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Seed dispersal is a key component in a plant's life cycle, allowing the colonization of new habitat and eventually enabling range shifts. For animal‐dispersed plants, the behaviour of seed‐dispersing animals has direct consequences for the fate of a seed. However, there is little empirical evidence on how individual behaviour of animals affects seed dispersal.Here we investigated the effects of individual behaviour on seed dispersal distance and location by analysing movement data of spotted nutcrackers (Nucifraga caryocatactes) during harvest and scatter‐hoarding of Swiss stone pine (Pinus cembra) seeds. To assess individual variation in seed dispersal patterns, we compared daytime hourly displacement patterns across individuals. We further identified seed caching locations of individual birds and analysed their potential for pine regeneration.We found that nutcrackers showed one of two distinct behaviours: short‐distance seed dispersal and long‐distance seed dispersal. The caching locations resulting from the two behaviours differed markedly in the regeneration potential of Swiss stone pine: seeds transported over short distances were cached at high elevations with high regeneration potential within the pine's current habitat, while seeds transported over long distances were cached at low elevations with low regeneration potential outside of the pine's habitat. The behaviours were not associated with bird body mass, relative wing length or sex.Our results emphasize that intraspecific individual behaviours of seed‐dispersing animals can have far‐reaching consequences for ecosystem functions. As a major determinant of seed dispersal dynamics, individual behaviour should be taken into account for a better understanding of ecosystem functions under current and future environmental conditions. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Swiss pine (Pinus cembra L.) is a montane Carpathian (Alpine-Carpathian) species. The modern distribution of the Swiss pine is disjunct, the two isolated areas are located in western and central Europe (Alps) and the middle and high mountains of the Carpathians. The largest areas of Swiss pine in Ukraine are preserved in the Gorgany region at the altitude of 1250‒1450 m above sea level, where it forms the upper forest line. In the Gorgany Nature Reserve, P. cembra grows in the altitude range from 1070 to 1475 m ASL. The lower boundary, in the form of individual trees, descends to 1000 m ASL, and the upper boundary rises to 1585 m ASL. To define the ecological preferences of the Swiss pine, a series of route surveys were conducted and research sites (permanent forest monitoring plots, stationary research profiles, and stationary areas for the counting of natural forest regeneration) were established. The study of the plant communities with P. cembra on the southwestern slopes of the Dzhurdzhi tract showed the dependence of the forest species composition on the altitude above sea level. The forest stands quantitative composition and productivity are also significantly influenced by slope exposure. The proportion of P. cembra in the forests on steep slopes (30‒55°) of west and north-west exposure is relatively high (from 17.1% to 49.0%). Under other conditions, the proportion of P. cembra in the stand composition gradually decreases. Swiss pine is almost completely absent on the slopes of eastern and northern exposures except for rare single trees in Pinus mugo Turra scrub on northern slopes. The forests with P. cembra are typical of sunny slopes where the available sum of active temperatures ranges between 1000° and 1400° and the average ambient temperatures from -12.2°С to +16°С. The optimal environmental conditions for the relict species P. cembra in the Dovbushanski Gorgany region are on the western slopes with a steepness of 17‒55° and southwestern and northwestern slopes with a steepness of 35°‒42°. In terms of soil fertility, oligotrophic edaphotopes with moderate moisture are optimal for the growth of Swiss pine. [ABSTRACT FROM AUTHOR]

The term 'Little Ice Age' (LIA) is classically used to define a period of repeated and extensive glacier advances during the last millennium. In the meanwhile, this term is also used to address the period of relatively low temperatures between the Medieval Climate Anomaly (MCA), or Medieval Warm Period, and present-day warming. The end of the LIA is generally set to the mid or late 1800s CE, however, the published onset dates of the LIA are more variable from the mid 1200s to the late 1500s. At Mont Miné and Morteratsch glaciers, Swiss Alps, we sampled and subsequently analysed detrital as well as in situ tree remnants from the early LIA period. At both glaciers, trees with lifespans of up to about 400 years were buried at various lateral moraine sites. The corresponding advance of both glaciers can be traced from the 1280s until the 1310s. At Morteratsch glacier, this early LIA advance phase culminated likely around 1375 CE. Evidence collected at both glaciers indicates that the ice surfaces were at least c. 12–15 m from the lateral moraine crests deposited during the maximum extent of the LIA. This suggests a similar (though very slightly weaker) magnitude than later LIA advances at our sites. The advances of Mont Miné and Morteratsch glaciers coincide with relatively cool summer temperatures from the late 1200s to the late 1300s. Taken together, the onset of the Little Ice Age in the Alps can be considered to be c. 1260 CE. The Little Ice Age was not a uniform period, but had several phases as can be derived from the records of Alpine glaciers and summer temperatures. We propose a subdivision of the LIA in the European Alps into an early (1260–1380 CE), an intermediate (1380–1575 CE) and a main (1575–1860 CE) phase. [ABSTRACT FROM AUTHOR]

Although several studies provide a broad overview of vegetation changes in the Carpathian Basin during the Holocene, stand-scale vegetation changes are lesser known because of the rarity of suitable sampling sites. In this study we investigated the sediment of a small closed-canopy site (Nagy-forrás forest hollow, 685 m a.s.l., 0.1 ha), located in the Mátra Mountains, on the north facing slope of Kékes (1014 m a.s.l.). We carried out detailed pollen, conifer stomata and plant macrofossil analyses, as well as radiocarbon dating to examine Late Glacial and Holocene dynamics of vegetation development. The site dates back to ca. 15,500 cal yr BP, when open boreal forests and wet tundra-like habitats occurred around the hollow. Closed forest cover developed around 14,600 cal yr BP, when a boreal European larch-Swiss stone pine (Larix decidua-Pinus cembra) forest surrounded the hollow. This vegetation type remained stable up to 7700 cal yr BP. We observed a hiatus between 7700 and 2710 cal yr BP, followed by a beech (Fagus sylvatica) dominated mixed temperate deciduous forest. Our results confirmed that the area was covered by a primary forest, as human influence was visible only from 175 cal yr BP. The relatively long lasting persistence of Pinus cembra in the Holocene at relatively low altitude was documented, which has never been found in Holocene sediments in the Pre-Carpathians before. We hypothesize that the north facing slope acted as a cold-stage refugium in the Early Holocene and could play the same role for the present-day beech forest that is threatened by recent climate change. [ABSTRACT FROM AUTHOR]

Widespread and locally severe foliar symptoms resembling Dothistroma Needle Blight (DNB), one of the most important infectious diseases of forest trees worldwide, were recently observed in La Sila Massif, a mountain plateau covered with native forests of Pinus nigra subsp. laricio in La Sila National Park, Southern Italy. At the same time, DNB symptoms were observed in Pinus cembra and Pinus mugo forests in the Paneveggio-Pale di San Martino Nature Park and in Val Sarentino, Northeastern Italy. Defoliation was extensive at all sites and severe on the majority of plants of affected species, both adult trees and renovation. In particular on Pinus cembra, the disease was so serious as to locally threaten the species' reproduction and survival, an unusually heavy damage on this host. Species-specific real time PCR diagnostics, recommended by EPPO, was applied to needle samples from these sites and the presence of Dothistroma septosporum was ascertained, while Dothistroma pini, the morphologically identical congeneric species causing the same disease, was not detected. The pathogen was isolated from conidiomata and species attribution was confirmed by sequencing of the ITS region. In addition, a culture independent survey based on the same molecular assays was carried out in other areas of Northern, Central and Southern Italy, where pines of various species were affected by similar symptoms, and gave negative results for both Dothistroma species. Results show that D. septosporum currently has in Italy a much larger distribution and host range than reported and is associated to life-threatening damage to native pine species growing in established populations for in situ conservation of genetic resources, which would require an update of specific conservation actions. [ABSTRACT FROM AUTHOR]

