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Maaike Y. Bader - One of the best experts on this subject based on the ideXlab platform.
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Treeline form a potential key to understanding Treeline dynamics
Global Ecology and Biogeography, 2011Co-Authors: Melanie A. Harsch, Maaike Y. BaderAbstract:Aim Treelines occur globally within a narrow range of mean growing season temperatures, suggesting that low-temperature growth limitation determines the position of the Treeline. However, Treelines also exhibit features that indicate that other mechanisms, such as biomass loss not resulting in mortality (dieback) and mortality, determine Treeline position and dynamics. Debate regarding the mechanisms controlling Treeline position and dynamics may be resolved by identifying the mechanisms controlling prominent Treeline spatial patterns (or ‘form’) such as the spatial structure of the transition from closed forest to the tree limit. Recent Treeline studies world-wide have confirmed a close link between form and dynamics. Location The concepts presented refer to alpine Treelines globally. Methods In this review, we describe how varying dominance of three general ‘first-level’ mechanisms (tree performance: growth limitation, seedling mortality and dieback) result in different Treeline forms, what ‘second-level’ mechanisms (stresses, e.g. freezing damage, photoinhibition) may underlie these general mechanisms, and how they are modulated by interactions with neighbours (‘third-level’ mechanisms). This hierarchy of mechanisms should facilitate discussions about Treeline formation and dynamics. Results We distinguish four primary Treeline forms: diffuse, abrupt, island and krummholz. Growth limitation is dominant only at the diffuse Treeline, which is the form that has most frequently responded as expected to growing-season warming, whereas the other forms are controlled by dieback and seedling mortality and are relatively unresponsive. Main conclusions Treeline form provides a means for explaining the current variability in Treeline position and dynamics and for exploring the general mechanisms controlling the responses of Treelines to climatic change. Form indicates the relative dependence of tree performance on various aspects of the external climate (especially summer warmth versus winter stressors) and on internal feedbacks, thus allowing inferences on the type as well as strength of climate-change responses.
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Treeline form – a potential key to understanding Treeline dynamics
Global Ecology and Biogeography, 2011Co-Authors: Melanie A. Harsch, Maaike Y. BaderAbstract:Aim Treelines occur globally within a narrow range of mean growing season temperatures, suggesting that low-temperature growth limitation determines the position of the Treeline. However, Treelines also exhibit features that indicate that other mechanisms, such as biomass loss not resulting in mortality (dieback) and mortality, determine Treeline position and dynamics. Debate regarding the mechanisms controlling Treeline position and dynamics may be resolved by identifying the mechanisms controlling prominent Treeline spatial patterns (or ‘form’) such as the spatial structure of the transition from closed forest to the tree limit. Recent Treeline studies world-wide have confirmed a close link between form and dynamics. Location The concepts presented refer to alpine Treelines globally. Methods In this review, we describe how varying dominance of three general ‘first-level’ mechanisms (tree performance: growth limitation, seedling mortality and dieback) result in different Treeline forms, what ‘second-level’ mechanisms (stresses, e.g. freezing damage, photoinhibition) may underlie these general mechanisms, and how they are modulated by interactions with neighbours (‘third-level’ mechanisms). This hierarchy of mechanisms should facilitate discussions about Treeline formation and dynamics. Results We distinguish four primary Treeline forms: diffuse, abrupt, island and krummholz. Growth limitation is dominant only at the diffuse Treeline, which is the form that has most frequently responded as expected to growing-season warming, whereas the other forms are controlled by dieback and seedling mortality and are relatively unresponsive. Main conclusions Treeline form provides a means for explaining the current variability in Treeline position and dynamics and for exploring the general mechanisms controlling the responses of Treelines to climatic change. Form indicates the relative dependence of tree performance on various aspects of the external climate (especially summer warmth versus winter stressors) and on internal feedbacks, thus allowing inferences on the type as well as strength of climate-change responses.
