐effectiveness framework, we identified effective frugivores and examined their responses to forest cover and fruit crop size. Results were idiosyncratic and were governed by plant and frugivore traits. Visitations to medium‐seeded Persea had a positive relationship with forest cover but the relationship was negative for the large‐seeded Myristica. In addition, two of the three effective frugivores for Persea responded to the interactive effect of forest cover and fruit crop size. Frugivore visitations to Heynea were not related to forest cover or fruit crop, and there were too few visitations to Canarium to discern any trends. These results highlight the context‐specific responses of plant–frugivore interactions to forest cover and fruit crop size influenced by plant and frugivore traits.

Sensitivity of stomatal conductance to vapor pressure deficit and its dependence on leaf water relations and wood anatomy in nine canopy tree species in a Malaysian wet tropical rainforest

Canopy tree species with a large mean xylem vessel diameter has a high sensitivity of stomatal conductance to vapor pressure deficit in a wet tropical rainforest in Malaysia. We investigated the diurnal variation of stomatal conductance to water vapor (gs) and leaf water relations in nine tropical rainforest canopy tree species in Malaysia to investigate the sensitivity of stomatal conductance to VPD and its dependence on leaf water relations. We focused on the effect of wood anatomical properties on the stomatal sensitivity to VPD. Negative correlations were obtained between leaf-to-air VPD (VPDleaf) and gs for all species, in which interspecific variation was obtained for the sensitivity of gs to VPDleaf with the range of VPDleaf being 1.2–5.9 kPa. The species with large mean xylem vessel diameter had high sensitivity of gs to VPDleaf. Although significant variations were obtained among the species for leaf water relations, such as relative water content at the turgor loss point (RWCtlp) and water potential at the turgor loss point (Ψtlp), these water relations were not related to the stomatal sensitivity to VPDleaf. In the wet tropical forest in the present study, VPDleaf was the main regulator of gs in the nine tree species. The high sensitivity of gs to VPDleaf in the trees with a large vessel area may contribute to the maintenance of an adequate leaf water status, e.g., high levels of Ψleaf, throughout the day, across a period of varying air temperature.

The effect of overwood competition on the long-term survival, growth and stocking of underplanted tree species in logged tropical rainforest in north Queensland, Australia

Enrichment of selectively logged rainforest by planting seedlings of commercially valuable species is often recommended to improve productivity, ecological functioning, and biodiversity. However, the survival and subsequent growth of enrichment plantings depend on how they respond to competition from neighbours. For successful forest restoration or commercial forest management, the challenge is to determine appropriate frequencies and intensities of silvicultural interventions, principally competition reduction. In this study, we use long-term data (49–60 years) from four enrichment planting experiments established after selective logging and girdling of non-commercial trees in a tropical rainforest in north Queensland, Australia, to assess the effects of competition on the survival and growth of enrichment plantings. We found that residual overwood development severely reduced the survival, diameter and volume growth of two widely planted rainforest species - Flindersia brayleyana (Rutaceae) and Agathis robusta (Araucariaceae). Both species responded well to overstory removal, either as an initial treatment or thereafter. Use of Hegyi’s competition index confirmed the strong suppressive effect of neighbours. The most abundant competitor was the fast-growing, early-secondary species Acacia aulacocarpa, which only became apparent after cessation of silvicultural treatments, 7 years after planting. Our results reaffirm the importance of an initial or early-age removal of the competing overstory for the success of enrichment planting. Further silvicultural treatments may be required for extended periods to control excessively increased overwood basal area and to remove late emerging pioneer or early secondary species.

Precipitation gradients, plant biogeography, and the incidence of drip‐tips in Cerrado plant species

AbstractExamining how both climate and species distribution patterns correlate with leaf morphology can give insights into the ecological and evolutionary patterns that drive adaptive selection of leaf form and function. Drip‐tips are a common feature of leaves in rain forest tree species; they are thought to be an adaptation that aids leaf drying and maximizes photosynthesis in areas with high‐rainfall climates. We tested whether this macroecological pattern holds true across the precipitation gradients in a non‐rain forest region—the woodland savannas of Brazil known as the Cerrado—and compared our results with previous studies from Amazonia. Drip‐tips were, as expected, less common overall in the drier Cerrado than in Amazonia. In addition, within the Cerrado, drip‐tips were more prevalent in areas with higher rainfall as well as in Cerrado sites that were closer to Amazonia. Moreover, species that occurred across both the Cerrado and Amazonia had drip‐tips more often than species that were found only in the Cerrado. These findings support the hypothesis that drip‐tips are adaptive and that either the cost of retaining drip‐tips is low or that in drier regions they have other benefits. Abstract in Portuguese is available with online material.

