Large Elevational Gradient Research Articles

Variable species establishment in response to microhabitat indicates different likelihoods of climate‐driven range shifts

Climate change is causing geographic range shifts globally, and understanding the factors that influence species' range expansions is crucial for predicting future biodiversity changes. A common, yet untested, assumption in forecasting approaches is that species will shift beyond current range edges into new habitats as they become macroclimatically suitable, even though microhabitat variability could have overriding effects on local population dynamics. We aim to better understand the role of microhabitat in range shifts in plants through its impacts on establishment by 1) examining microhabitat variability along large macroclimatic (i.e. elevational) gradients, 2) testing which of these microhabitat variables explain plant recruitment and seedling survival, and 3) predicting microhabitat suitability beyond species range limits. We transplanted seeds of 25 common tree, shrub, forb and graminoid species across and beyond their current elevational ranges in the Washington Cascade Range, USA, along a large elevational gradient spanning a broad range of macroclimates. Over five years, we recorded recruitment, survival, and microhabitat (i.e. high resolution soil, air and light) characteristics rarely measured in biogeographic studies. We asked whether microhabitat variables correlate with elevation, which variables drive species establishment, and whether microhabitat variables important for establishment are already suitable beyond leading range limits. We found that only 30% of microhabitat parameters covaried with elevation. We further observed extremely low recruitment and moderate seedling survival, and these were generally only weakly explained by microhabitat. Moreover, species and life stages responded in contrasting ways to soil biota, soil moisture, temperature, and snow duration. Microhabitat suitability predictions suggest that distribution shifts are likely to be species‐specific, as different species have different suitability and availability of microhabitat beyond their present ranges, thus calling into question low‐resolution macroclimatic projections that will miss such complexities. We encourage further research on species responses to microhabitat and including microhabitat in range shift forecasts.

Species richness: A pivotal factor mediating the effects of land use intensification and climate on grassland multifunctionality

Abstract Temperate seminatural grasslands harbour unique biodiversity, support livestock farming through forage production, and deliver many essential ecosystem services (ESs) to human society; they are highly multifunctional. However, temperate grassland ecosystems are also among the most threatened ecosystems on earth due to land use and climate changes. Understanding how biodiversity, climate and land use intensification impact grassland multifunctionality through complex direct and indirect pathways is critical to better anticipate the future of these fragile ecosystems. Here, we evaluate how local plant species richness (SR) modulates the effect of land use intensification and climate on grassland multifunctionality (using six key ESs: biomass productivity and stability, forage quality, carbon storage, pollination and local plant rarity) in the French Massif Central, the largest grassland in Western Europe. We sampled 100 grasslands with contrasted fertilization rates and SR, over large elevational and latitudinal gradients related to variation in mean annual temperature (MAT), and drought severity (DS), two key climate change drivers predicted to increase in the future. Using a confirmatory path analysis, we found that SR was the main driver of multifunctionality. We also found significant SR × MAT and SR × fertilization interactions suggesting that warm climate and high fertilization rates alter the biodiversity–ecosystem multifunctionality relationships. Furthermore, increasing temperature and fertilization indirectly influenced multifunctionality by decreasing SR and consequent multifunctionality in warm lowland and highly fertilized grasslands compared to colder montane grasslands or less fertilized ones. DS only impacted some ES individually (e.g. forage quality). Synthesis and applications: We identified species richness (SR) as a pivotal factor mediating the effects of land use intensification and climate on multifunctionality through both direct and indirect pathways. Failing to account for changes in SR could thus bias any prediction of, or aggravate, the effects of land use intensification and climate change on ecosystem services delivery in temperate grassland ecosystems. Considering that SR, mean annual temperature and fertilization are major proxies of three main global change drivers (biodiversity loss, climate change and land use intensification) our study may help to better anticipate the effect of multiple interacting global change drivers on grassland ecosystems.

