Montane Tree Research Articles

Above‐ and belowground strategies of tropical montane tree species are coordinated and driven by small‐scale nitrogen availability

Abstract The question whether the strategies of above‐ and belowground plant organs are coordinated as predicted by the plant economics spectrum theory is still under debate. We aim to determine the leading dimensions of tree trait variation for above‐ and belowground functional traits, and test whether they represent spectra of adaptation along a soil fertility gradient in tropical Andean forests. We measured leaf, stem and fine root functional traits, and individual‐level soil nutrient availability for 433 trees from 52 species at three elevations between 1000 and 3000 m a.s.l. We found close coordination between above– and belowground functional traits related to the trade‐off between resource acquisition and conservation, whereas root diameter and specific root length formed an independent axis of covarying traits. The position of a tree species along the acquisition–conservation axis of the trait space was closely associated with local soil nitrogen, but not phosphorus, availability. Our results imply that above‐ and belowground plant functional traits determine at which edaphic microhabitats coexisting tree species can grow, which is potentially crucial for understanding community assembly in species‐rich tropical montane forests. Read the free Plain Language Summary for this article on the Journal blog.

Variations in Wood Anatomy in Afrotropical Trees with a special emphasis on radial and axial parenchyma.

Understanding anatomical variations across plant phylogenies and environmental gradients is vital for comprehending plant evolution and adaptation. Prior studies on tropical woody plants have paid limited attention to quantitative differences in major xylem tissues, which serve specific roles in mechanical support (fibers), carbohydrate storage and radial conduction (radial parenchyma, rays), wood capacitance (axial parenchyma), and water transport (vessels). To address this gap, we investigate xylem fractions in 173 tropical tree species spanning 134 genera and 53 families along a 2200 m elevational gradient on Mount Cameroon, West Africa. We determined how elevation, stem height, and wood density affect interspecific differences in vessel, fiber, and specific axial (AP) and radial (RP) parenchyma fractions. We focus on quantifying distinct subcategories of homogenous or heterogeneous rays and apotracheal, paratracheal, and banded axial parenchyma. Elevation-related cooling correlated with reduced AP fractions and vessel diameters, while fiber fractions increased. Lower elevations exhibited elevated AP fractions due to abundant paratracheal and wide-banded parenchyma in tall trees from coastal and lowland forests. Vasicentric and aliform AP were predominantly associated with greater tree height and wider vessels, which might help cope with high evaporative demands via elastic wood capacitance. In contrast, montane trees featured a higher fiber proportion, scarce axial parenchyma, smaller vessel diameters, and higher vessel densities. The lack of AP in montane trees was often compensated by extended uniseriate ray sections with upright or squared ray cells or the presence of living fibers. Elevation gradient influenced specific xylem fractions, with lower elevations showing elevated AP due to abundant paratracheal and wide-banded parenchyma, securing greater vessel-to-parenchyma connectivity and lower embolism risk. Montane trees featured a higher fiber proportion and smaller vessel diameters, which may aid survival under greater environmental seasonality and fire risk.

Genomic divergence and demographic history of Quercus aliena populations

BackgroundQuercus aliena is a major montane tree species of subtropical and temperate forests in China, with important ecological and economic value. In order to reveal the species’ population dynamics, genetic diversity, genetic structure, and association with mountain habitats during the evolutionary process, we re-sequenced the genomes of 72 Q. aliena individuals.ResultsThe whole chloroplast and nuclear genomes were used for this study. Phylogenetic analysis using the chloroplast genome dataset supported four clades of Q. aliena, while the nuclear dataset supported three major clades. Sex-biased dispersal had a critical role in causing discordance between the chloroplast and nuclear genomes. Population structure analysis showed two groups in Q. aliena. The effective population size sharply declined 1 Mya, coinciding with the Poyang Glaciation in Eastern China. Using genotype–climate association analyses, we found a positive correlation between allele frequency variation in SNPs and temperature, suggesting the species has the capacity to adapt to changing temperatures.ConclusionOverall, this study illustrates the genetic divergence, genomic variation, and evolutionary processes behind the demographic history of Q. aliena.