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Mountain Treelines: a Roadmap for Research Orientation
Arctic Antarctic and Alpine Research, 2011Co-Authors: George P. Malanson, Friedrich Karl Holtmeier, Lynn M Resler, Maaike Y. Bader, David Butler, Daniel J. Weiss, Lori D. Daniels, Daniel B. FagreAbstract:For over 100 years, mountain Treelines have been the subject of varied research endeavors and remain a strong area of investigation. The purpose of this paper is to examine aspects of the epistemology of mountain Treeline research—that is, to investigate how knowledge on Treelines has been acquired and the changes in knowledge acquisition over time, through a review of fundamental questions and approaches. The questions Treeline researchers have raised and continue to raise have undoubtedly directed the current state of knowledge. A continuing, fundamental emphasis has centered on seeking the general cause of mountain Treelines, thus seeking an answer to the question, ‘‘What causes Treeline?’’ with a primary emphasis on searching for ecophysiological mechanisms of low-temperature limitation for tree growth and regeneration. However, Treeline research today also includes a rich literature that seeks local, landscape-scale causes of Treelines and reasons why Treelines vary so widely in three-dimensional patterns from one location to the next, and this approach and some of its consequences are elaborated here. In recent years, both lines of research have been motivated greatly by global climate change. Given the current state of knowledge, we propose that future research directions focused on a spatial approach should specifically address cross-scale hypotheses using statistics and simulations designed for nested hierarchies; these analyses will benefit from geographic extension of Treeline research.
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A Simple Spatial Model Exploring Positive Feedbacks at Tropical Alpine Treelines
Arctic Antarctic and Alpine Research, 2008Co-Authors: Maaike Y. Bader, Max Rietkerk, Arnold K. BregtAbstract:Climate change could cause alpine Treelines to shift in altitude or to change their spatial pattern, but little is known about the drivers of Treeline dynamics and patterning. The position and patterns of tropical alpine Treelines are generally attributed to land use, especially burning. Species interactions, in particular facilitation through shading, may also be important for Treeline patterning and dynamics. We studied how fire in alpine vegetation and shade dependence of trees may affect the position and spatial pattern of tropical alpine Treelines and their response to climatic warming, using a spatial minimal model of tree growth at Treeline. Neighboring trees provided shade and protection from fire. The positive feedback that resulted from these neighbor interactions strongly affected the emergent Treelines and always reduced the distance and speed of Treeline advance after a temperature increase. Our model demonstrated that next to fire, shade dependence of trees can also lead to abrupt Treelines and relatively low Treeline positions. This implies that these patterns do not necessarily indicate human disturbance. Strong abruptness of a Treeline may indicate that it will respond slowly to climatic changes.
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high solar radiation hinders tree regeneration above the alpine Treeline in northern ecuador
Plant Ecology, 2007Co-Authors: Maaike Y. Bader, Isabel Van Geloof, Max RietkerkAbstract:Many tropical alpine Treelines lie below their climatic potential, because of natural or anthropogenic causes. Forest extension above the Treeline depends on the ability of trees to establish in the alpine environment. This ability may be limited by different factors, such as low temperatures, excess solar radiation, competition, soil properties, dispersal ability, and fires. In this paper we address the following two questions: Do trees regenerate above the present Treeline, and what are the inhibiting factors for tree establishment? To answer these questions we described the spatial pattern of recent tree establishment below and above the present Treeline in northern Ecuador. Also, we experimentally transplanted seedlings into the alpine vegetation (paramo) and the forest, and investigated the effect of shade, neighboring plants, and substrate on their survival. The number of naturally occurring tree sprouts (seedlings, saplings and ramets) was highest just outside the forest, and decreased with distance to the forest edge. However, only two species that were radiation-tolerant made up these high numbers, while other species were rare or absent in the paramo. In the forest, the species diversity of sprouts was high and the abundance per species was relatively low. The transplanted seedlings survived least in experimental plots without artificial shade where neighboring plants were removed. Seedling survival was highest in artificially shaded plots and in the forest. This shade-dependence of most tree species can strongly slow down forest expansion toward the potential climatic Treeline. Due to the presence of radiation-tolerant species, the complete lack of forest expansion probably needs to be ascribed to fire. However, our results show that natural processes can also explain both the low position and the abruptness of tropical Treelines.
Christian Körner - One of the best experts on this subject based on the ideXlab platform.
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A climate-based model to predict potential Treeline position around the globe
Alpine Botany, 2014Co-Authors: Jens Paulsen, Christian KörnerAbstract:In situ temperature measurements revealed that the position of the high-elevation Treeline is associated with a minimum seasonal mean air temperature within a temperature-defined minimum season length across latitudes. Here, we build upon this experience and present the results of a global statistical analysis and a predictive model for low temperature Treeline positions. We identified 376 natural Treelines from satellite images across the globe, and searched for their closest climatic proxies using a climate database. The analysis included a snow and a water balance submodel to account for season length constraints by snow pack and drought. We arrive at thermal Treeline criteria almost identical to those that emerged from the earlier in situ measurements: tree growth requires a minimum length of the growing season of 94 days. The model yields best fit when the season is defined as all days with a daily mean temperature >0.9 °C, and a mean of 6.4 °C across all these days. The resultant Treeline model ‘TREELIM’ offers a robust estimation of potential Treeline elevation based on climate data only. Error terms include imprecise Treeline position in satellite images and climate approximations in mountainous terrain. The algorithm permits constraining low temperature limits of forest growth worldwide (including polar Treelines) and also permits a bioclimatic stratification of mountain biota, for instance, for biodiversity assessments. As a side product, the model yields the global potentially forested area. The results support the isotherm theory for natural Treeline formation. This completely independent statistical assessment of the climatic drivers of the global Treeline phenomenon confirmed the results of a multi-year measurement campaign.
