Upward Expansion Research Articles

From Africa to the Alps: risk assessment on an invasion by Cacyreus marshalli (Butler, 1898)

Cacyreus marshalli (Butler, 1898) is the only alien butterfly species in Italy, introduced from Southern Africa via the trade of ornamental Pelargonium plants (family Geraniaceae). In 2008, Quacchia and colleagues demonstrated that if Pelargonium plants are not available, females can lay eggs on Geranium spp., developing fertile offspring. C. marshalli is a thermophilous species, but in recent years some adults have been observed flying far from villages and at high altitudes (up to 2400 m a.s.l.) in the Orco valley (Gran Paradiso National Park, Aosta Valley). Due to the potential threat to native Geranium-consuming lycaenids and to evaluate the risk of naturalisation, we investigated: (i) dispersal abilities of gravid females, outside the National Park to avoid accidental establishment of the invasive species; (ii) pelargonium distribution and abundance; (iii) oviposition behaviour and preimaginal distribution; (iv) citizen care practices with pelargoniums. Pelargoniums were counted in the Orco Valley (5455 plants) and eggs and larvae were counted on 348 pelargoniums chosen on the basis of isolation and altitude. Flight experiments suggested that females were able to overcome barriers and fly at least 550 m looking for host plants. Eggs and larvae were unexpectedly abundant, but models showed that there was a temperature limit which prevented upward expansion of C. marshalli. Citizens were given a questionnaire to complete to investigate their propensity to replace pelargonium with other ornamental plants. We discuss the possibility of eradicating C. marshalli in the protected area in the light of our results.

Climate change, wildfire, and vegetation shifts in a high-inertia forest landscape: Western Washington, U.S.A.

Future vegetation shifts under changing climate are uncertain for forests with infrequent stand-replacing disturbance regimes. These high-inertia forests may have long persistence even with climate change because disturbance-free periods can span centuries, broad-scale regeneration opportunities are fewer relative to frequent-fire systems, and mature tree species are long-lived with relatively high tolerance for sub-optimal growing conditions. Here, we used a combination of empirical and process-based modeling approaches to examine vegetation projections across high-inertia forests of Washington State, USA, under different climate and wildfire futures. We ran our models without forest management (to assess inherent system behavior/potential) and also with wildfire suppression. Projections suggested relatively stable mid-elevation forests through the end of the century despite anticipated increases in wildfire. The largest changes were projected at the lowest and uppermost forest boundaries, with upward expansion of the driest low-elevation forests and contraction of cold, high-elevation subalpine parklands. While forests were overall relatively stable in simulations, increases in early-seral conditions and decreases in late-seral conditions occurred as wildfire became more frequent. With partial fire suppression, projected changes were dampened or delayed, suggesting a potential tool to forestall change in some (but not all) high-inertia forests, especially since extending fire-free periods does little to alter overall fire regimes in these systems. Model projections also illustrated the importance of fire regime context and projection limitations; the time horizon over which disturbances will eventually allow the system to shift are so long that the prevailing climatic conditions under which many of those shifts will occur are beyond what most climate models can predict with any certainty. This will present a fundamental challenge to setting expectations and managing for long-term change in these systems.

Demographic processes limit upward altitudinal range expansion in a threatened tropical palm.

Understanding the factors that determine species’ range limits is a key issue in ecology, and is fundamental for biodiversity conservation under widespread global environmental change. Elucidating how altitudinal variation affects demographic processes may provide important clues for understanding the factors limiting current and future species distributions, yet population dynamics at range limits are still poorly understood. Here, we tested the hypothesis that lower abundance at a species’ upper altitudinal range limit is related to lower vital rates. We compared the dynamics of two populations of the tropical palm Euterpe edulis, located near and at the edge of its altitudinal limit of distribution in the Brazilian Atlantic Forest. Data from four annual censuses, from 2012 to 2015, were used. We used matrix population models to estimate asymptotic population growth rates and the elasticity values for the vital rates of the two populations of E. edulis. Life table response experiments were used to compare population performance by measuring the contribution of each vital rate to population growth rates. Population growth rates were not significantly different from one in either population, indicating that both populations were stable during the study period. However, the abundance of all ontogenetic stages was lower at the altitudinal range limit, which was related to decreases in some vital rates, especially fecundity. Additionally, there were higher elasticity values for the survival of immatures and reproductive individuals, compared to all other vital rates, in both populations. Synthesis. Our results show that even a small‐scale environmental variation near range limits is sufficient to drive changes in the demography of this threatened palm. A minor increase in elevation approaching the limit of altitudinal distribution may reduce environmental suitability and affect population vital rates, thus contributing to setting upper altitudinal range limits for plants.

