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The climate‐driven encroachment of shrubs into the Arctic is accompanied by shifts in soil fungal communities that could contribute to a net release of carbon from tundra soils. At the same time, arctic grazers are known to prevent the establishment of deciduous shrubs and, under certain conditions, promote the dominance of evergreen shrubs. As these different vegetation types associate with contrasting fungal communities, the belowground consequences of climate change could vary among grazing regimes. Yet, at present, the impact of grazing on soil fungal communities and their links to soil carbon have remained speculative. Here we tested how soil fungal community composition, diversity and function depend on tree vicinity and long‐term reindeer grazing regime and assessed how the fungal communities relate to organic soil carbon stocks in an alpine treeline ecotone in Northern Scandinavia. We determined soil carbon stocks and characterized soil fungal communities directly underneath and >3 m away from mountain birches (Betula pubescens ssp. czerepanovii) in two adjacent 55‐year‐old grazing regimes with or without summer grazing by reindeer (Rangifer tarandus). We show that the area exposed to year‐round grazing dominated by evergreen dwarf shrubs had higher soil C:N ratio, higher fungal abundance and lower fungal diversity compared with the area with only winter grazing and higher abundance of mountain birch. Although soil carbon stocks did not differ between the grazing regimes, stocks were positively associated with root‐associated ascomycetes, typical to the year‐round grazing regime, and negatively associated with free‐living saprotrophs, typical to the winter grazing regime. These findings suggest that when grazers promote dominance of evergreen dwarf shrubs, they induce shifts in soil fungal communities that increase soil carbon sequestration in the long term. Thus, to predict climate‐driven changes in soil carbon, grazer‐induced shifts in vegetation and soil fungal communities need to be accounted for. [ABSTRACT FROM AUTHOR]

Savannas and grasslands throughout the world are experiencing bush encroachment, which has serious consequences for net primary productivity. In South Africa, Vachellia sieberiana is encroaching into the savannas and high-altitude grasslands of KwaZulu-Natal. We investigated the role of fire, frost and simulated grazing (mowing of the grass sward) on the establishment of transplanted V. sieberiana saplings (as change in stem diameter) along an altitudinal gradient in north-western KwaZulu-Natal using analysis of variance. Altitude had a significant effect on sapling size. There was no response to treatments at the high-altitude site. At the mid-altitude site, sapling stem diameter decreased in response to fire treatment and increased in response to mowing. At the low-altitude site, there was a negative response to frost and a positive response to fire and to mowing. At both the mid- and low-altitude sites there was a positive response when fire and mowing were combined. None of the treatments were able to prevent the establishment of V. sieberiana. Rangeland managers need to maintain a tree:grass ratio that provides the best production of forage. Fire is frequently used to control bush encroachment, but, with V. sieberiana being well adapted to survive fire, managers will need to devise other methods to conserve important grassy biomes. [ABSTRACT FROM AUTHOR]

Background and Purpose: Pinus heldreichii Christ. is a sub-endemic species occurring at tree-line locations in Kosovo and covering an area of 2500 ha. In high elevation sites radial growth is mainly controlled by low temperatures. The main purpose of this study was the analysis of radial growth of P. heldreichii and its response to local climate conditions. Materials and Methods: Research sites comprise of three high elevation stands of P. heldreichii with specific site conditions. Core samples were collected from 98 healthy dominant and co-dominant trees at breast height using increment borer. They were prepared and cross-dated using standard dendrochronological methods, while tree-ring widths were measured to the nearest 0.001 mm using the TSAP software. The ARSTAN program was used to standardize the tree-ring widths and to calculate dendrochronological statistical parameters. The growth-climate relationship was investigated using bootstrapped correlation function analysing the residual chronologies of each sampled site as a dependent variable and the climatic data from May of the (n-1) year up to the October of the n year for the common period 1951-2013 as an independent variable. Results: The length of Bosnian pine chronologies ranged from 175 to 541 years. All chronologies had high values of first-order autocorrelation indicating that radial growth of P. heldreichii is affected by the climate conditions of the previous growing year. Koritnik chronology had the highest values of the mean sensitivity due to the influence of drought stress. This conclusion is also supported by the result of growth-climate relationship where radial growth is negatively correlated with June temperatures and positively associated with July and August precipitation. We found that radial growth of young trees from Koritnik site is limited by the combined effect of temperatures and summer drought stress. In high elevation sites, temperature is expected to control the growth of P. heldreichii, but this effect is becoming more restrictive with age. The positive correlation between radial growth and winter temperatures suggests that favorable thermal conditions during winter months influence snow melting or soil moisture availability and indirectly affect the radial growth of P. heldreichii at all three sampled sites. Conclusions: The first tree-ring width chronologies from Kosovo are an important step towards a denser tree ring network in the Balkan region. Growth-climate relationships indicated that for P.heldreichii growth does not depend only on one single dominant factor, but also on various combinations of precipitation and temperature resulting in different climatic sensitivity. Our results provide an important basis for additional tree-ring parameters such as maximum latewood density and stable isotope ratios to be processed, improving the level of knowledge about P. heldreichii’s response versus site conditions.

