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Alpine habitats are regarded as particularly vulnerable to the effects of climate change. On one hand, global warming is supposed to contributes to alpine environments becoming less stressful. On the other hand, altered snowpack due to warmer temperatures can intensify the stress in these habitats. The presence of non‐native plants on some of these habitats is due to the facilitative effects exerted by native nurse plants, becoming an additional threat. According to the stress gradient hypothesis the importance of facilitative interactions with nurse species is expected to diminish as environmental harshness decreases due to climate change yet remains important if climate change heightens the stress in alpine habitats. However, the responses also depend on climate change's impact on the nurse species. We conducted an experimental warming experiment in the Andes of the central Chile to assess the effects of warmer temperatures on the growth, reproduction and photochemical efficiency of the cushion nurse plant Azorella madreporica. Further we performed a cushion removal experiment involving three native species (Gamocarpha ventosa, Nocaccea magellanica and Rytidosperma pictum) and two non‐native species (Cerastium arvense and Taraxacum officinale) to assess whether facilitative interactions changed with warming. We expected that under warmer conditions facilitation continued be important for the native species but decreased for the non‐natives as the latter are abundant at warmer low elevations. We found that warmer conditions increased the photochemical efficiency and growth of the nurse cushions. Removal of cushions resulted in high mortality rates for all species. However, under warmer conditions, native species exhibited lower survival rates, whereas non‐natives showed no significant changes compared to control groups. In summary, warmer temperatures were beneficial for the nurses maintaining the importance of facilitative interactions for native species, but not for the non‐natives. [ABSTRACT FROM AUTHOR]

Premise: The Caryophyllaceae (the carnation family) have undergone multiple transitions into colder climates and convergence on cushion plant adaptation, indicating that they may provide a natural system for cold adaptation research. Previous research has suggested that putative ancient whole‐genome duplications (WGDs) are correlated with niche shifts into colder climates across the Caryophyllales. Here, we explored the genomic changes potentially involved in one of these discovered shifts in the Caryophyllaceae. Methods: We constructed a data set combining 26 newly generated transcriptomes with 45 published transcriptomes, including 11 cushion plant species across seven genera. With this data set, we inferred a dated phylogeny for the Caryophyllaceae and mapped ancient WGDs and gene duplications onto the phylogeny. We also examined functional groups enriched for gene duplications related to the climatic shift. Results: The ASTRAL topology was mostly congruent with the current consensus of relationships within the family. We inferred 15 putative ancient WGDs in the family, including eight that have not been previously published. The oldest ancient WGD (ca. 64.4–56.7 million years ago), WGD1, was found to be associated with a shift into colder climates by previous research. Gene regions associated with ubiquitination were overrepresented in gene duplications retained after WGD1 and those convergently retained by cushion plants in Colobanthus and Eremogone, along with other functional annotations. Conclusions: Gene family expansions induced by ancient WGDs may have contributed to the shifts to cold climatic niches in the Caryophyllaceae. Transcriptomic data are crucial resources that help unravel heterogeneity in deep‐time evolutionary patterns in plants. [ABSTRACT FROM AUTHOR]

Little information is available about the vegetation impact on soil, comparing the effects of different woody plant species on topsoil properties in subalpine degraded grasslands. Therefore, we studied the effects of three native woody plants with different structural canopies (evergreen needle-leaved vs. deciduous broad-leaved and cushion vs. free canopy) on the nutrient topsoil properties. We selected 20 sites as 20 replications in which all four woody species were found closed to each other in each site. Then soil samples were collected under the canopy of each woody species in June 2019 and transported to the laboratory for physico-chemical analyses. The results showed that generally, woody species differed in their effects on physico-chemical topsoil properties. So that, the needle-leaved evergreen Juniperus sabina exerted the most influence on soil properties compared to Berberis integerrima and Onobrychis cornuta (p < 0.05). Topsoil total organic carbon content was significantly highest under J. sabina and B. integerrima (3.30% and 3.07% respectively), while lowest under O. cornuta and herbaceous vegetation (2.61% and 2.23%, respectively). In addition, soil total nitrogen content was significantly highest under J. sabina and B. integerrima (0.18% and 0.17%, respectively), while lowest under O. cornuta and herbaceous vegetation (0.16% and 0.15%, respectively). The results of this study indicated that in sub-alpine grasslands, the presence and maintaining of woody species is important due to its positive role on substratum soil, considering in the rangeland improvement projects. [ABSTRACT FROM AUTHOR]

There is no literature on outlier‐robust parametric mixed‐effects quantile regression models for continuous proportion data as an alternative to systematically identifying and eliminating outliers. To fill this gap, we formulate a robust method by extending the recently proposed fixed‐effects quantile regression model based on the heavy‐tailed Johnson‐t$$ t $$ distribution for continuous proportion data to the mixed‐effects modeling context, using a Bayesian approach. Our proposed method is motivated by and used to model the extreme quantiles of the vitality of cushion plants to provide insights into the ecology of the system in which the plants are dominant. We conducted a simulation study to assess the new method's performance and robustness to outliers. We show that the new model has good accuracy and confidence interval coverage properties and is remarkably robust to outliers. In contrast, our study demonstrates that the current approach in the literature for modeling hierarchically structured bounded data's quantiles is susceptible to outliers, especially when modeling the extreme quantiles. We conclude that the proposed model is an appropriate robust alternative to the current approach for modeling the quantiles of correlated continuous proportions when outliers are present in the data. [ABSTRACT FROM AUTHOR]

Ecology Letters 16: 478 - 86. 7 Callaway, R. M. 1995. Functional Ecology 28: 75 - 86. 31 Michalet, R., C. Schöb, S. Xiao, L. Zhao, T. Chen, L. An, and R. M. Callaway. Functional Ecology 30: 79 - 87. 32 Michalet, R., S. Xiao, B. Touzard, D. S. Smith, L. A. Cavieres, R. M. Callaway, and T. G. Whitham. Keywords: alpine; competition; cushion plants; dendrochronology; facilitation; growth rings; stress EN alpine competition cushion plants dendrochronology facilitation growth rings stress 1 5 5 05/03/23 20230501 NES 230501 "Your eyes can deceive you, don't trust them.". [Extracted from the article]

The new genus and species Pulvinatusia xuegulaensis (Brassicaceae) are described and illustrated. The species is a cushion plant collected from Xuegu La, Xizang, China. Its vegetative parts are most similar to those of Arenaria bryophylla (Caryophyllaceae) co-occurring in the same region, while its leaves and fruits closely resemble those of Xerodraba patagonica (Brassicaceae) from Patagonian Argentina and Chile. Family-level phylogenetic analyses based on both nuclear ITS and plastome revealed that it is a member of the tribe Crucihimalayeae, but the infra-/intergeneric relationships within the tribe are yet to be resolved. [ABSTRACT FROM AUTHOR]

A long-term study of a bolster heath–pond system at Newdegate Pass, Mount Field, Tasmania, was designed to test a theory of cyclical dynamics and to determine why there was constancy in the proportions of species in stable mosaic bolster heath, while their individual distributions changed. Groups of permanent plots were monitored approximately once every 5 years between 1983 and 2017, in apparently stable, apparently colonising, apparently recovering and apparently degrading bolster heath. The putatively stable sites exhibited an average of 37% spatial turnover in the three early 5-year periods, with reciprocal replacements between many pairs of species; however, there was little evidence of long-term directional change except for expansion of a gymnosperm shrub across the top of the bolster mosaic at one site. This pattern suggests a cyclical succession of species in the stable mosaic; however, the mechanism driving cyclicity remains unclear, with facilitation, competition and stochastic processes being implicated at different times and locations. These cyclic changes were likely to have been largely endogenous, given the variability and autocorrelations in relative growth rates of the stable mosaic over short horizontal distances, conforming with neutral theory. The process of dam vegetation loss after draining was rapid, as was vegetation colonisation of the floor of one dam and recovery from fire. On a putatively colonising site on rocky ground, changes were subdued but directionally consistent with the previously proposed model, which was consistent with all long-term observations. The dynamics of a pond and mosaic bolster heath complex monitored for 35 years conformed to a posited cyclic pattern of organic dam growth, organic dam draining, dam dissolution and recolonisation of the dam floor. The stable mosaic bolster heaths between the ponds constantly changed patterns of species distribution while maintaining the same proportionate cover of individual species, a phenomenon most consistent with the stochastics of neutral theory. [ABSTRACT FROM AUTHOR]

