scholarly journals Predicting arctic‐alpine lake dissolved oxygen responses to future tree line advance at the Swedish forest‐tundra transition zone

2021 ◽  
Author(s):  
Stephen F. Jane ◽  
Kevin C. Rose
Keyword(s):  
Dissolved Oxygen ◽  
Transition Zone ◽  
Alpine Lake ◽  
Tree Line ◽  
Forest Tundra

The Holocene evolution of permafrost near the tree line, on the eastern coast of Hudson Bay (northern Quebec)

1987 ◽  
Vol 24 (11) ◽  
pp. 2206-2222 ◽  
Author(s):  
Michel Allard ◽  
Maurice K. Seguin
Keyword(s):  
Climatic Conditions ◽  
Snow Accumulation ◽  
Eastern Coast ◽  
Permafrost Degradation ◽  
Tree Line ◽  
Stratigraphic Sequence ◽  
Forest Tundra ◽  
Discontinuous Permafrost ◽  
Shrub Tundra ◽  
Peat Plateaus

Permafrost evolution in postglacial marine silts near the tree line was reconstructed using landform analysis, 14C dating, and palynostratigraphic analysis of peat sections. In the forest–tundra, below the tree line, four sites in peat plateaus have a stratigraphic sequence indicating an alluvial plain environment from 6000 to 4800 BP followed by a wetland supporting trees and shrubs with deep snow accumulation and without permafrost. Ground heave occurred between 1900 and 1200 BP as peat plateaus and palsas were formed. In the shrub–tundra, above the tree line, three permafrost sites with buried peat beds suggest that climatic conditions were cold enough for discontinuous permafrost in the surrounding landscape starting from land emergence, about 5800 BP; however, fen expansion and sedge peat accumulation continued over unfrozen ground until 2300, 1560, and 1400 BP. At these dates, the sites were buried with silt, probably as a result of mass wasting on nearby permafrost mounds and then permafrost aggraded under the sites. Generally, the palynostratigraphic data reflect a marked cooling of climate starting by 3200–2700 BP and culminating in a major period of permafrost aggradation between 1900 and 1200 BP. Permafrost degradation has been dominant since then despite other possible cold intervals. Nowadays, the permafrost in marine silts is twice as thick and three times more widespread in the shrub–tundra than in the forest–tundra.

Ultra-high resolution assessment of potential impacts of vegetation shadows on satellite-derived spectral signals from small thermokarst lakes in the boreal forest-tundra transition zone (subarctic Canada)

2021 ◽  
Author(s):  
Pedro Freitas ◽  
Gonçalo Vieira ◽  
Carla Mora ◽  
João Canário ◽  
Diogo Folhas ◽  
...  
Keyword(s):  
High Resolution ◽  
Boreal Forest ◽  
Transition Zone ◽  
Satellite Data ◽  
Thermokarst Lakes ◽  
Forest Tundra ◽  
Permafrost Thaw ◽  
Spectral Signal ◽  
Tree Communities ◽  
Additional Support

<p>Warming of the circumpolar north is accelerating permafrost thaw, with implications for landscapes, hydrology, ecosystems and the global carbon cycle. In subarctic Canada, abrupt permafrost thaw is creating widespread thermokarst lakes. Little attention has been given to small waterbodies with area less than 10,000 m<sup>2</sup>, yet these are biogeochemically more active than larger lakes. Additionally, the landscapes where they develop show intense shrubification and terrestrialization processes, with increases in area and height of shrub and tree communities. Tall vegetation that is colonizing waterbody margins can cast shadows that impact productivity, thermal regime and the water spectral signal, which in satellite data generates pixels with mixed signatures between sunlit and shaded surfaces. We undertook UAV surveys using optical and multispectral sensors at long-term monitoring sites of the Center for Northern Studies (CEN) in subarctic Canada, from the sporadic (SAS/KWAK) to the discontinuous (BGR) permafrost zones in the boreal forest-tundra transition zone. This ultra-high spatial resolution data enabled spectral characterization and 3D reconstruction of the study areas. Ultra-high resolution digital surface models were produced to model shadowing at satellite overpass time (WorldView, PlanetScope and Sentinel-2). We then analyzed the impacts of surrounding vegetation and cast shadows on lake surface spectral reflectance derived from satellite imagery. Ultra-high resolution UAV data allows generating accurate shadow models and can be used to improve the assessment of errors and accuracy of satellite data analysis. Particularly, we identify different spectral signal impacts of cast shadows according to lake color, which highlight the need for special attention of this issue onto lakes with more turbidity.</p><p>This research is funded by the Portuguese Foundation for Science and Technology (FCT) under the project THAWPOND (PROPOLAR), by the Centre of Geographical Studies (FCT I.P. UIDB/00295/2020 and UIDP/00295/2020), with additional support from ArcticNet (NCE), Sentinel North (CFREF) and CEN and is a contribution to T-MOSAiC. PF is funded by FCT (SFRH/BD/145278/2019).</p>

