| 1. |
- Jonsson, Anton, et al.
(författare)
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Calcified carotid artery atheromas in individuals with cognitive dysfunction
- 2023
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Ingår i: Acta Odontologica Scandinavica. - : Taylor & Francis Group. - 0001-6357 .- 1502-3850. ; 81:4, s. 325-331
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The aim of this case-control study was to investigate whether cognitively impaired individuals have a higher burden of calcified carotid artery atheroma (CCAA) than controls without cognitive impairment.Material and methods: The study included 154 cases with Alzheimer’s disease (n = 52), mild cognitive impairment (n = 51), or subjective cognitive decline (n = 51) diagnosed at a university memory clinic. Seventy-six cognitively healthy controls were sampled through the Swedish population register. All participants underwent clinical oral and panoramic radiographic examinations. Two oral and maxillofacial radiologists performed blinded analyses of the panoramic radiographs for signs of CCAA, which was registered as absent or present and, if present, unilateral or bilateral. Consensus assessment was used for all statistical analyses.Results: CCAA was common (40%) in this middle-aged and older Swedish population. We found no differences in the prevalence of CCAA between cases and controls (40% vs. 42%).Conclusion: Cognitively impaired patients do not have a higher burden of CCAA than matched controls without cognitive impairment.
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| 2. |
- Kullman, Leif
(författare)
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A Richer, Greener and Smaller Alpine World : Review and Projection of Warming-Induced Plant Cover Change in the Swedish Scandes
- 2010
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Ingår i: Ambio. - : Springer Netherlands. - 0044-7447 .- 1654-7209. ; 39:2, s. 159-169
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Forskningsöversikt (refereegranskat)abstract
- Alpine plant life is proliferating, biodiversity is on the rise and the mountain world appears more productive and inviting than ever. Upper range margin rise of trees and low-altitude (boreal) plant species, expansion of alpine grasslands and dwarf-shrub heaths are the modal biotic adjustments during the past few decades, after a century of substantial climate warming in the Swedish Scandes. This course of biotic landscape evolution has reached historical dimensions and broken a multi-millennial trend of plant cover retrogression, alpine tundra expansion, floristic and faunal impoverishment, all imposed by progressive and deterministic neoglacial climate cooling. Continued modest warming over the present century will likely be beneficial to alpine biodiversity, geoecological stability, resilience, sustainable reindeer husbandry and aesthetic landscape qualities. These aspects are highlighted by an integrative review of results from long-term monitoring of subalpine/alpine vegetation in the Swedish Scandes. This forms the basis for some tentative projections of landscape transformations in a potentially warmer future. Notably, these results and projections are not necessarily valid in other regions and differ in some respects from model predictions. Continued monitoring is mandatory as a basis for generation of more realistic vegetation and ecosystem models.
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| 3. |
- Kullman, Leif
(författare)
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Alpine flora dynamics : a critical review of responses to climate change in the Swedish Scandes since the early 1950s
- 2010
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Ingår i: Nordic Journal of Botany. - : Wiley-Blackwell. - 0107-055X .- 1756-1051. ; 28:4, s. 398-408
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Tidskriftsartikel (refereegranskat)abstract
- Reports about changes of alpine plant species richness over the past 60 years in the Swedish Scandes are reviewed, synthesized and updated with data from recent reinventories. Methodologically, this endeavour is based on resurveys of the floristic composition on the uppermost 20 m of four high-mountain summits. The key finding is that the species pool has increased by 60-170% since the 1950s and later. Some of the invading species are new to the alpine tundra, with more silvine and thermophilic properties than the extant alpine flora. Not a single species of the original flora has disappeared from any of the summits. This circumstance is discussed in perspective of widespread expectations of pending temperature-driven extinction of alpine species in an alleged future warmer climate. These progressive changes coincided with distinct warming (summer and winter) since the late 1980s. During a short cooler period (1974-1994), the species numbers decreased and the upper elevational limits of some ground cover species descended. Thus, discernible responses, concurrent with both warming and cooling intervals, sustain a strong causal link between climate variability and alpine plant species richness. Methodologically, plot-less revisitation studies of the present kind are beset with substantial uncertainties, which may overstate floristic changes over time. However, it is argued here that carefully executed and critically interpreted, no other method can equally effectively sense the earliest phases of plant invasions into alpine vegetation.
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| 4. |
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| 5. |
- Kullman, Leif
(författare)
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Early postglacial appearance of tree species in northern Scandinavia : review and perspective
- 2008
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Ingår i: Quaternary Science Reviews. - Oxford : Pergamon Press. - 0277-3791 .- 1873-457X. ; 27:27-28, s. 2467-2472
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Tidskriftsartikel (refereegranskat)abstract
- This paper reviews megafossil evidence for the first postglacial records of different tree species in northern Scandinavia. Betula pubescens coll. appeared at the Arctic coast of northern Norway by 16. 900 yr BR In addition, Betula Pubescens (14, 000 yr BP), Pinus sylvestris (11, 700 yr BP) and Picea abies (11, 000 yr BP) existed on early ice- free mountain peaks (nunataks) at different locations in the Scandes during the Lateglacial. Larix sibirica, currently not native to Fennoscandia, and several thermophilous broadleaved tree species were recorded in the earliest part of the Holocene. The conventional interpretation of pollen and macrofossil records from peat and sediment stratigraphies do not consider the Occurrence of the species mentioned above that early at these northern and high altitude sites. This very rapid arrival after the local deglaciation implies that the traditional model of far distant glacial refugial areas for tree species has to be challenged. The Current results are more compatible with a situation involving scattered "cryptic" refugia quite close to margin of the ice sheet at its full-glacial extension. This fits a more general pattern currently emerging on different continents. In general, "cryptic" refugia should be considered in connection with modelling extinction risks related to modern and possible future "climatic crises".
