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In plant ecology, extreme environments are those that pose physiological or other limitations to plant growth, especially for non-adapted taxa. In these environments, the severity of climate conditions and/or the limitations imposed by particular soil substrates represent major selective pressures for plants, leading to the evolution of a wide array of functional traits, specific strategies and adapted taxa. In this special issue, we present a collection of papers that focuses on plants in various extreme environments, including the Arctic and Antarctic, regions with serpentine and gypsum soils, high mountain areas and deserts. The papers include a broad array of methods to study the ecology and evolution of plants in extreme environments, such as field surveys, greenhouse and field experiments, molecular phylogenetic analyses and/or physiological measurements. Overall, this special issue showcases research on how plants thrive in extreme environments which, in turn, may provide pointers to how plant communities might respond to living in increasingly challenging environments resulting from unprecedented land-use changes and climate warming at the present time and in the future. [ABSTRACT FROM AUTHOR]

Plot-based monitoring has yielded much information on the taxonomic diversity and carbon (C) storage in tropical lowland forests of the Amazon basin. This has resulted in an improved understanding of the relationship between lowland forest biomass dynamics and global change drivers, such as climate change and atmospheric CO2 concentration. Much less attention has been paid to the mountain ecosystems of South America that comprise montane forests and alpine vegetation (páramo, puna, high Andean grasslands, wetlands, and alpine heath). This vegetation complex provides a variety of ecosystem services and forms a natural laboratory along various physiographic, geological and evolutionary history/biogeography, and land use history gradients. Here, we review existing empirical understanding and model-based approaches to quantify the contribution of mountain ecosystems to ecosystem service provision in the rapidly changing socioecological setting of the South American mountains. The objective of this paper is to outline a broad road map for the implementation of mountain vegetation into dynamic global vegetation models (DGVM) for use in Earth System Models (ESM), based on our current understanding of their structure and function and of their responsiveness to global change drivers. We also identify treeline processes, critical in mountain ecosystems, as key missing elements in DGVMs/ESMs, and thus explore in addition a treeline model. Stocktaking of the availability of empirical data was undertaken from eight research sites along the Andes and in south-eastern Brazil. Out of eight sites, two (one each in Venezuela and Brazil) had some climate, ecological and ecophysiological data potentially suitable to parametrise a DGVM. Tree biomass data were available for six sites. A preliminary assessment of the Joint UK Land Environment Simulator (JULES) DGVM was made to identify gaps in available data and their impacts on model parametrisation and calibration. Additionally, the potential climate-determined elevation of the treeline was modelled to check the DGVM for its ability to identify the transition between the montane forest and alpine vegetation. Outcomes of the evaluation of the JULES land surface model identified the following key processes in montane forests: temperature-related decrease in net primary production, respiration, and allocation to above-ground biomass and increase in soil C stocks with elevation. There was a variable agreement between simulated biomass and those derived from field measurements via allometric equations. We identified major gaps between data availability and the needs for process-based modelling of South American mountain vegetation and its dynamics in DGVMs. To bridge this gap, we propose a transdisciplinary network, composed of members of the theoretical/modelling and empirical scientific communities, to study the natural dynamics of mountain ecosystems and their responses to global change drivers locally, regionally and at the continental scale, within a social-ecological system framework. The work presented here forms the basis for the design of data collection from field measurements and instrumental monitoring stations to parametrise and verify DGVMs. The network is designed to collaborate with and complement existing long-term research initiatives in the region and will adopt existing standard field protocols. Complementary protocols will ensure compatibility between field data collection and data needed for process-based and empirical models. [ABSTRACT FROM AUTHOR]

The present-day arctic flora replaced Arcto-Tertiary forest when global temperatures dropped markedly towards the end of the Pliocene 3-4 million years ago. During the Quaternary (from 1.8 mya) recurrent cycles of ice ages (glaciations) interspersed with shorter warmer periods (interglacials) have caused arctic and alpine plants to experience frequent range fragmentations and expansions. The application of molecular phylogenetic and phylogeographic analysis, along with an accumulating body of pollen and macrofossil evidence, is providing a greater understanding of the nature and effects of these events. To report what is new in this regard and also to assess what changes might lie ahead as a result of rapid climate warming, a Botanical Society of Scotland Symposium was held in June 2007 at the University of St Andrews on the History, evolution and future of arctic and alpine flora. This special issue contains papers based on presentations given at this meeting. Its aim is to highlight the fusion of recent fossil, molecular and ecological evidence that has advanced our understanding of events that moulded the origin and composition of arctic and alpine floras. In addition, a brief assessment is made of the future of these floras in a rapidly warming world. [ABSTRACT FROM AUTHOR]

Background:Some 3% of the area of Tyrol is covered by glaciers. Since the end of the Little Ice Age, these glaciers have shrunk by about 50%, providing open ground for succession of biota. As the exposed bare ground becomes available for colonisation, pedogenesis, and primary succession, glaciological data provide important information for the analysis of chronosequences of biological succession. Aims:This paper summarises long-term surveillance studies and provides information on annual glacier changes with a focus on the three Tyrolean LTER sites Hintereisferner, Kesselwandferner and Jamtalferner, together with two additional glaciers. Methods:Annual changes in the length of 54 glaciers were recorded, with the first measurements made in 1891. In addition, the long-term mass balance data of five glaciers are presented. Two of these glaciers have been surveyed since 1953. Results:Between 1901 and 2008, the temperature during the ablation season (May to September) increased by 1.7 °C (measured at one site in Vent). In the same period, winter (October to April) accumulation showed no significant trends. Measurements of length changes showed a general glacier retreat, with limited advances in the 1920s and 1980s. The mass balance measurements indicated mass losses since the 1980s at increasing rates, especially after 2000. The reaction of glaciers to the climate signal differed in timing and magnitude according to their topographic properties. Conclusions:Although the Tyrolean glaciers have generally retreated since the end of the Little Ice Age, the magnitude and pace of advance or recession differs from glacier to glacier. This is important to consider in studies on succession of biological communities in glacier forelands [ABSTRACT FROM PUBLISHER]

Background: Permafrost mounds covered by open or dense forests (or krummholz - stunted trees) correspond to the category of wooded palsas and wooded peat plateaux extensively distributed in wetlands of North America. Very few data exist on the origin and development of wooded palsas, in particular their inception during the Holocene and the structure and dynamics of their forest/krummholz cover over time. Aim: The main objective of this paper is to fill the gap of knowledge on the origin and structure of wooded palsas, with a focus on wooded palsas located at their range limit at the treeline in eastern Canada. Methods: Each of the nine sites studied was surveyed along a line transect to measure the topography, to record the vegetation cover, to infer the snow thickness and to measure the thickness of the active layer at the time of sampling. The size structure of the black spruce (Picea mariana) populations of three dense wooded palsas was described. Basal stem discs of living and dead Picea were recovered for age determination, except in one site where only dead stems were sampled. The minimum age of wooded palsas at each site was evaluated based on tree-ring dating of the oldest stems and radiocarbon dating of the organic layers. Results: The inception of wooded palsas occurred during two principal periods of permafrost expansion as shown by the combined tree-ring and radiocarbon dates obtained for each of the nine studied sites. Three wooded palsas formed between 750 and 1000 AD, whereas the inception of the other palsas occurred during the 1500s. The up-thrusting of the wetland surface associated with permafrost growth facilitated tree establishment more intensively during the first period than during the second period when full Little Ice Age conditions prevailed in wind-exposed peatlands. Conclusions: The maintenance of a permafrost mound under forest cover is a rare situation in northern environments, and wooded palsas in eastern Canada form peculiar ecosystems where forest and permafrost coexist; these have survived over the last 500 to 1000 years. It is believed that the inception of wooded palsas was facilitated during a prolonged period of snow-poor winter conditions. Tree establishment was possible due to well-drained soil conditions associated with palsa up-thrusting. Although thicker snowpack preventing deeper frost penetration into the soil is maintained by the development of a forest/krummholz cover, wooded palsas at the treeline can survive because of low annual temperatures, reduced solar radiation beneath the tree canopy, variable accumulation and duration of annual snowpack. [ABSTRACT FROM AUTHOR]

