Vascular plant diversity and climate change in the alpine zone of the Snowy Mountains,Australia

This study examines vascular plant species richness along an altitudinal gradient in alpine Australia. Vascular plant composition and soil temperature records were obtained for five summits (from 1729 m to 2114 m a.s.l.) using sampling protocols from the Global Observation Research Initiative in Alpine Environments program. Species richness was examined against altitude, aspect and climatic variables at different spatial scales (10 × 10 cm quadrats, 1 m² quadrats, clusters of 4 * 1 m² quadrats, for the summit area above a line 5 m altitudinally below the summit (the −5 m isoline), for the extended summit down to the −10 m isoline). About 75 taxa (70 species, 5 graminoid genera) were recorded, 9 of which are endemic to the small alpine area of ∼100 km². There were significant linear relationships between species richness and altitude and climatic variables for the top to −5 isolines on the summits. However, there was no consistent pattern for species richness at other spatial scales, altitude, aspect or climatic variables. The proportion of species for the whole summits with localised distributions (local endemics) increased with altitude. Predicted increasing temperatures and reduced snowcover is likely to result in an increase in species richness as shrubs, herbs and introduced weeds become more common at higher altitude. Because Australian alpine areas occur in narrow altitudinal bands with no nival zone, there are no higher altitudinal refuges available for alpine species. Therefore many of these species are likely to be at risk of extinction from climate change.     

Vascular plant diversity and climate change in the alpine zone of the Lefka Ori,Crete

The aim of this study is to analyse the vascular flora and the local climate along an altitudinal gradient in the Lefka Ori massif Crete and to evaluate the potential effects of climate change on the plant diversity of the sub-alpine and alpine zones. It provides a quantitative/qualitative analysis of vegetation-environment relationships for four summits along an altitude gradient on the Lefka Ori massif Crete (1664–2339 m). The GLORIA multi-summit approach was used to provide vegetation and floristic data together with temperature records for every summit. Species richness and species turnover was calculated together with floristic similarity between the summits. 70 species were recorded, 20 of which were endemic, belonging to 23 different families. Cretan endemics dominate at these high altitudes. Species richness and turnover decreased with altitude. The two highest summits showed greater floristic similarity. Only 20% of the total flora recorded reaches the highest summit while 10% is common among summits. Overall there was a 4.96°C decrease in temperature along the 675 m gradient. Given a scenario of temperature increase the ecotone between the sub-alpine and alpine zone would be likely to have the greatest species turnover. Southern exposures are likely to be invaded first by thermophilous species while northern exposures are likely to be more resistant to changes. Species distribution shifts will also depend on habitat availability. Many, already threatened, local endemic species will be affected first.     

Changes in plant species richness over the last century in the eastern Swiss Alps: elevational gradient, bedrock effects and migration rates

Areas of 2,800–3,000 m a.s.l. represent the alpine-nival ecotone in the Alps. This transition zone connecting the closed swards of the alpine belt and the scattered vegetation of the nival belt may show particularly strong climate warming driven fluctuations in plant species richness compared to the nival belt. To test this hypothesis, 12 summits within this range were investigated in the canton of Grisons, Switzerland in 2004. Complete lists of vascular plant species consisting of 5–70 species were collected on each summit and the elevation of the uppermost occurrence of each species was recorded. These data were compared to historical records over 120 years in age. Within this time, vascular plant species richness increased by 11% per decade on summits in the alpine-nival ecotone. Despite this considerable change, a comparison with nival summits did not support the hypothesis that species richness increase at the alpine-nival ecotone is higher than in the nival belt. A general trend of upward migration in the range of several metres per decade could be observed. Anemochorous species were more often found to be migrating than zoochorous or autochorous species and migration was higher on calcareous than on siliceous bedrock. A comparison between the summits with the adjacent slopes in our study revealed that changes in species number could be used as an indicator for climate-induced changes—if at all—only for the narrow summit areas.     

