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81 results for “treeline”
Data for: Red foxes enhance long-term tree growth near the Arctic treeline
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Data from: Density-dependent species interactions modulate alpine treeline shifts
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Insect seed and cone predation reduces reproductive potential of treeline conifers across northern Canada
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Forests on the move: Tracking climate-related treeline changes in mountains of the northeastern United States
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Contrasting responses to climate change at Himalayan treelines revealed by population demographics of two dominant species
<ol> <li><span>Alpine treelines are expected to shift upward due to recent climate change. However, interpretation of changes in montane systems has been problematic because effects of climate change are frequently confounded with those of land use changes. The eastern Himalaya, particularly Langtang National Park, Central Nepal, has been relatively undisturbed for centuries and thus presents an opportunity for studying climate change impacts on alpine treeline uncontaminated by potential confounding factors.</span></li> <li><span>We studied two dominant species, <i>Abies spectabilis </i>and <i>Rhododendron campanulatum</i>, above and below the treeline on two mountains. We constructed 13 transects, each spanning up to 400m in elevation, in which we recorded height and state (dead or alive) of all trees, as well as slope, aspect, canopy density, and measures of anthropogenic and animal disturbance. In a subset of individuals, we determined the age of the plants with tree rings.</span></li> <li>All size classes of <i>R. campanulatum</i> plants had lower mortality above treeline than below it, and young <i>R. campanulatum</i> plants (<2m tall) were at higher density above treeline than below. <i>A. spectabilis</i> shows little evidence of a position change from the historic treeline, with a sudden extreme drop in density above treeline compared to below. Recruitment, as measured by size class distribution, was greater above treeline than below for both species but <i>A. spectabilis</i> is confined to ~25m above treeline whereas <i>R. campanulatum</i> is luxuriantly growing up to 200m above treeline. </li> <li> <i>Synthesis.</i> Evidence suggests that the elevational limits of <i>R. campanulatum</i> have shifted upward both because (1) young <i>R. campanulatum</i> plants above treeline benefited from facilitation of recruitment by surrounding vegetation, allowing upward expansion of recruitment, and (2) increased adult survival due to a general temperature amelioration to mature plants. We predict that the current pure stand of <i>R. campanulatum</i> growing above treeline will be colonized by <i>A. spectabilis</i> that will, in turn, outshade and eventually relegate <i>R. campanulatum </i>to be a minor component of the community, as is the current situation below the treeline. </li> </ol>
Data from: Reindeer control over subarctic treeline alters soil fungal communities with potential consequences for soil carbon storage
<p>Here we present the data and R script from "<em>Reindeer control over subarctic treeline alters soil fungal communities with potential consequences for soil carbon storage</em>" by Henni Ylänne, Rieke L. Madsen, Carles Castaño, Daniel B. Metcalfe and Karina E. Clemmensen (Global Change Biology, 2021). In this study we reported the impacts of grazing regime and mountain birch vicinity on the abundance, diversity and community composition of the soil fungal community, and explored how the soil fungal communities relate to vegetation and, ultimately, to the observed variation in soil carbon stocks. The study was conducted at a treeline ecotone in northern Fennoscandia, where two adjacent 65-year-old grazing regimes with or without summer grazing by reindeer (<i>Rangifer tarandus</i>) could be compared. As these grazing regimes differ in the abundance of mountain birch (<i>Betula pubescens</i> ssp. <i>czerepanovii</i>), the own effects of mountain birch vicinity on the fungal communities were assessed by collecting soil samples directly underneath and > 3 m away from mountain birches.</p> <p>This dataset includes data of soil properties, soil carbon and nitrogen stocks, vegetation community composition (as deterred from plant reads captured by the high-throughput sequencing of ITS2 region), fungal abundance (ITS2 copy numbers), fungal diversity and the taxonomic and functional composition of the soil fungal communities.</p>
Data from: The importance of biotic filtering on boreal conifer recruitment at alpine treeline