Co-limitation of resources reveals adaptations of a tropical tree to heterogeneous environments along an elevational cline

IntroductionPlant species often exhibit significant variation in functional traits in populations along elevational gradients to cope with varying stress conditions. While plant development has been assumed to be most limited by a single resource, growing evidence suggests the potential for interactions of co-limiting resources to impact plant performance. Here, we aimed to determine how light, nitrogen, and water availability influence the growth and physiology of different populations of koa (Acacia koa), a tree species of concern that occurs across a large elevational gradient in tropical Hawaii, United States.MethodsPopulations from three seed sources [low (L), mid (M), and high (H) elevation] were grown in a controlled greenhouse experiment and exposed to co-limiting light, water, and nutrient (nitrogen) conditions. Light response, gas exchange, water status, resource use efficiency, nutrients and shoot non-structural carbohydrate concentrations, and growth and biomass allocation responses were quantified.ResultsWe found that resource co-limitation sometimes interacted to determine responses of the measured parameters. In general, the low elevation (L) koa population was more sensitive to conditions where both moisture and nutrients were limiting, while the high elevation (H) koa population was more sensitive to conditions where either light and moisture or light and nitrogen were co-limiting. The M population performed well overall regardless of resource limitation.DiscussionOur findings lend support to the theory that multiple resources limit growth and physiology of populations rather than the traditional view of a single resource limiting performance. Therefore, the possibility that multiple resource limitations drive population differences should be considered when developing population-based guidelines for forest and tree species restoration.

Leaf carbon isotope tracks the facilitation pattern of legume shrubs shaped by water availability and species replacement along a large elevation gradient in Trans-Himalayas.

Understanding patterns and mechanisms of nurse plant facilitation is important to predict the resilience of arid/semi-arid ecosystems to climate change. We investigate whether water availability and nurse species turnover interact to shape the facilitation pattern of widespread legume shrubs along a large elevation gradient. We also investigate whether leaf δ13C of nurse plants can track the facilitation pattern. We measured the relative interaction index (RII) of the number of species within and outside the canopy of two widespread legume shrub species (Caragana gerardiana and Caragana versicolor) alternatively distributed along a large elevation gradient in the Trans-Himalayas. We also assessed the proportional increase of species richness (ISR) at the community level using the paired plot data. To determine site-specific water availability, we measured the leaf δ13C of nurse shrubs and calculated the Thornthwaite moisture index (MI) for each elevation site. Elevational variations in RII, ISR and δ13C were mainly explained by the MI when the effects of soil nitrogen and plant traits (leaf nitrogen and shrub size) were controlled. Variations in RII and ISR across the two nurse species were explained better by δ13C than by smoothly changing climatic factors along elevation. At the transition zone between the upper limit of C. gerardiana (4100 m) and the lower limit of C. versicolor (4200 m), RII and ISR were much higher in C. versicolor than in C. gerardiana under a similar MI. Such an abrupt increase in facilitation induced by nurse species replacement was well tracked by the variation of δ13C. Water availability and nurse species replacement are crucial to shaping facilitation patterns by legume shrubs along a large elevation gradient in dry mountainous regions, such as the Trans-Himalayas. Turnover in nurse species under global change might significantly alter the pattern of nurse plant facilitation associated with water availability, which can be well tracked by leaf δ13C.

New species of <i>Lepanthes</i> (Orchidaceae: Pleurothallidinae) to honour “Bachué”, the mythological mother of the indigenous Muisca people.

In an expedition of 341 plots across a large elevation (1,100-3,880 m) and spatial gradient (~270 km) in the eastern cordillera we found a new species of the genus Lepanthes in Santuario de Fauna y Flora de Iguaque, Boyaca, Colombia. We propose L. bachue as a new species. It is most similar to L. papallactae but it can be distinguished by its proliferous plants (vs. non proliferous), the petals with the upper lobe 2.5 mm long, the lower lobe 4.5 mm long, larger than the upper one, and the margins fimbriate (vs. lobes subequal, 4.5 mm long and shortly pubescent) and the lip with the blades oblong, sub-sigmoid, adnate to the middle of the column with a short oblong, bifid, yellow appendix hiding in the middle (vs. blades narrowly elliptical-oblong, connate to the column above the middle with a recurved, pedunculate, biglandular appendix). Our large elevational and geographical sampling suggest that the species is geographically restricted and have high habitat specialization, thus urging to protect its natural habitat and population.

Does pollinator dependence decrease along elevational gradients?

