Amplifying effects of recurrent drought on the dynamics of tree growth and water use in a subalpine forest.

Despite recent advances in our understanding of drought impacts on tree functioning, we lack knowledge about the dynamic responses of mature trees to recurrent drought stress. At a subalpine forest site, we assessed the effects of three years of recurrent experimental summer drought on tree growth and water relations of Larix decidua Mill. and Picea abies (L. Karst.), two common European conifers representative for contrasting water-use strategies. We combined dendrometer and xylem sap flow measurements with analyses of xylem anatomy and non-structural carbohydrates and their carbon-isotope composition. Recurrent drought increased the effects of soil moisture limitation on growth and xylogenesis, and to a lesser extent on xylem sap flow. P. abies showed stronger growth responses to recurrent drought, reduced starch concentrations in branches and increased water-use efficiency when compared to L. decidua. Despite comparatively larger maximum tree water deficits than in P. abies, xylem formation of L. decidua was less affected by drought, suggesting a stronger capacity of rehydration or lower cambial turgor thresholds for growth. Our study shows that recurrent drought progressively increases impacts on mature trees of both species, which suggests that in a future climate increasing drought frequency could impose strong legacies on carbon and water dynamics of treeline species.

Reindeer control over subarctic treeline alters soil fungal communities with potential consequences for soil carbon storage.

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

Temperature and soil fertility as regulators of tree line Scots pine growth and survival-implications for the acclimation capacity of northern populations.

The acclimation capacity of leading edge tree populations is crucially important in a warming climate. Theoretical considerations suggest that adaptation through genetic change is needed, but this may be a slow process. Both positive and catastrophic outcomes have been predicted, while empirical studies have lagged behind theory development. Here we present results of a 30-year study of 55,000 Scots pine (Pinus sylvestris) trees, planted in 15 common gardens in three consecutive years near and beyond the present Scots pine tree line. Our results show that, contrary to earlier predictions, even long-distance transfers to the North can be successful when soil fertility is high. This suggests that present northern populations have a very high acclimation capacity. We also found that while temperature largely controls Scots pine growth, soil nutrient availability plays an important role-in concert with interpopulation genetic variation-in Scots pine survival and fitness in tree line conditions. These results suggest that rapid range expansions and substantial growth enhancements of Scots pine are possible in fertile sites as seed production and soil nutrient mineralization are both known to increase under a warming climate. Finally, as the ontogenetic pattern of tree mortality was highly site specific and unpredictable, our results emphasize the need for long-term field trials when searching for the factors that control fitness of trees in the variable edaphic and climatic conditions of the far North.

Open tundra persist, but arctic features decline-Vegetation changes in the warming Fennoscandian tundra.

In the forest-tundra ecotone of the North Fennoscandian inland, summer and winter temperatures have increased by two to three centigrades since 1965, which is expected to result in major vegetation changes. To document the expected expansion of woodlands and scrublands and its impact on the arctic vegetation, we repeated a vegetation transect study conducted in 1976 in the Darju, spanning from woodland to a summit, 200 m above the tree line. Contrary to our expectations, tree line movement was not detected, and there was no increase in willows or shrubby mountain birches, either. Nevertheless, the stability of tundra was apparent. Small-sized, poorly competing arctic species had declined, lichen cover had decreased, and vascular plants, especially evergreen ericoid dwarf shrubs, had gained ground. The novel climate seems to favour competitive clonal species and species thriving in closed vegetation, creating a community hostile for seedling establishment, but equally hostile for many arctic species, too. Preventing trees and shrubs from invading the tundra is thus not sufficient for conserving arctic biota in the changing climate. The only dependable cure is to stop the global warming.

Long-term forest resilience to climate change indicated by mortality, regeneration, and growth in semiarid southern Siberia.