Estimation of the surface area-to-volume ratios of litter components of the Brazilian rainforest and their impact on litter fire rate of spread and flammability

The surface-area-to-volume ratio (SAV) is a significant parameter in vegetation description, although different researchers have presented diverging estimates for forest litter. However, considering litter as a unique entity and disregarding the SAV of its components provides a misleading fire rate of spread. Undoubtedly, the leaves are more relevant than the twigs for the rate of spread of surface fires, as the former has a higher SAV. Therefore, based on the proven hyperdominance of tree species in the Brazilian rainforest, this work presents an accurate method to estimate the SAV. Furthermore, it demonstrates the critical role played by the SAV in the litter flammability and fire rate of spread assessments and shows that the leaf moisture content does not influence its SAV. Besides, comparing SAV data using the methodology presented herein with other authors’ assessments, the results differ by up to 49%. Finally, using the Brazilian rainforest litter in the methodologies of two distinct authors showed a difference of at least 36% in the results. The primary outcome of this study is the estimation of the SAV of leaves and thin, medium, and thick twigs, representative of the Brazilian rainforest, at 12,680 m−1, 1360 m−1, 620 m−1, and 310 m−1, respectively. The estimated SAV values are essential input data to numerical simulation models, and for comparison purposes with other authors’ work, the litter SAV is 8460 m−1.

Orchid Diversity and Biomass on a Native Host Tree Species in a Semi-deciduous Rain Forest of Cameroon

ABSTRACT Triplochiton scleroxylon K. Schum is among an intensively exploited tree species in the Congo basin forest including the humid forest of Cameroon. As most tropical tree species, it is a potential host of epiphytic orchids for which little information is available. The aim of this study was to assess the biomass and orchids diversity that colonize T. scleroxylon in a semi-deciduous rain forest of Cameroon. Orchid species were inventoried exclusively on 20 felled T. scleroxylon. Orchid biomass obtained by destructive harvest was expressed in kg/tree. Orchid biomass was estimated in four randomized plots of 250 m × 20 m each, using allometric equations established. Twenty-nine orchid species were recorded on T. scleroxylon, while the mean orchid biomass was 1.23 kg/tree. Minimum T. scleroxylon diameter for orchid occurrence was 68.6 cm. The relationship between orchid biomass and T. scleroxylon diameter was low (Adj.R2˂0.4) and height did not improve the model. According to orchid biomass on T. scleroxylon (14.63 kg/ha), an estimated loss associated with T. scleroxylon’s exploitation was 10.47 kg/ha. This study expanded knowledge of orchid species linked to highly exploited T.scleroxylon in the Congo basin forest that impose conservation strategy, in the light of current degradation of their natural habitat and climate change mitigation.

Modelling the distribution of Amazonian tree species in response to long‐term climate change during the Mid‐Late Holocene

AbstractAimTo (a) assess the environmental suitability for rainforest tree species of Moraceae and Urticaceae across Amazonia during the Mid‐Late Holocene and (b) determine the extent to which their distributions increased in response to long‐term climate change over this period.LocationAmazonia.TaxonTree species of Moraceae and Urticaceae.MethodsWe used MaxEnt and inverse distance weighting interpolation to produce environmental suitability and relative abundance models at 0.5‐degree resolution for tree species of Moraceae and Urticaceae, based on natural history collections and a large plot dataset. To test the response of the Amazon rainforest to long‐term climate change, we quantified the increase in environmental suitability and modelled species richness for both families since the Mid‐Holocene (past 6,000 years). To test the correlation between the relative abundance of these species in modern vegetation versus modern pollen assemblages, we analysed the surface pollen spectra from 46 previously published paleoecological sites.ResultsWe found that the mean environmental suitability in Amazonia for species of Moraceae and Urticaceae showed a slight increase (6.5%) over the past 6,000 years, although southern ecotonal Amazonia and the Guiana Shield showed much higher increases (up to 68%). The accompanied modelled mean species richness increased by as much as 120% throughout Amazonia. The mean relative abundance of Moraceae and Urticaceae correlated significantly with the modern pollen assemblages for these families.Main ConclusionsIncreasing precipitation between the Mid‐ and Late Holocene expanded suitable environmental conditions for Amazonian humid rainforest tree species of Moraceae and Urticaceae, leading to rainforest expansion in ecotonal areas of Amazonia, consistent with previously published fossil pollen data.

Climatic limits of temperate rainforest tree species are explained by xylem embolism resistance among angiosperms but not among conifers.

Hydraulic failure explains much of the increased rates of drought-induced tree mortality around the world, underlining the importance of understanding how species distributions are shaped by their vulnerability to embolism. Here we determined which physiological traits explain species climatic limits among temperate rainforest trees in a region where chronic water limitation is uncommon. We quantified the variation in stem embolism vulnerability and leaf turgor loss point among 55 temperate rainforest tree species in New Zealand and tested which traits were most strongly related to species climatic limits. Leaf turgor loss point and stem P50 (tension at which hydraulic conductance is at 50% of maximum) were uncorrelated. Stem P50 and hydraulic safety margin were the most strongly related physiological traits to climatic limits among angiosperms, but not among conifers. Morphological traits such as wood density and leaf dry matter content did not explain species climatic limits. Stem embolism resistance and leaf turgor loss point appear to have evolved independently. Embolism resistance is the most useful predictor of the climatic limits of angiosperm trees. High embolism resistance in the curiously overbuilt New Zealand conifers suggests that their xylem properties may be more closely related to growing slowly under nutrient limitation and to resistance to microbial decomposition.