New records of vegetation and climate changes in the Sea of Marmara during the Marine Isotope Stages 3, 4 and 5 (a-c)

A giant piston core MRS-CS27 sedimentary sequence in the Sea of Marmara (SoM) was investigated by palynological analysis to evaluate the paleoenvironmental and climate changes, corresponding to the Marine Isotope Stages MIS-5 (c-a), MIS-4, MIS-3, and the earliest part of the MIS-2. During MIS-5c, the palynological analysis indicates a warm and humid climate in the SoM. The pollen assemblage is characterized by the presence of broad-leaved deciduous woody taxa, with a predominance of deciduous Quercus. Following MIS-5c, a relatively colder and drier climate is inferred during MIS-5b, as indicated by the herbaceous assemblages found in the sedimentary sequence. The presence of herbaceous plants in the pollen record suggests less favorable conditions for woody vegetation and a shift towards a cooler and drier climate compared to the previous phase. Within the MIS-5a interval, the palynological analysis reveals the presence of abundant mesophyllous woody taxa. This indicates a return to a warm and humid climate during this period, supporting the growth of diverse forest vegetation. Distinct changes in vegetation are observed during MIS-4, with the presence of abundant Cedrus pollen. This suggests the survival of montane trees in the region under a cooler climate compared to the previous stages. Relict plants such as Cathaya, Tsuga, and Carya are identified during MIS-3 and MIS-4. Their presence can be attributed to the reworking of older sediments during these periods, indicating that these plants were not contemporary with the sediment but were preserved from earlier time periods.

Wildfire facilitates upslope advance in a shade-intolerant but not a shade-tolerant conifer.

Wildfires may facilitate climate tracking of forest species moving upslope or north in latitude. For subalpine tree species, for which higher elevation habitat is limited, accelerated replacement by lower elevation montane tree species following fire may hasten extinction risk. We used a dataset of postfire tree regeneration spanning a broad geographic range to ask whether the fire facilitated upslope movement of montane tree species at the montane-to-subalpine ecotone. We sampled tree seedling occurrence in 248 plots across a fire severity gradient (unburned to >90% basal area mortality) and spanning ~500 km of latitude in Mediterranean-type subalpine forest in California, USA. We used logistic regression to quantify differences in postfire regeneration between resident subalpine species and the seedling-only range (interpreted as climate-induced range extension) of montane species. We tested our assumption of increasing climatic suitability for montane species in subalpine forest using the predicted difference in habitat suitability at study plots between 1990 and 2030. We found that postfire regeneration of resident subalpine species was uncorrelated or weakly positively correlated with fire severity. Regeneration of montane species, however, was roughly four times greater in unburned relative to burned subalpine forest. Although our overall results contrast with theoretical predictions of disturbance-facilitated range shifts, we found opposing postfire regeneration responses for montane species with distinct regeneration niches. Recruitment of shade-tolerant red fir declined with fire severity and recruitment of shade-intolerant Jeffrey pine increased with fire severity. Predicted climatic suitability increased by 5% for red fir and 34% for Jeffrey pine. Differing postfire responses in newly climatically available habitats indicate that wildfire disturbance may only facilitate range extensions for species whose preferred regeneration conditions align with increased light and/or other postfire landscape characteristics.