Several studies have documented that regional climate warming and the resulting increase in drought stress have triggered increased tree mortality in semiarid forests with unavoidable impacts on regional and global carbon sequestration. Although climate warming is projected to continue into the future, studies examining long-term resilience of semiarid forests against climate change are limited. In this study, long-term forest resilience was defined as the capacity of forest recruitment to compensate for losses from mortality. We observed an obvious change in long-term forest resilience along a local aridity gradient by reconstructing tree growth trend and disturbance history and investigating postdisturbance regeneration in semiarid forests in southern Siberia. In our study, with increased severity of local aridity, forests became vulnerable to drought stress, and regeneration first accelerated and then ceased. Radial growth of trees during 1900-2012 was also relatively stable on the moderately arid site. Furthermore, we found that smaller forest patches always have relatively weaker resilience under the same climatic conditions. Our results imply a relatively higher resilience in arid timberline forest patches than in continuous forests; however, further climate warming and increased drought could possibly cause the disappearance of small forest patches around the arid tree line. This study sheds light on climate change adaptation and provides insight into managing vulnerable semiarid forests.

Monitoring small pioneer trees in the forest-tundra ecotone: using multi-temporal airborne laser scanning data to model height growth.

Monitoring of forest resources through national forest inventory programmes is carried out in many countries. The expected climate changes will affect trees and forests and might cause an expansion of trees into presently treeless areas, such as above the current alpine tree line. It is therefore a need to develop methods that enable the inclusion of also these areas into monitoring programmes. Airborne laser scanning (ALS) is an established tool in operational forest inventories, and could be a viable option for monitoring tasks. In the present study, we used multi-temporal ALS data with point density of 8-15 points per m2, together with field measurements from single trees in the forest-tundra ecotone along a 1500-km-long transect in Norway. The material comprised 262 small trees with an average height of 1.78 m. The field-measured height growth was derived from height measurements at two points in time. The elapsed time between the two measurements was 4 years. Regression models were then used to model the relationship between ALS-derived variables and tree heights as well as the height growth. Strong relationships between ALS-derived variables and tree heights were found, with R 2 values of 0.93 and 0.97 for the two points in time. The relationship between the ALS data and the field-derived height growth was weaker, with R 2 values of 0.36-0.42. A cross-validation gave corresponding results, with root mean square errors of 19 and 11% for the ALS height models and 60% for the model relating ALS data to single-tree height growth.

Seasonal transfer of oxygen isotopes from precipitation and soil to the tree ring: source water versus needle water enrichment.

For accurate interpretation of oxygen isotopes in tree rings (δ(18) O), it is necessary to disentangle the mechanisms underlying the variations in the tree's internal water cycle and to understand the transfer of source versus leaf water δ(18) O to phloem sugars and stem wood. We studied the seasonal transfer of oxygen isotopes from precipitation and soil water through the xylem, needles and phloem to the tree rings of Larix decidua at two alpine sites in the Lötschental (Switzerland). Weekly resolved δ(18) O records of precipitation, soil water, xylem and needle water, phloem organic matter and tree rings were developed. Week-to-week variations in needle-water (18) O enrichment were strongly controlled by weather conditions during the growing season. These short-term variations were, however, not significantly fingerprinted in tree-ring δ(18) O. Instead, seasonal trends in tree-ring δ(18) O predominantly mirrored trends in the source water, including recent precipitation and soil water pools. Modelling results support these findings: seasonal tree-ring δ(18) O variations are captured best when the week-to-week variations of the leaf water signal are suppressed. Our results suggest that climate signals in tree-ring δ(18) O variations should be strongest at temperate sites with humid conditions and precipitation maxima during the growing season.

A cool experimental approach to explain elevational treelines, but can it explain them?

