Printer Friendly

Ancient subalpine clonal spruces (Picea abies): sources of postglacial vegetation history in the Swedish Scandes.

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 stems. 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 (Betulapubescens 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.

Key words: Picea abies, clones, megafossils, immigration, Holocene, cryptic refugia, Swedish Scandes

RESUME. La presente etude porte sur la question de longue date relative a 1'immigration postglaciaire de Picea abies (epinette de Norvege) en Scandinavie. Du point de vue methodologique, ['accent a ete mis sur ['utilisation de restes d'arbres megafossiles (bois et cones) provenant d'epinettes et d'autres especes prelevees de la limite forestiere de Tecotone dans les Scandes suedoises en tant qu'outil de reamenagement de la vegetation. Les donnees fondamentales proviennent de la datation au carbone 14 des megafossiles preserves dans le sol sous des groupements clonaux de Picea abies, formes par 1'enracinement de branches qui, au fil du temps, donnent naissance a de nouvelles tiges droites. En haute altitude, nous avons trouve des clones vivants d'epinettes qui, dans certains cas, pourraient faire partie d'une serie clonale continue remontant au debut de l'Holocene (9500 cal. annees BP). La presence de Picea dans les Scandes suedoises a ce stade initial vient confirmer les inferences anterieures concernant les megafossiles. Cette date, qui place Tarrivee de Picea peu apres la deglaciation regionale, se trouve a etre des millenaires avant la date d'arrivee inferee par les donnees deduites du pollen. La persistance de certains clones Picea individuels du debut de Poptimum thermique de l'Holocene jusqu'a present implique qu'il existait des endroits ouverts ou semi-ouverts en permanence dans le paysage des hautes montagnes meme pendant les periodes ou les limites forestieres en general etaient beaucoup plus elevees qu'a present. Initialement, les clones Picea semblent avoir existe au sein d'une matrice de vegetation non-analogue regionale de pins largement eparpilles (Pinus sylvestris), de bouleaux fontinaux {Betula pubescens ssp. czerepanovii), de melezes de Siberie (Larix sibiricd) et d'especes thermophiliques caduques a feuilles larges. En reaction au refroidissement neoglaciaire subsequent, le caractere alpin du paysage a ete ameliore grace a une limite forestiere de pins moins elevee et a la disparition des melezes et des thermophiles. L'endurance des epinettes, qui ont echappe aux incendies et a d'autres calamites, est attribuable a leur plasticite phenotypique inherente. L'intensification de la durete du climat pendant l'Holocene a donne lieu a leur conservation sous la forme de krummholz rabougri, protege de la durete de l'hiver par une eouverture de neige quasi-complete. L'apparition exclusive de Picea abies dans l'ouest de la Scandinavie peu apres la deglaciation pourrait laisser entendre que cette espece a immigre de refuges [much less than] cryptiques [much greater than] de la periode glaciaire beaucoup plus pres de la Scandinavie qu'on ne le pensait auparavant.

Mots des: Picea abies, clones, megafossiles, immigration, Holocene, refuge cryptique, Scandes suedoises

(Received 25 May 2010; accepted in revised form 3 November 2010)

Traduit pour la revue Arctic par Nicole Giguere.

INTRODUCTION

During the past two decades, Late Glacial and early Holocene phylogeography has entered a new and dynamic phase. Analyses of ancient DNA, molecular genetics, and dynamic modeling have revitalized interest in long-standing paleo-ecological issues (Willis et al., 2000; Hu et al., 2008; Stewart and Cooper, 2008). One challenging question concerns the location of "hibernation" sites for biota during the last glacial phase and also the timing and routes for postglacial re-immigration into deglaciated territories. More specifically, mounting evidence suggests that plants and animals could have thrived in mid- and high-latitude cryptic refugia (Aim, 1993; Kullman, 2000, 2002; Stewart and Lister, 2001) close to the continental ice margins during glacial and late-glacial episodes. These are ideas with potentially far-reaching consequences for population genetics concerning the possibility for species to adapt to future climate change and the consequent evolution of biodiversity (e.g., Barnosky, 2008; Hampe and Petit, 2010). Therefore, more firm evidence is urgently needed.

Despite recent methodological progress, there are no shortcuts to firm knowledge: testing of emerging hypotheses must still rely on "concrete fossil" evidence, rather than only pollen or molecular data (Godwin, 1975; Stewart and Lister, 2001). One option is the use of megafossils: large pieces of wood such as trunks, roots, and cones preserved in peat or lake sediments, which are unlikely to have been moved around in the landscape by wind or other forces (Kullman, 2000; Kullman and Kjaligren, 2006). Although non-quantitative, laborious, and somewhat fortuitous, this method provides data that can show unambiguously that a specific species grew at a specific site at a specific point of time. When conflicting with other paleosources, such as pollen analysis, positive evidence of this kind can hardly be disputed (Stewart and Cooper, 2008). One variant of the megafossil approach, and a new investigation tool, is life-history analysis of long-lived clonally regenerating tree species growing in low-disturbance environments. The feasibility of this tool is demonstrated by several studies (Vasek, 1980; Lavoie and Payette, 1996; Kullman, 2000; May et al., 2009). Here we employ this method to study the early Holocene immigration and first appearance of Norway spruce (Picea abies) in the Swedish Scandes and the implications for possible glacial and late-glacial refuge areas.

Together with Pinus sylvestris (Scots pine), Picea abies is the dominant and economically most important tree species in northern (boreal) Fennoscandia, which makes studies of its Quaternary history particularly relevant. On the basis of pollen analysis, it has long been taken as almost axiomatic that Picea was a late Holocene immigrant to northern and central Scandinavia. The predominant paradigm is that the species spread westward over northern Scandinavia from ice-age refugia in central Russia, thousands of kilometers to the east, during the past 3000-4000 years. Spruce is assumed to have reached the Scandes (the study region included) around 2000-2500 years ago (Lund-qvist, 1969; Moe, 1970; Tallantire, 1977; Huntley and Birks, 1983; Hafsten, 1992; Lang, 1994; Latalowa and van der Knaap, 2006; Seppa et al., 2009; Tollefsrud et al., 2009). However, another quite different interpretation was advocated long ago by researchers who found stray amounts of Picea pollen and even macroremains in early postglacial stratigraphies. Some of these early works are reviewed in more detail by Kullman (2000) and Lindbladh (2004).

During the past decade, the radiocarbon dating of Picea megafossils recovered from widespread sites along the mid and northern Swedish Scandes has given an entirely new perspective on this issue (Kullman, 2000, 2002, 2004a). These radiocarbon dates are distributed over virtually the entire Holocene, and about 50% represent wood pieces buried in the soil underneath the canopy of living subalpine and alpine spruce clones of the krummholz type (Kullman, 2000). The term "krummholz" refers to environmentally stunted and crippled individuals with dense infra-nival foliage (cf. Holtmeier, 1981, 1986). Some clones seem to be of high antiquity, as suggested by dead wood embracing the past 8000-9000 years unearthed below their canopies. The oldest living stem belonging to a clone of this kind contained somewhat more than 600 tree rings (Kullman, 2001) (Fig. 1). The propensity for longevity is suggested a)so by the observation that mortality of extant spruce clones is an extremely rare phenomenon. On these grounds, we have good reason to believe that some subalpine spruce clones are "living relicts" (cf. Laberge et al., 2000; Holtmeier, 2003) with unbroken continuity from the early Holocene immigration or spreading phase. Consequently, we believe that ancient spruce clones could be used to increase our knowledge about the early Holocene performance of Picea abies in the Scandes. This approach provides a way to detect the oldest individuals and populations that is more focused and less dependent on chance than the blind, time-consuming search for mega- and macrofossils in stratigraphical contexts such as peat and lake sediments, which are rarely optimal spruce habitats. This thinking is the general background of our study, which was carried out in a subalpine region of the Swedish Scandes, where modern data on Holocene vegetation history are very scarce. Some of the dates have been presented previously in more popular contexts.

The data presented here add to the existing knowledge about early Holocene phylogeographic history in the south-central Scandes. The timing of the first Holocene spruce immigration is a central issue for this entire research field. An aspect of particular relevance is whether early mega-fossils represent isolated outposts of only local importance, as maintained by Giesecke (2005), or whether they consti-tute a more general pattern in the early Holocene landscape. We have reconstructed the vegetation matrix that contained the earliest spruces by radiocarbon dating of megafossil remains of tree species other than spruce, which are pre-served in peat and small lakes at high altitudes in the same region. The present study contributes to improved comprehension, in general, of Holocene landscape evolution at the taiga-tundra interface. We also discuss the discrepancy between the results we obtained by applying this type of megafossil analysis to ancient spruce clones and previous results based on traditional analyses of pollen records.

[FIGURE 1 OMITTED]

STUDY AREA

General Setting: Topography and Geology

The study area (approximately 12 000 km2) is located in the counties of Dalarna and Harjedalen, in the southernmost Swedish Scandes (Fig. 2). With respect to the life history of spruce clones, we focused on investigating six different mountain areas (sites 1-6). From north to south, these are (1) Mt. Sonfjallet (max. 1278 m a.s.l.), (2) Mt. Bar-fredhagna (max. 1022 m a.s.l.), (3) Mt. Stadjan (max. 1131 m a.s.l.), (4) Mt. Harjehagna (max. 1185 m a.s.l.), (5) Mt. Fulufjallet (max. 1039 m a.s.l.), and (6) Mt. Koarskarsfjal-let (max 875 m a.s.l.). In addition, we retrieved megafossils of Scots pine from two more sites, (7) Mt. Storvatteshagna (max. 1204 m a.s.l.) and (8) Mt. Nipfjallet (max. 1192 m a.s.l.). The valley floors range between 750 and 850 m a.s.l.