The nature of tree-line habitats in the Andes has long been a contentious topic in the ecological literature. Palynological studies suggest that a combination of anthropogenic and natural processes throughout the Holocene contributed to its present form and species composition. This is the first study to use zooarchaeological evidence to reconstruct possible prehistoric changes in these alpine habitats. I analysed the remains of birds from the La Chimba archaeological site in northern Ecuador to assess changes in the bird tree-line community over three distinct phases (Early, 2640-2390 year BP; Middle, 2390-1994 year BP; Late, 1994-1700 year BP) of this prehistoric settlement. The elevation of this site (3200 m) places it near a steep elevational gradient in vegetation, with the modern tree-line here at 3500-3600 m. Therefore, non-local specimens of birds from the lowlands would hint at long-distance trade. The composition of birds changes through time: species associated with high montane forest and shrubby páramos decrease and species from dry or open montane habitats increase. This trend is dominated by the decrease of Curve-billed Tinamous Nothoprocta curvirostris (current elevational range 3000-3900 m) and a corresponding increase of specimens of Andean Tinamous Nothoprocta pentlandii (current elevational range 1000-2300 m). The large number of Andean Tinamous is surprising given that presently it occurs no closer than 300 km to the south of the La Chimba site. Overall, 18 of the 43 species of birds identified from La Chimba are likely to be the result of trade. This includes species from the eastern and western lowlands of Ecuador and one possible long-distance transport from Peru. Prehistoric trade of birds and bird parts was probably common, and prehistoric anthropogenic landscape change and trade in birds should be considered as alternative explanations for species with disjunct populations in and across the Andes. [ABSTRACT FROM AUTHOR]

Abstract: In arctic ecosystems, winter soil respiration can contribute substantially to annual CO2 release, yet the source of this C is not clear. We analysed the 14C content of C released from plant-free plots in mountain birch forest and tundra-heath. Winter-respired CO2 was found to be a similar age (tundra) or older (forest) than C released during the previous autumn. Overall, our study demonstrates that the decomposition of older C can continue during the winter, in these two contrasting arctic ecosystems. [Copyright &y& Elsevier]

We examined the premise that changing abundance and environmental conditions influence the seasonal dispersion and distribution of migratory tundra caribou (Rangifer tarandus groenlandicus). The Ahiak herd's (north-central Nunavut, Canada) calving shifted from dispersed on islands to gregarious calving on the mainland coast. As abundance further increased, the calving ground elongated east and west such that we proposed a longitudinal climate gradient. As well, the calving ground's east and west ends are different distances from the tree-line, which dips south closer to Hudson Bay. We proposed that whether caribou winter on the tundra or within boreal forest and the different climate across the long calving ground could contribute to differential survival and productivity such that sub-population structure would result. At the scale of the individual cows (identified through satellite-collars), we did not find inter-annual spatial fidelity to either the western or eastern parts of the calving ground. At the population scale (aerial surveys of calving distribution), we also did not find discontinuities in calving distribution. The spatial association of individual cows during calving compared with their association during the rut was inconsistent among years, but overall, cows that calve together, rut together. At this time and with the available evidence, we could not infer sub-population structure from shifts in dispersion and distribution as influenced by geography and changes in abundance for the Ahiak herd. [ABSTRACT FROM AUTHOR]

Few studies have found strong evidence to suggest that ecotones promote species richness and diversity. In this study we examine the responses of a high-Andean bird community to changes in vegetation and topographical characteristics across an Andean tree-line ecotone and adjacent cloud forest and puna grassland vegetation in southern Peru. Over a 6-month period, birds and vegetation were surveyed using a 100 m fixed-width Distance Sampling point count method. Vegetation analyses revealed that the tree-line ecotone represented a distinctive high-Andean vegetation community that was easily differentiated from the adjacent cloud forest and puna grassland based on changes in tree-size characteristics and vegetation cover. Bird community composition was strongly seasonal and influenced by a pool of bird species from a wider elevational gradient. There were also clear differences in bird community measures between tree-line vegetation, cloud forest and puna grassland with species turnover (β-diversity) most pronounced at the tree-line. Canonical Correspondence Analysis revealed that the majority of the 81 bird species were associated with tree-line vegetation. Categorizing patterns of relative abundance of the 42 most common species revealed that the tree-line ecotone was composed primarily of cloud forest specialists and habitat generalists, with very few species from the puna grassland. Only two species, Thlypopsis ruficeps and Anairetes parulus, both widespread Andean species more typical of montane woodland vegetation edges, were categorized as ecotone specialists. However, our findings were influenced by significant differences in species detectability between all three vegetation communities. Our study highlights the importance of examining ecotones at an appropriate spatial and temporal scale. Selecting a suitable distance between sampling points based on the detection probabilities of the target bird species is essential to obtain an unbiased picture of how ecotones influence avian richness and diversity. [ABSTRACT FROM AUTHOR]