It is generally accepted that the spatial distribution of neutral genetic diversity within a species' native range mostly depends on effective population size, demographic history, and geographic position. However, it is unclear how genetic diversity at adaptive loci correlates with geographic peripherality or with habitat suitability within the ecological niche. Using exome‐wide genomic data and distribution maps of the Alpine range, we first tested whether geographic peripherality correlates with four measures of population genetic diversity at > 17,000 SNP loci in 24 Alpine populations (480 individuals) of Swiss stone pine (Pinus cembra) from Switzerland. To distinguish between neutral and adaptive SNP sets, we used four approaches (two gene diversity estimates, FST outlier test, and environmental association analysis) that search for signatures of selection. Second, we established ecological niche models for P. cembra in the study range and investigated how habitat suitability correlates with genetic diversity at neutral and adaptive loci. All estimates of neutral genetic diversity decreased with geographic peripherality, but were uncorrelated with habitat suitability. However, heterozygosity (He) at adaptive loci based on Tajima's D declined significantly with increasingly suitable conditions. No other diversity estimates at adaptive loci were correlated with habitat suitability. Our findings suggest that populations at the edge of a species' geographic distribution harbour limited neutral genetic diversity due to demographic properties. Moreover, we argue that populations from suitable habitats went through strong selection processes, are thus well adapted to local conditions, and therefore exhibit reduced genetic diversity at adaptive loci compared to populations at niche margins. [ABSTRACT FROM AUTHOR]

Climate sensitivity of populations at the margins of their distribution range is of key importance to understand species’ responses to future warming conditions. Pinus cembra is of particular interest being a typical high-elevation taxon, spread with mostly scattered populations within its actual range, but still overlooked in traditional dendrochronological researches due to low tree-ring variability and climate sensitivity. With a different approach, we analyzed time series of xylem anatomical traits, split into intra-ring sectors, and used daily climate records over 89 years (1926-2014) aiming to improve the quality and time resolution of the climate/growth associations. From nine trees growing at their altitudinal limit and on 1.5 × 106 tracheids, we measured ring width (MRW), cell number per ring, lumen area (LA), and cell-wall thickness (CWT). We then computed correlations with monthly and fortnightly climate data. Late-spring and summer temperature emerged as the most important factors. LA and especially CWT showed a stronger temperature response than MRW, starting in mid-May and early June, respectively. CWT also evidenced the longest period of correlations with temperature and a significant difference between latewood radial and tangential walls. Analysis of xylem anatomical traits at intra-ring level and the use of daily temperature records proved to be useful for high resolution and detailed climate/growth association inferences in Pinus cembra. [ABSTRACT FROM AUTHOR]

Abstract: Fungi are both agents of disease and mutualistic partners of plants. Previous studies have tested the effects of abiotic or biotic factors on plant‐associated fungal communities in isolation. However, to better understand patterns of plant–fungal associations, the combined effects of abiotic and biotic drivers across environmental gradients may be important. We investigated the effects of temperature, pH, soil moisture, vegetation cover and distance to host plant on the occurrence and abundance of fungi associated with Swiss stone pine (Pinus cembra). We did this by DNA metabarcoding 288 soil samples taken across and beyond the elevation range of P. cembra (i.e. 1,850–2,250 m a.s.l.) in two valleys in the Swiss Alps. We modelled the effects of abiotic and biotic factors on DNA read abundance of pathogenic and mutualistic fungal operational taxonomic units (OTUs) associated with P. cembra. We also tested whether abiotic and biotic factors differentially affected fungi of varying host specificity (i.e. host generalists, host specialists). We found that the occurrences of both host generalist and specialist fungi exceeded the current elevational range of their host plant. Abiotic factors had only minor effects on the abundances of all fungal OTUs. However, we found positive effects of the host plant on the abundance of a host specialist pathogenic fungus, providing support for a Janzen–Connell effect of high pathogen accumulation close to conspecific host plants. We also found a positive response to the host plant in a specialist ectomycorrhizal fungus, suggesting an “inverse” Janzen–Connell effect. Synthesis. Our findings imply that negative distance dependence shapes not only the distribution of host‐specific fungal pathogens, but also host‐specific fungal mutualists. We conclude that the occurrence of both pathogenic and mutualistic fungi beyond the current elevational range of host plants may determine their potential range shifts under projected climate warming. [ABSTRACT FROM AUTHOR]

In alpine regions, tree hydraulics are limited by low temperatures that restrict xylem growth and induce winter frost drought and freezing stress. While several studies have dealt with functional limitations, data on elevational changes in functionally relevant xylem anatomical parameters are still scarce. In wood cores of Pinus cembra L. and Picea abies (L.) Karst. trunks, harvested along five elevational transects, xylem anatomical parameters (tracheid hydraulic diameter dh, wall reinforcement (t/b)2), pit dimensions (pit aperture Da, pit membrane Dm and torus Dt diameters) and respective functional indices (torus overlap O, margo flexibility) were measured. In both species, tracheid diameters decreased and (t/b)² increased with increasing elevation, while pit dimensions and functional indices remained rather constant (P. cembra: Dt 10.3 ± 0.2 μm, O 0.477 ± 0.005; P. abies: Dt 9.30 ± 0.18 μm, O 0.492 ± 0.005). However, dh increased with tree height following a power trajectory with an exponent of 0.21, and also pit dimensions increased with tree height (exponents: Dm 0.18; Dt 0.14; Da 0.11). Observed elevational trends in xylem structures were predominantly determined by changes in tree size. Tree height-related changes in anatomical traits showed a remarkable robustness, regardless of the distributional ranges of study species. Despite increasing stress intensities towards the timberline, no adjustment in hydraulic safety at the pit level was observed. [ABSTRACT FROM AUTHOR]

Treeline position is mainly determined by growth season temperature, but the response of treelines to climate warming is not uniform worldwide. We compared treeline structure, dynamics and thermal profile in nearby areas with different treeline type, species composition and bioclimatic conditions. We performed a detailed survey of different treeline types in three areas of Italian Alps and northern Apennines. Every tree individual was recorded along altitudinal transects from the closed forest to the species limit. Treeline structure and dynamics were described through altitudinal limits of tree height, density and age. Data were elaborated by principal components analysis. Temperature regime of the three sites was assessed from homogeneous historical climatic data. Treeline was different in the three areas for species composition, shape and dynamics. Both Alpine sites showed diffuse treeline, but only one showed advancing dynamics. Apennine treeline was abrupt and static, with higher temperature at the tree limit. Our study showed the variable dynamics of treelines within a relatively restricted area and the connection between treeline shape and dynamics. An important role is played by species composition, determined by bioclimatic and historical features. These factors should be taken into account when modelling future treeline dynamics at global scale. [ABSTRACT FROM AUTHOR]

[Display omitted] • Summer temperature remained a key factor affecting the growth of Swiss stone pine. • Summer precipitation is not the main factor limiting the growth of Swiss stone pine now. • The climate-growth relationship in stone pine is not stable over time. • Small-scale disturbances on cliffs have randomly affected trees over the last centuries. • The disturbance regime cannot be linked to any specific climatic extremes in the Tatras. Tree rings are an ecological indicator, useful for studying the adaptation of trees in a changing environment, especially in the unique habitat of high-elevation cliff forests. The main aim of this study was to characterize tree-ring changes in Stone pine (Pinus cembra L.) growing in the extreme conditions of cliff forests of the Western Carpathians (at elevation 1300–1600 m a.s.l.), in order to reconstruct the growth release pattern and to better understand the influence of climate. The study was based on 104 tree ring series covering a 449-year-long chronology (1561–2009). In the last century, mean annual temperature has increased by +2.0 °C and precipitation has decreased slightly in the Tatras. The growth of stone pine was strongly related to summer temperature of June and July. In the last decades, the negative influence of summer precipitation on tree growth has abated; this may be related to warmer summers and decreasing precipitation. Temperature of the previous autumn, winter, and early spring, which had a significant influence on stone pine growth in the past, is not an important factor now. In the extreme environment of mountain cliffs, the influence of temperature and precipitation on tree growth is not stable over time under changing climate. The current changes in climate seem to promote stone pine and its potential upward elevational shift. The numerous past disturbance events have affected a limited number of trees, suggesting that single individuals have been randomly eliminated from the cliff stands during the last three centuries. Our results highlight the complex pattern of the reaction of stone pine on cliffs to changes in the environment. Swiss stone pine, a long-lived tree species, shows high adaptability for colonization of mountain cliffs and is an excellent object for studying the response of plants to changing climate. Understanding the effect of interactions between climate, disturbances, and the radial growth of trees in extreme environments of cliff forests on different temporal scales (monthly, seasonal, yearly) should increase our knowledge of such ecologically valuable areas. [ABSTRACT FROM AUTHOR]