Plants have long been thought to be less dependent on pollinators for seed production at higher elevations due to adverse pollination environments. However, recent research has yet to consistently support the generality of this expectation. In this study, we asked whether pollinator dependence decreases along an elevational gradient and how it varies with various reproductive traits. To answer these questions, we quantified pollinator–plant associations and various reproductive traits for 112 flowering plants spanning a large elevational gradient (990–4260 m a.s.l.) in the Qinghai-Tibet Plateau. We found that flowering plants in the Qinghai-Tibet Plateau region are highly dependent on pollinators for seed production (76.2% of seed production was contributed by animal pollinators and 44.6% of plants would produce no seed without pollinator visitation). Contrary to our expectation, there was no significant elevational gradient in pollinator dependence index. Although the pollinator dependence index was not significantly correlated with pollen limitation, flower size, floral longevity, or reward type, it was correlated with compatibility status and flowering time. These findings indicate that pollinator dependence does not decrease along an elevational gradient in the Qinghai-Tibet Plateau. Our study also highlights the severe vulnerability of flowering plant seed production to pollinator declines under global change in the Qinghai-Tibet Plateau region, particularly for early-flowering or self-incompatible plants growing at higher elevations (e.g., subnival belt).

Tree species composition, stand structure and distribution patterns across three Kashmir Himalayan forests, India

ABSTRACT Himalayan ecosystems provide a unique opportunity to analyze the determinants of species richness across large elevation gradients. Understanding forest diversity and structure is fundamental to set conservation priorities. A quantitative assessment of tree species was conducted in Kashmir Himalayan forests to ascertain their composition, stand structure and distribution in 143 plots of 50 × 50 m2. Altogether, 13 species were recorded, ranging from five in subalpine (SA) forests to 10 in mixed conifer (MC) forests. There was a compositional dissimilarity among forest types. Pinus wallichiana was the most important species in low-level blue pine (BP) forests, whereas Abies pindrow prevailed in mid-elevation MC and high-elevation SA forests. Pinaceae contributed around 98% of stems and was the most speciose family, followed by Sapindaceae and Betulaceae. Stand density and basal area differed among forest types and were significantly correlated with elevation and slope. The tree diameter class distribution displayed an approximate reverse J-shaped pattern indicating the influence of disturbance. As the first two axes of the canonical correspondence analysis explained more than 93% of the inertia in the species-environment relation, elevation and slope are the main drivers of species distribution. Information about these forest attributes could provide better ecological insights for sustainable forest management.

Impact of vegetation and climate types on vertical stratification of wood‐boring longhorn and bark beetles (Coleoptera: Cerambycidae and Scolytinae) along altitude gradients in Yunnan, Southwest China

Abstract1. Better understanding of wood‐boring beetle distribution patterns and underlying mechanisms is a central issue for forest protection and management. The primary aim of this study was to detect how these pest guilds are distributed in forests and optimize elimination and control strategies.2. We placed flight intercept traps in the canopy and understory areas of three climatically different forest types across a large elevation gradient and focussed on two important wood‐boring beetles, longhorn and bark beetles, in Yunnan, Southwest China.3. The results showed that species richness and abundance of two selected wood‐boring beetles between the canopy and understory areas had different patterns across the climatically different forest vegetation types. Bark and longhorn beetles tended to stay in understory and canopy areas, respectively, based on the recorded abundance data. However, richness data showed different responses to the climatically different forest types for both longhorn and bark beetles assemblages. Bark beetles species richness did not significantly differ between the canopy and understory areas across all three forest types in the present study. Longhorn beetles had significantly higher richness values in the canopy areas of tropical and subtropical forests but lower in temperate forest.4. The community compositions of both the longhorn and bark beetles varied greatly among forest vegetation types but relatively little between the canopy and understory areas across the vegetation types. Thus, considering different heights and positions in different forests during trap deployment is necessary and needed to optimize wood‐boring pest control strategies when various forest types and pests are targeted.

Strong partitioning of soil bacterial community composition and co-occurrence networks along a small-scale elevational gradient on Zijin Mountain