Vegetation Composition in a Typical Mediterranean Setting (Gulf of Corinth, Greece) during Successive Quaternary Climatic Cycles

The Gulf of Corinth is a semi-isolated basin in central Greece interrupting the Pindus Mountain Range, which nowadays is a biodiversity hotspot. Considering its key location, deep drilling was carried out within the International Ocean Discovery Program (IODP; Expedition 381: Corinth Active Rift Development) aiming to improve our understanding of climatic and environmental evolution in the region. Here, we present a new long pollen record from a Mediterranean setting in the southernmost tip of the Balkan Peninsula recording the vegetation succession within the Quaternary. The Corinth pollen record shows no major shifts in arboreal pollen between glacial and interglacial intervals, while Mediterranean and mesophilous taxa remain abundant throughout the study interval. During interglacials, the most frequent reconstructed biomes are cool mixed evergreen needleleaf (CMIX) and deciduous broadleaf forests (DBWB), while graminoid with forb (GRAM) and xerophytic shrubs (XSHB) dominate within glacials. Our findings support the hypothesis that the study area was a significant refugium, providing suitable habitats for Mediterranean, mesophilous and montane trees during successive Quaternary climate cycles.

A taxonomic revision of the ecologically important Ochna holstii (Ochnaceae) complex using molecular and morphological data

Background and aims – Ochna holstii and its allies represent an ecologically important group in a variety of lowland to montane habitats in tropical eastern and southern Africa. Identifying and delimiting species within this group has proved challenging due to a lack of variation in morphological characters. We combine genomic-scale data of multiple accessions per species with morphological data to generate a taxonomic revision for the Ochna holstii complex using a multi-evidence approach. Material and methods – A total of 50 samples representing eight species were analysed using target enrichment and a custom bait kit. Phylogenetic analysis was conducted using the multi-species coalescent model and a concatenation maximum likelihood method, and gene tree discordance was investigated. Herbarium specimens of the O. holstii complex were studied in detail for informative morphological characters, supplemented where possible from field collections, and a full taxonomic revision is provided. Key results – Within Ochna sect. Schizanthera Clade I, our study confirms that all species are monophyletic and supported by morphological data with the exception of O. holstii, which is paraphyletic. A new species, O. mchanga, previously confused with O. polyneura, is described, and the placement of another recently described species, O. maguirei, is confirmed for the first time using molecular data. Conclusion – The widespread montane tree Ochna holstii is non-monophyletic in its current circumscription and likely gave rise to the more range-restricted O. oxyphylla and O. stolzii. We suggest that an integrated taxonomy approach, using both molecular and morphological data, is essential for deciphering difficult species relationships in Ochna.

Seasonality in the equatorial tropics: Flower, fruit, and leaf phenology of montane trees in the highlands of Southwest Uganda

AbstractPhenology influences many forest functions and can inform forest conservation and management, yet representative phenological data for most common tropical forest tree species remain sparse or absent. Between June 2011 and December 2013, we investigated flowering, fruiting, and leafing patterns in the Bwindi Impenetrable National Park, a montane forest located near the equator in Uganda, drawing on 16,410 observations of 530 trees of 54 species located between 2066 and 2527 m in elevation. The park's climate is equatorial with two wet and dry seasons each year. Flowering and fruiting were strongly seasonal while patterns in leafing were less pronounced. Flower occurrence peaked at the beginning of the short dry season followed by a pronounced trough during the beginning and the middle of the short wet season. Fruit occurrence had a pronounced peak during high rainfall months in March through April with most fruits ripening during drier months in May through July. Fruit scarcity was observed for a 4‐month period spanning September to December and most flushing of leaves noted at the end of the wet season in November and December. Our binomial generalized linear mixed models indicated that flowering and fruiting were negatively associated with temperature and that leafing activity was positively associated with rainfall and temperature. These findings are consistent with the insolation‐ and water‐limitation hypotheses suggesting that the seasonally varying availability of resources such as light, water, and nutrients determines these phenological patterns. Ideally, prolonged, multi‐year community‐level studies would be supported so as to better characterize the influence of climate and of climate variability.