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| 6. |
- Kullman, Leif
(författare)
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Ecological tree line history and palaeoclimate : review of megafossil evidence from the Swedish Scandes
- 2013
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 42:3, s. 555-567
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Forskningsöversikt (refereegranskat)abstract
- The postglacial tree line and climate history in the Swedish Scandes have been inferred from megafossil tree remains. Investigated species are mountain birch (Betula pubescens ssp. czerepanovii), Scots pine (Pinus sylvestris) and grey alder (Alnus incana). Betula and Pinus first appeared on early deglaciated nunataks during the Lateglacial. Their tree lines peaked between 9600 and 9000 cal. a BP, almost 600m higher than present-day elevations. This implies (adjusted for land uplift) that early Holocene summer temperatures may have been 2.3 degrees C above modern ones. Elevational tree line retreat characterized the Holocene tree line evolution. For short periods, excursions from this trend have occurred. Between c. 12000 and 10000 cal. a BP, a pine-dominated subalpine belt prevailed. A first major episode of descent occurred c. 8200 cal. a BP, possibly forced by cooling and an associated shift to a deeper and more persistent snow pack. Thereafter, the subalpine birch forest belt gradually evolved at the expense of the prior pine-dominated tree line ecotone. A second episode of pine descent took place c. 4800 cal. a BP. Historical tree line positions are viewed in relation to early 21st century equivalents, and indicate that tree line elevations attained during the past century and in association with modern climate warming are highly unusual, but not unique, phenomena from the perspective of the past 4800 years. Prior to that, the pine tree line (and summer temperatures) was consistently higher than present, as it was also during the Roman and Medieval periods, c. 1900 and 1000 cal. a BP, respectively.
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| 7. |
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| 8. |
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| 9. |
- Kullman, Leif
(författare)
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Higher-than-present medieval pine (Pinus sylvestris) treeline along the Swedish scandes
- 2015
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Ingår i: Landscape Online. - : International Association for Landscape Ecology. - 1865-1542. ; 42:1, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- The upper treeline of Scots pine (Pinus sylvestris L.) is renowned as a sensitive indicator of climate change and variability. By use of megafossil tree remains, preserved exposed on the ground surface, treeline shift over the past millennium was investigated at multiple sites along the Scandes in northern Sweden. Difference in thermal level between the present and the Medieval period, about AD 1000-1200, is a central, although controversial, aspect concerning the detection and attribution of anthropogenic climate warming. Radiocarbon-dated megafossil pines revealed that the treeline was consistently positioned as much as 115 m higher during the Medieval period than today (AD 2000-2010), after a century of warming and substantial treeline upshift. Drawing on the last-mentioned figure, and a lapse rate of 0.6oC/100 m, it may be inferred that Medieval summer temperatures were about 0.7 oC warmer than much of the past 100 years. Extensive pine mortality and treeline descent after the Medieval warming peak reflect substantially depressed temperatures during the Little Ice Age. Warmer-than-present conditions during the Medieval period concur with temperature reconstructions from different parts of northern Fennoscandia, northwestern Russia and Greenland. Modern warming has not been sufficient to restore Medieval treelines. Against this background, there is little reason to view further modest warming as unnatural.
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| 10. |
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| 11. |
- Kullman, Leif, et al.
(författare)
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New Aspects of High-Mountain Palaeobiogeography : A Synthesis of Data from Forefields of Receding Glaciers and Ice Patches in the Tarna and Kebnekaise Mountains, Swedish Lapland
- 2015
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Ingår i: Arctic. - : The Arctic Institute of North America. - 0004-0843 .- 1923-1245. ; 68:2, s. 141-152
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Tidskriftsartikel (refereegranskat)abstract
- Recent recession of high-mountain glacier ice and perennial snow and ice patches has exposed megafossil and macrofossil tree remnants and peat, offering a new source of Holocene high alpine vegetation history in the Scandes. Radiocarbon dates of 90 tree megafossils from Swedish Lapland, 29 of which had not previously been published, range from 11 980 to 1950 cal yr BP. During the interval 9500-8500 cal yr BP, mountain birch (Betula pubescens ssp. czerepanovii) and Scots pine (Pinus sylvestris) grew 600-700 m higher upslope than they do today, which is a new and remarkable discovery. Subsequently, tree density gradually declined at higher elevations, and as the tree line moved downslope, the ratio of Betula to Pinus increased. Tree growth ceased around 4500 cal yr BP, presumably in response to the return of perennial ice and snow. A short episode of resumed tree growth of Betula indicates conditions warmer than present around 2000 years ago. Between c. 8500 and 7300 cal yr BP, Picea abies, Larix sibirica, Populus tremula, Sorbus aucuparia and Alnus incana were subordinate species on a forest floor dominated by plant species characteristic of prealpine or subalpine woodlands. Growth of trees as much as 700 m higher upslope than today around 9500 cal yr BP implies that summer temperatures at that time may have been 3.0 degrees C warmer than today's temperatures (corrected for land uplift). This inferred temperature difference between the early Holocene and the present concurs with changes in the Earth's orbital parameters.
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| 12. |
- Kullman, Leif, et al.