Characteristically, the mountains investigated are smoothly rounded and reach a maximum of 300-400 m above the upper limit of the continuous forest. They all have the character of "islands" in a matrix of broad valleys and uplands covered with boreal coniferous forests and mires. Dominating geological substrates are acidic and nutrient-poor quartzites and Dala sandstone. Exten-sive frost-shattered boulder fields cover the peak plateaux of most of the highest mountains. At lower elevations, the slopes are clothed with an undifferentiated cover of glacial till. Minor peat accumulations exist near and above the tree-line. Small lakes, ponds, and rivulets are scarce as a result of early melting of a relatively thin snow cover (Lundqvist, 1951, 1969).

[FIGURE 2 OMITTED]

Climate

The climate of the study area is moderately continental in character, and the effective humidity is low in comparison with most other parts of the Swedish Scandes. Mean annual temperatures, as recorded by official meteorological stations, range between 2.0 and 0.0[degrees]C, and precipitation varies between 700 and 1000 mm per year (Raab and Vedin, 1995). Data collected at two meteorological stations, Sveg (360 m a.s.l.) and Sarna (435 m a.s.l.), represent climatic conditions within the northern and southern part of the study area, respectively. For Sveg, the mean temperatures are -10.5[degrees]C for January, 14.4[degrees]C for July, and 2.1[degrees] for the year, respectively. Corresponding data for Sarna are -12.1[degrees], 13.3[degrees], and 0.8[degrees]C. Annual precipitation is 624 mm for Sveg and 601 mm for Sarna. All data were obtained from the Swedish Meteorological and Hydrological Institute (SMHI) and represent the period 1961 -90.

During the past c. 100 years, regional standard meteor-ological records display distinct warming for all seasons. Although the Sveg meteorological station is located slightly outside the study area, it is considered to be representa-tive of a larger region of the southern Swedish Scandes that includes the study area (Alexandersson, 2006). Its homog-enized long-term data show a positive linear trend of 1.4[degrees]C for the mean annual temperature over the past 131 years (1876-2007), with the most consistent warming occurring between 1876 and 1940. The overall climate-warming trend hides a large inter-annual scatter, with a slight reversal of the trend in some decades after the mid-20th century. Pre-cipitation has increased steadily throughout the past cen-tury (Alexandersson, 2006), and a tendency for increasing oceanity is perceivable, particularly in the past few decades (Tuomenvirta et al., 2000). A long-term decreasing trend in days with snow cover characterizes the past century (Moberg et al., 2005).

Treeline and Treeline Ecotone

The treeline for each tree species at a specific location is defined as the elevation (m a.s.l.) of the uppermost individual attaining a height of 2 m.

The treeline ecotone is broad and indistinct, extending from the uppermost outliers of spruce and pine trees in the subalpine mountain birch belt up to the treeless alpine tundra. In this mainly continental part of the southern Swedish Scandes, the birch belt is only fragmentarily developed or even lacking (Samuelsson, 1917; Kullman, 2004a). It is most discrete and extensive in the snow-rich western parts of the area. On Mt. Stadjan, Mt. Barfredhagna and Mt. Har-jehagna, the uppermost treeline is marked by spruce, while on Mt. Storvatteshagna, pine is the uppermost, followed in order by spruce and birch treeline. On Mt. Koarskarsfjal-let and Mt. Fulufjallet, the spruce treeline reaches almost as high as birch and pine (to 5-10 m below them).

As a consequence of climatic continentality, the study area comprises the highest treelines of both Norway spruce (1115 m a.s.l.) and Scots pine (1045 m a.s.l) in the Swedish Scandes, both at Mt. Stadjan. Additionally, the second highest treeline of mountain birch (Betula pubescens ssp czerepanovii) is found at Mt. Sonfjallet, 1135 m a.s.l. (Kullman and Oberg, 2009).

During the past 100 years, concomitantly with a linear warming trend of c. 1.3[degrees]C, mountain birch, spruce, and pine shifted their treelines upslope by a maximum of c. 185 m, with mean shifts of 55-100 m in the specific area here concerned (Kullman and Oberg, 2009; Kullman, 2010).

The spruce treeline rose mainly by means of this species' high phenotypic plasticity and ability to switch from prostrate krummholz to arborescent growth form in response to climate warming. Pine expanded its treeline by establishing new individuals (genotypic change). In the case of mountain birch, both genotypic and phenotypic treeline changes have occurred, although the latter process seems to have prevailed (Kullman and Oberg, 2009; Kullman, 2010).

The groundcover vegetation within the treeline ecotone is dominated by ericaceous dwarf-shrub heaths (Vaccinium myrtillus, V. uliginosum, Betula nana, Empetrum hermaph-roditum) with some low herbs, sedges, and grasses, alternating with boulder fields and open mires. As a rule, the heath communities contain a bottom layer with variable proportions of reindeer lichens. The vascular alpine flora is strikingly poor in species (Samuelsson, 1917).

Phytogeographically, the study area belongs to the northern boreal zone (Ahti et al., 1968). A more detailed account of the treeline ecotone and its geoecological and climatic context is provided by Kullman (2005a, 2010).

The Coniferous Foothill Forests

The well-drained, nutrient-poor valley floors at the foot-hills of the mountains are dominated by lichen-rich pine forest, while spruce often predominates along streams and rivers. With increasing altitude, pine is gradually replaced by spruce, which often forms the uppermost coniferous forest at 600-800 m a.s.l. On a smaller scale, spruce is most competitive on humid hillsides and interfluvial uplands with fine-textured, nutrient-rich soils, heavy snow load, and insignificant seasonal ground frost (Engelmark and Hytte-born, 1999).

Observations of charred logs indicate that both the upper coniferous forest and the subalpine region have been influenced by wildfires in the past (Arnborg, 1949, 1951; Sander, 2005). Interviews with local residents indicate that during their lifetime, fires have been few and of minor extension. Stratigraphical studies in the vicinity of Mt. Sonfjallet support the theory that wildfires have played only a minor role during the Holocene (Giesecke, 2005).

Human Impact

Humans have used natural resources extensively in the coniferous forests, and to a lesser extent in the treeline ecotone, for haymaking, reindeer husbandry, livestock grazing, lichen harvesting, and selective tree-felling (Ericsson et al., 2000; Ljung, 2004; Ljungdahl, 2007; Oberg, 2009). These practices were most pronounced from the late 19th century until the 1940s, after which they virtually ceased. Despite the more or less heavy use of natural resources, treeline positions within the study area do not seem to have been affected by these land-use activities (Kjallgren and Kullman, 1998). This contention is supported by the accounts of several botanists and geographers working in the study area during the late 19th century and the first half of the 20th (Kellgren, 1891; Smith, 1920).

Grazing and trampling by reindeer (Rangifer tarandus L.) are ubiquitous and chronic disturbances to alpine and subalpine vegetation, with a history spanning many millennia of mutual adaptation (Cairns and Moen, 2004; Eriksson et al., 2007; Oberg, 2009). Since 20th century treeline history does not differ between areas with and without semi-domestic reindeer, the treeline position per se has probably not been determined by reindeer action (Kullman, 2004a, 2005b; Kullman and Oberg, 2009).

Recent archaeological findings indicate human presence in parts of the study area since about 9000 cal. yr BP (Jons-son, 2009).

METHODS

Sampling for this study focused exclusively on mega-fossil tree remains (dead wood and cones). The basic sampling method draws on experiences from similar studies (e.g., Kullman, 2000) in more northerly parts of the Scandes, where we learned by trial and error to distinguish between genuine old-growth spruce clones and more recently established specimens. Criteria for high age were multi-stemmed clones with a muddle of stout, interlacing boles below a dense, infra-nival skirt of branches. Moreover, we found that a minimum depth of 20-30 cm for the organic layer of raw humus or peat was essential for long-term preservation of dead wood and cones. Despite their compliance with these criteria, most sampling sites produced no datable megafossils.

In connection with other research projects on treeline dynamics (Oberg, 2002, 2008; Kullman and Oberg, 2009), we had the opportunity to survey large mountain areas for the potentially most rewarding spruce specimens. Intentionally, we tried to get an even spread of sampling sites over a larger region, mainly within the current treeline eco-tone where almost all such clones are found. Selectively, we focused on the uppermost clones, supposed to be the oldest (Kullman, 2000).

Subfossil wood was unearthed by digging through the organic layers and down to the upper mineral layer of the soil, usually 10-50 cm below the surface. When several wood pieces were retrieved from a single clone, the largest and most decayed specimens were selected for radiocarbon dating. Species confirmation relied on bark fragments attached to the wood, which in most cases left no doubt about the correct identification. A few ambiguous samples were subjected to wood anatomical analysis, conducted by Dr. Thomas Bartholin (National Museum, Copenhagen University), a renowned dendrologist with documented capability to diagnose spruce wood (e.g., Bartholin, 1979). Cones were unambiguously determined to species. Only complete wood pieces (rather than composite samples) were. dated. Henceforth, "wood" refers to unspecified woody material, except for roots.