At alpine treeline, trees give way to low-stature alpine vegetation. The main reason may be that tree canopies warm up less in the sun and experience lower average temperatures than alpine vegetation. Low growth temperatures limit tissue formation more than carbon gain, but whether this mechanism universally determines potential treeline elevations is the subject of debate. To study low-temperature limitation in two contrasting treeline tree species, Fajardo and Piper (American Journal of Botany 101: 788-795) grew potted seedlings at ground level or suspended at tree-canopy height (2 m), introducing a promising experimental method for studying the effects of alpine-vegetation and tree-canopy microclimates on tree growth. On the basis of this experiment, the authors concluded that lower temperatures at 2 m caused carbon limitation in one of the species and that treeline-forming mechanisms may thus be taxon-dependent. Here we contest that this important conclusion can be drawn based on the presented experiment, because of confounding effects of extreme root-zone temperature fluctuations and potential drought conditions. To interpret the results of this elegant experiment without logistically challenging technical modifications and to better understand how low temperature leads to treeline formation, studies on effects of fluctuating vs. stable temperatures are badly needed. Other treeline research priorities are interactions between temperature and other climatic factors and differences in microclimate between tree canopies with contrasting morphology and physiology. In spite of our criticism of this particular study, we agree that the development of a universal treeline theory should include continuing explorations of taxon-specific treeline-forming mechanisms.

Characterization of an alpine tree line using airborne LiDAR data and physiological modeling.

Understanding what environmental drivers control the position of the alpine tree line is important for refining our understanding of plant stress and tree development, as well as for climate change studies. However, monitoring the location of the tree line position and potential movement is difficult due to cost and technical challenges, as well as a lack of a clear boundary. Advanced remote sensing technologies such as Light Detection and Ranging (LiDAR) offer significant potential to map short individual tree crowns within the transition zone despite the lack of predictive capacity. Process-based forest growth models offer a complementary approach by quantifying the environmental stresses trees experience at the tree line, allowing transition zones to be defined and ultimately mapped. In this study, we investigate the role remote sensing and physiological, ecosystem-based modeling can play in the delineation of the alpine tree line. To do so, we utilize airborne LiDAR data to map tree height and stand density across a series of altitudinal gradients from below to above the tree line within the Swiss National Park (SNP), Switzerland. We then utilize a simple process-based model to assess the importance of seasonal variations on four climatically related variables that impose non-linear constraints on photosynthesis. Our results indicate that all methods predict the tree line to within a 50 m altitudinal zone and indicate that aspect is not a driver of significant variations in tree line position in the region. Tree cover, rather than tree height is the main discriminator of the tree line at higher elevations. Temperatures in fall and spring are responsible for the major differences along altitudinal zones, however, changes in evaporative demand also control plant growth at lower altitudes. Our results indicate that the two methods provide complementary information on tree line location and, when combined, provide additional insights into potentially endangered forest/grassland transition zones.

Microsite affects willow sapling recovery from bank vole (Myodes glareolus) herbivory, but does not affect grazing risk.

BACKGROUND: Large herbivores are often removed or reduced as part of vegetation restoration programmes, but the resultant increase in vegetation biomass and changes in vegetation structure may favour small mammals. Small mammals may have large impacts on plant community composition via granivory and sapling herbivory, and increased small mammal populations may reduce any benefits of large herbivore removal for highly preferred species. This study tested the impacts of small mammal herbivory, microsite characteristics and their interaction on growth and survival of three montane willow species with differing chemical compositions, Salix lapponum, S. myrsinifolia and S. arbuscula. METHODS: In two separate years, 1-year-old saplings were planted within a 180 ha, large-mammal scrub regeneration exclosure, and either experimentally protected from or exposed to small mammals (bank voles). Saplings were planted in one of two microsite treatments, vegetation mown (to mimic a grazed sward) or disturbed (all above- and below-ground competition removed), and monitored throughout the first year of growth. KEY RESULTS: Approximately 40 % of saplings planted out in each year were damaged by bank voles, but direct mortality due to damage was very low (<2 %). There were no strong species differences in susceptibility to vole damage. Microsite treatment had no impact on the proportion of saplings attacked, but in 2004 saplings in mown microsites were more severely damaged and had smaller increases in size than those in disturbed microsites. In 2003, saplings in mown microsites had smaller increases in stem diameter following attack than those in disturbed microsites. CONCLUSIONS: Planting 1-year-old willow saplings into disturbed microsites may aid growth, reduce the severity of small mammal damage and improve recovery following sub-lethal small mammal damage. Restoration management of montane willow scrub should therefore consider manipulating the planting site to provide disturbed areas of soil.