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early season temperature controls cambial activity and total tree ring width at the alpine Treeline
Plant Ecology & Diversity, 2013Co-Authors: Armando Lenz, Gunter Hoch, Christian KörnerAbstract:Background: Temperature directly affects xylogenesis at high-elevation Treelines. The low-temperature limitation of meristematic processes is thus key to understand Treeline formation. Aims: We aimed to experimentally test in situ the direct low-temperature effect on wood tissue formation at the alpine Treeline. Methods: We applied controlled Peltier-mediated cooling and warming (±3 K) to branch segments in Pinus uncinata at the Treeline in the Swiss Alps. In addition, we studied xylogenesis in untreated trees during the growing season by sequential micro-coring. Results: Micro-cores indicated that the cambial zone was fully developed by the time the cooling and warming treatment started, shortly after snowmelt. Presumably, because of this, experimental cooling of branches did not significantly reduce the number of cells produced per season. Warming extended the formation of early wood into the late season, and thus reduced the fraction of late wood. Conclusions: We conclude that temperatures very early i...
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Treeline formation - currently, in the past and in the future
Alpine Treelines, 2012Co-Authors: Christian KörnerAbstract:This closing chapter summarizes the current understanding of the global Treeline phenomenon with a focus on overarching biological principles. These causes of Treeline formation are than re-visited from a palaeo-ecological point of view. The chapter closes by providing evidence for the likely action of global change on current and future Treelines.
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Alpine Treelines : functional ecology of the global high elevation tree limits
2012Co-Authors: Christian KörnerAbstract:1. High elevation Treelines 1.1 The task 1.2 Previous works 2. Definitions and conventions 2.1 The life form 'tree' 2.2 Lines and transitions 2.3 Limitation, stress and disturbance 2.4 Altitude-related and other environmental drivers 2.5 Treeline nomenclature 3. Treeline patterns 3.1 Treeline taxa 3.2 The summit syndrome and other Treeline depressions 3.3 Mass elevation effect 3.4 Treeline elevation 3.5 Time matters 3.6 Forest structure near Treeline 4. Treeline climate 4.1 Specific aspects of Treeline climatology 4.2 Criteria to define temperature regimes at Treeline 4.3 Treeline temperatures in different bioclimatic regions 4.4 Seedbed and branch temperatures 4.5 Whole forest temperatures 5. Global mountain statistics based on Treeline elevation 5.1 Mountain geostatistics 5.2 Elevational belts 5.3 Global Treeline ecotones 6. Structure and stature of Treeline trees 6.1 Foliage properties 6.2 Wood properties 6.3 Bark properties 6.4 Root traits 6.5 Tree stature 6.6 Dry matter allocation in Treeline trees 7. Growth and development 7.1 Tree growth near Treeline 7.2 Xylogenesis at Treeline 7.3 Apical growth dynamics 7.4 Root growth 7.5 Phenology at Treeline 8. Evolutionary adjustments to life at Treeline 8.1 Phylogenetic selection 8.2 Genotypic responses of growth and development 8.3 Genotypic responses of physiological traits 9. Reproduction, early life stages and tree demography 9.1 Amount and quality of seeds at high elevation 9.2 Germination, seedling and sapling stage 9.3 Tree demography at Treeline 10. Freezing and other forms of stress 10.1 Stress at Treeline in a fitness context 10.2 Mechanisms and principles of freezing resistance 10.3 Freezing resistance in Treeline trees 10.4 Other forms of stress at Treeline 11. Water, nutrient and carbon relations 11.1 Tree water relations during the growing season 11.2 Nutrient relations 11.3 Carbon relations 12. Treeline formation - currently, in the past and in the future 12.1 Causes of current Treelines 12.2 Treelines in the recent past 12.3. Treelines in the distant past (Holocene) 12.4 Future Treelines References Taxonomic index Subject index
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Nitrogen status of conifer needles at the alpine Treeline
Plant Ecology & Diversity, 2009Co-Authors: Katrin Birmann, Christian KörnerAbstract:Background and Aims: High elevation Treelines occur worldwide at similar mean growing season temperatures. Does this result from direct impact of low temperature on growth or carbon metabolism, or does nutrient limitation, induced by low soil temperature, play a role? Similar Treeline elevations at contrasting soil fertility argue against the latter, but the actual nutritional status of Treeline trees (here addressed as foliage nitrogen concentration) has never been assessed systematically. Although needle nitrogen (N) concentration does not necessarily indicate growth limitation by N, the relative abundance of N would indicate obvious depletions at the Treeline. Methods: A central problem with any foliage nutrient assay is that the units for describing the element concentration are dependent on elevation themselves. Here we separate changes in N per unit tissue from changes in reference units. Results: Needles of Pinus cembra and Picea abies in the Alps do not show elevational differences in N concentrat...