Plant co-occurrence patterns can be driven by both abiotic and biotic conditions. Biotic interactions can affect the co-occurrence of seedlings and adult plants through the nurse effect, a form of facilitation where adult plants create favourable conditions for seedlings. However, other mechanisms, including seed trapping, can also cause the aggregation of seedlings around adult plants, resulting in similar co-occurrence patterns as the nurse effect, but this is yet to be examined. This study, therefore, tests if seed trapping drives co-occurrence patterns of two dominant plant species on sub-Antarctic Marion Island; the grass Agrostismagellanica and the cushion plant Azorellaselago. We compared A.magellanica seed, seedling and reproductive plant densities around A.selago plants, around similarly sized rocks and on the adjacent substrate. The abundance of A.magellanica seeds and seedlings did not differ significantly between different substrate types or direction (reflecting differing wind exposure). The abundance of mature A. magellanica individuals was significantly related to both substrate and wind exposure, although only weakly so. This suggests that neither cushion plants nor rocks trap seeds and that the high densities of A. magellanica observed with A. selago reflect stage-specific facilitation (i.e. improving the growth and/or survival of established plants). However, this is not consistently the case since complementary seed density datasets demonstrated that under some conditions cushion plants do act as seed traps. This study, therefore, highlights the need to explicitly consider the role of both seed dispersal and biotic interactions in plant communities, particularly before inferring nurse effects based on spatial co-occurrence patterns. [ABSTRACT FROM AUTHOR]

Soil and plants in natural ecosystems interact with each other. The different structures and characteristics of plant species in an area in the long term affect environmental variables, especially on the soil. This study aimed to investigate the effect of two plant species, Astragalus myriacanthus, and Acantholimon spinosum, on soil chemical properties in different spatial locations. Soil sampling was done in early fall 2018 by randomly selecting 20 replicates (10 individuals of each species) from four locations (upward slope edge, downward slope edge, center, and outside (as control)) in sycamore rangelands Naz, Yazd province. A total of 80 soil samples were collected. Then, soil chemical properties, including pH, EC, total organic matter (TOM), particulate organic matter (POM), and total nitrogen (TN) were measured in the laboratory. The effect of plant presence on soil properties showed that the parameters of organic matter (mean 1.66%), total nitrogen (mean 0.22%), electrical conductivity (mean 368.97 Ms/cm), and POM (with an average of 1.28%) in beneath A. myriacanthus were significantly higher than the soil outside the floor (with averages of 0.92%, 0.13%, Ms/cm 139.5, 58, respectively (P <0.05). TN and POM in the upslope edge were significantly higher than other edges. hr A. spinosum, there were no significant differences of TOM (1.77%), TN (0.23%), EC (215.46 Ms/cm), and pH (7.97) in beneath with outside the canopy. However, the POM with an average of 1.49% had the highest amount under the canopy relative to the outside soil and other sampling sides. In general, this study expresses the different roles of different cushion plants on the chemical and qualitative characteristics of the soil, which by recognizing this role can help improve, develop and maintain their habitats. [ABSTRACT FROM AUTHOR]

Cushion plants (as nurse species) can ameliorate soil conditions under their canopy in alpine environments. However, this amelioration (or the intensity of soil fertility islands) related with the size of plants is rarely studied. To assess size effects of Thylacospermum caespitosum on soil fertility islands, soil properties (pH; electric conductivity, EC; soil organic carbon, SOC; available nitrogen, AN; available phosphorus, AP; available potassium, AK) and microbial biomass (soil microbial biomass carbon, SMBC; soil microbial biomass nitrogen, SMBN) were investigated at three different elevations in the Qilian Mountains. Plant size significantly influenced (P < 0.001) soil properties (pH, EC, SOC, AN, AP, AK) and microbial biomass (SMBC and SMBN) at all three elevations. A size-dependent fertile island effect occurred beneath T. caespitosum, where the relative interaction index (RII) of soil properties and SMBC was affected (P < 0.001) by plant size at the three elevations. Moreover, most parameters of soil nutrition and microbial biomass under T. caespitosum were reduced (P < 0.001) with increases in elevation, but the RII was increased (P < 0.05). In short, soil amelioration by T. caespitosum was clearly dependent on plant size at all elevations, and this effect on soil increased with elevation. Thus, the existence of size-dependent fertility islands together with elevation should be regarded as a central mechanism of the nurse effect of T. caespitosum in harsh alpine ecosystems, where many ecological processes rely on the nurse effect of cushion plants. [ABSTRACT FROM AUTHOR]

Abstract Cushion plants are life forms with a hemispherical or mat‐like, prostrate canopy well adapted to the extreme conditions of cold regions that have appealed to scientists for their ability to cope with extreme environments in most mountains, arctic, and subantarctic regions of the world. They can buffer the effects of low temperature and drought and improve soil conditions, which makes them notable facilitator species. Living at the edge in the Atacama Desert is one such species, Azorella compacta (yareta or llareta), in the Apiaceae family that can reach much over 6 m (~20 ft) in diameter with a mat‐like shape that tends to hemispherical growth form. Azorella compacta can be found in the dry Puna system, which spreads from northern Chile and Argentina to southern Peru and western Bolivia, between 3800 and 5200 m elevation, making it one of the woody plant species occurring at highest elevations in the world. In this deserted edge of the Atacama, nutrient limitation adds to other stressors such as water scarcity and high UV radiation. A compact canopy and the fact that they are embedded in resin prevent beneficiary species from growing within the cushion and condition how senesced leaves decompose inside the canopy. They can reach 3000 yr old and have to deal with episodic disturbance and herbivory events. Plants in such environments may potentially act as microbial refuges, and it could be expected that bacterial endophytes and mycorrhizal fungi have a main role in the functioning of these survival champions.

Aim: Local effects of ecosystem engineers on biodiversity can scale up to the landscape level, stressing the importance of ecological processes as determinants of species richness at larger spatial scales. In harsh environments, cushion plants often act as ecosystem engineers given their ability to buffer extreme abiotic conditions, thus providing unique and more favorable niches for the establishment of less stress‐tolerant plant species. We assessed if facilitation by cushion plants influences patterns of plant diversity at increasing spatial scales. Location: Northern Patagonian Andes, Argentina. Methods: Based on plant species records within and outside cushions, we compared plant diversity in the presence and absence of cushions at the community, mountain and regional scale. Specifically, observed and estimated numbers of species occurring in either cushion plants or in the surrounding open areas were compared with the species numbers of the open areas. Results: The presence of cushion plants significantly increased species richness at all spatial levels analyzed. At the patch level, a higher number of species was recorded growing within cushion plants than in open area plots of similar size. Consistently, hypothetical communities lacking cushion plants showed significantly lower species richness than observed communities with cushion plants. These differences in species richness at patch and community scales increased with altitude, hence facilitation by cushion plants became more important at higher elevations. Moreover, according to asymptotic non‐parametric estimators, cushion plants could increase overall regional species richness up to 40%. Conclusions: Our findings suggest that about one third of the high‐Andean flora of the region owes its presence to the existence of nursing plants, defying the view that abiotic factors alone are enough to fully determine species occurrences at large spatial scales. This study provides evidence that local‐scale ecological processes can be crucial in promoting and maintaining biodiversity at any spatial scale. [ABSTRACT FROM AUTHOR]