An exhaustive search for megafossils of tree species other than spruce was conducted in peat deposits and shallow ponds from slightly below the modern treeline up to the highest peaks in the study area. Our goal was to obtain a sample that represented forest history and changes in tree-line elevation throughout the Holocene.

Radiocarbon dating of recovered megafossils was conducted by Beta Analytic Inc., Miami, Florida. All dates are expressed as calibrated years before the present (cal. yr BP), with "present" = AD 1950. Calibration was conducted using CALIB 5.0.2 software (Stuiver et al., 2005) in combination with INTCAL04. For simplicity, the values given for radiocarbon ages represent the intercept of radiocarbon age with the calibration curve. Where multiple dates are given, we used the midpoint between the oldest and the youngest intercepts. Age determination of individual tree stems was conducted by boring at different stem positions above ground level. The tree rings were counted in the laboratory under a stereomicroscope.

The nomenclature follows Mossberg and Stenberg (2003) for vascular plants and Moberg and Holmasen (1982) for lichens.

RESULTS AND INTERPRETATION

Holocene Landscape and Climate Context of the Spruce Clones

We synthesized the broad outline of treeline ecotone evolution during the Holocene from 46 megafossil tree remains (39 pine, 3 birch, 2 larch, 1 hazel, and 1 oak). Table 1 lists the radiocarbon dates and calibrated ages for these remains. Figure 3A shows the dates obtained and the position of each megafossil in relation to the pine treeline prevailing at the end of the Little Ice Age, or around AD 1900 (Kullman and Oberg, 2009).
TABLE 1. Radiocarbon dates of megafossil pine and some other tree
species from different sites within the study area.

Species  Site  Lab. no.     l4C yr   2[alpha]cal.  Intercept  Material
         no.                BP       yr BP         cal. yr
                                                   BP

Pine        1  Beta-246095  5680 [+     6570-6390       6450      Wood
                              or -]
                                 50

Pine        7  Beta-158304  4310 [+     5040-4710       4875      Wood
                                 or
                               -]70

Pine        7  Beta-158306  6770 [+     7700-7560       7630      Wood
*        1080     Kullman,
                                 or

                               -]60

Pine        7  Beta-158307  1590 [+     1570-1360       1465      Wood
                                 or
                               -]50

Pine        7  Beta-158308  5930 [+     6940-6560       6750      Wood
                                 or
                               -]80

Pine        7  Beta-158314  8380 [+     9500-9280       9390      Wood
                            or -]50
                                  '

Pine        7  Beta-169411  8050 [+     9120-8660       8890      Wood
                              or -]
                                 70

Pine        7  Beta-169412  6040 [+     7010-6730       6870      Wood
                              or -]
                                 60

Pine        7  Beta-172305  9070 [+   10380-10150      10265      Wood
                              or -]
                                 70

Pine        7  Beta-172316  8040 [+     9050-8710       8880      Wood
                              or -]
                                 60

Pine        7  Beta-172317  8500 [+     9550-9440       9445      Wood
                              or -]
                                 60

Pine        7  Beta-178795  9230 [+   10540-10240      10390      Wood
                              or -]
                                 50

Pine        7  Beta-178798  5840 [+     6750-6510       6630      Wood
                              or -]
                                 50

Pine        7  Beta-179446  4440 [+     5310-4850       5080      Wood
                              or -]
                                 70

Pine        7  Beta-179447  4360 [+     5050-4840       4945      Wood
                              or -]
                                 50

Pine        7  Beta-180218  3440 [+     3870-3490       3680      Wood
                              or -]
                                 70

Pine        2       ST-396  7330 [+     8290-7995       8145      Wood
                                 or
                              -]130

Pine        2       ST-397  6840 [+     7800-7580       7690      Wood
                                 or
                              -]140

Pine        2       ST-398  6520 [+     7560-7330       7745      Wood
                                 or
                              -]170

Pine        2      ST-5747   910 [+       975-765        870      Wood
                                 or
                               -]90

Pine        2      ST-5750   835 [+       935-710        825      Wood
                              or -]
                                 90

Pine            Beta-57644  1190 [+     1170-1070       1120      Wood
                              or -]
                                 90

Pine        8  Beta-169410  8050 [+    9120- 8660       8890      Wood
                              or -]
                                 70

Pine        8  Beta-173414  7720 [+     8630-8380       8505      Wood
                              or -]
                                 80

Pine        8     ST-12023  1155 [+      1230-950       1090      Wood
                                 or
                              -]110

Pine        3  Beta-158302  4680 [+     5580-5310       5445      Wood
                              or -]
                                 50

Pine        3  Beta-158303  4160 [+     4660-4440       4550      Wood
                                 or
                               -]80

Pine        3  Beta-158305    10500   12870-11980      12425      Wood
                              [+ or
                              -] 60

Pine        3     Beta-178   6140[+     7260-6750       7005      Wood
                       793    or -]
                                100

Pine        3  Beta-178794  8190 [+     9300-9010       9155      Wood
                                 or
                               -]60

Pine        3  Beta-178797  7890 [+     8990-8550       8770      Wood
                              or -]
                                 60

Pine        5  Beta-195539  6610 [+     7590-7420       7480     Trunk
                                 or
                               -]60

Pine        5  Beta-195540  8230 [+     9420-9020       9240     Trunk
                              or -]
                                 60

Pine        5  Beta-195541  7800 [+     8760-8420       8580     Trunk
                              or -]
                                 70

Pine        5  Beta-195542  8380 [+     9510-9270       9440     Trunk
                              or -]
                                 60

Pine        5  Beta-195543  8570 [+     9600-9490       9540    Branch
                              or -]
                                 60

Pine        5  Beta-195544  8340 [+     9490-9220       9410     Trunk
                              or -]
                                 60

Pine        5  Beta-195545  8050 [+     9120-8660       9000     Trunk
                              or -]
                                 70

Pine        5  Beta-195550  8690 [+     9920-9520       9600     Trunk
                              or -]
                                 80

Birch       7  Beta-178448  4440 [+     5310-4850       5080      Wood
                              or -]
                                 70

Birch       7  Beta-178799  8360 [+     9500-9250       9375      Wood
                              or -]
                                 60

Birch       5  Beta-195546   320 [+       510-280        370     Trunk
                              or -]
                                 60

Larch       2  Beta-178796  8160 [+     9290-9000       9145  Twig + 1
                                 or                               cone
                               -]70

Larch       5  Beta-195537  7390 [+     8350-8040       8180     Cones
                              or -]
                                 60

Hazel       7  Beta-158309  8670 [+     9720-9540       9630     Acorn
                              or -]
                                 40

Oak         7  Beta-158310  8560 [+     9560-9500       9530  Nutshell
                              or -]
                                 40

Species  Altitude  Source
         (m
         a.s.l.)

Pine         1015  This study
Pine         1010    Kullman,
                        2004a
Pine
*
                        2004a
Pine          920    Kullman,
                        2004a
Pine          990    Kullman,
                        2004a
Pine         1070    Kullman,
                        2004a
Pine         1035    Kullman,
                        2004a
Pine         1035    Kullman,
                        2004a
Pine         1180    Kullman,
                        2004a
Pine          940    Kullman,
                        2004a
Pine         1180    Kullman,
                        2004a
Pine         1180    Kullman,
                        2004a
Pine         1010    Kullman,
                        2004a
Pine          940    Kullman,
                        2004a
Pine          950    Kullman,
                        2004a
Pine          945    Kullman,
                        2004a
Pine          940  Lundqvist,
                         1959
Pine          900  Lundqvist,
                         1959
Pine          915  Lundqvist,
                         1959
Pine          910    Kullman,
                         1980
Pine          910    Kullman,
                         1980
Pine          990    Kullman,
                         2000
Pine         1160    Kullman,
                        2004a
Pine         1150    Kullman,
                        2004a
Pine          975    Kullman,
                         2000
Pine         1045    Kullman,
                        2004a
Pine         1015    Kullman,
                        2004a
Pine         1100    Kullman,
                        2004a
Pine         1085    Kullman,
                        2004a
Pine         1035    Kullman,
                        2004a
Pine         1055    Kullman,
                        2004a
Pine          890  This study
Pine          920  This study
Pine          920  This study
Pine          920  This study
Pine          935  This study
Pine          905  This study
Pine          905  This study
Pine         1030  This study
Birch         920    Kullman,
                        2004a
Birch         915    Kullman,
                        2004a
Birch         935  This study
Larch         915    Kullman,
                        2004a
Larch         890  This study
Hazel         910    Kullman,
                        2004a
Oak           910    Kullman,
                        2004a


Early Holocene growth of trees (about 10000 cal. yr BP) at least 350 m above the treeline position that prevailed about 100 years ago attests to the rapid evolution of a climate more favourable to high-elevation tree growth than at present, presumably representing a Holocene thermal optimum around 9500 cal. yr BP (cf. Hoek and Bos, 2007). Subsequently, and throughout the Holocene, the upper elevational range of pine declined almost linearly (c. 28 m per millennium) until the late 19th century. Possibly a distinct short-term downslope excursion occurred around 8100-8200 cal. yr BP (Fig. 3B). This episode may reflect the so-called 8.2 event of near-global climate cooling (e.g., Rohling and Palite, 2005). Obviously, the long-term process of treeline descent was driven by a progressive general temperature decrease, steadily forced by reduced summer insolation (COHMAP Members, 1988; Shemesh et al., 2001; Marchal et al., 2002) and isostatic land uplift throughout the Holocene. Further indications of climate forcing behind secular treeline evolution are provided by similar megafossil results from adjacent parts of the Swedish and Norwegian Scandes (Kullman and Kjallgren, 2006; Paus, 2010). Pollen records from the same regions are broadly consistent with these megafossil records (Segerstrom and von Sted-ingk, 2003; Bergman et al., 2005; Giesecke, 2005).