Signals of range expansions and contractions of vascular plants in the high Alps: observations (1994–2004) at the GLORIA* master site Schrankogel,Tyrol, Austria

High mountain ecosystems are defined by low temperatures and are therefore considered to react sensitively to climate warming. Responding to observed changes in plant species richness on high peaks of the European Alps, an extensive setup of 1 m × 1 m permanent plots was established at the alpine‐nival ecotone (between 2900 and 3450 m) on Mount Schrankogel, a GLORIA master site in the central Tyrolean Alps, Austria, in 1994. Recording was repeated in a representative selection of 362 quadrats in 2004. Ten years after the first recording, we observed an average change in vascular plant species richness from 11.4 to 12.7 species per plot, an increase of 11.8% (or of at least 10.6% at a 95% confidence level). The increase in species richness involved 23 species (about 43% of all taxa found at the ecotone), comprising both alpine and nival species and was pronouncedly higher in plots with subnival/nival vegetation than in plots with alpine grassland vegetation. Only three species showed a decrease in plot occupancy: one was an annual species, one was rare, and one a common nival plant that decreased in one part of the area but increased in the uppermost part. Species cover changed in relation to altitudinal preferences of species, showing significant declines of all subnival to nival plants, whereas alpine pioneer species increased in cover. Recent climate warming in the Alps, which has been twice as high as the global average, is considered to be the primary driver of the observed differential changes in species cover. Our results indicate an ongoing range contraction of subnival to nival species at their rear (i.e. lower) edge and a concurrent expansion of alpine pioneer species at their leading edge. Although this was expected from predictive distribution models and different temperature‐related habitat preferences of alpine and nival species, we provide first evidence on – most likely – warming‐induced species declines in the high European Alps. The projected acceleration of climate warming raises concerns that this phenomenon could become the major threat to biodiversity in high mountains.     

Short-term variation in species richness across an altitudinal gradient of alpine summits

In response to climate warming, high altitude alpine vegetation may be replaced by typically lower altitude species, as species re-assemble and migrate to new areas. However, empirical evidence showing vegetation change in response to climate warming is largely unavailable for Australian alpine areas. Here, we examine changes in species richness with respect to climate and altitude over a 7?year period at a range of spatial scales in a re-survey of five alpine summits that are part of the Global Observation Research Initiative in Alpine Environments monitoring network. Eighty species were recorded in 2011 across all summits, an increase of 6 species since 2004. Mean species richness increased at the whole-of-summit scale from 45 to 50 species (about 12?%). At this scale, the rate of species richness increase was almost one new species per year, with 15 new species recorded at one summit. Here, shrub and graminoid species showed the largest increases. At the smaller spatial scales, changes in species richness were less pronounced. Turnover at the species and community level was typically moderate at all spatial scales and on all summits. The strength and direction of species richness change (the difference in species richness between the two sample periods, +/?) was not related to altitude nor variation in climate. Future re-surveys of the summits will confirm whether these short-term variations in species richness, particularly increases in shrubs, are indeed signals of longer-term trends and interactions with a changing climate.     

Latitudinal and altitudinal patterns of plant community diversity on mountain summits across the tropical Andes