Abstract: Tree-line ecotones are strongly climatically limited and serve as potential monitors of climate change. We employed annual growth increment from tree-rings, and tree density and age structure data derived from two Juniperus przewalskii tree-line sites in the eastern part of the Qilian Mountains, northeastern Tibetan Plateau, to detect the responses of tree growth and population dynamics to climate change. High temperature favors tree growth and is associated with increased tree density at tree-line, and an advance in tree-line position. Significantly positive correlations were found between ring-width and mean monthly air temperatures in current and previous June, July and August. Tree recruitment began to increase rapidly at the two sites after the Little Ice Age, but then decreased starting in the 1970s. The number of trees established coincides with temperature changes. The warming trend after the Little Ice Age favors increases of tree density and an advance of tree-line. The majority of trees established during the period of 1931–1970, which coincides well with the rapid radial growth of the trees. [Copyright &y& Elsevier]

Shrubs and trees are expected to expand in the sub-Arctic due to global warming. Our study was conducted in Abisko, sub-arctic Sweden. We recorded the change in coverage of shrub and tree species over a 32- to 34-year period, in three 50 × 50 m plots; in the alpine-tree-line ecotone. The cover of shrubs and trees (<3.5 cm diameter at breast height) were estimated during 2009-2010 and compared with historical documentation from 1976 to 1977. Similarly, all tree stems (≥3.5 cm) were noted and positions determined. There has been a substantial increase of cover of shrubs and trees, particularly dwarf birch ( Betula nana), and mountain birch ( Betula pubescens ssp. czerepanovii), and an establishment of aspen ( Populus tremula). The other species willows ( Salix spp.), juniper ( Juniperus communis), and rowan ( Sorbus aucuparia) revealed inconsistent changes among the plots. Although this study was unable to identify the causes for the change in shrubs and small trees, they are consistent with anticipated changes due to climate change and reduced herbivory. [ABSTRACT FROM AUTHOR]

Abstract  Climate change is occurring and insects are responding. Current challenges for ecologists and managers are predicting how organisms will respond to continuing climate change and determining how to mitigate potential negative effects. In contrast to broad scale predictions for climate change involving the distribution of species, in this article we highlight the many ways in which local populations of the Rocky Mountain Apollo butterfly (Parnassius smintheus Doubleday) are predicted to respond to climate change. Using experimental and observational data collected over the past 15 years, we detail both direct and indirect effects. In addition, we identify limitations in our knowledge restricting the ability to predict how populations will respond to climate change. Some changes, such as warmer winter temperatures, may have beneficial effects; however, most of the effects of climate change will be detrimental. Variability in snow cover during the overwintering period and habitat loss due to forest encroachment have the largest potential negative effects. [ABSTRACT FROM AUTHOR]

Little is known about the relationships between fossil oribatid mite assemblages in lake and mire sediments and the composition, abundance, and richness of their living communities. Because oribatid mites are a relatively new area of palaeolimnological study, there is a great lack of knowledge about the taphonomic processes that might affect fossil mite assemblages. The DOORMAT (Direct Observation Of Recent Macrofossils Across Tree-line) project was designed to study the transport and deposition of oribatid mites and plant remains in the tree-line area of western Norway. The present study also compares modern oribatid assemblages with fossil oribatid assemblages in a Holocene lake-sediment sequence from the nearby Trettetjørn, and considers the optimal location for studying fossil oribatid mites within a lake basin. Seven novel terrestrial traps (50 × 80 cm Astroturf doormats) were placed at major vegetational transitions along an altitudinal transect crossing the tree-line ecotone from 633 to 1,120 m a.s.l. at Upsete, west Norway. Three sediment traps were placed in Trettetjørn (810 m a.sl.) at the inlet, the middle, and near the outlet. In each terrestrial trap, the oribatid assemblage was found to be characteristic of the surrounding habitat. The lake-trap analyses showed that aquatic or moist-habitat species had the highest chance of being incorporated into the lake sediments; the number of terrestrial species decreased considerably from both outlet and inlet traps to the central trap in the deepest water. The area adjacent to the inlet of Trettetjørn would therefore be the optimal location for a sediment core for oribatid analysis. However, this conclusion is not supported when the modern trap results are compared with the Trettetjørn sequence from the lake centre. [ABSTRACT FROM AUTHOR]

Abstract: In South America, the arid and semiarid subtropical regions through the Atacama Desert and north-central Chile between 19° and 32°S are currently a gap in the tree-ring chronology network. Only a short tree-ring chronology has been published for this vast region and little is known about the suitability of many woody species for tree-ring analysis and dendroclimatology. In this paper we present the first detailed analysis of the climate responses and influences of the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) on the tree-rings of three species new to dendrochronology and that typically occur at high elevations in the Andes of central and north-central Chile. Three well-replicated tree-ring chronologies of Kageneckia angustifolia, Proustia cuneifolia and Fabiana imbricata are compared with century-long regional records of precipitation and temperature, and with the N3.4 SST and PDO indices in both time and frequency-domains using correlation and wavelet analysis. The radial growth of these species is controlled by winter precipitation and is also positively correlated with temperature during most of the rainy season from April to September (autumn–spring). The regional climate as well as tree growth is strongly modulated by ENSO and ENSO-like conditions in the equatorial Pacific at both interannual and interdecadal timescales. The decadal and interdecadal variability is not correlated with PDO and appears to be related to the Interdecadal Pacific Oscillation (IPO), a Pacific-wide ENSO-like mode of climate variability. Despite their relatively short lifespans, these three new species have a high potential for dendrochronological and dendroclimatic studies in the semiarid region of Chile over the last two centuries. [Copyright &y& Elsevier]