<p>Treeline, the ecotone where forest transitions to alpine or tundra ecosystems, is considered the thermal limit to tree growth and survival. Despite temperature increases across mountainous areas and high latitudes globally, there has been no ubiquitous change in treeline position. The process of range expansion must initially depend on increased recruitment at, or beyond current range limits and recruitment limitations have been hypothesized as a mechanism for the variable response of treeline position to climate warming.<b> </b>We conducted a unique series of observational and experimental studies to quantify early-life stage constraints, from seed production to seedling establishment, on black spruce (<i>Picea mariana</i>) and tamarack (<i>Larix laricina</i>) recruitment at a model alpine treeline in Newfoundland, Canada.<b> </b>We found recruitment at treeline to be simultaneously seed and establishment limited. The treeline population produced fewer seeds than the forest population and black spruce seeds produced at treeline were less viable. Tamarack was more seed limited than black spruce where seed viability was low regardless of altitudinal position.<b> </b>Post-dispersal seed predation greatly constrained recruitment across the altitudinal gradient; however, black spruce seeds experienced the lowest levels of invertebrate seed predation on the lichen mat at treeline. If seeds were not consumed, individuals at treeline were establishment limited where germination and seedling establishment was both less abundant and delayed on lichen substrate. Our study highlights the need for multiple factors to align temporally for significant recruitment at treeline to occur.</p>
Data from: Integrating demographic niches and black spruce range expansion at subarctic treelines
<p>When investigating relationships between species' niches and distributions, niches can be divided demographically, resulting in unique niches for different life stages. This approach can identify changing substrate requirements throughout a species' life cycle. Using non-metric multidimensional scaling, we quantified microsite conditions associated with successful recruitment in the tundra landscape and successful seed production amongst adult trees of black spruce (<em>Picea mariana</em>) at subarctic treeline in Yukon, Canada to assess how life stage-specific requirements may impact the distribution of this widespread boreal tree species. Treeline ecotones in this region showed high heterogeneity in tundra microsites available for establishment. Black spruce exhibited changing microsite associations from germination to reproductive maturity, which were mainly driven by changes in plant community and soil moisture. These associations limit the microsites where individuals can establish and reproduce to a subset available within the heterogeneous landscape. Overall, we suggest that (1) substrates suitable for early recruitment are limited at the range edge; and (2) reproductive adults have a narrow niche, limiting successful seed production in adults and forming sink populations where suitable conditions are limited. Our multivariate assessment of microsite suitability can provide valuable insights into the spatial distribution of a species throughout its life cycle and identify life stage-specific constraints to range expansion.</p>
Data from: Climate overrides the influence of microsite conditions on radial growth of the tall multi-stemmed shrub Alnus alnobetula at treeline
<p><strong>Data are documented in the following article:</strong></p> <p>Oberhuber W., A-L. Dobler, T. Heinzle, F. Scandurra, A. Gruber, G. Wieser (2023) Climate overrides the influence of microsite conditions on radial growth of the tall multi-stemmed shrub <em>Alnus alnobetula</em> at treeline. Plants 12, 1708. doi: 10.3390/plants12081708.</p> <p> </p> <p><strong>Summary:</strong></p> <p>Green alder (<em>Alnus alnobetula</em>), a tall multi-stemmed deciduous shrub characterized by shoots showing arched ascending growth, is widespread at high elevations in the European Central Alps. Its growth form frequently leads to asymmetric radial growth and anomalous growth ring patterns making development of representative ring width series needed for analyzing climate-growth relationships or site-specific growth rates and long-term growth trends quite a challenge. In order to assess the variability among radii of one shoot, among shoots belonging to one individual (=stock) and among individuals, 60 stem discs were sampled at treeline on Mt. Patscherkofel (Tyrol, Austria). Annual increments were measured along 188 radii and analyzed in terms of its variability by applying dendrochronological techniques. Results revealed a high agreement in ring width variation among radii of one shoot, among shoots of one individual and largely among individuals from different sites, which confirms the pronounced limitation of radial stem growth by climate forcing at the alpine treeline. In contrast to this, a high variability in absolute growth rates and long-term growth trends was found among shoots belonging to one individual and among individuals, which we attribute to different microsite conditions and disturbances. These factors also override climate control of radial growth under growth limiting environmental conditions, i.e., the agreement in inter-annual variations of radial growth is directly related to the growth rate. Based on these findings we provide recommendations for the number of samples needed to carry out inter- and intra-annual studies of radial growth in this tall multi-stemmed shrub.</p>