Quercus insignis seedling response to climatic transfer distance in the face of climate change

Rising temperatures are causing increased tree mortality at lower elevations and upward migrations in montane tree communities. To reduce the risk of extinction from climate change, managed translocation or assisted migration could serve to support the management of endangered species, but is currently a controversial strategy with very limited information available from experimental field studies in the tropics. We examined the effect of climatic transfer distance (CTD; the climatic difference between the site of seed origin and the site of plantation) on the establishment of Quercus insignis, an endangered oak with a distribution restricted to cloud forests. If the natural population (seed origin) occurs at its optimum climate, a decline in seedling transplant performance is expected to occur with greater CTD. Enrichment plantings were established in three sites near the seed origin area (at 1400 m a.s.l.), and in five sites from an elevation similar to the seed source up to high elevations (1365 to 2531 m a.s.l.) in Mexico. We examined the effect of CTD on seedling survival and Relative Growth Rate (RGR) over a period of four years. In the provenance area, a 1.4 °C increase and a 25–30 % annual precipitation decrease were estimated to have occurred during the study period (2018–2021), relative to the reference climate (1960–1990) in which the population in the provenance area developed. We found no significant evidence to support lower seedling survival with greater CTD. High survival occurred in sites with a warmer temperature at present (up to 80 % survival), but also in colder sites at higher elevation (up to 90 %), revealing the high tolerance of Q. insignis to a wide range of climatic conditions. The RGR showed the expected decrease with greater CTD of the Aridity Index, reflecting the importance of the balance between temperature and water availability. These findings support the potential of Q. insignis enrichment plantings, both near the seed origin area and at higher elevation (currently 2–3 °C colder than in the provenance area) to compensate for the expected temperature increase. However, the projected reduction in precipitation and cloud immersion within the cloud forest belt associated with climate change, could act to limit growth and lead to lower establishment success.

Variations in the reproductive cycle of Bornean montane tree species along elevational gradients on ultrabasic and non‐ultrabasic soils

AbstractAlthough lowland tree species in the ever‐wet regions of Southeast Asia are characterized by the supra‐annual cycle of reproduction, the reproductive phenology of montane tree species remains poorly understood. In this study, we investigated the reproductive phenology of montane tree species using litter samples that were collected every 2 weeks from six rainforest sites, consisting of three elevations (1700, 2700, and 3100 m), on Mount Kinabalu, Borneo. At each elevation, one site was on infertile ultrabasic soil and one was on relatively fertile non‐ultrabasic soil. We used a composite sample from 10 or 20 litter traps per site and sorted it by species. Therefore, the obtained data captured reproductive phenology in the population of each species rather than in an individual tree. Ten‐year time series of flower and fruit litterfall were obtained for 30 and 39 tree species, respectively. Fourier analysis was used to identify the dominant cycle of each time series. The most abundant cycle across species was supra‐annual, followed by sub‐annual, and annual cycles. Many species at higher elevations showed supra‐annual cycles of flower litterfall, whereas species in the 1700 m sites often showed annual or sub‐annual cycles regardless of soil types. No systematic differences were found among sites for fruit litterfall. Mechanisms underlying these elevational patterns in reproductive cycle remain unclear but may include more severe El Niño droughts, lower primary productivity, lower soil fertility, and the absence of some sub‐annually or annually reproducing families at higher elevations.

Canopy gaps facilitate upslope shifts in montane conifers but not in temperate deciduous trees in the Northeastern United States