On the basis of a temperature lapse rate of 0.6[degrees]C per 100 m elevational change (Laaksonen, 1976) and a treeline at least 350 m higher than a century ago, we can tentatively suggest that summer temperatures in the southern Scandes during the early Holocene were about 2.0[degrees]C higher than at present (cf. Nesje et al., 1991). Given a warming trend of slightly more than 1[degrees]C from the late 19th century to the present (Kullman and Oberg, 2009), we may infer that trees growing in the study area at the beginning of the Holocene could prosper in a summer climate 1[degrees]C warmer than during the past few dec-ades. Presumably this is an underestimate, since the potential position of the early Holocene pine treeline could obviously not be attained given the relatively low maximum peak altitudes in the study area (cf. Kullman, 2004a).

Only a few megafossils of tree birch have been recovered at the elevations surveyed (Table 1), and the small number of datings obtained does not allow any detailed comparison with pine. It is clear, however, that tree birch grew at fairly high elevations in the early Holocene, virtually as early as the first Holocene pine dates. We suggest tentatively that birch has never played any important role in the treeline ecotone, and consequently, pine has been the dominating species in that ecotone throughout the Holocene. Experiences from other parts of the southern Scandes indicate that a discrete mountain birch belt evolved quite late in the Holocene in response to neoglacial cooling (Kullman, 1995, 2004b; Barnett et al., 2001).

It is particularly interesting that megafossil remains (cones and twigs) of Larix sibirica (larch) have been recov-ered at two sites in the treeline ecotone (Fig. 4). These remains range in age between 9100 and 8200 cal. yr BP (Table 1). Until quite recently, Larix was not assumed to have grown in any part of Scandinavia during the Holocene. Analogous discoveries of macroremains of this species have also been made at scattered localities farther north in the Scan-des (Kullman, 1998a). In addition, pollen records from the alpine region of northern Sweden and central Norway indicate the presence of Larix in the early Holocene (Bergman et al., 2004; Paus, 2010). According to present-day climatic correlates (Putenikkin and Martinsson, 1995), the occurrence of Larix is indicative of low winter and high summer insolation, implying a dry continental and strongly seasonal climate during the early Holocene (cf MacDonald et al., 2008). A climate drier than at present is further suggested by the fact that both larch and pine megafossils have been recovered from small ponds in the treeline ecotone (Fig. 4).

In addition to the relatively high pine treeline during the early Holocene, macrofossils of thermophilic tree species (hazel, Corylus avellana, and oak, Quercus robur) in the current treeline ecotone (Table 1) speak for a climate warmer than present. Likewise, their disappearance from the paleorecord in the mid-Holocene argues for enhanced cooling thereafter. The presence of species belonging to this group of truly warmth-demanding trees during the early Holocene is consistent with pollen data from the high mountains of the study area (Lundqvist, 1951; Giesecke, 2005). This aspect of the early Holocene tree landscape is further sustained by macrofossil and pollen data gathered in other high-mountain regions of the south-central Scan-des (Kullman, 1998b; Bergman et al., 2005).

[FIGURE 3 OMITTED]

Clonal Spruces: Growth and Site Characteristics

The ability of Picea abies to regenerate clonally by lay-ering close to the treeline is well documented and described in the Scandinavian literature (Kihlman, 1890; Kallio et al., 1971; Kullman, 1986). The same strategy prevails for Picea species in other parts of the world, for example, in the European Alps (Holtmeier, 2003), Russia (MacDon-ald et al., 2008; Kharuk et al., 2009) and in North America (Payette et al., 1985; Gamache and Payette, 2004). At the Arctic treeline in North America, living Picea clones in fire-free landscapes have been found to be at least 3000 years old (Payette and Morneau, 1993). Even greater ages are postulated for extant tree islands in the forest tundra of northern Russia (Lavrinenko and Lavrinenko, 1999). Obviously, this growth form is primarily a response to a harsh, cold, and windy winter climate at the taiga-tundra interface or in analogous cold-marginal situations (e.g., Lavoie and Payette, 1994; Kullman, 1996; Hammer and Walsh, 2009).

Typically, the state of wood preservation was poor in our samples; most of the cellulose content was decayed and only the structural lignin components were preserved. The basic preconditions for long-term preservation of wood fragments were provided by a cold and dry continental climate. In addition, deep layers of continuously accumulating needle litter, transforming into raw humus or peat, further promoted conservation. Dead trunks and branches often remained in situ before falling to the ground. In the upright position, the wood dries and hardens to a state quite resistant to further weathering and biological decay before it is incorporated into the soil beneath the canopy of the clone.

[FIGURE 4 OMITTED]

The general appearance of the clonal spruces is shown in the photographs of Figures 5 and 6. The majority are multi-stemmed (5-20 stems, > 1 m high), with a maximum height of 4-8 m. As a rule, each clone is characterized by an infra-nival "skirt" of dense foliage (cf. Lavoie and Payette, 1994) that covers an area of 15-30 m2. Quite often, this near-ground and snow-protected part of the clone appears to be the most vital part and is estimated to contain the largest photosynthetically active biomass.

Most of the clones we investigated are located at altitudes between the position of the spruce treeline in the early 20th century and its present position (Fig. 3C, D). This is the "advance zone," where the treeline shifted upslope by transformation from krummholz to arborescent form (phe-notypic plasticity) in response to recent climate warming (Oberg, 2008; Kullman and Oberg, 2009; Kullman, 2010). Within this zone, no extant stem was higher than 2 m in the early 20th century. Emergence of upright stems distinctly protruding from the infra-nival krummholz morphs began here in the late 1930s, as is evident in general for the entire study region (Kullman, 1986). This course of life-history evolution is expressed by some of the clones that were specifically analyzed in this respect (Figs. 5 and 6).

The clones we focused on in this study all grow in open landscapes, on patches of exposed and dry-fresh alpine tundra without fire indications. Closer inspection reveals that they occupy minor depressions in the local topography and quite often are found in association with running water. Surrounding plant cover is commonly dwarf-shrub heath with different admixtures of reindeer lichens.

[FIGURE 5 OMITTED]

Clonal spruces appear to be distributed without obvious relation to the aspect or inclination of a site and are generally located on landscape segments prone to intermediate snow conditions. Typically, large snowdrifts pile up over and in lee of the clones, protecting them (except their supra-nival stems) from wind stress and frost desiccation. The moisture snow adds to the soil also helps the clones to endure the harsh alpine environment (Fig. 6).

Radiocarbon Ages of Megqfossil Spruce Remains

A total of 19 dates, originating from 10 spruce clones, were the particular focus of this study (Table 2). In some cases, more than one wood sample was retrieved and dated for a specific spruce clone. In addition, we dated two spruce cones recovered from peat deposits, which had no spatial association with any living spruce.
TABLE 2. Radiocarbon dates of megafossil spruce from six different sites
within the study area. Site numbers with the same letter refer to the
same clone.

Site  Lab. no.     (14)C   2[alpha]cal.  Intercept  Material
no.                yr BP   yr BP         cal. yr
                                         BP

la    Beta-246094    2300     2360-2180       2340      wood
                    [+ or
                    -] 40

lb    Beta-246091    8450     9540-9320       9480      wood
                    [+ or
                    -] 60

lb    Beta-246092    7530     8400-8310       8370      wood
                    [+ or
                    -] 40

lc    Beta-246093    2300     2360-2160       2340      wood
                    [+ or
                    -] 50

2     Beta-108767    8490     9530-9380       9465      cone
                    [+ or
                    -] 70

3a    Beta-179449    3970    4540 -4280       4420      wood
                    [+ or
                    -] 50

3b    Beta-238423    3940     4580-4150       4420      cone
                    [+ or
                    -] 80

3b    Beta-238424  260 [+         480-0        300      wood
                    or -]
                       60

4a    Beta-238419    7890     8990-8540       8640      wood
                    [+ or
                     -]70

4b    Beta-238418    5550    6440 -6280       6310      wood
                    [+ or
                     -]60

4b    Beta-238421    1400     1410-1180       1300      wood
                    [+ or
                     -]70

4b    Beta-238422  160 [+         310-0        135      wood
                    or -]
                       60

4c    Beta-238420    4800     5640-5330       5580      wood
                    [+ or
                    -] 60

5a    Beta-195547    4870     5720-5480       5600      cone
                    [+ or
                    -] 60

5a    Beta-195548  350 [+      520 -290        385     trunk
                    or -]
                       60

5a    Beta-195549    8630     9720-9520       9550     trunk
                    [+ or
                    -] 60

5a    Beta-195551    8050     9120-8660       9000     trunk
                    [+ or
                    -] 70

