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1. Plant functional traits determine plant performance and have therefore the potential to shape and predict species distributions along environmental gradients. This study analyses how traits affect tree species distribution along an elevational gradient in the Himalayas, Nepal. We addressed three questions: (a) what plant strategies can be distinguished among tree species? (b) how are plant traits and strategies associated with elevation? and (c) what plant traits are the best predictors of species positions along elevational gradient? 2. We quantified for 31 tree species a set of 39 plant traits related to resource uptake, use and conservation. We analysed how traits cluster into separate functions using a cluster analysis, and how traits and clusters associate into distinct plant strategies using a principal component analysis. 3. The cluster analysis showed five clusters of traits, reflecting (a) efficiency in vertical expansion, (b) efficiency in horizontal expansion, (c) efficiency in metabolism, (d) physical defence and (e) tree functional groups (conifers vs. broadleaf species). The first PCA axis reflects trade-offs in traits and clusters linked to elevation: highland species had trait values that increase safety against freezing induced cavitation, high solar radiation and strong wind, and that increase resource conservation. In contrast, lowland species had trait values that increase efficiency of resource acquisition, metabolism and expansion. Additionally, a bivariate analysis showed that the first PCA axis is more strongly related to elevation than the individual traits, indicating that the combination of traits is more important than the individual traits. An all subsets regression analysis showed that a small set of traits best explain species distribution: highland species had smaller size (low basal area), safer hydraulics (low conduit diameter) and lower leaf and branch display efficiency (low leaf area per xylem area, specific branch length) that increase persistence under harsh conditions. Remarkably, leaf traits were poor predictors of species' elevational positions. 4. Synthesis. Multiple trade-offs in plant size, hydraulics and light competitiveness shape species distribution along the elevational gradient. Along this extreme environmental gradient, stem and branch traits that integrate multiple plant organs and functions are better predictors of species' elevational distributions than leaf traits. [ABSTRACT FROM AUTHOR]

Landslides are common natural disturbances in tropical montane forests. While the geomorphic drivers of landslides in the Andes have been studied, factors controlling post‐landslide forest recovery across the steep climatic and topographic gradients characteristic of tropical mountains are poorly understood.Here we use a LiDAR‐derived canopy height map coupled with a 25‐year landslide time‐series map to examine how landslide, topographic and biophysical factors, along with residual vegetation, affect canopy height and heterogeneity in regenerating landslides. We also calculate above‐ground biomass accumulation rates and estimate the time for landslides to recover to mature forest biomass levels.We find that age and elevation are the biggest determinants of forest recovery, and that the jump‐start in regeneration that residual vegetation provides lasts for at least 18 years. Our estimates of time to biomass recovery (31.6–37.1 years) are surprisingly rapid, and as a result we recommend that future research pair LiDAR with hyperspectral imagery to estimate forest above‐ground biomass in frequently disturbed landscapes.Synthesis. Using a high‐resolution LiDAR dataset and a time‐series inventory of 608 landslides distributed across a wide elevational gradient in Andean montane forest, we show that age and elevation are the most influential predictors of forest canopy height and canopy variability. Other features of landslides, in particular the presence of residual vegetation, shape post‐landslide regeneration trajectories. LiDAR allows for a detailed analysis of forest structural recovery across large landscapes and numbers of disturbances, and provides a reasonable upper bound on above‐ground biomass accumulation rates. However, because this method does not capture the effect of compositional change through succession on above‐ground biomass, wherein high‐wood density species gradually replace light‐wooded pioneer species, it overestimates above‐ground biomass. Given previously estimated stem turnover rates along this elevational gradient, we posit that above‐ground biomass recovery takes at least three times as long as our recovery time estimates based on LiDAR‐derived structure alone. [ABSTRACT FROM AUTHOR]

Plant‐fungal interactions are important for plant community assembly, but quantifying these relationships remains challenging. High throughput sequencing of fungal communities allows us to identify plant‐fungal associations at a high level of resolution, but often fails to provide information on taxonomic and functional assignment of fungi.We transplanted seeds of Pinus cembra across an elevational gradient (1850–2250 m a.s.l.) and identified environmental factors and known fungal associates important for seedling establishment and survival. We then applied null model tests to identify taxonomically unassigned fungi associated with pine recruitment.Early seedling establishment was determined by abiotic environmental factors, while seedling survival was predominantly affected by biotic environmental factors (i.e., the abundance of a fungal pathogen known from literature and the distance to adult trees). Null model tests identified known mycorrhizal partners and a large number of unknown operational taxonomic units (OTUs) associated with seedling survival, including saprotrophic and pathogenic species. These results highlight that unknown fungal OTUs, which are usually discarded from analyses, could play a crucial role for plant survival.Synthesis. We conclude that high throughput metabarcoding paired with null model tests, is a valuable approach for identifying hidden plant‐fungal associations within large and complex DNA metabarcoding datasets. Such an approach can be an important tool in illuminating the black box of plant‐microbe interactions, and thus understanding ecosystem dynamics. [ABSTRACT FROM AUTHOR]

