Elevation Gradient Research Articles

Temperature dependence of pollen germination and tube growth in conifers relates to their distribution along an elevational gradient in Washington State, USA.

Pollen germination and tube growth are essential processes for successful fertilization. They are among the most temperature-vulnerable stages and subsequently affect seed production and determine population persistence and species distribution under climate change. Our study aims to investigate intra- and inter-specific variations in the temperature dependence of pollen germination and tube length growth and to explore how these variations differ for pollen from elevational gradients. We focused on three conifer species, Pinus contorta, Picea engelmannii, and Pinus ponderosa, with pollen collected from 350 to 2200m elevation in Washington State, USA. We conducted pollen viability tests at temperatures from 5 to 40°C in 5°C intervals. After testing for four days, we took images of these samples under a microscope to monitor pollen germination percentage (GP) and tube length (TL). We applied the Gamma function to describe the temperature dependence of GP and TL and estimated key parameters, including the optimal temperature for GP (Topt_GP) and TL (Topt_TL). Results showed that pollen from three species and different elevations within a species have different GP, TL, Topt_GP, and Topt_TL. The population with a higher Topt_GP would also have a higher Topt_TL, while Topt_TL was generally higher than Topt_GP, i.e., a positive but not one-to-one relationship. However, only Pinus contorta showed that populations from higher elevations have lower Topt_GP and Topt_TL and vice versa. The variability in GP increased at extreme temperatures, whereas the variability in TL was greatest near Topt_TL. Our study demonstrates the temperature dependences of three conifers across a wide range of temperatures. Pollen germination and tube growth are highly sensitive to temperature conditions and vary among species and elevations, affecting their reproduction success during warming. Our findings can provide valuable insights to advance our understanding of how conifer pollen responds to rising temperatures.

Predation, but not herbivory, declines with elevation in a tropical rainforest

AbstractNaturally, insect herbivore populations are controlled by their plant hosts and predators. These ‘bottom-up’ and ‘top-down’ controls influence leaf area lost to herbivory. Bottom-up control of herbivory may be driven by leaf nutrients and plant defences. Top-down control can be driven by abundance and species richness of natural enemies, host or prey specificity, and predation strategies (e.g., active searching or sit-and-wait ‘ambush’ predation). The relative importance of bottom-up and top-down controls is unresolved but likely to vary spatially and temporally and under different environmental conditions such as changing temperature. We surveyed leaf carbon and nitrogen, leaf area loss, and attacks on plasticine caterpillars across a tropical elevational gradient in Xishuangbanna, Yunnan Provence, China. We show that predatory foraging activity decreases with elevation and temperature, whereas leaf nutrients and leaf area loss from herbivory remains more or less constant. Predation patterns were driven by ants, which are thermophiles and therefore more active, abundant, and diverse at warmer, lower elevations. Leaf nutritional values are important in driving herbivory patterns as herbivory was stable across this gradient, but other factors such as mechanical defences and herbivore-induced plant volatiles demand further study. Elevational studies provide insight into how ecosystem function will shift under climate change. As increasing temperatures following climate change allows predatory groups like ants to exploit higher elevations, top-down control in high elevation habitats could increase, resulting in re-wiring of these ecologically sensitive communities. At the same time, top-down control at lower elevations may be at risk if critical thermal maxima for natural enemies are exceeded.

Elevational variation in morphology and biomass allocation in carpathian snowbell Soldanella carpatica (Primulaceae).