5b    Beta-195538    8140     9270-9000       9030      cone
                    [+ or
                    -] 60

6     Beta-264389    7100     8020-7790       7940      wood
                    [+ or
                     -]70

Site  Latitude            Longitude           Altitude  Source
no.                                           (m
                                              a.s.l.)

la           62[degrees]         13[degrees]       945      This
                 16.980'             30.475'               study
lb           62[degrees]         13[degrees]       990      This
                 16.665'             28.162'               study
lb           62[degrees]         13[degrees]       990      This
                 16.665'             28.162'               study
lc           62[degrees]         13[degrees]       995      This
                 16.660'             28.171'               study
2            62[degrees]         12[degrees]       860  Kullman,
                 03.226'             24.325'                2000
3a           61[degrees]         12[degrees]       998  Kullman,
                 54.835'             53.026'               2004a
3b           61[degrees]         12[degrees]       907      This
                 54.502'             52.814'               study
3b           61[degrees]         12[degrees]       907      This
                 54.502'             52.814'               study
4a           61[degrees]         12[degrees]       985      This
                 43.355'             09.438'               study
4b           61[degrees]         12[degrees]       984      This
                 43.312'             09.343'               study
4b           61[degrees]         12[degrees]       984      This
                 43.312'             09.343'               study
4b           61[degrees]         12[degrees]       984      This
                 43.312'             09.343'               study
4c           61[degrees]         12[degrees]       971      This
                 43.256'             09.540'               study
5a           61[degrees]         12[degrees]       905      This
                 38.356'             40.589'               study
5a           61[degrees]         12[degrees]       905      This
                 38.356'             40.589'               study
5a           61[degrees]         12[degrees]       905      This
                 38.356'             40.589'               study
5a           61[degrees]  12[degrees]40.589'       905      This
                 38.356'                                   study
5b    61[degrees]38.218'         12[degrees]       890      This
                                     40.933'               study
6            61[degrees]         13[degrees]       826      This
                 10.255'             07.994'               study


[FIGURE 6 OMITTED]

The ages we obtained range from 9550 cal. yr BP to the present. Two clones and one cone, representing well-separated localities, attest to the presence of spruce around 9500 cal. yr BR As indicated above, treelines were generally much higher in that period than at present as a consequence of a warmer climate. Presumably, spruce benefited from these conditions to establish itself at strictly localized sites with ample soil moisture and snow protection.

It appears that throughout the Holocene and over the entire study region, spruce has been growing in the area between its present-day (2007) treeline and a point some-what below the lower position of that treeline in the early 20th century (Fig. 3C, D). None of the dated spruce remains displayed any physical connection with living parts of the clones. This could, a priori, suggest that they do not represent the same genet as the living spruce. However, different lines of circumstantial evidence support the view that the extant clone is genetically identical with the ancient wood remains, A first indication in that direction is that wood samples of widely different ages were found right underneath the same clone. The clones, with their dense basal canopies, produce a deep layer of desiccated needle litter-, superimposed on a 20-50 cm thick layer of raw humus or peat, which does not allow root penetration of spruce seedlings (cf Laberge et al., 2000; Holtmeier, 2003; Malanson et al., 2009). In no case have new spruce genets (seedlings or saplings) been recorded within these or other clones (Kull-man and Oberg, 2009), a clear indication that seed regeneration is virtually impossible underneath these clones. The possibility that spruce seeds have intermittently germinated in the debris formed by different clones, living and dying at the same specific spot, is not supported by any recent observations. In fact, the remains of one dead clone (indeed a rare phenomenon) have been observed for more than 30 years, without indication of germination of spruce or other plant species (L. Kullman, pers. observ.). Taken together, these circumstances make it less likely that the old clones in the treeline ecotone are the outcome of multiple seed regeneration episodes at the same spot (cf. Holtmeier, 1974).

It appears that individual longevity of spruce is condi-tional upon a stunted and mainly horizontal growth form (krummholz), which implies a relatively large leaf-to-wood ratio. Such a situation can be maintained more eas-ily in a harsh and open environment, where severe winter conditions prevent the emergence of tall and relatively less productive arborescent stems (Laberge et al., 2000). By implication, current treeline ecotones with abundant krum-mholz spruces have probably been virtually as open as today throughout the Hoiocene, even during the early part of the thermal optimum when lower-than-present C02 con-centrations and the associated less-efficient use of water by plants (cf. Cowling and Sykes, 1999), in combination with strong windiness (Paus, 2010), may have helped to maintain the open landscape. Without this openness, it is unlikely that so many clones would have survived to the present day. Obviously, strong wind and associated factors are major forces that keep some parts of the high-mountain land-scape open and woodless even during prolonged periods of warming (cf Holtmeier and Broil, 2010). This interpretation is quite in line with the results from megafossil research in adjacent regions (Kullman and Kjallgren, 2006), as well as with the recent regional study of treeline performance over the past century (Kullman and Oberg, 2009). The lat-ter study showed that in strongly wind-exposed topography, some old krummholz spruces within and above the treeline remained in that stage, and thus treelines were unable to take full advantage of climate warming to advance uphill and reach the potential thermal limit. This fact also implies that even in the hypothetical case of a warmer future, large expanses of the alpine world would remain unforested.

Aspects of Immigration History

From around 9500 cal. yr BP to the present, scattered spruces have grown at high elevations in a sparse matrix of predominant pine and scattered mountain birches and larches. The no-analogue character of this arboreal landscape and the climate behind it is further stressed by occurrences of thermophilic broadleaved deciduous tree species, Quercus robur and Corylus avellana, at high elevations. Low abundances of spruce and some other tree species are not peculiar oddities, since similar occurrences, supported by macroremains, are recorded farther north in the Scandes (Kullman, 1998b, 2000). Rather, they represent the regional climatic situation and associated plant invasion patterns.

The presence of spruce already at the very beginning of the Holocene, as evidenced by megafossils, counters the prevailing idea of a late Holocene immigration and regional spread of Picea abies into northern and western Scandinavia (e.g., Moe, 1970; Huntley and Birks, 1983; Tollefsrud et al., 2008, 2009). Indisputably, Picea abies was among the first tree species to colonize the virgin postglacial tundra in the southern Scandes.

It stands out quite clearly from this and earlier studies (Kullman, 2000) that the majority of genuinely early (> 7000 cal. yr BP) spruce megafossils line up from north to south along the Swedish Scandes. The same broad pattern can also be deduced from existing pollen records (Lundqvist, 1969; Segerstrom and von Stedingk, 2003; Giesecke and Bennett, 2004; Hornberg et al., 2006) if a less conservative interpretational paradigm is used: that is, if we accept that a pollen threshold of ca. 1% could in some cases represent actual local occurrence (cf. Segerstrom and von Stedingk, 2003; Terhurne-Berson, 2005; Zazula et al., 2006). Given these premises, pollen records from southern Norway could support early Holocene occurrence of spruce even to the west of the main watershed of the Scandes (Velle et al., 2005; Eide et al., 2006; Bjune et al., 2009). In this context, it should be considered also that Tollefsrud et al. (2008) found a strongly deviating genetic structure of spruce populations in central Scandinavia (the study area included). This structure could suggest a different and earlier immigration history for this area than for the rest of Scandinavia. Taken together, these circumstances are compatible, although not conclusively, with an immigration route from the west in this part of Scandinavia.

The ca. 1800 km distance to the putative refuge areas in central Russia and the difficulty of spreading, against prevailing westerly winds, over the Baltic Sea or temporary land bridges (as speculated by Tollefsrud et al., 2008), speak against the orthodox notion of an eastern origin for Scandinavian spruce. Nevertheless, there is macrofossil evidence for late-glacial presence of spruce just to the southeast of Sweden, in Latvia and Lithuania (e.g., Heikkila et al., 2009). These occurrences could a priori have served as sources for the first spruce immigration into Sweden. However, neither megafossil nor pollen records are available to suggest the presence of spruce in eastern and southeastern Sweden (above the highest coast line) as early or earlier than is now recorded for the Scandes and adjacent regions in the west. In favour of first arrival from the west to the Swedish Scandes is the rapidity with which spruce, according to the megafossil record, appears in the early Holocene, for example, on late-glacial nunataks in the Scandes (Kullman, 2000; Paus et al., 2011). Reasonably, these circumstances could argue for late-glacial "bridgeheads, quite close to the Scandes, near the continental ice sheet. Megafossils indicate that birch trees existed early during the late-glacial period (Younger Dryas included) on the Arctic coast of northern Norway (Kullman, 2008). Predominant westerly winds (cf. Koc et al., 1993) may have contributed to rapid spread from such putative source areas.

In fact, there is mounting evidence in general that postglacial tree migration from full glacial areas has originated from relatively nearby minor cryptic refugia, rather than being mediated by expansion from far distant refugia (Payette et al., 2002; Schauffler and Jacobson, 2002; Brubaker et al., 2005; Anderson et al., 2006, 2009; Opgenoorh et al., 2009; Hampe and Petit, 2010).