The elevational distributions of bacterial communities in natural mountain forests, especially along large elevational gradients, have been studied for many years. However, the distributional patterns that underlie variations in soil bacterial communities along small-scale elevational gradients in urban ecosystems are not yet well understood. Using Illumina MiSeq DNA sequencing, we surveyed soil bacterial communities at three elevations on Zijin Mountain in Nanjing City: the hilltop (300 m a.s.l.), the hillside (150 m a.s.l.), and the foot of the hill (0 m a.s.l.). The results showed that edaphic properties differed significantly with elevation. Bacterial community composition, rather than alpha diversity, strongly differed among the three elevations (Adonis: R2 = 0.12, P<0.01). Adonis and DistLM analyses demonstrated that bacterial community composition was highly correlated with soil pH, elevation, total nitrogen (TN), and dissolved organic carbon (DOC). The degree scores, betweenness centralities, and composition of keystone species were distinct among the elevations. These results demonstrate strong elevational partitioning in the distributions of soil bacterial communities along the gradient on Zijin Mountain. Soil pH and elevation together drove the small-scale elevational distribution of soil bacterial communities. This study broadens our understanding of distribution patterns and biotic co-occurrence associations of soil bacterial communities from large elevational gradients to short elevational gradients.

Intraspecific morphological variation of Bellidiastrum michelii (Asteraceae) along a 1,155 m elevation gradient in the Tatra Mountains.

Plant species that inhabit large elevation gradients in mountain regions are exposed to different environmental conditions. These different conditions may influence plant morphology via plastic responses and/or via genetic adaptation to the local environment. In this study, morphological variation was examined for Bellidiastrum michelii Cass. (Asteraceae) plants growing along a 1,155 m elevation gradient in the Tatra Mountains in Central Europe. The aim was to contribute to gaining a better understanding of within-species morphological variation in a mountain species across elevation gradients. Twelve morphological traits, which were measured for 340 plants collected from 34 sites, were plotted against elevation using Generalised Additive Models. Significant variation in B. michelii morphology was found across the elevation gradient. Plant size, in the form of plant height, total aboveground mass and total leaf mass, decreased significantly with increasing elevation. Similarly, floral traits, such as flower head mass, total flower mass, individual flower mass, flower head diameter and ligulate and tubular flower length, also decreased significantly with increasing elevation. However, the changes in these floral traits were not as large as those observed for plant size traits. Interestingly, the number of flowers produced by the plant, both ligulate and tubular, did not change across the studied elevation gradient. In this study, elevation was found to be an important gradient across which significant intraspecific morphological variation occurred in a mountain plant. These morphological changes may have occurred in response to various abiotic and biotic factors that change along elevation gradients.

A Novel Rapid GNSS Network Solution in Mountainous Region Monitoring considering the Tropospheric Delay at Ground Points

Due to the short peak observation time of global navigation satellite systems (GNSS), the accuracy of the tropospheric delay estimation and the positioning are poor. In this study, a rapid GNSS network solution for mountainous regions is presented. The high‐precision tropospheric delay at ground points is obtained from long‐term ground observation data and used as a priori constraint in the double‐difference equation of short‐time synchronous peak observations to realize rapid and high‐precision positioning. Chinese mountain survey networks with large elevation gradient (1000~2000 m) were selected for the experimental verification of the proposed method. The results show that the rapid peak positioning method weakened the effect of the residual tropospheric delay caused by the elevation difference, significantly improving the accuracy and reliability of the results. The positioning accuracy of the peak in upward direction was better than 1.1 cm, which meets the requirements of rapid short‐span (~1 h) high‐precision monitoring and achieves 24 h positioning accuracy. Compared with the traditional solution strategy, the precision of the method with respect to the north (N), east (E), upward (U), and zenith tropospheric delay (ZTD) significantly improved. The accuracy of U improved by more than 47%. Therefore, based on the high accuracy and reliability, information of ground stations can be fully utilized to significantly reduce the peak observation time and the operation costs of surveys in mountain regions.

Reduced tree density and basal area in Andean forests are associated with bamboo dominance