Plants growing along wide elevation gradients in mountains experience considerable variations in environmental factors that vary across elevations. The most pronounced elevational changes are in climate conditions with characteristic decrease in air temperature with an increase in elevation. Studying intraspecific elevational variations in plant morphological traits and biomass allocation gives opportunity to understand how plants adapted to steep environmental gradients that change with elevation and how they may respond to climate changes related to global warming. In this study, phenotypic variation of an alpine plant Soldanella carpatica Vierh. (Primulaceae) was investigated on 40 sites distributed continuously across a 1,480-m elevation gradient in the Tatra Mountains, Central Europe. Mixed-effects models, by which plant traits were fitted to elevation, revealed that on most part of the gradient total leaf mass, leaf size and scape height decreased gradually with an increase in elevation, whereas dry mass investment in roots and flowers as well as individual flower mass did not vary with elevation. Unexpectedly, in the uppermost part of the elevation gradient overall plant size, including both below-and aboveground plant parts, decreased rapidly causing abrupt plant miniaturization. Despite the plant miniaturization at the highest elevations, biomass partitioning traits changed gradually across the entire species elevation range, namely, the leaf mass fraction decreased continuously, whereas the flower mass fraction and the root:shoot ratio increased steadily from the lowest to the highest elevations. Observed variations in S. carpatica phenotypes are seen as structural adjustments to environmental changes across elevations that increase chances of plant survival and reproduction at different elevations. Moreover, results of the present study agreed with the observations that populations of species from the 'Soldanella' intrageneric group adapted to alpine and subnival zones still maintain typical 'Soldanella'-like appearance, despite considerable reduction in overall plant size.

Soil properties constrain forest understory plant distributions along an elevation gradient.

Projections of spatial biodiversity dynamics under climate warming are often based on models including only climate variables, and when non-climatic factors (e.g. soil) are included, data are often at much coarser spatial resolutions than those experienced by plants. Field studies along elevation gradients permit the gathering of detailed soil data, while still covering a wide climatic gradient. Here, an intensive field survey of four spring forest herbs along an elevation gradient showed that soil properties had substantial impacts on the occurrence/abundance of all species, and that soil effects were more pronounced at higher elevations. For Trillium erectum and Claytonia caroliniana, very infrequent occurrences at high elevation were strongly associated with rare microsites with high pH or nutrients. In a seven-year transplant experiment with T. erectum, we found that individuals grew to much smaller sizes at high than low elevation, suggesting that environmental factors rather than dispersal limitation constrain the species' upper range limit, despite substantial warming in recent decades. Our study demonstrates that soil factors interact strongly with climate to determine plant range limits along climatic gradients. Unsuitable soils for plants at high elevations or latitudes may represent an important constraint on future plant migration and biodiversity change. This article is part of the theme issue 'Ecological novelty and planetary stewardship: biodiversity dynamics in a transforming biosphere'.

Modelling air, ground surface and permafrost temperature variability across four dissimilar valleys, Yukon, Canada

Spatial maps of the air and ground thermal regime were generated for four Yukon valleys. The aim was to model air, ground surface and ground temperature (at fine spatial resolution) using locally measured inverted surface lapse rates (SLR), to better predict temperature along an elevation gradient. These local models were then compared to a regional permafrost probability model, which utilized differing inversion assumptions, as well as circumpolar and national models generated without considering inversions. Overall, permafrost probability in the regional model matched well with the local models where assumptions of treeline and inverted SLRs held true. When normal SLRs were assumed, permafrost presence was overestimated in each valley. This discrepancy was greatest at high elevations where permafrost was predicted to be coldest and most widespread. However, the difference between valleys was dependent on surface and subsurface characteristics such as higher snow cover, mature forest or thick organic layers showed a greater disassociation from the air temperature overall. Appropriate characterization of the SLR is essential for accurate predictions of the ground thermal regime’s spatial distribution and permafrost presence. These models also provide a starting point for better predictions of warming in these valleys and other areas subject to inversions of similar magnitudes.

Food resource partitioning between males and females of Volcano Sunbird (Cinnyris preussi) on Mount Cameroon

Competition for nectar is expected to result in feeding niche differentiation. Here, we targeted the sexually size-dimorphic Volcano Sunbird (Cinnyris preussi) on Mount Cameroon. We investigated whether males and females feed on different plant species, whether females with shorter bills than males prefer shorter flowers, and whether larger dominant males visit more energetic flowers that produce higher amounts of nectar sugars. We also asked whether feeding niches were spatially separated along the elevation gradient and whether this separation varied between the two contrasting seasons. We collected data on the frequency of visits to individual plant species and analyzed the male-to-female ratios in the mist-netted dataset. In addition, we estimated production of nectar sugar in individual habitats and seasons. Despite the large dataset collected, encompassing 6476 bird–plant interactions, our findings did not provide evidence of differences in the spectra of the visited plant species. In addition, females did not visit flowers with shorter tubes, nor did males visit flowers that produced higher amounts of sugars. However, we observed a sex-specific dispersion of sunbirds during the wet season. During the dry breeding season, both males and females feed mainly in nectar-rich montane and submontane forests. In the wet season, the production of nectar sugar in these habitats decreased dramatically, and females largely disappeared. In contrast, female activity increased in the lowest and highest parts of the altitudinal range. Our findings on elevational movements are important in the current context, in which species face potential threats from habitat destruction and climate change.