The vegetation of the high-Andean cushion-plant peatlands is mainly characterized by the cushion-forming Juncaceae of the genus Oxychloe, Distichia and Patosia, as well as Cyperaceae of the genus Zameioscirpus. This particularity of Southern Hemisphere cushion peatlands is unique and exclusive to the high-Andean regions of South America. The floristic composition and site factors of 340 peatlands were studied between 1995-2013 to investigate changes in the vegetation of the high Andean peatlands from its southernmost distribution in Argentina (39° S, province of Neuquén) to the limit with Bolivia (22° S, province of Jujuy). Site factors were characterized based on water samples. Data for precipitation and temperature conditions was obtained from the WorldClim 2.0 dataset. Cushion-plant species and their accompanying flora clearly reflect the changing ecological conditions along the marked climatic gradient from south to north. A group of species is limited to the southern region of the study area (provinces of Neuquén and Mendoza), and another group is limited almost exclusively to the northern region (provinces of San Juan, La Rioja, Catamarca, Salta and Jujuy). Some Oxychloe species are distributed only in the transition zone between the winter and predominantly summer rainfall zone, however, many accompanying species show wide ecological amplitudes. The quality in the supply of minerals does not seem to play a decisive role in the differentiation of vegetation, except for the concentration of salts. Climatic conditions seem to be more relevant to the presence of the species. Our research shows that the survival of the plants is closely linked to the rainfall regime and seasonal temperature fluctuations. Similarly, the survival of plants and the potential formation of flowers and mature seeds depends on the presence of pollinators and species that disperse seeds (e.g. birds and camelids). Mobility by dispersion is also necessary for plant survival in the high Andean regions, which have experienced repeated climatic changes over the past centuries and millennia. This brought about the permanent displacement of the zoning of vegetation, and with it, the displacement of zones favorable for cushion-plant growth. The phylogenetic relationships and the spatial distribution suggest that the cushion-forming Juncaceae, depending on the evolution of climate, geomorphological processes and local site conditions, progressed step by step from the south to the north. Their current distribution is therefore largely understood as a result of short-term and long-term climatic changes. [ABSTRACT FROM AUTHOR]

Cushion plants are life forms with a hemispherical or mat-like, prostrate canopy well adapted to the extreme conditions of cold regions that have appealed to scientists for their ability to cope with extreme environments in most mountains, arctic, and subantarctic regions of the world. They can buffer the effects of low temperature and drought and improve soil conditions, which makes them notable facilitator species. Living at the edge in the Atacama Desert is one such species, Azorella compacta (yareta or llareta), in the Apiaceae family that can reach much over 6 m (~20 ft) in diameter with a mat-like shape that tends to hemispherical growth form. Azorella compacta can be found in the dry Puna system, which spreads from northern Chile and Argentina to southern Peru and western Bolivia, between 3800 and 5200 m elevation, making it one of the woody plant species occurring at highest elevations in the world. In this deserted edge of the Atacama, nutrient limitation adds to other stressors such as water scarcity and high UV radiation. A compact canopy and the fact that they are embedded in resin prevent beneficiary species from growing within the cushion and condition how senesced leaves decompose inside the canopy. They can reach 3000 yr old and have to deal with episodic disturbance and herbivory events. Plants in such environments may potentially act as microbial refuges, and it could be expected that bacterial endophytes and mycorrhizal fungi have a main role in the functioning of these survival champions. [ABSTRACT FROM AUTHOR]

Shifts in species geographic distributions in response to climate change have spurred numerous studies to determine which abiotic (e.g. climatic) and, less commonly, biotic (e.g. competitive) processes determine range limits. However, the impact of disturbances on range limits and their interactions with climatic and biotic effects is not well understood, despite their potential to alter competitive relationships between species or override climatic effects. Disturbance might have differential effects at contrasting range limits, based on Darwin's theory that biotic interactions set abiotically benign range limits and abiotic factors set abiotically stressful range limits.We predicted that plants at lower elevation (abiotically benign) range limits experience a net positive effect of disturbance, whereas those at higher elevation (abiotically stressful) range limits experience a net neutral effect. We examined plant populations along elevational gradients in the Colorado Rocky Mountains, in order to quantify the effects of human trampling disturbance at lower and upper elevational range limits of the common alpine cushion plants Silene acaulis and Minuartia obtusiloba.Our results are consistent with Darwin's theory. A disturbance‐mediated reduction of competitive effects increases the performance of cushion plants at lower elevations, suggesting a range limit set by biotic factors. At higher elevations, where biotic interactions are minimal, disturbance has neutral or negative effects on cushion plants.Synthesis and applications. Human trampling disturbance exerts differential effects on alpine cushion plant populations at contrasting range limits, emphasizing the need to account for the effects of climate change into the management and conservation of disturbed areas. Disturbance can diminish plant–plant competitive interactions at lower elevational range limits, and thus possibly stabilize alpine species populations susceptible to climate change‐mediated encroachment by lower elevation species. Conservation and management approaches should therefore particularly account for the differential effects of disturbance across climatic gradients. Human trampling disturbance exerts differential effects on alpine cushion plant populations at contrasting range limits, emphasizing the need to account for the effects of climate change into the management and conservation of disturbed areas. Disturbance can diminish plant–plant competitive interactions at lower elevational range limits, and thus possibly stabilize alpine species populations susceptible to climate change‐mediated encroachment by lower elevation species. Conservation and management approaches should therefore particularly account for the differential effects of disturbance across climatic gradients. [ABSTRACT FROM AUTHOR]

Variation in size may influence the abundance of visitors and reproductive allocation for cushion plants in the extreme alpine environments. To assess effects of plant size on the abundance of main visitors and reproductive allocation in Thylacospermum caespitosum populations at two altitudes, the abundance of the visitors, visiting frequency, total number of flowers, number of fruits, number of unseeded flowers, and reproductive allocation were investigated during the period of reproductive growth. Concurrently, the effects of plant size on the visitors' contributions to fruit setting rate were assessed by a bagging experiment. Our results showed that flies (Musca domestica and Dasyphora asiatica) were the main pollinating insects of T. caespitosum, and they could obvious facilitate (p < 0.05) the fruit setting rate of this cushion plant. Seed set and floral visitation were significantly influenced (p < 0.001) by plant size. Moreover, the reproductive allocation and fruit setting rate of T. caespitosum was influenced (p < 0.001) by plant size. More biomass was allocated to reproduction in plants of greater diameter. There is an increase in reproductive success (increases of fruit number with increase in plant size) in relation to plant size. In conclusion, the extent of M. domestica and D. asiatica to facilitate the fruit setting rate mainly depended on the size of T. caespitosum. Size‐dependent reproductive allocation occurred in T. caespitosum and was the chief factor affecting the contribution of flies to fruit setting rate. These traits reflect reproductive fitness of T. caespitosum related to plant size in extreme alpine environments. [ABSTRACT FROM AUTHOR]

Astelia pumila (G.Forst.) Gaudich. (Asteliaceae, Asparagales) is a major element of West Patagonian cushion peat bog vegetation. With the aim to identify appropriate chloroplast markers for the use in a phylogeographic study, the complete chloroplast genomes of five A. pumila accessions from almost the entire geographical range of the species were assembled and screened for variable positions. The chloroplast genome sequence was obtained via a mapping approach, using Eustrephus latifolius (Asparagaceae) as a reference. The chloroplast genome of A. pumila varies in length from 158,215 bp to 158,221 bp, containing a large single copy region of 85,981-85,983 bp, a small single copy region of 18,182-18,186 bp and two inverted repeats of 27,026 bp. Genome annotation predicted a total of 113 genes, including 30 tRNA and four rRNA genes. Sequence comparisons revealed a very low degree of intraspecific genetic variability, as only 37 variable sites (18 indels, 18 single nucleotide polymorphisms, one 3-bp mutation)-most of them autapomorphies-were found among the five assembled chloroplast genomes. A Maximum Likelihood analysis, based on whole chloroplast genome sequences of several Asparagales accessions representing six of the currently recognized 14 families (sensu APG IV), confirmed the phylogenetic position of A. pumila. The chloroplast genome of A. pumila is the first to be reported for a member of the astelioid clade (14 genera with c. 215 species), a basally branching group within Asparagales. [ABSTRACT FROM AUTHOR]