Forest structure and composition play an essential role in determining the carbon storage capacity of tropical forests. Andean forests, with great potential for carbon accumulation, include large expanses of high-density woody bamboo communities. Woody bamboos can potentially alter forest structure, composition and dynamics and thus can affect carbon storage capacity; however, they are commonly excluded from forest monitoring and modelling. With the aim of documenting patterns of bamboo abundance and disentangling its association with forest structure, we carried out a bamboo census in seven 1-ha long-term forest monitoring plots situated across a large elevation gradient (1000–3600 m a.s.l.) in the Peruvian Andes. We determined that bamboo is a dominant plant group in the study area. In every plot, bamboos were the most common genera in terms of number of stems, and in two of the plots bamboo species were among those with the greatest basal area. We used a combination of Generalized linear mixed models (GLMM) and structural equation modelling (SEM) to hypothesize a causal framework and determine the direction and size of the effects of bamboo abundance (basal area) on number of individual trees, total tree basal area, mean tree basal area, mean tree growth rate and tree mortality rate. We found an overall negative association between bamboo abundance and total tree basal area driven mainly by reduced tree density (directly and indirectly mediated by an increase in tree mortality). However, the decrease in tree density and the increase in tree mortality are also associated with a small increase in tree diameter (mean tree basal area). Overall, the negative association between bamboo abundance and tree basal area suggests a lower biomass accumulation and thus a lower carbon storage capacity of trees in Andean forests where bamboo is dominant. Our results, which show the importance of bamboo in determining forest function, highlight the need for including bamboo in monitoring efforts and modeling studies.

Cluster-Based Empirical Tropospheric Corrections Applied to InSAR Time Series Analysis

Interferometric synthetic aperture radar (InSAR) allows for mapping of crustal deformation on land with high spatial resolution and precision in areas with high signal-to-noise ratios. Efforts to obtain precise displacement time series globally, however, are severely limited by radar path delays within the troposphere. The tropospheric delay is integrated along the full path length between the ground and the satellite, resulting in correlations between the interferometric phase and elevation that can vary dramatically in both space and time. We evaluate the performance of spatially variable, empirical removal of phase-elevation dependence within SAR interferograms through the use of the $K$ -means clustering algorithm. We apply this method to both synthetic test data, as well as to C-band Sentinel-1a/b time series acquired over a large area in south-central Mexico along the Pacific coast and inland—an area with a large elevation gradient that is of particular interest to researchers studying tectonic- and anthropogenic-related deformation. We show that the clustering algorithm is able to identify cases where tropospheric properties vary across topographic divides, reducing total root mean square (rms) by an average of 50%, as opposed to a spatially constant phase-elevation correction, which has insignificant error reduction. Our approach also reduces tropospheric noise while preserving test signals in synthetic examples. Finally, we show the average standard deviation of the residuals from the best-fit linear rate decreases from approximately 3 to 1.5 cm, which corresponds to a change in the error on the best-fit linear rate from 0.94 to 0.63 cm/yr.

Does social thermal regulation constrain individual thermal tolerance in an ant species?

In ants, social thermal regulation is the collective maintenance of a nest temperature that is optimal for individual colony members. In the thermophilic ant Aphaenogaster iberica, two key behaviours regulate nest temperature: seasonal nest relocation and variable nest depth. Outside the nest, foragers must adapt their activity to avoid temperatures that exceed their thermal limits. It has been suggested that social thermal regulation constrains physiological and morphological thermal adaptations at the individual level. We tested this hypothesis by examining the foraging rhythms of six populations of A. iberica, which were found at different elevations (from 100 to 2,000m) in the Sierra Nevada mountain range of southern Spain. We tested the thermal resistance of individuals from these populations under controlled conditions. Janzen's climatic variability hypothesis (CVH) states that greater climatic variability should select for organisms with broader temperature tolerances. We found that the A. iberica population at 1,300m experienced the most extreme temperatures and that ants from this population had the highest heat tolerance (LT50=57.55°C). These results support CVH's validity at microclimatic scales, such as the one represented by the elevational gradient in this study. Aphaenogaster iberica maintains colony food intake levels across different elevations and mean daily temperatures by shifting its rhythm of activity. This efficient colony-level thermal regulation and the significant differences in individual heat tolerance that we observed among the populations suggest that behaviourally controlled thermal regulation does not constrain individual physiological adaptations for coping with extreme temperatures.

Variation in Stem Xylem Traits is Related to Differentiation of Upper Limits of Tree Species along an Elevational Gradient