AbstractMany montane tree species are expected to migrate upslope as climate warms, but it is not clear if forest canopy gaps, which can facilitate tree seedling recruitment, serve as an important mechanism driving tree species range shifts. Patterns of tree seedling establishment can inform us about early stages of tree species migrations and are critical to examine in the context of global climate change.We contrasted elevational distributions of tree seedlings both within and outside of forest canopy gaps with the distributions of conspecific adults and saplings across the deciduous‐coniferous ecotone on ten mountains in four states of the Northeastern United States. We tested if seedling distributions of four dominant tree species (Abies balsamea,Picea rubens,Acer saccharumandFagus grandifolia) were shifted upslope of conspecific adult and sapling distributions. We also examined if this shift was facilitated by canopy gaps and what environmental drivers affected species distributions.There was limited seedling recruitment of dominant tree species at the temperate‐coniferous ecotone, which we attributed to (i) an observed downslope shift of seedling distributions of the low‐elevation deciduous species (Acer saccharum,Fagus grandifolia) and (ii) an upslope shift in seedling distributions of the high‐elevation conifers (Abies balsamea,Picea rubens). The upslope shift of conifer seedlings contrasts with our previous research at these sites which observed downslope shifts of sapling distributions inPicea rubens, suggesting that seedlings may be responding to more recent climate warming. Canopy gaps in high‐elevation conifer forests facilitated these upslope shifts by promoting conifer seedling recruitment. However, gaps at lower elevations did not play a significant role in seedling recruitment or the observed downslope shifts of the dominant deciduous species. Climate was the dominant predictor of adult tree distributions whereas both climate and soil were important predictors of seedling distributions.Synthesis.Our study illustrates that tree seedlings have the potential for monitoring the early stages of tree species migrations, and particularly so in canopy gaps in high‐elevation conifer forests. Further, we stress that species range shifts are sensitive to local scale heterogeneity in light availability (i.e. canopy gaps) and other non‐climatic factors.

Temperature acclimation of net photosynthesis and its underlying component processes in four tropical tree species.

The effect of temperature change on leaf physiology has been extensively studied in temperate trees and to some extent in boreal and tropical tree species. While increased temperature typically stimulates leaf CO2 assimilation and tree growth in high-altitude ecosystems, tropical species are often negatively affected. These trees may operate close to their temperature optima and have a limited thermal acclimation capacity due to low seasonal and historical variation in temperature. To test this hypothesis, we studied the extent to which the temperature sensitivities of leaf photosynthesis and respiration acclimate to growth temperature in four common African tropical tree species. Tree seedlings native to different altitudes and therefore adapted to different growth temperatures were cultivated at three different temperatures in climate-controlled chambers. We estimated the acclimation capacity of the temperature sensitivities of light-saturated net photosynthesis, the maximum rates of Rubisco carboxylation (Vcmax) and thylakoid electron transport (J), and dark respiration. Leaf thylakoid membrane lipid composition, nitrogen content and leaf mass per area were also analyzed. Our results showed that photosynthesis in tropical tree species acclimated to higher growth temperatures, but that this was weakest in the species originating from the coolest climate. The temperature optimum of J acclimated significantly in three species and variation in J was linked to changes in the thylakoid membrane lipid composition. For Vcmax, there was only evidence of significant acclimation of optimal temperature in the lowest elevation species. Respiration acclimated to maintain homeostasis at growth temperature in all four species. Our results suggest that the lowest elevation species is better physiologically adapted to acclimate to high growth temperatures than the highest elevation species, indicating a potential shift in competitive balance and tree community composition to the disadvantage of montane tree species in a warmer world.

Handling the heat - photosynthetic thermal stress in tropical trees.

Warming climate increases the risk for harmful leaf temperatures in terrestrial plants, causing heat stress and loss of productivity. The heat sensitivity may be particularly high in equatorial tropical tree species adapted to a thermally stable climate. Thermal thresholds of the photosynthetic system of sun-exposed leaves were investigated in three tropical montane tree species native to Rwanda with different growth and water use strategies (Harungana montana, Syzygium guineense and Entandrophragma exselsum). Measurements of chlorophyll fluorescence, leaf gas exchange, morphology, chemistry and temperature were made at three common gardens along an elevation/temperature gradient. Heat tolerance acclimated to maximum leaf temperature (Tleaf ) across the species. At the warmest sites, the thermal threshold for normal function of photosystem II was exceeded in the species with the highest Tleaf despite their higher heat tolerance. This was not the case in the species with the highest transpiration rates and lowest Tleaf . The results point to two differently effective strategies for managing thermal stress: tolerance through physiological adjustment of leaf osmolality and thylakoid membrane lipid composition, or avoidance through morphological adaptation and transpiratory cooling. More severe photosynthetic heat stress in low-transpiring montane climax species may result in a competitive disadvantage compared to high-transpiring pioneer species with more efficient leaf cooling.