Upward expansion of distribution ranges of tree species: Contrasting results from two national parks in Western Carpathians

We analysed the distribution of trees along the elevation gradient in two national parks located in the Western Carpathians (49°30′–49°37′ N; 19°28′–20°15′ E), dominated by natural forest stands to answer two questions: do immature trees occur at higher elevations compared to mature ones? Has the upper limit of the distribution of the seedlings increased during the period under study, and were the changes proportional to the increase in the mean annual temperature in that period? Data used in our study had been collected in permanent sample plots, distributed regularly over the entire forest area in two national parks. The measurements were taken twice, separated by at least 12 years. We analysed the upper distribution range of the most abundant tree species following tree ontogenic stages for two measurement times. The analysed tree species showed contrasting patterns of the distributions of saplings related to the distributions of mature individuals. In one of the national parks, two species (Silver fir and European beech) showed a significant upward expansion. As three measurements were taken in this park, we found that the expansion has increased over time. In the second national park, located only 45 km to the west from the first one, we found no upward expansion in the distribution of both European beech and Silver fir, while Sycamore maple showed a slight downward trend. We conclude that the dynamics of the tree distributions along the elevation gradient in the mountain areas do not follow a uniform path; the indirect effects of changes in environmental conditions may produce different patterns, reflecting the complex nature of the interactions shaping the distributions of the trees.

Biotic factors and increasing aridity shape the altitudinal shifts of marginal Pyrenean silver fir populations in Europe

Rear-edge tree populations are currently at the forefront of habitat conservation. Understanding the dynamics of such marginal and peripheral populations is necessary to improve their preservation in the face of global change. Focusing on the south-western rear edge populations of silver fir (Abies alba) in Europe (Spanish Pyrenees) and using 763 resampled plots from the Spanish National Forest Inventory (1989–2000 and 2001–2010), we analyzed temporal changes in demographic parameters such as regeneration, growth and mortality as well as changes in diameter distribution and vitality of silver fir to identify shifts in the distribution. For this purpose, montane (900–1600 m a.s.l.) and subalpine (1600–2000 m a.s.l.) silver fir populations were considered separately. We then assessed the relative effects of various biotic and abiotic factors on the observed changes and specifically on each of the studied demographic parameters. In montane forests, early recruitment and the proportion of trees exhibiting high vitality decreased, while the amount of dead trees increased. In subalpine forests, silver fir has become more abundant and displays the highest growth and recruitment rates as well as the lowest mortality rate. The increase in radial growth and saplings were positively related to elevation but negatively associated with warmer and drier conditions, coinciding with the intensified aridification observed in the study area over recent decades. Our findings point to the contraction of montane silver fir forests but also to an upward expansion of subalpine forests. The results also indicate that the dynamics of marginal tree populations are driven not only by climate warming, but particularly, by biotic factors, suggesting a positive impact of interspecific interactions with tree species displaying differentiated ecophysiological traits. Given the singularity of marginal Pyrenean silver fir populations, their importance as regards the conservation of forest biodiversity at European scale, and the demographic changes revealed in this study, an integral conservation strategy to ensure their long-term preservation is necessary.