Yafeng Wang - One of the best experts on this subject based on the ideXlab platform.
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Research advances in disturbance and ecological processes of the Treeline ecotone
Chinese Science Bulletin, 2019Co-Authors: Yafeng Wang, Eryuan LiangAbstract:The Treeline ecotone refers to the transition from the timberline to treeless alpine vegetation. As either the upper-elevation or northern-most limit of erect trees, Treeline will be sensitive to environmental change. An increasing number studies have focused on influence of climatic change on Treeline dynamics. Treeline shift rate is also considered to be a fingerprint of influence of global change on terrestrial ecosystems. However, less is known about how disturbance, as an important non-climatic factor, mediates the response of Treelines to climate change. Such studies can provide useful information to guide implementation of key ecological protection and rehabilitation measures in these comparatively cold biomes. Herein, we review research progress relating to impacts of different disturbances on ecological processes on the Treeline ecotone. Based on the Web of Science and CNKI database, only a modest 10.8% of 1002 Treeline-related publications from 1950 to 2018 focused on disturbance. Disturbances include natural and human-caused categories according to their causes. Natural disturbances mainly include volcanic eruptions, glacier fluctuations, wildfire, snow avalanche, biological activities, extreme low temperature, and strong wind. Human-caused disturbances mainly include deforestation, grazing, human-caused fire, mining, farming, medicinal plant collecting and tourism. In most cases, due to differences in intensity, frequency and time duration, different disturbances could have different effects on the ecological processes of the Treeline ecotone. Under some circumstances, the impacts of natural and human-caused disturbances on Treelines may not differ significantly. For example, natural wildfires and human-caused fires, as well as wildlife activities and livestock grazing, may contribute similar forcing in driving Treeline dynamics. In disturbed areas, based on soil habitat regimes, Treeline changes would follow two main stages, i.e., primary succession or secondary succession processes driven by multiple environmental factors and climate-driven stand changes. Observational data for the common disturbance influences (e.g. fire and grazing) were rare in recent studies, failing to distinguish relative effects of disturbances and climate change on ecological processes in the Treeline ecotone. Additionally, attention should be paid to both the negative and positive effects of disturbances at the Treeline ecotone. In particular, more studies are necessary to better understand positive effects of disturbances driving Treeline shifts and ecological strategies of trees at disturbed Treelines. To adapt to frequent disturbances, Treeline trees might counteract disturbance through bark and cone characteristics, by clumped distributions, or by clonal reproduction (e.g. sprout-regeneration). Ecological strategies of trees under different disturbance regimes provide a new perspective for explaining non-linear responses of Treeline shift to climate change. Humans cannot control most natural disturbances (e.g. volcanic eruption, glacier fluctuations, wildfire and snow avalanche), whereas we can control human-caused disturbances (e.g. grazing, deforestation and tourism). In this context, human-caused disturbance is a key issue for forest management policies. Further work should consider incorporating disturbance factors into Treeline modelling. In most forest regions, monitoring data for common disturbance factors are very scarce. In order to have a better understanding of Treeline ecological processes, it is necessary to model changes of disturbed Treelines in response to disturbance regimes. Based on multiple approaches, researchers should focus on key ecological processes and perform long-term tracking surveys at the disturbed Treelines. It should be noted that the Tibetan Plateau not only hosts the Northern Hemisphere’s highest natural Treelines but also diverse disturbed Treelines. The Tibetan Plateau could be an ideal location to investigate different contributions of disturbance and climatic change in driving Treeline dynamics. In particular, it would be interesting to investigate how fire or grazing shapes Treeline structure, and how interactions between disturbances and climatic change drive Treeline shift on the Tibetan Plateau.
