Sea ice has been suggested to be an important factor for dispersal of vascular plants in the Arct... more Sea ice has been suggested to be an important factor for dispersal of vascular plants in the Arctic. To assess its role for postglacial colonization in the North Atlantic region, we compiled data on the first Late Glacial to Holocene occurrence of vascular plant species in East Greenland, Iceland, the Faroe Islands and Svalbard. For each record, we reconstructed likely past dispersal events using data on species distributions and genetics. We compared these data to sea-ice reconstructions to evaluate the potential role of sea ice in these past colonization events and finally evaluated these results using a compilation of driftwood records as an independent source of evidence that sea ice can disperse biological material. Our results show that sea ice was, in general, more prevalent along the most likely dispersal routes at times of assumed first colonization than along other possible routes. Also, driftwood is frequently dispersed in regions that have sea ice today. Thus, sea ice may act as an important dispersal agent. Melting sea ice may hamper future dispersal of Arctic plants and thereby cause more genetic differentiation. It may also limit the northwards expansion of competing boreal species, and hence favour the persistence of Arctic species.
Recent studies from mountainous areas of small spatial extent (<2500 km 2 ) suggest that fine-gra... more Recent studies from mountainous areas of small spatial extent (<2500 km 2 ) suggest that fine-grained thermal variability over tens or hundreds of metres exceeds much of the climate warming expected for the coming decades. Such variability in temperature provides buffering to mitigate climate-change impacts. Is this local spatial buffering restricted to topographically complex terrains? To answer this, we here study fine-grained thermal variability across a 2500-km wide latitudinal gradient in Northern Europe encompassing a large array of topographic complexities. We first combined plant community data, Ellenberg temperature indicator values, locally measured temperatures (LmT) and globally interpolated temperatures (GiT) in a modelling framework to infer biologically relevant temperature conditions from plant assemblages within <1000-m 2 units (community-inferred temperatures: CiT). We then assessed:
The dwarf shrub Cassiope tetragona (Arctic bell-heather) is increasingly used for arctic climate ... more The dwarf shrub Cassiope tetragona (Arctic bell-heather) is increasingly used for arctic climate reconstructions, the reliability of which depends on the existence of a linear climate-growth relationship. This relationship was examined over a high-arctic to sub-arctic temperature gradient and under multi-year artificial warming at a high-arctic site. Growth chronologies of annual shoot length, as well as total leaf length, number of leaves and average leaf length per year, were constructed for three sites. Cassiope tetragona was sampled near its cold tolerance limit at Ny-Ålesund, Svalbard, at its assumed climatic optimum in Endalen, Svalbard, and near its European southern limit at Abisko, Sweden. Together these sites represent the entire temperature gradient of this species. Leaf life span was also determined. Each growing season from 2004 to 2010, 17 open top chambers (OTCs) were placed near Ny-Ålesund, thus increasing the daily mean temperatures by 1·23°C. At the end of the 2010...
We address the impact of the ice age cycles on intraspecific cpDNA diversity, for the first time ... more We address the impact of the ice age cycles on intraspecific cpDNA diversity, for the first time on the full circumboreal-circumarctic scale. The bird-dispersed bog bilberry (or arctic blueberry, Vaccinium uliginosum ) is a key component of northern ecosystems and is here used to assess diversity in previously glaciated vs. unglaciated areas and the importance of Beringia as a refugium and source for interglacial expansion. Eighteen chloroplast DNA haplotypes were observed in and among 122 populations, grouping into three main lineages which probably diverged before, and thus were affected more or less independently by, all major glaciations. The boreal 'Amphi-Atlantic lineage' included one haplotype occurring throughout northern Europe and one occurring in eastern North America, suggesting expansion from at least two bottlenecked, glacial refugium populations. The boreal 'Beringian lineage' included seven haplotypes restricted to Beringia and the Pacific coast of USA. The 'Arctic-Alpine lineage' included nine haplotypes, one of them fully circumpolar. This lineage was unexpectedly diverse, also in previously glaciated areas, suggesting that it thrived on the vast tundras during the ice ages and recolonized deglaciated terrain over long distances. Its largest area of persistence during glaciations was probably situated in the north, stretching from Beringia and far into Eurasia, and it probably also survived the last glaciation in southern mountain ranges. Although Beringia apparently was important for the initial divergence and expansion of V. uliginosum as well as for continuous survival of both the Beringian and Arctic-Alpine lineages during all ice ages, this region played a minor role as a source for later interglacial expansions.