Study on the deformation and failure modes of filling slope in loess filling engineering: a case study at a loess mountain airport

Lvliang airport is a typical loess filling engineering located in 20.5 km north of Lvliang City in Shanxi Province, China. By the end of March 2012, 14 fissures extending more than 7.5 m were observed in a loess-filled slope, of which the longest fissure is up to 82 m. Field monitoring and laboratory tests have been performed to investigate the slope failure modes. The test program includes wetting tests on unsaturated compacted samples and stress path tests on saturated samples. Field monitoring and observations show that differential settlement caused by non-homogeneity in compacted loess density might lead to the formation of fissures in the loess-filled slope. It was founded that the wetting deformation contributed to the development of differential settlement. Fissures are the essential factor for the loess-filled slope failure. Four deformation stages exhibit in the loess-filled slope prior final failure including development of the fissures, softening of the compacted loess, creeping of the slope leading edge and fissuring of the trailing edge and formation of the through-sliding surface. Development of the sliding surface mainly includes upward and downward expansion of the fissures. Upward expansion is a wetting failure process in loading condition, while downward expansion is a load-off wetting process. In addition, development of the sliding surface is accelerated by softening of the compacted soils as a result of water infiltration. Therefore, the key for taking countermeasures against filling landslides is to monitor and control the development of differential settlement and fissures in the slope shoulders. Digging out and extra-filling the fissures are an effective way for preventing these landslides.

Context-dependent effects of fire and browsing on woody alien invasion in mountain ecosystems.

Anthropogenic activities have increased disturbances and alien woody invasion in mountain ecosystems worldwide. Whether disturbances promote or counteract upward movement of woody aliens is poorly understood. We assessed if the most successful woody invader of low mountains of central Argentina (Gleditsia triacanthos) might expand its elevational distribution in response to the principal disturbances of these ecosystems (fire and livestock browsing) across increasing climatic severity. We assessed seedling emergence, growth and mycorrhizal colonization on sown plots distributed in burned and unburned sites, with and without browsing at the lower and upper elevation belts (i.e. 1000 and 2400m a.s.l.). Additionally, several abiotic variables were measured to relate their influence on the seedling establishment. Disturbances reduced seedling emergence at both elevations. Burned conditions increased seedling growth and arbuscular colonization only in the lower belt. Seedling success (total seedling biomass per plot) was not modified by disturbances at the upper elevation, but was reduced by browsing and enhanced by fire in the lower elevation. The overall reduction in seedling emergence and growth in the upper elevation despite the higher soil nutrient content places climate as the strongest regulator of G. triacanthos seedling establishment. Accordingly, climate rather than disturbances would be the main limiting factor of upward expansion of this woody alien. Our findings differ from general patterns described for mountain invasion by herbaceous species, highlighting that mountain invasibility is highly growth-form dependent, and that upper range expansion by woody aliens interacting with multiple disturbances should be assessed worldwide.

Forming of aluminum foam using steel mesh as die during foaming of precursor by optical heating

Ultralightweight aluminum foam (Al foam) is expected to be used for the components of vehicles and construction materials. To apply Al foam in these industrial fields, the fabrication of Al foam with complex shapes is an important requirement. In this study, a steel mesh was used as a die for fabricating Al foam with a complex shape during the foaming of a precursor by employing optical heating. From the free foaming of the ADC12 precursor, it was shown that the precursor can be foamed by passing light through the steel mesh similarly to the foaming without the steel mesh. In addition, it was shown that ADC12 foams with similar porosity and pore structures were obtained both with and without the steel mesh. From the foaming of the ADC12 precursor while restricting its upward expansion by the steel mesh, it was shown that ADC12 foam with plane surface can be obtained. No protrusion of ADC12 foam through the mesh openings was observed. The steel mesh was easily peeled off from the ADC12 foam after the foam had solidified. Similar pore structures to those in the case of free foaming were obtained and no collapse of the pores at the surface in contact with the steel mesh was observed. From the foaming of the ADC12 precursor in steel mesh dies with triangular and square cross sections, it was shown that ADC12 foam with similar shapes to the steel mesh die and similar pore structures to those in the case of free foaming can be obtained. Consequently, it was demonstrated that a steel mesh can be used as a die for the forming of ADC12 foam with little effect on the pore structures of the obtained foam.