(författare)
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New Aspects of High-Mountain Palaeobiogeography : A Synthesis of Data from Forefields of Receding Glaciers and Ice Patches in the Tarna and Kebnekaise Mountains, Swedish Lapland
- 2015
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Ingår i: Arctic. - 0004-0843 .- 1923-1245. ; 68:2, s. 141-152
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Tidskriftsartikel (refereegranskat)abstract
- Recent recession of high-mountain glacier ice and perennial snow and ice patches has exposed megafossil and macrofossil tree remnants and peat, offering a new source of Holocene high alpine vegetation history in the Scandes. Radiocarbon dates of 90 tree megafossils from Swedish Lapland, 29 of which had not previously been published, range from 11 980 to 1950 cal yr BP. During the interval 9500-8500 cal yr BP, mountain birch (Betula pubescens ssp. czerepanovii) and Scots pine (Pinus sylvestris) grew 600-700 m higher upslope than they do today, which is a new and remarkable discovery. Subsequently, tree density gradually declined at higher elevations, and as the tree line moved downslope, the ratio of Betula to Pinus increased. Tree growth ceased around 4500 cal yr BP, presumably in response to the return of perennial ice and snow. A short episode of resumed tree growth of Betula indicates conditions warmer than present around 2000 years ago. Between c. 8500 and 7300 cal yr BP, Picea abies, Larix sibirica, Populus tremula, Sorbus aucuparia and Alnus incana were subordinate species on a forest floor dominated by plant species characteristic of prealpine or subalpine woodlands. Growth of trees as much as 700 m higher upslope than today around 9500 cal yr BP implies that summer temperatures at that time may have been 3.0 degrees C warmer than today's temperatures (corrected for land uplift). This inferred temperature difference between the early Holocene and the present concurs with changes in the Earth's orbital parameters.
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| 13. |
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| 14. |
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| 15. |
- Kullman, Leif
(författare)
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One century of treeline change and stability : experiences from the Swedish scandes
- 2010
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Ingår i: Landscape Online. - : International Association for Landscape Ecology (IALE-D). - 1865-1542. ; 17:1, s. 1-31
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Tidskriftsartikel (refereegranskat)abstract
- This paper elaborates and visualizes processes recorded in a recent regional and multi-site study of elevational treeline dynamics during the period 1915 to 2007 in the Swedish Scandes. The purpose is to give a concrete face of the landscape transformation which is associated with the recorded treeline shifts. The main focus is on stand-level structure of past and present treelines and the advance zones, where climate change elicited responses by Betula pubescens ssp. czerepanovii, Picea abies and Pinus sylvestris. All species shifted their treelines upslope by a maximum of c. 200 m in elevation. Most sites, however, manifested changes of smaller magnitudes. This relates to topoclimatic constraints which decouple treeline performance from the macroclimate. The general character of sites which support large and small treeline shifts, respectively, are outlined. The spacing, age structure, growth rates of the tree advance zones are accounted for each of the concerned species. In temporal and spatial detail, the different tree species responded individualistically according to their specific ecologies. Current spread of young seedlings and saplings to increasingly higher elevations in the alpine tundra is particularly highlighted as it may represent the forefront of future treeline advance. It is argued that the current evolution of the treeline ecotone represents a fundamental, although not necessarily entirely unique, reversal of the long-term (Holocene) trend of neoglacial treeline descent.
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| 16. |
- Kullman, Leif
(författare)
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One hundred years later and in a warmer climate : A case of ecotonal treeline change in the Swedish Scandes
- 2020
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Ingår i: Ecology & Conservation Science: Open Access. - Irvine : Juniper Publishers. - 2689-4637. ; 1:3
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Forskningsöversikt (refereegranskat)abstract
- This paper accounts for a case of substantial transformation of the treeline ecotone (Picea abies (L.) Karst.) in the Swedish Scandes. Duringthe past 100 years, coinciding with summer warming by 1.6 °C, the ecotonal landscape changed from predominance of stunted krummholzindividuals to a mosaic of tree groves and intervening alpine tundra.
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| 17. |
- Kullman, Leif, et al.
(författare)
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Post-Little Ice Age tree line rise and climate warming in the Swedish Scandes: a landscape ecological perspective.
- 2009
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 97:3, s. 415-429
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Forskningsöversikt (refereegranskat)abstract
- Elevational tree line change in the southern Swedish Scandes was quantified for the period 1915-2007 and for two sub-periods 1915-1975 and 1975-2007. The study focused on Betula pubescens ssp. czerepanovii, Picea abies and Pinus sylvestris at a large number of sites distributed over an 8000-km(2) area. The basic approach included revisitations of fixed sites (elevational belt transects) and measurements of tree line positions (m a.s.l.) during these three periods. Over the past century, tree lines of all species rose at 95% of the studied localities, with means of 70-90 m. All three species displayed maximum upshifts by about 200 m, which manifests a near-perfect equilibrium with instrumentally recorded air temperature change. This magnitude of response was realized only in particular topographic situations, foremost wind-sheltered and steep concave slopes. Other sites, with more wind-exposed topoclimatic conditions, experienced lesser magnitudes of upshifts. Thus, spatial elevational tree line responses to climate change are markedly heterogeneous and site-dependent. Modelling of the future evolution of the forest-alpine tundra transition has to consider this fact. Even in a hypothetical case of substantial climate warming, tree lines are unlikely to advance on a broad front and a large proportion of the alpine tundra will remain treeless. During the period 1975-2007, the tree lines of Picea and Pinus (in particular) advanced more rapidly than that of Betula towards the alpine region. These species-specific responses could signal a potential trajectory for the evolution of the ecotone in a warmer future. Thereby a situation with some resemblance with the relatively warm and dry early Holocene would emerge. Substantial tree line upshifts over the past two to three decades coincide with air and soil warming during all seasons. This implies that both summer and winter temperatures have to be included in models of climate-driven tree line performance. Synthesis. Maximum tree line rise by 200 m represents a unique trend break in the long-term Holocene tree line regression, which has been driven by average climate cooling for nearly 10 000 years. Tree line positions are well-restored to their pre-Little Ice Age positions. Recent tree line ascent is a truly anomalous event in Holocene vegetation history and possibly unprecedented for seven millennia.