Holocene glacier records from the western European Alps are still sparse, although a number of sites are well suited to constraining pre- and early- Little Ice Age (LIA) glacier advances. The present study provides the first dendrochronologically-based and calendar-dated Neoglacial glacier chronology for the Mont Blanc massif, French Alps. It is based on the analysis of over 240 glacially buried Pinus cembra subfossil logs and wood remains found either embedded-in-till or as detrital material in the Mer de Glace right lateral moraine. Only a few of the samples were found to be ‘formally in situ ’ but we show that some logs were ‘virtually in situ ’ (not rooted but showing little or no evidence of reworking) and could be used to accurately reconstruct past glacier margin behavior in space and time. Uncertainties regarding the other samples may relate to original growth location and/or to outer wood decay. The resulting dates (followed by a ‘+’) were therefore considered maximum-limiting ages for glacier advances. The main burial events – interpreted as glacier advances – occurred between ca 1655+ and 1544+ BC, between ca 1230+ and 1105+ BC, between ca 1013+ and 962+/937+ BC, at ca 802–777 BC, after 608+ BC, between 312 and 337 AD, between ca 485+ AD and 606+ AD, between 1120 and 1178 AD, between ca 1248 and 1278+/1296 AD, and after 1352+ AD. These advances predate the late LIA maxima known from historical sources. The magnitude of the advances gradually increased to culminate in three near-Neoglacial maxima during the 7th, 12th and 13th centuries AD, followed by a first LIA/Neoglacial maximum in the second half of the 14th century AD. The pattern of Neoglacial events described here is coherent with Central and Eastern Alpine glacier chronologies. This indicates marked synchronicity of late Holocene glacier variability and forcing at a regional scale, although occasional differences could be detected between ‘Western’ and ‘Eastern’ records. The Mer de Glace record also confirms the link between the timing of sediment erosion in a high-elevation glaciated Alpine catchment and subsequent deposition in the sub-alpine Lake Bourget. [ABSTRACT FROM AUTHOR]

Many animals hoard seeds for later consumption and establish seed caches that are often located at sites with specific environmental characteristics. One explanation for the selection of non-random caching locations is the avoidance of pilferage by other animals. Another possible hypothesis is that animals choose locations that hamper the perishability of stored food, allowing the consumption of unspoiled food items over long time periods., We examined seed perishability and pilferage avoidance as potential drivers for caching behaviour of spotted nutcrackers ( Nucifraga caryocatactes) in the Swiss Alps where the birds are specialized on caching seeds of Swiss stone pine ( Pinus cembra)., We used seedling establishment as an inverse measure of seed perishability, as established seedlings cannot longer be consumed by nutcrackers. We recorded the environmental conditions (i.e. canopy openness and soil moisture) of seed caching, seedling establishment and pilferage sites., Our results show that sites of seed caching and seedling establishment had opposed microenvironmental conditions. Canopy openness and soil moisture were negatively related to seed caching but positively related to seedling establishment, i.e. nutcrackers cached seeds preferentially at sites where seed perishability was low. We found no effects of environmental factors on cache pilferage, i.e. neither canopy openness nor soil moisture had significant effects on pilferage rates. We thus could not relate caching behaviour to pilferage avoidance., Our study highlights the importance of seed perishability as a mechanism for seed-caching behaviour, which should be considered in future studies. Our findings could have important implications for the regeneration of plants whose seeds are dispersed by seed-caching animals, as the potential of seedlings to establish may strongly decrease if animals cache seeds at sites that favour seed perishability rather than seedling establishment. [ABSTRACT FROM AUTHOR]

Whole-tree water use of nine Pinus cembra trees was estimated in the treeline ecotone of the Central Austrian Alps. Sap flow density using Granier-type thermal dissipation probes and environmental parameters was monitored along an elevational gradient from the forest limit up to treeline and finally mediating the krummholz limit throughout two growing seasons. Normalized sap flow density ( Q) was significantly correlated with solar radiation ( R) and vapor pressure deficit ( D) throughout the treeline ecotone. Multiple regression analysis indicated that at the forest limit and at treeline, D had a similar effect on Q than R. At the krummholz limit by contrast, D had a greater effect on Q than R due to partially stomatal closure and wind-induced clustering of the needles, which impaired their response to available irradiance. Whole-tree water use scaled to crown surface area estimated for an entire growing (172 days) declined from 449 mm at the forest limit to 274 mm at treeline and was 251 mm at the krummholz limit, which is within the values estimated for other European forest ecosystems. Nevertheless, the observation above the forest limit in the central Tyrolean Alps tree transpiration scaled to crown surface area is comparable to the water use of adjacent low-stature vegetation, which should also be taken into account when forecasting potential effects of global change on the water balance of the treeline ecotone. [ABSTRACT FROM AUTHOR]

Tree-ring series from a single site and a single species were used as proxies to reconstruct past summer temperatures over 550 years in the Eastern Carpathian Mountains. The chronology was built using standard procedures in order to provide comparable information about this under-sampled region while preserving the low-frequency signals. The studied site offered abundant samples of both living trees and dead wood, which were carefully selected in order to minimize heterogeneity sources owing to a reduced availability of suitable material as e.g. in the Alps. The ring-width chronology spanned over 550 years with satisfying replication and showed an even segment length. The chronology correlated to temperature over quite a narrow window, temperatures of June and July only being significant. The reconstruction showed that the last 180 years was the warmest period with only three short episodes of anomalies. We present evidence that the summer temperatures in the Eastern Carpathian Mountains showed divergences as compared to the Alps and a clear regionality, the coolest period over the last 600 years occurring during 1720-1850. [ABSTRACT FROM AUTHOR]

Recent studies on non-structural carbohydrate (NSC) reserves in trees focused on xylem NSC reserves, while still little is known about changes in phloem carbohydrate pools, where NSC charging might be significantly different. To gain insight on NSC dynamics in xylem and phloem, we monitored NSC concentrations in stems and roots of Pinus cembra (L.) and Larix decidua (Mill.) growing at the alpine timberline throughout 2011. Species-specific differences affected tree phenology and carbon allocation during the course of the year. After a delayed start in spring, NSC concentrations in L. decidua were significantly higher in all sampled tissues from August until the end of growing season. In both species, NSC concentrations were five to seven times higher in phloem than that in xylem. However, significant correlations between xylem and phloem starch content found for both species indicate a close linkage between long-term carbon reserves in both tissues. In L. decidua also, free sugar concentrations in xylem and phloem were significantly correlated throughout the year, while a lack of correlation between xylem and phloem free sugar pools in P. cembra indicate a decline of phloem soluble carbohydrate pools during periods of high sink demand. [ABSTRACT FROM PUBLISHER]