Temperature sensitivity of tree recruitment at alpine treelines increases along latitudinal gradients
<p>Alpine treeline is highly sensitive to temperature change, and treelines worldwide have been rapidly responding to temperature warming by increasing tree density. However, often inconsistent or even conflicting results regarding the response of tree recruitment to temperature change across regions, still challenge our profound comprehension of warming-induced treeline dynamics. Here, we identified the temperature sensitivity of tree recruitment within alpine treeline ecotones (i.e., the strength of the relationship between tree recruitment and temperature change), and tested whether and how the temperature sensitivity changed along latitudinal gradients by examining 124 alpine treelines across North America and Asia. Our analyses demonstrated that temperature changes could significantly influence tree recruitment at treeline ecotones and the sensitivity of tree recruitment to temperature change was significantly and positively associated with latitude, showing that tree recruitment was more sensitive to temperature change at high latitudes than at low latitudes. Our findings highlighted the heterogeneous responses of tree recruitment at alpine treelines to temperature changes across latitudinal gradients, which should be incorporated into assessment models to improve future projections of global warming impacts across alpine ecosystems.</p>
Data from: Integrating demographic niches and black spruce range expansion at subarctic treelines
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Data from: The importance of biotic filtering on boreal conifer recruitment at alpine treeline
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Data from: Effects of advancing treelines and melting glaciers on alpine lake ecosystems: A mesocosm experiment
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Disentangling seed availability and establishment filters at alpine treelines through a decade-long field manipulation
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Data from: Reindeer control over subarctic treeline alters soil fungal communities with potential consequences for soil carbon storage
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Contrasting responses to climate change at Himalayan treelines revealed by population demographics of two dominant species
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Temperature sensitivity of tree recruitment at alpine treelines increases along latitudinal gradients
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Data from: Spatial dynamics of alpine treelines under global warming: what explains the mismatch between tree densification and elevational upward shifts at the treeline ecotone?
<p><b>Aim</b></p> <p>Most studies focusing on the alpine treeline responses to climate warming have used either the tree densification within the ecotone or its elevational upshift as indicators. However, it is acknowledged that the relation between densification and upshift is spatially heterogeneous, making inferences and comparability among studies tricky. The lack of consistent empirical evidence on this potential mismatch and its drivers leads us to focus on this issue in this study. The aim was twofold: (i) to quantify the mismatch between the two processes at a regional scale, and (ii) to identify its site-specific determinants.</p> <p><b>Location</b></p> <p>French eastern Pyrenees</p> <p><b>Time period</b></p> <p>1953-2015</p> <p><b>Major taxa studied </b></p> <p><i>Pinus</i><i> uncinata </i>(Ramond ex DC)</p> <p><b>Methods</b></p> <p>An object-oriented supervised classification procedure was performed on historical (1953) and current (2015) air-photos. Based on the resulting rasters, densification of the treeline ecotone and upward shift of the treeline were estimated at the two dates in 191 sites, then standardized, before finally being compared. Three site clusters were derived (no mismatch, densification prevalence, upshift prevalence). After having characterized their spatial patterns through join count statistics, a multinomial logistic regression model was computed to identify the correlates of these clusters among a list of site variables.</p> <p><b>Results</b></p> <p>No spatial pattern among the categories of responses emerges at a local scale, but buffers with no mismatch tend to aggregate at a larger scale. Changes in minimum air temperatures, site elevation, mean slope, slope morphometry and lithology appear as significant drivers of the observed mismatch, implying that the relation between densification and elevational upshift is context-specific.</p> <p><b>Main conclusions</b></p> <p><a name="_Hlk17817327">Our findings suggest that both </a><a name="_Hlk17816517">densification and upshift </a>should be considered in quantitative analyses of treeline spatial dynamics, since these two ecological processes are not controlled by the same drivers.</p>