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Fire facilitates warming-induced upward shifts of alpine Treelines by altering interspecific interactions
Trees-structure and Function, 2019Co-Authors: Yafeng Wang, Eryuan Liang, Josep Peñuelas, Bradley S. Case, Xiaoming Lu, Aaron M. Ellison, J. Julio CamareroAbstract:Moderate-severity fire disturbances can accelerate upslope shifts of alpine Treelines by reducing interspecific interactions, providing additional evidence for the species interaction mechanism in controlling Treeline dynamics. Biotic interactions between trees and other plants may modulate the responses of alpine Treelines to climate. Moderate disturbances could, therefore, accelerate upward shifts of alpine Treelines as the climate warms by reducing the coverage of competitor plants and resetting interspecific interactions. Larch (Larix potaninii var. macrocarpa) Treelines disturbed by fire on the southeastern Tibetan Plateau are good locales for testing this hypothesis. We characterized Treelines in five large rectangular plots spanning undisturbed and fire-disturbed fir (Abies georgei) and larch Treelines. The fires in the 1960s caused gaps in the reconstructed age structures of the larches during the 1970s but did not lead to downslope shifts in Treeline position. Recruitment has instead increased since the 1980s within the disturbed larch Treelines, with Treelines shifting upward by 11–44 m. In contrast, the undisturbed larch and fir Treeline positions remained mostly unchanged. We hypothesize that upslope shifts of alpine Treelines are likely a consequence of climatic warming, but fire disturbances can accelerate these dynamics by altering interspecific interactions.
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moisture mediated responsiveness of Treeline shifts to global warming in the himalayas
Global Change Biology, 2018Co-Authors: Shalik Ram Sigdel, Eryuan Liang, J. Julio Camarero, Yafeng Wang, Josep PeñuelasAbstract:Among forest ecosystems, the alpine Treeline ecotone can be considered to be a simplified model to study global ecology and climate change. Alpine Treelines are expected to shift upwards in response to global warming given that tree recruitment and growth are assumed to be mainly limited by low temperatures. However, little is known whether precipitation and temperature interact to drive long-term Himalayan Treeline dynamics. Tree growth is affected by spring rainfall in the central Himalayan Treelines, being good locations for testing if, in addition to temperature, precipitation mediates Treeline dynamics. To test this hypothesis, we reconstructed spatiotemporal variations in Treeline dynamics in 20 plots located at six alpine Treeline sites, dominated by two tree species (birch, fir), and situated along an east-west precipitation gradient in the central Himalayas. Our reconstructions evidenced that Treelines shifted upward in response to recent climate warming, but their shift rates were primarily mediated by spring precipitation. The rate of upward shift was higher in the wettest eastern Himalayas, suggesting that its ascent rate was facilitated by spring precipitation. The drying tendency in association with the recent warming trends observed in the central Himalayas, however, will likely hinder an upslope advancement of alpine Treelines and promote downward Treeline shifts if moisture availability crosses a critical minimum threshold. Our study highlights the complexity of plant responses to climate and the need to consider multiple climate factors when analyzing Treeline dynamics.
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Moisture‐mediated responsiveness of Treeline shifts to global warming in the Himalayas
Global change biology, 2018Co-Authors: Shalik Ram Sigdel, Eryuan Liang, J. Julio Camarero, Yafeng Wang, Haifeng Zhu, Josep PeñuelasAbstract:Among forest ecosystems, the alpine Treeline ecotone can be considered to be a simplified model to study global ecology and climate change. Alpine Treelines are expected to shift upwards in response to global warming given that tree recruitment and growth are assumed to be mainly limited by low temperatures. However, little is known whether precipitation and temperature interact to drive long-term Himalayan Treeline dynamics. Tree growth is affected by spring rainfall in the central Himalayan Treelines, being good locations for testing if, in addition to temperature, precipitation mediates Treeline dynamics. To test this hypothesis, we reconstructed spatiotemporal variations in Treeline dynamics in 20 plots located at six alpine Treeline sites, dominated by two tree species (birch, fir), and situated along an east-west precipitation gradient in the central Himalayas. Our reconstructions evidenced that Treelines shifted upward in response to recent climate warming, but their shift rates were primarily mediated by spring precipitation. The rate of upward shift was higher in the wettest eastern Himalayas, suggesting that its ascent rate was facilitated by spring precipitation. The drying tendency in association with the recent warming trends observed in the central Himalayas, however, will likely hinder an upslope advancement of alpine Treelines and promote downward Treeline shifts if moisture availability crosses a critical minimum threshold. Our study highlights the complexity of plant responses to climate and the need to consider multiple climate factors when analyzing Treeline dynamics.