Updating knowledge of vegetation belts on a complex oceanic island after 20 years under the effect of climate change

Climate change is causing major changes in terrestrial ecosystems and biomes around the world. This is particularly concerning in oceanic islands, considered reservoirs of biodiversity, even more in those with a significant altitudinal gradient and high complexity in the vegetation they potentially harbour. Here, in Tenerife (Canary Islands), we have evaluated the changes in potential vegetation belts during the last 20 years by comparing them with a previous study. Considering the intimate linkage between vegetation and climate, we used a methodology based on phytosociological knowledge, ordination techniques and geostatistics, using multivariate spatial interpolations of bioclimatic data. This has allowed us to spatially detect the variations experienced by eight vegetation units during the last 20 years and incorporating a set of vulnerability metrics. New bioclimatic and vegetation cartography are provided according to the current scenario studied (1990–2019). Our results indicate that summit vegetation, humid laurel forest and thermo-sclerophyllous woodland are the habitats that have experienced a very high area loss and mismatch index, strong changes, if we consider that we are only comparing a period of 20 years. Simultaneously, the more xeric vegetation belts, the dry laurel forest and the pine forest would have benefited from this new warmer and drier climate, by gaining area and experiencing strong upward movements. These changes have not been spatially uniform, indicating that the elevational gradient studied not explain completely our results, showing the influence of the complex island topography. Effective landscape management should consider current remnants, transition capacity and movement limitations to better understand current and future vegetation responses in a global change context.

Effect of Altitude Gradients on the Spatial Distribution Mechanism of Soil Bacteria in Temperate Deciduous Broad-Leaved Forests.

Soil bacteria are an important part of the forest ecosystem, and they play a crucial role in driving energy flow and material circulation. Currently, many uncertainties remain about how the composition and distribution patterns of bacterial communities change along altitude gradients, especially in forest ecosystems with strong altitude gradients in climate, vegetation, and soil properties. Based on dynamic site monitoring of the Baiyun Mountain Forest National Park (33°38'-33°42' N, 111°47'-111°51' E), this study used Illumina technology to sequence 120 soil samples at the site and explored the spatial distribution mechanisms and ecological processes of soil bacteria under different altitude gradients. Our results showed that the composition of soil bacterial communities varied significantly between different altitude gradients, affecting soil bacterial community building by influencing the balance between deterministic and stochastic processes; in addition, bacterial communities exhibited broader ecological niche widths and a greater degree of stochasticity under low-altitude conditions, implying that, at lower altitudes, community assembly is predominantly influenced by stochastic processes. Light was the dominant environmental factor that influenced variation in the entire bacterial community as well as other taxa across different altitude gradients. Moreover, changes in the altitude gradient could cause significant differences in the diversity and community composition of bacterial taxa. Our study revealed significant differences in bacterial community composition in the soil under different altitude gradients. The bacterial communities at low elevation gradients were mainly controlled by stochasticity processes, and bacterial community assembly was strongly influenced by deterministic processes at middle altitudes. Furthermore, light was an important environmental factor that affects differences. This study revealed that the change of altitude gradient had an important effect on the development of the soil bacterial community and provided a theoretical basis for the sustainable development and management of soil bacteria.