Winter habitat use by ptarmigan, snowshoe hares, red foxes, and river otters in the boreal forest – tundra transition zone of western Quebec

1995 ◽  
Vol 73 (4) ◽  
pp. 755-764 ◽  
Author(s):  
Mario St-Georges ◽  
Simon Nadeau ◽  
Daniel Lambert ◽  
Robert Décarie
Keyword(s):  
Boreal Forest ◽  
Transition Zone ◽  
Species Abundance ◽  
Habitat Type ◽  
Riparian Habitat ◽  
Red Foxes ◽  
Winter Habitat ◽  
Forest Tundra ◽  
River Otters ◽  
Snowshoe Hares

We investigated species–habitat relationships of the midsized fauna inhabiting the transition zone between the boreal forest and forest tundra of subarctic Quebec. Data were collected during a winter aerial track survey of 46 randomly selected 25-km2 plots. The presence of species tracks and habitat variables were recorded for each 1-km section of riparian edge habitat within a plot. Sections of non-riparian habitat were also surveyed. Logistic regression was used to construct habitat models for ptarmigan (Lagopus spp.), snowshoe hares (Lepus americanus), red foxes (Vulpes vulpes), and river otters (Lutra canadensis). Species' habitat type selection was studied by comparing use and availability. Kendall's correlation coefficients were computed to analyze interrelations between variables. Significant logistic regressions were obtained for each species. The index of rank correlation between the observed responses and predicted probabilities for all pairs of observations ranged from 0.67 for ptarmigan to 0.84 for river otters. Species abundance was negatively associated with latitude except for that of snowshoe hare, which showed a stronger negative link with open habitat. For all species, distribution was not proportional to the frequency of occurrence of habitat types. Non-riparian habitat was either avoided or not significantly preferred by all species. Herbivorous species and river otter selected edge habitats along watercourses. Our study suggests that differences presented by the forest tundra and boreal forest are of importance for wildlife.

Modern and Holocene stomate records of tree-line variations in northwestern Quebec

2004 ◽  
Vol 82 (6) ◽  
pp. 726-734 ◽  
Author(s):  
Ruth Leitner ◽  
K Gajewski
Keyword(s):  
Boreal Forest ◽  
Lake Sediments ◽  
Vegetation History ◽  
Vegetation Distribution ◽  
Tree Line ◽  
Forest Tundra ◽  
The Past ◽  
Pollen Concentrations ◽  
Broad Scale

Conifer stomates in lake sediments from the forest to tundra transition in northwestern Quebec were analysed to reconstruct tree-line history during the past 6000 years. The pollen from these sites had already been analysed. Stomate concentrations in modern sediments generally conform to the vegetation distribution, although stomates were lacking in some forested sites. Results from nine cores on a transect from boreal forest to tundra show broad-scale correspondence between Picea stomate and pollen concentrations. At a smaller scale, however, discrepancies were found, such as the absence of stomates from a forest tundra site. A broad-scale correspondence between pollen and stomate concentrations of Larix was also found, although the low numbers of Larix stomates make interpretation difficult. Neither stomate absence nor presence can unambiguously be used to indicate the absence or presence of trees in the area immediately surrounding the lake.Key words: tree line, palynology, stomate, vegetation history, Picea, Larix.

scholarly journals Complex Changes in Plant Communities across a Subarctic Alpine Tree Line in Labrador, Canada + Supplementary Appendix Table (See Article Tools)

ARCTIC ◽  
2015 ◽  
Vol 68 (4) ◽  
pp. 500 ◽  
Author(s):  
Andrew J. Trant ◽  
Keith Lewis ◽  
Brittany H. Cranston ◽  
Julia A. Wheeler ◽  
Ryan G. Jameson ◽  
...  
Keyword(s):  
Plant Communities ◽  
Species Turnover ◽  
Abiotic Factors ◽  
Elevation Gradient ◽  
Alpine Tundra ◽  
Tree Cover ◽  
Tree Line ◽  
Forest Tundra ◽  
Abrupt Changes ◽  
Species Establishment