Abstract: Abiotic factors, biotic interactions and dispersal ability determine the spatial distribution of species. Theory predicts that abiotic constraints set range limits under harsh climatic conditions and biotic interactions set range limits under benign climatic conditions, whereas dispersal ability should limit both ends of the distribution. However, empirical studies exploring how these three components jointly affect species across environmental gradients are scarce. Here, we present a study that jointly examines these factors to investigate the constraints of the recruitment of Swiss stone pine (Pinus cembra) at and beyond its upper and lower elevational range limits in the Swiss Alps. We investigated the natural recruitment of pines and additionally conducted seed transplant experiments to test how much abiotic factors (mean summer and winter temperatures, soil moisture), biotic interactions (understorey vegetation cover, canopy cover, seed predation) and/or seed deposition by the spotted nutcracker (Nucifraga caryocatactes) affect pine establishment. We found significant effects of biotic interactions and seed deposition by spotted nutcrackers on the recruitment of Swiss stone pine at both the upper and lower elevational range, but could not detect significant effects of abiotic factors. Importantly, dispersal limitation rather than temperature and soil moisture restricted the recruitment of pines at the upper elevational range. Synthesis. Our study highlights the importance of biotic interactions and dispersal ability in setting the upper range limits of species that have been regarded as mainly controlled by climate. This suggests that potential range shifts of plants in response to climate warming may strongly depend on seed dispersal and biotic interactions and not only on climatic factors. [ABSTRACT FROM AUTHOR]

By the end of this century, temperature is predicted to increase by about 6 °C at higher latitudes and about 3 °C in the tropics. Although values predicted for tropical latitudes are lower, rising temperatures in the tropics are likely to have more severe consequences for tropical species that are generally assumed to have narrower climatic niches due to a higher degree of climatic stability and higher niche specialization., Even though temperature affects all ontogenetic stages, the regeneration niche of a species is fundamental for overall niche breadth and hence represents a potential major bottleneck for its distribution., We conducted germination experiments along a range of temperatures with 41 epiphytic bromeliad species to determine thermal germination traits (thermal niche breadth, lower and upper thermal limit, thermal optimum). Based on these traits, we asked whether the thermal germination niche breadth of these species is wide enough to cope with the predicted increase in temperature. Furthermore, we conducted phylogenetic comparative analyses to detect possible niche conservatism of these traits in Bromeliaceae., For 93% of all tested bromeliad species, the predicted mean annual temperature range does not exceed the thermal niche breadth. Moreover, for 85% of all tested species, the current mean annual temperature across the distribution range is well below our estimates of their thermal optima. Furthermore, we found evidence for phylogenetic niche conservatism in most assessed traits., Synthesis. Our report represents an important first step to understand and predict present and future responses of epiphytic bromeliads to global warming. At least with regard to seed germination, epiphytic bromeliads should not be negatively affected by the predicted temperature rise of 3 °C. To the contrary, future temperatures are closer to the thermal optima of most species, potentially leading to an increase in performance. However, since niche conservatism in Bromeliaceae may limit their adaptability to novel climatic conditions, a negative effect of increasing temperatures cannot be completely rejected when considering ontogenetic niche shifts. [ABSTRACT FROM AUTHOR]

The elevational limit of trees (henceforth, the 'tree line') is widely considered to be a sensitive indicator of environmental change. Here, we document the 20th century tree line advance and increase in the tree population at the tree line ecotone, along a Pinus sylvestris-dominated slope in north-eastern Finland, in conditions where growth and recruitment have generally been linked to temperature variation., Using tree recruitment ages (growth to 1.3 m height) along an elevational transect, we compared recruitment to variation in environmental conditions associated with tree line dynamics, seed and cone crops, and reindeer densities. We further investigated the relationships among temperature and tree-level growth variables., Results show the existence of a former tree line at approximately 400 m a.s.l. and an advance of trees that began in the 1920s and reached the top of the fell (at 470 m a.s.l.) in the 1980s. During this time, the population density of P. sylvestris increased from 4 to 468 trees within the 5.6 ha study plot. Needle and shoot lengths were positively related to air temperature but recruitment was not., Average rate of P. sylvestris advance over the 20th century was consistent with earlier studies, but the temporal patterns of both upslope advance and population density increase were unexpected: both were characterized by a strongly stepwise pattern, culminating in a rapid advance and density increase in the 1970-1980s, and returning to low levels in the 1990s., Despite a positive relationship between growth and temperature variables at the tree level, climatic variables, or seed and cone crops were inconsistent with recruitment patterns. For most part of the 20th century, the increase corresponded to the gradual atmospheric CO2 increase, but of the variables screened only the changes in reindeer densities coincided with the stepwise pattern., Synthesis. Our results confirmed the connection between tree-level processes and temperature variability as expected from earlier studies. However, recruitment was not correlated with any of the environmental variables. Our findings point towards complex tree line dynamics, in which biotic agents may play a major role in mediating tree line response to environmental change. [ABSTRACT FROM AUTHOR]