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| 18. |
- Kullman, Leif
(författare)
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Recent cooling and dynamic responses of alpine summit floras in the southern Swedish Scandes
- 2014
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Ingår i: Nordic Journal of Botany. - : Wiley. - 0107-055X .- 1756-1051. ; 32:3, s. 369-376
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Tidskriftsartikel (refereegranskat)abstract
- Changes in plant species richness on alpine summits in the southern Swedish Scandes were analyzed between 2004/2006 and 2012. This period experienced consistent summer and winter cooling and finalized with a cold and snow rich summer 2012. Re-surveys of these summits had previously documented substantial increases in species numbers in concordance with climate warming since the mid-20th century. Over the present study period, species richness decreased by 25-46%. The majority of lost species were those that had advanced upslope during the previous warm episode. Cooling since the mid 2000s and particularly the unusually short and snow-rich growth period in 2012 caused a floristic retrogression. Taken together with extensive upshifts of many species during previous relative warm decades, recent downshifts highlight the large capability of certain alpine species to track their ecological niches as climate changes. The pivotal importance of unusually late-lying snow in 2012, suggests that snow cover phenology exerts a more direct effect on the composition of the alpine flora than ambient temperatures. Dynamic modeling of future ecological landscape evolution needs to consider episodes of the kind reported here.
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| 19. |
- Kullman, Leif, et al.
(författare)
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Shrinking glaciers and ice patches disclose megafossil trees and provide a vision of the Late-glacial and Early post-glacial subalpine/alpine landscape in the Swedish Scandes : review and perspective
- 2020
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Ingår i: Journal of Natural Sciences. - Madison : American Research Institute for Policy Development. - 2334-2943 .- 2334-2951. ; 8:2, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- Extensive glacier recession has prevailed for almost 100 years in the Scandes and other parts of the world. At the lower fringe and forefields of shrinking alpine glaciers and ice patches, a plethora of ancient tree remnants is recovered. This is presumably the first time of exposure since burialby ice thousands of years ago. These remains represent prior stands of virtually all boreal tree species, currently growing in northern Scandinavia. As a consequence, a previously unexpected and patchily treed high-mountain landscape emerges, in some cases 600-700 m higher than present-day treelines. This difference in treeline positions between then and now (corrected for land uplift) indicates that summer temperatures have declined by about 3 °C since the early Holocenetreeline maximum. Radiocarbon-dating reveals that the age of the tree remnants ranges between c. 16 800 and 2000 cal. yr BP. Initially,the high-mountainpeaks stood out asnunataks in a surrounding for long glaciated landscape at lower elevations. As the ice sheet gradually shrinked, glacier cirques and hollows became filled with tree groves, in a matrix of alpine tundra. In addition to Betulapubescens ssp. czerepanovii, Piceaabies and Pinussylvestris, these high-elevation enclaves contained tree species, previously unknown to such high positions and so early. These are Piceaabies and a species currently considered as exotic to Scandinavia, namely Larixsibirica. In response to gradual climate cooling since the middle Holocene, the tree stands declined and dead trees were eventually entombed by glacier ice, which is currently disintegrating.
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| 20. |
- Kullman, Leif
(författare)
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The alpine treeline ecotone in the southernmost Swedish scandes : dynamism on different scales
- 2013. - 1
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Ingår i: Ecotones between forest and grassland. - New York : Springer. - 9781461437970 - 9781461437963 ; , s. 271-298
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Bokkapitel (refereegranskat)abstract
- Alpine (altitudinal) treeline ecotones are elusive, spatially heterogeneous and dynamic transitional zones between closed mountain forest and treeless alpine tundra. From a distance the may look sharp, but a closer view usually reveals a highly complex structural pattern (Kullman 1979). Thermal growth limitation is considered as the fundamental part of the mechanism that creates and maintains the treeline ecotone (Grace et al. 2002; Hoch and Körner 2003; Holtmeier 2003; Kullman 1998, 2007a, 2010a; Diaz et al. 2003; Lloyd and Fastie 2002). At finer scales, the straight thermal forcing is modulated by other agents, e.g., topography, geomorphology, wind, soil depth, species interactions, fire, herbivory, human impacts, and site history (Walsh et al. 1994; Holtmeier and Broll 2005; Gehrig-Fasel et al. 2007; Kullman and Öberg 2009; Leonelli et al. 2011; Aune et al. 2011). Among these, wind appears to have a superior role (cf. Seppälä 2004; Holtmeier and Broll 2010; Kullman 2010a).
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| 21. |
- Kullman, Leif, et al.
