Paleoclimatic potential of the northernmost juniper trees in Europe

In late summer 2004 stem discs were collected from about 40 juniper trees (Juniperus Siberica Burgsd) growing at the remote central part of Kola Peninsula behind the polar circle at the northern timberline. Up to now these juniper trees are oldest ones found at Kola Peninsula. Data processing was difficult due to extremely small tree rings as well as the occurrence of missing and false rings. However, finally it was possible to build up a 676-year long chronology and retrieve information on the past climatic variations at Kola Peninsula that could partly be linked to extraterrestrial factors such as changes in solar activity and galactic cosmic ray activity. It was obtained that:

(1) There is a rather good agreement between long-term climatic variation in Europe and at Kola Peninsula.

(2) The minima of solar activity Sporer (1416–1534 AD), Maunder (1645–1715 AD) and Dalton (1801–1816 AD) were accompanied by temperature decreases. Cooling during the end of the Wolf minimum (until 1350) is reflected in the juniper tree-ring series from Kola Peninsula whereas it is not reflected in the European temperature reconstructions.

(3) Some recent decreases in solar activity around 1900 and 1960 are linked to phases of reduced growth in juniper.

(4) The juniper chronologies from Kola Peninsula do not indicate a temperature rise at the end of the XX century.

(5) MTM spectral and wavelet analysis of juniper tree-ring records showed:

(a) more pronounced 22- and 80–100-year periodicities;

(b) the main cycle of solar activity, the 11-year Schwabe cycle, was not present;

(c) 20–22-year periodicity was not significant throughout the entire ca.700-year period, but during certain time intervals: 1328–1550, 1710–1800, 1985 to present.

The influence of the de Vries (∼ 200-year) solar cycle on climate variations: Results from the Central Asian Mountains and their global link

Long-term climatic changes related to solar forcing were examined using millennium-scale palaeoclimatic reconstructions from the Central Asian mountain region, i.e. summer temperature records for the Tien Shan mountains and precipitation records for the Tibetan Plateau. The reconstructions were based on juniper tree-ring width records, i.e. Juniperus turkestanica for the Tien Shan and Sabina przewalskii for the Tibetan Plateau. The data were processed using spectral and wavelet analysis and filtered in the frequency range related to major solar activity periodicities. The results obtained for various tree-ring chronologies indicate palaeoclimatic oscillations in the range of the de Vries (～ 210-year) solar cycles through the last millennium.The quasi-200-year variations revealed in the palaeoclimatic reconstructions correlate well (R² = 0.58–0.94) with solar activity variations (Δ¹⁴C variations). The quasi-200-year climatic variations have also been detected in climate-linked processes in Asia, Europe, North and South America, Australia, and the Arctic and Antarctica. The results obtained point to a pronounced influence of solar activity on global climatic processes.Analysis has shown that climate response to the long-term global solar forcing has a regional character. An appreciable delay in the climate response to the solar signal can occur (up to 150 years). In addition, the sign of the climate response can differ from the solar signal sign. The climate response to long-term solar activity variations (from 10s to 1000s years) manifests itself in different climatic parameters, such as temperature, precipitation and atmospheric and oceanic circulation. The climate response to the de Vries cycle has been found to occur not only during the last millennia but also in earlier epochs, up to hundreds of millions years ago.     

A millennium-long tree-ring chronology of Sabina przewalskii on northeastern Qinghai-Tibetan Plateau

Long tree-ring records on the Qinghai-Tibetan Plateau (QTP) are important for understanding better the Asian monsoon variability and its linkage with other global climate systems such as El Niño/Southern Oscillation activities. Here we report a 1017-year tree-ring chronology of Sabina przewalskii Kom. from the northeastern QTP. Climate–growth response function and correlation analyses show that radial growth of Sabina trees is positively associated with total precipitation in May and June of the growth year. Multidecadal variation in Delingha tree-ring chronology exhibits similar pattern with those of Dulan and Wulan chronologies of the nearby areas, suggesting that spring precipitation is a major factor limiting the growth of Sabina trees over a large spatial scale. Corresponding to the Little Ice Age, the three chronologies indicate spring droughts during 1440s to mid-1510s, mid-1640s to 1720s, late 1780s to late 1820s, and around mid-1870s. Examination of the tree-ring record in two largest historically documented El Niño events of 1789–93 and 1877–79 reveals that these very strong El Niño events were associated with conditions of spring droughts, and weakening of pre-monsoon circulation may precede occurrence of El Niño in some cases. The relationship between reduced monsoonal precipitation and very strong El Niño activity is, however, much complex and worth further study by spatio-temporal expansion of data coverage in the future.     