In the southern Andes mountains (27-39∘S) Azorella madreporica and Laretia acaulis, two Apiaceae cushion plant species commonly known as yaretas, conform a well-established altitudinal vegetation belt along the lower Andean zone. These species have been considered as fundamental components of several ecological dynamics within their communities; however, high-mountain ecosystems are increasingly threatened worldwide by natural and anthropogenic pressures and the southern Andes are not the exception. Recognizing that genetic information is crucial for the success of any conservation or restoration initiative in wild populations, we developed and cross-amplified 28 specifically designed microsatellite markers (14 in A. madreporica and 14 in L. acaulis), and also tested the cross amplification of 25 markers from the related species Azorella selago. In a region which is particularly vulnerable to global change trends, this new polymorphic microsatellite loci will be useful in the study of the genetic diversity of these high-mountain cushion plants, which are pivotal in the structuring of their native ecosystems. [ABSTRACT FROM AUTHOR]

For the first time, an isolated cushion-plant peat hillock was investigated, a so far neglected feature of high-Andean spring ecosystems. These small hillocks typically cluster around springs within the upper catchment areas of larger cushion-plant peatlands at altitudes ranging from 4000 m to 5000 m a.s.l. The size of the investigated peat hillock, located within the Río Viscas catchment area (Lucanas province, District of Ayacucho) at 4250 m a.s.l., is relatively small (about 10 m in diameter). Due to its dome-shaped and densely green habitus, it overlooks the surrounding vegetation by about 1–2 m and stands out by its color. Terrestrial laser scanning (TLS) techniques are used in order to provide insights into the spatial extension of the Distichia muscoides -dominated vegetation stand. For the reconstruction of environmental dynamics during the past millennium, plant micro-/macrofossil analyses and total carbon/total nitrogen measurements were applied. Based on radiocarbon dating, the peat archive provides a chronology for the past 1050 years. We interpret phases of relatively high abundances of Poaceae pollen in our record as an expansion of Andean grasslands during humid phases. Drier conditions are indicated by a decrease of Poaceae pollen and higher abundances of Asteraceae pollen. The results reflect significant climate oscillations and provide evidence for a sustained dry phase between AD 900 and AD 1100. A more humid and cooler phase prevailed from around AD 1300 to AD 1825, during the Little Ice Age. Our data provide evidence that such a spatially defined peat-accumulating ecosystem, as represented by the studied peat hillock, is capable to survive pronounced climatic oscillations as long as it does not lose its protective cushion-plant surface. As peat hillocks are heavily affected by grazing, multitemporal studies should be carried out to document changes and to provide new insights into adaption strategies of vegetation to changing environmental conditions. [ABSTRACT FROM AUTHOR]

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We describe patterns of plant species and growth form abundance in the puna vegetation of Parque Nacional Lauca, Chile. At more than 4,300 m, the extreme habitat of the study site supported relatively few species. These few species, however, represented a diverse array of growth forms that were organized with respect to distinct environmental gradients. Both species richness and growth form diversity increased with the degree of habitat rockiness and on more xeric north and east facing slopes. These xeric, rocky sites supported the greatest overall abundance of cushion forms. Less rocky sites with more soil development supported a greater abundance of tussock grass and shrub forms. Congeneric species occupied distinct microhabitats and were often markedly divergent in growth form. These patterns suggest that water and thermal stress are critical forces shaping functional form as well as community organization in the high Andean punaDescribimos los patrones de abundancia de las especies vegetales y las formas de vida en la vegetación de puna en el Parque Nacional Lauca, Chile. A una altitud que excede los 4.300 m de altitud, el hábitat extremo de nuestro sitio de estudio presenta relativamente pocas especies. Dichas especies, sin embargo, representan un arreglo diverso de formas de vida organizadas con respecto a distintos gradientes ambientales. Tanto la riqueza de especies como el hábito de crecimiento aumentaron en los suelos más rocosos y en las pendientes expuestas al norte y al este, cuya vegetación es más xerófila. Dichos sitios presentaron la mayor abundancia en formas de cojines. Los sitios menos rocosos con un suelo más desarrollado presentaron una mayor abundancia de pastos y arbustos. Distintos microhábitats fueron ocupados por especies congénericas que con frecuencia divergieron en su hábito de crecimiento. Los patrones observados sugieren que el agua y el estrés térmico son fuerzas críticas que moldean la forma funcional de las especies vegetales así como la organización de las comunidades de plantas en la puna altoandina

A herbarium-based revision is provided for Paepalanthus pilosus and allies, five commonly confused species of cushion plants native to Andean paramo. These are placed in the recircumscribed Paepalanthus subsect. Cryptanthella Suess. The group includes P. pilosus, P. dendroides, and P. lodiculoides. An additional two species and one variety are newly described: Paepalanthus caryonauta, P. huancabambensis, and P. pilosus var. leoniae. The latter two are Peruvian endemics, while P. caryonauta is known from four countries, and has long been confused with other species. An additional, possibly undescribed taxon is noted from the Serrania de Perijá, Colombia. Five new synonyms and three lectotypes are proposed, and the common misapplication of some names is noted. Within the P. pilosus complex, species differences were found in timing of peduncle elongation, sex ratio, and leaf, perianth, diaspore and nectary morphology. Ecological differences are suggested by specimen data and a review of ecological literature. Descriptions, photographs and maps are provided for all species, as is a key to the groups of eriocaulaceous cushion plants from Andean South America. [ABSTRACT FROM AUTHOR]

Cushion-forming species occur in all cold and dry environments worldwide, where they play important engineering roles. Understanding the origins of cushion plants may thus provide insights into the evolutionary assembly of biomes under extreme climatic conditions. Here we investigate the evolutionary and biogeographic history of cushions in Angiosperms based on a global checklist of all cushion plants, along with phylogenetic, climatic, and biogeographic information. Our aim is to measure the frequency of this evolutionary convergence and to identify its historic, environmental, and biogeographic drivers. We show that cushions appeared at least 115 times in Angiosperms and that they mainly belong to families that occupy the coldest and driest environments on Earth. We found that cushions have intensively diversified in the Himalayas, the Andes, or New Zealand, while other regions like Patagonia have probably been hubs enabling cushion species to migrate between different alpine regions. We conclude that the cushion life form is a remarkable example of convergent key innovation, which has favored the colonization of cold and dry habitats. [ABSTRACT FROM AUTHOR]

Aims Positive interactions are defined as non-trophic interactions where at least one of the interacting species is benefited in terms of fitness and the other remains unaffected. Nevertheless, the bidirectional feedbacks between species may be positive, neutral or negative. Thus, if facilitated species induce negative effects on their 'nurses', the assumed definition of positive interactions could be reconsidered. Methods We assessed if ecological interactions between cushions of Azorella madreporica and their facilitated species are positive. Specifically, we tested if cover of facilitated species has any costs for cushion plants from an ecophysiological perspective, and if these costs increase with the amount of cover of facilitated species. In addition, through pathway analysis and correlations, we assessed if cover and richness of facilitated species have a direct and/or indirect effect on the fitness of cushion plants. Important Findings We found that facilitated plant species induced a significant cost for their nurses (cushion plants), and this cost increases with cover of the facilitated species. Additionally, the facilitated species exert a strong direct negative effect on the cushion's fitness and a moderate indirect negative cost evident through the nutrient status and physiological performance of cushion plants. We thus contribute evidence that positive interactions between high mountain cushion plants of central Chile and their 'facilitated' species may be an artifact more than a fact, especially when bidirectional effects are considered; contrasting with the majority of studies that document only one side of the interaction. [ABSTRACT FROM AUTHOR]

