Understanding how the traits of lineages are related to diversification is key for elucidating the origin of variation in species richness. Here, we test whether traits are related to species richness among lineages of trees from all major biogeographical settings of the lowland wet tropics. We explore whether variation in mortality rate, breeding system and maximum diameter are related to species richness, either directly or via associations with range size, among 463 genera that contain wet tropical forest trees. For Amazonian genera, we also explore whether traits are related to species richness via variation among genera in mean species-level range size. Lineages with higher mortality rates—faster life-history strategies—have larger ranges in all biogeographic settings and have higher mean species-level range sizes in Amazonia. These lineages also have smaller maximum diameters and, in the Americas, contain dioecious species. In turn, lineages with greater overall range size have higher species richness. Our results show that fast life-history strategies influence species richness in all biogeographic settings because lineages with these ecological strategies have greater range sizes. These links suggest that dispersal has been a key process in the evolution of the tropical forest flora.

Aim: We test the hypothesis that wind dispersal is more common among emergent tree species given that being tall increases the likelihood of effective seed dispersal. Location: Americas, Africa and the Asia-Pacific. Time period: 1970-2020. Major taxa studied: Gymnosperms and Angiosperms. Methods: We used a dataset consisting of tree inventories from 2821 plots across three biogeographic regions (Americas, Africa and Asia- Pacific), including dry and wet forests, to determine the maximum height and dispersal strategy of 5314 tree species. A web search was used to determine whether species were wind-dispersed. We compared differences in tree species maximum height between biogeographic regions and examined the relationship between species maximum height and wind dispersal using logistic regression. We also tested whether emergent tree species, that is species with at least one individual taller than the 95% height percentile in one or more plots, were disproportionally wind dispersed in dry and wet forests within each biogeographic region. Results: Our dataset provides maximum height values for 5314 tree species, of which more than half (2914) had no record of this trait in existing global databases. We found that, on average, tree species in the Americas have lower maximum heights compared to those in Africa and the Asia Pacific. The probability of wind dispersal increased significantly with tree species maximum height and was significantly higher among emergent than non-emergent tree species in both dry and wet forests in all three biogeographic regions. Main conclusion: Wind dispersal is more prevalent in tall, emergent tree species than in non-emergent species and may thus be an important factor in the evolution of tree species maximum height. By providing the most comprehensive dataset so far of tree species maximum height and wind dispersal strategies, this study paves the way for advancing our understanding of the eco-evolutionary drivers of tree size.

D.H. Janzen argued that tropical mountains, for their heights, pose greater migration barriers than temperate mountains owing to lower temperature seasonality, and consequent greater niche and ecosystem specialization. These result in distinct altitudinal zonation under hardly varying temperature lapse rates. The Asian Far East alone provides an opportunity to test this hypothesis owing to latitudinal continuity of evergreen forests from equator to warm temperate zone. With data from four mountains, we find Janzen's hypothesis broadly correct. The primary and most consistent mediator of forest zonation and therefore species' habitat specificity is soil, itself indirectly mediated by climate. But declining habitat niche specificity does not proceed north along a continuum, instead in a series of latitudinal steps initiated by quite sudden habitat changes. Tropical montane forests are altitudinally floristically and structurally zoned by factors only indirectly mediated by temperature. Equatorial forests experience continuously wet climates and a frost line at c.4100 m. North of 8 degrees N, temperature and rainfall seasonality increases and winter air frosts descend to c.2000 m. Upper montane forest becomes truncated, while lower montane forest continues to the frost line which remains constant in moist climates. The margin of the wet tropics is pushed north to 27 degrees N by the Himalaya. Annual frost at c.2000 m here marks a narrow ecotone between tropical lower montane forest and warm temperate evergreen lucidophyll forest, a formation unique to east Asia. In equably moist South China, the lowland tropical-warm temperate ('subtropical') margin returns to the Tropic of Cancer and appears to be narrow at all altitudes. The temperate forests exhibit less distinct and inconsistent altitudinal zonation, instead manifesting an altitudinal floristic and structural continuum mediated by winter frost frequency and intensity.