As climate warms, abiotic factors, as well as plant community and biodiversity structure, may constrain or promote the movement of ecotone boundaries. Our study sought to examine how plant communities change across the tree-line ecotone of the Mealy Mountains in Labrador, Canada. We established eight transects (50–100 m in length) along an elevation gradient in three tree-line zones (forest, forest-tundra, and alpine-tundra) and recorded all species and cover of vegetation in contiguous 1 × 1 m quadrats. Companion abiotic parameters of nutrients and soil temperature were also measured. The absence of abrupt changes in important soil nutrients and growing season temperatures suggests that these factors do not limit tree species establishment beyond the current tree line. Vegetation cover and richness, however, were highly variable and in some cases changed non-linearly across the tree-line ecotone. Tree cover and species density generally decreased with elevation, while some field layer species (< 25 cm in height) increased; the latter change seems to be influenced by ground shrubs rather than herbaceous species. As expected, transects separated by the greatest difference in elevation were the least similar (higher beta diversity/species turnover); however, species turnover between the forest and forest-tundra transects was higher than it was between forest-tundra and alpine-tundra transects, even though the latter were separated by a greater elevation. Community structure and species turnover vary greatly across a tree line with the greatest differences between the forest and the forest-tundra, suggesting a biotic or abiotic barrier. While our ability to predict how the tree line will respond to continued climate change is complicated by these patterns in plant communities, the potential barriers investigated and others identified will be a useful focus for future studies.

scholarly journals The impacts of physical processes on oxygen variations in the North Sea-Baltic Sea transition zone

2011 ◽  
Vol 8 (4) ◽  
pp. 1723-1755 ◽  
Author(s):  
L. Jonasson ◽  
Z. Wan ◽  
J. H. S. Hansen ◽  
J. She
Keyword(s):  
Dissolved Oxygen ◽  
Baltic Sea ◽  
Transition Zone ◽  
North Sea ◽  
Late Summer ◽  
Physical Processes ◽  
The North ◽  
The North Sea ◽  
Seasonal Hypoxia ◽  
Benthic Ecosystems

Abstract. The bottom water of the North Sea-Baltic Sea transition zone suffers from seasonal hypoxia, usually during late summer and autumn. These hypoxic events are critical for the benthic ecosystems and the concentration of dissolved oxygen is an important measure of the water quality. However, to model the subsurface dissolved oxygen is a major challenge, especially in estuaries and coastal regions. In this study a simple oxygen consumption model is coupled to a 3-D hydrodynamical model in order to analyse oxygen variations in the transition zone. The benthic and pelagic consumption of oxygen is modelled as a function of water temperature and oxygen concentration. A quantitative assessment of the model demonstrates that the model is able to resolve both seasonal and interannual variations in dissolved oxygen. Results from several experimental simulations highlight the importance of physical processes in the regulation of dissolved oxygen. Advective oxygen transport and wind induced mixing are two key processes that control the extent of hypoxia in the transition zone.

scholarly journals The impacts of physical processes on oxygen variations in the North Sea-Baltic Sea transition zone

Ocean Science ◽  
2012 ◽  
Vol 8 (1) ◽  
pp. 37-48 ◽  
Author(s):  
L. Jonasson ◽  
J. L. S. Hansen ◽  
Z. Wan ◽  
J. She
Keyword(s):  
Dissolved Oxygen ◽  
Baltic Sea ◽  
Transition Zone ◽  
North Sea ◽  
Late Summer ◽  
Physical Processes ◽  
The North ◽  
The North Sea ◽  
Seasonal Hypoxia ◽  
Benthic Ecosystems

Abstract. The bottom water of the North Sea–Baltic Sea transition zone suffers from seasonal hypoxia, usually during late summer and autumn. These hypoxic events are critical for the benthic ecosystems and the concentration of dissolved oxygen is an important measure of the water quality. However, to model the subsurface dissolved oxygen is a major challenge, especially in estuaries and coastal regions. In this study a simple oxygen consumption model is coupled to a 3-D hydrodynamical model in order to analyse oxygen variations in the transition zone. The benthic and pelagic consumption of oxygen is modelled as a function of water temperature and oxygen concentration. A quantitative assessment of the model demonstrates that the model is able to resolve both seasonal and interannual variations in dissolved oxygen. Results from several experimental simulations highlight the importance of physical processes in the regulation of dissolved oxygen. Advective oxygen transport and wind induced mixing are two key processes that control the extent of hypoxia in the transition zone.

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