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In the European Alps, mean temperature has risen by 2.5 K since the end of the nineteenth century. A 2 K warming of the growing season has taken place in the last 4 decades only. The 2.5 K warming should rise the position of the climatic treeline by about 400 m. Actual shifts in uppermost tree positions reported here for the Austrian Defereggen Valley and the Swiss Lower Engadine region of the Eastern Alps reach only around 140 m of elevation above the limit of old trees that date back to the nineteenth century. Uppermost Pinus cembra trees of > 2 m height currently occur at c. 2500 m, representing elevation records for the Eastern Alps. In situ temperature records for 2022–2023 revealed seasonal mean temperatures for uppermost trees that are 1–3 K higher than the equilibrium treeline isotherm of c. 6 °C in both regions (corrected for temperature anomalies from long-term records). The 2 K span reflects microhabitat differences and two ways to define the season. Thus, tree advances lag behind the upslope shift of the treeline isotherm, on average, by more than 200 m. The uppermost trees currently grow under quite warm conditions with annual shoot length increments frequently reaching 20 cm. Even without additional future warming, the new steady-state climatic treeline will exceed the Holocene maximum elevation in the Eastern Alps substantially. [ABSTRACT FROM AUTHOR]

Pinus cembra L. is a coniferous European mountain range tree rich in oleoresins and essential oils. Twig tips with needles are the most common tree parts used to obtain essential oils. As the whole tree contains volatiles, the essential oil composition from different parts was studied, including twig tips with needles from the bottom, the top and the cone bearing branches, cones, twigs without needles from the lower and upper part of the crown as well as wood and bark from the trunk. The variability in essential oil composition between these plant parts and between individual trees has been studied using multivariate statistical analyses. α-Pinene was present in all samples, being highest in cones (49.3%) and lowest in sapwood (0.7%). Twig tips with needles from different parts of the crown had similar essential oil composition with α-pinene (43.9–48.3%), β-phellandrene (13.1–17.2%), β-pinene (6.6–9.3%), germacrene D (5.1–6.8%) and limonene (4.1–6.1%) as main compounds. Twig essential oils had usually more β-phellandrene (23.9–29.8%) than α-pinene (23.3–24.3%) and also appreciable amounts of β-pinene (13.5–15.1%) and limonene (11.9–17.9%). Cone essential oils contained mainly α-pinene, β-pinene (20.1%) and limonene (13.9%). The essential oils from wood and bark were rich in diterpenes as cembratrienol (4.9–21.4%), cembrene (4.8–14.3%) and methyl daniellate (2.7–6.8%). Sapwood distillates contained also notable amounts of alkane derivatives. Finally, the solvent free SPME technique has been employed to analyse the volatiles in the plant parts. For needles and cones the observed patterns were in good accordance with the compositions of the respective essential oils. [ABSTRACT FROM AUTHOR]

Key message: The lack of elevational changes in electrical resistivity in Pinus cembra trunks indicated consistent growth and hydraulics across elevations. Though, electrical resistivity tomograms exhibited pronounced temperature-driven seasonal changes. Alpine conifers growing at high elevation are exposed to low temperatures, which may limit xylogenesis and cause pronounced seasonal changes in tree hydraulics. Electrical resistivity (ER) tomography enables minimal invasive monitoring of stems in situ. We used this technique to analyze Pinus cembra trunks along a 400 m elevational gradient up to the timberline and over seasons. Furthermore, ER data of earlywood across tree rings were compared with the respective specific hydraulic conductivity (KS), measured on extracted wood cores. ER tomograms revealed pronounced changes over the year and a strong correlation between average ER (ERmean) and air and xylem temperatures. Surprisingly, no elevational changes in ERmean, earlywood ER or KS were observed. ER data corresponded to variation in earlywood KS, which decreased from the youngest (ca. 4–5 cm2s−1 MPa−1) to the oldest tree rings (0.63 ± 0.22 cm2s−1 MPa−1). The lack of changes in ER data and earlywood KS along the study transect indicated consistent growth patterns and no major changes in structural and functional hydraulic traits across elevation. The constant decrease in earlywood KS with tree ring age throughout all elevations highlights the hydraulic relevance of the outermost tree rings in P. cembra. Seasonal measurements demonstrated pronounced temperature effects on ER, and we thus recommend a detailed monitoring of trunk temperatures for ER tomography. [ABSTRACT FROM AUTHOR]