Background: Many alpine plants are rare in Scotland. Their persistence depends on their ability t... more Background: Many alpine plants are rare in Scotland. Their persistence depends on their ability to withstand habitat fragmentation and loss due to changes in land use, increased grazing pressure, and climate change. Aims: We use a phylogeographic approach to address the origin and genetic diversity of Scottish populations, which is relevant for their future management and protection.
Although it is generally agreed that the Arctic flora is among the youngest and least diverse on ... more Although it is generally agreed that the Arctic flora is among the youngest and least diverse on Earth, the processes that shaped it are poorly understood. Here we present 50 thousand years (kyr) of Arctic vegetation history, derived from the first large-scale ancient DNA metabarcoding study of circumpolar plant diversity. For this interval we also explore nematode diversity as a proxy for modelling vegetation cover and soil quality, and diets of herbivorous megafaunal mammals, many of which became extinct around 10 kyr BP (before present). For much of the period investigated, Arctic vegetation consisted of dry steppe-tundra dominated by forbs (non-graminoid herbaceous vascular plants). During the Last Glacial Maximum (25-15 kyr BP), diversity declined markedly, although forbs remained dominant. Much changed after 10 kyr BP, with the appearance of moist tundra dominated by woody plants and graminoids. Our analyses indicate that both graminoids and forbs would have featured in megafaunal diets. As such, our findings question the predominance of a Late Quaternary graminoid-dominated Arctic mammoth steppe.
Aim The oceanic Saxifraga rivularis L. presents one of the most extreme disjunctions known in the... more Aim The oceanic Saxifraga rivularis L. presents one of the most extreme disjunctions known in the arctic flora: it has a small amphi-Beringian range and a larger amphi-Atlantic one. It was recently suggested to have had a single allopolyploid origin in Beringia at least one glacial cycle ago, followed by gradual expansion in a more humid period and differentiation into two allopatric subspecies (the Atlantic ssp. rivularis and the Beringian ssp. arctolitoralis). Here we explore the history of its extreme disjunction.
Aim During the last ice age large parts of the north boreal and subarctic zones were covered by i... more Aim During the last ice age large parts of the north boreal and subarctic zones were covered by ice, while the climate in ice-free regions of northern Asia was extremely cold and dry. The extensive peatlands of these zones with their characteristic vegetation developed at the beginning of the Holocene. We combine a phylogeographical approach with maps of pollen records to identify regions where Rubus chamaemorus, a plant of moist, peaty soils, was likely to grow during this period.
Recent studies from mountainous areas of small spatial extent (<2500 km 2 ) suggest that fine-gra... more Recent studies from mountainous areas of small spatial extent (<2500 km 2 ) suggest that fine-grained thermal variability over tens or hundreds of metres exceeds much of the climate warming expected for the coming decades. Such variability in temperature provides buffering to mitigate climate-change impacts. Is this local spatial buffering restricted to topographically complex terrains? To answer this, we here study fine-grained thermal variability across a 2500-km wide latitudinal gradient in Northern Europe encompassing a large array of topographic complexities. We first combined plant community data, Ellenberg temperature indicator values, locally measured temperatures (LmT) and globally interpolated temperatures (GiT) in a modelling framework to infer biologically relevant temperature conditions from plant assemblages within <1000-m 2 units (community-inferred temperatures: CiT). We then assessed:
Global change is expected to lead to range shifts of plant species. The ecological mechanisms und... more Global change is expected to lead to range shifts of plant species. The ecological mechanisms underpinning these shifts are currently not well understood. Here, we compared ecological responses possibly underlying southern range contraction and northern range expansion of Empetrum nigrum, a key species in northern heathlands, which may be related to global change. We hypothesized a negative response to warming in the 'south' (i.e. the Netherlands) and a positive response at the northern range margin (the tundra on Svalbard). Open top chambers (OTCs) were used to simulate global warming. In the 'south', OTC warming caused enhanced shoot growth and growth rate, biomass increment, advanced phenology, larger and heavier berries of Empetrum, while its growing season was extended by 75 days. Under OTC warming co-occurring Calluna vulgaris also showed an increased growing season length (by 98 days) as well as increased shoot growth rate and biomass growth, plant cover and height. Still, we found no evidence for increased competitiveness relative to Empetrum. In the 'north', Empetrum responded with increased shoot and biomass growth, enhanced berry development and ripening to warming. These responses exceeded those of co-occurring Cassiope tetragona with the exception of its biomass response. The direct and indirect ecological responses found do not readily explain the observed northward retreat of Empetrum at the southern range margin. The direct ecological responses found at its northern range margin are, on the other hand, in line with the increased occurrences of this species on Svalbard.