Reconstruction of climate and ecology of Skagit Valley, Washington, from 27.7 to 19.8 ka based on plant and beetle macrofossils

AbstractGlacial lake sediments exposed at two sites in Skagit Valley, Washington, encase abundant macrofossils dating from 27.7 to 19.8 cal ka BP. At the last glacial maximum (LGM) most of the valley floor was part of a regionally extensive arid boreal (subalpine) forest that periodically included montane and temperate trees and open boreal species such as dwarf birch, northern spikemoss, and heath. We used the modern distribution and climate of 14 species in 12 macrofossil assemblages and a probability density function approach to reconstruct the LGM climate. Median annual precipitation (MAP) at glacial Lake Concrete (GLC) was ~50% lower than today. In comparison, MAP at glacial Lake Skymo (GLS) was only ~10% lower, which eliminated the steep climate gradient observed today. Median January air temperature at GLC was up to 10.8°C lower than today at 23.5 cal ka BP and 8.7°C lower at GLS at 25.1 cal ka BP. Median July air temperature declines were smaller at GLC (3.4°C–5.0°C) and GLS (4.2°C–6.3°C). Warmer winters (+2°C to +4°C) and increases in MAP (+200 mm) occurred at 27.7, 25.9, 24.4, and 21.2–20.7 cal ka BP. These changes accord with other regional proxies and Dansgaard–Oeschger interstades in the North Atlantic.

Limited thermal acclimation of photosynthesis in tropical montane tree species.

The temperature sensitivity of physiological processes and growth of tropical trees remains a key uncertainty in predicting how tropical forests will adjust to future climates. In particular, our knowledge regarding warming responses of photosynthesis, and its underlying biochemical mechanisms, is very limited. We grew seedlings of two tropical montane rainforest tree species, the early-successional species Harungana montana and the late-successional species Syzygium guineense, at three different sites along an elevation gradient, differing by 6.8℃ in daytime ambient air temperature. Their physiological and growth performance was investigated at each site. The optimum temperature of net photosynthesis (ToptA ) did not significantly increase in warm-grown trees in either species. Similarly, the thermal optima (ToptV and ToptJ ) and activation energies (EaV and EaJ ) of maximum Rubisco carboxylation capacity (Vcmax ) and maximum electron transport rate (Jmax ) were largely unaffected by warming. However, Vcmax , Jmax and foliar dark respiration (Rd ) at 25℃ were significantly reduced by warming in both species, and this decline was partly associated with concomitant reduction in total leaf nitrogen content. The ratio of Jmax /Vcmax decreased with increasing leaf temperature for both species, but the ratio at 25℃ was constant across sites. Furthermore, in H. montana, stomatal conductance at 25℃ remained constant across the different temperature treatments, while in S. guineense it increased with warming. Total dry biomass increased with warming in H. montana but remained constant in S. guineense. The biomass allocated to roots, stem and leaves was not affected by warming in H. montana, whereas the biomass allocated to roots significantly increased in S. guineense. Overall, our findings show that in these two tropical montane rainforest tree species, the capacity to acclimate the thermal optimum of photosynthesis is limited while warming-induced reductions in respiration and photosynthetic capacity rates are tightly coupled and linked to responses of leaf nitrogen.

Functional assembly of tropical montane tree islands in the Atlantic Forest is shaped by stress tolerance, bamboo presence, and facilitation.