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The Coupling of Treeline Elevation and Temperature is Mediated by Non-Thermal Factors on the Tibetan Plateau
Forests, 2017Co-Authors: Yafeng Wang, Shalik Ram Sigdel, Eryuan Liang, Bo Liu, J. Julio CamareroAbstract:Little is known about the relationships between Treeline elevation and climate at regional and local scales. It is compelling to fill this research gap with data from the Tibetan Plateau where some of the highest alpine Treelines in the world are found. This research question partially results from the lack of in situ temperature data at Treeline sites. Herein, Treeline variables (e.g., elevation, topography, tree species) and temperature data were collected from published investigations performed during this decade on the Tibetan Plateau. Temperature conditions near Treeline sites were estimated using global databases and these estimates were corrected by using in situ air temperature measurements. Correlation analyses and generalized linear models were used to evaluate the effects of different variables on Treeline elevation including thermal (growing-season air temperatures) and non-thermal (latitude, longitude, elevation, tree species, precipitation, radiation) factors. The commonality analysis model was applied to explore how several variables (July mean temperature, elevation of mountain peak, latitude) were related to Treeline elevation. July mean temperature was the most significant predictor of Treeline elevation, explaining 55% of the variance in Treeline elevation across the Tibetan Plateau, whereas latitude, tree species, and mountain elevation (mass-elevation effect) explained 30% of the variance in Treeline elevation. After considering the multicollinearity among predictors, July mean temperature (largely due to the influence of minimum temperature) still showed the strongest association with Treeline elevation. We conclude that the coupling of Treeline elevation and July temperature at a regional scale is modulated by non-thermal factors probably acting at local scales. Our results contribute towards explaining the decoupling between climate warming and Treeline dynamics.
J. Julio Camarero - One of the best experts on this subject based on the ideXlab platform.
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Fire facilitates warming-induced upward shifts of alpine Treelines by altering interspecific interactions
Trees-structure and Function, 2019Co-Authors: Yafeng Wang, Eryuan Liang, Josep Peñuelas, Bradley S. Case, Xiaoming Lu, Aaron M. Ellison, J. Julio CamareroAbstract:Moderate-severity fire disturbances can accelerate upslope shifts of alpine Treelines by reducing interspecific interactions, providing additional evidence for the species interaction mechanism in controlling Treeline dynamics. Biotic interactions between trees and other plants may modulate the responses of alpine Treelines to climate. Moderate disturbances could, therefore, accelerate upward shifts of alpine Treelines as the climate warms by reducing the coverage of competitor plants and resetting interspecific interactions. Larch (Larix potaninii var. macrocarpa) Treelines disturbed by fire on the southeastern Tibetan Plateau are good locales for testing this hypothesis. We characterized Treelines in five large rectangular plots spanning undisturbed and fire-disturbed fir (Abies georgei) and larch Treelines. The fires in the 1960s caused gaps in the reconstructed age structures of the larches during the 1970s but did not lead to downslope shifts in Treeline position. Recruitment has instead increased since the 1980s within the disturbed larch Treelines, with Treelines shifting upward by 11–44 m. In contrast, the undisturbed larch and fir Treeline positions remained mostly unchanged. We hypothesize that upslope shifts of alpine Treelines are likely a consequence of climatic warming, but fire disturbances can accelerate these dynamics by altering interspecific interactions.
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moisture mediated responsiveness of Treeline shifts to global warming in the himalayas
Global Change Biology, 2018Co-Authors: Shalik Ram Sigdel, Eryuan Liang, J. Julio Camarero, Yafeng Wang, Josep PeñuelasAbstract:Among forest ecosystems, the alpine Treeline ecotone can be considered to be a simplified model to study global ecology and climate change. Alpine Treelines are expected to shift upwards in response to global warming given that tree recruitment and growth are assumed to be mainly limited by low temperatures. However, little is known whether precipitation and temperature interact to drive long-term Himalayan Treeline dynamics. Tree growth is affected by spring rainfall in the central Himalayan Treelines, being good locations for testing if, in addition to temperature, precipitation mediates Treeline dynamics. To test this hypothesis, we reconstructed spatiotemporal variations in Treeline dynamics in 20 plots located at six alpine Treeline sites, dominated by two tree species (birch, fir), and situated along an east-west precipitation gradient in the central Himalayas. Our reconstructions evidenced that Treelines shifted upward in response to recent climate warming, but their shift rates were primarily mediated by spring precipitation. The rate of upward shift was higher in the wettest eastern Himalayas, suggesting that its ascent rate was facilitated by spring precipitation. The drying tendency in association with the recent warming trends observed in the central Himalayas, however, will likely hinder an upslope advancement of alpine Treelines and promote downward Treeline shifts if moisture availability crosses a critical minimum threshold. Our study highlights the complexity of plant responses to climate and the need to consider multiple climate factors when analyzing Treeline dynamics.