An ultra-long tree-ring width chronology (9111 years long, 7109 BC to AD 2002) has been established based on the analysis and dating of 1432 subfossil/dry dead wood samples and cores from 335 living trees. The material was collected from treeline or near-treeline sites (c. 2000 to 2400 m a.s.l.) mainly in the Eastern Alps. The availability of preserved samples through time at high altitudinal sites is influenced by Alpine forest history and is partly climatically controlled, as shown by comparisons of the sample depth record of the Eastern Alpine Conifer Chronology (EACC) with the Holocene glacier record. The similarity of variations over time between the sample depth of the chronology and the mid-Holocene GISP2 10Be record suggest a relationship between sample depth and solar activity. The Eastern Alpine Conifer Chronology has already been used as a dating base in environmental studies, eg, on glacier fluctuations, as well as in archaeological studies. [ABSTRACT FROM AUTHOR]

Studies of feedback between ecological pattern and process can benefit from the analysis of visually striking patterns, as they may reveal underlying processes and clarify the relative role of exogenous versus endogenous factors in driving vegetation change. Roughly linear forest patches are common in subalpine environments, including 'hedges', 'ribbon forest', and 'Shimagare' or 'wave regenerated forests' (waves). The influence of wind is common among these patterns, but the role of positive feedback, the most important component of self-organization in biological systems, varies. Hedges are orientated parallel to prevailing winds in several mid-latitude mountain ranges worldwide. Desiccation and ice-particle abrasion kills windward foliage while the vegetation shelters leeward seedlings and growth, so that the patches migrate slowly across the slope. Ribbon forest consists of strips orientated perpendicular to prevailing winds. They have been examined only in the US Rocky Mountains and are the least studied and understood of these phenomena. There are at least three distinct types of ribbon forest, which appear to develop in different ways. Waves are migrating strips of mortality and regeneration orientated perpendicular to prevailing winds in the USA, Japan and Argentina, and dominant controls vary by site. Hedges and waves can develop endogenously with a constant wind, and so can be considered self-organizing in the sense that feedback at the scale of individual trees creates a pattern across the scale of many trees without exogenous forcing. Most ribbon forests seem to be dominated by exogenous forces, but more work is needed to fully characterize the different types. [ABSTRACT FROM AUTHOR]

Abstract: White spruce (Picea glauca (Moench) Voss) trees were sampled to investigate the relationship between ring width and δ 13C as well as between these descriptors and climate. Cross-sections from eight white spruce trees growing in the Hudson Bay Lowlands, subartic Manitoba, with an establishment date prior to 1775 were selected from our archive. For each cross-section, two radii were measured to produce ring-width chronologies. For stable-carbon isotope measurements, every fifth ring (2000, 1995, … 1750) was analyzed separately from each tree, whereas approximately equal masses from the eight trees were pooled into composite samples for each of the intermediate years mixing masses from each tree equal to that from the tree with the least amount. Alpha-cellulose was extracted and δ 13C was determined using continuous-flow mass spectrometry. The ring-width residual chronology derived from eight trees was highly correlated to that previously developed for the area. A small but significant correlation was also found between the ring-width and the δ 13C residual chronologies. The climate signal contained in both ring-width and the δ 13C residual chronologies suggests that warm early summers were conducive to larger rings whereas the δ 13C best reflects the overall growing season temperature. Precipitation, relative humidity and/or drought index have little to no association with either chronology. Significant correlations were observed between δ 13C and the historical ice records from the Hudson Bay Co. archive data suggesting that during long (warm) growing season the 13C content of alpha-cellulose increases. Our results indicate that both ring-width and δ 13C provide complementary information. Future work will involve looking at long-term trends in carbon isotope ratios and the potential use of δ 13C for dendroclimatic reconstruction. [Copyright &y& Elsevier]