Massively parallel sequencing of cDNA is an efficient route for generating sequence collections that represent expressed genes under different environmental control. The analysis of their sequence helps in developing molecular markers, such as SNPs, which represent a useful tool in detecting adaptive signals in populations. In this study novel PCR markers, based on stress responsive genes, were designed from the transcriptome of the haploxylon Swiss stone pine (Pinus cembra L.) and tested for SNPs in the diploxylon Scots pine (Pinus sylvestris L.). 84 primers were tested on P. sylvestris DNA samples originating from three different types of habitat. After sequencing and BLAST search of the amplified products, parts of 19 different candidate genes were analysed by considering the polymorphic sites, insertions/deletions as well as synonymous and non-synonymous SNPs. In a total of 3735 sites no indels, eight synonymous and 11 non-synonymous SNPs were found. By providing de novo molecular markers developed in P. cembra and tested for transferability in Scots pine, our results give support for the use of de novo markers targeting conserved regions across different pines. The SNPs detected may have important applications in further studies of adaptive genetic variation, providing tools to study relevant genes important in the long-term adaptation of pine species. [ABSTRACT FROM AUTHOR]

Key Message: Mosaicism has been confirmed in several studied old trees from both gymnosperms and angiosperms, in a pattern not always following the actual branching of the tree. Eight individuals from two gymnosperm and three angiosperm species of trees were studied for age-related mosaicism. We compare the level of intra-organismal genetic variability found within an individual old and an individual young tree of the same species to prove its relation to age. In five cases, we found statistically significant differences in intra-organismal genetic variability between young and old trees. In three cases of mosaicism, the constructed dendrogram corresponded with the actual branching of the tree, but it differed in the remaining two. We offer an explanation of the cases when the dendrogram does not correspond with the branching structure of the tree through the patterns of sectorial and mericlinal chimerism. In the studied gymnosperms, we found that the growth rate possibly influenced the level of intra-organismal variability, while in angiosperms the dependence was rather on age. The differences between angiosperm and gymnosperm molecular evolution and meristem stratification may play a role in this, but further research is needed in this area. [ABSTRACT FROM AUTHOR]

Key message: The axial structure of the hydraulic system in trees is relatively invariant and insensitive to temperature, while trees plastically adjust the number of cells within the tree ring. At higher elevations and latitudes in the treeline ecotone, reduction in the heat accrued during the growing season is reflected in gradually decreasing tree size. Due to low temperatures, treeline trees might produce smaller xylem cells and, as a consequence, tree growth could be limited. However, some xylem traits (i.e., cell lumen area) are considered relatively insensitive to climatic factors but highly dependent on tree size because of the natural widening of xylem conduits towards the stem base. We tested the hypothesis that earlywood cell lumen area is essentially invariant and depends largely on tree size. Tracheid traits in four conifer species from the lower ("timberline") and upper ("treeline") parts of the treeline ecotone (Picea engelmannii, Picea abies, Pinus cembra and Larix decidua) were measured in the Colorado Front Range (U.S.A.), Krkonoše Mts. (Czech Republic) and Dolomites (Italy). On transversal sections sampled at 1 m of stem height, we measured cell lumen areas, transversal cell size, cell wall thickness, tree-ring width and number of cells per radial file. Cell lumen areas were always greater at the timberline than treeline. When tree height is accounted for, the earlywood cell area did not differ between the two sites, thus showing that difference in temperature did not affect earlywood cell area in any of the four measured species. The number of cells within tree rings exhibited high inter-annual variability according to environmental factors. The fundamental hydraulic structure in trees is relatively rigid and insensitive to temperature, while trees plastically adjust the number of cells within the tree ring as a result of inter-annual climate variability and leaf production. [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]