Positive interactions have started to gain a place as important drivers of community structure and biological diversity. Defined as non-trophic interspecific interactions that increase the average individual fitness of one species, by definition, the presence of one plant species enhances the chances that another species co-occur in the same place, indicating that positive interactions may determine biological diversity. However, this has been poorly explored., The majority of the studies addressing community-level consequences of facilitation have compared the diversity of the plant assemblages growing within nurses vs. those growing outside them, reporting contrasting results among them. Nonetheless, nurses and their alternative microhabitats (open areas among nurses) are part of the same community. Thus, if nurses allow for the persistence of species that otherwise would be excluded from the community, a net increase in the species diversity at the entire community level will be generated even though nurse plants contained fewer species than open areas., Here, we conducted a bibliographic search using the ISI Web of Knowledge data base and reviewed the literature conducted on alpine plant communities where assessments of the diversity of plants growing within and outside a nurse species were available. In most cases nurse species substantially increased species richness at the community level, despite the fact that in some cases, they contained lower species numbers than open areas. Nurse species enhanced species richness more in systems with impoverished local diversity, suggesting that facilitative interactions in alpine habitats act as an insurance policy that sustains diversity under very harsh conditions. [ABSTRACT FROM AUTHOR]

In facilitative interactions, the beneficiary feedback effect ( BFE) has been defined as the effect of beneficiary species (facilitated species) on their benefactor. BFEs have been shown to be dependent on environmental conditions and the composition of the beneficiary community. In alpine cushion systems, BFEs are more negative with more abundant, diverse and phylogenetically aggregated communities of beneficiary species., We tested the hypothesis that the functional composition of the beneficiary communities correlates with the direction and strength of BFE received by alpine cushion benefactors and specifically that a more negative BFE would occur with increasing density of graminoids and a more positive BFE would occur with increasing density of forbs and legumes. Additionally, we predicted that the negative BFE of graminoids would increase with increasing summer aridity., We used a data base of alpine cushion communities from 30 sites throughout the world to assess the overall relationship between the composition of beneficiary communities and the total flower density of cushion benefactors, and its variation with increasing drought. Additionally, in order to assess more precisely the role of the functional composition of the beneficiary communities on BFE in a very dry site with cushion benefactors exhibiting contrasting functional compositions of beneficiary communities, we also designed a field study in the Qilian Shan mountain range (China). At this site with a highly continental climate, we compared the number of flowers and fruits of different phenotypes of the alpine cushion species Thylacospermum caespitosum hosting numerous graminoids, numerous forbs or very few beneficiary species., In the intercontinental study, we found a negative relationship between graminoids and cushion benefactor flower density but no effect of other functional groups. The negative BFE of graminoids increased with increasing summer drought. In the dry Qilian Shan range, we found both a negative effect of graminoids on total flower density and a positive effect of forbs on flower density and fruit set., Our study indicates that the context dependence of BFE may be partially explained by the composition of beneficiary communities and in particular the negative effect of graminoids. [ABSTRACT FROM AUTHOR]

Las plantas en cojín que crecen en ambientes de alta montaña modifican microclimáticamente su entorno, generando microhábitats favorables para el establecimiento de otras especies, actuando como nodrizas. Varios estudios han demostrado que los cojines contienen una mayor riqueza de especies que los espacios abiertos. Sin embargo, hasta ahora, no se ha evaluado el efecto de los cojines sobre otros parámetros comunitarios como la abundancia de individuos, la diversidad y la equitatividad. En este trabajo se analiza el efecto que posee Oreopolus glacialis, una planta en cojín de la cordillera andina, sobre la riqueza, abundancia, diversidad y equitatividad de la comunidad vegetal en un ambiente de alta montaña ubicado a 1.900 m en Chile central. Se determino la riqueza y abundancia de especies que crecen tanto sobre cojines de O. glacialis como en los espacios abiertos entre cojines. Los resultados mostraron que la riqueza de especies y la abundancia de individuos por unidad de área es mayor dentro de los cojines que fuera de ellos. Sin embargo, los valores de diversidad y equitatividad sobre O. glacialis fueron menores que fuera de ellos debido a la presencia de algunas especies dominantes. Análisis particulares de la frecuencia y abundancia de cada especie mostraron que no todas las especies son afectadas de la misma manera por la presencia de este cojín, por lo que O. glacialis actuaría como nodriza sólo para una parte limitada de los componentes de la comunidadCushion plants growing in high mountain habitats can modify the microclimate within their canopy generating microhabitats more favorable for the recruitment of other plant species, acting as nurse plants. Although several studies have shown that species richness is higher within cushions than outside them, no attempts have been made in order to assess the effect of cushions on other community aspects such as total and individual abundance, diversity and evenness. In this study we analyzed the effect of Oreopolus glacialis -a cushion plant from the South American Andes- on the species richness, total and individual abundance, diversity and evenness of a plant community located in a high mountain environment at 1,900 m of altitude in central Chile. Species richness and abundance were determined both within and outside O. glacialis cushions. Results showed that, per area, species richness and individual abundance were higher within cushions. In contrast, diversity and evenness within O. glacialis cushions were lower than outside. This apparent incongruence was caused by some species being highly dominant within cushions. Analyses of the frequency and abundance of each species showed that not all the species were affected in the same way by the cushions, with only four species growing more frequently within cushions. This suggests that nurse effect of O. glacialis is a species-specific phenomenon

While there is a large consensus that plant–plant interactions are a crucial component of the response of plant communities to the effects of climate change, available data remain scarce, particularly in alpine systems. This represents an important obstacle to making consistent predictions about the future of plant communities. Here, we review current knowledge on the effects of climate change on facilitation among alpine plant communities and propose directions for future research. In established alpine communities, while warming seemingly generates a net facilitation release, earlier snowmelt may increase facilitation. Some nurse plants are able to buffer microenvironmental changes in the long term and may ensure the persistence of other alpine plants through local migration events. For communities migrating to higher elevations, facilitation should play an important role in their reorganization because of the harsher environmental conditions. In particular, the absence of efficient nurse plants might slow down upward migration, possibly generating chains of extinction. Facilitation–climate change relationships are expected to shift along latitudinal gradients because (1) the magnitude of warming is predicted to vary along these gradients, and (2) alpine environments are significantly different at low vs. high latitudes. Data on these expected patterns are preliminary and thus need to be tested with further studies on facilitation among plants in alpine environments that have thus far not been considered. From a methodological standpoint, future studies will benefit from the spatial representation of the microclimatic environment of plants to predict their response to climate change. Moreover, the acquisition of long-term data on the dynamics of plant–plant interactions, either through permanent plots or chronosequences of glacial recession, may represent powerful approaches to clarify the relationship between plant interactions and climate change.

Nurse plant facilitation is a commonly reported plant–plant interaction and is an important factor influencing community structure in stressful environments. Cushion plants are an example of alpine nurse plants that modify microclimatic conditions within their canopies to create favourable environments for other plants. In this meta-analysis, the facilitative effects of cushion plants was expanded from previous syntheses of the topic and the relative strength of facilitation for other plants and for arthropods were compared globally.The abundance, diversity, and species presence/absence effect size estimates were tested as plant responses to nurse plants and a composite measure was tested for arthropods. The strength of facilitation was on average three times greater for arthropods relative to all plant responses to cushions. Plant species presence, i.e., frequency of occurrence, was not enhanced by nurse-plants. Cushion plants nonetheless acted as nurse plants for both plants and arthropods in most alpine contexts globally, and although responses by other plant species currently dominate the facilitation literature, preliminary synthesis of the evidence suggests that the potential impacts of nurses may be even greater for other trophic levels.