Abstract: The sensitivity of altitudinal and latitudinal tree-line ecotones to climate change, particularly that of temperature, has received much attention. To improve our understanding of the factors affecting tree-line position, we used the spatially explicit dynamic forest model TreeMig. Although well-suited because of its landscape dynamics functions, TreeMig features a parabolic temperature growth response curve, which has recently been questioned, and the species parameters are not specifically calibrated for cold temperatures. Our main goals were to improve the theoretical basis of the temperature growth response curve in the model and develop a method for deriving that curve''s parameters from tree-ring data. We replaced the parabola with an asymptotic curve, calibrated for the main species at the subalpine (Swiss Alps: Pinus cembra, Larix decidua, Picea abies) and boreal (Fennoscandia: Pinus sylvestris, Betula pubescens, P. abies) tree-lines. After fitting new parameters, the growth curve matched observed tree-ring widths better. For the subalpine species, the minimum degree-day sum allowing growth (kDDMin) was lowered by around 100 degree-days; in the case of Larix, the maximum potential ring-width was increased to 5.19mm. At the boreal tree-line, the kDDMin for P. sylvestris was lowered by 210 degree-days and its maximum ring-width increased to 2.943mm; for Betula (new in the model) kDDMin was set to 325 degree-days and the maximum ring-width to 2.51mm; the values from the only boreal sample site for Picea were similar to the subalpine ones, so the same parameters were used. However, adjusting the growth response alone did not improve the model''s output concerning species’ distributions and their relative importance at tree-line. Minimum winter temperature (MinWiT, mean of the coldest winter month), which controls seedling establishment in TreeMig, proved more important for determining distribution. Picea, P. sylvestris and Betula did not previously have minimum winter temperature limits, so these values were set to the 95th percentile of each species’ coldest MinWiT site (respectively −7, −11, −13). In a case study for the Alps, the original and newly calibrated versions of TreeMig were compared with biomass data from the National Forest Inventory (NFI). Both models gave similar, reasonably realistic results. In conclusion, this method of deriving temperature responses from tree-rings works well. However, regeneration and its underlying factors seem more important for controlling species’ distributions than previously thought. More research on regeneration ecology, especially at the upper limit of forests, is needed to improve predictions of tree-line responses to climate change further. [Copyright &y& Elsevier]

Remains of subfossil Siberian larch trees in the Holocene deposits of the Yamal Peninsula (Western Siberia) have been collected in order to develop a continuous, multimillennium tree-ring-width chronology. This work has produced a calendar-age dated 4000-year (2000 BC to AD 1996) series. From these data, summer-temperature variability in this region has been estimated on annual to multidecadal timescales. Radiocarbon dating of selected older material shows that the oldest subfossil wood is 9400 years old and the dates of the sampled material are generally distributed evenly through time. It will, therefore, be possible to develop a tree-ring chronology for more than nine millennia. An initial assessment of long-term fluctuations in Yamal summer warmth has been realized through the reconstruction of tree-line dynamics using a combination of dendrochronological (absolute) dated material and less precisely (radiocarbon) dated older subfossils. [ABSTRACT FROM AUTHOR]

A comparative investigation of pollen deposition in peat and limnic sediments from the Pinus sylvestris-Alnus incana forest line in Dividalen, central Troms, northern Norway was performed by pollen analyses of sub-modern sediments. The possibilities of using 210Pb and 137Cs-datings in calculations of pollen influx in peat and limnic sediments are discussed. Correlation between the lead–cesium peat chronology and a marker-based limnic chronology is achieved at AD 1945–1946 by comparing the percentual pollen-curves. The upper 14 cm of the peat and 12 cm of the limnic sequence are hence supposed to represent the period ca. 1945–ca. 1996. The mean percentual representation of Pinus pollen is nearly twice as high in the peat sediments as in the limnic sediments, probably due to a slight over-representation from pine trees at the edge of the mire. The mean percentual pollen values for Alnus and Betula pubescens-type is fairly equal in peat and lake sediments, while the pollen influx rates are higher for all tree taxa in the lake sediments. This may be caused by the lake being exposed to a larger regional component than the smaller and topographically more sheltered mire. To achieve reliable pollen influx data at a near annual resolution, one needs a good control of the sedimentation processes, close intervals of isotope measurements and additional chronostratigraphically fixed marker horizons. [Copyright &y& Elsevier]

Living, dead and subfossil trees of black spruce (Picea mariana [Mill.] BSP.) were used to build a 1300-year chronology based on ring width and wood density. All density variables (maximum, minimum, earlywood and latewood densities) among the three types of trees were similar, whereas ring width was significantly higher in living trees than in dead and subfossil trees. Correlation of the indexed series from living and dead trees and from dead and subfossil trees that grew during the same periods were higher for maximum density (r = 0.70, 0.63) and mean latewood density (r = 0.65, 0.66) than for minimum density (r = 0.16, 0.35) and ring width (r = 0.15, 0.49), respectively. Maximum density and mean latewood density were significantly correlated with all temperature variables: mean annual (January–December) and growing season (May– September) temperatures, sum of degree days and frost-free days. Accordingly, maximum and latewood density in tree-rings of spruce stems at tree-line can be considered as a function of summer-temperature distributions and different types of trees can be combined for the reconstruction of long-term climatic trends due to their synchronous variations. [ABSTRACT FROM AUTHOR]