Background: Evidence strongly suggests that Beringia was a refugium for tundra taxa throughout the Quaternary (the last 2 million years). However, the genetic consequences of the repeated formation and flooding of the Bering Land Bridge remain uncertain. Aims: The goal of this paper was to determine the role that the unique environmental history of Beringia played in the diversification of tundra flora. Methods: I adopted a comparative coalescent approach to test models of divergence for arctic flora within Beringia. The literature was surveyed for phylogeographic studies that sampled broadly across the region and incorporated molecular markers appropriate for coalescent analyses. Of the 13 possible taxa, only two fit these criteria: Saxifraga oppositifolia (Saxifragaceae) and Vaccinium uliginosum (Ericaceae). Observed gene trees were compared with a distribution of trees simulated under neutral coalescence to test models of population divergence. Population models fell within two major categories reflecting the importance of either the Bering Land Bridge or the Bering Sea dispersal barrier on the distribution of genetic diversity in the species. Results: Both species fit 'bridge' models, but S. oppositifolia supported a model of eastward migration while V. uliginosum fits a unified Beringia refugium model. The evolutionary implications of these findings are discussed. Conclusions: The limited number of studies emphasises the need for more sequence-based research in the region. This will help resolve the history of the Beringia tundra ecosystem, which has important implications for the diversification of tundra flora, the history of Beringia, and the potential consequences of climate change on the distribution of biological diversity. [ABSTRACT FROM AUTHOR]

Species distribution models (SDMs) have been widely used to predict species ranges and their future distribution under climate change scenarios, mostly using only climatic variables. An important factor that is usually neglected, is the habitat of the species that are being modelled. Even when included, it is often considered a fixed factor, but in reality, it is also subjected to changes. In this study, we assessed if this omission can lead to different projected distributions of the species. For this purpose, we applied an ensemble of SDMs, and we projected the distribution of rare bryophyte species in Scotland in the 2050s. Bryophytes are generally very climate-reliant and lend themselves to bioclimatic studies, and we selected species different grades of affinity with blanket bogs, which are threatened by climate change. Blanket bog extension was included in the model as an explanatory variable, and the models were run for three 2050s scenarios: once with the current blanket bog distribution and twice using the blanket bog distribution derived from two bioclimatic models (Lindsay modified and Blanket Bog Tree model), under the same climate change projections. The results showed some differences in the predicted future distribution of those species with a strong relationship with blanket bogs, when habitat changes were accounted for. For example, Sphagnum majus, the species with the highest affinity with blanket bog in our study, was not predicted to change its future distribution when blanket bog is held constant at the current level, but was predicted to lose up to 60% of its current suitable area when the projected loss of blanket bog is included. Our results suggest that adding future habitat changes could improve the reliability of SDMs in the first steps of planning for conservation and restoration. [ABSTRACT FROM AUTHOR]

The Antarctic is an extreme environment for plants. Several invasive plant species, however, have invaded the sub-Antarctic Southern Ocean islands and increasingly threaten the vulnerability of maritime and continental Antarctica, particularly with changes in climate. We provide an overview of issues to consider with regard to the impact, ecology and management of non-native plants in the Antarctic, focusing on knowledge gained and recent research results from the sub-Antarctic with possible application to Antarctica. We provide a brief review of literature and bring together experience and previously unpublished research with Poa annua and Stellaria media on Macquarie Island. While no one set of biological characteristics predicts plant invasiveness in the sub-Antarctic, all are adapted to survive extreme cold conditions and persistence is enabled through large and long-lived soil seed banks. Ecological drivers for invasion include accidental human introductions and continuing movement, along with animal and other disturbance to soil. The invasive cold-tolerant plant species now prevalent on sub-Antarctic islands also pose a threat to Antarctica due to a warming climate and so efforts should continue to prevent further spread, while developing effective, low-impact control and eradication options to protect these high-value extreme ecosystems. [ABSTRACT FROM AUTHOR]

To facilitate climatic change adaptation, landscape and conservation managers require understanding of spatio-temporal patterns of expansion of potential dominant species. Studying past expansions of canopy-dominant trees can contribute such understanding. Test hypotheses about expansions of dominants using as a model the mid-Holocene expansion of forests dominated by Pinus sylvestris in the Scottish Highlands. Pollen analysis and radiocarbon dating of Holocene sediments of a larger basin and several small hollows were performed in three landscapes along a north–south transect. A larger basin records expansion timing at landscape scale, whilst small hollows evidence within-landscape spatio-temporal patterns. Vegetation existing prior to the expansion of pinewoods influenced landscape-scale spatio-temporal expansion patterns of P. sylvestris. Open vegetation generally was invaded earlier and/or to a greater extent; invasion was often later, or did not occur, where woodland with a substantial temperate broadleaved tree and shrub component (e.g. Corylus avellana, Quercus spp.) was present. Most small hollows, not just those where pinewoods became locally established, recorded vegetation change during the expansion. Some present landscape-scale forest composition patterns were established at that time. Studying past expansions of dominants provides evidence relevant to planning conservation and landscape management to facilitate ecological adaptation as species adjust their distributions and abundances in response to climatic change. [ABSTRACT FROM AUTHOR]

The concept of potential natural vegetation (PNV) refers to self-sustaining mature vegetation matching the environmental conditions a site offers. Despite its widespread use, the applicability of the concept under the current level of human impacts on the environment has been criticised. We re-examine the original publication of the PNV concept and its development over time to identify the sources of tension between theory and application and to direct the discourse onto a common ground of understanding. Our focus is on the relationship between human impacts and PNV. Based on extended excerpts and detailed interpretation, we affirm that PNV applies to a specific point in time. Consequently, PNV is independent of any realised vegetation including past undisturbed (pre-human) vegetation. We track possible routes and reasons for alternative interpretations. We identify PNV as a mental concept, or a neutral model, that represents baseline vegetation potential that excludes contemporary human management but includes past environment-modifying impacts. We address how a concept reflecting unmanaged vegetation can be important for application in a world transformed by humans. Rather than abandoning the concept, we advocate adhering to using it in the original sense of its definition. This way PNV can serve research as a neutral model and support sustainable land use planning. [ABSTRACT FROM AUTHOR]