Two-dimensional numerical simulation of chimney fluidization in a granular medium using a combination of discrete element and lattice Boltzmann methods.

We present here a numerical study dedicated to the fluidization of a submerged granular medium induced by a localized fluid injection. To this end, a two-dimensional (2D) model is used, coupling the lattice Boltzmann method (LBM) with the discrete element method (DEM) for a relevant description of fluid-grains interaction. An extensive investigation has been carried out to analyze the respective influences of the different parameters of our configuration, both geometrical (bed height, grain diameter, injection width) and physical (fluid viscosity, buoyancy). Compared to previous experimental works, the same qualitative features are recovered as regards the general phenomenology including transitory phase, stationary states, and hysteretic behavior. We also present quantitative findings about transient fluidization, for which several dimensionless quantities and scaling laws are proposed, and about the influence of the injection width, from localized to homogeneous fluidization. Finally, the impact of the present 2D geometry is discussed, by comparison to the real three-dimensional (3D) experiments, as well as the crucial role of the prevailing hydrodynamic regime within the expanding cavity, quantified through a cavity Reynolds number, that can presumably explain some substantial differences observed regarding upward expansion process of the fluidized zone when the fluid viscosity is changed.

Coastal upwelling events along the southern coast of Java during the 2008 positive Indian Ocean Dipole

To understand the coastal upwelling system along the southern coast of Java, we investigated ocean temperature and salinity obtained from an Argo float. In 2008, a positive Indian Ocean Dipole (IOD) event began to develop in early May and anomalously cool SST developed around south of Java from May to September. During the peak of the IOD, an Argo float successfully observed vertical structure of temperature and salinity within 90 km from Java. The float observed two intraseasonal-scale temperature cooling events in July and August, with significant upward movements of the thermocline more than 90 m. Concurrent with the signals, anomalous southeasterly alongshore winds, lowering of local SST and sea level, and upward expansion of high-salinity water were also observed. During the event in August, vertical velocity estimated by the anomalous wind stress agreed well with the observations. These results indicate that the Argo float observed the coastal upwelling, which was enhanced by the 2008 positive IOD, along the southern coast of Java.

Interannual Modulation of Northern Hemisphere Winter Storm Tracks by the QBO

AbstractStorm tracks, defined as the preferred regions of extratropical synoptic‐scale disturbances, have remarkable impacts on global weather and climate systems. Causes of interannual storm track variation have been investigated mostly from a troposphere perspective. As shown in this study, Northern Hemisphere winter storm tracks are significantly modulated by the tropical stratosphere through the quasi‐biennial oscillation (QBO). The North Pacific storm track shifts poleward during the easterly QBO winters associated with a dipole change in the eddy refraction and baroclinicity. The North Atlantic storm track varies vertically with a downward shrinking (upward expansion) in easterly (westerly) QBO winters associated with the change of the tropopause height. These results not only fill the knowledge gap of QBO‐storm track relationship but also suggest a potential route to improve the seasonal prediction of extratropical storm activities owing to the high predictability of the QBO.

Rapid southward and upward range expansion of a tropical songbird, the Thrush-like Wren (Campylorhynchus turdinus), in South America: a consequence of habitat or climate change?

The Thrush-like Wren (Campylorhynchus turdinus) is a polytypic, non-migratory, cooperatively breeding species of bird widely distributed in central South America. In recent decades it has expanded its range by approximately 24%, based on a published map of its distribution in the mid-1980s and recent reports submitted to eBird up through March 2017. The northwestern subspecies, C. t. hypostictus, dramatically expanded its elevation range upward from approximately 1200 m to 4200 m a.s.l. in the Peruvian Andes. During 1977–2015 the southwestern subspecies, C. t. unicolor, dramatically expanded the southern border of its range from central Brazil and northern Paraguay (approximately 22°06’S) southward into northeastern Argentina and throughout Paraguay to 29°40’S in southeastern Brazil, extending its range east-southeast approximately 934 km at a rate of 24.6 km/yr, and latitudinally southward 838 km at a rate of 22.1 km/yr. It also expanded its range westward into the relatively dry Chaco of western Paraguay and north-central Argentina. Midwinter records near the southern border of its range in northeastern Argentina suggest it is non-migratory. Because of its affinity for disturbed habitats, its range expansion has been attributed to deforestation, but its range expansion is also consistent with the prediction that organisms are extending their geographic distribution toward higher latitudes and elevations as a consequence of climate change.