To investigate subalpine vegetation history on the Olympic Peninsula, Washington (USA), two pollen, macrofossil and charcoal records were studied in climatically distinct zones: Martins Lake (1415 m) in the moist Tsuga mertensiana zone and Moose Lake (1508 m) in the drier Abies lasiocarpa zone. The interpretation of fossil pollen assemblages was aided by comparisons with 308 modern assemblages from the Olympic Peninsula and western North America. Both pollen records show a cold/dry period following deglaciation (.10000 radiocarbon years BP) with sparse tundra and little similarity to any modern pollen assemblage. In the early Holocene, when summer temperatures are thought to have been higher than present, high percentages of Alnus sinuata-type pollen at both lakes suggest increased avalanche activity. At Martins Lake warmer summers were not accompanied by forest establishment, possibly because persistent spring snow pack, snow avalanches, and/or edaphic constraints limited tree establishment at this site. The Martins Lake record shows a steplike shift in vegetation to modern Tsuga mertensiana/Abies amabilis parkland across the Mazama tephra (6730 BP). In contrast to Martins Lake, Abies lasiocarpa forest quickly established at Moose Lake in the early Holocene, though forests were probably initially open and fires may have been frequent. From 7800 to 5100 BP forests near Moose Lake shifted gradually to cooler and moister species composition, with the addition of Chamaecyparis nootkatensis, Tsuga mertensiana and Pinus, though Abies lasiocarpa remained dominant. Forest cover was probably greatest during this transition, with parklike conditions at Moose Lake beginning at c. 5100 BP. The major differences in the records between the two sites may be due to differences in the local expression of regional climatic change and/or differences in soil development and stabilization. [ABSTRACT FROM AUTHOR]

This study presents the results of pollen analysis and radiocarbon dates of a peat section from Ortino, in the Pechora lowland in northern Russia. A pollen stratigraphy is provided for at least the last 9200 years and it provides a basis for the reconstruction of the vegetational and mire history in the northernmost part of European Russia. Conifer stomata content was recorded as a complement to pollen studies to achieve a better resolution of tree-line fluctuations. The onset of Holocene warming initiated a vegetation succession that started first with herb-dominated tundra vegetation, and later with herb-shrub tundra. Combined pollen and stomata evidence suggests that Picea accompanied by Betula spp. spread to Ortino soon after 9000 14 C yr BP. Trees and a climate warmer than at present persisted until c. 3000 14 C yr BP, when forests disappeared and modern dwarf-shrub tundra vegetation developed. [ABSTRACT FROM AUTHOR]

A combination of pollen and macrofossil analyses from six lakes at altitudes between 370 and 999 m above sea level (a.s.l.) in the Torneträsk area reflect the Holocene vegetation history. The main field study area has been the Abisko valley at altitudes around 400 m a.s.l. The largest lake, Vuolep Njakajaure has annually laminated (varved) sediments. The chronology and sedimentation rates in the pollen-influx calculations are based on varve yrs in this lake and on radiocarbon dated terrestrial plant macrofossils in the other lakes. A strong increase of mountain birch ( Betula pubescens ssp. tortuosa) during the early Holocene with a tree-line c. 300 m above the present, indicates that the summer temperature was c. 1.5 °C higher than today, assuming that the land uplift has been 100 m since then. Scattered stands of pine ( Pinus sylvestris) may have been growing in the area immediately after the deglaciation but a forest consisting of pine and mountain birch expanded first at low elevations and reached the eastern parts of the Torneträsk area at c. 8300 cal BP and the western parts at c. 7600 cal BP. The highest pine-birch forest limit was not reached until 6300 cal BP (110 m above present pine limit). Warm and dry conditions during the pine forest maximum led to lowering of the water level documented in Lake Badsjön in the Abisko valley about 1-1.5 m lower than today. Pine and mountain birch were growing at the maximum altitude until c. 4500 cal BP. Assuming that land uplift has been in the range of 20-40 m since the mid-Holocene, this implies that the temperature was then c. 1.5-2 °C higher than today. Rising lake-levels and lowering limits of pine and mountain birch since c. 4500 cal BP indicate a more humid and cool climate during the late Holocene. [ABSTRACT FROM AUTHOR]

During recent years a number of fragments of Pinus cembra and Larix decidua as well as peat were found in front of the tongue of the Pasterze Glacier in the Eastern Alps. These were washed out by the stream from under the present ice. The wood originates from trees which reached ages of up to 400 years or more. Radiocarbon dating shows them to come from the early Holocene. They indicate that between cal. bc 8100 and cal. bc 6900 the Pasterze Glacier was smaller than at present. The Pasterze Glacier advanced around cal. bc 6900. A lump of peat shows that around cal. bc 6300 at the latest the Pasterze Glacier was again smaller than today. The radiocarbon age of the fulvic acid fraction of the peat suggests that growth could have continued until cal. bc 5430–5080. Further wood samples, dated to around cal. bc 4800 and cal. bc 3800, show that at these times the Pasterze Glacier was smaller than at present. The Pasterze Glacier had a relatively limited extent over long periods in the early Holocene. Thus mostly favourable climatic conditions can be inferred for these time periods. [ABSTRACT FROM AUTHOR]