The Himalayas have been experiencing a higher rate of temperature increase than the global average. How such climate warming and changes in the precipitation regime may affect the growth responses of individual tree species is little known but is required so that adequate projections of future distributions and management plans can be formulated. This study was carried out to investigate the influence of intra- and interannual climate variability on the radial growth of Pinus wallichiana, a conifer species that typically colonises glacier forelands and screes. Tree core samples collected for chronology development that spanned over a 119-year-long (1899–2017) period and the relationship of ring width with climatic data was analysed using correlation analysis. Radial growth in P. wallichiana was negatively correlated with mean temperature in March and over the pre-monsoon (March – May) seasonal average and it was positively correlated with monthly precipitation in March and September. Monthly standardised precipitation index (SPI) values indicated that overall the growth of P. wallichiana was mainly controlled by precipitation availability during the pre-monsoon season, particularly in March. Moisture availability especially in spring is crucial for the radial growth of P. wallichiana. However, how this response varies throughout the elevational range of the species deserves further study to be able to make projections on the likely range expansion or contraction of the species in response to ongoing climate change. [ABSTRACT FROM AUTHOR]

Background: Climate change is projected to alter the elevation and latitude of treeline globally. Seed germination and seedling survival are critical controls on treeline expansion. Neighbouring alpine plants, either through competition for resources or through altered microclimate, also affect seedlings emerging in the alpine zone. With warming, alpine plant species may interact with each other more or less strongly. Aims: To determine whether establishing tree seedlings and an alpine herb are similarly sensitive to alpine plant neighbours under ambient and altered climate. Methods: We imposed active heating, watering, and removed all plants adjacent to emerging conifer seedlings and an alpine herb. Results: Picea engelmannii seedlings showed lower survival compared with Pinus flexilis 3 weeks following neighbour removal, and after 1 year only survived in watered plots. Pinus seedlings responded to neighbour removal by lowering the quantum yield of photosynthesis (ϕPSII). Contrary to expectations from the stress gradient hypothesis, survival was reduced without neighbours near the low-elevation range limit of Chionophila jamesii. Conclusions: Pinus flexilis has higher expansion potential into the alpine, while Picea engelmannii requires moist conditions that could be facilitated by neighbours to expand its range. This implies likely range expansion by P. flexilis with consequences for alpine plant diversity and ecosystem function. [ABSTRACT FROM AUTHOR]

Background: Tropical mountain ecosystems of the Northern Andes have long fascinated researchers because of the unique conditions associated with cold climates in equatorial latitudes. More than six decades have elapsed since the beginning of systematic ecological research in the Venezuelan páramos, making them one of the best-studied tropical alpine regions in the world. Aims: We review the conceptual development and state of the art of ecological research in the Venezuelan páramos, with emphasis on environmental and plant ecology research, presenting a general framework for the studies included in this special issue. Methods: We provide a historical sketch of the periods that have marked ecological studies in the Venezuelan páramos. Then, we synthesise research on environmental drivers, plant population and community ecology, ecosystem functioning, the response of the páramo to climate change and human disturbance; we finally consider agroecology and conservation. Results and conclusions: This review demonstrates the significant contributions made to alpine ecology in key areas such as biodiversity/ecosystem function changes during succession, nutrient cycling, species interactions and socio-ecological research. We indicate the need to develop a more integrated view of the links between evolutionary processes, functional diversity, community dynamics and ecosystem services both in natural and human-impacted areas. [ABSTRACT FROM AUTHOR]

Background: Classifying species from the high tropical Andes into plant life forms (PLF) can provide a more functional understanding of tropical treeline dynamics. However, little is known about the potential response of PLFs to climate warming. Aims: The objective of this work was to evaluate the response of PLFs to environmental conditions above the upper montane forest in the Venezuelan Andes and forecast their potential distribution under warming scenarios using habitat suitability models. Methods: We classified species into nine PLFs, analysed their current distribution using CCA and non-linear multiple regressions and forecasted their potential distribution under warming scenarios. We used anatomical leaf traits for shrubs and caulescent rosettes to refine their potential responses to climate. Results: Tree cover sharply decreased with increasing elevation, while shrub and caulescent rosette distribution differed depending on their leaf traits. Projections suggested an upslope shift of all PLFs with warming and an increase in tree cover. Conclusions: The analysis of the distribution of PLFs, by linking plant adaptive strategies to topography/climate, allowed projecting changes in vegetation physiognomy in response to warming. Projections of a moderate increase in tree cover in the grassland páramo did not indicate the formation of closed forests above the forest line. [ABSTRACT FROM AUTHOR]

Background: Alpine and arctic tundra are particularly sensitive ecosystems to the impacts of global climate change. Yet, warming studies versus observational studies in these ecosystems yield different and sometimes conflicting results. Many short-term changes may be phenotypic responses to warming rather than shifts at the community level. Aims: We posit that long-term monitoring of permanently marked plots provides data for making predictions of the impact of climate change on alpine tundra communities. Methods: We surveyed plant community composition and cover at four sampling time points over a forty-year span (1971–2011). Results: We observed an expansion of shrub cover, both within the shrub tundra and encroaching into moist and dry meadow communities. This shrub cover expansion coincides with increased litter and decreased species richness at the plot level. Overall, despite some shifts in functional group cover and species richness, plant community composition remained mostly intact across forty years. Conclusions: Our results corroborate with other published studies demonstrating the rapid expansion and impacts of woody shrubs in tundra ecosystems. This study demonstrates a surprising resistance of alpine tundra plant communities under current global climate change over a 40-year period. Additional studies are needed to disentangle the many potential drivers that explain plant community shifts and community stability. [ABSTRACT FROM AUTHOR]

Background: Araucaria forests are mountain ecosystems that might have expanded in the late Holocene, however past distributions remain uncertain. If current distribution reflects climatic conditions, past and future distributions may be projected using climate models. Aims: To contribute to the understanding of past and future distribution of Araucaria forests as a function of climate, we hypothesised that (1) they have increased their geographic distribution since the Last Glacial Maximum (LGM) until the present; and (2) would contract under predicted future climates. Methods: We modelled the spatial distributions of Araucaria forests under current, past and future climatic scenarios. Ecological niche models of 12 indicator species were developed using ensemble modelling. Results: The greatest extent of distribution of Araucaria forests appeared to have occurred during the LGM, after which a continuous retraction followed until the present. Our models suggested that Araucaria forests would experience an even greater retraction in the future. Conclusion: Araucaria forests could have covered larger areas during the LGM than suggested by earlier palynological studies, because climate was suitable for their distribution. The degree of loss of modelled distribution area since the LGM until today indicate these forests are likely to continue to shrink under projected future climatic changes. [ABSTRACT FROM AUTHOR]

Background: Climate change may increase the risk of biological invasions. However, current knowledge of this interaction is limited. Aims: We aimed to quantify (1) the effect of climate change on the potential distribution of invasive plant species in Spain, (2) the importance of the area of origin of such species and (3) the vulnerability of different biogeographic provinces to future changes in climatic suitability for invaders. Methods: We applied six methods of species distribution modelling to assess the variation of climatically suitable areas for 40 alien plants. We developed a Potential Area Change Index and used it as the response variable in modelling for three future emissions scenarios and three global circulation models over three time periods. The area of origin and biogeographic province in Spain were also considered. Results: We found a highly specific response for each plant species rather than a clear trend for the entire set of species. Predicted climate suitability increased over higher emission scenarios and longer projected time lags. Neotropical species showed the greatest potential climatic range expansion. We detected a strong interaction between the geographic origin of a species and the biogeographic province. Conclusions: Special attention should be given to the areas where aridification of climate is projected and where introduced neotropical species are likely to expand their range. Future work should develop accurate species-specific approaches that allow the management invasive plant species. [ABSTRACT FROM AUTHOR]