Mammalian community responses in relation to anthropogenic disturbances and resource gradients in the shade coffee forest ecosystem of Southwestern Ethiopia

Understanding the effects of variation in resource availability and habitat disturbance on the ecology of mammals is vital for successful conservation management. In this study, we examined how human disturbances, resource availability and elevation gradients influence mammal assemblages in both managed coffee forest and natural forest of the Belete-Gera National Forest Priority Area, southwestern Ethiopia. We surveyed mammals using motion-detecting infrared camera traps in 90 locations for a total of 4142 camera days. We measured distance from main roads and settlements as disturbance factors, and distance from water sources, key grazing sites, and forest edges and woody plant diversity as resource variables. We assessed the mammal assemblages in coffee forest and natural forests using generalized linear models. Further, we used linear modelling to compare the relationships of mammal detection rates by feeding guilds and body size to resource variables. In total, we recorded 8815 videos identifying 23 different mammal species. The mammal assemblages in coffee forests were negatively associated with increasing distances from key grazing sites, water sources, and elevation. In contrast, the association with increasing distance from the road and woody plant diversity was positive. In addition, herbivores and large (25–200 kg) and very large (≥200 kg) mammals, were all negatively associated with increasing distance from the natural forest edges. With the conversion of natural forest to coffee forest and the intensification of coffee forest management, sustainable management of key grazing sites, water sources, and diverse woody plant species will be essential to the conservation of mammals. In addition, to ensure mammal conservation, adjacent natural forests around coffee forests should also be protected.

Variation in soil erosion rate under typical land uses and vertical zones in an agricultural catchment of the Daliangshan region, Southwest China

AbstractThe Daliangshan region (DLS) is characterized by significant vertical differentiation in human activity and land use owing to the high elevation gradient, which may affect the soil erosion pattern in the vertical direction. However, the spatial variability of soil erosion rates along a hillslope at the catchment scale remains poorly understood. In this study, we used the cesium‐137 tracer technique to estimate soil erosion rates under different land uses and vertical zones from a small agricultural catchment, the Luowugou catchment in the DLS. Ten plots comprising four typical vertical zones (valley, low mountain, middle mountain and sub‐alpine) and five land‐use types (sloping farmland, grassland, abandoned farmland, forest land and horizontal terrace) were selected. In addition, two parallel downslope transects were built in each plot, and soil samples were collected at 3–7 m intervals along these transects. The results indicated that the soil erosion rates on sloping farmland (4.82 kg·m−2·y−1) and grassland (4.09 kg·m−2·y−1) were significantly higher than those on abandoned farmland (0.91 kg·m−2·y−1) and forest land (0.80 kg·m−2·y−1). In contrast, the horizontal terrace showed net deposition, with a deposition rate of 0.62 kg·m−2·y−1. The erosion rates varied across different zones, with the low mountain zone having the highest erosion rate (5.65 kg·m−2·y−1), followed by the middle mountain (2.96 kg·m−2·y−1) and subalpine (1.46 kg·m−2·y−1) zones, and the valley zone having the lowest erosion rate (1.28 kg·m−2·y−1). Furthermore, there were significant correlations (P < 0.05) between the soil erosion rates from different vertical zones and the proportion of sloping farmland, implying that sloping farmland plays a dominant role in shaping soil erosion along a vertical gradient. These comparisons suggest that the highest soil erosion rate occurred in the low mountain zone, indicating that the steeply sloping farmlands, resulting from migration from high‐altitude areas, have intensified soil erosion in the vertical zone. These findings highlight the role of agricultural activities originating from sloping farmlands in influencing soil erosion across different vertical zones, which has important implications for mitigating soil erosion and optimizing agricultural layout in the region.

An experimental test of niche versus dispersal limitation of the distribution limit of the Ghost Antler Lichen, Pseudevernia cladonia, along a temperate–boreal elevation gradient

Understanding the mechanisms underlying species’ distribution limits is critical for predicting how species may respond to environmental change. For species restricted to mountain summits, there is concern that climatic changes may result in increasingly restricted distributions. Two central mechanisms govern species distribution limits: (i) niche limitations–environmental conditions beyond distribution limits that are insufficient for survival and reproduction, and (ii) dispersal limitations that prevent colonization of suitable habitat beyond distribution limits. Here, we conducted a transplant experiment to examine the effect of niche versus dispersal limitation on the altitudinal distribution limit of the Ghost Antler Lichen ( Pseudevernia cladonia (Tuck.) Hale & Culb.) that, within Québec, Canada, is restricted to high-elevation mountain summits in the southeast. Along an elevation gradient, we transplanted individuals into sites within its distribution, at the edge, and beyond its distribution. We observed that survival and performance were greatest within its distribution and decreased markedly beyond its distribution, supporting our prediction that this lichen is niche limited along the elevation gradient. We suggest that cooler and more humid conditions at the summit are important environmental factors for this species’ persistence. Our findings suggest that projected climatic changes in these montane habitats may result in less suitable habitat for this species.