The high tropical Andes host one of the richest alpine floras of the world, with exceptionally high levels of endemism and turnover rates. Yet, little is known about the patterns and processes that structure altitudinal and latitudinal variation in plant community diversity. Herein we present the first continental‐scale comparative study of plant community diversity on summits of the tropical Andes. Data were obtained from 792 permanent vegetation plots (1 m²) within 50 summits, distributed along a 4200 km transect; summit elevations ranged between 3220 and 5498 m a.s.l. We analyzed the plant community data to assess: 1) differences in species abundance patterns in summits across the region, 2) the role of geographic distance in explaining floristic similarity and 3) the importance of altitudinal and latitudinal environmental gradients in explaining plant community composition and richness. On the basis of species abundance patterns, our summit communities were separated into two major groups: Puna and Páramo. Floristic similarity declined with increasing geographic distance between study‐sites, the correlation being stronger in the more insular Páramo than in the Puna (corresponding to higher species turnover rates within the Páramo). Ordination analysis (CCA) showed that precipitation, maximum temperature and rock cover were the strongest predictors of community similarity across all summits. Generalized linear model (GLM) quasi‐Poisson regression indicated that across all summits species richness increased with maximum air temperature and above‐ground necromass and decreased on summits where scree was the dominant substrate. Our results point to different environmental variables as key factors for explaining vertical and latitudinal species turnover and species richness patterns on high Andean summits, offering a powerful tool to detect contrasting latitudinal and altitudinal effects of climate change across the tropical Andes.     

Changes in the Altitudinal Distribution of Alpine Plants in Katunskiy Biosphere Reserve (Central Altai) Revealed on the Basis of Multiyear Monitoring Data

In order to reveal climate-related changes in the plant diversity of alpine ecosystems in recent decades, a target region of the GLORIA (Global Observation Research Initiative in Alpine Environments) worldwide network consisting of four mountain summits representing an elevation gradient from the subalpine to the upper part of alpine ecotone (2181, 2231, 2358, and 2475 m above sea level) has been established in Katunskiy Biosphere Reserve (Russia, Central Altai). In the course of the observation period (2005–2015), species in the target region have shifted towards higher altitudes by 5.3 m on average. The plant species richness has increased on the three higher summits and decreased on the lowest summit.     

Long‐term geobotanical observations of climate change impacts in the Scandes of West‐Central Sweden

In the context of projected future human‐caused climate warming, the present study reports and analyses the performance of subalpine/alpine plants, vegetation and phytogeographical patterns during the past century of about 1 °C temperature rise. Historical baseline data of altitudinal limits of woody and non‐woody plants in the southern Scandes of Sweden are compared with recent assessments of these limits at the same locations. The methodological approach also includes repeat photography, individual age determinations and analyses of permanent plots. At all levels, from trees to tiny herbs, and from high to low altitudes, the results converge to indicate a causal association between temperature rise and biotic evolution. The importance of snow cover phenology is particularly evident. Treeline advance since the early‐20th century varies between 75 and 130 m, depending on species and site. Tendencies and potentials for further upshift in a near future are evident from the appearance of young saplings of all tree species, growing 400–700 m atop of the treeline. Subalpine/alpine plant species have shifted upslope by average 200 m. In addition, present‐day repetitions of floristic inventories on two alpine mountain summits reveal increases of plant species richness by 58 and 67%, respectively, since the early‐1950s. Obviously, many plants adjust their altitudinal ranges to new climatic regimes much faster than generally assumed. Nevertheless, plants have migrated upslope with widely different rates. This produces non‐analogous alpine plant communities, i.e. peculiar mixtures of alpine and silvine species. The alpine region is shrinking (higher treeline), and the character of the remaining alpine vegetation landscape is changing. For example, extensive alpine grasslands are replacing snow bed plant communities.     

Foliar freezing resistance of Australian alpine plants over the growing season

We assessed the freezing resistance of leaves ex situ of 25 Australian alpine plant species. We compared the freezing resistance of forb, graminoid and shrub species from three alpine summits of different altitudes; from a low altitude site just above treeline, to a fully alpine tundra site. Foliar freezing resistance (LT₅₀) in spring varied from ?5.9°C to ?18.7°C and standardized LT₅₀ values within species were significantly related to site altitude. Additionally, when comparing all the species in the study, freezing resistance was significantly related to site; the LT₅₀ of samples from a low‐altitude summit (1696 m) were significantly lower than those of samples from mid‐ (1805 m) and high‐altitude (1860 m) summits. The LT₅₀ of juvenile foliage did not differ significantly from that of adult foliage. Shrubs were highly resistant to freezing. At the highest summit, we examined the course of seasonal freezing resistance from early summer to early autumn across three alpine plant communities that differed in the time of natural snowmelt; from sheltered (snowpatch) to exposed (open heath). No differences in freezing resistance over the growing season were detected for exposed or sheltered communities and there were no consistent trends indicating frost hardening over the growing season. Overall, the common Australian alpine species we investigated appear well adapted to freezing conditions throughout the snow‐free growing season. We have no evidence to suggest that freezing temperatures soon after snowmelt in spring are especially damaging to the alpine plants at these summits.     