AimsAmidst the Campos de Altitude (Highland Grasslands) in the Brazilian Atlantic Forest, woody communities grow either clustered in tree islands or interspersed within the herbaceous matrix. The functional ecology, diversity, and biotic processes shaping these plant communities are largely unstudied. We characterized the functional assembly and diversity of these tropical montane woody communities and investigated how they fit within Grime's CSR (C—competitor, S—stress‐tolerant, R—ruderal) scheme, what functional trade‐offs they exhibit, and how traits and functional diversity vary in response to bamboo presence/absence.MethodsTo characterize the functional composition of the community, we sampled five leaf traits and wood density along transects covering the woody communities both inside tree islands and outside (i.e., isolated woody plants in the grasslands community). Then, we used Mann–Whitney test, t test, and variation partitioning to determine the effects of inside versus outside tree island and bamboo presence on community‐weighted means, woody species diversity, and functional diversity.ResultsWe found a general SC/S strategy with drought‐related functional trade‐offs. Woody plants in tree islands had more acquisitive traits than those within the grasslands. Trait variation was mostly taxonomically than spatially driven, and species composition varied between inside and outside tree islands. Leaf thickness, wood density, and foliar water uptake were unrelated to CSR strategies, suggesting independent trait dimensions and multiple drought‐coping strategies within the predominant S strategy. Islands with bamboo presence showed lower Simpson diversity, lower functional dispersion, lower foliar water uptake, and greater leaf thickness than in tree islands without bamboo.ConclusionsThe observed functional assembly hints toward large‐scale environmental abiotic filtering shaping a stress‐tolerant community strategy, and small‐scale biotic interactions driving small‐scale trait variation. We recommend experimental studies with fire, facilitation treatments, ecophysiological and recruitment traits to elucidate on future tree island expansion and community response to climate change.

Response of leaf morphological traits of relict-endemic Symplocos species (S. coccinea and S. speciosa) to elevation and abiotic fluctuations

Abiotic fluctuations in montane ecosystems trigger changes in the hydric functional traits of tree species. These variations are better recognized in tree species inhabiting montane humid ravine slopes with different elevation, as is the case of many areas across the Mexican Neotropical montane forests. Little is known about the response of tree towards elevation gradients and abiotic changes. In this study, we analyzed the leaf morphological variation of two rare and Mexican endemic Symplocos species (S. coccinea and S. speciosa) occurring eastern Mexico on sites with different microclimate and elevation but similar floristic composition. We quantified how the abiotic factors (i.e. canopy openness, soil temperature, soil moisture, and litter depth) and site elevation influence the leaf traits of these tree species. Symplocos coccinea (with toothed leaf margins) is adapted to high humid conditions and high canopy coverage, while S. speciosa (with almost entire leaf margins) is resilient to environments with moisture deficit and high temperatures. Process-based research with fine-spatial scales at montane ecosystems are needed to understand the resilience and morphological variations of montane tree species under climate change worldwide. In this study, we confirmed that the Symplocos leaf morphological traits (i.e. leaf length, leaf width, leaf shape index, leaf base angle and vein density) are strongly influenced by abiotic conditions (i.e. canopy openness, litterfall depth, soil moisture and soil temperature).

Population genetics under the Massenerhebung effect: The influence of topography on the demography of Acer morrisonense