Climate‐competition tradeoffs shape the range limits of European beech and Norway spruce along elevational gradients across the Carpathian Mountains

Basic ecological theory suggests that a tradeoff between competitiveness and stress tolerance dictates species range limits at regional extents. However, empirical support for this key theory remains deficient because the necessary spatial and temporal coverage and scalability of field observations has rarely been achieved. We harnessed an extensive dendroecological network (> 22 000 tree‐ring samples from 816 forest inventory plots) to disentangle competition‐limited from climate‐limited growth in both overstory and understory trees. Growth synchrony among trees thereby served as an integral metric of climate sensitivity, an approach that we justify in supplementary analyses of growth responses to temperature, precipitation, and the standardized precipitation‐evapotranspiration index. Sampling plots were arranged along elevational climate and vegetation gradients throughout the Carpathian Mountains, ranging from mixed‐species lowland forests to coniferous forests at high elevations. With mixed‐effect modelling, we also identified non‐climatic factors (stand characteristics, species diversity, and disturbance history) that modulate spatial patterns in the growth rate and synchrony of European beech Fagus sylvatica and Norway spruce Picea abies. Beech exhibited reduced growth and increased climate sensitivity towards higher elevations but performed better when species diversity was higher. The growth of spruce increased towards its lower range boundary, but understory cohorts grew poorly under interspecific competition. Overall, climate sensitivity was lower in more productive stands with benign climatic conditions and in recently disturbed sites with reduced stand density. These contrasting performances at mid‐elevations where the two species overlap (900–1300 m a.s.l.) reflect their evolutionary history, which enables them to be competitive (beech) or cold‐stress tolerant (spruce). This history will affect interactions between the two species under climate warming and shape macroecological patterns in the Carpathian ecoregion and likely other parts of Europe. Our findings point to a growing advantage of competitively stronger species in montane and subalpine vegetation zones.

Influence of climate, soil and vegetation diversity on the leaf area index as measured by canopy hemispherical photography in tropical rainforests across a wide elevational gradient

Tropical rainforests (TRFs) play an important role in regulating the global climate and conserving biodiversity. Leaf area index (LAI) determines the capacity of TRFs for radiation interception and carbon sequestration via photosynthesis while also influencing the water loss from TRF canopies via transpiration. Elevational gradients in tropical environments provide an approach to investigate the influence of environmental variations on key vegetation properties such as the LAI. In this work we determined the concurrent, interactive influences of the elevational gradients of the environment (i.e. selected climatic and soil properties) and vegetation (tree diversity and structure) in determining the variation of LAI of one-hectare permanent sampling plots (PSPs) within TRFs across a wide elevational gradient (from 117 m to 2132 m above sea level). Eight rounds of canopy hemispherical photography were carried out at three-month intervals over a 24-month period from 2019 to 2022. Canopy LAI was estimated using HemiView image processing software. Long-term mean climatic data from 1990 to 2021 were extracted for the PSPs from monthly global weather database of CRU-TS-4.06-bias corrected with WorldClim-2.1. Key soil properties were measured at 0–15 cm and 15–30 cm depths via soil sampling. Tree diversity was determined by a complete census of all trees with equal or greater than 10 cm in diameter at breast height. Total tree biomass was estimated using allometric equations. Linear mixed model analysis of LAI showed significant (p < 0.05) variance for the random effects of elevation and elevation × time interaction. In a majority of measurement rounds, variance of LAI due to elevation was significant while at a majority of elevations, the fixed effect of measurement round on LAI was significant. Leaf area index showed significant linear reductions with elevation in all rounds, at rates ranging from 0.175 to 0.357 per 1000 m. Linear and multiple regression analyses identified increasing maximum cumulative soil water deficit, CSWDMax (an index of water deficit computed as the difference between evapotranspiration and precipitation), as the major climatic factor responsible for the reduction of LAI with elevation. Decreasing solar irradiance (SR) and increasing day-night temperature difference (DTR) with elevation also contributed to the observed LAI trend. Multiple regression analysis showed soil exchangeable potassium (KEx) and available phosphorus (PAv) influencing LAI positively while electrical conductivity (EC) and total nitrogen (NTot) influencing LAI negatively. Variation of Shannon-Wiener tree diversity index (H) and total tree biomass per hectare (TBM) contributed positively to the observed elevational variation of LAI. Factor analysis extracted two underlying factor constructs which accounted for 86 % of the combined variation in climate, soil and vegetation across the elevational gradient. Plot-wise scores of Factor 1, which had CSWDMax, SR, DTR, soil EC, NTot and H loading strongly and accounting for 70 % of the variation, showed a significant linear relationship with LAI. A cluster analysis incorporating the elevational variation of LAI, climate, soil and vegetation clearly classified the TRFs into four ranges of elevation at a linkage distance of 0.75. We conclude that LAI of TRFs in our study decreases with increasing elevation and identify increasing water deficits with elevation as the major climatic factor controlling this reduction.