Vegetation patterns at the alpine treeline ecotone: the influence of tree cover on abrupt change in species composition of alpine communities

Aims: The upper elevation limit of forest vegetation in mountain ranges (the alpine treeline ecotone) is expected to be highly sensitive to global change. Treeline shifts and/or ecotone afforestation could cause fragmentation and loss of alpine habitat, and are expected to trigger considerable alterations in alpine vegetation. We performed an analysis of vegetation structure at the treeline ecotone to evaluate whether distribution of the tree population determines the spatial pattern of vegetation (species composition and diversity) across the transition from subalpine forest to alpine vegetation. Location: Iberian eastern range of the Pyrenees. Methods: We studied 12 alpine Pinus uncinata treeline ecotones. Rectangular plots ranging from 940 to 1900 m² were placed along the forest‐alpine vegetation transition, from closed forest to the treeless alpine area. To determine community structure and species distribution in the treeline ecotone, species variation along the forest‐alpine vegetation transition was sampled using relevés of 0.5 m² set every 2 m along the length of each plot. Fuzzy C‐means clustering was performed to assess the transitional status of the relevés in terms of species composition. The relation of P. uncinata canopy cover to spatial pattern of vegetation was evaluated using continuous wavelet transform analysis. Results: Vegetation analyses revealed a large degree of uniformity of the subalpine forest between all treeline ecotone areas studied. In contrast, the vegetation mosaic found upslope displayed great variation between sites and was characterized by abrupt changes in plant community across the treeline ecotone. Plant richness and diversity significantly increased across the ecotone, but tree cover and diversity boundaries were not spatially coincident. Conclusions: Our results revealed that no intermediate communities, in terms of species composition, are present in the treeline ecotone. Ecotone vegetation reflected both bedrock type and fine‐scale heterogeneity at ground level, thereby reinforcing the importance of microenvironmental conditions for alpine community composition. Tree cover did not appear to be the principal driver of alpine community changes across the treeline ecotone. Microenvironmental heterogeneity, together with effects of past climatic and land‐use changes on ecotone vegetation, may weaken the expected correlation between species distribution and vegetation structure.     

The subnival–nival vascular plant species of Iran: a unique high-mountain flora and its threat from climate warming

This study provides a first country-wide overview of the vertical distribution patterns and the chorology of vascular plant species that occur in the uppermost elevation zones in Iran. The current distribution patterns are discussed with respect to potential warming-induced species losses. Iran’s subnival and nival vegetation zones are found at elevations above 3600–3900 m in a highly fragmented distribution across Alborz, Zagros, and NW-Iran. Based on literature research and on field observations, all vascular plant species living in the subnival–nival zone of Iranian mountains were identified (151 species) and classified into three altitudinal groups: Group A comprises species that occur mainly in subnival–nival habitats (51 species). Group B are species being common in subnival–nival areas but are equally present in the alpine zone (56 species). Group C are species that can reach to subnival areas but also grow in alpine, subalpine and sometimes lower altitudes (44 species). The chorological patterns differ among the three groups. The percentage of species being endemic to Iran decreases from group A, to B and C, with 68, 53 and 20%, respectively. A narrow altitudinal distribution at high elevations is clearly related to a small-scaled geographical distribution range. The outstanding rate of high-altitude endemism appears to result mainly from orographic isolation of the country’s highly scattered cold areas and by the absence of extensive Pleistocene glaciations. The narrow distribution of most of Iran’s cold-adapted mountain flora and the low potential of alternative cold habitats render it highly vulnerable to climate change.     