(författare)
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The recent history of subalpine krummholz pines (Pimus sylvestris) in the Swedish Scandes
- 2020
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Ingår i: International Journal of Research in Geography. - : ARC Publications. - 2454-8685. ; 6:1, s. 16-28
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Tidskriftsartikel (refereegranskat)abstract
- This paper accounts for photographic surveys of stunted old-growth krummholz pines (Pinussylvestris) in the context of climate change and variability since the late 1970s and early 1980s. The study was conducted within the alpine-tundra ecotone of the southern Swedish Scandes. The life-histories of pineswith this shrubby and stunted growth mode are little studied. They may play some role as dispersal nuclei, contributing to elevational treeline rise in cases of future climate warming. In contrast to earlier assumptions, it now appears that pines, growing in open spaces of the subalpine birch forest belt, may regenerate vegetatively by layering, enabling surprisingly old ages. Having survived the harsh centuries of the Little Age, they have recently attained tree stature and started to produce offspring in their near vicinity. Thereby they contribute to ongoing pine treeline rise and transformation of the forest-alpine tundra ecotone.
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| 22. |
- Kullman, Leif
(författare)
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Thermophilic tree species reinvade subalpine Sweden - Early responses to anomalous late holocene climate warming
- 2008
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Ingår i: Arctic, Antarctic and Alpine research. - : BioOne. - 1523-0430 .- 1938-4246. ; 40:1, s. 104-110
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Tidskriftsartikel (refereegranskat)abstract
- Consistent with general predictions and earlier empirical studies, it appears that recent climate warming has started to affect large-scale biogeographical patterns in northern Sweden. Long-term, systematic monitoring in permanent altitudinal belt transects reveals spread of broadleaved thermophilic tree species with quite different life histories into the subalpine forest belt. Saplings of Quercus robur, Ulmus glabra, Acer platanoides, Alnus glutinosa, and Betula pendula have responded to altered climatic conditions by jump-dispersal in the order of 50-300 km northwards and 500-800 m upwards. Thereby, they have reinvaded elevations where they grew during the warmest phase of the Holocene, 9500-8000 years ago, but were subsequently extirpated by Neoglacial cooling. Confined to the past 15 years or so, these unique observations are consistent with background climatic data, i.e. warming of all seasons. The results contribute to more realistic vegetation models by stressing that at least certain plant species are able to track climate warming without substantial migration lag.
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| 23. |
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| 24. |
- Kullman, Leif, 1948-
(författare)
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Treeline (Pinus sylvestris) landscape evolution in the Swedish Scandes - a 40-year demographic effort viewed in a broader temporal context
- 2014
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Ingår i: Norsk Geografisk Tidsskrift. - : Taylor & Francis Group. - 0029-1951 .- 1502-5292. ; 68:3, s. 155-167
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Tidskriftsartikel (refereegranskat)abstract
- The article reports the outcome of long-term demographic monitoring of elevational treeline ecotonal stands of Scots pine (Pinus sylvestris L.) in the southern Swedish Scandes. Annual censuses were undertaken of recruitment, mortality, growth, seed viability, and causes of mortality during the period 1973-2012 in a set of 18 permanent plots. A net gain in total population size occurred over the study period as the result of periodic fluctuations in recruitment and mortality, broadly congruent with annual variations in summer and winter temperatures. Summer temperatures affected seed viability, establishment, and height growth. Winter temperatures exerted an impact foremost by changing the incidence of winter desiccation injury. As a result of infilling, pine has become a more prominent and vital component of the landscape around the forest limit, which has advanced insignificantly into the bordering mountain birch forest. The results highlight a rigid climate-forest disequilibrium and falsify models suggesting extensive and swift expansion of the treeline ecotone and closed forest at the expense of alpine tundra in response to anticipated future warming during the present century. The balance of evidence suggests that patchy forest expansion is likely to occur at a very slow (plurisecular) pace, given that climate warming prevails.
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| 25. |
- Kullman, Leif, et al.
(författare)
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Trädgräns i fjällen : Sammanställning och utvärdering av en metodstudie för klimatrelaterad miljöövervakning
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Klimatet påverkar våra ekosystem i olika grad och fjällen är ett område där klimatförändringar skulle kunna orsaka stora och snabba förändringar. Genom att studera de övre träden på fjällsluttningar kan man följa hur klimatet bidrar till en förändrad trädgräns. Med trädgräns menas på vilken höjd över havet som träd kan finnas utifrån rådande klimat på platsen. I denna rapport redovisas förändringar i trädgränsen i Dalarna, Härjedalen och Jämtland mellan perioderna 2006-2007 och 2010-2013. Resultaten sammanfattas och utvärderas översiktligt i relation till meteorologiska data under samma tidsintervall. Dessutom diskuteras hur man kan utveckla projektets inriktning och metodik i framtida miljöövervakning.Rapporten visar att inga förändringar av trädgränsens position kan påvisas under det studerade tidsintervallet, även om tidigare studier över ett längre intervall visat på en stigning av trädgränsen. Orsaken till denna uteblivna ökning under det senaste tidsintervallet diskuteras i rapporten.Trädgräns i fjällen är ett gemensamt delprogram inom den regionala miljöövervakningen mellan Länsstyrelserna i Dalarna och Jämtland. Programet påbörjades 2006 som ett utvecklingsprojekt i syftet att utveckla en metod för övervakning av den alpina trädgränsen för att indikera klimatförändringar i fjällen. Uppföljningen av förändringar i trädgränsens position grundar sig på äldre data (från 1915) och tidigare studier av trädgränsernas läge och förändringar i olika tidsskalor genomförda av Leif Kullman vid Umeå universitet från 1970-talet och framåt. De alpina trädgränserna är viktiga i avseende att tidigt upptäcka förändringar i det biologiska fjällandskapet och för att förstå de klimatberoende ekologiska processer som på sikt kan påverka den biologiska mångfalden. Resultaten bidrar till att följa upp miljömålet Storslagen fjällmiljö.