Differences in effects between phenotypes of foundation species on subordinate species have been reported, but no study has separated their heritable and plastic components. In a subalpine community of the French Pyrenees, we observed two phenotypes of Festuca gautieri: tight cushions in dry convex outcrops with few subordinate species and loose cushions in wet concave slopes with many subordinate species, suggesting differences in effects of the two phenotypes on subordinates., Using two reciprocal transplantation gardens, we studied the responses of the two phenotypes to changes in environmental conditions, thus assessing the contribution of heritability and plasticity to the phenotypic variation. Using a target cross-transplantation experiment, we assessed the plasticity and heritability bases of their contrasting effects. We also quantified the recolonization of resident plants within the reciprocally transplanted cushions., We found that morphological differences between cushions had both heritability and plasticity bases. The two competition experiments showed heritable increase in competitive effects from loose to tight cushions. This was counteracted by plasticity effects, which decreased competition from the benign to the stressful garden., Synthesis. We conclude that heritable effects overcome plasticity effects resulting in higher diversity in the loose phenotype from the benign habitats. [ABSTRACT FROM AUTHOR]

Foundation species can change plant community structure by modulating important ecological processes such as community assembly, yet this topic is poorly understood. In alpine systems, cushion plants commonly act as foundation species by ameliorating local conditions. Here, we analyze diversity patterns of species' assembly within cushions and in adjacent surrounding open substrates (83 sites across five continents) calculating floristic dissimilarity between replicate plots, and using linear models to analyze relationships between microhabitats and species diversity. Floristic dissimilarity did not change across biogeographic regions, but was consistently lower in the cushions than in the open microhabitat. Cushion plants appear to enable recruitment of many relatively stress-intolerant species that otherwise would not establish in these communities, yet the niche space constructed by cushion plants supports a more homogeneous composition of species than the niche space beyond the cushion's influence. As a result, cushion plants support higher adiversity and a larger species pool, but harbor assemblies with lower β-diversity than open microhabitats. We conclude that habitats with and without dominant foundation species can strongly differ in the processes that drive species recruitment, and thus the relationship between local and regional species diversity. [ABSTRACT FROM AUTHOR]

Question The biotic resistance hypothesis states that species diversity is a barrier for plant biological invasions because alien species are more likely to find strong competitors as diversity of native plants increases. In stressful environments, however, these negative relationships could be diluted because increased physical harshness might reduce the importance of competition as a structuring force in plant communities. Nevertheless, if nurse plants facilitate other species and create more diverse vegetation patches than those found in their surroundings, the performance of invaders should be negatively related to diversity within these patches. Conversely, diversity would not regulate invasibility in the surroundings of nurses because these habitats are subjected to higher levels of environmental harshness. Location A high-Andean landscape of central Chile, dominated by cushion plants that facilitate native species and field chickweed ( Cerastium arvense), an invasive exotic species. Methods To test our hypotheses we used observational data taken in two consecutive growing seasons by sampling plant assemblages within and outside cushion-protected patches. Additionally, a field experiment with artificially assembled plant communities was conducted to assess why the abundance and performance of the invasive species was related to native plant diversity. Results Contrary to our expectations, observational data indicated that the abundance of the invader species was positively related to native plant diversity within cushion patches, while negative relationships were found in the surrounding habitat. Similarly, the field experiment indicated that the performance of C. arvense increased with plant diversity within cushion patches but, in this case, neutral relationships were found in the surrounding open areas. Conclusions Our findings indicate that nurse plants can modulate invasibility-diversity relationships in harsh environments. Overall, the results suggest that the biotic resistance hypothesis may fail to predict the direction of these relationships within nurse-protected patches. Instead, these results suggest that the alternative biotic acceptance hypothesis could operate at small spatial scales. [ABSTRACT FROM AUTHOR]

Questions What is the community-level consequence of biotic processes, in particular the importance of facilitation, in determining patterns of diversity in alpine plant communities of the Himalayan Hengduan Mountains? Does facilitation intensity change with environmental severity, and are these changes due to environmental severity or nurse trait effects? Location Eleven alpine plant communities dominated by cushion plants in the Himalayan Hengduan Mountains, within the mountain system of south-central China. Methods We determined plant species richness and abundance in habitats created by cushions and cushion-free areas, and assessed the cushion effects on species richness and abundance with rarefaction curves and the relative interaction index, respectively. We examined the relationship between cushion effects on diversity and habitat severity and tested if changes in the net cushion effects along the severity gradient were due to a change in the performance of species without cushions (environmental severity effect) and/or with cushions (nurse trait-mediated effect). Results The presence of cushion plants increased species richness and abundance in most studied plant communities. The net facilitation effect of cushions increased with increasing habitat severity, an effect that could be attributed mainly to a reduction in species richness in cushion-free areas with increasing severity. However, the changes in magnitude of facilitation of particular cushion species growing in high and low severity habitats could be attributed to both environmental severity and neighbour trait effects. Despite the overall positive effect of cushion plants on plant species richness, not all cushion species contributed to higher species richness. The deviation of individual cushion species from the general pattern of increasing facilitation with increasing severity indicated the species specificity of facilitation depends on the traits of nurse species. Conclusion The presence of cushion plants generally increased species richness in alpine plant communities of the Himalayan Hengduan Mountains, with the importance of the cushion effect increasing with habitat severity due to a buffering effect by cushions of the negative effect of habitat severity on species richness observed in cushion-free areas. This indicates the pivotal role of facilitative interactions among plant species in supporting high diversity in these severe environments. [ABSTRACT FROM AUTHOR]

The Siberian cushion plants have been little studied. This research aimed to reveal their morphological and ecological features as enabling them to survive and to protect biodiversity in a changing environment. The research was conducted in the Altai Mountains, Russia, at 1750–4000 m a.s.l. The temperature of cushion plants, the surrounding air and soil were studied. Substrate samples from cushions and topsoil were taken and analysed. Indices of hydrolytic acidity, loss on ignition and percentage of humus, phosphorus and nitrogen were taken into account in soil analysis. Bryophytes and vascular plants inhabiting cushions were studied. Fifty-four cushion plant species were classified into six morphological types based on the cushion skeleton construction and divided into ‘obligate’ and ‘facultative’ cushion plants. The temperature inside the cushions is much more stable, than that of their environment. Accumulation of organic matter within the cushions and in the sphere of their vital functions represents a process of local primary soil formation and makes cushion plant communities indifferent to the ground quality. The functional features of the cushion plants allow them to occupy high-mountain habitats and to be the centres of communities including other plants and animals, which can be found in an extreme environment only within or near the cushions, increasing the biological diversity of the alpine mountain zone. [ABSTRACT FROM PUBLISHER]

