Intraspecific trait variability is a key feature underlying high Arctic plant community resistance to climate warming

In the high Arctic, plant community species composition generally responds slowly to climate warming, whereas less is known about the community functional trait responses and consequences for ecosystem functioning. The slow species turnover and large distribution ranges of many Arctic plant species suggest a significant role of intraspecific trait variability in functional responses to climate change. Here we compare taxonomic and functional community compositional responses to a long-term (17-year) warming experiment in Svalbard, Norway, replicated across three major high Arctic habitats shaped by topography and contrasting snow regimes. We observed taxonomic compositional changes in all plant communities over time. Still, responses to experimental warming were minor and most pronounced in the drier habitats with relatively early snowmelt timing and long growing seasons (Cassiope and Dryas heaths). The habitats were clearly separated in functional trait space, defined by 12 size- and leaf economics-related traits, primarily due to interspecific trait variation. Functional traits also responded to experimental warming, most prominently in the Dryas heath and mostly due to intraspecific trait variation. Leaf area and mass increased and leaf δ15N decreased in response to the warming treatment. Intraspecific trait variability ranged between 30% and 71% of the total trait variation, reflecting the functional resilience of those communities, dominated by long-lived plants, due to either phenotypic plasticity or genotypic variation, which most likely underlies the observed resistance of high Arctic vegetation to climate warming. We further explored the consequences of trait variability for ecosystem functioning by measuring peak season CO2 fluxes. Together, environmental, taxonomic, and functional trait variables explained a large proportion of the variation in net ecosystem exchange (NEE), which increased when intraspecific trait variation was accounted for. In contrast, even though ecosystem respiration and gross ecosystem production both increased in response to warming across habitats, they were mainly driven by the direct kinetic impacts of temperature on plant physiology and biochemical processes. Our study shows that long-term experimental warming has a modest but significant effect on plant community functional trait composition and suggests that intraspecific trait variability is a key feature underlying high Arctic ecosystem resistance to climate warming.publishedVersio

Challenging Current Paradigms in Community Phylogenetics: Including Source Range Phylogenetic Structure and Transforming Phylogenetic Branches to Reflect Trait Evolution

Quantifying the diversity of life, the processes that generate and maintain it, and the effects it has upon the environment are central challenges in the biological sciences. With the increasing availability of phylogenetic data there has been a concurrent rise of interest in using patterns of phylogenetic relatedness among species to address these challenges. This approach, called community phylogenetics or ecophylogenetics, typically utilizes metrics of phylogenetic distance between species as a measure of the overall phenotypic similarity of those species. This approach is built on several assumptions, some more explicit than others, the most prominent of which is the assumption that phylogenetic distance is correlated to phenotypic distance. Two assumptions that are common in the field are that the community phylogenetic structure a species has co-occurred within in the past is irrelevant in the present, and that phylogenetic branches measured in time are the most appropriate for describing phylogenetic structure. The first half of my thesis focuses on this assumption that the past community phylogenetic structure does not matter in the context of biological invasion. Nearly all attempts to use phylogenetic metrics to understand which species can or cannot establish within a new community have focused on two hypotheses relating the distance of an introduced species to the recipient community. In my first chapter, my collaborators and I discuss why the source region a species evolved in may also be important, and highlight three hypotheses as to how source range phylogenetic structure may be important for understanding introduction success. In my second chapter, we test this suite of hypotheses pertaining to both source and recipient region community phylogenetic structure using a dataset of successful and failed bird introductions. We find that, despite the widespread disregard of source region phylogenetic structure, source region metrics improved models of establishment success, and were sometimes more important than recipient region metrics. Our results suggest that species are most successful when coming from a region with many close-relatives and introduced into a region with many distant-relatives, consistent with predictions based on a relatively strong role of competition and/or apparent competition structuring communities in both the source and recipient regions. The second half of my thesis focuses on the assumption that phylogenetic branches are most usefully measured in units of time (or, less commonly, genetic differences). My third chapter explains why time or genetic differentiation may not be strongly correlated with phenotypic differentiation, and advocates an alternative method of re-scaling phylogenetic branch lengths to represent the inferred amounts of evolution along those branches. My collaborators and I use two common use-cases to demonstrate how these re-scaled phylogenies provide a novel source of information for understanding global diversity patterns, and how this improved understanding of global diversity can meaningfully impact conservation decisions. My fourth and final chapter applies the proposed method “trait-scaling” phylogenies to understand how climate change may impact communities. My collaborators and I utilize phylogenetic metrics calculated with both time- and trait-scaled phylogenies, as well as analogous functional metrics, to quantify expected community changes with increasing temperature and/or precipitation in southern Norway. We do this using two different study designs: a natural gradient in temperature and precipitation, and a turf-transplant experiment where whole communities were transplanted to warmer and/or wetter conditions. We find evidence that suggests climate change may have both a “filtering” effect by limiting the overall breadth of species that can occur within a site and also a “repulsion” effect by limiting the similarity of species that co-occur. We found that trait-scaled phylogenies improved our ability to detect community changes, and that utilizing both trait- and time-scaled phylogenetic metrics along with functional metrics provided a more complete picture of the changes expected under climate change. We found differences between results for transplant and gradient approaches which indicate that community phylogenetic and functional structure may be relatively slow to respond to changes in climate, or may respond in ways not predicted from natural gradients. Together, these chapters provide strong support for the increased consideration of both source region phylogenetic structure and alternative methods of phylogenetic branch scaling in future community phylogenetic studies, and may also warrant the re-analysis of existing studies