UAV-based modelling of vegetation recovery under extreme habitat stresses in the water level fluctuation zone of the Three Gorges Reservoir, China

Impoundment of the Three Gorges Reservoir on the upper Yangtze River has remarkably altered hydrological regime within the dammed reaches, triggering structural and functional changes of the riparian ecosystem. Up to date, how vegetation recovers in response to compound habitat stresses in the water level fluctuation zone remains inexplicitly understood. In this study, plant above-ground biomass (AGB) in a selected water level fluctuation zone was quantified to depict its spatial and temporal pattern using unmanned aerial vehicle (UAV)-derived multispectral images and screened empirical models. The contributions of multiple habitat stressors in governing vegetation recovery dynamics along the environmental gradient were further explored. Screened random forest models indicated relatively higher accuracy in AGB estimation, with R2 being 0.68, 0.79 and 0.62 during the sprouting, growth, and mature periods, respectively. AGB displayed a significant linear increasing trend along the elevational gradient during the sprouting and early growth period, while it showed an inverted U-shaped pattern during late growth and mature period. Flooding duration, magnitude and timing were found to exert greater negative effects on plant sprouting and biomass accumulation and acted as decisive factors in governing the elevation-dependent pattern of AGB. Localized spatial variations in AGB were modulated by other stressors such as sediment burial, soil erosion, soil moisture and nutrient content. Occurrence of episodic summer floods and vegetation distribution were responsible for an inverted U-shaped pattern of AGB during the late growth and mature period. Generally, AGB reached its peak in August, thereafter an obvious decline by an unprecedent dry-hot climatic event. The water level fluctuations with cumulative flooding effects exerted substantial control on AGB temporal dynamics, while climatic condition played a secondary role. Herein, further restorative efforts need to be directed to screening suitable species, maintaining favorable soil condition, and improving vegetation pattern to balance the many trade-offs.

Patterns and driving factors of functional traits of desert species with different elevational distributions in the Tibetan Plateau and adjacent areas

Variations in functional traits serve as measures of plants’ ability to adapt to environment. Exploring the patterns of functional traits of desert plants along elevational gradients is helpful to understand the responses and adaptation strategies of species to changing environments. However, it is unknown whether the relationship between functional traits and elevation is affected by differences in the species’ elevational distributions (elevation preference and species’ range). Importantly, most researches have concerned with differences in mean trait values and ignored intraspecific trait variation. Here, we measured functional traits of desert plants along a wide elevational gradient in the Tibetan Plateau and adjacent areas and explored functional trait patterns over elevation in species with different elevational distributions. We decomposed trait variation and further investigated characterizations of intraspecific variation. Ultimately, the main drivers of trait variation were identified using redundancy analysis. We found that species’ elevational distributions significantly influenced the relationship of functional traits such as plant height, leaf dry matter content, leaf thickness, leaf nitrogen and carbon content with elevation. Species with a lower elevational preference showed greater trait variation than species with a higher elevational preference, suggesting that species that prefer high elevation are more conservative facing environmental changes. We provide evidence that interspecific trait variation in leaf thickness and leaf carbon content decreased with increasing species’ range, indicating that increased variations in resistance traits within species make greater responsiveness to environmental changes, enabling species a wider range. Elevation, temperature and precipitation were the main drivers of trait variation in species with a low elevational preference, while the effect of precipitation on trait variation in species with a high elevational preference was not significant. This study sheds new insights on how plants with different elevational distributions regulate their ecological strategies to cope with changing environments.