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Moisture‐mediated responsiveness of Treeline shifts to global warming in the Himalayas
Global change biology, 2018Co-Authors: Shalik Ram Sigdel, Eryuan Liang, J. Julio Camarero, Yafeng Wang, Haifeng Zhu, Josep PeñuelasAbstract:Among forest ecosystems, the alpine Treeline ecotone can be considered to be a simplified model to study global ecology and climate change. Alpine Treelines are expected to shift upwards in response to global warming given that tree recruitment and growth are assumed to be mainly limited by low temperatures. However, little is known whether precipitation and temperature interact to drive long-term Himalayan Treeline dynamics. Tree growth is affected by spring rainfall in the central Himalayan Treelines, being good locations for testing if, in addition to temperature, precipitation mediates Treeline dynamics. To test this hypothesis, we reconstructed spatiotemporal variations in Treeline dynamics in 20 plots located at six alpine Treeline sites, dominated by two tree species (birch, fir), and situated along an east-west precipitation gradient in the central Himalayas. Our reconstructions evidenced that Treelines shifted upward in response to recent climate warming, but their shift rates were primarily mediated by spring precipitation. The rate of upward shift was higher in the wettest eastern Himalayas, suggesting that its ascent rate was facilitated by spring precipitation. The drying tendency in association with the recent warming trends observed in the central Himalayas, however, will likely hinder an upslope advancement of alpine Treelines and promote downward Treeline shifts if moisture availability crosses a critical minimum threshold. Our study highlights the complexity of plant responses to climate and the need to consider multiple climate factors when analyzing Treeline dynamics.
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The Coupling of Treeline Elevation and Temperature is Mediated by Non-Thermal Factors on the Tibetan Plateau
Forests, 2017Co-Authors: Yafeng Wang, Shalik Ram Sigdel, Eryuan Liang, Bo Liu, J. Julio CamareroAbstract:Little is known about the relationships between Treeline elevation and climate at regional and local scales. It is compelling to fill this research gap with data from the Tibetan Plateau where some of the highest alpine Treelines in the world are found. This research question partially results from the lack of in situ temperature data at Treeline sites. Herein, Treeline variables (e.g., elevation, topography, tree species) and temperature data were collected from published investigations performed during this decade on the Tibetan Plateau. Temperature conditions near Treeline sites were estimated using global databases and these estimates were corrected by using in situ air temperature measurements. Correlation analyses and generalized linear models were used to evaluate the effects of different variables on Treeline elevation including thermal (growing-season air temperatures) and non-thermal (latitude, longitude, elevation, tree species, precipitation, radiation) factors. The commonality analysis model was applied to explore how several variables (July mean temperature, elevation of mountain peak, latitude) were related to Treeline elevation. July mean temperature was the most significant predictor of Treeline elevation, explaining 55% of the variance in Treeline elevation across the Tibetan Plateau, whereas latitude, tree species, and mountain elevation (mass-elevation effect) explained 30% of the variance in Treeline elevation. After considering the multicollinearity among predictors, July mean temperature (largely due to the influence of minimum temperature) still showed the strongest association with Treeline elevation. We conclude that the coupling of Treeline elevation and July temperature at a regional scale is modulated by non-thermal factors probably acting at local scales. Our results contribute towards explaining the decoupling between climate warming and Treeline dynamics.
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Back to the Future: The Responses of Alpine Treelines to Climate Warming are Constrained by the Current Ecotone Structure
Ecosystems, 2016Co-Authors: J. Julio Camarero, Juan Carlos Linares, Ana I. García-cervigón, Enric Batllori, Isabel Martínez, Emilia GutiérrezAbstract:Alpine Treeline ecotones are considered early-warning monitors of the effects of climate change on terrestrial ecosystems, but it is still unclear how accurately Treeline dynamics may track the expected temperature rises. Site-specific abiotic constraints, such as topography and demographic trends may make Treelines less responsive to environmental fluctuations. A better understanding on how local processes modulate Treelines’ response to warming is thus required. We developed a model of Treeline dynamics based on individual data of growth, mortality and reproduction. Specifically, we modeled growth patterns, mortality rates and reproductive size thresholds as a function of temperature and stand structure to evaluate the influence of climate- and stand-related processes on Treeline dynamics. In this study, we analyze the dynamics of four Pyrenean mountain pine Treeline sites with contrasting stand structures, and subjected to differing rates of climate warming. Our models indicate that Pyrenean Treelines could reach basal areas and reproductive potentials similar to those currently observed in high-elevation subalpine forest by the mid twenty-first century. The fastest paces of Treeline densification are forecasted by the late twenty-first century and are associated with higher warming rates. We found a common densification response of Pyrenean Treelines to climate warming, but contrasting paces arise due to current size structures. Treelines characterized by a multistratified stand structure and subjected to lower mean annual temperatures were the most responsive to climate warming. In monostratified stands, tree growth was less sensitive to temperature than in multistratified stands and trees reached their reproductive size threshold later. Therefore, our simulations highlight that stand structure is paramount in modulating Treeline responsiveness to ongoing climate warming. Synthesis. Treeline densification over the twenty-first century is likely to occur at different rates contingent on current stand structure and its effects on individual-level tree growth responses to warming. Accurate projections of future Treeline dynamics must thus incorporate site-specific factors other than climate, specifically those related to stand structure and its influence on tree growth.