A method developed to calculate lateral earth pressure on a sheet pile wall with counterforts

A method has been developed for calculating the lateral earth pressure on a sheet pile wall with counterforts of various shapes – rectangular, trapezoidal with downward expansion, and trapezoidal with upward expansion. Moreover, in the design scheme, two characteristic areas are distinguished along the height of the wall – with and without a counterfort. As a result of considering the equilibrium conditions for elementary volume, equations for determining the lateral earth pressure along the height of the wall have been obtained in the considered sections. The study has produced a mathematical modeling of the system “a sheet pile wall with counterforts plus the soil environment”. Diagrams of the lateral earth pressure are considered for a sheet pile with counterforts. A quantitative evaluation of the relief action of counterforts of various shapes has been obtained.The conducted tests show that the use of counterforts in a sheet pile wall with the considered parameters reduces the pressure of the filling soil to 26 % due to the friction forces along the lateral surface of the counterforts.The introduction of the developed calculation method into engineering practice will allow designing hydraulic engineering structures such as a sheet pile wall with various shapes of counterforts. This will enable the construction of new deepwater hydraulic structures with an increased bearing capacity.

On the evolution of planetary‐scale fields and genesis of monsoon depressions over the Indian region

Daily composite Fourier coefficients of height, zonal, meridional and vertical velocity, temperature, vorticity and divergence for zonal wave numbers 0–4, during 7 days of pre‐ and 4 days of post‐depression, from 1000 to 200 hPa in the latitude belt 0–30°N are obtained for six monsoon depressions formed over the Bay of Bengal in the years 2006–2008. The planetary‐scale fields zonally averaged over the Indian region (75–96°E) are examined. Consistent with the quasi‐geostrophic approximation, in the northern sector (15–30°N) the monsoon trough, the low‐level westerlies and the vorticity are strongly intensified and progressively extended upward to 400 hPa preceding depressions. Wave number 1 is the dominant contributor towards the strengthening and vertical upward expansion of these entities linked to an increase of its amplitude in the lower‐ and a large westward phase shift in the mid‐troposphere, respectively. The cyclonic shear zone in the lower troposphere is developed to the north of 15°N due to the combined effect of intensification and sharp decrease of meridional scale of the westerlies. Different northward speeds of the zonal wind reversal and westerly maximum creates a strong cyclonic zone 2 days before depressions at 400 hPa. The planetary‐scale zonal flow in the troposphere satisfies the necessary condition for barotropic instability. The northward (westward) movement of wave number 1 at 400 hPa is 0.73° latitude (5.6° longitude) day−1. An intensification of direct thermal meridional circulation is associated with a southward and upward shift of the primary rising motion zone.The planetary waves have captured the main characteristics of observed vertical and latitudinal profiles of unstable background zonal flow, used earlier for instability studies. It is concluded that wave number 1 is the main contributor to genesis of a depression. The planetary fields weakened in the presence of depressions mainly due to wave numbers 3 and 4.

Effect of tool eccentricity on the properties of friction stir welded AA6061 aluminum alloys

This paper investigates the effect of tool eccentricity on material flow of friction stir welded (FSW) AA6061 aluminum alloy. Samples were butt joined using a threaded conical shaped tool pin with 1200 rpm rotational speed and 63 mm/min travel speed with and without 0.2 mm tool offset. A 0.1 mm thin Al foil was inserted at the faying surface prior to welding process to enhance the observation of faying surface material flow. Results show that tool eccentricity enhances nugget zone's material flow. Evidence show upward and horizontal expansion of the soft region in the nugget zone due to the eccentric setup. In addition, the pin-driven region of the nugget zone experiences increased softening with the soft region expanding upwards owing to the eccentric setup. However, tensile tests have shown minimal effect of the tool eccentricity to the strength and elongation of the weld joint. It can be concluded that the tool eccentric motion due to the 0.2 mm tool offset can enhance material flow in the nugget zone and expand the soft region of the nugget zone, but has shown no effect on the mechanical properties of AA6061 alloy.