Facilitation has been proposed to be a fundamental mechanism for plant coexistence, being particularly important in highly stressful environments such as alpine environments. In this type of environment, species called “cushion plants” can ameliorate the stressful conditions, acting as nurses for other plants. Of the several mechanisms proposed in the positive-interactions framework, plant–microorganism interaction may be one of the most common, but least documented. Here we show that the presence of endophytes isolated from the roots of cushion plants Laretia acaulis can play a fundamental role in the establishment, performance and survival of both native and exotic plant seedlings that are known to be facilitated by the cushion species. To test this, we measured survival and growth of two native and one invasive species at 3200 m in the Andes of Central Chile. Plants were grown inside artificial cushions filled with native soil, with or without sterilization, and with or without fungal endophytic inoculation to evaluate the role of fungal endophytes on survival and growth. In addition, we conducted a second experiment in a greenhouse with the invasive species to evaluate the effect of fungal endophytic infection/association on plant ecophysiological performance, dry biomass and seed output. Overall, our results showed a strong positive effect of fungal endophytes on the survival and growth of both native and invasive species. Moreover, maximum quantum efficiency (Fv/Fm), biomass accumulation and seed production were enhanced in the invasive species when soils were inoculated with endophytes. Thus, facilitation by root endophytic fungi on native and invasive alpine plants could determine survival and establishment in this harsh environment. Several studies have shown that direct facilitation by cushion plants in alpine environments improves the performance and fitness of both native and exotic plants. Our results suggest that there are indirect effects, mediated by microorganism associations that may also help to explain the successful establishment of native and invasive species in these environments. If indirect plant–plant facilitation through root fungal endophytes proves to be a widespread phenomenon in alpine ecosystems, it could be a key component in the structuring of plant communities in those stressful environments. [ABSTRACT FROM AUTHOR]

Questions Are variable effects of different phenotypes of foundation plant species on subordinates across contrasting habitat conditions (with varying stress and disturbance levels) due to either varying environmental conditions or heritable differences in traits between phenotypes? To evaluate the contribution of environmental effects we quantified the effects of contrasting phenotypes of a foundation legume shrub on their subordinate species across exposure (drought stress) and grazing conditions. Location A sub-alpine xerophytic community of western Mount Lebanon, Lebanon. Methods For two phenotypes of the spiny cushion shrub Onobrychis cornuta, a facilitative phenotype that occurs in concave topographies (mesic soil) and a competitive phenotype that occurs in convex topographies (xeric soil), we quantified cushion traits, environmental conditions and subordinate plant species abundances (within and outside the cushions) for the two phenotypes in northern (low stress) and southern (high stress) exposures, and with and without grazing. Relative interaction index ( RII) for subordinate species richness and abundance was calculated in the eight treatment combinations and a correspondence analysis ( CA) was conducted on species composition. Results Drought stress exacerbated phenotypic effects in southern exposure, with loose phenotypes being more facilitative and tight phenotypes more competitive than in northern exposure. This was related to both changes in cushion traits of the two phenotypes and to an increase in the pool of subordinate species sensitive to cushion effects. In contrast, grazing increased cushion positive effects of both phenotypes through the occurrence of indirect facilitation, with loose phenotypes becoming more facilitative and tight phenotypes less competitive. This was due both to changes in cushion traits of the two phenotypes and to their shared spiny phenotype limiting grazing effects. Conclusions Because increasing stress from northern to southern exposure did not increase competitive effects of either phenotype, and because the cessation of grazing did not cancel out differences in facilitative effects between phenotypes, neither drought stress nor grazing disturbance appeared to be the main drivers of the observed phenotypic effects on subordinate species across habitats. We conclude that differences in phenotypic effects of this legume shrub are very likely due to heritable differences in traits between phenotypes. [ABSTRACT FROM AUTHOR]

While there is a large consensus that plant-plant interactions are a crucial component of the response of plant communities to the effects of climate change, available data remain scarce, particularly in alpine systems. This represents an important obstacle to making consistent predictions about the future of plant communities. Here, we review current knowledge on the effects of climate change on facilitation among alpine plant communities and propose directions for future research. In established alpine communities, while warming seemingly generates a net facilitation release, earlier snowmelt may increase facilitation. Some nurse plants are able to buffer microenvironmental changes in the long term and may ensure the persistence of other alpine plants through local migration events. For communities migrating to higher elevations, facilitation should play an important role in their reorganization because of the harsher environmental conditions. In particular, the absence of efficient nurse plants might slow down upward migration, possibly generating chains of extinction. Facilitation-climate change relationships are expected to shift along latitudinal gradients because (1) the magnitude of warming is predicted to vary along these gradients, and (2) alpine environments are significantly different at low vs. high latitudes. Data on these expected patterns are preliminary and thus need to be tested with further studies on facilitation among plants in alpine environments that have thus far not been considered. From a methodological standpoint, future studies will benefit from the spatial representation of the microclimatic environment of plants to predict their response to climate change. Moreover, the acquisition of long-term data on the dynamics of plant-plant interactions, either through permanent plots or chronosequences of glacial recession, may represent powerful approaches to clarify the relationship between plant interactions and climate change. [ABSTRACT FROM AUTHOR]

Cushion plants have long fascinated botanists for their ability to cope with extreme environments in most mountains and arctic regions of the world. One century ago, a first worldwide catalogue of species forming cushions was published by Hauri and Schröter (Bot Jahrb Syst Pflanzengesch Pflanzengeogr 50:618-656, ). Here, we defined a simplified typology of cushion plants and updated the worldwide catalogue of cushion species, along with information on their geographic distribution. This compilation was based on available information in floras and catalogues but also in efloras and virtual encyclopedias, which were screened using automated database queries. We established a list of 1,309 cushion-forming species distributed in 272 genera and 63 families of angiosperms. Compact cushions are represented by 678 species, among which 587 species exhibit a hemispherical shape, and 91 species exhibit a flat to mat shape. We found 398 species forming non-compact hemispherical cushions. The list of cushion species has significantly increased since Hauri and Shröter, due to the description of new species, updated regional inventories, and improved access to electronic databases. Uncertainties in the delineation of the cushion life form are discussed, notably for non-compact growth forms. A website has been launched to display the catalogue and enable a collaborative improvement of the database (). The distribution of the species is presented on the basis of the world geographical scheme for recording plant distributions and global biodiversity information facility data. This catalogue will serve as a reference database for further analyses on the biogeography and evolutionary history of cushion plants and arctico-alpine biotas. [ABSTRACT FROM AUTHOR]

A recent article published by Molina-Montenegro et al. ( Journal of Vegetation Science24: 463) examines the association of Antarctic native plant and lichen species to the lichen Usnea antarctica on Fildes Peninsula, King George Island, maritime Antarctica. The authors report that on two sites, five out of 13 and four out of 11 species of lichens and mosses were spatially associated with U. antarctica, suggesting positive interactions between them. Although Deschampsia antarctica does not grow naturally associated with U. antarctica, Molina-Montenegro et al. carried out a transplantation experiment to demonstrate that the macrolichen acts as a nurse plant, improving the survival of the grass. Serious conceptual and methodological discrepancies emerge from a critical evaluation of this study, challenging their conclusions. First, we suspect that the author confused some lichen taxa, and we also disagree with macrolichens being treated as cushion plants, because rootless, poikilohydric and poikilothermic thallophytes such as lichens are unable to create a stable, enclave-like microhabitat as vascular cushion plants do. Indeed, a critical evaluation of some of the micro-environmental parameters measured indicates that there are no biologically meaningful differences between the U. antarctica thalli and surrounding open areas. Second, the lack of consideration of the life history of the species under study leads to confusion when (a) referring to the succession sequence of species that colonize the studied area and (b) interpreting the putative distribution patterns promoted by Usnea versus the substrate preferences of associated species. Third, the authors intend to demonstrate experimentally that Usnea can facilitate the survival of D. antarctica plants, transplanting adult plants and not seedlings between the lichen thalli, and it is not clear how the grass was planted - between or within the lichens - as at both experimental sites the lichens grow on stones or rocks. Facilitative interactions are present in the Antarctic and may play a pivotal role in the structure and functioning of the fragile Antarctic ecosystems. However, more rigorous and well-planned research is needed to assess its presence, importance and involved mechanisms. [ABSTRACT FROM AUTHOR]