Radiocarbon dates were obtained from 24 samples of Pinus sylvestris L. (Scots pine) wood recovered from sites beyond the modern conifer tree-line on the Kola Peninsula of Russia. Twenty-one of the samples came from the shallow waters and eroding peats at the edges of two small lakes at 68°439N, 35°109E, located north of the modern conifer tree-line. Three samples came from a small pond located above the modern elevational limits of Pinus sylvestris at 68°259N, 35°199E. The radiocarbon dates indicate that pine trees grew approximately 20 km north of the mapped modern limits of the species from 6680 BP to 3830 BP. Pine trees were also growing some 40 m above their modern elevational limits between 5890 BP and 3450 BP. Nineteen of the samples date from 6680 BP to 5070 BP, suggesting that the density of trees north of the modern tree-line was greatest between |7000 and 5000 BP. The timing of tree-line advance and greatest density on the Kola Peninsula are in agreement with the results of similar studies from northern Fennoscandia which indicate that maximum northern and elevational extension of tree-line occurred between 7000 BP and 4000 BP. The general agreement between tree-line reconstructions suggests that the climatic changes that promoted mid-Holocene tree-line extension along the North Atlantic margins in northern Fennoscandia propagated eastward to the Kola Peninsula. The late timing of initial pine expansion on the Kola and in adjacent northern Fennoscandia remains problematic and may relate to lower winter insolation, temperature regimes in the adjacent oceans or slow rates of migration. [ABSTRACT FROM AUTHOR]

Pollen diagrams from four sites along an altitudinal sequence on Mt Hauhungatahi support fossil wood data (Ogden et al., 1997) in suggesting a fluctuating Holocene tree-line not exceeding the altitude reached in the early Holocene. Tree-line forest at 1340–1390 m during the periods 10 100–7500 and 5400–3800 cal. BP was associated with patchy Subalpine scrub communities above and below this altitude. Rapid decline of this Halocarpus-Phyllocladus forest at c. 7500 cal. BP, and again c. 3800 cal. BP was probably due to volcanism. During 7500–5400 and 3800–1718 cal. BP tree-line forest was replaced by Subalpine scrub. The failure of forest to replace scrub during these two periods implies a long-lasting influence of the event which destroyed the forest, a continuation of disturbance events, or changed environmental conditions. After the Taupo volcanic eruption (1718 cal. BP) expansion of Libocedrus indicates an upwards movement of forest species into Subalpine scrub, followed by a decline. Volcanism has probably affected the vegetation of Mt Hauhungatahi directly and indirectly (through effects on soil drainage) throughout the Holocene. Results are consistent with increased climatic variability since 7500 cal. BP, and support the hypothesis that disturbance events can have persistent long-term effects on community composition and species distribution patterns. [ABSTRACT FROM AUTHOR]

The northern Fennoscandian tree-line area consists of fairly distinct vegetation zones. The pollen stratigraphies of two boreal sites and two tundra sites were studied and the palynological data analysed numerically. The main aim was to measure palynological richness, using rarefaction analysis, and to assess its value in reflecting patterns of past floristic richness. Rates of palynological change were measured using both chord distance and Euclidean distance as the dissimilarity coefficient. The results show low palynological richness during the Younger Dryas. The values increase rapidly at the transition to the Holocene. During the Holocene the values are in reversed order in relation to present vegetation density, the tundra sites having the highest palynological richness. This suggests that differences in the size of the pollen catchment may have an important role in palynological richness estimates and that no straight comparisons of palynological richness should be made between sites from different vegetation zones. Most pronounced changes in palynological richness take place in the Lake Rautuselka core, where high Pinus pollen influx is correlated with low palynological richness. At the boreal sites, high rates of change are associated with higher palynological richness whereas no similar relationship is observed at the tundra sites. [ABSTRACT FROM AUTHOR]

Palaeoecological investigations of a small mire in Ötztal, Tyrol, Austria, situated about 50 m above the potential tree-line, indicates that human impact on the landscape started with burning of heath at approximately 5300 B.P. At about 4800 B.P. a weak increase in important apophytes may reflect the local presence of domestic animals. Between 4000 and 3500 B.P. a clear decline in pastoral activity occurred. From 3000 B.P. a strong increase in the representation of apophytes suggests local summer settlement, while in the interval 2600-2200 B.P. anthropogenic activity declined. After 2150 B.P. there was a marked increase in summer farm activity. Fresh information is presented on tree-line fluctuations during the Holocene: Pinus cembra forest ascended above the present potential tree-line by more than 50-100 m between 9000-8000 B.P., 6000-5500 B.P., and 3800-3000 B.P. A Betula maximum between 7000 and 5500 B.P. is probably due to succession in nearby avalanche tracks, as well as to a higher tree-line. Low humification and low loss-on-ignition values around 6000 B.P. may reflect the Frosnitz stadial (6900-6000 B.P.). The Rootmoos I stadial (5400 B.P.) and probably the early Sub-Atlantic stadial maximum (3000-2300) are also reflected in the physical properties of the peat profile. [ABSTRACT FROM AUTHOR]