Assessing the potential of translocating vulnerable forest birds by searching for novel and enduring climatic ranges.

Hawaiian forest birds are imperiled, with fewer than half the original >40 species remaining extant. Recent studies document ongoing rapid population decline and project complete climate‐based range losses for the critically endangered Kaua'i endemics ‘akeke’e (Loxops caeruleirostris) and ‘akikiki (Oreomystis bairdi) by end‐of‐century due to projected warming. Climate change facilitates the upward expansion of avian malaria into native high elevation forests where disease was historically absent. While intensified conservation efforts attempt to safeguard these species and their habitats, the magnitude of potential loss and the urgency of this situation require all conservation options to be seriously considered. One option for Kaua’i endemics is translocation to islands with higher elevation habitats. We explored the feasibility of interisland translocation by projecting baseline and future climate‐based ranges of ‘akeke’e and ‘akikiki across the Hawaiian archipelago. For islands where compatible climates for these species were projected to endure through end‐of‐century, an additional climatic niche overlap analysis compares the spatial overlap between Kaua’i endemics and current native species on prospective destination islands. Suitable climate‐based ranges exist on Maui and Hawai'i for these Kaua'i endemics that offer climatically distinct areas compared to niche distributions of destination island endemics. While we recognize that any decision to translocate birds will include assessing numerous additional social, political, and biological factors, our focus on locations of enduring and ecologically compatible climate‐based ranges represents the first step to evaluate this potential conservation option. Our approach considering baseline and future distributions of species with climatic niche overlap metrics to identify undesirable range overlap provides a method that can be utilized for other climate‐vulnerable species with disjointed compatible environments beyond their native range.

An upward elevation shift of native and non‐native vascular plants over 40 years on the island of Hawai'i

AbstractQuestionsHave vascular plants shifted in elevation along a tropical mountain gradient on Mauna Loa, Hawai'i over the past 40 yr? If so, do native and non‐native species differ in their shifts of mean elevation range, upper elevation limit or lower elevation limit?LocationHawai'i Volcanoes National Park, southeast slope of Mauna Loa, Hawai'i.MethodsWe resurveyed an elevation belt transect of vegetation plots that was first surveyed in the early 1970s. Differences between 1970 and 2010 were calculated for 69 plant species’ mean elevation, upper elevation limit, lower elevation limit and elevation range. Statistical significance of differences was assessed by Monte Carlo permutation tests.ResultsAveraging across all 69 species, a statistically significant upward shift of 65.2 m was detected in mean elevation. Both upper and lower elevation limits shifted significantly upward by 31.6 and 90.5 m, respectively. Elevation range did not change significantly. For the 49 native species, the upper elevation limit did not change, but the lower elevation limit shifted significantly upward by 94.1 m. In contrast, the 20 non‐native species displayed a different pattern of a significant upward shift in both their upper and lower elevation limits, by 126.4 and 81.6 m, respectively. Native species seemed to display a contracting elevation range of 101.2 m, but this was not significant (P = 0.053), while non‐native species maintained a stable elevation range (P = 0.365).ConclusionsVascular plants have shifted upward in elevation on the tropical island of Hawai'i, but the shifting trend differs between native and non‐native species. Non‐native species, which were often found at lower elevations, are in an upward niche expansion phase. Native species show trends toward range contraction due to lack of expansion in upper elevation limit, probably due to drought stress correlating with a trade‐wind inversion (TWI) that severely limits rainfall at higher elevations. As more non‐native species reach theTWIelevation, their upward expansion may also become more limited.