Summary The dipterocarp tribe Shoreae, perhaps more than any other members of this elegant family of often giant emergent trees, is familiar to all who visit the once ubiquitous lowland forests of tropical Asia. Timbers of the genus Shorea comprised the bulk of hardwood traded on international markets for thirty years, since the nineteen seventies. Distinct species groups came to be recognised by taxonomists: for their characteristic androecia, and sometimes differences in bark and wood anatomy, while generic status for some was then proposed on embryological evidence. A new molecular phylogeny of the family, and this tribe, substantially confirms the embryological case. This paper formalises resultant nomenclatural changes. Those of us who recall the majestic forested former landscapes of the Sunda lands may regret this decision. But now, with landscapes irretrievably changed by serried ranks of oil palm and forest degradation, the case for recognition of the proposed new entities can guide conservation planners in recognising and making the case for permanently conserving surviving undisturbed stands of exceptional composition or diversity.

The evolution and diversification of ancient megathermal angiosperm lineages with Africa-India origins in Asian tropical forests is poorly understood because of the lack of reliable fossils. Our palaeobiogeographical analysis of pollen fossils from Africa and India combined with molecular data and fossil amber records suggest a tropical-African origin of Dipterocarpaceae during the mid-Cretaceous and its dispersal to India during the Late Maastrichtian and Paleocene, leading to range expansion of aseasonal dipterocarps on the Indian Plate. The India-Asia collision further facilitated the dispersal of dipterocarps from India to similar climatic zones in Southeast Asia, which supports their out-of-India migration. The dispersal pathway suggested for Dipterocarpaceae may provide a framework for an alternative biogeographic hypothesis for several megathermal angiosperm families that are presently widely distributed in Southeast Asia.

Tropical evergreen forests are transitional to subtropical evergreen forests at the tropical margin of southern China, where ecotones exist. Forest structure, physiognomy and canopy tree flora. mainly from 4 permanent plots in the transitional area in southern China, are studied here, and the ecotones and their recognition features are clarified. Due to the different topography in southwestern and southeastern China, the forest ecotones occur along altitudinal gradients in the southwestern mountains of China, while the ecotone occurs along the latitudinal gradient in the southeastern lowlands. Two ecotones evidently exist in the southwestern mountains: At 800-1200 m asl, the tropical lowland seasonal rain forest with 3 tree layers and typical emergent tropical trees in the canopy changes to tropical lower montane evergreen broad-leaved forest with 2 tree layers and with mainly tropical southeastern Asian and tropical margin distributed Fagaceae and Theaceae canopy trees constituting their flattening canopy: at 1800-2100(2200) m asl. the tropical lower montane evergreen broad-leaved forest changes to subtropical (warm temperate) evergreen broad-leaved forest with a largely subtropical (warm temperate) Himalayan and Chinese endemic tree flora. In southeastern lowland China, the evergreen forest ecotone occurs at 22 degrees 30'N and nearby, where tropical-margin lowland seasonal rain forest changes to subtropical lowland evergreen broad-leaved forest. In the latter. the subtropical endemic Chinese and eastern Asia trees dominate the flattening canopy. We consider that the ecotones of the tropical-subtropical evergreen forest transition could be limited by air frost, because typical tropical canopy trees could be damaged and can survive only in the frost-free habitats. The ecotone between the tropical lower montane evergreen forest and subtropical (warm temperate) evergreen forest in southwestern China and the one at 22 degrees 30'N and nearby between the tropical margin lowland seasonal rain forest and the subtropical lowland evergreen broad-leaved forest are suggested as a tropical margin (boundary). Beyond the margin, tropical trees in the canopy vanish, although some tropical flora can persist in the subcanopy and understory. We fmd that isolated tropical floras survive in the subcanopy and underneath of the subtropical evergreen broad-leaved forests in lowland southeastern China. We suppose that the northern margin of the tropics in southeastern China was much further north before the Quaternary period than it is today, and that, on the other hand, the subtropical forest canopy could shelter subcanpy and understory tropical plants by resisting air frost penetration inside to some extent. These could explain why tropical plants survive in the subcanopy and understory of the subtropical evergreen broad-leaved forest in East Asia. We also find that tropical plants could diversify (mostly from their tropical congener taxa) in isolated free-frost climatic refuges and the understory of subtropical evergreen forests beyond the tropical margin, while the east Asian temperate flora could hardly diversify in tropical SE Asia, which needs to be studied in detail. Issues related to the ecotones at the tropical-subtropical transition of East Asia are identified for further research.