Thermal niches are more conserved at cold than warm limits in arctic-alpine plant species.

AIM: Understanding the stability of realized niches is crucial for predicting the responses of species to climate change. One approach is to evaluate the niche differences of populations of the same species that occupy regions that are geographically disconnected. Here, we assess niche conservatism along thermal gradients for 26 plant species with a disjunct distribution between the Alps and the Arctic. LOCATION: European Alps and Norwegian Finnmark. METHODS: We collected a comprehensive dataset of 26 arctic-alpine plant occurrences in two regions. We assessed niche conservatism through a multispecies comparison and analysed species rankings at cold and warm thermal limits along two distinct gradients corresponding to (1) air temperatures at 2 m above ground level and (2) elevation distances to the tree line (TLD) for the two regions. We assessed whether observed relationships were close to those predicted under thermal limit conservatism. RESULTS: We found a weak similarity in species ranking at the warm thermal limits. The range of warm thermal limits for the 26 species was much larger in the Alps than in Finnmark. We found a stronger similarity in species ranking and correspondence at the cold thermal limit along the gradients of 2-m temperature and TLD. Yet along the 2-m temperature gradient the cold thermal limits of species in the Alps were lower on average than those in Finnmark. MAIN CONCLUSION: We found low conservatism of the warm thermal limits but a stronger conservatism of the cold thermal limits. We suggest that biotic interactions at the warm thermal limit are likely to modulate species responses more strongly than at the cold limit. The differing biotic context between the two regions is probably responsible for the observed differences in realized niches.

A palaeoecological perspective on the transformation of the tropical Andes by early human activity.

Palaeoecological records suggest that humans have been in the Andes since at least 14 000 years ago. Early human impacts on Andean ecosystems included an increase in fire activity and the extinction of the Pleistocene megafauna. These changes in Andean ecosystems coincided with rapid climate change as species were migrating upslope in response to deglacial warming. Microrefugia probably played a vital role in the speed and genetic composition of that migration. The period from ca 14 500 to 12 500 years ago was when novel combinations of plant species appeared to form no-analogue assemblages in the Andes. By 12 000 years ago most areas in what are today the Andean grasslands were being burned and modified by human activity. As the vegetation of these highland settings has been modified by human activity for the entirety of the Holocene, they should be regarded as long-term manufactutred landscapes. The sharp tree lines separating Andean forests from grasslands that we see today were probably also created by repeated burning and owe their position more to human-induced fire than climatic constraints. In areas that were readly penetrated by humans on the forested slopes of the Andes, substantial modification and settlement had occurred by the mid-Holocene. In hard-to-reach areas, however, the amount of human modification may always have been minimal, and these slopes can be considered as being close to natural in their vegetation. This article is part of the theme issue 'Tropical forests in the deep human past'.

Isolated alpine habitats reveal disparate ecological drivers of taxonomic and functional beta-diversity of small mammal assemblages.