The distribution limits of many plants are dictated by environmental conditions and species’ functional traits. While many studies have evaluated how plant distribution is driven by environmental conditions, there are not many studies investigating xylem vessel properties with altitude, and whether these traits correlate with altitudinal distribution of tree. Here, we investigated the upper limits of distribution for ten deciduous broadleaf tree species from three temperate montane forest communities along a large elevational gradient on the north-facing slope of Changbai Mountain in Northeast China. We measured stem xylem traits associated with a species’ ability to transport water and resist freezing-induced cavitation that theoretically represent important adaptations to changes in climatic conditions along the elevational gradient. Hydraulically weighted vessel diameter (Dh) was negatively correlated with with the upper limit across the ten studied tree species; however, the correlation seems to be driven by the large differences between ring- and diffuse-porous tree species groups. The ring-porous tree species (e.g., Fraxinus mandshurica Rupr., Maackia amurensis Rupr. et Maxim., and Phellodendron amurense Rupr.) had considerably wider vessels than the diffuse-porous species and were all limited to low-elevation communities. The coefficient of variation (CV) for Dh was 0.53 among the 10 studied species, while the intraspecific analysis showed that the highest CV was only 0.22 among the 10 species. We found no evidence of a relationship between Dh and the upper limits across the seven diffuse-porous species. In contrast to elevation, hydraulic-related xylem traits had no clear patterns of change with precipitation, indicating that hydraulic functionality was largely decoupled from the influences of precipitation in the study area. This finding suggests that xylem traits are associated with altitudinal limits of species distribution, which is mostly evidenced by the contrasts between ring- and diffuse-porous species in xylem anatomy and their altitudinal distributions.

Geographical distribution of dioecy and its ecological correlates based on fine‐scaled species distribution data from a subtropical island

AbstractDioecy is a rather rare sexual expression system guarantees outcrossing to avoid the deleterious effects of inbreeding. The incidence of dioecy varied among local floras and suggested inclining to tropical and oceanic environments, but its eco‐correlates received little research attention. In this article, we explored geographical patterns and variations in sexual expression systems of angiosperms in mountainous environments of Taiwan, a subtropical island in East Asia. A comprehensive geo‐database of vegetation inventories and herbarium specimens were used to identify eco‐correlates causing variations in the horizontal geographical extent and along a large elevational gradient of more than 3,500 m. We found the average incidence of dioecy in the flora of Taiwan to be 8.2%, but it exhibits geographical variations from islets in the Taiwan Strait to the Pacific Ocean. Detailed studies on the main island of Taiwan revealed that the incidence of dioecy varied among land cover types and elevational zones. An apparent two‐step decreasing pattern of dioecy percentages with elevation was found, with the highest proportion in the lowlands (0–600 m; 23.96%), followed by middle elevations (600–2,700 m; 20.87%) and subalpine regions (2,700–3,900 m; with a range of 11.38–0%). We found that spatial variations of dioecy were associated with eco‐correlates of land cover, elevation, woodiness, species richness, and mean annual temperature. Results of this study partially support Bawa's hypothesis of a higher incidence of dioecy on oceanic islands, and is consistent with Baker and Cox's observations of richer dioecious species on high‐mountain islands in the tropics and subtropics.

Strengthening mycorrhizal research in South America.

Strengthening mycorrhizal research in South America.

Simulating Future Runoff in a Complex Terrain Alpine Catchment with EURO-CORDEX Data

AbstractWith large elevation gradients and high hydrometeorological variability, Alpine catchments pose special challenges to hydrological climate change impact assessment. Data from seven regional climate models run within the Coordinated Regional Climate Downscaling Experiments (CORDEX), each driven with a different boundary forcing, are used to exemplarily evaluate the reproduction of observed flow duration curves and access the future discharge of the Ammer River located in Alpine southern Germany applying the hydrological simulation model called the Water Flow and Balance Simulation Model (WaSiM). The results show that WaSiM reasonably reproduces the observed runoff for the entire catchment when driven with observed precipitation. When applied with CORDEX evaluation data (1989–2008) forced by ERA-Interim, the simulations underestimate the extreme runoff and reproduce the high percentile values with errors in the range from −37% to 55% with an ensemble mean of around 15%. Runs with historical data 1975–2005 reveal larger errors, up to 120%, with an ensemble mean of around 50% overestimation. Also, the results show a large spread between the simulations, primarily resulting from deficiencies in the precipitation data. Results indicate future changes for 2071–2100 in the 99.5th percentile runoff value of up to 9% compared to 1975–2005. An increase in high flows is also supported by flow return periods obtained from a larger sample of highest flows over 50 years, which reveals for 2051–2100 lower return periods for high runoff values compared to 1956–2005. Obtained results are associated with substantial uncertainties leading to the conclusion that CORDEX data at 0.11° resolution are likely inadequate for driving hydrologic analyses in mesoscale catchments that require a high standard of fidelity for hydrologic simulation performance.