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| 26. |
- Kullman, Leif, et al.
(författare)
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Trädgränsen som indikator på ändrat klimat (2019-2023) - Rapport från trädgränsprojektet i Jämtland
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Trädgränsens dynamik är, vid sidan av glaciärernas och de större snölegornas förändringar, en av våra viktigaste naturliga klimatindikatorer, som integrerar klimatutvecklingen och dess ekologiska effekter över varierande tidsskalor (Smithson et al. 2002; Smith et al. 2009; Vinós 2022). Detta har verifierats genom fältstudier i Skandinaviska fjäll under senare år (Aas 1969; Lundqvist 1969; Kullman 1981, 1998, 2001a, 2007, 2013, 2014 a,b, 2015 a,b, 2018a,b; Kullman & Öberg 2009, 2018a; Nesje & Dahl 2000; Hofgaard et al. 2009; Öberg 2013; Aakala et al. 2014). Till bilden av ett ändrat klimat och dess ekologiska konsekvenser hör observationer av spridning av exotiska trädarter i fjällmiljö (Kullman 2023).
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| 27. |
- Kullman, Leif
(författare)
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Trädgränsens förändring 1974 till 2013 : fotoserie från fjället Östra Barfredhågna i norra Dalarna
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Kommer Dalarnas fjäll vara helt trädklätt inom 100 år? Vissa hävdar det, men finns det forskning som styrker det? Leif Kullman, Umeå universitet har inventerat träden på Östa Barfredhågna i norra Dalarna. Han har jämfört bilder tagna från 1974 fram till 2013. Det finns utifrån denna enskilda studie, ingen större anledning att befara att fjällen skulle bli helt trädbevuxet den närmaste 50 årsperioden. Även om de flesta träd har förflyttat sina gränser uppåt sedan 1915, så reagerar trädslagen något olika. Både fjällbjörk och gran tycks ha det svårt med nyetablering av nya plantor , medan tall verkar klara sig något bättre.
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| 28. |
- Oberg, Lisa, et al.
(författare)
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Ancient Subalpine Clonal Spruces (Picea abies) : Sources of Postglacial Vegetation History in the Swedish Scandes
- 2011
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Ingår i: Arctic. - 0004-0843 .- 1923-1245. ; 64:2, s. 183-196
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Tidskriftsartikel (refereegranskat)abstract
- This study addresses the long-standing issue of postglacial immigration of Picea abies (Norway spruce) into Scandinavia. The main methodological focus is on using megafossil tree remains (wood and cones) of spruce and other species retrieved from the treeline ecotone of the Swedish Scandes as a tool for vegetation reconstruction. The core data come from radiocarbon dating of megafossils preserved in the soil underneath clonal groups of Picea abies, formed by rooting of branches that over time give rise to new upright sterns. At high elevations, we found living spruce clones, which in some cases may be part of a continuous clonal series dating back to-the early Holocene (9500 cal. yr BP). The presence of:Picea in the Swedish Scandes at this early stage concurs with previous megafossil inferences. This date, which places the arrival of Picea very soon after regional deglaciation, is several millennia earlier than the arrival date inferred from pollen data. The persistence of some individual Picea clones from the early Holocene thermal optimum to the present implies that permanently open or semi-open spots existed in the high-mountain landscape even during periods when treelines in general were much higher than at present. Initially, Picea clones appear to have existed in a regional no-analogue vegetation matrix of widely scattered pine (Pinus sylvestris), mountain birch (Betula pubescens ssp. czerepanovii), Siberian larch (Larix sibirica) and thermophilic broadleaved deciduous species. In response to subsequent neoglacial cooling, the alpine character of the landscape has been enhanced through a lowered pine treeline and the disappearance of larch and thermophiles. The endurance of spruces, which escaped fire and other calamities, is due to their inherent phenotypic plasticity. Increasing climatic harshness throughout the Holocene conserved them as crippled krummholz, protected from winter stress by almost complete snow coverage. The appearance of Picea abies exclusively in western Scandinavia shortly after the deglaciation could suggest that the species immigrated from "cryptic" ice age refugia much closer to Scandinavia than conventionally thought.
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| 29. |
- Öberg, Lisa, 1958-, et al.