1. Closely related taxa may be maintained as distinct species by a variety of reproductive isolating mechanisms. These include: inability to produce hybrid offspring, endogenous selection against hybrids in the form of genomic incompatibilities, and exogenous selection observable in genotype-by-environment interactions. To understand the relative importance of these three isolating mechanisms, we performed hand-pollination and reciprocal transplant experiments in a natural plant hybrid zone. 2. We measured reproductive isolation by making crosses between two parent species of Penstemon and naturally occurring hybrids. Inclusion of reciprocal hybrid crosses allowed us to determine whether fitness components differed depending on the identity of the mother. 3. Hybrid performance was evaluated in the greenhouse and in a reciprocal transplant experiment in the field. We measured fruit set, seed set, seed weight, time required for fruits to mature and seedling growth for potted plants. To test for exogenous isolation, we planted pure parents, reciprocal F1 hybrids and later generation hybrids in a reciprocal transplant experiment, and measured survival. 4. On average, interspecific crosses produced as many seeds as conspecific crosses. Hybrid performance was also equal to or greater than parents in all environments, including the greenhouse and all field gardens, indicating a lack of endogenous isolation. Parent species and reciprocal F1 hybrids differed in many traits measured. In each field garden, the hybrid with the native cytoplasm had a higher survival rate, suggesting local adaptation to different elevations. 5. Synthesis. Exogenous factors that differ along elevational gradients can be more important than intrinsic genetic incompatibilities in determining the fitness of plant hybrids. Our results illustrate the importance of studying hybrid performance in multiple environments and in generating reciprocal hybrids to test for isolating mechanisms in natural hybrid zones. [ABSTRACT FROM AUTHOR]

1 We examined in situ diversity and distribution of vascular epiphytes, as well as site environmental variables at six sites along a continuous elevational gradient (30–2600 m a.s.l.) of old-growth forest in Costa Rica. 2 A total of 555 species of vascular epiphytes from 130 genera of 53 families were identified to species or morphospecies. The ferns were the most diverse group, with 138 species, followed by orchids (112 species). Cloud forest at 1000 m was the richest site, representing the maximum of a pronounced mid-elevation peak in epiphyte species richness. 3 Spatial randomizations of recorded elevational ranges suggest that the overall elevational richness pattern of most epiphyte groups on this transect is substantially influenced by the mid-domain effect (MDE, the mid-elevation overlap of large-ranged species). Among the environmental factors considered (rainfall, temperature and canopy light environment), only rainfall was significantly correlated with richness. 4 Different patterns of richness for vascular epiphytes and for trees indicate that mechanisms differ between life forms. 5 We collected 26% of the estimated epiphyte species of Costa Rica along a single mountain transect. This, together with the finding that different groups and life forms varied in the elevation at which species richness peaked, highlights the need to conserve the few remaining intact elevational gradients in Latin America. [ABSTRACT FROM AUTHOR]

Summary1 It is unclear whether soil seed banks in alpine environments are a result of selection for extended seed dormancy, of ideal conditions for seed preservation in the soil, or a combination of both. 2 The nature of the soil seed bank was investigated in the perennial herb Phacelia secunda (Hydrophyllaceae) through reciprocal burial experiments using seeds obtained from populations growing at 1600, 2200, 2900 and 3400 m a.s.l. in the mediterranean Andes of central Chile. At the four elevations, six replicates of 50 seeds each, from each of the four elevational sources, were buried at 5 cm depth in mesh envelopes, placed in wire cages to protect against predation. Seeds were retrieved 1, 2 and 3 years after burial, and numbers of ungerminated seeds, and of those that remained viable, were determined. 3 At all elevations of seed burial, increasing proportions of seeds remained ungerminated, and proportionately more of the ungerminated seeds remained viable, as elevation of source of seed increased. For seed from low elevation, more seeds remained viable in the soil at the higher burial sites. However, for the seeds from higher elevation sources, seeds remaining viable were similar in number at all sites for seed burial. Half-lives of seed buried at the source elevation, calculated from the log-logistic distribution, increased with elevation, and ranged from 188 days at 1600 m to 354 days at 3400 m. 4 The results suggest that the propensity to form a persistent seed bank in P. secunda increases with elevation. Seeds from the highest elevations had the longest persistence, and this was largely unaffected by soil preservation conditions. Seeds from lower elevations survived for less time, and this was modifiable by preservation conditions. These results suggest that both selective effects and soil conditions may be involved in soil seed bank expression in the alpine environment. [ABSTRACT FROM AUTHOR]