Plant traits and associated data from a warming experiment, a seabird colony, and along elevation in Svalbard.

Acknowledgements: This research was conducted at the University Centre in Svalbard (UNIS), which provided background knowledge of the study sites and systems, accommodation, lab space, and logistical support for lab and field work during the PFTC4 course. Funding provided by the Norwegian Center for International Cooperation in Education (SIU) and the Research Council of Norway (grants 2013/10074, HNP2015/10037, INTPART 274831) made it possible to conduct this field course at Svalbard with 21 students from 12 nationalities and 4 continents as participants and co-authors to this data paper. The ITEX experiment and field site was funded by UNIS and the University of Iceland Research Funds (grants to ISJ) and the Research Council of Norway (grant 246080/E10). We thank Pernille Bronken Eidesen for introducing us to the local study systems and invaluable assistance with taxonomic identifications, Geir Wing Gabrielsen for background information on the seabird nutrient input gradient below the little auk colony in Bjørndalen, and Christine Schirmer and her team of internship students at the University of Arizona for assistance with stoichiometric and isotope analysis.The Arctic is warming at a rate four times the global average, while also being exposed to other global environmental changes, resulting in widespread vegetation and ecosystem change. Integrating functional trait-based approaches with multi-level vegetation, ecosystem, and landscape data enables a holistic understanding of the drivers and consequences of these changes. In two High Arctic study systems near Longyearbyen, Svalbard, a 20-year ITEX warming experiment and elevational gradients with and without nutrient input from nesting seabirds, we collected data on vegetation composition and structure, plant functional traits, ecosystem fluxes, multispectral remote sensing, and microclimate. The dataset contains 1,962 plant records and 16,160 trait measurements from 34 vascular plant taxa, for 9 of which these are the first published trait data. By integrating these comprehensive data, we bridge knowledge gaps and expand trait data coverage, including on intraspecific trait variation. These data can offer insights into ecosystem functioning and provide baselines to assess climate and environmental change impacts. Such knowledge is crucial for effective conservation and management in these vulnerable regions

Plant traits and associated data from a warming experiment, a seabird colony, and along elevation in Svalbard.