In a uniformitarian perspective, spruce in krummholz form is equally or even more hardy than mountain birch (Kullman, 2010). Consequently, there is actually no rational reason to discard, on the basis of climatic tolerance, the theory that spruce and other boreal trees grew throughout the Wechselian in ice-age refugia close to the ice sheet, although their presence is still in need of macro- or mega-fossil verification. The results of this study have highlighted the capacity of spruce for a virtually eternal life, provided that it is kept in prostrate krummholz form by a harsh climate. Certainly, the latter presumption was fulfilled throughout the glacial phase in proglacial habitats. In a complex topography, with local ample snow accumulation providing foliage protection during the coldest parts of the winters, long-term glacial survival is not untenable (cf. Petit et al., 2008; Anderson et at, 2009).

Despite the firm foundation of fossil data, some interpretations launched above are hypothetical and in definite need of further "fossil" and molecular genetical evidence. Nonetheless, it is evident that the late-Quaternary history of Picea abies, and reasonably of other taxa in northwestern Europe, is an unsettled, complex, and scientifically more challenging affair than has generally been assumed.

CONCLUSIONS

Living clonal spruces, growing in open cold-marginal landscapes, have attained ages of 9500 years and possibly more. They represent a highly conservative structural element of the landscape and the legacy of a warmer-than-present early Holocene climate. Ancient spruce clones constitute high-resolution tools that enable detection of small and scattered early Holocene populations beyond the reach of other approaches such as pollen analysis.

Radiocarbon-dated spruce clones attest to a pattern of widespread spruce occurrences at high elevations along the Swedish Scandes in the early Holocene. This circumstance demonstrates that the first arrival of spruce in Sweden occurred several millennia earlier that has traditionally been believed.

Together with predominant pine, mountain birch, Siberian larch, and broadleaved deciduous species, spruce constituted a regular component of the early Holocene high-mountain vegetation, although with low abundance.

Longevity of spruce clones presupposes open and wind-exposed habitats. Consequently, their local environments have probably been as open as they are today even during the warmest parts of the Holocene. Presumably, they may remain open even in the hypothetical case of future climate warming.

Rapid postglacial immigration and spread of spruce along the entire Swedish Scandes could indicate that multiple "cryptic" glacial refugia existed much closer to Scandinavia than was previously thought.

ACKNOWLEDGEMENTS

Financial support for this study was provided by the Jamtland County Administrative Board, the Department of Natural Sci-ence, Engineering and Mathematics of Mid Sweden University, and the Swedish Research Council. We are very thankful to Pro-fessor Bengt-Gunnar Jonsson and the anonymous reviewers for their valuable comments on an early draft of this manuscript.

(1) Department of Natural Science, Engineering and Mathematics, Mid Sweden University, SE-851 70 Sundsvall, Sweden; Iisa.oberg@miun.se

(2) Department of Ecology and Environmental Science, Umea University, SE-901 87 Umea, Sweden

REFERENCES

Ahti, T., Hamet-Ahti, L., and Jalas, J. 1968. Vegetation zones and their sections in northwestern Europe. Annales Botanici Fennici 5:169-211.

Alexandersson, H. 2006. Klimat i forandring. En jamfdrelse av temperatur och nederbord 1991-2005 med 1961-1990 [Climate change: A comparison of temperature and precipitation between 1991-2005 and 1961-1990]. SMHI Faktablad29:l-8.

Aim, T. 1993. 0vre AErasvatn - palynostratigraphy of a 22,000 to 10,000 cal. yr BP lacustrine record on Andoya, northern Norway. Boreas 22:171 -188.

Anderson, L.L., Hu, F.S., Nelson, D.M., Petit, R.J., and Paige, K.N. 2006. Ice-age endurance: DNA evidence of a white spruce refugium in Alaska. Proceedings of the National Academy of Sciences, USA 103: 12447 -12450.

Anderson, P.M., Lozhkin, A.V., Solomatkina, T.B., and Brown, T. A. 2009. Paleoclimatic implications of glacial and postglacial refugia for Pinus pumila in western Beringia. Quaternary Research 73:269-276.

Arnborg, T. 1949. Dalarnas skogar [Dalarna's forests]. In: Forsslund, K.-H.T., and Curry-Lindahl, K., eds. Natur i Dalarna. Stockholm: Bokforlaget Svensk Natur. 78-86.

__. 1951. Sanfjallets nationalpark. In: Arnborg, T., and

Curry-Lindahl, K., eds. Natur i Halsingland och Harjedalen. Stockholm: Bokforlaget Svensk Natur. 107-116.

Barnett, C, Dumayne-Peaty, L., and Matthews, J.A. 2001. Holocene climatic change and tree-line response in Leirdalen, central Jotunheimen, south central Norway. Review of Paleobotany and Palynology 117:119-137.

Barnosky, A.D. 2008. Climatic change, refugia, and biodiversity: Where do we go from here? An editorial comment. Climatic Change 86:29-32, doi:10.1007/sl0584-007-9333-5.

Bartholin, T. 1979. The Picea-Larix problem. IAWA Bulletin 1979:7-10.

Bergman, I., Olofsson, A., Hornberg, G., Zackrisson, O., and Hellberg, E. 2004. Deglaciation and colonization: Pioneer settlement in northern Fennoscandia. Journal of World Prehistory 18:155-177, doi:10.1007/sl0963-004-2880-z.

Bergman, J., Hammarlund, D., Hannon, G., Barnekow, L., and Wohlfarth, B. 2005. Deglacial vegetation succession and Holocene tree-limit dynamics in the Scandes Mountains, west-central Sweden: Stratigraphic data compared to megafossil evidence. Review of Palaeobotany and Paleoecology 134:129-151.

Bjune, A.E., Ohlson, M., Birks, H.J.B., and Bradshaw, R.H.W. 2009. The development and local stand-scale dynamics of a Picea abies forest in southeastern Norway. The Holocene 19:1073-1082.

Brubaker, L.B., Anderson, P.M, Edwards, M.E., and Lozhkin, A.V. 2005. Beringia as a glacial refugium for boreal trees and shrubs: New perspectives from mapped pollen data. Journal of Biogeography 32:833-848.

Cairns, D.M., and Moen, J. 2004. Herbivory influences treelines. Journal of Ecology 92:1019-1024.

COHMAP Members. 1988. Climate changes of the last 18,000 years: Observations and model simulations. Science 241:1043-1052.

Cowling, S.A., and Sykes, M.T. 1999. Physiological significance of low atmospheric C02 for plant-climate interactions. Quaternary Research 52:237-242.

Eide, W., Birks, H.H., Bigelow, N.H., Peglar, S.M., and Birks, HJ.B. 2006. Holocene forest development along the Setesdal valley, southern Norway, reconstructed from macrofossil and pollen evidence. Vegetation History and Archaeobotany 15:65-85.

Engelmark, O., and Hytteborn, H. 1999. Coniferous forests. Acta Phytogeographica Suecica 84:55-74.

Ericsson, S., Ostlund, L., and Axelsson, A.-L. 2000. A forest of grazing and logging: Deforestation and reforestation history of a boreal landscape in central Sweden. New Forests 19:227-240, doi:10.1023/A:1006673312465.

Eriksson, O., Niva, M., and Caruso, A. 2007. Use and abuse of eindeer range. Acta Phytogeographica Suecica 87. 102 p.

Gamache, I., and Payette, S. 2004. Height growth response of tree line black spruce to recent climate warming across the forest-tundra of eastern Canada. Journal of Ecology 92:833-845.

Giesecke, T. 2005. Holocene forest development in the central Scandes Mountains, Sweden. Vegetation History and Archaeobotany 14:133-147, doi:10.1007/s00334-005-0070-2.

Giesecke, T., and Bennett, K.D. 2004. The Holocene spread of Picea abies (L.) Karst. in Fennoscandia and adjacent areas. Journal of Biogeography 31:1523-1548, doi:10.1111/j.l365-2699.2004.01095.x.

Godwin, H. 1975. The history of the British flora: A factual basis for phytogeography. Cambridge: Cambridge University Press.

Hafsten, U. 1992. The immigration and spread of Norway spruce (Picea abies (L.) Karst.) in Norway. Norsk Geografisk Tidsskrift 46:121-158.

Hammer, E.S., and Walsh, S.J. 2009. Canopy structure in the krummholz and patch forest zones. In: Butler, D.R., Malanson, G.P., Walsh, S.J., and Fagre, D.B., eds. The changing alpine treeline. Amsterdam: Elsevier. 120-150.

Hampe, A., and Petit, R.J. 2010. Cryptic forest refugia on the "Roof of the World." New Phytologist 185:5-7.

Heikkila, M., Fontana, S.L., and Seppa, H. 2009. Rapid Lateglacial tree population dynamics and ecosystem changes in the eastern Baltic region. Journal of Quaternary Science 24:802-815.

Hoek, W.Z., and Bos, J.A. 2007. Early Holocene climate oscillations-causes and consequences. Quaternary Science Reviews 26:1901-1906.

Holtmeier, F.-K. 1974. Geookologische Beobachtungen und Studien an der subarktischen und alpinen Waldgrenze in vergeichender Sicht [Geoecological observations and studies at the subarctic and alpine forest limits]. Wiesbaden: Franz Steiner Verlag GMBH.

__. 1981. What does the term "krummholz" really mean? Observations with special reference to the Alps and the Colorado Front Range. Mountain Research and Development 1:253-260.