Question Have there been shifts in abundance and distribution of alpine and sub-alpine plant species along an elevational gradient in an arid North American mountain range during the last half-century? Location Elevational gradient in the White Mountains, California, USA (37°30′ N, 118°10′ W). Methods We conducted a 49-yr re-survey of plant species distribution and abundance in areas originally surveyed in 1961. Species abundance data were collected along line transects between elevations of 2900 and 4000 m. We evaluated the degree of plant community shift over time across elevations; specifically, we expected species ranges to shift upward such that species peak abundances would be observed higher in elevation in 2010 than in 1961. To address this expectation we conducted a permutational multivariate linear model analysis with elevation, soil type and year as factors. We further performed single-species analyses to evaluate how focal species contributed to the multivariate community-level shifts between 2010 and 1961, and how these varied across elevations and soil types. Growing season climate data (June 1 through October 31) collected between 1961 and 2010 were analysed to quantify the change in annual mean temperature and precipitation at this site. Results We found that Artemisia rothrockii increased in abundance at the upper reaches of its distribution between the 2010 and 1961 surveys. Additionally, we recorded significant declines in abundances in the lower elevation ranges of three alpine cushion plants: Trifolium andersonii, Phlox condensata and Eriogonum ovalifolium. These shifts coincided with a 0.98 °C increase in mean growing season temperatures and a 53 mm decrease in mean annual precipitation between 1961 and 2010. Conclusions These results suggest that rising temperatures and decreasing precipitation are negatively impacting alpine plant species while promoting expansion of sub-alpine species, possibly signalling the transition of this alpine plant community to sagebrush steppe. [ABSTRACT FROM AUTHOR]

Background:The relationship between plant traits and environmental factors will be of value in understanding of functional strategies that plants have developed to cope with the environmental constraints on plant life in Mediterranean high mountain ecosystems. Aims:The aims of this study were (1) to explore the variation in plant traits in relation to environmental variability; (2) to analyse the functional strategies of species; and (3) to assess the habitat constraints for the species in the study area. Methods:We sampled the floristic composition of 76 1 m × 1 m plots on five summits over 2,100 m above sea level in the mountains of the Sistema Central, Spain. Soil properties and temperature and grazing disturbance parameters were recorded. Eight plant traits were assessed in 21 species. Environmental variability and the co-variation of functional traits were analysed by RDA and PCA, respectively. Plant traits and environmental variability were related using fourth-corner analysis. Results:Traits related to resource acquisition, such as leaf size and N concentration, varied with soil temperature and estimated summer water availability. Leaf dry matter content was found to be related to estimated water availability and soil pH. Seed mass was a factor of snow cover duration and water availability, and clonality to the duration of the vegetative period and estimated water availability. Grazing disturbance was related to the mean plant height of the species. Conclusions:The results suggest that low temperatures, rather than water shortage, may be the principal limiting factor for resource acquisition in plants. Nevertheless species establishment is limited by water shortage during summer in these Mediterranean high mountain communities. [ABSTRACT FROM PUBLISHER]

Aim We still have limited understanding of the contingent and deterministic factors that have fostered the evolutionary success of some species lineages over others. We investigated how the interplay of intercontinental migration and key innovations promoted diversification of the genus Androsace. Location Mountain ranges and cold steppes of the Northern Hemisphere. Methods We reconstructed ancestral biogeographical ranges at regional and continental scales by means of a dispersal-extinction-cladogenesis analysis using dated Bayesian phylogenies and contrasting two migration scenarios. Based on diversification analyses under two frameworks, we tested the influence of life form on speciation rates and whether diversification has been diversity-dependent. Results We found that three radiations occurred in this genus, at different periods and on different continents, and that life form played a critical role in the history of Androsace. Short-lived ancestors first facilitated the expansion of the genus' range from Asia to Europe, while cushions, which appeared independently in Asia and Europe, enhanced species diversification in alpine regions. One long-distance dispersal event from Europe to North America led to the diversification of the nested genus Douglasia. We found support for a model in which speciation of the North American- European clade is diversity-dependent and close to its carrying capacity, and that the diversification dynamics of the North American subclade are uncoupled from this and follow a pure birth process. Main conclusions The contingency of past biogeographical connections combined with the evolutionary determinism of convergent key innovations may have led to replicated radiations of Androsace in three mountain regions of the world. The repeated emergence of the cushion life form was a convergent key innovation that fostered radiation into alpine habitats. Given the large ecological similarity of Androsace species, allopatry may have been the main mode of speciation. [ABSTRACT FROM AUTHOR]

Positive interactions between species are known to play an important role in the structure and dynamics of alpine plant communities. The balance between negative and positive interactions is known to shift along spatial and temporal gradients, with positive effects prevailing over negative ones as the environmental stress increases. Thus, this balance is likely to be affected by climate change. We hypothesized that increases in temperature (a global warming scenario) should decrease the importance of positive interactions for the survival and growth of alpine plant species. To test this hypothesis, we selected individuals of the native grass species Hordeum comosum growing within the nurse cushion species Azorella madreporica at 3,600 m.a.s.l. in Los Andes (Chile), and performed nurse removal and seedling survival experiments under natural and warmer conditions. For warmer conditions, we used open-top chambers, which increased the temperature by 4 °C. After two growing seasons, we compared the effect of nurse removal on the survival, biomass, and photochemical efficiency of H. comosum individuals under warmer and natural conditions. Nurse removal significantly decreased the survival, biomass, and photochemical efficiency of H. comosum, demonstrating the facilitative effects of nurse cushions. Seedling survival was also enhanced by cushions, even under warmer conditions. However, warmer conditions only partially mitigated the negative effects of nurse removal, suggesting that facilitative effects of cushions do not wane under warmer conditions. Thus, facilitative interactions are vital to the performance and survival of alpine species, and these positive interactions will continue to be important in the warmer conditions of the future in high-alpine habitats. [ABSTRACT FROM AUTHOR]

• Premise of the study: Plant movement is more widespread than often recognized, involving different organs and mechanisms. Hygrochasy (opening in response to moisture) is a capsule-opening movement that is widely believed to be predominantly a feature of plants of desert and arid zones, where it may protect against seed predators and harsh climatic conditions and restrict dispersal to favorable germination times and sites. However, recently it has been reported from a wider range of environments. This study demonstrates that hygrochasy is much more common than previously realized, extending the phenomenon to plants of alpine habitats. • Methods: Capsules of 23 species of New Zealand Veronica were collected, and we used light microscopy to investigate the anatomy and biomechanics responsible for the opening mechanism. Additionally, we collected morphological data to identify common traits of hygrochastic species. • Key results: Hygrochastic capsule dehiscence was found in 10 alpine Veronica species. The opening mechanism is based on an antagonistic reaction between a nonlignified swelling tissue and a lignified resistance tissue. In Veronica, hygrochasy is associated with erect, narrowly angustiseptate capsules on short peduncles of creeping subshrubs or cushion plants. • Conclusion: Hygrochasy is a common dehiscence type in New Zealand alpine Veronica. and for the first time, this mechanism is described in detail for plants in alpine habitats. We propose that hygrochasy provides an effective seed dispersal mechanism in solitary capsules embedded in cushion plants and may restrict dispersal within habitat patches. [ABSTRACT FROM AUTHOR]

It is well known that life forms reflect the impact of the environment. An interesting task in ecology is to study the connection between the morphological characteristics of life forms and physical and geographical processes, taking place in the environment. This study may profit from the application of symmetry theory which is a universal methodology in science. According to this theory both the object, that is, life form, and the environment are characterised by their own types of symmetry, which may differ from each other. If the environment acts sufficiently intensively on a plant, its form may show deformations - dissymmetry according to Curie. From the observed dissymmetry character of the vegetation it is possible to judge the symmetry of the environment, its specific impact on the vegetation, and the direction and intensity of natural matter and energy flows. All these are clearly apparent in the cushion plants growing on the abrupt slopes of south-east Altay canyons. [ABSTRACT FROM AUTHOR]