Exploring the spectral variation hypothesis for α- and β-diversity: a comparison of open vegetation and forests

Airborne hyperspectral imaging holds great promise for estimating plant diversity and composition, given its unprecedented combination of aerial coverage, spatial resolution, and spectral detail. Recently, there has been renewed attention toward the spectral variation hypothesis (SVH), which predicts that higher spectral variation is correlated with greater plant diversity. While several studies have highlighted methodological challenges involved with the SVH, there is little consensus about when it yields strong predictions of taxonomic, functional, and phylogenetic diversity. In part, this may be because prior studies have not explicitly considered how underlying environmental gradients drive changes in spectral and species composition. In this study, we tested the SVH separately in open vegetation (i.e. grasses and shrubs) and in forests at five sites across Canada. Generalized additive models revealed that spectral diversity was a better predictor of functional α-diversity than of taxonomic or phylogenetic α-diversity in both vegetation types. Mantel tests and Procrustes analyses revealed weak to moderate associations between spectral and plant β-diversity and composition in open vegetation, and moderate associations in forests. The better fit in forests appeared to be influenced by the presence of an elevational gradient and associated species turnover (from deciduous to coniferous trees); we observed weaker relationships when examining only a subset of this gradient. We suggest that the high variability in the strength of associations between plant and spectral diversity reported to date might be affected by the presence of environmental gradients. Finally, we found that different wavelength bands contributed to spectral α-diversity in open vegetation vs. forests, suggesting different spectral features are important for different vegetation types. In conclusion, spectral diversity is a potentially powerful tool for biodiversity assessment, but it requires a context-specific approach.

Debris cover effects on energy and mass balance of Batura Glacier in the Karakoram over the past 20 years

Abstract. The influence of supraglacial debris cover on glacier mass balance in the Karakoram is noteworthy. However, understanding of how debris cover affects the seasonal and long-term variations in glacier mass balance through alterations in the glacier's energy budget is incomplete. The present study coupled an energy–mass balance model with heat conduction within debris layers on debris-covered Batura Glacier in Hunza Valley to demonstrate the influence of debris cover on glacial surface energy and mass exchanges during 2000–2020. The mass balance of Batura Glacier is estimated to be -0.262±0.561 m w.e. yr−1, with debris cover accounting for a 45 % reduction in the negative mass balance. Due to the presence of debris cover, a significant portion of incoming energy is utilized for heating debris, leading to a large energy emission to the atmosphere via thermal radiation and turbulent sensible heat. This, in turn, reduces the melt latent heat energy at the glacier surface. We found that the mass balance exhibits a pronounced arch-shaped structure along the elevation gradient, which is associated with the distribution of debris thickness and the increasing impact of debris cover on the energy budget with decreasing elevation. Through a comprehensive analysis of the energy transfer within each debris layer, we have demonstrated that the primary impact of debris cover lies in its ability to modify the energy flux reaching the surface of the glacier. Thicker debris cover results in a smaller temperature gradient within debris layers, consequently reducing energy reaching the debris–ice interface. Over the past 2 decades, Batura Glacier has exhibited a trend towards less negative mass balance, likely linked to a decrease in air temperature and reduced ablation in areas with thin or sparse debris cover.