European larch ( Larix decidua) forests of the western Alps form extensive cultural landscapes whose resilience to global changes is currently unknown. Resilience describes the capacity of ecological systems to maintain the same state, i.e., the same function, processes, structure, and composition despite disturbances, environmental changes and internal fluctuations. Our aim is to explore the resilience of larch forests to changes in climate and land use in the western Italian Alps. To do so, we examined whether larch forests can be described as an alternative stable state in mountain forest ecosystems. We used tree basal area data obtained from field forest inventories in combination with topography, forest structure, land use, and climate information. We applied three different probabilistic methods: frequency distributions, logistic regressions, and potential analyses to infer the resilience of larch forests relative to that of other forest types. We found patters indicative of alternative stable states: bimodality in the frequency distribution of the percent of larch basal area, and the presence of an unstable state, i.e., mixed larch forests, in the potential analyses. We also found: (1) high frequency of pure larch forests at high elevation, (2) the probability of pure larch forests increased mostly with elevation, and (3) pure larch forests were a stable state in the upper montane and subalpine belts. Our study shows that the resilience of larch forests may increase with elevation, most likely due to the altitudinal effect on climate. Under the same climate conditions, land use seems to be the main factor governing the dominance of larch forests. In fact, subalpine larch forests may be more resilient, and natural succession after land abandonment, e.g., towards Pinus cembra forests, seems slower than in montane larch forests. In contrast, in the upper montane belt only intense land use regimes characterized by open canopies and forest grazing may maintain larch forests. We conclude that similar approaches could be applied in other forest ecosystems to infer the resilience of tree species. [ABSTRACT FROM AUTHOR]

Alpine regions represent an interesting biome for studying local adaptation in forest trees. Strong genetic differentiation is expected along elevational gradients in spite of extensive gene flow. We sampled 18 and 20 natural populations of Pinus cembra and Pinus mugo, in two subregions and four elevational gradients. To investigate the effects of elevation on genetic diversity and adaptation, 768 and 1152 single nucleotide polymorphisms (SNPs) were genotyped in P. cembra and P. mugo. We found low but significant genetic differentiation among populations in both species. To discover outliers, we applied Bayesian simulation and hierarchical island model analyses. A larger number of outliers were found using the first method. Some SNPs were detected with both analyses: one SNP in P. cembra and three in P. mugo when using two subregions and four SNPs in P. cembra and one in P. mugo when using four elevational gradients. The association between environmental and genetic variation was tested with Bayesian simulation (Bayenv) and a latent factor mixed model (LFMM). The first method, using all populations, detected 6 and 20 SNPs associated to temperature in P. cembra and in P. mugo, respectively, 3 SNPs associated to precipitation in P. cembra, and 14 SNPs to elevation in P. mugo. The LFMM found a higher number of SNPs associated to temperature in P. mugo than in P. cembra (37 vs. 27), with a stronger association with maximum temperature (April–June). In P. cembra, the majority of associations (51 SNPs) were found with precipitation (January–March). Five SNPs in common between species were found on genes potentially involved in plant response to abiotic stress. Using these results, we confirmed that temperature was an important driver of adaptive potential for each species so that continued changes to global temperatures will likely involve continued adaptation as ranges shift upwards. [ABSTRACT FROM AUTHOR]

Mating systems have long been recognized as key factors determining genetic structure within and between populations. Outcrossing promotes genetic diversity and gene flow between populations, while inbreeding, on the other hand, decreases recombination rates, facilitating fixation of co-adapted genes. In small populations, selfing moderates pollen limitation because of low mate availability, but at the cost of increased inbreeding depression. These conflicts are of more than theoretical interest; they are critical for the management of endangered species. In order to help designing conservation strategies for the management of the gene pool of fragmented populations of Pinus cembra, a protected species in Poland, we have characterized pollen flow and mating structure using nuclear microsatellite markers. We demonstrated that P. cembra in the studied stands of the Tatra Mts. is characterized by an average outcrossing rate ( t) of 0.72. Unlike with the existing approaches, using the newly developed Bayesian method, we found that population size and seasonal variation had confounding effects on outcrossing rates. In concordance with predictions, large populations showed significantly higher outcrossing rates ( t = 0.89) than smaller ones ( t = 0.51). Temporal variation revealed in the outcrossing rate might be linked with masting behavior of the species. On the other hand, we showed that outcrossing rates were not associated with a trunk diameter of a mother tree. Our study also demonstrated that biparental inbreeding is a significant component of mating system. However, we further show that pollen dispersal follows a fat-tailed distribution (with the average dispersal distance of 1,267 m) so that at least some long-distance pollen dispersal must be occurring. Overall, we conclude that the high inbreeding (both selfing and mating between relatives) found in P. cembra buffers for pollen limitation. We argue that small, isolated stands can be at risk of gene pool erosion, despite the potential for long-distance pollen and seed dispersal. [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]