(författare)
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Ancient subalpine clonal spruces (Picea abies) – sources of postglacial vegetation history in the Swedish Scandes
- 2011
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Ingår i: Arctic. - 0004-0843 .- 1923-1245. ; 64:2, s. 183-196
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Tidskriftsartikel (refereegranskat)abstract
- This study addresses the long-standing issue of postglacial immigration of Picea abies (Norway spruce) into Scandinavia. Methodologically, the main focus is on megafossil tree remains (wood and cones) of spruce and other species, retrieved from the treeline ecotone (Swedish Scandes), as a tool for vegetation reconstruction. Radiocarbon dating of megafossils, preserved in the soil underneath layering clonal groups of Picea abies, provide the core data. Living spruce clones, with in some cases likely continuity back to the early Holocene (9500 cal. yr BP onwards), were found at high-elevations. First postglacial arrival to the Swedish Scandes at this stage concurs with previous megafossil inferences. This is several millennia earlier than inferred from pollen data and very soon after regional deglaciation. Persistence of some individual Picea clones since the early Holocene thermal optimum and up to the present is indicative of permanently open or semi-open spots in the high-mountain landscape, also at times when treelines in general were much higher than present. Initially, Picea clones appear to have existed in a regional no-analogue vegetation matrix of widely scattered pine (Pinus sylvestris), mountain birch (Betula pubescens ssp. czerepanovii), Siberian larch (Larix sibirica) and thermophilic broadleaved deciduous species. In response to subsequent neoglacial cooling, the alpine character of the landscape has been enhanced through a lowered pine treeline and disappearance of larch and thermophiles. Spruces, which escaped fire and other calamities, endured due to their inherent phenotypic plasticity. Increasing climatic harshness throughout the Holocene conserved them as crippled krummholz, protected from winter stress by almost complete snow coverage. Appearance of Picea abies exclusively in the west, shortly after the deglaciation, could suggest that it has immigrated from “cryptic” ice age refugia much closer to Scandinavia than conventionally thought.
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| 30. |
- Öberg, Lisa, 1958-, et al.
(författare)
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Contrasting short-term performance of mountain birch (Betula pubescens ssp. czerepanovii) treeline along a latitudinal continentality-maritimity gradient in the southern Swedish Scandes
- 2012
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Ingår i: Fennia. - Helsinki : Geographical Society of Finland. - 0015-0010. ; 190:1, s. 19-40
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Tidskriftsartikel (refereegranskat)abstract
- Positional treeline shift is a fundamental aspect and indicator of high-mountain vegetation response to climate change. This study analyses treeline performance during the period 2005/2007-2010/2011 in the Swedish Scandes. Focus is on mountain birch (Betula pubescens ssp. czerepanovii) along a regional climatic maritimity-continentality gradient. Treeline upshift by 3.0 yr-1 in the maritime part differed significantly from retreat by 0.4 m yr-1 in the continental part of the transect. This discrepancy is discussed in terms of differential warming-induced snow cover phenology patterns and their influence on soil moisture conditions. In the continental area, earlier and more complete melting of prior relatively rare late-lying snow patches, even high above the treeline, has progressed to a state when melt water irrigation ceases. As a consequence, soil drought sets back the vigor of existing birches and precludes sexual regeneration and upslope advance of the treeline. In the maritime area, extensive and deep snow packs still exist above the treeline and constrain its position, although some release is taking place in the current warm climate. Thereby, the birch treeline expands upslope as the alpine snow patches shrink, but continue to provide sufficient melt water throughout the summer. Treeline rise appears to have been based primarily on seed regeneration over the past few decades. This is a novelty, since prior (1915-2007) treeline advance was accomplished mainly by in situ shifts in growth form of relict krummholz birches, in some cases millennial-old, prevailing above the treeline. By the snow phenology mechanism, birch can benefit from climate warming in the maritime region, which contrasts with the situation in the continental region. This discrepancy should be accounted for in projective models. In a hypothetical case of sustained warming, the subalpine birch forest belt may expand less extensively than often assumed, although advance may continue for some time in snow rich maritime areas.
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| 31. |
- Öberg, Lisa, 1958-, et al.
(författare)
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Recent Glacier Recession – a New Source of Postglacial Treeline and Climate History in the Swedish Scandes
- 2012
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Ingår i: Landscape Online. - Bonn : Geographisches Institut,Universität Bonn. - 1865-1542. ; 26, s. 1-38
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Tidskriftsartikel (refereegranskat)abstract
- Climate warming during the past century has imposed recession of glaciers and perennial snow/ice patches along the entire Swedish Scandes. On the newly exposed forefields, subfossil wood remnants are being outwashed from beneath ice and snow bodies. In Scandinavia, this kind of detrital wood is a previously unused source of postglacial vegetation and climate history. The present study reports radiocarbon dates of a set of 78 wood samples, retrieved from three main sites, high above modern treelines and stretching along the Swedish Scandes. In accord with previous studies, pine (Pinus sylvestris) colonized early emerging nunataks already during the Late Glacial. Around 9600-9500 cal. yr BP a first massive wave of tree establishment, birch and pine, took place in "empty" glacier cirques. Both species grew 400-600 m above their present-ay treeline position and the summer temperatures may have been 3.5 °C warmer than present. In respons to Neoglacial cooling, treelines of both birch and pine descended until their final disappearance from the record 4400 and 5900 cal. yr BP, respectively. During the entire interval 9600 to 4400 cal. yr BP, birch prospered in a 100-150 broad belt above the uppermost pines. The recent emergence of tree remnants in the current habitats relates to the contemporary episode of climate warming, possibly unprecedented for several past millennia. It is inferred, by an anology with the past, that in a future scenario with summers 3.5 ° warmer than present, the birch treeline may rise by 600 m or so.