This paradigm established. Using demographic data for ten we tested the generality of the growth-mortality trade-off and evaluated its underlying drivers using two species-specific parameters describing resource-allocation strategies: tolerance of resource limitation and responsiveness of allocation to resource access. Globally, a canonical growth-mortality trade-off emerged, but only in less- disturbance prone forests, which contained diverse resource allocation strategies, was the trade-off strongly observed. Only half of disturbance-prone forests, which lacked tolerant species, exhibited the trade-off. Supported by a theoretical model, our findings raise questions about whether the trade-off is a universally applicable organizing framework for

In the southern mountain ranges of Yunnan province, China, deep valleys of several large rivers create rain shadows with hot dry summers, and are locally designated tropical; towards the north, notably in the Lancang (Upper Mekong) valley, these regions may experience frost during winter. The woody forest canopy of these valleys is predominantly deciduous, with evergreen elements in the north, where the canopy is open and the forest savanna-like. However, we here present tall forest with a closed deciduous canopy and semi-evergreen subcanopy observed in hot dry valleys of these rivers and their tributaries in the tropical south. The structure and physiognomy of these forests resemble the tall (moist) deciduous forest formation widespread in South Asia and Indo-Burma. Furthermore, these forests are largely composed of tropical elements at both the generic (80%) and the species level (>70%), indicating that these forests are indeed tropical. We originally hypothesized that these isolated forests represent refugia of a pre-Holocene extension of tall (moist) deciduous forest formation of South Asia and Indo-Burma. The sample plot we established to test this hypothesis confirmed that these forests share the structure and physiognomy of the tall (moist) deciduous forest formation; however, the plots also showed that these forests lack the characteristic and dominant species of the formation's Indo-Burmese range. The tree flora, in particular, indicates that both deciduous and evergreen elements are instead mostly derived from the adjacent tropical semi-evergreen forests of tropical southern China; yet they also include an important endemic element, which implies that these forests have survived as refuges possibly since the Pliocene. The exceptional representation of evergreen elements in these forests indicates that they have rarely been subject to hot fires or domestic cattle browsing, adding to the unique nature of the forests and further justifying their strict conservation.

BiotropicaVolume 53, Issue 4 p. 1004-1006 COMMENTARY Is introgression an increasing threat to tree species diversity in hyperdiverse rain forest communities? Peter S. Ashton, Corresponding Author Peter S. Ashton pashton@oeb.harvard.edu Organismic and Evolutionary Biology, Harvard University and Royal Botanic Gardens, Kew, Cambridge, MA, USA Correspondence Peter S. Ashton, Organismic and Evolutionary Biology, Harvard University and Royal Botanic Gardens, Kew, Cambridge, MA, USA. Email: pashton@oeb.harvard.eduSearch for more papers by this author Peter S. Ashton, Corresponding Author Peter S. Ashton pashton@oeb.harvard.edu Organismic and Evolutionary Biology, Harvard University and Royal Botanic Gardens, Kew, Cambridge, MA, USA Correspondence Peter S. Ashton, Organismic and Evolutionary Biology, Harvard University and Royal Botanic Gardens, Kew, Cambridge, MA, USA. Email: pashton@oeb.harvard.eduSearch for more papers by this author First published: 24 June 2021 https://doi.org/10.1111/btp.12983 Associate Editor:: Jennifer Powers Handling Editor:: Jennifer Powers Read the full textAboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume53, Issue4July 2021Pages 1004-1006 RelatedInformation