According to the hypotheses advanced by Wardle (1971) and Tranquillini (1979), failure of trees at their altitudinal limit is caused by poor development of the cuticle and a corresponding inability to conserve water in winter when the soil is frozen. This hypothesis was tested at a natural tree line of Scots pine in the Cairngorm mountains of Scotland. There was no sign of poor cuticular development, but needles from old krummholz at high altitudes and young isolated trees at higher altitude did lose water more rapidly than those at low altitude, over a range of water content during desiccation in the laboratory. The results are best attributed to stomatal dysfunction caused by mechanical damage to the leaf and also by direct damage to the cuticle, rather than to a thinner or less developed cuticle. Calculations show that a small increase in cuticular transpiration is quite unlikely to cause frost-drought. [ABSTRACT FROM AUTHOR]

Temperatures of terminal meristems of forest, krummholz and dwarf shrub vegetation were measured at altitudes of 450, 600, 650 and 850 m in the Cairngorm Mountains of Scotland. Simultaneously, the air temperature above the vegetation was recorded, so that it was possible to calculate the difference between meristem and air temperature, sometimes called the excess temperature. This temperature increased linearly with the net radiation absorbed at each station, and the slope was dependent on wind speed and the height of the vegetation. In the extreme cases the slopes were practically zero for forest and 0.028° C W m for dwarf shrubs. The latter implies a temperature excess of about 15° C in bright sunshine and low wind speeds. A model is developed to calculate the excess temperature from a knowledge of vegetational height and climatological variables. [ABSTRACT FROM AUTHOR]

A sediment core that spans the last c. 15 000 yr BP was raised from Elgennya Lake (62°05'N 149°00'E, 1040 m) which is located near the altitudinal forest limit in the western Annachag Mountains of the Upper Kolyma region, northeastern Siberia. Palynological data indicate the presence of a relatively unpro ductive herb-Salix tundra during full-glacial times. Although Betula shrubs first appeared in this upland valley at c. 12 100 yr BP, they probably were few in number. More significant changes in the vegetation date to c. 10 100 yr BP when Alnus shrubs, and perhaps a few Larix trees, colonized the Elgennya catchment. A Larix dahurica forest established in the valley by c. 9400 yr BP. By c. 8600 yr BP, Pinus pumila grew within the forest understorey and formed a shrub tundra beyond altitudinal tree-line. Arrival times for Betula, Alnus, Larix and Pinus differ by 400 (for both Betula and Pinus), 2500 and 2200 radiocarbon years, respectively, when compared to mid-elevation sites located in the eastern Annachag Mountains. Evidence for tree-line fluctuations, originally inferred from these eastern sites, is absent in the Elgennya record. Palaeoclimatic interpretations of the pollen data from the Upper Kolyma region suggest that both summer temperature and late fall/early winter snowfall play key roles in determining the observed palaeovegetational patterns. This relationship contrasts with the Alaskan pollen records which primarily seem to reflect changes in summer conditions. [ABSTRACT FROM PUBLISHER]

The focus of this study is the possible correlation between changes in the climate of Scandinavian and changes in solar irradiation. Reliable information about Holocene climatic change in Sweden and Norway is currently available from two main sources: the 14C dating of pine wood retrieved from above the present pine-tree limit and studies of glacier variations based on proglacial lacustrine sediments and on moraines. The reconstructed alpine tree-limit reveals that summer temperature in general was warmer during the early Holo cene than it was during the late Holocene. Superimposed on this general trend are several fluctuations of a few hundred years' duration. Relatively cold periods with a duration of the order of 300-600 years occurred frequently during the Holocene. In this paper, dates of the major climatic events are compared with an index of solar activity, the so-called δ14C anomalies. For most of the last 9000 years a good correspondence is demonstrated between the timing of cold events in Scandinavia and the timing of major δ14 C anomalies (low solar irradiation). The general Holocene cooling trend is believed to be partly a result of land uplift following deglaciation and partly a result of orbitally forced changes in irradiation. Large fluctuations in Scandinavian summer temperature can be reconciled with the pattern of climatic change presented in several recent studies in the North Atlantic region. A link between these areas could be provided by changes in the production of North Atlantic Deep Water. [ABSTRACT FROM PUBLISHER]

Changes in the distribution of sub-alpine tree species in western North America have been attributed to climatic change and other environmental stresses. These changes include tree-line fluctuations throughout the Holocene and recent invasion of sub-alpine meadows by forest. Most palaeoecological studies suggest that the tree-line was higher during a period of warmer climate approximately 9000 to 5000 BP and lower during the last 5000 years, with short periods of local tree-line advance. Recent advances in sub-alpine tree distribution can be compared with weather records, allowing an examination of relationships between tree advance and climate at a finer resolution. In general, recent sub-alpine forest advances in western North America, based on studies representing three climatic zones (maritime, Mediterranean and continental), have been associated with climatic periods favouring tree germination and growth, although factors such as fire and grazing by domestic livestock have had an impact in some areas. Limitations to tree establishment (e.g., winter snow accumulation, summer drought) vary in relative importance within each climate zone, as do predicted consequences of anthropogenic climatic change. Recent increases in establishment of sub-alpine trees may continue if climatic change alleviates the limitations to tree establishment important in each climatic zone. However, factors such as topography and disturbance may modify tree establishment on a local scale. [ABSTRACT FROM PUBLISHER]