Background and Aims The most plausible explanation for treeline formation so far is provided by the growth limitation hypothesis (GLH), which proposes that carbon sinks are more restricted by low temperatures than by carbon sources. Evidence supporting the GLH has been strong in evergreen, but less and weaker in deciduous treeline species. Here a test is made of the GLH in deciduous–evergreen mixed species forests across elevational gradients, with the hypothesis that deciduous treeline species show a different carbon storage trend from that shown by evergreen species across elevations. Methods Tree growth and concentrations of non-structural carbohydrates (NSCs) in foliage, branch sapwood and stem sapwood tissues were measured at four elevations in six deciduous–evergreen treeline ecotones (including treeline) in the southern Andes of Chile (40°S, Nothofagus pumilio and Nothofagus betuloides; 46°S, Nothofagus pumilio and Pinus sylvestris) and in the Swiss Alps (46°N, Larix decidua and Pinus cembra). Key Results Tree growth (basal area increment) decreased with elevation for all species. Regardless of foliar habit, NSCs did not deplete across elevations, indicating no shortage of carbon storage in any of the investigated tissues. Rather, NSCs increased significantly with elevation in leaves (P < 0·001) and branch sapwood (P = 0·012) tissues. Deciduous species showed significantly higher NSCs than evergreens for all tissues; on average, the former had 11 % (leaves), 158 % (branch) and 103 % (sapwood) significantly (P < 0·001) higher NSCs than the latter. Finally, deciduous species had higher NSC (particularly starch) increases with elevation than evergreens for stem sapwood, but the opposite was true for leaves and branch sapwood. Conclusions Considering the observed decrease in tree growth and increase in NSCs with elevation, it is concluded that both deciduous and evergreen treeline species are sink limited when faced with decreasing temperatures. Despite the overall higher requirements of deciduous tree species for carbon storage, no indication was found of carbon limitation in deciduous species in the alpine treeline ecotone. [ABSTRACT FROM PUBLISHER]

Abstract: The integrated stratigraphic, radiocarbon and palynological record from an end-moraine system of the Oglio valley glacier (Italian Alps), propagating a lobe upstream in a lateral reach, provided evidence for a complete cycle of glacial advance, culmination and withdrawal during the Last Glacial Maximum and early Lateglacial. The glacier culminated in the end moraine shortly after 25.8 ± 0.8 ka cal BP, and cleared the valley floor 18.3–17.2 ± 0.3 ka cal BP. A primary paraglacial phase is then recorded by fast progradation of the valley floor. As early as 16.7 ± 0.3 ka cal BP, early stabilization of alluvial fans and lake filling promoted expansion of cembran pine. This is an unprecedented evidence of direct tree response to depletion of paraglacial activity during the early Lateglacial, and also documents the cembran pine survival in the mountain belt of the Italian Alps during the last glaciation. Between 16.1 and 14.6 ± 0.5 ka cal BP, debris cones emplacement points to a moisture increase favouring tree Betula and Pinus sylvestris-mugo. A climate perturbation renewed paraglacial activity. According to cosmogenic ages on glacial deposits and AMS radiocarbon ages from lake records in South-Eastern Alps such phase compares favourably with the Gschnitz stadial and with the oscillations recorded at lakes Ragogna, Längsee and Jeserzersee, most probably forced by the latest freshening phases of the Heinrich Event 1. A further sharp pine rise marks the subsequent onset of Bølling interstadial. The chronology of the Oglio glacier compares closely with major piedmont glaciers on the Central and Eastern Alpine forelands. On the other hand, the results of the present study imply a chronostratigraphic re-assessment of the recent geological mapping of the Central Italian Alps. [Copyright &y& Elsevier]

The chemical composition of essential oil samples from needles of six species of five-needle pines ( Pinus pumila, Pinus sibirica, Pinus parviflora, Pinus armandii, Pinus koraiensis, and Pinus cembra) and one natural interspecific hybrid Pinus sibirica × Pinus pumila has been studied by the chromato-mass spectrometry method. Essential oils have been prepared by simultaneous steam distillation-extraction. The analysis of the samples' composition showed that the main constituents of the essential oils were the following mono- and sesquiterpenic compounds: α-pinene (5-63%), camphene (0.7-3.6%), β-pinene (0.7-7%), β-myrcene (0.5-3.4%), 3-carene (0-16%), limonene (0.6-7.9%), β-phellandrene (0.7-5.3%), terpinolene (0.4-6.7%), bornyl acetate (0.2-12%), α-terpenyl acetate (0-4.6%), caryophyllene (0.4-24%), humulene (0.1-4%), germacrene D (0.1-24%), bicyclogermacrene (0.1-3.6%), γ-cadinene (0.9-2.3%), δ-cadinene (2.2-6.1%), germacrene D-4-ol (0-6.8%), T-cadinol (0.7-2.9%), and α-cadinol (0.7-6.0%). [ABSTRACT FROM AUTHOR]

In low temperature-adapted plants, including treeline trees, light-saturated photosynthesis is considerably less sensitive to temperature than growth. As a consequence, all plants tested so far show increased nonstructural carbohydrate (NSC) tissue concentrations when exposed to low temperatures. Reduced carbon supply is thus an unlikely cause for low temperature range limits of plants. For altitudinal treeline trees there is, however, a possibility that high NSC genotypes have been selected., Here, we explored this possibility using afforestations with single-provenance conifers along elevational gradients in the Southern Chilean Andes and the Swiss Alps., Tree growth was measured at each of four approximately equidistant elevations at and below the treeline. Additionally, at the same elevations, needle, branch and stem sapwood tissues were collected to determine NSC concentrations., Overall, growth decreased and NSC concentrations increased with elevation. Along with previous empirical and experimental studies, the findings of this study provide no indication of NSC reduction at the treeline; NSC increased in most species (each represented by one common population) towards their upper climatic limit. The disparity between carbon acquisition and structural carbon investment at low temperature (accumulation of NSC) thus does occur even among genotypes not adapted to treeline environments. [ABSTRACT FROM AUTHOR]

An appropriate bioproxy is required to decipher Holocene tree biomass dynamics from the stand scale in relation to local processes such as disturbance or global climate change. Here we used plant litter collected in traps placed in subalpine forests, and data on the surrounding stands, to develop calibration equations for converting the observed macroremain accumulation rates to tree biomass (basal area) values. The needle accumulation rate (NAR) was modeled for Larix decidua and Pinus cembra. We then used the calibration equation developed from the trapped macroremains to reconstruct past tree biomass for sedimentary Holocene series from two subalpine lakes in the Alps. Our data show that NAR is significantly correlated with basal area. We found a clear overrepresentation of L. decidua NAR compared with its real basal area. This distortion potentially masks the occurrence of P. cembra, another important functional species of subalpine ecosystems, when macroremains are not calibrated. Without calibration, the use of NAR to describe past plant biomass always leads to an overestimation of L. decidua biomass and an underestimation of P. cembra biomass. Several shifts between the dominance of the two species, which were masked when using unadjusted NAR, were apparent and occurred at both sites. By comparing the reconstructed basal areas with fire frequencies, we found that P. cembra biomass accumulation preceded the increase of fire frequency and that fire frequencies superior to 0.0085 fire/yr could induce a long-term loss of resilience of cembra pine forest to the benefit of larch. This results to a slight dominance of Larix biomass from 2500 to 2000 cal. BP until the present day at the two sites. Our results provide increased understanding of tree biomass dynamics associated with specific vegetation phases, and shifts in dominant species, and highlight the needs to understand the causes of these shifts and identify how such processes are related to local environmental conditions. [ABSTRACT FROM AUTHOR]

Background and Aims: In contrast to the wealth of information on sap flow characteristics of forest trees at low-elevation sites, knowledge is scarce for trees within the treeline ecotone. Thus, our aim was to identify environmental controls on water loss in P. cembra trees at the treeline. Methods: Three isolated individuals were equipped with thermal dissipation probes for monitoring sap flow density (QS ). A Jarvis-type model and multiple linear regression, with irradiance and vapour pressure deficit as explanatory variables, were applied to compare predicted and measured sap flow density. Results: Both models successfully predicted measured QS . The Jarvis model tended to underestimate QS values by 25% on average, as compared with an underestimate of 8% by multiple linear regression analysis. The multiple linear regression analysis also allowed discrimination between effects of irradiance (RS ) and vapour pressure deficit (D) on QS , indicating that RS (ß-coefficient = 0.70) had a greater effect on QS than D (ß-coefficient = 0.25). Whole-tree water loss scaled to ground surface area (1.9 ± 0.5 mm d−1) was within the range reported for adjacent low-stature vegetation. Conclusions: The results suggest that the multiple linear regression approach is superior to the non-linear Jarvis-type model, as this approach allows discrimination between the effects of RS and the effects of D on QS . [ABSTRACT FROM PUBLISHER]