The Arctic is warming at a rate four times the global average, while also being exposed to other global environmental changes, resulting in widespread vegetation and ecosystem change. Integrating functional trait-based approaches with multi-level vegetation, ecosystem, and landscape data enables a holistic understanding of the drivers and consequences of these changes. In two High Arctic study systems near Longyearbyen, Svalbard, a 20-year ITEX warming experiment and elevational gradients with and without nutrient input from nesting seabirds, we collected data on vegetation composition and structure, plant functional traits, ecosystem fluxes, multispectral remote sensing, and microclimate. The dataset contains 1,962 plant records and 16,160 trait measurements from 34 vascular plant taxa, for 9 of which these are the first published trait data. By integrating these comprehensive data, we bridge knowledge gaps and expand trait data coverage, including on intraspecific trait variation. These data can offer insights into ecosystem functioning and provide baselines to assess climate and environmental change impacts. Such knowledge is crucial for effective conservation and management in these vulnerable regions

Plant traits and associated data from a warming experiment, a seabird colony, and along elevation in Svalbard

Abstract The Arctic is warming at a rate four times the global average, while also being exposed to other global environmental changes, resulting in widespread vegetation and ecosystem change. Integrating functional trait-based approaches with multi-level vegetation, ecosystem, and landscape data enables a holistic understanding of the drivers and consequences of these changes. In two High Arctic study systems near Longyearbyen, Svalbard, a 20-year ITEX warming experiment and elevational gradients with and without nutrient input from nesting seabirds, we collected data on vegetation composition and structure, plant functional traits, ecosystem fluxes, multispectral remote sensing, and microclimate. The dataset contains 1,962 plant records and 16,160 trait measurements from 34 vascular plant taxa, for 9 of which these are the first published trait data. By integrating these comprehensive data, we bridge knowledge gaps and expand trait data coverage, including on intraspecific trait variation. These data can offer insights into ecosystem functioning and provide baselines to assess climate and environmental change impacts. Such knowledge is crucial for effective conservation and management in these vulnerable regions

Plant traits and associated data from a warming experiment, a seabird colony, and along elevation in Svalbard

Acknowledgements: This research was conducted at the University Centre in Svalbard (UNIS), which provided background knowledge of the study sites and systems, accommodation, lab space, and logistical support for lab and field work during the PFTC4 course. Funding provided by the Norwegian Center for International Cooperation in Education (SIU) and the Research Council of Norway (grants 2013/10074, HNP2015/10037, INTPART 274831) made it possible to conduct this field course at Svalbard with 21 students from 12 nationalities and 4 continents as participants and co-authors to this data paper. The ITEX experiment and field site was funded by UNIS and the University of Iceland Research Funds (grants to ISJ) and the Research Council of Norway (grant 246080/E10). We thank Pernille Bronken Eidesen for introducing us to the local study systems and invaluable assistance with taxonomic identifications, Geir Wing Gabrielsen for background information on the seabird nutrient input gradient below the little auk colony in Bjørndalen, and Christine Schirmer and her team of internship students at the University of Arizona for assistance with stoichiometric and isotope analysis.The Arctic is warming at a rate four times the global average, while also being exposed to other global environmental changes, resulting in widespread vegetation and ecosystem change. Integrating functional trait-based approaches with multi-level vegetation, ecosystem, and landscape data enables a holistic understanding of the drivers and consequences of these changes. In two High Arctic study systems near Longyearbyen, Svalbard, a 20-year ITEX warming experiment and elevational gradients with and without nutrient input from nesting seabirds, we collected data on vegetation composition and structure, plant functional traits, ecosystem fluxes, multispectral remote sensing, and microclimate. The dataset contains 1,962 plant records and 16,160 trait measurements from 34 vascular plant taxa, for 9 of which these are the first published trait data. By integrating these comprehensive data, we bridge knowledge gaps and expand trait data coverage, including on intraspecific trait variation. These data can offer insights into ecosystem functioning and provide baselines to assess climate and environmental change impacts. Such knowledge is crucial for effective conservation and management in these vulnerable regions