Snow avalanche activity in Żleb Żandarmerii in a time of climate change (Tatra Mts., Poland)

This paper reports from a survey of the occurrence of large avalanches in Żleb Żandarmerii. This couloir is known to be one of the most hazardous avalanche paths in the Tatra Mountains and has one of the longest histories of avalanche observation. This survey looked at the runout distance, return period, dynamics and geoecological implications of avalanches in the context of current climate change. The study took advantage of the longest record of meteorological data available in the Tatra Mountains, as well as archival avalanche observations, topographical maps, orthophotomaps and a high-resolution digital terrain model. Avalanche data were obtained using geomorphological and dendrogeomorphic methods and through modelling with the RAMMS numerical avalanche dynamics simulation software. The largest avalanches reach the foot of its counter slope. Their length, release volume, flow velocity and pressure can exceed respectively 1000m, 80000m3, 45m/s and 600kPa. The results of our study suggest that current climate warming has been accompanied by thinning and shortening of the duration of snow cover, as well as by an upward expansion of the timberline (including in the large-avalanche runout zones) of up to 80m since the mid-1920s. No distinct temporal trend was identified in the large avalanche return period since 1909, but their mass and intensity have declined. Forests and timberline expansion were found to have no influence on the extent of the avalanches in our study, while ground relief could determine both their downward extent and lateral expansion.

Human disturbance and upward expansion of plants in a warming climate

A large proportion of European alpine plants are able to spread upslope faster than current climate velocities. Nevertheless, invasive species tend to be particularly effective dispersers, making them an additional pressure on the vulnerable native flora. Climate change is expected to trigger an upward expansion of plants in mountain regions1,2 and, although there is strong evidence that many native species have already shifted their distributions to higher elevations1,3,4,5,6, little is known regarding how fast non-native species might respond to climate change. By analysing 131,394 occurrence records of 1,334 plant species collected over 20 years in the European Alps, we found that non-natives are spreading upwards approximately twice as fast as natives. Whereas the spread of natives was enhanced by traits favouring longer dispersal distances, this was not the case for non-natives. This was due to the non-native species pool already being strongly biased towards species that had traits facilitating spread. A large proportion of native and non-native species seemed to be able to spread upwards faster than the current velocity of climate change. In particular, long-distance dispersal events and proximity to roads proved to be key drivers for the observed rapid spread. Our findings highlight that invasions by non-native species into native alpine communities are a potentially significant additional pressure on these vulnerable ecosystems that are already likely to suffer dramatic vegetation changes with ongoing warming and increasing human activity in mountain regions.

High-elevation plants have reduced plasticity in flowering time in response to warming compared to low-elevation congeners

Global warming has caused shifts in the flowering time of many plant species. In alpine regions the temperature rise has been especially pronounced and together with decreasing winter precipitation has led to earlier snowmelt. The close association between time of snowmelt and plant growth at high elevations makes climate change for alpine plants particularly threatening. Here we transplanted eleven congeneric pairs of high- and low-elevation herbaceous species to common gardens differing c. 800m in elevation, and c. 4°C in mean growing season temperature to test whether reproductive phenologies of high- and low-elevation plants differ in their respective responses to temperature. Results indicate that high-elevation plants were less plastic in response to transplantation than their low-elevation congeners as the onsets of phenophases on average shifted 7days less than in low-elevation plants. Plasticity of phenophase durations was overall weaker than that of phenophase onsets, and slightly stronger in high-elevation species compared to low-elevation congeners. We suggest that weaker plasticity in the onsets of early stages of reproductive phenology of high-elevation plants is related to spring frost, which constitutes a strong selective agent against early loss of winter hardiness. Some of the plastic responses of both low- and high-elevation species might potentially be adaptive under predicted climate change. However, the observed plasticity can be largely explained as a passive response to temperature and not as the result of natural selection in heterogeneous environments. The strong temperature-sensitivity of low-elevation species might promote their upward range expansion, but only to a certain threshold after which it becomes limited by the short growing season.