Understanding the interplay between environmental factors contributing to treeline formation and how these factors influence different life stages remains .a major research challenge. We used an afforestation experiment including 92 000 trees to investigate the spatial and temporal dynamics of tree mortality and growth at treeline in the Swiss Alps. Seedlings of three high-elevation conifer species (Larix decidua, Pinus mugo ssp. uncinata, and Pinus cembra) were systematically planted along an altitudinal gradient at and above the current treeline (2075 to 2230 m above sea level [a.s.l.]) in 1975 and closely monitored during the following 30 years. We used decision-tree models and generalized additive models to identify patterns in mortality and growth along gradients in elevation, snow duration, wind speed, and solar radiation, and to quantify interactions between the different variables. For all three species, snowmelt date was always the most important environmental factor influencing mortality, and elevation was always the most important factor for growth over the entire period studied. Individuals of all species survived at the highest point of the afforestation for more than 30 years, although mortality was greater above 2160 m a.s.l., 50-100 m above the current treeline. Optimal conditions for height growth differed from those for survival in all three species: early snowmelt (ca. day of year 125-140 [where day 1 is 1 January]) yielded lowest mortality rates, but relatively later snowmelt (ca. day 145-150) yielded highest growth rates. Although snowmelt and elevation were important throughout all life stages of the trees, the importance of radiation decreased over time and that of wind speed increased. Our findings provide experimental evidence that tree survival and height growth require different environmental conditions and that even small changes in the duration of snow cover, in addition to changes in temperature, can strongly impact tree survival and growth patterns at treeline. Further, our results show that the relative importance of different environmental variables for tree seedlings changes during the juvenile phase as they grow taller. [ABSTRACT FROM AUTHOR]

As an efficient seed-disperser, Eurasian nutcrackers (Nucifraga caryocatactes) generally consume and hoard mature, edible pine seeds for future use. In 2009, when the Arolla pine, Pinus. cembra, produced a mast-crop, we investigated cones discarded by nutcrackers. Most cones were only partly eaten and some mature seeds remained in the distal part. This was in contrast to years of lower seed production when nearly all seeds were harvested from the majority of cones. To determine whether nutcracker cone-discarding behaviour maximised intake rate, seed kernels and the aborted seeds rate were measured from the different cone parts. In 2009, seeds from cone-tops were on average 17% lighter than in the base and middle sections, and the proportion of aborted seeds in the top part was 81% higher than in the other sections. There was no difference in seed mass and proportion of aborted seeds in cone-tops of intact cones and cones handled by nutcrackers. Regarding each cone as a patch, cone discarding behaviour can be considered as an optimal cone-leaving rule, maximising rate of energy-intake, supporting the Marginal Value Theorem. Hence, we suggest that increased food abundance leads to more selective seed harvesting in nutcrackers. [ABSTRACT FROM AUTHOR]

Abstract: This paper examines fourteen fossil pollen datasets from Romania. It aims to investigate the temporal and spatial variability in the range distribution and abundance of three forest taxa, Pinus, Picea abies, and Quercus, during the Holocene. This is essential for understanding their current status in the forests of Eastern Europe, the conditions under which they arose, and the timing and processes responsible for their variability. Results from this synthesis do not indicate any apparent time lag in the establishment of Pinus diploxylon type (Pinus sylvestris and Pinus mugo), Pinus cembra, P. abies, and Quercus across Romania within the limits of the dating resolution. However, the onset of the mass expansion of P. abies was not uniform, spreading earlier from sites in the western and north-western Carpathians (11,000–10,500 yr BP) than in the east (10,000 yr BP). We found that sites from the western, north-western, and northern Carpathians contained higher abundances of P. abies, whilst Quercus was in higher abundances in sites from the east, but there was no regional distinctiveness in the abundance of Pinus across the study area. However, P. diploxylon type was found in much higher abundance than P. cembra. Additionally, results indicate a greater proportion of Pinus (mainly P. diplxylon type) at high elevations, P. abies at mid to high elevations, and Quercus at low elevations (<500 m). The dominance of Pinus in the early Holocene boreal forest is likely the legacy of its local glacial refugia, fast life history strategies, high stress tolerance, and large habitat availability. In contrast, Pinus exhibited poor competitive abilities and was quickly replaced with P. abies and temperate deciduous taxa after 10,500 yr BP. P. abies has persisted in large abundances at higher elevations (above 1000 m) until the present day, as a result of good competitive abilities, and resilience to climate change and disturbance. The long-term dominance of P. abies appears to have been spatially constrained, as populations below ca 1000 m were replaced by Fagus sylvatica from ca 4000 years ago, Recently, Pinus (mainly P. sylvestris) and P. abies have both experienced range expansions a consequence of forest management. Quercus is the only continental deciduous tree that has maintained high abundance throughout the whole Holocene. Members of this genus demonstrated high resilience to climate change and disturbance; following a period of decline it was capable of recovery during subsequent intervals of warm conditions or disturbance. [Copyright &y& Elsevier]

This paper presents and discusses the use of soil charcoal analysis (pedoanthracology) to reconstruct past forest dynamics in a larch forest of the upper Guil valley (French Alps, Queyras). We also discuss the role of anthropogenic fire in forest dynamics. The radiocarbon dates from this site demonstrate that arolla pine (Pinus cembra) and larch were present in the area since 7566-7673 cal. BP and 5934-6123 cal. BP, respectively. The identification of a piece of charcoal to fir (Abies alba) dated to 5734-5908 cal. BP suggests that this species was present at 1980 m a.s.l. since c. 6000 cal. BP and had a higher ecological tolerance than previously assumed. The cover of larch forests has increased since the second half of the Holocene because of anthropogenic practices (eg, clearing with fire, cattle grazing). However, today, owing to the abandonment of pastoral practices, the arolla pine has become dominant, which greatly modifies the forest structure and the landscape. [ABSTRACT FROM AUTHOR]

High altitude alpine ecosystems are likely to be highly sensitive to future climate change. Understanding long-term tree stand dynamics may be a key requirement for forecasting such changes. Here, we present a high resolution record of paleobotanical macroremains covering the last 11 700 years, from a small subalpine pond situated in the inner French Alps, at 2035 m a.s.l. The early presence of larch (Larix decidua), arolla pine (Pinus cembra) and birch (Betula) at this elevation, just after the end of the Younger Dryas cold transition, suggests the occurrence of either glacial tree-refugia located nearby in the northwestern Alps, or a previously unrecorded early and rapid tree migration. The 8200 cal. BP cooling event is characterized by a rapid and limited expansion of mountain pine (Pinus mugo/uncinata type).Mixed stands of larch, birch and arolla pine established at 8300 cal. BP and were present through the mid Holocene. After the Holocene climatic optimum, at 5600 cal. BP, recurrent fires led to the development of highly dynamic and more diversified forests, with larch, birch, arolla pine, mountain pine and fir (Abies alba). Natural and anthropogenic disturbances, e.g., fires, avalanches, slash-and-burn and other agricultural practices, influenced subsequent vegetation until the last millennium when tree-pasture established around the lake. The data indicate that the vegetation was progressively dominated by open larch woodland from 4000 years ago, and was clearly established during the Middle Ages (1250 cal. BP) up to the nineteenth century, when land began to be abandoned. The modern vegetation, dominated by larch and arolla pine and resulting from land abandonment, tends to resemble the communities that occurred from 8300 to 4000 cal. BP, before the postulated anthropogenic alteration of subalpine forest ecosystems. The plant macroremains analysis provides a unique and precise record of stand-to-local vegetation composition and dynamics that can bridge paleoecology and forest management. [ABSTRACT FROM AUTHOR]