Background: Topoclimate can influence tree establishment within treeline ecotones. Yet much less is known about how regional topography, such as the Continental Divide, Rocky Mountains, mediates the role of climate in governing treeline dynamics. Aims: To utilise the Continental Divide to test whether contrasts in growing-season moisture regimes to the west (summer-dry) and east (summer-wet) impact the spatio-temporal patterns of tree establishment and rates of treeline advance in the Northern Rocky Mountains. Methods: We sampled trees at sites on north- and south-facing slopes, west and east of the Continental Divide. We used dendroecological techniques to reconstruct patterns of tree establishment. Age-structure data were quantitatively compared with climate to evaluate possible mechanistic linkages. Results: Across all sites, 96% of trees established after 1950. There was a treeline advance (range = 39-140 m) accompanied by increases in tree density. Significantly more trees established during wet springs on both sides of the Divide. Conclusions: Overall, snow duration in spring and autumn temperatures appear to influence patterns of tree recruitment at the treeline. Continued warming will likely amplify the role of autumn climate in regulating tree establishment throughout treeline ecotones in the Northern Rocky Mountains, particularly west of the Divide where summer-dry conditions persist. [ABSTRACT FROM AUTHOR]

Background: Temporary ponds, an abundant habitat in the Maghreb region and notably in Morocco, have a high conservation value. However, they are mainly known from the north of the country. Aims: The aim of this work was to characterise the vegetation of Moroccan temporary ponds along a combined gradient of latitude and anthropogenic pressure. Methods: Eighty-five ponds distributed along a north–south gradient of 750 km were sampled. For each pond, all vegetation was surveyed (flooded and dry parts) and the local abiotic characteristics were measured during two successive hydrological cycles. The prevailing anthropogenic pressures were also identified and were attributed an impact score. Results: Eighty-one characteristic pond species (including 17 rare species) were recorded, with several new distribution data in the southern part of the latitudinal gradient. Plant communities were related to climatic and anthropogenic factors, but mostly to local factors, such as maximum water depth and soil pH. The northern ponds (wettest macroclimate) were rich in characteristic species and rare species, while the southern (driest macroclimate) ponds were more species poor. Conclusions: In addition to the direct impact of increasing human activity, a further reduction of the floristic richness of temporary ponds is expected due to climatic changes. This is particularly the case for characteristic species which have a high conservation value. [ABSTRACT FROM PUBLISHER]

Background:Current understanding of treeline or forest-alpine ecotone (FAE) dynamics does not fully explain past and present FAE patterns and their underlying processes, nor allow prediction of their response to climate change. Aims:We address the overarching hypothesis that the FAE is a mosaic of distinct landscape units of vegetation and landforms that result in differential responses to climate change. We focus on climate-related, landscape and vegetation characteristics, but also consider the effect of landscape heterogeneity on biogeochemistry and overall resilience of the FAE to climate change. Results: There are three distinct FAE land units at Niwot Ridge, generated by different interactions of climate with vegetation, landforms and topography. Within these FAEs, a process of self-organisation takes place from organism to patch to landscape scales, and is modulated by positive and negative feedback loops along an elevation gradient. The underlying controls cannot be attributed solely to temperature, but to a combination of interactions along a physical/biotic gradient. Conclusions:FAE dynamics result from interactions among mechanisms and processes at the microsite, patch and landscape scales: (1) tree persistence; (2) forest patch establishment; (3) drivers of patch forest configurations and (4) resilience, increasing along a gradient of biotic control. [ABSTRACT FROM PUBLISHER]

Background: Animals that hoard food to mediate seasonal deficits in resource availability might be particularly vulnerable to climate-mediated reductions in the quality and accessibility of food during the caching season. Central-place foragers might be additionally impacted by climatic constraints on their already restricted foraging range. Aims: We sought evidence for these patterns in a study of the American pika (Ochotona princeps), a territorial, central-place forager sensitive to climate. Methods: Pika food caches and available forage were re-sampled using historical methods at two long-term study sites, to quantify changes over two decades. Taxa that changed in availability or use were analysed for primary and secondary metabolites. Results: Both sites trended towards warmer summers, and snowmelt trended earlier at the lower latitude site. Graminoid cover increased at each site, and caching trends appeared to reflect available forage rather than primary metabolites. Pikas at the lower latitude site preferred species higher in secondary metabolites, known to provide higher-nutrient winter forage. However, caching of lower-nutrient graminoids increased in proportion with graminoid availability at that site. Conclusions: If our results represent trends in climate, cache quality and available forage, we predict that pikas at the lower latitude site will soon face nutritional deficiencies. [ABSTRACT FROM PUBLISHER]

Background:High-elevation mountain systems may be particularly responsive to climate change. Aims: Here we investigate how changes along elevation gradients in mountain systems can aid in predicting vegetation distributional changes in time, focusing on how changing climatic controls affect meso-scale transitions at the lower and upper boundaries of alpine vegetation (with forest and subnival zones, respectively) as well as micro-scale transitions among plant communities within the alpine belt. We focus on climate-related drivers, particularly in relation to climate change, but also consider how species interactions, dispersal and responses to disturbance may influence plant responses to these abiotic drivers. Results:Empirical observations and experimental studies indicate that changing climatic controls influence both meso-scale transitions at the upper and lower boundaries of alpine vegetation and micro-scale transitions among plant communities within tundra. Micro-scale heterogeneity appears to buffer response in many cases, while interactions between climate and other changes may often accelerate change. Conclusions:Interactions with microtopography and larger edaphic gradients have the capacity to both facilitate rapid changes and reinforce stability, and that these interactions will affect the responsiveness of vegetation to climate change at different spatial scales. [ABSTRACT FROM PUBLISHER]

Background: Subsurface ice preserved as ice lenses and within rock glaciers as well as glacial and lake ice provides sensitive indicators of climate change and serve as a late-season source of meltwater. Aims: We synthesise the results of geomorphological, geophysical and geochemical studies during the period of 1995–2014, building on a long history of earlier work focused on ice and permafrost studies on Niwot Ridge and the adjacent Green Lakes Valley (GLV), which is part of the Niwot Ridge Long Term Ecological Research Site. Methods: These studies are discussed in the context of how bodies of ice and rock glaciers reflect changing local climate. We review recent results from geophysical investigations (resistivity, seismic refraction and ground-penetrating radar) of the shallow subsurface, ongoing monitoring of the Arikaree Glacier, three rock glaciers and lake ice in the GLV, and interpretations of how subsurface ice melt regulates the flow and chemistry of alpine surface water after seasonal snowfields melt. Results and conclusions: Permafrost conditions reported from Niwot Ridge in the 1970s are generally absent today, but ice lenses form and melt seasonally. Ice is present permanently within the Green Lakes 5 rock glacier and at nearby favourable sites. The Arikaree Glacier has shown a marked decline in cumulative mass balance during the past 12 years after a 30-year period when net mass balance was ca. 0. Duration of seasonal lake ice increases with elevation in GLV, but duration has decreased at all seven lakes that have been monitored during the last three decades. This decrease has been most marked at the lowest elevation where it amounted to a reduction of about 1 d year−1and least at Green Lake 5 where the loss has been at a rate of 0.5 d year−1. Surface temperature measurements from rock glaciers have not shown strong trends during the past 15 years. It has been suggested that almost all of the 2.5-mm year−1increase in stream discharge from the upper GLV in September and October has been derived from melting of subsurface ice. [ABSTRACT FROM PUBLISHER]