The interpretation of patterns of biodiversity requires the disentanglement of geographical and environmental variables. Disjunct alpine communities are geographically isolated from one another but experience similar environmental impacts. Isolated homogenous habitats may promote speciation but constrain functional trait variation. In this study, we examined the hypothesis that dispersal limitation promotes taxonomic divergence, whereas habitat similarity in alpine mountains leads to functional convergence. We performed standardized field investigation to sample non-volant small mammals from 18 prominent alpine sites in the Three Parallel Rivers area. We estimated indices quantifying taxonomic and functional alpha- and beta-diversity, as well as beta-diversity components. We then assessed the respective importance of geographical and environmental predictors in explaining taxonomic and functional compositions. No evidence was found to show that species were more functionally similar than expected in local assemblages. However, the taxonomic turnover components were higher than functional ones (0.471±0.230 vs. 0.243±0.215), with nestedness components showing the opposite pattern (0.063±0.054 vs. 0.269±0.225). This indicated that differences in taxonomic compositions between sites occurred from replacement of functionally similar species. Geographical barriers were the key factor influencing both taxonomic total dissimilarity and turnover components, whereas functional beta-diversity was primarily explained by climatic factors such as minimum temperature of the coldest month. Our findings provide empirical evidence that taxonomic and functional diversity patterns can be independently driven by different ecological processes. Our results point to the importance of clarifying different components of beta-diversity to understand the underlying mechanisms of community assembly. These results also shed light on the assembly rules and ecological processes of terrestrial mammal communities in extreme environments.

Variability in the expansion of trees and shrubs in boreal Alaska.

The expansion of shrubs and trees across high-latitude ecosystems is one of the most dramatic ecological manifestations of climate change. Most of the work quantifying these changes has been done in small areas and over relatively recent time scales. These land-cover transitions are highly spatially variable, and we have limited understanding of the factors underlying this variation. We use repeat photography to generate a data set of land-cover changes in Denali National Park and Preserve, Alaska, stretching back a century and spanning a range of edaphic, topographic, and climatic conditions. Most land-cover classes were quite stable, with low probabilities of transitioning to other land-cover types. The advance of woody vegetation into low-stature tundra, and the spread of conifer trees into shrub-dominated areas, were both more likely at low elevations and in areas without permafrost. Permafrost also reduced the likelihood of herbaceous vegetation transitioning to woody cover. Exceptions to the general trend of relative stability included nearly all (96%) of the broadleaf forest-dominated areas being invaded by conifers, an expected successional trajectory, and many open gravel river bars (17.8%) transitioning to thick shrubs. These floodplain areas were distinctly not at equilibrium, as only 0.1% of shrub-dominated areas converted to gravel. Warming temperatures in coming decades and concomitant declines in the extent of permafrost are predicted to enhance the spread of woody vegetation in Denali further, but only by ~3%. Land-cover transitions, notably the rapid advance of trees and shrubs observed in other studies, could be less likely and more spatially heterogeneous here than in other high-latitude systems.

Mass-loss rates from decomposition of plant residues in spruce forests near the northern tree line subject to strong air pollution.

Mass-loss rates during the early phase of decomposition of plant residues were studied for a period of 3 years in Norway spruce forests subjected to air pollution by Cu-Ni smelters on the Kola Peninsula, northwest Russia. Litterbags were deployed in two main patches of forests at the northern tree line, between and below the crowns of spruce trees older than 100 years. The study results demonstrated the dependence of the decomposition rates on the initial concentrations of nutrients and the C/N and lignin/N ratios in plant residues. Lower rates of mass loss in forests subject to air pollution may be related to low quality of plant residues, i.e. high concentrations of heavy metals, low concentrations of nutrients, and high lignin/N and C/N ratios. The increased losses of Ca, Mg, K, and Mn from plant residues in these forests compared to the reference were, probably, related to leaching of their compounds from the residues. The relatively high rates of heavy metal accumulation in the residues were most likely related to uptake of pollutants from the atmosphere, as well as to the lower mass-loss rates. The present study results demonstrate that the forest patchiness should be taken into account in assessment and predictions of decomposition rates in Norway spruce forests. Mass-loss rates of plant residues below the crowns of old spruce trees were significantly lower than those in the patches between the crowns. This was explained by the high C/N and lignin/N ratios in the residues of evergreens which contribute significantly to litterfall below the crowns and by lower soil temperature during winter and spring below the crowns. In addition, a lower amount of precipitation reaching the forest floor below the dense, long crowns of old Norway spruce trees may result in considerably lower washing out of the organic compounds from the residues. Lower mass-loss rates below the crowns of old spruce trees may be part of the evidence that the old-growth spruce forests can continue to accumulate carbon in soil.