The study presented here from the southern French Alps demonstrates the reliability of soil charcoal analysis for the study of Holocene past treeline positions. The occurrence of charcoal in mineral soils along transects from 1950 m up to 2920 m demonstrates the role of fire in the establishment of the present vegetation patterns. The abrupt decrease of charcoal concentration at about 2400-2600 m (which varies across the study sites) corresponds to the modern transition between subalpine forest and alpine tundra. Charcoal particles formed in situ provide high spatial-resolution data for the reconstruction of past forest and treeline changes. Soil charcoal analysis indicated that: (1) treeline was 300 m higher around 6800 cal. BP than today; and (2) the uppermost forest belt up to 2810 m was colonized by larch (Larix decidua Mill.) and arolla pine (Pinus cembra L.). This pine is present today but patchily distributed: it is absent from the three areas studied. Radiocarbon dates, ranging from c. 6800 cal. BP to the modern period, along with historical and archaeological data, suggest that the present pattern of the uppermost forest belt, and the patchy distribution of arolla pine in the studied area are the results of anthropogenic fire (mainly agropastoral activities). The question of global warming consequences on treelines in this part of the French Alps is discussed. [ABSTRACT FROM AUTHOR]

Background and Aims: High elevation treelines occur worldwide at similar mean growing season temperatures. Does this result from direct impact of low temperature on growth or carbon metabolism, or does nutrient limitation, induced by low soil temperature, play a role? Similar treeline elevations at contrasting soil fertility argue against the latter, but the actual nutritional status of treeline trees (here addressed as foliage nitrogen concentration) has never been assessed systematically. Although needle nitrogen (N) concentration does not necessarily indicate growth limitation by N, the relative abundance of N would indicate obvious depletions at the treeline. Methods: A central problem with any foliage nutrient assay is that the units for describing the element concentration are dependent on elevation themselves. Here we separate changes in N per unit tissue from changes in reference units. Results: Needles of Pinus cembra and Picea abies in the Alps do not show elevational differences in N concentration per dry weight, water content, area or volume, thus, there is no N depletion near the elevational tree limit. Hence, nutrient supply is either unaltered, or growth is adjusted so that nutrient depletion in needle tissue does not occur. Conclusions: Chronic N shortage at needle level is not an explanation for low tree vigour at the treeline. [ABSTRACT FROM AUTHOR]

Tree-ring width, wood density, anatomical structure and 13C/12C ratios expressed as δ13C-values of whole wood of Picea abies were investigated for trees growing in closed canopy forest stands. Samples were collected from the alpine Renon site in North Italy, the lowland Hainich site in Central Germany and the boreal Flakaliden site in North Sweden. In addition, Pinus cembra was studied at the alpine site and Pinus sylvestris at the boreal site. The density profiles of tree rings were measured using the DENDRO-2003 densitometer, δ13C was measured using high-resolution laser-ablation-combustion-gas chromatography-infra-red mass spectrometry and anatomical characteristics of tree rings (tracheid diameter, cell-wall thickness, cell-wall area and cell-lumen area) were measured using an image analyzer. Based on long-term statistics, climatic variables, such as temperature, precipitation, solar radiation and vapor pressure deficit, explained <20% of the variation in tree-ring width and wood density over consecutive years, while 29–58% of the variation in tree-ring width were explained by autocorrelation between tree rings. An intensive study of tree rings between 1999 and 2003 revealed that tree ring width and δ13C-values of whole wood were significantly correlated with length of the growing season, net radiation and vapor pressure deficit. The δ13C-values were not correlated with precipitation or temperature. A highly significant correlation was also found between δ13C of the early wood of one year and the late wood of the previous year, indicating a carry-over effect of the growing conditions of the previous season on current wood production. This latter effect may explain the high autocorrelation of long-term tree-ring statistics. The pattern, however, was complex, showing stepwise decreases as well as stepwise increases in the δ13C between late wood and early wood. The results are interpreted in the context of the biochemistry of wood formation and its linkage to storage products. It is clear that the relations between δ13C and tree-ring width and climate are multi-factorial in seasonal climates. [ABSTRACT FROM AUTHOR]

Aim To characterize the genetic structure and diversity of Pinus cembra L. populations native to two disjunct geographical areas, the Alps and the Carpathians, and to evaluate the rate of genetic differentiation among populations. Location The Swiss Alps and the Carpathians. Methods We screened 28 populations at three paternally inherited chloroplast simple sequence repeats (cpSSRs) for length variation in their mononucleotide repeats. Statistical analysis assessed haplotypic variation and fixation indices. Hierarchical analysis of molecular variance (AMOVA), Mantel test, spatial analysis of molecular variance (SAMOVA) andbarrier analyses were applied to evaluate the geographical partitioning of genetic diversity across the species’ range. Results Haplotypic diversity was generally high throughout the natural range of P. cembra, with the mean value substantially higher in the Carpathians ( H = 0.53) than in the Alps ( H = 0.35). The isolated Carpathian populations showed the highest haplotype diversity among the populations originating from the High Tatras (Velka Studena Dolina) and South Carpathians (Retezat Mountains). AMOVA revealed that only 3% of the total genetic variation derived from genetic differentiation between the two mountain ranges. Differentiation among Carpathian populations was higher ( FST = 0.19) than among Alpine populations ( FST = 0.04). Low, but significant, correlation was found between the geographical and genetic distances among pairs of populations ( r = 0.286, P < 0.001). SAMOVA results revealed no evident geographical structure of populations.barrier analysis showed the strongest differentiation in the eastern part of the species’ range, i.e. in the Carpathians. Main conclusions The populations of P. cembra within the two parts of the species’ range still share many cpDNA haplotypes, suggesting a common gene pool conserved from a previously large, continuous distribution range. Carpathian populations have maintained high haplotypic variation, even higher than Alpine populations, despite their small population sizes and spatial isolation. Based on our results, we emphasize the importance of the Carpathian populations of Swiss stone pine for conservation. These populations comprise private haplotypes and they may represent a particular legacy of the species’ evolutionary history. [ABSTRACT FROM AUTHOR]

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]

1. Changes in the frequency and intensity of disturbances are expected to occur during the coming decades as a consequence of climatic changes. Mountain forests are sensitive to climate variability, disturbances and changes in human activities; this is particularly true for subalpine forests located close to the limits of tree-growth. Here we test the role of surface fires on the structure and the dynamics of a subalpine forest compared to a control stand not affected by fire events for at least two centuries. 2. The fire events are deduced from fire scars, the age-structure from tree-ring counting, regeneration from sapling and seedling counts, necromass from the volume of woody debris, and the understorey structure from shrub and herb cover, height and biomass. Land-use history is assessed from livestock and human inventories. 3. Four surface fires occurred during the last 200 years in the burned stand. Tree density is greater in the burned stand, and, even 50 years after the last fire, burning could still be having a positive effect on regeneration density. Land-use history, mainly grazing by cattle and sheep, explains the modern forest structure through its promotion of Larix decidua. The understorey composition is the same within the two stands, suggesting a rapid recovery of dwarf shrubs ( Rhododendron ferrugineum and Vaccinium myrtillus) after the latest fire, which coincided with the final change in land-use. The exception is V. vitis-idaea cover, which is higher in the control stand. The removal of livestock in the 1940s indirectly triggered a decline in L. decidua regeneration, which was formerly promoted by grazing and trampling. Conversely, Pinus cembra seedlings have begun to establish during the last 70 years. 4. Synthesis. Expansion of forests dominated by P. cembra is expected during the 21st century, unless current global warming leads to a significant and lethal increase in fire frequency, that is, a reduction of fire-return intervals, which would reduce the number of sexually mature trees. The re-introduction of grazing could maintain the mixed subalpine forests, whereas surface fires would alter the woody debris load, promoting greater regeneration of L. decidua and P. cembra. [ABSTRACT FROM AUTHOR]