Ashes to ashes: Characterization of organic matter in Andosols along a 3400 m elevation transect at Mount Kilimanjaro using analytical pyrolysis

Tropical mountain ecosystems cover a broad variety of climatic and vegetation zones and are global hotspots of biodiversity. These ecosystems are severely threatened by climate and land-use change, which also strongly affect soil properties. Mt. Kilimanjaro, with its large elevation gradient and relatively homogeneous geology of volcanic rocks and ashes, provides a unique opportunity to study and interpret soil organic matter (SOM) responses to climatic changes.Our objectives were to identify key SOM compounds in six elevation zones (covering ecosystems from tropical dry-lowland, through montane forest, up to alpine heathlands) that are affected by the climatic changes along a 3400 m transect, and to relate these SOM changes to ecosystem specific characteristics. The SOM composition in four topsoils (0–10 cm) samples per ecosystem was characterized by analytical double-shot pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS). Evolving-gas analysis-mass spectrometry (EGA-MS) was used to quantitatively compare the thermal desorption (first shot: <280 °C) and pyrolysis step (second shot: 280–600 °C).The percentage of thermally desorbed compounds increased 10 fold from lowland (<900 m) to mountain forest soils (>2000 m), followed by a 40% decrease in alpine ecosystems (>4000 m). Alkanes/-enes/-ols contributed between 4% and 30% to the identified SOM composition, with a maximum at mid elevation (2120 m). Fatty acids and fatty acid esters contributed with <3% to SOM composition and decreased to a minimum of <1% at Podocarpus forest soils (2900 m), followed by a re-increase at higher elevation. The percentage of lignin-derived compounds followed a similar pattern but also responded to reduced woody inputs above the tree line.Two main factors that seem to affect SOM quality and composition at Mt. Kilimanjaro were: 1) the rate and composition of organic matter inputs that in turn are controlled by climatic characteristics and the vegetation type and 2) the decomposition rate and efficiency, mainly controlled by soil pH, temperature and water availability. High forest productivity at mid elevations (2200 m) leads to high amounts of volatile compounds and increases stable SOM pools. The overall carbon accumulation in Andosols of Mt. Kilimanjaro is linked to the percentage of bound lipids (mainly alkanes, alkenes and alcohols), while site specific input patterns (e.g. vegetation or wild fires) are strongly reflected by sterols, lignin derived compounds or polycyclic aromatic compounds in SOM.

Daily Maximum Temperatures Induce Lagged Effects on Leaf Unfolding in Temperate Woody Species Across Large Elevational Gradients.

The timing of leaf unfolding in temperate woody species is predominantly controlled by the seasonal course of temperature in late winter and early spring. However, quantifying lagged temperature effects on spring phenology is still challenging. Here, we aimed at investigating lagged and potentially non-linear effects of daily maximum temperatures on the probability of leaf unfolding in temperate woody species growing across large elevational gradients. We analyzed 5280 observations of leaf-out time of four tree species (European beech, horse chestnut, European larch, Norway spruce) and one shrub species (common hazel) that were recorded by volunteers over 40 years at 42 locations in Switzerland. We used a case-crossover sampling design to match leaf-out dates with control dates (i.e., dates before or after leaf-out), and analyzed these data with conditional logistic regression accounting for lagged temperature effects over 60 days. Multivariate meta-analyses were used to synthesize lagged temperature and elevational effects on leaf unfolding across multiple phenological stations. Temperature effects on the probability of leaf unfolding were largest at relatively short lags (i.e., within ca. 10 days) and decreased with increasing lags. Short- to mid-term effects (i.e., within ca. 10 to 20 days) were larger for late-leafing species known to be photoperiod-sensitive (beech, Norway spruce). Temperature effects increased for the broadleaved species (horse chestnut, hazel, beech) with decreasing elevation, particularly within ca. 10 to 40 days, i.e., leaf unfolding occurs more rapidly at low elevations for a given daily maximum temperature. Our novel findings provide evidence of cumulative and long-term temperature effects on leaf unfolding, whereby the efficiency of relatively high temperatures to trigger leaf-out becomes higher shortly before bud burst. These lagged associations between temperature and leaf unfolding improve our understanding of phenological responses across temperate woody species with differing ecological requirements that occur along elevational gradients.