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]

The correct evaluation of the age of small tree individuals is of great importance in ecological studies, and can be performed if growth units are identifiable even under strong environmental constraints. We aimed to assess the reliability of age evaluation of small individuals of four species commonly occurring at the treeline in the Alps and the Apennines (N Italy), Picea abies, Pinus cembra, Larix decidua and Fagus sylvatica. A total of 224 individuals were sampled along an altitudinal gradient up to the treeline. For each species, we assessed the growth architecture and the appearance of annual growth units; for each individual, age and evaluation uncertainty were estimated. To verify the estimation a core or a cross-section was obtained. The estimated age was compared with the tree-ring age through linear regression and reduced chi square test, and the estimation accuracy was evaluated as function of tree age, dimension and environmental parameters. A good estimation was possible for all species, even when loss of vertical growth occurred. The highest error occurred for Larix, the lowest for Pinus; the error was generally correlated with tree age and dimension, and was affected by altitude and geomorphology. Good reduced chi square values were reached considering only the youngest individuals for Fagus and Picea and the smallest for Fagus and Larix; the uncertainty was generally underestimated for Pinus. Even though reliable age estimation could be obtained, a realistic and species-specific evaluation of the estimation uncertainties is necessary to assess estimation accuracy for ecological studies. [ABSTRACT FROM AUTHOR]

For assessing the impact of soil temperature on tree growth in remote areas such as the alpine timberline, we introduce a new method for soil temperature manipulations. This new approach is based on roofing of the rooting zone and allows either soil cooling or soil warming without significantly influencing soil water availability and the above ground microclimate. [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]

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We investigated carbon (C) uptake and respiratory losses of an adult Pinus cembra tree at the alpine timberline throughout an entire year by means of an automated, multiplexing gas exchange system. These chamber measurements were then combined with biomass data for scaling up the C budget to the tree level. Integrated over an entire year, the cumulative C gain of the tree under study was 23.5 kg of C in 2002. The daily C balance was negative for 5 months and the estimated total wintertime respiratory losses were 9% of the amount of C fixed during the growing season. The total annual C loss of the tree consumed 55% of the annual net C gain and the remaining surplus was stored in new tissues (36%) and used for fine root growth (9%). Thus, the overall C budget of P. cembra at the upper timberline is balanced fairly well, although the C sink strength in fine roots is strongly limited owing to low root zone temperatures when compared to conifers at lower elevation sites. [ABSTRACT FROM AUTHOR]

The difference in cone colonization by specialized insects that had been observed between Swiss stone pine ( Pinus cembra L.) and mountain pine ( P. uncinata Ram.) prompted us to test whether volatiles and oleoresin of Swiss stone pine cones may serve as a barrier for insect attack. The volatiles emitted by cones of both pine species were sampled using headspace techniques in the French Alps. The cone volatiles of both species essentially consisted of seven similar monoterpenes, but the terpene profiles markedly differed between species. α-Pinene (67% of the total), β-pinene, and limonene + β-phellandrene were dominant in the cone volatiles of Swiss stone pine, while the cone emissions of mountain pine showed no dominant terpenoid. The cone oleoresin of P. cembra significantly differed from cone volatiles by a lower level of α-pinene and higher levels of β-pinene and limonene + β-phellandrene. Field sprays of mountain pine cones with oleoresin extracts of Swiss stone pine cones significantly reduced the overall damage of specialized cone insects. None of the cones sprayed with oleoresin were attacked, whereas 11% and 31% of the unsprayed control cones were damaged by insects. Specific cone damage due to a cone weevil, Pissodes validirostris Gyll. (Coleoptera: Curculionidae), and a cone pyralid, Dioryctria mutatella Fuchs (Lepidoptera: Pyralidae), were significantly decreased in one year. The volatile profile of the sprayed cones differed markedly from that of unsprayed mountain pine cones, especially in the higher level of myrcene. However, the volatile profile of the sprayed cones also differed from that of the oleoresin extract used for spraying. The role of monoterpenes in protecting the sprayed cones from insect attack is discussed. [ABSTRACT FROM AUTHOR]