Sea ice has been suggested to be an important factor for dispersal of vascular plants in the Arct... more Sea ice has been suggested to be an important factor for dispersal of vascular plants in the Arctic. To assess its role for postglacial colonization in the North Atlantic region, we compiled data on the first Late Glacial to Holocene occurrence of vascular plant species in East Greenland, Iceland, the Faroe Islands and Svalbard. For each record, we reconstructed likely past dispersal events using data on species distributions and genetics. We compared these data to sea-ice reconstructions to evaluate the potential role of sea ice in these past colonization events and finally evaluated these results using a compilation of driftwood records as an independent source of evidence that sea ice can disperse biological material. Our results show that sea ice was, in general, more prevalent along the most likely dispersal routes at times of assumed first colonization than along other possible routes. Also, driftwood is frequently dispersed in regions that have sea ice today. Thus, sea ice may act as an important dispersal agent. Melting sea ice may hamper future dispersal of Arctic plants and thereby cause more genetic differentiation. It may also limit the northwards expansion of competing boreal species, and hence favour the persistence of Arctic species.
Recent studies from mountainous areas of small spatial extent (<2500 km 2 ) suggest that fine-gra... more Recent studies from mountainous areas of small spatial extent (<2500 km 2 ) suggest that fine-grained thermal variability over tens or hundreds of metres exceeds much of the climate warming expected for the coming decades. Such variability in temperature provides buffering to mitigate climate-change impacts. Is this local spatial buffering restricted to topographically complex terrains? To answer this, we here study fine-grained thermal variability across a 2500-km wide latitudinal gradient in Northern Europe encompassing a large array of topographic complexities. We first combined plant community data, Ellenberg temperature indicator values, locally measured temperatures (LmT) and globally interpolated temperatures (GiT) in a modelling framework to infer biologically relevant temperature conditions from plant assemblages within <1000-m 2 units (community-inferred temperatures: CiT). We then assessed:
The dwarf shrub Cassiope tetragona (Arctic bell-heather) is increasingly used for arctic climate ... more The dwarf shrub Cassiope tetragona (Arctic bell-heather) is increasingly used for arctic climate reconstructions, the reliability of which depends on the existence of a linear climate-growth relationship. This relationship was examined over a high-arctic to sub-arctic temperature gradient and under multi-year artificial warming at a high-arctic site. Growth chronologies of annual shoot length, as well as total leaf length, number of leaves and average leaf length per year, were constructed for three sites. Cassiope tetragona was sampled near its cold tolerance limit at Ny-Ålesund, Svalbard, at its assumed climatic optimum in Endalen, Svalbard, and near its European southern limit at Abisko, Sweden. Together these sites represent the entire temperature gradient of this species. Leaf life span was also determined. Each growing season from 2004 to 2010, 17 open top chambers (OTCs) were placed near Ny-Ålesund, thus increasing the daily mean temperatures by 1·23°C. At the end of the 2010...
We address the impact of the ice age cycles on intraspecific cpDNA diversity, for the first time ... more We address the impact of the ice age cycles on intraspecific cpDNA diversity, for the first time on the full circumboreal-circumarctic scale. The bird-dispersed bog bilberry (or arctic blueberry, Vaccinium uliginosum ) is a key component of northern ecosystems and is here used to assess diversity in previously glaciated vs. unglaciated areas and the importance of Beringia as a refugium and source for interglacial expansion. Eighteen chloroplast DNA haplotypes were observed in and among 122 populations, grouping into three main lineages which probably diverged before, and thus were affected more or less independently by, all major glaciations. The boreal 'Amphi-Atlantic lineage' included one haplotype occurring throughout northern Europe and one occurring in eastern North America, suggesting expansion from at least two bottlenecked, glacial refugium populations. The boreal 'Beringian lineage' included seven haplotypes restricted to Beringia and the Pacific coast of USA. The 'Arctic-Alpine lineage' included nine haplotypes, one of them fully circumpolar. This lineage was unexpectedly diverse, also in previously glaciated areas, suggesting that it thrived on the vast tundras during the ice ages and recolonized deglaciated terrain over long distances. Its largest area of persistence during glaciations was probably situated in the north, stretching from Beringia and far into Eurasia, and it probably also survived the last glaciation in southern mountain ranges. Although Beringia apparently was important for the initial divergence and expansion of V. uliginosum as well as for continuous survival of both the Beringian and Arctic-Alpine lineages during all ice ages, this region played a minor role as a source for later interglacial expansions.