Background:The forests of western Amazonia are known to be more dynamic that the better-studied forests of eastern Amazonia, but there has been no comprehensive description of the carbon cycle of a western Amazonian forest. Aims:We present the carbon budget of two forest plots in Tambopata in south-eastern Peru, western Amazonia. In particular, we present, for the first time, the seasonal variation in the detailed carbon budget of a tropical forest. Methods:We measured the major components of net primary production (NPP) and total autotrophic respiration over 3–6 years. Results:The NPP for the two plots was 15.1 ± 0.8 and 14.2 ± 1.0 Mg C ha−1year−1, the gross primary productivity (GPP) was 35.5 ± 3.6 and 34.5 ± 3.5 Mg C ha−1year−1, and the carbon use efficiency (CUE) was 0.42 ± 0.05 and 0.41 ± 0.05. NPP and CUE showed a large degree of seasonality. Conclusions:The two plots were similar in carbon cycling characteristics despite the different soils, the most notable difference being high allocation of NPP to canopy and low allocation to fine roots in the Holocene floodplain plot. The timing of the minima in the wet–dry transition suggests they are driven by phenological rhythms rather than being driven directly by water stress. When compared with results from forests on infertile forests in humid lowland eastern Amazonia, the plots have slightly higher GPP, but similar patterns of CUE and carbon allocation. [ABSTRACT FROM PUBLISHER]

Background:The forests of north-west Amazonia are characterised by the highest levels of tree diversity in the world, high rainfall and relatively fertile soils. Aims:Here we present a comprehensive description of the carbon cycle of two 1 ha forests plots in Allpahuayo, near Iquitos, Peru, one on an occasionally inundated alisol/gleysol landscape, the other on an arenosol (sandy soil). Methods:Data on the components of net primary productivity (NPP) and autotrophic respiration were collected over the period 2009–2011, and summed to estimate gross primary productivity (GPP) and carbon use efficiency (CUE). Results:Overall, these forests showed high values of GPP (39.05 ± 4.59 and 41.88 ± 4.60 Mg C ha−1year−1). Despite the lack of a dry season, the forests showed distinct seasonality in tree growth, litterfall, flowering and fine root productivity. This showed that tropical forests with little seasonality in water supply can still exhibit distinct seasonality in NPP and carbon use, apparently synchronised to the solar radiation cycle. We found remarkably little difference in productivity between the alisol/gleysol plot and the arenosol plot. Conclusions:The GPP was higher than those reported for forests in Brazilian Amazonia on more infertile soils. The CUE was also higher, which may be related to the high forest dynamism and natural disturbance rate. These two factors combined to result in amongst the highest NPP values reported for Amazonia. [ABSTRACT FROM PUBLISHER]

Background:There is much interest in how the Amazon rainforest may respond to future rainfall reduction. However, there are relatively few ecosystem-scale studies to inform this debate. Aims:We described the carbon cycle in a 1 ha rainforest plot subjected to 8–10 consecutive years of ca. 50% through-fall reduction (TFR) and compare these results with those from a nearby, unmodified control plot in eastern Amazonia. Methods:We quantified the components of net primary productivity (NPP), autotrophic (Ra) and heterotrophic respiration, and estimate gross primary productivity (GPP, the sum ofNPPandRa) and carbon-use efficiency (CUE, the ratio ofNPP/GPP). Results:The TFR forest exhibited slightly lowerNPPbut slightly higherRa, such that forestCUEwas 0.29 ± 0.04 on the control plot but 0.25 ± 0.03 on the TFR plot. Compared with four years earlier, TFR plot leaf area index and small tree growth recovered and soil heterotrophic respiration had risen. Conclusions:This analysis tested and extended the key findings of a similar analysis 4 years earlier in the TFR treatment. The results indicated that, while the forest recovered from extended drought in some respects, it maintained higher overallRarelative to the undroughted control, potentially causing the droughted forest to act as a net source of CO2. [ABSTRACT FROM PUBLISHER]

Background:The dry transitional forests of the southern Amazonia have received little attention from a carbon cycling and ecosystem function perspective, yet they represent ecosystems that may be impacted by global climate change in the future. Aims:To compare the full carbon cycle for two 1-ha forest plots that straddle the ecotone between humid forest and dry forest in Amazonia, ca. 100 km from Santa Cruz, Bolivia. Methods:2.5 years of measurements of the components of net primary production (NPP) and autotrophic respiration were collected. Results:Total NPP was 15.5 ± 0.89 Mg C ha−1year−1at the humid site and 11.27 ± 0.68 Mg C ha−1year−1at the dry site; a total Gross Primary Production (GPP) of 34.14 ± 2.92 Mg C ha−1year−1and 26.88 ± 2.70 Mg C ha−1year−1at the two sites. Carbon use efficiency for both sites was higher than reported for other Amazonian forests (0.45 ± 0.05 and 0.42 ± 0.05). Conclusions:Drier soil conditions selected for the dry deciduous tree species which had higher leaf photosynthesis and total GPP. NPP allocation patterns were similar at the two sites, suggesting that in terms of carbon allocation, the dry forests of the southern Amazonia behave as a scaled-down version of wetter humid forests. [ABSTRACT FROM PUBLISHER]

Background:Previous work has shown that Amazonian tropical forests have experienced two widespread changes in dynamics over recent decades, increases in both tree stem turnover and above-ground biomass. However, data from an Amazonian monodominant forest dominated byPeltogyne gracilipeshave shown that the above-ground biomass of this forest type has declined slightly (<5%) over an 11-year period. Aims:To determine whether the tree communities in three types of forest, with or withoutPeltogyne gracilipes(Peltogyne-rich forest (PRF),Peltogyne-poor (PPF) and forest withoutPeltogyne(FWP)) on Maracá Island, Roraima, have experienced a change in structure and floristic composition over a 20-year period. Methods:We have quantified the variation in the occurrence and abundance of tree species, the above-ground biomass (AGB) and change in total stand biomass from mortality, recruitment and growth for trees, palms and large lianas, ≥10 cm diameter at breast height, in three plots of 0.25 ha in each of the three forest types. Results:Floristic composition showed little change, with no shift in the rank abundance amongst the 10 most important tree species, although in FWP there was a reduction in species richness from 51 to 43. Recruitment is shown to offset the losses caused by mortality in PRF and FWP. The annual mean mortality rates were low, at around 1%. In 2011 AGB in the three forest types varied from 434 Mg ha−1(PPF) to 363 Mg ha−1(FWP). PRF experienced an AGB decline of 4.1%, associated with the death of large trees, while FWP showed a slight increase in biomass (2.6%). Conclusions:Over the last 20 years Maracá forest stands appear to have been stable in terms of their floristic composition and structure, some showing a persistent monodominance byPeltogyne gracilipes. [ABSTRACT FROM PUBLISHER]