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| 32. |
- Öberg, Lisa, 1958-
(författare)
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Treeline dynamics in short and long term perspectives : observational and historical evidence from the southern Swedish Scandes
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Treelines in high-mountain regions are constrained by heat deficiency, although the working mechanisms are still not entirely understood. Observational and paleoecological studies on treeline performance may contribute to increased understanding of the treeline phenomenon in general. The present thesis addresses elevational shifts of alpine treelines in the Swedish Scandes. By various analytical tools, the studies embrace widely different temporal scales.The concept treeline refers to the elevation (m a.s.l.) at a specific site of the upper individual tree of a certain tree species, at least 2 m tall. All the principal tree species in the Scandes are concerned, i.e. mountain birch (Betula pubescens ssp. czerepanovii), Norway spruce (Picea abies) and Scots pine (Pinus sylvestris).Paper I deals with regional treeline dynamics at more than 100 sites over the past 100 years. Concurrent with temperature rise by c. 1.4 °C over the same period, maximum treeline advances of all species amount to about 200 m. Thus, under ideal conditions, treelines respond in close equilibrium with air temperature evolution. However, over most parts of the landscape, treeline upshifts have been much smaller than 200 m, which relates to the combined action of geomorphology, wind, snow distribution and soil depth. After 1975, the birch has lost its role as the most rapidly advancing tree species, being superseded by pine and spruce.Paper II is a short-term (2005/2007-2010/2011) study of mountain birch treeline performance along a regional maritimity-continentality gradient. Upshift by 3.0 yr-1 in the maritime part of the gradient contrasts to retreat by 0.4 m yr-1 in the continental part. In the latter area, earlier and more complete melting of late-lying snow patches has seemingly progressed to a state when soil drought sets back the vigour of existing birches and precludes sexual regeneration and upslope advance of the treeline. In the maritime area, extensive and deep snow packs still exist above the treeline and constrain its position, although some release is taking place in the current warm climate.Paper III explores treeline change by phenotypic transformation of old-established stunted and prostrate spruce individuals (krummholz) growing high above the treeline and is based on analyses of radiocarbon-dated megafossils, preserved in the soil underneath clonal groups of spruce. Living spruce clones, which in some cases may date back to the early Holocene (9500 cal. yr BP), suggests that spruce immigrated from “cryptic” ice age refugia much closer to Scandinavia than conventionally thought. As the krummholz form presupposes open and windy habitats, it is inferred that permanently open spots prevailed in the high-mountain landscape even during periods when treelines in general were much higher than today.Paper IV reports radiocarbon dates of wood samples, retrieved from newly exposed glacier forefields at three main sites, located high above the modern treelines and embracing the entire Swedish Scandes. It appears that pine colonized early emerging nunataks already during the Late Glacial. Around 9600-9500 cal. yr BP a first massive wave of tree establishment, birch and pine, took place in “empty” glacier cirques. Both species grew 400-600 m above their present day treeline position and accordingly, the summer temperatures may have been 3.5 °C warmer than present (uncorrected for land uplift). During the entire interval 9600 to 4400 cal. yr BP, birch prospered 100-150 m above the uppermost pines. In response to Neoglacial cooling, treelines of both birch and pine descended until their final disappearance from the record 4400 and 5900 cal. yr BP, respectively. Thereafter, these habitats experienced increased snow accumulation and glacier inception.
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| 33. |
- Öberg, Lisa, 1958-
(författare)
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Treeline dynamics in short and long term perspectives : observational and historical evidence from the southern Swedish Scandes
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Against the background of past, recent and future climate change, the present thesis addresses elevational shifts of alpine treelines in the Swedish Scandes. By definition, treeline refers to the elevation (m a.s.l.) at a specific site of the upper trees of a specific tree species, at least 2 m tall.Based on historical records, the first part of the thesis reports and analyzes the magnitude of treeline displacements for the main trees species (Betula pubescens ssp. czerepanovii, Picea abies and Pinus sylvestris) since the early 20th century. The study covered a large and heterogeneous region and more than 100 sites. Concurrent with temperature rise by c. 1.4 °C over the past century, maximum treeline advances of all species amount to about 200 m. That is virtually what should be predicted from the recorded temperature change over the same period of time. Thus, it appears that under ideal conditions, treelines respond in close equilibrium with air temperature evolution. However, over most parts of the landscape, conditions are not that ideal and treeline upshifts have therefore been much smaller. The main reason for that discrepancy was found to be topoclimatic constraints, i.e. the combined action of geomorphology, wind, snow distribution, soil depth, etc., which over large parts of the alpine landscape preclude treelines to reach their potential thermal limit.Recorded treeline advance by maximum 200 m or so over the past century emerges as a truly anomalous event in late Holocene vegetation history.The second part of the thesis is focused more on long-term changes of treelines and one specific and prevalent mechanism of treeline change. The first part of the thesis revealed that for Picea and Betula, treeline shift was accomplished largely by phenotypic transformation of old-established stunted and prostrate individuals (krummholz) growing high above the treeline. In obvious response to climate warming over the past century, such individuals have transformed into erect tree form, whereby the treeline (as defined here) has risen. As a means for deeper understanding of this mode of positional treeline change, extant clonal spruces, growing around the treeline, were radiocarbon dated from megafossil remains preserved in the soil underneath their canopies. It turned out that Picea abies in particular may attain almost eternal life due to its capability for vegetative reproduction and phenotypic plasticity. Some living clones were in fact inferred to have existed already 9500 years ago, and have thus persisted at the same spot throughout almost the entire Holocene. This contrasts with other tree species, which have left no living relicts from the early Holocene, when they actually grew equally high as the spruce. Thereafter they retracted by more than 300 m in elevation supporting that also on that temporal scale, treelines are highly responsive to climate change.The early appearance of Picea in the Scandes, suggests that Picea “hibernated” the last glacial phase much closer to Scandinavia than earlier thought. It has also immigrated to northern Sweden much earlier than the old-established wisdom.The experiences gained in this thesis should constitute essential components of any model striving to the project landscape ecological consequences of possible future climate shifts.
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