Background: Many alpine plants are rare in Scotland. Their persistence depends on their ability t... more Background: Many alpine plants are rare in Scotland. Their persistence depends on their ability to withstand habitat fragmentation and loss due to changes in land use, increased grazing pressure, and climate change. Aims: We use a phylogeographic approach to address the origin and genetic diversity of Scottish populations, which is relevant for their future management and protection.
Although it is generally agreed that the Arctic flora is among the youngest and least diverse on ... more Although it is generally agreed that the Arctic flora is among the youngest and least diverse on Earth, the processes that shaped it are poorly understood. Here we present 50 thousand years (kyr) of Arctic vegetation history, derived from the first large-scale ancient DNA metabarcoding study of circumpolar plant diversity. For this interval we also explore nematode diversity as a proxy for modelling vegetation cover and soil quality, and diets of herbivorous megafaunal mammals, many of which became extinct around 10 kyr BP (before present). For much of the period investigated, Arctic vegetation consisted of dry steppe-tundra dominated by forbs (non-graminoid herbaceous vascular plants). During the Last Glacial Maximum (25-15 kyr BP), diversity declined markedly, although forbs remained dominant. Much changed after 10 kyr BP, with the appearance of moist tundra dominated by woody plants and graminoids. Our analyses indicate that both graminoids and forbs would have featured in megafaunal diets. As such, our findings question the predominance of a Late Quaternary graminoid-dominated Arctic mammoth steppe.
Aim The oceanic Saxifraga rivularis L. presents one of the most extreme disjunctions known in the... more Aim The oceanic Saxifraga rivularis L. presents one of the most extreme disjunctions known in the arctic flora: it has a small amphi-Beringian range and a larger amphi-Atlantic one. It was recently suggested to have had a single allopolyploid origin in Beringia at least one glacial cycle ago, followed by gradual expansion in a more humid period and differentiation into two allopatric subspecies (the Atlantic ssp. rivularis and the Beringian ssp. arctolitoralis). Here we explore the history of its extreme disjunction.
Aim During the last ice age large parts of the north boreal and subarctic zones were covered by i... more Aim During the last ice age large parts of the north boreal and subarctic zones were covered by ice, while the climate in ice-free regions of northern Asia was extremely cold and dry. The extensive peatlands of these zones with their characteristic vegetation developed at the beginning of the Holocene. We combine a phylogeographical approach with maps of pollen records to identify regions where Rubus chamaemorus, a plant of moist, peaty soils, was likely to grow during this period.
Recent studies from mountainous areas of small spatial extent (<2500 km 2 ) suggest that fine-gra... more Recent studies from mountainous areas of small spatial extent (<2500 km 2 ) suggest that fine-grained thermal variability over tens or hundreds of metres exceeds much of the climate warming expected for the coming decades. Such variability in temperature provides buffering to mitigate climate-change impacts. Is this local spatial buffering restricted to topographically complex terrains? To answer this, we here study fine-grained thermal variability across a 2500-km wide latitudinal gradient in Northern Europe encompassing a large array of topographic complexities. We first combined plant community data, Ellenberg temperature indicator values, locally measured temperatures (LmT) and globally interpolated temperatures (GiT) in a modelling framework to infer biologically relevant temperature conditions from plant assemblages within <1000-m 2 units (community-inferred temperatures: CiT). We then assessed:
Global change is expected to lead to range shifts of plant species. The ecological mechanisms und... more Global change is expected to lead to range shifts of plant species. The ecological mechanisms underpinning these shifts are currently not well understood. Here, we compared ecological responses possibly underlying southern range contraction and northern range expansion of Empetrum nigrum, a key species in northern heathlands, which may be related to global change. We hypothesized a negative response to warming in the 'south' (i.e. the Netherlands) and a positive response at the northern range margin (the tundra on Svalbard). Open top chambers (OTCs) were used to simulate global warming. In the 'south', OTC warming caused enhanced shoot growth and growth rate, biomass increment, advanced phenology, larger and heavier berries of Empetrum, while its growing season was extended by 75 days. Under OTC warming co-occurring Calluna vulgaris also showed an increased growing season length (by 98 days) as well as increased shoot growth rate and biomass growth, plant cover and height. Still, we found no evidence for increased competitiveness relative to Empetrum. In the 'north', Empetrum responded with increased shoot and biomass growth, enhanced berry development and ripening to warming. These responses exceeded those of co-occurring Cassiope tetragona with the exception of its biomass response. The direct and indirect ecological responses found do not readily explain the observed northward retreat of Empetrum at the southern range margin. The direct ecological responses found at its northern range margin are, on the other hand, in line with the increased occurrences of this species on Svalbard.
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