Background:Global changes are challenging the equilibrium in the Amazon. Understanding how that biome responds to seasonality in water availability is essential to build scenarios of ecosystem functioning in the near future. Aims:Our aim was to test for seasonal variations in leaf traits related to primary productivity. Methods:Chemical composition, mass to area ratio and photosynthetic response curves to light and CO2and of stomatal conductance (gs) to leaf-to-air water pressure deficit (ν) were determined from leaves of Amazonian trees and lianas. Results:Weak responses ofgsto ν suggested limited stomatal control over transpiration. Dry season stomatal limitation of photosynthesis was not a common feature as only one individual studied (out of 14) exhibited concomitant decreases in light saturated photosynthetic rate (ASat) andgs(measured duringASat) associated with the dry season. Furthermore, 75% of the individuals evaluated did not show decreased photosynthetic capacity (Vcmax) during the dry season, suggesting limited seasonal leaf acclimation. Grouped analyses indicated that most parameters evaluated remained constant across seasons. The exceptions were leaf nitrogen and its isotopic signature, and the integrated stomatal sensitivity to light, CO2and ν. Conclusions:These findings reinforce the notion that the dry season in eastern Amazonia is not associated with significant limitations in leaf-level photosynthesis. [ABSTRACT FROM PUBLISHER]

Background:Climate change is driving ecosystem shifts, which has implications for tropical forest system function and productivity. Aim:To investigate Amazon forest dynamics and test for compositional changes between 1985 and 2005 across different plant groups. Methods:Tree census data from 46 long-term RAINFOR forest plots in Amazonia for three climate-functional groups were used: dry-affiliate, climate-generalist and wet affiliate. Membership of each group was ascribed at genus level from the distribution of individuals across a wet–dry gradient in Amazonia, and then used to determine whether the proportions of these functional groups have changed over time, and the direction of any change. Results:In total, 91 genera, representing 59% of the stems and 18% of genera in the plots, were analysed. Wet-affiliates tended to move from a state of net basal area gain towards dynamic equilibrium, defined as where gain ≈ loss, governed by an increase in loss rather than a decrease in growth and mainly driven by plots in north-west Amazonia, the wettest part of the region. Dry-affiliates remained in a state of strong net basal area gain across western Amazonia and showed a strong increase in stem recruitment. Wet-affiliates and climate-generalists showed increases in stem mortality, and climate-generalists showed increased stem recruitment, resulting in overall equilibrium of stem numbers. Conclusions:While there were no significant shifts in most genera, the results suggest an overall shift in climate-functional forest composition in western Amazonia away from wet-affiliates, and potential for increased forest persistence under projected drier conditions in the future. [ABSTRACT FROM PUBLISHER]

Background:As the climate warms, plant interactions between shrubs and conifer seedlings may affect migration of boreal trees into alpine areas; however these interactions have not been widely tested across conifer life stages. Aims:Determine the role of shading byBetula glandulosashrubs on earlyPicea marianarecruitment in the forest-tundra ecotone of the Mealy Mountains, Labrador (Canada). Methods:Four shrub treatments were established with varying degrees of shade (unaltered, trimmed, cleared, shaded). Emergence and growth ofP. marianain treatment plots were compared to control plots without shrubs. Results:Seedling emergence was facilitated; seedlings beneath shrubs emerged at greater levels (16% ± 5.1%) than in the control (0.5% ± 0.3%); however, evidence of facilitation post-emergence was weak, likely due to stronger interactions with seedbed species at this stage. Vertical growth of young seedlings was greatest in control and shaded plots, but needle production significantly decreased with increased shade suggesting that seedlings may compete with shrubs for light early in life. Conclusions:Although facilitation has been previously implicated as an important mechanism in stressful environments, our study indicates that the early life stages of some conifers at the tree line are not strongly facilitated by shrubs as has been previously suggested for adults. [ABSTRACT FROM PUBLISHER]

Background:Steep environmental gradients, coupled with predicted high temperature rises in the Arctic make arctic mountain vegetation highly suitable for surveillance of changes related to global warming. However, guidelines and baselines for such a purpose are widely lacking since arctic mountain vegetation has been little explored. Aims:We explore options for long-term surveillance on the basis of a detailed analysis of extant plant community patterns and their underlying environmental conditions in the mountainous inland of West Greenland. Methods:Distribution, abundance and site conditions of vegetation types were analysed, using 664 vegetation samples and detailed vegetation maps in four altitudinal belts. Results:Most plant communities had a restricted elevation distribution and were confined to special habitats predominantly defined by mesotopography and soil moisture. Conclusions:Based on the strong linkage to habitat conditions, horizontal and vertical changes of species distribution and vegetation pattern are excellent indicators for inferring underlying environmental changes on three different scales. The recommendations given concerning climate sensitive species and plant communities, ecotones for setting up observation sites as well as stratification of analysis by habitats can be the basis for establishing long-term surveillance programmes on arctic mountain vegetation. [ABSTRACT FROM PUBLISHER]

Background:There have been few studies on the effects on alpine flora and vegetation of an increase in nutrient availability. Two main potential sources of increased nutrient availability in alpine ecosystems are enhanced mineralisation caused by climate warming and atmospheric nitrogen deposition. Little is known on how life history traits of different species are related at individual and community levels to enhanced nutrient availability. Aims:We investigated the effects of nitrogen and phosphorus addition on the modular growth, flowering and germination of four species: two snowbed specialists and two alpine generalists. Methods:We established in a late snowbed at the Gavia Pass, Italian Alps, a factorial experiment with four fertiliser treatments (N, P, Low N+P, and High N+P) and an unfertilised control. Nutrients were applied in 2003–2006 and we recorded the number of modules per individuals, total number of flowers, number of flowers per flowering module, and calculated the percentage of flowering modules in 2005 and 2006, and counted the number of seedlings in 2006. Results:The modular growth and flowering effort of the species appeared to be co-limited by N and P. The alpine generalists showed greater responses to fertilization in vegetative growth and flowering compared with snowbed specialists. The number of seedlings recorded indicated species-specific responses to nutrient addition. Conclusions:Our results suggest that enhanced nutrient availability stimulates modular growth and flowering effort in responsive alpine generalist species. This, in turn, could lead to an increase in their abundance, leading to changes in community structure in snowbeds with enhanced nutrient availability. [ABSTRACT FROM PUBLISHER]

Background:In the alpine zone of the Snowy Mountains, grazing by mammals is limited. However, introduced European hare numbers have increased since the 1970s. Aims:To estimate the density of hares and hence grazing pressure among years. To assess the response of biomass, vegetation height and composition to a cessation of hare grazing. Methods:We used indices of hare abundance based on spotlighting and counts of hare pellets on a transect. The effect of hare grazing on tall alpine herbfield was assessed by using 15 paired exclosure and control quadrats for six years. Results:The indices of hare abundance suggested densities similar to those in upland areas of Britain. Grazing did not affect the composition, cover of herbs or graminoids or, for 2010, vegetation height or biomass. Variation in vegetation and hare numbers among years was not correlated with climatic variables. Observations of selective grazing suggested that impacts on vegetation may be localised and restricted to certain species. Prior analyses of hare pellets indicated that hares might spread seed of native and exotic species. Conclusions:Hares are having no general effect on tall alpine herbfield but may affect certain plant species via selective grazing or by spread of viable seed. [ABSTRACT FROM PUBLISHER]