Data from: Reproduction as a bottleneck to treeline advance across the circumarctic forest tundra ecotone
The fundamental niche of many species is shifting with climate change, especially in sub-arctic ecosystems with pronounced recent warming. Ongoing warming in sub-arctic regions should lessen environmental constraints on tree growth and reproduction, leading to increased success of trees colonising tundra. Nevertheless, variable responses of treeline ecotones have been documented in association with warming temperatures. One explanation for time lags between increasingly favourable environmental conditions and treeline ecotone movement is reproductive limitations caused by low seed availability. Our objective was to assess the reproductive constraints of the dominant tree species at the treeline ecotone in the circumpolar north. We sampled reproductive structures of trees (cones and catkins) and stand attributes across circumarctic treeline ecotones. We used generalized linear mixed models to estimate the sensitivity of seed production and the availability of viable seed to regional climate, stand structure, and species-specific characteristics. Both seed production and viability of available seed were strongly driven by specific, sequential seasonal climatic conditions, but in different ways. Seed production was greatest when growing seasons with more growing degree days coincided with years with high precipitation. Two consecutive years with more growing degree days and low precipitation resulted in low seed production. Seasonal climate effects on the viability of available seed depended on the physical characteristics of the reproductive structures. Large-coned and -seeded species take more time to develop mature embryos and were therefore more sensitive to increases in growing degree days in the year of flowering and embryo development. Our findings suggest that both moisture stress and abbreviated growing seasons can have a notable negative influence on the production and viability of available seed at treeline. Our synthesis revealed that constraints on predispersal reproduction within the treeline ecotone might create a considerable time lag for range expansion of tree populations into tundra ecosystems.
Data from: Competitor or facilitator? The ambiguous role of alpine grassland for the early establishment of tree seedlings at treeline
Alpine treelines are expected to move upslope with a warming climate. However, so far treelines have responded inconsistently and future shifts remain difficult to predict since many factors unrelated to temperature, such as biotic interactions, affect responses at the local scale. Especially during the earliest regeneration stages, trees can be strongly influenced by alpine vegetation via both competition and facilitation. We aimed to understand the relative importance of these two types of interaction in different vegetation structures for treeline regeneration dynamics. Effects of herbaceous alpine vegetation on seedling emergence and first-year performance were studied in a field experiment in the French Alps (2100 m a.s.l.) with five important European treeline tree species: Larix decidua, Picea abies, Pinus cembra, Pinus uncinata and Sorbus aucuparia. Total emergence and locally-germinated seedling survival were not affected, but for seedlings planted at two months of age, negative vegetation impacts dominated for all response parameters: first-year survival, growth and carbohydrate accumulation. However, in the winter half-year, evergreen tree seedlings increased carbohydrate reserves under the protection of senescent herbs. Also, responses of locally-germinated seedlings suggest facilitative vegetation effects in the first two months after emergence. Thus, the interaction switched between competition and facilitation according to ontogenetic stage and seasons. Still, the net outcome after one year was negative, but species differed in their susceptibilities. Because initial establishment is the first bottleneck determining whether treelines remain stable or move upslope, understanding establishment, including site-, life-stage and species-specific processes, is essential for understanding observed treeline spatial patterns and dynamics. When developing predictive models of treeline dynamics, all these 'local' aspects should be incorporated in addition to more global drivers like changes in temperature.
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