Medieval Arab traders, bartering for forest products with indigenous tribes along the unending coastlines of the Malesian archipelago were first to recognise the value of the magnificent dipterocarps, for their camphor-bearing resin which they introduced to the Middle east and therefrom to Europe. Knowledge grew, and then value in international trade, reaching its peak over the last half century when, for a time, their timber comprised the leading hardwood on international markets. Now all but exhausted, the majority of the lowland forests they dominated are threatened with destruction, and their species with extinction. Their history in science and the market is reviewed, and unanswered research questions identified. Priorities in conservation methods and policies are emphasised. But time is short, as their existence retreats into the realm of paleontology: A warning to future researchers in systematics and ecology, and for the continued funding of their institutions.

Resource allocation within trees is a zero-sum game. Unavoidable trade-offs dictate that allocation to growth-promoting functions curtails other functions, generating a gradient of investment in growth versus survival along which tree species align, known as the interspecific growth-mortality trade-off. This paradigm is widely accepted but not well established. Using demographic data for 1,111 tree species across ten tropical forests, we tested the generality of the growth-mortality trade-off and evaluated its underlying drivers using two species-specific parameters describing resource allocation strategies: tolerance of resource limitation and responsiveness of allocation to resource access. Globally, a canonical growth-mortality trade-off emerged, but the trade-off was strongly observed only in less disturbance-prone forests, which contained diverse resource allocation strategies. Only half of disturbance-prone forests, which lacked tolerant species, exhibited the trade-off. Supported by a theoretical model, our findings raise questions about whether the growth-mortality trade-off is a universally applicable organizing framework for understanding tropical forest community structure.

Aim Palms are an iconic, diverse and often abundant component of tropical ecosystems that provide many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically and physiologically distinct from other trees, and these differences have important consequences for ecosystem services (e.g., carbon sequestration and storage) and in terms of responses to climate change. We quantified global patterns of tree palm relative abundance to help improve understanding of tropical forests and reduce uncertainty about these ecosystems under climate change. Location Tropical and subtropical moist forests. Time period Current. Major taxa studied Palms (Arecaceae). Methods We assembled a pantropical dataset of 2,548 forest plots (covering 1,191 ha) and quantified tree palm (i.e., >= 10 cm diameter at breast height) abundance relative to co-occurring non-palm trees. We compared the relative abundance of tree palms across biogeographical realms and tested for associations with palaeoclimate stability, current climate, edaphic conditions and metrics of forest structure. Results On average, the relative abundance of tree palms was more than five times larger between Neotropical locations and other biogeographical realms. Tree palms were absent in most locations outside the Neotropics but present in >80% of Neotropical locations. The relative abundance of tree palms was more strongly associated with local conditions (e.g., higher mean annual precipitation, lower soil fertility, shallower water table and lower plot mean wood density) than metrics of long-term climate stability. Life-form diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many non-tree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of above-ground biomass, but the magnitude and direction of the effect require additional work. Conclusions Tree palms are not only quintessentially tropical, but they are also overwhelmingly Neotropical. Future work to understand the contributions of tree palms to biomass estimates and carbon cycling will be particularly crucial in Neotropical forests.