Spatial patterns of plant richness across treeline ecotones in the Pyrenees reveal different locations for richness and tree cover boundaries

Aim  To forecast the responses of alpine flora to the expected upward shift of treeline ecotones due to climatic warming, we investigated species richness patterns of vascular plants at small spatial scales across elevational transects.
Location  Richness patterns were assessed at local scales along the elevational gradient in two undisturbed treeline ecotones and one disturbed treeline ecotone in the Spanish Pyrenees.
Methods  We placed a rectangular plot (0.3–0.4 ha) in each treeline ecotone. We estimated and described the spatial patterns of plant richness using the point method and Moran's I correlograms. We delineated boundaries based on plant richness and tree cover using moving split windows and wavelet analysis. Then, to determine if floristic and tree cover boundaries were spatially related, overlap statistics were used.
Results  Plant richness increased above the forest limit and was negatively related to tree cover in the undisturbed sites. The mean size of richness patches in one of these sites was 10–15 m. Moving split windows and wavelets detected the sharpest changes in plant richness above the forest limit at both undisturbed sites. Most tree cover and plant richness boundaries were not spatially related.
Main conclusions  The upslope decrease of tree cover may explain the increase of plant richness across alpine treeline ecotones. However, the detection of abrupt richness boundaries well above the forest limit indicates the importance of local environmental heterogeneity to explain the patterns of plant richness at smaller scales. We found highly diverse microsites dominated by alpine species above the forest limit, which should be monitored to describe their response to the predicted upward shift of forests.     

Diaspore traits discriminate good from weak colonisers on high-elevation summits

The richness of plant species in Swiss alpine-nival summits increased during the climate warming of the 20th century. Thirty-seven summits (2797–3418 m a.s.l.) with both old (～1900–1920) and recent (～2000) plant inventories were used to test whether biological species traits can explain the observed rates of summit colonisation. Species were classified into two groups: good colonisers (colonising five or more summits) and weak colonisers (fewer than five new summits). We compared species traits related to growth, reproduction and dispersal between these two groups and between the good colonisers and a group of high alpine grassland species. The observed colonisation pattern was subsequently compared with a simulated random colonisation pattern.The distribution of new species on the summits was not random, and 16 species exhibited a colonisation rate higher than expected by chance. Taraxacum alpinum aggr. and Cardamine resedifolia were the best colonisers. Results showed that diaspore traits enhancing long-distance dispersal were more frequent among good colonisers than among weak colonisers. Good colonisers were mostly characterised by pappi or narrow wings on their diaspores. Both groups were able to grow on soils more bare and rocky than species from the alpine grasslands. All other biological traits that we considered were similar among the three alpine species groups. These results are important for improving predictive models of species distribution under climate change.     

Upward shift of alpine plants increases floristic similarity of mountain summits

Question: Does the upward shift of species and accompanied increase in species richness, induced by climate change, lead to homogenization of Alpine summit vegetation? Location: Bernina region of the Swiss Alps. Methods: Based on a data set from previous literature we expand the analysis from species richness to beta‐diversity and spatial heterogeneity. Species compositions of mountain summits are compared using a two‐component heterogeneity concept including the mean and the variance of Sørensen similarities calculated between the summits. Non‐metric multidimensional scaling is applied to explore developments of single summits in detail. Results: Both heterogeneity components (mean dissimilarity and variance) decrease over time, indicating a trend towards more homogeneous vegetation among Alpine summits. However, the development on single summits is not strictly unidirectional. Conclusions: The upward shift of plant species leads to homogenization of alpine summit regions. Thus, increasing alpha‐diversity is accompanied by decreasing beta‐diversity. Beta‐diversity demands higher recognition by scientists as well as nature conservationists as it detects changes which cannot be described using species richness alone.     