Background:Genetic differentiation in phenotypic traits is often observed among forest tree populations, but less is known about patterns of adaptive variation within populations. Such variation is expected to enhance the survival likelihood of extant populations under climate change. Aims:Scots pine (Pinus sylvestris) occurs over a spatially and temporally heterogeneous landscape in Scotland. Our goal was to examine whether populations had differentiated genetically in timing of bud flush in response to spatial heterogeneity and whether variation was also maintained within populations. Methods:Two common-garden studies, involving maternal families of seedlings from 21 native pinewoods, were established and variation in the trait was measured at the beginning of the second growing season. Results:Populations showed genetic differences in the trait correlated with the length of growing season at their site of origin, but the majority of variation was observed within populations. Populations also differed in their levels of variation in the trait; a pattern that may be influenced by spatial variation in the extent of temporal climate variability. Conclusions:Our findings suggest that populations have adapted to their home environments and that they also have substantial ability to adapt in situ to changes in growing season length. [ABSTRACT FROM PUBLISHER]

Background:Arctic lichens and mosses are covered by snow for more than half the year and are generally considered as being dormant for most of this period. However, enhanced frequency of winter warming events due to climate change can cause increased disturbance of their protective subnivean environment. Aim:To further understand cryptogamic responses to midwinter warming we compared the ecophysiological performance of one lichen and one moss species during a simulated warming event. Methods:We measured photosynthesis and dark respiration in samples of the mossHylocomium splendensand the lichenPeltigera aphthosaremoved from under snow, and on natural refreezing after the warming event, which was simulated by using infrared heaters suspended above the ground. Results:The moss exposed to light at +5 °C immediately after removal from their subnivean environment and from warmed plots showed positive net gas exchange within 332 s; the lichen required 1238 s. Photosynthesis and nitrogen fixation rates were equal to that, or higher than, during the preceding growing season. Upon refreezing after the event, moss photosynthesis declined considerably. Conclusions:The moss, and to a lesser extent the lichen, may contribute to subnivean midwinter ecosystem respiration, and both are opportunistic, and can take advantage of warmer winter phases for photosynthesis and growth. This ought to be taken into account in vegetation change projections of cryptogam-rich ecosystems. [ABSTRACT FROM PUBLISHER]

Background:The effect of the anticipated climate change on the stability of vegetation and the factors underlying this stability are not well understood. Aims:Our objective was to quantify long-term vegetation changes in a range of habitats in northern Europe by exploring species co-occurrences and their links to diversity and productivity gradients. Methods:We re-sampled vegetation in 16 arctic, mountain and mire sites 20 to 90 years after the original inventories. A site-specific change in species assemblages (stability) was quantified using species co-occurrences. Using a randomisation test we tested whether the changes observed were significantly greater than those expected by chance. Relationships between patterns in vegetation stability and time between surveys, numbers of plots, or species diversity and proxies for productivity, were tested using regression analysis. Results:At most sites the changes in species co-occurrences of vascular plants and bryophytes were greater than those expected by chance. The changes observed were found to be unrelated to gradients in productivity or diversity. Conclusions:Changes in species co-occurrences are not strongly linked to diversity or productivity gradients in vegetation, suggesting that other gradients or site-specific factors (e.g. land use or species interactions) may be more important in controlling recent compositional shifts in vegetation in northern Europe. [ABSTRACT FROM AUTHOR]

Background: Broad-scale analysis of interspecific trait variation is a fundamental approach in comparative ecology to investigate general species–environment relationships, but inferences from environmental and phylogenetic signals are still controversially discussed. Aims: The aim of this study was to globally analyse the genus Pinus and the interspecific variation of morphological traits with latitude as a surrogate of broad-scale environmental changes, and to compare latitudinal trait correlations with biogeographic, environmental and phylogenetic signals in trait variation. Methods: Based on native range maps of 103 Pinus species, the latitudinal correlations of nine morphological traits, including needle characters, cone length and tree height were calculated. Principal component analysis was used to explore trait covariation. Variation partitioning was applied to disentangle environmental and phylogenetic signals in trait variation. Results: Strong latitudinal correlations were detected for traits, such as needle length:width ratio or needle longevity, with similar trends for different taxonomic species subsets and geographic regions. Strong latitudinal correlations were related to a decrease in the pure phylogenetic signal and to an increase in the phylogenetically structured environmental variation (PSEV), whereas the pure environmental signal was almost negligible. Conclusions: Besides a ranking of traits that differ in environmental and phylogenetic signals, our results showed a general relationship between increasing latitudinal trait correlation and an increase in PSEV, which indicates phylogenetic niche conservatism. Thus, for the investigated morphological traits of the genus Pinus both environmental and phylogenetic signals are directly linked by PSEV to broad-scale spatial patterns in trait variation. [ABSTRACT FROM PUBLISHER]

Background: Under the current warming process, with its implications of higher temperatures, less rainfall, snowfall and snow cover, low-edge populations of high-mountain plants are expected to decline. Demographic studies are useful to foresee the future dynamics of species ranges. Adaptation, phenotypic plasticity, and demographic compensation have been proposed as mechanisms to cope with climate change. Aim: We studied the population dynamics of the high-mountain narrow endemic Armeria caespitosa at the extremes of its altitude distribution (low versus high edge), the high edge representing colonised summits that provide optimal growing conditions. The focus of the study was to establish if the species is retracting at its lower distribution range. Methods: We used 4 years of population censuses and soil seed bank data. Population matrix models allowed us to study the stochastic population growth rates, the species long-term viability under higher frequency of extreme years, and the life cycle transitions responsible for the differences in population dynamics between elevation range edges. Results: The low edge of the A. caespitosa elevation range appeared stable, with positive population growth rates under current environmental conditions, and a null quasi-extinction probability in the long-term under scenarios of high frequency of extremely dry years. Conclusions: The species will likely withstand the current climate-warming scenario along its elevation range. Results supported the role of so-called demographic compensation at a small spatial scale, which we argue might be common in the Mediterranean mountains. [ABSTRACT FROM PUBLISHER]

Background: Botanical records have been collected from mountain summits worldwide since the sixteenth century. Such records are of particular interest following the end of the Little Ice Age, when alpine climate changed. Aims: To review the evolution of alpine summit flora research and define appropriate re-surveys for documenting floristic changes since the mid-nineteenth century. Methods: The history of botanical observations of mountain summits worldwide conducted between the mid-sixteenth and mid-twentieth century is outlined. Secondly, we review evidence for floristic change on mountain summits from studies made between 1980 and 2010. Thirdly, we examine the methods used in earlier summit surveys and suggest appropriate approaches for reconducting such surveys. Results: We found ca. 300 summit flora studies up to 200 years old that are potentially suitable for re-surveying; most of them are in the Alps. Recent studies showed an increase in species numbers and an upward range extension of some species from lower elevations. For re-surveying it is judged best to carry out data collection by individual surveyors for sound comparisons with earlier studies. Conclusions: Data collected in historical summit flora studies allow their exploitation for long-term observation provided contemporary methods are replicated and the detection rate is estimated in the re-surveys. [ABSTRACT FROM PUBLISHER]

