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  • 1.
    Kullman , Leif
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Öberg , L
    Post-Little Ice Age tree line rise and climate warming in the Swedish Scandes: a landscape ecological perspective2009In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 97, no 3, p. 415-429Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Kullman, L
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    A face of global warming – “Ice birches” and a changing alpine plant cover2004In: Geoöko, Vol. 25, p. 181-202Article in journal (Refereed)
  • 3.
    Kullman, L
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Early Holocene appearance of Mountain birch (Betula pubescens ssp. tortuosa) at unprecedented high elevations in the Swedish Scandes: megafossil evidence exposed by recent snow and ice recession2004In: Arctic, Antarctic, and Alpine Research, Vol. 36, p. 172-180Article in journal (Refereed)
  • 4.
    Kullman, L
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    The changing face of the alpine world2004In: Global Change Newsletter, Vol. 57, p. 12-14Article in journal (Refereed)
  • 5.
    Kullman, L
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Tree-limit landscape evolution at the southern fringe of the Swedish Scandes (Dalarna province) – Holocene and 20th century perspectives2004In: Fennia, Vol. 182, p. 141-162Article in journal (Refereed)
  • 6.
    Kullman, Leif
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    A Richer, Greener and Smaller Alpine World: Review and Projection of Warming-Induced Plant Cover Change in the Swedish Scandes2010In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 39, no 2, p. 159-169Article, review/survey (Refereed)
    Abstract [en]

    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.

  • 7.
    Kullman, Leif
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Alpine flora dynamics: a critical review of responses to climate change in the Swedish Scandes since the early 1950s2010In: Nordic Journal of Botany, ISSN 0107-055X, E-ISSN 1756-1051, Vol. 28, no 4, p. 398-408Article in journal (Refereed)
    Abstract [en]

    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.

  • 8.
    Kullman, Leif
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Early postglacial appearance of tree species in northern Scandinavia: review and perspective2008In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 27, no 27-28, p. 2467-2472Article in journal (Refereed)
    Abstract [en]

    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".

  • 9.
    Kullman, Leif
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ecological tree line history and palaeoclimate: review of megafossil evidence from the Swedish Scandes2013In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 42, no 3, p. 555-567Article, review/survey (Refereed)
    Abstract [en]

    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.

  • 10.
    Kullman, Leif
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    High species turnover and decreasing plant species richness on mountain summits in Sweden: reindeer grazing overrides climate change? Comment2009Other (Other academic)
  • 11.
    Kullman, Leif
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Long-term geobotanical observations of climate change impacts in the Scandes of West-Central Sweden2006In: Nordic Journal of Botany, ISSN 0107-055X, E-ISSN 1756-1051, Vol. 24, p. 445-467Article in journal (Refereed)
  • 12.
    Kullman, Leif
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Old and new trees on Mt Fulufjället in Dalarna, central Sweden [Gamla och nya träd på Fulufjället - Vegetationshistoria på hög nivå]2005In: Svensk Botanisk Tidskrift, ISSN 0039-646X, Vol. 99, no 6, p. 315-Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    Gran, tall och björk återfinns nu på allt högrehöjder i de svenska fjällen. Leif Kullman harföljt trädgränsens snabba förändringar påFulufjället.

  • 13.
    Kullman, Leif
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Recent cooling and dynamic responses of alpine summit floras in the southern Swedish Scandes2014In: Nordic Journal of Botany, ISSN 0107-055X, E-ISSN 1756-1051, Vol. 32, no 3, p. 369-376Article in journal (Refereed)
    Abstract [en]

    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.

  • 14.
    Kullman, Leif
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Tree line population monitoring of Pinus sylvestris in the Swedish Scandes, 1973-2005: implications for tree line theory and climate change ecology2007In: Journal of Ecology, Vol. 95, p. 41-52Article in journal (Refereed)
  • 15.
    Kullman, Leif
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Treeline (Pinus sylvestris) landscape evolution in the Swedish Scandes - a 40-year demographic effort viewed in a broader temporal context2014In: Norsk Geografisk Tidsskrift, ISSN 0029-1951, E-ISSN 1502-5292, Vol. 68, no 3, p. 155-167Article in journal (Refereed)
    Abstract [en]

    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.

  • 16.
    Kullman, Leif
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Oberg, Lisa
    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 Lapland2015In: Arctic, ISSN 0004-0843, E-ISSN 1923-1245, Vol. 68, no 2, p. 141-152Article in journal (Refereed)
    Abstract [en]

    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.

  • 17. Oberg, Lisa
    et al.
    Kullman, Leif
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ancient Subalpine Clonal Spruces (Picea abies): Sources of Postglacial Vegetation History in the Swedish Scandes2011In: Arctic, ISSN 0004-0843, E-ISSN 1923-1245, Vol. 64, no 2, p. 183-196Article in journal (Refereed)
    Abstract [en]

    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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