Facilitation in subnival vegetation patches

Abstract. We examined spatial relationships among species in the subnival zone of the central Caucasus. The species composition of 300 vegetation patches was analysed. 144 of them contained only one species, whereas the other 156 contained 2.36 ± 1.31 species, with species numbers distributed as follows: 59 patches with two species, 41 with three, 39 with four and 17 with five species. In the multi-species patches, the 22 most frequent species were examined and 46 statistically significant species associations, 36 positive and 10 negative, were found. Ten of these 22 species were typical subnival plants very rarely occurring at lower altitudes. The other 12 species are ‘invaders’ as they have broader altitudinal ranges of occurrence and are common in alpine and even in subalpine belts. Contrary to the typical subnival species the invaders were found exclusively in the patches with more than one species. Invader species were significantly more associated with subnival species while they were significantly less associated with other species than expected by chance. Our interpretation is that typical subnival species nurse plants from lower altitudes and facilitate their invasion to more adverse subnival environments.     

Seedling occurrence in alpine treeline conifers: A case study from the central Rocky Mountains,USA

Information concerning the occurrence of very young (1- to 10-year-old) tree seedlings in the alpine treeline ecotone is rare. Seedling occurrence of the dominant conifers Picea engelmannii and Abies lasiocarpa was measured in the treeline ecotone of the Medicine Bow Mountains, Wyoming (central Rocky Mountains, USA), an area composed of elongated tree islands separated by open meadows (ribbon forest) that grade into the closed forest. No seedlings were found on the windward sides of tree islands, while a mean of 0.6 seedlings.m^–2 occurred on the leeward (downward) sides. These values compared to the 4.2 seedlings.m^–2 in the closed forest. In addition, a strong correspondence was found between snowpack depth and seedling abundance, with depths that were either too shallow (< 0.5 m) or too deep (> 1.5 m) associated with fewer or no seedlings. A. lasiocarpa seedlings made up much less of the overall seedling population in the ribbon forest (6 %) than in the closed forest (22 %). Seedling establishment in this portion of the alpine treeline ecotone appears to be occurring at a low rate that differs between the two dominant species and may be strongly influenced by wind-driven snow accumulation patterns.     

COMMUNITY STUDIES IN POLLINATION ECOLOGY IN THE HIGH TEMPERATE ANDES OF CENTRAL CHILE. I. POLLINATION MECHANISMS AND ALTITUDINAL VARIATION

Pollination mechanisms and pollinators are reported for a total of 137 species (75% of the non-abiotically pollinated flora) as they occur at three altitudinal levels (subandean scrub: 2,200–2,600 m; cushion-plant zone: 2,700–3,100 m; subnival feldfield: 3,200–3,600 m) in the Andean (alpine) zone on the Cordon del Cepo (33°17'S) in central Chile as part of community oriented research in reproductive biology in the high temperate Andes of South America. Only around 4% of the species studied failed to be visited by potential pollinators. Hymenopterans (principally bees) are important pollinators of 50% of the biotically pollinated flora, butterflies of 24% and flies of 46%. Other vectors include beetles, moths, and hummingbirds. An estimated 17% of the flora is anemophilous. Bee species-richness, specialist feeding, and melittophily reach maxima in the subandean scrub; thereafter, bees diminish rapidly in number, with bees pollinating only 13% of the subnival flora as contrasted with 68% of the subandean flora. Although fly and butterfly species-richness also decline with increasing altitude, the proportions of species pollinated by these vectors actually increases. High-altitude populations of melittophilous species with broad altitudinal ranges are invariably serviced by fewer bee species as compared with lower populations. The rich bee fauna at the lower end of the Andean zone in central Chile appears to have resulted from upward colonization from that of the subtending lowland Mediterranean sclerophyllous woodland vegetation. Altitudinal variation in pollination spectra is discussed in relation to contrasting life history characteristics and different modes of thermoregulation in the insect groups involved.     