AbstractAimThe Massenerhebung effect (Mass elevation effect) refers to heat‐ or wind‐driven altitudinal distribution patterns of temperature‐dependent parameters among massifs with narrower range and lower elevation around peripheral and isolated mountains compared to core and continuous ones. Although common in ecology, this effect is rarely discussed in population genetics. Here, we use genetic markers to reveal population genetic patterns and also test the mountain‐ and sky‐barrier hypotheses relevant to the Massenerhebung distribution pattern of Acer morrisonense in Taiwan's rugged topography and varied local climates.LocationThe alpine and cloud forest of Taiwan.TaxonAcer morrisonense Hayata.MethodsTwo chloroplast DNA (cpDNA) fragments and 17 expressed sequence tag‐simple sequence repeat (EST‐SSR) loci, respectively, from 200 to 286 individuals were used to elucidate the phylogeographic pattern of pollen and seed dispersal of A. morrisonense. These data were combined with ecological niche modeling (ENM) to infer distribution range shifts and refugia. We also correlated the genetic‐divergence indices with spatial factors to clarify latitudinal and altitudinal effects on genetic diversity.ResultsThe incongruent phylogeographic patterns of genetic distributions between nuclear and cpDNA markers indicate unhindered pollen flow but spatially constrained seed dispersal. Taken together with ENM, the genetic pattern further reflects historical colonization from central‐mountain refugia to edges since the Holocene. The Massenerhebung reduces the gene flow by the surrounding mountains and also causes lower genetic diversity compared to central alpine populations.Main conclusionsThis study is the first to reveal the influence of Massenerhebung effect on cpDNA genetic structure of montane trees and reflect the spatial trends of seed dispersal. This population genetic pattern can also be attributed to the demography‐related range shifts with paleoclimate fluctuations under complex mountain topography, supporting the mountain‐barrier hypothesis. The results have important implications for conserving the genetic diversity of species with a wide altitudinal distribution range.

Can species distribution models and molecular tools help unravel disjunct distribution of Rhododendron arboreum?

The apparent absence of Himalayan low-elevation taxa in the central Indian region and resumption of their distribution in the high elevation of Western Ghats has puzzled biogeographers for several decades. Many theories have been proposed to explain this but attempts remain futile owing to insufficient empirical support. Here, we have employed a montane tree species, Rhododendron arboreum to investigate this pattern by integrating past ecological niche modelling with molecular signatures. Reconstruction of paleo-ecological niche from interglacial to Last Glacial Maxima (LGM) portrayed a gradual depletion of vegetation cover with extreme impoverishment in the Holocene. A similar pattern was also reflected from genetic signatures; population history revealed a very recent split between the Himalayas and Western Ghats in the late Quaternary. A few other tree species exhibiting the same disjunction demonstrated a similar modification of paleo-ecological niche from last interglacial. The study clearly indicated that the populations in the Western Ghats to be a relictual remnants of a once continuous distribution of R. arboreum.

The montane trees of the Cameroon Highlands, West-Central Africa, with Deinbollia onanae sp. nov. (Sapindaceae), a new primate-dispersed, Endangered species

We test the hypothesis that the tree species previously known as Deinbollia sp. 2. is a new species for science. We formally characterise and name this species as Deinbollia onanae (Sapindaceae-Litchi clade) and we discuss it in the context of the assemblage of montane tree species in the Cameroon Highlands of West-Central Africa. The new species is a shade-bearing, non-pioneer understorey forest tree species reaching 15 m high and a trunk diameter that can attain over 40 cm at 1.3 m above the ground. Seed dispersal has been recorded by chimpanzees (Pan troglodytes ellioti) and by putty-nose monkeys (Cercopithecus nictitans) and the species is used by chimpanzees for nesting. Cameroon has the highest species-diversity and species endemism known in this African-Western Indian Ocean genus of 42, mainly lowland species. Deinbollia onanae is an infrequent tree species known from six locations in surviving islands of montane (sometimes also upper submontane) forest along the line of the Cameroon Highlands, including one at Ngel Nyaki in Mambilla, Nigeria. Deinbollia onanae is here assessed as Endangered according to the IUCN 2012 standard, threatened by severe fragmentation of its mountain forest habitat due to extensive and ongoing clearance for agriculture. The majority of the 28 tree species of montane forest (above 2000 m alt.) in the Cameroon Highlands are also widespread in East African mountains (i.e. are Afromontane wide). Deinbollia onanae is one of only seven species known to be endemic (globally restricted to) these highlands. It is postulated that this new species is morphologically closest to Deinbollia oreophila, a frequent species at a lower (submontane) altitudinal band of the same range. Detailed ecological data on Deinbollia onanae from the Nigerian location, Ngel Nyaki, where it has been known under the name Deinbollia “pinnata”, is reviewed.