__. 1986. Uber Bauminseln (Kollektive) an der klimatischens Waldgrenze - unter besonderer Beriicksichtigung von Beobachtungen in verschiedenen Hochgebirgen Nordamerikas [About tree islands at the climatic forest limit, with particular consideration of observations in various high-mountain areas of North America]. Wetter und Leben 38:121-139.

__. 2003. Mountain timberlines: Ecology, patchiness, and dynamics, 1st ed. Advances in Global Change Research 14. Dordrecht: Kluwer Academic Publishers.

Holtmeier, F.-K., and Broil, G. 2010. Wind as an ecological agent at treelines in North America, the Alps and the European Subarctic. Physical Geography 31:203-233.

Hornberg, G., Bohlin, E., Hellberg, E., Bergman, I., Zackrisson, O., Olofsson, A., Wallin, J.-E., and Passe, T. 2006. Effects of Mesolithic hunter-gatherers on local vegetation in a nonuniform glacio-isostatic land uplift area, northern Sweden. Vegetation History and Archaeobotany 15:13-26, doi:10.1007/ s00334-005-0006-x.

Hu, F.S., Hampe, A., and Petit, R.J. 2008. Paleoecology meets genetics: Deciphering past vegetational dynamics. Frontiers in Ecology and the Environment 7:371 -379, doi:10.1890/070160.

Huntley, B., and Birks, H.J.B. 1983. An atlas of past and present pollen maps for Europe 0-13,000 years ago. Cambridge: Cambridge University Press.

Jonsson, A. 2009. The first hunters. In: Oberg, L. ed. The heart of Harjedalen - Sonfjallet / Im Herzen Harjedalens). Jamtli Forlag. 124-127.

Kallio, P., Laine, U., and Makinen, Y. 1971. Vascular flora of Inari-Lappland. 2. Pinaceac and Cupressaceae. Reports from the Kevo Subarctic Research Station 8:73-100.

Kellgren, A.G. 1891. De skogbildande tradens utbredning i Dalarnes fjalltrakter [The distribution of forest-forming tree species in the mountain regions of Dalarna]. Botaniska Notiser 1891:185-192.

Kharuk, V.I., Ranson, K.J., Im, ST., and Dvinskaya, M.L. 2009. Response of Pinus sibirica and Larix sibirica to climate change in southern Siberian alpine forest-tundra ecotone. Scandinavian Journal of Forest Research 24:130-139.

Kihlman, A.O. 1890. Pflanzenbiologische Studien aus Russisch Lappland [Plant biological studies in Russian Lapland]. Acta Societatis Pro Fauna et Flora Fennica 68(3). 263 p.

Kjallgren, L., and Kullman, L. 1998. Spatial patterns and structure of the mountain birch tree-limit in the southern Swedish Scandes - a regional perspective. Geografiska Annaler 80A:1-16.

K0C, N., Jansen, E., and Haflidason, H. 1993. Paleooceanographic reconstructions of surface ocean conditions in the Greenland, Iceland and Norwegian seas through the last 14 ka based on diatoms. Quaternary Science Reviews 12:115-140.

Kullman, L. 1980. Radiocarbon dating of subfossil Scots pine (Pinus sylvestris L.) in the southern Swedish Scandes. Boreas 9:101-106.

----. 1986. Late Holocene reproductional patterns of Pinus sylvestris and Picea abies at the forest limit in central Sweden. Canadian Journal of Botany 64:1682-1690.

__.1995. Holocene tree-limit and climate history from the Scandes Mountains, Sweden. Ecology 76:2490-2502.

__.1996. Recent cooling and recession of Norway spruce(Picea abies (L.) Karst.) in the forest-alpine tundra ecotone of the Swedish Scandes. Journal of Biogeography 23:843-854, doi:10.1111/j.l365-2699.1996.tb00042.x.

__. 1998a. Palaeoecological, biogeographical and palaeoclimatological irnpJications of early Holocene immigration of Larix sibirica Ledeb. into the Scandes Mountains, Sweden. Global Ecology and Biogeography Letters 7:181-188.

__. 1998b. Non-analogous tree flora in the Scandes Mountains, Sweden, during the early Holocene - macrofossil evidence of rapid geographic spread and response to palaeoclimate. Boreas 27:153-161, doi:10.1111/j.l502-3885.1998.tb00875.x.

__. 2000. The geoecological history of Picea abies in northern Sweden and adjacent parts of Norway. A contrarian hypothesis of postglacial tree immigration patterns. Geo-Oko 21:141-172.

__. 2001. Granens invandring i Sverige. En gammal historia i nytt ljus [Postglacial immigration of spruce into Sweden: An old story in new light]. Fauna och Flora 96:117--128.

__. 2002. Boreal tree taxa in the central Scandes during the Late-Glacial: Implications for Late-Quaternary forest history. Journal of Biogeography 29:1117-1124, doi:10.1046/j.l365-2699.2002.00743.x.

__. 2004a. Tree-limit landscape evolution at the southern fringe of the Swedish Scandes (Dalarna province) - Holocene and 20th century perspectives. Fennia 182:(2)73-94.

__. 2004b. 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 recession. Arctic, Antarctic, and Alpine Research 36:172-180.

__. 2005a. The mountain taiga of Sweden. In: Seppala, M., ed. The physical geography of Fennoscandia. Oxford: Oxford University Press. 163-171.

__. 2005b. Gamla och nya trad pa Fulufjallet i Dalarna - vegetationshistoria pa hog niva [Old and new trees on Mt. Fulufjallet in Dalarna: Vegetation history at high elevations].Svensk Botanisk Tidskrift 99:315-329.

__. 2008. Early postglacial appearance of tree species in northern Scandinavia: Review and perspective. Quaternary Science Reviews 27:2467-2472.

__. 2010. One century of treeline change and stability - experiences from the Swedish Scandes. Landscape Online 17:1-31.

Kullman, L., and Kjallgren, L. 2006. Holocene pine tree-line evolution in the Swedish Scandes: Recent tree-line rise and climate change in a long-term perspective. Boreas 35:159-168, doi:10.1111/j.l502-3885.2006.tb011I9.x.

Kullman, L., and Oberg, L. 2009. Post-Little Ice Age tree line rise and climate warming in the Swedish Scandes: A landscape ecological perspective. Journal of Ecology 97:415-429, doi:10.1111/j.l365-2745.2009.01488.x.

Laaksonen, K. 1976. The dependence of mean air temperatures upon latitude and altitude in Fennoscandia (1921-1950). Annales Academiae Scientiarum Fennicae Series AIII 119:5-19.

Laberge, M.-J., Payette, S., and Bousquet, J. 2000. Life span and biomass allocation of stunted black spruce clones in the subarctic environment. Journal of Ecology 88:584-593.

Lang, G. 1994. Quartare Vegetationsgeschichte Europas [Quaternary vegetation history of Europe]. Jena, Germany: Gustav Fischer Verlag. 462 p.

Latalowa, M., and van der Knaap, W.O. 2006. Late Quaternary expansion of Norway spruce Picea abies (L.) Karst. in Europe according to pollen data. Quaternary Science Reviews 25:2780-2805.

Lavoie, C., and Payette, S. 1994. Recent fluctuations of the lichen-spruce forest limit in subarctic Quebec. Journal of' Ecology 82:725-734.

__. 1996. The long-term stability of the boreal forest limit in subarctic Quebec. Ecology 77:1226-1233.

Lavrinenko, I.A., and Lavrinenko, O.V. 1999. Relict spruce forest "islands" in the Bolshezemelskaya tundra - Control sites for long-term climatic monitoring. Chemosphere - Global Change Science 1:389-402.

Lindbladh, M. 2004. Nar granen kom till byn - nagra tankar kring granens invandring i sodra Sverige [When spruce came to the village: Some thoughts about its immigration into southern Sweden]. Svensk Botanisk Tidskrift 98:249-262.

Ljung, T. 2004. Odebygdsminnen. Berattelser om manniskorna nord i marken [Memories from the wasteland: Stories about people in the North]. Lansstyrelsen i Dalarnas Lan, Falun.

Ljungdahl, E. 2007. Det tysta arkivet - om samisk narvaro i fjallen [The silent archive: The presence of the Sami in the mountains]. Jamten 100:64-71.

Lundqvist, G. 1951. Beskrivning till jordartskarta over Kopparbergs lan [Description to the Quaternary map of Kopparberg County]. Sveriges Geologiska Undersokning (SGU) Ser. Ca 21.

__. 1959. C 14-daterade tallstubbar fran fjallen [C14-dated pine stumps from the mountains]. Sveriges Geologiska Undersokning (SGU) Ser. C. 565.

Lundqvist, J. 1969. Beskrivning till jordartskarta over Jamtlands lan [Description to the Quaternary map of Jamtland County]. Sveriges Geologiska Undersokning (SGU) Ser. Ca 45.

MacDonald, G.M., Kremenetski, K.V., and Beilman, D.W. 2008. Climate change and the northern Russian treeline zone. Philosophical Transactions of the Royal Society London B: Biological Science 363(1501):2285-2299.

Malanson, G.P., Brown, D.G., Butler, D.R., Cairns, D.M., Fagre, D.B., and Walsh, S.J. 2009. Ecotone dynamics: Invisibility of alpine tundra by tree species from the subalpine forest. In: Butler, D.R., Malanson, G.P, Walsh, S.J., and Fagre, D.B., eds. The changing alpine treeline. Amsterdam: Elsevier. 35-61.