Uncoupled changes in tree cover and field layer vegetation at two Pyrenean treeline ecotones over 11 years

Background: The alpine treeline ecotone is regarded as a sensor of the effects of global change on alpine plant communities. However, little is known about how treeline dynamics influence the diversity and composition of alpine plant communities. Such information is necessary to forecast how ascending montane forests may affect the composition of alpine flora.

Aims: We analysed the temporal variations in tree cover, plant diversity and composition, and the effect of tree cover dynamics on field layer vegetation over a period of 11 years, at two alpine treeline ecotones in the central Pyrenees, Spain.

Methods: Tree and field layer vegetation was sampled in permanent transects in 1998 and 2009, using the point-intercept method. Temporal changes in tree cover, plant species richness and abundance were characterised along the ecotone by using a randomisation approach, rarefaction curves, and a non-parametric multivariate test, respectively.

Results: Tree cover increased significantly at one of the sites, whereas plant species richness only increased at the other site where tree cover had not changed. Vegetation composition changed significantly at both sites, but it was not spatially coupled with changes in tree cover along the ecotone.

Conclusions: A change of tree cover does not necessarily trigger changes in the ground flora at the treeline over relatively short periods (decade scale). The results challenge our ability to infer short-term biodiversity impacts from upslope advance of forests. Integrated tree and field layer monitoring approaches are necessary to produce a better understanding of the impact of ongoing global change on treeline ecotones.     

Vascular plant diversity and climate change in the upper zone of Sierra Nevada,Spain

Abstract

This study examines the effects of altitudinal, temperature and aspect gradients on vascular plant species richness on mountain tops in Sierra Nevada (Spain) at different spatial scales (1 m² quadrats, plot clusters of 4 m², upper summit area down to the 5-m contour line, entire summit down to the 10-m contour line). The methodology follows the Global Observation Research Initiative in Alpine Environments (GLORIA) programme. Floristic and soil temperature data of eight summits sites in two neighbouring regions of the high part of Sierra Nevada (from 2668 m to 3327 m a.s.l.) were used in this study. In total, 102 taxa were recorded (84 genera; 29 families). The species richness decreased, whereas the proportion of endemic taxa increased with elevation. There were significant linear relationships between species richness and altitude and average soil temperature at each spatial scale. However, there was no significant relationship between species richness and aspect variables. Facing continued climate change, the high-altitude flora of Sierra Nevada is expected to be particularly vulnerable and prone to warming-induced biodiversity losses due to the high proportion of endemic taxa, ranging from 23% at lower elevations up to 67% at higher ones.     

Climate‐driven speedup of alpine treeline forest growth in the Tianshan Mountains,Northwestern China

Forest growth is sensitive to interannual climatic change in the alpine treeline ecotone (ATE). Whether the alpine treeline ecotone shares a similar pattern of forest growth with lower elevational closed forest belt (CFB) under changing climate remains unclear. Here, we reported an unprecedented acceleration of Picea schrenkiana forest growth since 1960s in the ATE of Tianshan Mountains, northwestern China by a stand‐total sampling along six altitudinal transects with three plots in each transect: one from the ATE between the treeline and the forest line, and the other two from the CFB. All the sampled P. schrenkiana forest patches show a higher growth speed after 1960 and, comparatively, forest growth in the CFB has sped up much slower than that in the ATE. The speedup of forest growth at the ATE is mainly accounted for by climate factors, with increasing temperature suggested to be the primary driver. Stronger water deficit as well as more competition within the CFB might have restricted forest growth there more than that within the ATE, implying biotic factors were also significant for the accelerated forest growth in the ATE, which should be excluded from simulations and predictions of warming‐induced treeline dynamics.