Xylem conduits increase in size from the apex downwards. While conduit tapering in the stem has often been reported to converge towards a common pattern among all plants, information on conduit tapering in small plants and roots is extremely scarce. We selected 10 small trees (height < 3 m) of Pinus cembra L. and Larix decidua Miller along an altitudinal gradient and measured diameter and conduit dimensions along stems and roots in the last annual ring. Sections of 10 µm were cut from wooden disks taken at different heights in the stem and in the roots and then stained with safranine. Slides were observed under a microscope, the lumen areas of conduits were measured and mean hydraulic diameters (Dh) calculated. Dh increased from stem tip (Dh at 1 cm from the apex averaged 10.75 µm; s = 2.33) to base (Dh from 20.70 to 30.54 µm), following a power trajectory (i.e., Dh = a·Lb, with L being the distance from the tip). Such degrees of conduit tapering may have a considerable effect in minimizing the hydraulic constraints. Despite trees at the treeline being older and smaller than in the subalpine forest (age: 28–70 years at the treeline; 18–39 years in the subalpine forest), conduit tapering did not differ significantly between sites, suggesting that tree height is the main factor controlling the basipetal increase in conduit lumens. In the roots, the increase in conduit dimensions continued towards their tips, even more steeply than in the stem. The widest conduits were measured around the root tips (around 40 µm). Conduit tapering resulted as a stable structural feature in small plants as well as in tall trees. [ABSTRACT FROM AUTHOR]

It has been predicted that global climate change will lead to increasing drought in the Alps during the 21st century, as well as an increased fire risk, fires being currently rare in these mountains. Herein we describe fire frequency reconstruction using high-resolution analyses of macroscopic sedimentary charcoal, pollen, and plant macrofossils. Sediments were sampled from a subalpine pond within the dry western French Alps. Results show that the early-Holocene expansion of Pinus cembra (7200 calibrated years BP) occurred in Acer/Alnus incana/Betula woodlands, which were affected by fires with moderate mean fire-free intervals (MFFI = 173 ± 61 yr [mean ± SE]). Superposed Epoch Analyses show that the abundance of P. cembra macroremains decreased significantly after burning, although they never disappeared entirely. Statistics suggest that fires spread through cembra pine communities; they were not stand-replacing fires but mainly surface fires, probably killing nonreproductive pines. An increase in fire frequency occurred 6740 years ago, when four fires appear to have occurred within 140 years. These fires may have been associated with a regional drought and could have affected the composition of the subalpine forest by depleting the local P. cembra population in the short term. The predicted increase in drought in the future could, therefore, affect the cembra pine ecosystem in the Alps if fire frequency is reduced to intervals of less than 80 years. [ABSTRACT FROM AUTHOR]

Questions: What is the structure of the anthropogenic upper forest-grassland ecotone and are there differences in the spatial relationships between the tree species involved? Location: Valfurva Valley, Italian central Alps. Methods: We conducted a spatial distribution and structure analysis in three 1-ha permanent plots along an altitudinal gradient, from the treeline to the sub-alpine forest. We reconstructed the age structure from cores from each individual with diameter > 4 cm at 50 cm height. Results: All tree species and age classes examined had a clumped structure. The cluster tendency was more evident at the treeline where the environmental conditions are more severe. In the sub-alpine forest there was a repulsion between Pinus cembra and Pious mugo but at the treeline P. cembra was frequently found downslope from P. mugo. Conclusions: Although human influence has been the main driving force in shaping the present forest structure, in the last few decades natural dynamics have become the predominant force acting on forest structure and processes, showing a higher magnitude as altitude increases. Our results emphasize the existence of facilitating and interfering mechanisms between different species. P. cembra seems to be favoured compared to the other tree species. [ABSTRACT FROM AUTHOR]

The distribution of tree species and the elevation of the alpine treeline are strongly affected by climate continentality. In the present work we performed a detailed survey of the upper limits of tree vegetation in two areas with contrasting climate located in the central Italian Alps, in order to evaluate the structure of the treeline under different degrees of continentality. Tree and krummholz (stunted) individual position, their dimension and life form were recorded from the upper limit of the closed forest to the species limit. The results were compared with an estimation of tree species distribution at the treeline in the whole Lombardy Alps, performed by a survey of tree species occurrence in areas of known climatic traits. The structure of the treeline (upper limits, life form altitudinal arrangement) and its ongoing dynamics were different in the two areas: climate continentality assessed by hygric and thermal continentality indices influenced the distribution of some treeline species. Although the influence of human and geomorphologic disturbance could not be excluded, the importance of the degree of continentality must be stressed when evaluating the response of the treeline to past and present climatic change. [ABSTRACT FROM AUTHOR]

Abstract: Tree squirrels are arboreal granivores that harvest and consume tree seeds both prior to and after seed-dispersal. Inter- and intraspecific patterns of seed predation suggest that squirrels may exert strong selective pressure on cone morphology and patterns of cone production, and suggest coevolutionary interactions between squirrels and conifers. In some pine species (genus Pinus), mutualistic relationships have evolved between cone (seed) traits and seed-dispersal behaviour by birds and rodents. In other species, feeding by seed predators has selected for cone traits that decrease intensity of seed consumption. In mixed conifer forests, red squirrels (Sciurus vulgaris) feed intensively in some (target) trees but avoid others (nontarget trees). Here we explore defensive cone traits and seed traits correlated with tree selection for conifer species with different seed-dispersal strategies. No selection for cone traits existed in Pinus cembra, which has large wingless seeds, dispersed by birds and rodents. In Picea abies, the most favoured species, target trees had cones with more seeds per cone than nontarget trees, and number of seeds increased with cone length. Cone selection was most pronounced in Pinus sylvestris, where target trees had bigger cones with more seeds and higher total seed mass than nontarget trees. However, ratio of seed mass on cone mass did not differ among target and nontarget trees, suggesting that bigger cones also had more protective tissue, probably increasing difficulties for seed predators to gain access to seeds. Our results suggest that cone and seed traits of P. cembra facilitate seed consumption by squirrels, but that defensive cone traits of small-seeded conifers, in combination with annual differences in seed production (masting), might be the result of coevolution with seed-eating squirrels. [Copyright &y& Elsevier]

Abstract: The comparison of six pollen diagrams from French Alps allows us to reconstruct the past changes of vegetation structure at the upper limit of Subalpine range. Dense populations of Pinus cembra developed between 6500 and 2400 cal. BP, both in the southern Alps and the northern ones. Southern Alps seem however to be characterised by higher altitudinal limits, as shown by the past development of fir forests at 2080 m a.s.l. in the Ubaye valley. This study highlights the importance of taking in account local parameters in regional or continental reviews. To cite this article: S.D. Muller et al., C. R. Biologies 329 (2006). [Copyright &y& Elsevier]