ABSTRACT: The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting global climate change. Although short-term drying and warming are known to affect forests, it is unknown if such effects translate into long-term responses. Here, we analyze 590 permanent plots measured across the tropics to derive the equilibrium climate controls on forest carbon. Maximum temperature is the most important predictor of aboveground biomass (−9.1 megagrams of carbon per hectare per degree Celsius), primarily by reducing woody productivity, and has a greater rate of decline in the hottest forests (>32.2°C). Our results nevertheless reveal greater thermal resilience than observations of short-term variation imply. To realize the long-term climate adaptation potential of tropical forests requires both protecting them and stabilizing Earth’s climate.

The transition from tropical to subtropical (warm temperate) evergreen forests is more clearly apparent in East Asia, from Nepal to the western Pacific coast, than elsewhere in the tropics. We review the nature of this transition and hypothesize the physical, ultimately climatic, factors that may maintain it, with a special focus on how the increasing instability and warming of climates will affect these forests. A primary climatic mediator of the transition is proposed, thereby offering a testable hypothesis for the climate-forest tran-sition relationship. What is known of this transition is summarized in context of the primary climatic mediators of elevational zonation of forest formations in equatorial Asia to the tree line, in the Himalaya at the India-Indo-Burma northern tropical margin, and as both elevational and latitudinal zonation in southern China. Consequent secondary edaphic and other physical changes are described for the Himalaya, and hy-pothesized for southern China. The forest ecotones are seen to be primarily defined by tree floristic change, on which account changes in structure and physiognomy are determined. The montane tropical-subtropical transition in the Himalaya is narrow and observed to correlate with an as yet ill-defined frost line. A distinct tropical-subtropical transition forest is recognized in the southwest China mountains. There is a total change in canopy species at the Himalayan ecotone, but subcanopy tropical species persist along an elevational decline of c. 400 m. The latitudinal transition in South China is analogous, but here the tropical subcanopy component extends north over ten degrees latitude, albeit in decline. The tropical-subtropical transition is uniquely clear in East Asia because here alone a tropical wet summer-dry winter monsoon extends to 35° north latitude, encompassing the subtropical evergreen forest, whereas subtropical evergreen forests elsewhere exist under drier temperate summer climate regimes.

ForestGEO is a network of scientists and long-term forest dynamics plots (FDPs) spanning the Earth's major forest types. ForestGEO's mission is to advance understanding of the diversity and dynamics of forests and to strengthen global capacity for forest science research. ForestGEO is unique among forest plot networks in its large-scale plot dimensions, censusing of all stems >= 1 cm in diameter, inclusion of tropical, temperate and boreal forests, and investigation of additional biotic (e.g., arthropods) and abiotic (e.g., soils) drivers, which together provide a holistic view of forest functioning. The 71 FDPs in 27 countries include approximately 7.33 million living trees and about 12,000 species, representing 20% of the world's known tree diversity. With >1300 published papers, ForestGEO researchers have made significant contributions in two fundamental areas: species coexistence and diversity, and ecosystem functioning. Specifically, defining the major biotic and abiotic controls on the distribution and coexistence of species and functional types and on variation in species' demography has led to improved understanding of how the multiple dimensions of forest diversity are structured across space and time and how this diversity relates to the processes controlling the role of forests in the Earth system. Nevertheless, knowledge gaps remain that impede our ability to predict how forest diversity and function will respond to climate change and other stressors. Meeting these global research challenges requires major advances in standardizing taxonomy of tropical species, resolving the main drivers of forest dynamics, and integrating plot-based ground and remote sensing observations to scale up estimates of forest diversity and function, coupled with improved predictive models. However, they cannot be met without greater financial commitment to sustain the long-term research of ForestGEO and other forest plot networks, greatly expanded scientific capacity across the world's forested nations, and increased collaboration and integration among research networks and disciplines addressing forest science.