Modeling of bud break of Scots pine in northern Finland in 1908-2014.

Bud break and height-growth of Scots pine (Pinus sylvestris L.) in the northern boreal zone in Lapland, Finland, was followed through the entire growing seasons in the periods 2001-2003 and 2008-2010 in sapling stands in two different locations in northern Finland set some 250 km apart along a latitudinal transect. Field measurements continued at the southern site also in 2011-2013. Air temperature was recorded hourly at the sites. A simple optimization algorithm (GA) was used to adjust parameters of the models predicting the timing of bud break of Scots pine in order to minimize the difference between observed and predicted dates. The models giving the best performance and century-long daily temperatures were used to reconstruct bud-break time series. The temperature observations were recorded for the period 1908-2014 in Sodankylä, which is located in-between the sapling stands in the north-south direction and for the period 1877-2014 in Karasjok, which is in Norway about 145 km north-west from the northernmost stand of this study. On average buds began to extend in the beginning of May in the southernmost stand and in mid-May in the northernmost stands, and the variation between years was in the range of 3 weeks. A simple day-length-triggered (fixed date) model predicted most accurately the date of bud break; root mean square error (RMSE) was 2 and 4 days in the northern and southern site, respectively. The reconstructed bud-break series indicated that based on temperature observations from Sodankylä, growth onset of Scots pine has clearly advanced since the 1960s, though it currently matches that of the early 1920s and early 1950s. The temperature record from Karasjok indicated a similar variation, though there was a weak linear trend advancing bud break by about 3-4 days over a 100-year period.

Climate and the meristem temperatures of plant communities near the tree-line.

Temperatures of terminal meristems of forest, krummholz and dwarf shrub vegetation were measured at altitudes of 450, 600, 650 and 850 m in the Cairngorm Mountains of Scotland. Simultaneously, the air temperature above the vegetation was recorded, so that it was possible to calculate the difference between meristem and air temperature, sometimes called the excess temperature. This temperature increased linearly with the net radiation absorbed at each station, and the slope was dependent on wind speed and the height of the vegetation. In the extreme cases the slopes were practically zero for forest and 0.028° C W-1 m2 for dwarf shrubs. The latter implies a temperature excess of about 15° C in bright sunshine and low wind speeds. A model is developed to calculate the excess temperature from a knowledge of vegetational height and climatological variables.

Cuticular water loss unlikely to explain tree-line in Scotland.

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

Growth and protection against oxidative stress in young clones and mature spruce trees (Picea abies L.) at high altitudes.

Clones of Norway spruce (Picea abies L.) were grown for several years on an altitudinal gradient (1750 m, 1150 m and 800 m above sea level) to study the effects of environmental × genetic interactions on growth and foliar metabolites (protein, pigments, antioxidants). Clones at the tree line showed 4.3-fold lower growth rates and contained 60% less chlorophyll (per gram of dry matter) than those at valley level. The extent of growth reduction was clone-dependent. The mortality of the clones was low and not altitude-dependent. At valley level, but not at high altitude, needles of mature spruce trees showed lower pigment and protein concentrations than clones. In general, antioxidative systems in needles of the mature trees and young clones did not increase with increasing altitude. Needles of all trees at high altitude showed higher concentrations of dehydroascorbate than at lower altitudes, indicating higher oxidative stress. In one clone, previously identified as sensitive to acute ozone doses, this increase was significantly higher and the growth reduction was stronger than in the other genotypes. This clone also displayed a significant reduction in glutathione reductase activity at high altitude. These results suggest that induction of antioxidative systems is apparently not a general prerequisite to cope with altitude in clones whose mother plants originated from higher altitudes (about 650-1100 m above sea level, Hercycnic-Carpathian distribution area), but that the genetic constitution for maintenance of high antioxidative protection is important for stress compensation at the tree line.