Marchal, O., Cacho, L, Stocker, T.F., Grimalt, J.O., Calvo, E., Martrat, B., Shackleton, N., et al. 2002. Apparent long-term cooling of the sea surface in the northeast Atlantic and Mediterranean during the Holocene. Quaternary Science Reviews 21:455-483.

May, M.R., Provance, M.C., Sanders, A.C., Ellstrand, N.C., and Ross-Ibarra, J. 2009. A Pleistocene clone of Palmer's oak persisting in southern California. PLoS ONE 4:1-5.

Moberg, A., Tuomenvirta, H., and Nordli, 0. 2005. Recent climatic trends. In: Seppala, M., ed. The physical geography of Fennoscandia. Oxford: Oxford University Press. 112-133.

Moberg, R., and Holmasen I. 1982. Lavar. En falthandbok [Lichens: A field handbook]. Stockholm: Interpublishing.

Moe, D. 1970. The post-glacial immigration of Picea abies into Fennoscandia. Botaniska Notiser 123:61 -66..

Mossberg, B., and Stenberg, L. 2003. Den nya Nordiska Floran [The new Nordic flora]. Stockholm: Wahlstrom & Widstrand.

Nesje, A., Kvamme, M., Rye, N., and Lovlie, R. 1991. Holocene glacial and climate history of the Jostedalsbreen region, western Norway: Evidence from lake sediments and terrestrial deposits. Quaternary Science Reviews 10:87-114.

Oberg, L. 2002. Tradgransdynamik i Sanfjallsomradet, Harjedalen [Treeline dynamics on Mount Sanfjallet, Harjedalen]. Svensk Botanisk Tidskrift 96:177-185.

__. 2008. Tradgransen som indikator for ekologiska

klimateffekter i fjallen [Treeline as an indicator of ecological effects in the mountains]. Lansstyrelsen Jamtlands Ian. Miljo/ Fiske Miljoovervakning rapport 2008:01.

__. ed. 2009.1 hjartat av Harjedalen - Sonfjallet [The heart of Harjedalen - Sonfjallet/Im Herzen Harjedalens]. Jamtli Forlag.

Opgenoorh, L., Vendramin, G.G., Mao, K., Miehe, G., Miehe, S., Liepelt, S., Liu, J., and Ziegenhagen, B. 2009. Tree endurance on the Tibetan Plateau marks the world's highest known tree line of the Last Glacial Maximum. New Phytologist 185:332-342.

Paus, A. 2010. Vegetation and environment of the Rodalen alpine area, Central Norway, with emphasis on the early Holocene. Vegetation History and Archaeobotany 19:29-51, doi:10.1007/ S00334-009-0228-4.

Paus, A., Velle, G., and Berge, J. 2011. The Lateglacial and early Holocene vegetation and environment in the Dovre mountains, central Norway, as signalled in two Lateglacial nunatak lakes. Quaternary Science Reviews, doi:10.1016/j. quascirev.2011.04.010.

Payette, S., and Morneau, C. 1993. Holocene relict woodlands at the eastern Canadian treeline. Quaternary Research 39:84-89, doi:10.1006/qres.l993.1010.

Payette, S., Filion, L., Gauthier, L., and Boutin, Y. 1985. Secular climate change in old-growth tree-line vegetation of northern Quebec. Nature 315:135-138, doi: 10.1038/315135a0.

Payette, S., Eronen, M., and Jasinski, J. J.P 2002. The circumboreai tundra-taiga interface: Late Pleistocene and Holocene changes. AmbioSpecial Report 12: Dynamicsofthecircumboreal tundra-taiga interface. 15-22.

Petit, R.J., Hu, F.S., and Dick, C.W. 2008. Forests of the past: A window to future changes. Science 320:1450-1452, doi:10.1126/science.H55457.

Putenikkin, V.P., and Martinsson, O. 1995. Present distribution of Larix sukaczewii Dyl. in Russia. Department of Silviculture. Swedish University of Agricultural Sciences Reports 38. 78 p.

Raab, B., and Vedin, H. 1995. Climate, lakes and rivers. In: National Atlas of Sweden. Stockholm: Sveriges Nationalatlas Forlag.

Rohling, E.J., and Palike, H. 2005. Centennial-scale climate cooling with a sudden cold event around 8,200 years ago. Nature 434:975-979, doi:10.1038/nature03421.

Samuelsson, G. 1917, Studien iiber die Vegetation der Hochgebirgsgegenden von Dalarne [Vegetation studies in the high mountain regions of Dalarna]. Nova Acta Regiae Societatis Scientiarum Upsaliensis Series 4:4:8.

Sander, J. 2005. Brand i Fulufjallets nationalpark [About fire in the Fulufjallet National Park]. Rapport 2005.1 Miljovardsenheten, Lansstyrelsen i Dalarnas Lan.

Schauffler, M., and Jacobson, G.L., Jr. 2002. Persistence of coastal spruce refugia during the Holocene in northern New England, USA, detected by stand-scale pollen stratigraphies. Journal of Ecology 90:235-250.

Segerstrom, U., and von Stedingk, H. 2003. Early-Holocene spruce, Picea abies (L.) Karst., in west central Sweden as revealed by pollen analysis. The Holocene 13:897-906.

Seppa, H., Alenius, T., Bradshaw, R.H.W., Giesecke, T., Heikkila, M., and Muukkonen, P. 2009. Invasion of Norway spruce (Picea abies) and the rise of the boreal ecosystem in Fenno-scandia. Journal of Ecology 97:629-640.

Shemesh, A., Rosqvist, G., Rietti-Shati, M., Rubensdotter, L., Bigler, C, Yam, R., and Karlen, W. 2001. Holocene climatic change in Swedish Lapland inferred from an oxygen-isotope record of lacustrine biogenic silica. The Holocene 11:447-454.

Smith, H. 1920. Vegetationen och dess utvecklingshistoria i det centralsvenska hogfjallsomradet [Vegetation and vegetation history in the central Swedish Scandes]. Uppsala: Almqvist & Wiksells.

Stewart, J.R., and Cooper, A. 2008. Ice age refugia and Quaternary extinctions: An issue of evolutionary palaeoecology. Quaternary Science Reviews 27:2443-2448, doi:10.1016/j. quascirev.2008.10.005.

Stewart, J.R., and Lister, A.M. 2001. Cryptic northern refugia and the origins of the modern biota. Trends in Ecology and Evolution 16:608-613.

Stuiver, M., Reimer, P. J., and Reimer, R. 2005. CALIB radiocarbon calibration, execute version 6.0. http://calib.qub.ac.uk/calib/.

Tallantire, P. A. J 977. A further contribution to the problem of the spread of spruce (Picea abies (L.) Karst.) in Fennoscandia. Journal of Biogeography 4:219-227.

Terhurne-Berson, R. 2005. Changing distribution patterns of selected conifers in the Quaternary of Europe caused by climatic variations. PhD dissertation, Rheinischen- Friedrich-Wilhelms-Universitat Bonn.

Tollefsrud, M.M., Kissling, R., Gugerli, F., Johnsen, 0., Skrappa, T, Cheddadi, R., van der Knaap, W.O., et al. 2008. Genetic consequences of glacial survival and postglacial colonization in Norway spruce: Combined analysis of mitochondrial DNA and fossil pollen. Molecular Ecology 17:4134-4150.

Tollefsrud, M.M., Sonstebo, J.H., Brochmann, C, Johnsen, 0., Skroppa, T., and Vendramin, G.G. 2009. Combined analysis of nuclear and mitochondrial markers provide new insight into the genetic structure of North European Picea abies. Heredity 102:549-562, doi:10.1038/hdy.2009.16.

Tuomenvirta, H., Alexandersson, H., Drebs, A., Frich, P., and Nordli, P.O. 2000. Trends in Nordic and Arctic temperature extremes and ranges. Journal of Climate 13:977-990.

Vasek, F.C. 1980. Creosote bush: Long-lived clones in the Mojave Desert. American Journal of Botany 67:246-255.

Velle, G., Larsen, J., Eide, W., Peglar, S.M., and Birks, H.J.B. 2005. Holocene environmental history and climate of Ratasjoen, a low-alpine lake in south-central Norway. Journal of Paleolimnology 33:129-153.

Willis, K.J., Rudner, E., and Surnegi, P. 2000. The full-glacial forests of central and southeastern Europe. Quaternary Research 53:203-213.

Zazula, G.D., Telka, A.M., Harington, C.R., Schweger, C.E., and Mathewes, R.W. 2006. New spruce (Picea spp.) macrofossils from Yukon Territory: Implications for Late Pleistocene refugia in Eastern Beringia. Arctic 59:391 -400.
COPYRIGHT 2011 Arctic Institute of North America of the University of Calgary
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2011 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Oberg, Lisa; Kullman, Leif
Publication:Arctic
Article Type:Report
Geographic Code:4E0SC
Date:Jun 1, 2011
Words:11240
Previous Article:Connections between river runoff and limnological conditions in adjacent High Arctic Lakes: cape bounty, Melville Island, Nunavut.
Next Article:Molting, staging, and wintering locations of common eiders breeding in the gyrfalcon archipelago, Ungava Bay.
Topics:

Terms of use | Privacy policy | Copyright © 2021 Farlex, Inc. | Feedback | For webmasters