A supra-annual, community-level synchronous flowering prevails in several parts of the tropical forests of Southeast Asia and its evolution has been hypothesized to be linked to pollinator shifts. The aseasonal Southeast Asian lowland rainforests are dominated by Dipterocarpaceae, which exhibit great floral diversity, a range of pollination syndromes and include species with annual and supra-annual gregarious flowering. Phylogenetic relationships within this family are still unclear, especially in the tribe Shoreeae. Here, we develop a pipeline to maximize recovery of genome-wide SNPs from restriction-site associated DNA sequencing (RADseq) in non-model organisms across wide phylogenetic scales. We then infer phylogenomic relationships in the tribe Shoreeae using both traditional and coalescent analyses. The phylogenetic trees obtained with these methods are congruent to each other and highly resolved. They allow reconstructing the evolutionary patterns of floral traits (number of stamens, anther structure and anther/appendage size) in the group. Our inferences indicate that species with many stamens, but smaller, globose anthers and longer appendages and have evolved multiple times from species with fewer stamens, but larger, oblong anthers and shorter appendages. This could have happened in parallel to iterative shifts in pollinators across the uncovered phylogeny from larger, longer generation to smaller, shorter-generation insects that can quickly build up the necessary population sizes during mass flowering episodes.

Little now remains of the lowland dipterocarp forest, logged over the last fifty years as home markets were neglected in favour of exportation, increasingly exacerbated by conversion to oil palm on those soils where techniques for sustainable silvicultural management had become known. What remains will be amenable only to selective silvicultural management methods based on deep knowledge of tree flora, growth rates, and methods developed by continuing research and trials, with oversight by highly trained researchers and technicians. These will be costly. In view of the increasing global value of tropical forests for atmospheric carbon sequestration and biodiversity conservation, as well as for local and regional services, success must depend on international investment and support. But a residue of traditional forest knowledge and skills still resides among traditional forest communities. By investing in them, the desperately needed diversification of rural economies can still be achieved.

The pantropical network of large tree demography plots coordinated by the Smithsonian’s Center for Tropical Forest Science has now gone global, as part of the Smithsonian Institution Global Earth Observatories. Some four million tropical trees, representing about 10,000 species, are now tagged, provisionally identified and periodically recensused. Some 3,000 species are captured in the six plots within Malesia. These include species rarely collected and many that are now endangered. Easy location of trees for periodic examination for fertile material and detailed ecological data, together with seasoned in-country research teams, provide unique opportunities for research collaboration.

BACKGROUND AND AIMS:Phylogenetic relationships within tribe Shoreeae, containing the main elements of tropical forests in Southeast Asia, present a long-standing problem in the systematics of Dipterocarpaceae. Sequencing whole plastomes using next-generation sequencing- (NGS) based genome skimming is increasingly employed for investigating phylogenetic relationships of plants. Here, the usefulness of complete plastid genome sequences in resolving phylogenetic relationships within Shoreeae is evaluated. METHODS:A pipeline to obtain alignments of whole plastid genome sequences across individuals with different amounts of available data is presented. In total, 48 individuals, representing 37 species and four genera of the ecologically and economically important tribe Shoreeae sensu Ashton, were investigated. Phylogenetic trees were reconstructed using maximum parsimony, maximum likelihood and Bayesian inference. KEY RESULTS:Here, the first fully sequenced plastid genomes for the tribe Shoreeae are presented. Their size, GC content and gene order are comparable with those of other members of Malvales. Phylogenomic analyses demonstrate that whole plastid genomes are useful for inferring phylogenetic relationships among genera and groups of Shorea (Shoreeae) but fail to provide well-supported phylogenetic relationships among some of the most closely related species. Discordance in placement of Parashorea was observed between phylogenetic trees obtained from plastome analyses and those obtained from nuclear single nucleotide polymorphism (SNP) data sets identified in restriction-site associated sequencing (RADseq). CONCLUSIONS:Phylogenomic analyses of the entire plastid genomes are useful for inferring phylogenetic relationships at lower taxonomic levels, but are not sufficient for detailed phylogenetic reconstructions of closely related species groups in Shoreeae. Discordance in placement of Parashorea was further investigated for evidence of ancient hybridization.