Richard P Duncan - One of the best experts on this subject based on the ideXlab platform.
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A novel framework for disentangling the scale‐dependent influences of abiotic factors on alpine Treeline position
Ecography, 2014Co-Authors: Bradley S. Case, Richard P DuncanAbstract:Low-temperature growth limitation largely determines alpine Treeline position globally, but Treeline elevation also varies locally at a range of scales in response to multiple biotic and abiotic factors. In this study, we conceptualise how variability in Treeline elevation is related to abiotic factors that act as thermal modifiers, physiological stressors, or disturbance agents. We then present a novel analytical framework for quantifying how abiotic factors influence Treeline elevation at different spatial scales using New Zealand Nothofagus Treelines as a case study. We delineated Nothofagus Treelines in a GIS, along which we extracted data for Treeline elevation and eight abiotic explanatory variables at 54 000 points. Each location was classified at each of five spatial scales based on nested river catchments, ranging from large regional to small hillslope catchments. We used hierarchical linear models to partition the variation in both Treeline elevation and the eight abiotic variables by spatial scale, and then quantified the relationships between these at each spatial scale in turn. Nothofagus Treeline elevation varied from 800–1740 m a.s.l. across New Zealand. Abiotic factors explained 82% of the variation in Treeline elevation at the largest (regional) scale and 44–52% of variation at the four finer scales. Broad-scale variation in Nothofagus Treeline elevation was strongly associated with thermal modifiers, consistent with the idea that Treelines coincide with a temperature-driven, physiological limit. However, much of the finer-scale variation in Treeline elevation was explained by a combination of thermal, physiological stress-related, and disturbance variables operating at different spatial scales. The conceptual model and analytical methods developed here provide a general framework for understanding Treeline variation at different spatial scales.
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are Treelines advancing a global meta analysis of Treeline response to climate warming
Ecology Letters, 2009Co-Authors: Melanie A. Harsch, Matt S. Mcglone, Philip E Hulme, Richard P DuncanAbstract:Treelines are temperature sensitive transition zones that are expected to respond to climate warming by advancing beyond their current position. Response to climate warming over the last century, however, has been mixed, with some Treelines showing evidence of recruitment at higher altitudes and/or latitudes (advance) whereas others reveal no marked change in the upper limit of tree establishment. To explore this variation, we analysed a global dataset of 166 sites for which Treeline dynamics had been recorded since 1900 AD. Advance was recorded at 52% of sites with only 1% reporting Treeline recession. Treelines that experienced strong winter warming were more likely to have advanced, and Treelines with a diffuse form were more likely to have advanced than those with an abrupt or krummholz form. Diffuse Treelines may be more responsive to warming because they are more strongly growth limited, whereas other Treeline forms may be subject to additional constraints.
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Are Treelines advancing? A global meta‐analysis of Treeline response to climate warming
Ecology letters, 2009Co-Authors: Melanie A. Harsch, Matt S. Mcglone, Philip E Hulme, Richard P DuncanAbstract:Treelines are temperature sensitive transition zones that are expected to respond to climate warming by advancing beyond their current position. Response to climate warming over the last century, however, has been mixed, with some Treelines showing evidence of recruitment at higher altitudes and/or latitudes (advance) whereas others reveal no marked change in the upper limit of tree establishment. To explore this variation, we analysed a global dataset of 166 sites for which Treeline dynamics had been recorded since 1900 AD. Advance was recorded at 52% of sites with only 1% reporting Treeline recession. Treelines that experienced strong winter warming were more likely to have advanced, and Treelines with a diffuse form were more likely to have advanced than those with an abrupt or krummholz form. Diffuse Treelines may be more responsive to warming because they are more strongly growth limited, whereas other Treeline forms may be subject to additional constraints.