Background: Numerous Cape Floristic Region (CFR) clades are found in the Afromontane region of Africa, causing speculation on the source of their distribution. The southern Escarpment has been postulated as a key link in the movement of Cape species between the CFR and these Afromontane areas. Aims: The strengths of three purported connections (the north-west, Matjiesfontein and south-east) between the CFR and the southern Escarpment are considered, and of the southern Escarpment track itself. Methods: A comprehensive database was compiled from which floristic comparisons and multivariate analyses were undertaken. Palaeo-connectivity was assessed from phylogenetic relationships determined from 19 phylogenies. Results: There is evidence of both palaeo- and current connectivity between the Escarpment and the CFR, most strongly for the SE connection. Current connectivity along the southern Escarpment track is relatively well supported between the eastern Nuweveldberge and Main Drakensberg but not between the Hantam–Roggeveld and Nuweveldberge. Palaeo-connectivity along the southern Escarpment track is well supported by the phylogenies. Conclusions: Climate regime may be a more important factor in floristic connectivity than geomorphological continuity. Historical connectivity along the southern Escarpment track suggests cyclical connectivity, probably in response to glacial–interglacial cycles and associated shifts in rainfall regimes along the southern Escarpment. [ABSTRACT FROM PUBLISHER]

Background: Plants occupying wide altitudinal gradients may be adapted to their altitude of origin. Upward expansion of lowland populations in response to climate change might therefore facilitate species persistence at higher elevations by introducing pre-adapted genes. Aim: We compared plant growth and fitness in Scabiosa columbaria originating from low and high elevations (ca. 600 m and ca. 1200 m above sea level (a.s.l.)) under current and warmer climatic conditions to evaluate evidence for adaptation to altitude and phenotypic plasticity. Methods: Two approaches were used: a climate chamber experiment with current and warmer temperatures; and a common garden experiment at 600 m and 1200 m a.s.l. (two gardens each). Results: Performance of plants grown in their local environment was similar to plants from the foreign environment and independent of altitude of origin. Plant growth was reduced at low temperature. Growth and fitness did not differ between altitudes of treatments but varied among gardens. Reproduction in plants from higher altitudes increased in the lower gardens in one of 2 years of study. Conclusion: We found high phenotypic plasticity and no evidence for adaptation to altitude. Our results indicate that S. columbaria might have the capacity to persist in a warming world at higher elevation without additional gene inflow from lower altitudes. [ABSTRACT FROM PUBLISHER]

Background: A key current issue in studies of global CO2 is the cause of the recent pronounced changes in the timing (phase) and amplitude of its annual cycle. Aim: To use a sensitivity analysis in order to identify the most influential parameters in a new four-box diffusion model of global CO2 transport. Methods: A new diffusion model of global atmospheric transport is developed, implemented by optimisation and used to assess the effects of oceanic, terrestrial and anthropogenic CO2 fluxes on the annual CO2 cycle. As the terrestrial phenology of living organisms in the temperate zones is identified as the central process of concern an improved phenological model for the temperate zones is proposed and used in up-scaling from plant to planet. Results: The diffusion model is found to be able to mimic many of the features observed by the GLOBALVIEW-CO2 network, including the global trend, latitudinal gradient, and annual waveform. Conclusions: It is concluded that, out of five rival hypotheses considered at the outset, the springtime phenology of terrestrial biomes is the dominant controller of recent changes to the annual CO2 cycle. [ABSTRACT FROM PUBLISHER]

Background: Past studies of first and last occurrence dates of phenological events have revealed close associations with climatic parameters. Consequently, it is widely acknowledged that recent shifts in the beginning, duration or ending of such events are a response to present climate change. In addition, in recent times, there have tended to be many more observers than in earlier times, especially in urban areas. Furthermore, the number of individuals (plants or animals) observed has often changed markedly. In many situations it is not possible to obtain the average first or last occurrence date of a group of individuals, and only the most extreme occurrence is recorded. This common observational difficulty leads to sampling bias that needs to be taken into account. Aim: Our aim is to use statistical models to quantify the sampling bias and its dependence on sample size and the variability and correlation amongst the individuals under consideration. Methods: n-dimensional multivariate normal distribution and two-way fixed-effects analysis of variance models were developed to examine the dependence of the sampling bias on the above factors. Our results are compared with real data. Results: For first and last occurrence observations, which are the most common index in many phenological studies, we found that changes in observational practice and sample size can, in certain circumstances, easily produce changes in bias that can swamp (or indeed reverse) any climatic change effects. Conclusions: Our new, realistic statistical models allow the sampling bias to be quantified and calculated in terms of the number of individuals under observation, their variability and the degree of correlation between individuals. [ABSTRACT FROM PUBLISHER]

Background: A key current issue in pelagic ecosystem modelling is obtaining better representations of the growth of phytoplankton so as to increase our understanding of the links between climate change and ocean biogeochemistry. Aims: Here we explore the use of cost-benefit analysis within the context of assessing the optimal distribution of resources for maximizing phytoplankton growth. Methods: We focus on capital and running costs by revisiting some of John Raven's cost-benefit analyses of chloroplast structure/function relations. Then, we describe a general framework for application of cost-benefit considerations in models of phytoplankton growth. Conclusions: Key to applying optimality criteria to phytoplankton growth models is quantifying the costs and benefits of alternative acclimation strategies. Costs include (1) capital costs of the structural and functional components of the cell, (2) running costs of CO2 fixation, nutrient acquisition, biosynthesis and repair, (3) opportunity costs for exploiting variability in the environment, and (4) taxes imposed by losses associated with transport to unfavourable environments, grazers and parasites. On short timescales of phytoplankton blooms, benefits can be assessed through influences on net growth rate, which can be increased by maximising resource gain (r-strategy) or minimizing losses (K-strategy). On longer timescales from years to millennia, the benefit is survival. [ABSTRACT FROM AUTHOR]

The present cold adapted floras of arctic and alpine regions are frequently considered as being at risk from climatic warming. However, the prospect of higher temperatures liberating large areas of land from permanent ice cover in the Arctic plus a retreat of the nival zone on higher mountains could provide new terrain for the continued existence and expansion of both arctic and alpine floras. Examination in detail of these floras reveals numerous examples of species that have sufficient genetic variability to adapt phenologically and physiologically to warmer and drier conditions. The calcicole flora of the Alps is well placed to withstand the drier conditions that may arise with climatic warming. In the Arctic the polar night will persist whatever changes may take place in the temperature regime. There will therefore always be features of the arctic environment that will be distinctive and can be expected to provide a habitat for a polar flora. The polar bear with its complete dependence on sea ice for hunting seals may disappear. However, cold climate floras by contrast will find sufficient heterogeneity in the arctic and alpine habitats and variation within species to evolve and provide adapted species that may benefit from higher temperatures and longer growing seasons. [ABSTRACT FROM AUTHOR]