Non-linear response of Norway spruce to climate variation along elevational and age gradients in the Carpathians

Climate change, namely increased warming coupled with a rise in extreme events (e.g., droughts, storms, heatwaves), is negatively affecting forest ecosystems worldwide. In these ecosystems, growth dynamics and biomass accumulation are driven mainly by environmental constraints, inter-tree competition, and disturbance regimes. Usually, climate–growth relationships are assessed by linear correlation due to the simplicity and straightforwardness of modeling. However, applying this method may bias results, since the ecological and physiological responses of trees to environmental factors are non-linear, and usually bell-shaped.In the Eastern Carpathian, Norway spruce is at the southeasternmost edge of its natural occurrence; this region is thus potentially vulnerable to climate change. A non-linear assessment of climate–growth relationships using machine-learning techniques for Norway spruce in this area had not been conducted prior to this study. To address this knowledge gap, we analyzed a large tree-ring network from 158 stands, with over 3000 trees of varying age distributed along an elevational gradient. Our results showed that non-linearity in the growth-climate response of spruce was season-specific: temperatures from the previous autumn and current growing season, along with water availability during winter, induced a bell-shaped response. Moreover, we found that at low elevations, spruce growth was mainly limited by water availability in the growing season, while winter temperatures are likely to have had a slight influence along the entire elevational gradient. Furthermore, at elevations lower than 1400 m, spruce trees were also found to be sensitive to previous autumn water availability. Overall, our results shed new light on the response of Norway spruce to climate in the Carpathians, which may aid in management decisions.

Environmental and Biogeographic Drivers behind Alpine Plant Thermal Tolerance and Genetic Variation.

In alpine ecosystems, elevation broadly functions as a steep thermal gradient, with plant communities exposed to regular fluctuations in hot and cold temperatures. These conditions lead to selective filtering, potentially contributing to species-level variation in thermal tolerance and population-level genetic divergence. Few studies have explored the breadth of alpine plant thermal tolerances across a thermal gradient or the underlying genetic variation thereof. We measured photosystem heat (Tcrit-hot) and cold (Tcrit-cold) thresholds of ten Australian alpine species across elevation gradients and characterised their neutral genetic variation. To reveal the biogeographical drivers of present-day genetic signatures, we also reconstructed temporal changes in habitat suitability across potential distributional ranges. We found intraspecific variation in thermal thresholds, but this was not associated with elevation, nor underpinned by genetic differentiation on a local scale. Instead, regional population differentiation and considerable homozygosity within populations may, in part, be driven by distributional contractions, long-term persistence, and migrations following habitat suitability. Our habitat suitability models suggest that cool-climate-distributed alpine plants may be threatened by a warming climate. Yet, the observed wide thermal tolerances did not reflect this vulnerability. Conservation efforts should seek to understand variations in species-level thermal tolerance across alpine microclimates.

Substantial variation of the two‐dimensional spectrum of senescent leaf in subalpine forest along elevational gradients

AbstractLeaf senescence have shed light on its contribution to the recovery of nutrients and signaling of the transition from the active to the dormant stage in winter. The manner by which climatic and edaphic factors and plant phylogeny affect the senescent leaf economics spectrum (more mineral elements included) of different growth habits along elevational gradients in mountain ecosystems is highly uncertain. To fill this knowledge gap, we examined 15 representative subalpine forest species' senescent leaf functional traits (i.e., specific leaf area [SLA], leaf dry matter content [DMC], pH, carbon [C], nitrogen [N], phosphorus [P], potassium [K], calcium [Ca], sodium [Na], magnesium [Mg], manganese [Mn], aluminum [Al], iron [Fe], C:N, N:P, and C:P ratios) to determine the senescent leaf economics spectrum along elevational gradients in the Hengduan Mountains, China. Our results demonstrate that all the functional traits of senescent leaf showed strong correlations with one another, and K was observed as the hub for the leaf economics spectrum. Irrespective of the difference among growth habits (arbor vs. shrub), leaf habits (deciduous vs. evergreen), and leaf types (broad vs. needle), the variations in the two‐dimensional spectrum of the senescent leaf trait exhibited uniformly positive associations with elevation, primarily attributed to climatic drivers. However, the modulation of the senescent leaf economics spectrum by soil properties and plant phylogeny was surprisingly modest. Collectively, our results revealed that the resource trade‐off of senescent leaf showed a trend from acquisition to conservation along elevational gradients, which could broaden the plant economics spectrum to include senescent leaf.