1 The Early Holocene sediment of a lake at tree line (Gouillé Rion, 2343 m a.s.l.) in the Swiss Central Alps was sampled for plant macrofossils. Thin (0.5 cm) slices, representing time intervals of c. 50 years each from 11 800 to 7800 cal. year bp, were analysed and the data compared with independent palaeoclimatic proxies to study vegetational responses to environmental change. 2 Alpine plant communities (e.g. with Salix herbacea) were established at 11 600–11 500 cal. year bp, when oxygen-isotope records showed that temperatures increased by c. 3–4 °C within decades. Larix decidua trees reached the site at c. 11 350 cal. year bp, probably in response to further warming by 1–2 °C. Forests dominated by L. decidua persisted until 9600 cal. year bp, when Pinus cembra became more important. 3 The dominance of Larix decidua for two millennia is explained by dry summer conditions, and possibly low winter temperatures, which favoured it over the late-successional Pinus cembra. Environmental conditions were a result of variations in the earth's orbit, leading to a maximum of summer and a minimum of winter solar radiation. Other heliophilous and drought-adapted species, such as Dryas octopetala and Juniperus nana, could persist in the open L. decidua forests, but were out-competed when the shade-tolerant P. cembra expanded. 4 The relative importance of Larix decidua decreased during periods of diminished solar radiation at 11 100, 10 100 and 9400 cal. year bp. Stable concentrations of L. decidua indicate that these percentage oscillations were caused by temporary increases of Pinus cembra, Dryas octopetala and Juniperus nana that can be explained by increases in moisture and/or decreases in summer temperature. 5 The final collapse of Larix decidua at 8400 cal. year bp was possibly related to abrupt climatic cooling as a consequence of a large meltwater input to the North Atlantic. Similarly, the temporary exclusion of Pinus cembra from tree line at 10 600–10 200 cal. year bp may be related to slowing down of thermohaline circulation at 10 700–10 300 cal. year bp. 6 Our results show that tree line vegetation was in dynamic equilibrium with climate, even during periods of extraordinarily rapid climatic change. They also imply that forecasted global warming may trigger rapid upslope movements of the tree line of up to 800 m within a few decades or centuries at most, probably inducing large-scale displacements of plant species as well as irrecoverable biodiversity losses. [ABSTRACT FROM AUTHOR]

In this study, charcoal-based data for Pinus cembra L . (arolla pine) were gathered from soil and travertine sequences in order to reconstruct its historical biogeography at the landscape level in the inner western Alps during the Holocene. The study sites are located between 1700 and 2990 m a.s.l., in the southern (Queyras Massif and Ubaye Valley) and the northern (Maurienne Valley) parts of the inner French Alps. Charcoal fragments were extracted from sediments by water sieving, using meshes of 5, 2, 0.8 and 0.4 mm. The charcoal mass of P. cembra was determined in each charcoal assemblage. Accelerator mass spectrometry and conventional 14C measurements were used to date the fragments. Supported by 40 14C datings, the fragments show that, over 2000 m a.s.l., P. cembra accounts for around 40% (mean value) of identified fragments. Data reveal that arolla pine once extended between 260 and 375 m above the present-day local tree lines. It was established in the southern and the northern French Alps from at least c. 9000 and 6000 cal yr bp, respectively. While present-day populations of P. cembra are very fragmented in the inner French Alps, charcoal records indicate large past occurrences of this tree since the early Holocene. Human disturbance since the Neolithic seems to be the main reason for the regression of the arolla pine woodlands. On the south-facing slopes of the study sites, currently deforested, this species extended up to 2800 m a.s.l. In the northern areas, charcoal records of the P. cembra expansion are consistent with the regional pollen archives, but in the southern massifs charcoal records indicate its presence c. 2600 years earlier than other palaeobotanical studies suggest. This discrepancy highlights the necessity to crosscheck data using several different proxies in order to assess the validity of conclusions regarding tree development in space and time. [ABSTRACT FROM AUTHOR]

Subfossil pollen from two bogs in temperature-sensitive, high-altitude regions were analysed in order to reconstruct early- to mid-Holocene summer temperature fluctuations in the Eastern Alps. The pollen records showed four centennial-scale cooling intervals with low growing-season temperatures, resulting in decreasing pollen production and/or lower treeline position during the period 9000–6000 cal. BP. For the first time, the 8200 cal. BP cold event and an equivalent to the Misox cold phase in the Swiss Alps were detected in the Eastern Alps. The oscillations recorded in the pollen curves for Swiss stone pine (Pinus cembra) and sedges (Cyperaceae) at c. 8200 cal. BP match, in time and magnitude, the δ18O excursion in the Greenland GRIP ice-core record as well as sea-surface cooling in the North Atlantic. The close congruence between the pollen records covering 3000 years and climate proxy-data from both Hemispheres indicates that large-scale environmental changes, possibly caused by North Atlantic freshwater pulses and/or fluctuations in solar activity, caused decreases in pollen production and/or treeline shifts in the Alps. Although the 8200 cal. BP climatic deterioration was of a global character, its impact on biological productivity of temperature-sensitive sites at high altitude has only rarely been demonstrated. The data indicate that pollen analyses near and above the timberline within high-altitude, herb-dominated plant communities are of considerable and yet largely unexplored potential to detect abrupt short-term as well as long-term climatic variations. [ABSTRACT FROM AUTHOR]

The current AOT40 concept for inferring risks in forest trees by ozone (O3) injury is based on an accumulated external O3 exposure rather than an internal O3 dose or uptake rate. AOT40 assumes O3 concentrations below 40 nl l−1 and night-time exposure to be negligible. Hence, this concept is rather inconsistent with observed forest conditions. In contrast, the flux concept of cumulative O3 uptake (CU) into the leaves has the potential of reflecting a physiologically meaningful internal O3 dose experienced by trees. In this paper, we relate AOT40 to cumulative O3 uptake into European beech (Fagus sylvatica), Norway spruce (Picea abies), European larch (Larix decidua) and cembran pine (Pinus cembra) trees differing in size, age and site conditions. We demonstrate that the flux concept can be extended to the tree and the stand level, making use of sap flow measurements through tree trunks. Although in both seedlings and adult trees AOT40 may show some linearity in correlations with average CU, the latter varies, at given AOT40, by 25±11% within and between species. This is because O3 flux is primarily influenced by stomatal aperture, the latter being affected by climate, canopy position, leaf and tree age while varying between species. In particular, if weighed by detoxification capacity, we suggest, therefore, O3 uptake related air quality indices to be promoted towards ecologically meaningful standards in forest protection, overcoming the shortcomings of exposure concepts. As O3 injury results from the balance between O3 uptake and detoxification in the leaf mesophyll, we conclude the flux concept in combination with measures of biochemical defence to have the capacity for predicting tree response to O3 stress. [Copyright &y& Elsevier]

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]

Background: Genetic processes shape the modern-day distribution of genetic variation within and between populations and can provide important insights into the underlying mechanisms of evolution. The resulting genetic variation is often unequally partitioned within species' distribution range and especially large differences can manifest at the range limit, where population fragmentation and isolation play a crucial role in species survival. Despite several molecular studies investigating the genetic diversity and differentiation of European Alpine mountain forests, the climatic and demographic constrains which influence the genetic processes are often unknown. Here, we apply non-coding microsatellite markers to evaluate the sporadic peripheral and continuous populations of cembra pine (Pinus cembra L.), a long-lived conifer species that inhabits the subalpine treeline ecotone in the western Alps to investigate how the genetic processes contribute to the modern-day spatial distribution. Moreover, we corroborate our findings with paleoecological records, micro and macro-remains, to infer the species' possible glacial refugia and expansion scenarios. Results: Four genetically distinct groups were identified, with Bayesian and FST based approaches, across the range of the species, situated in the northern, inner and south-western Alps. We found that genetic differentiation is substantially higher in marginal populations than at the center of the range, and marginal stands are characterized by geographic and genetic isolation due to spatial segregation and restricted gene flow. Moreover, multiple matrix regression approaches revealed effects of climatic heterogeneity in species' spatial genetic pattern. Also, population stability tests indicated that all populations had experienced a severe historical bottleneck, no heterozygosity excess was detected, suggesting that more recently population sizes have remained relatively stable. Conclusions: Our study demonstrated that cembra pine might have survived in multiple glacial refugia and subsequently recolonized the Alps by different routes. Modern-day marginal populations, at the edge of the species' range, could maintain stable sizes over long periods without inbreeding depression and preserve high amounts of genetic variation. Moreover, our analyses indicate that climatic variability has played a major role in shaping differentiation, in addition to past historical events such as migration and demographic changes. [ABSTRACT FROM AUTHOR]