Waves and synchrony in Epirrita autumnata/Operophtera brumata outbreaks. II. Sunspot activity cannot explain cyclic outbreaks

1. In recent studies, it has been argued that sunspot activity forces the Epirrita autumnata 9-10-year outbreak periodicity in the mountain birch forest of Fennoscandia. For the following reasons, we challenge this conclusion. 2. With a 10-year outbreak cycle of E. autumnata and the 11-year sunspot cycle, it is expected that the cycles will run in-phase, out-of-phase and in-phase within 10 x 11 years. Hence, given such cycle lengths, sunspot activity should not affect outbreak periods. For a test, the E. autumnata series should be at least 110 years in length. 3. A well-documented E. autumnata outbreak series of 81 years (1888-1968; outbreak periods IV-XII) exists. This series is here lengthened to 114 years by adding outbreak frequencies for three decades (1969-2001). 4. By lengthening the series, three more E. autumnata/Operophtera brumata periods (XIII, XIV, XV) are identified. Period XV, like several earlier periods, was of the moving type, i.e. outbreaks moved in a wavelike manner from northern Fennoscandia to southern Norway. 5. As with several earlier outbreak periods in central northern Fennoscandia, the main timing of periods XIII-XV centred at the middle of the decades. In contrast, outbreaks at the extreme north-western coast of Norway centred at the decadal shifts, i.e. about 1979, 1989 and 1999. Supported by historical documents, we explain the 1979 and 1999 outbreaks as the final expressions of east-west outbreak waves that branched off from the main waves which moved southward during periods XIII and XV. These side-waves in the north are new observations. Outbreaks at the decadal shift 1989/1990 may have been of a more complex nature. 6. We find that sunspot activity does not explain outbreak waves. Furthermore, a test of our 114-year long E. autumnata series against the contemporaneous sunspot series shows that the two series run in-phase and out-of-phase. The observed interval between the two cycles coming in-phase agrees with the expected interval. This challenges the hypothesis of sunspot synchronization of the E. autumnata (and O. brumata) outbreaks.     

Predation as a probable mechanism relating winter weather to population dynamics in a North American porcupine population

An abundance index of an eastern Quebec population of North American porcupines (Erethizon dorsatum) has cycled with superimposed periodicities of 11 and 22 years from 1868 to 2000. This cycle closely followed 11- and 22-year cycles in solar irradiance and local weather (e.g., winter precipitation and spring temperature), generating the hypothesis that solar activity may affect porcupine abundance through effects on local weather. We investigated the mechanisms linking porcupine abundance to local weather conditions using a 6-year study (2000–2005) involving individual mark-recapture, radio tracking, seasonal survival analyses and identification of mortality causes. Summer (May–August) survival was high and constant over the study period, whereas winter (August–May) survival was lower and varied during the duration of our study. Variations in local winter precipitation explained 89% of the variation in winter survival. Porcupine predation rates appeared strongly related to snow conditions; 95% of depredated porcupines were killed when snow was covering the ground, and predation rates were higher in years with increased winter precipitation. Our data thus support the hypothesis that changes in predation rates under different snow conditions were the mechanism relating climate to porcupine population dynamics, via modifications of the local predator–prey interactions and impacts on porcupine winter survival. Our study adds to the growing body of evidence supporting an effect of climate on predator–prey processes. Also, it identifies one possible mechanism involved in the relationship between solar irradiance and porcupine population cycles observed at this study site over a 130-year period.     

Tree-ring-based reconstruction of precipitation in the Changling Mountains, China, since A.D.1691

Seven different tree-ring parameters were obtained from Chinese pine (Pinus tabulaeformis) in the Changling Mountains, China. The chronologies were analyzed individually and then compared with each other. The climate response analysis shows that total precipitation (September–July) is the main factor limiting the radial growth of Chinese pine in the Changling Mountains. Thus, the residual earlywood width chronology was used to estimate precipitation (September–July) for the period AD 1691–2006, and explained 46.9% of the precipitation variance. Drought events in our reconstruction are compared to historical archives for Gansu and north-central China. The results reveal the climatic extremes over much of Gansu. Some events have had profound impacts on the Gansu people over the past several centuries. Spatial analysis shows that the precipitation reconstruction has strong common signals for North-central China. The reconstructed series is correlated significantly with Helan Mountains Palmer drought severity index (PDSI), as well as with previous results from Jiuquan, Shandan, Huashan, Luya Mountains, and even the state of Mongolia. Our results suggest that some dry periods are coincident with solar minima over the past several hundred years. Multitaper spectral analysis reveals the existence of significant 24.4-year, 12.2-year, and 2.4- to 3.4-year periods of variability.     

Forward to the north: two Euro-Mediterranean bumblebee species now cross the Arctic Circle

In recent decades, several animal and plant species have been in regression (population size decrease and geographical distribution shrinking). This loss of biodiversity can be due to various factors such as the destruction and fragmentation of habitat, urban development, pesticides or climate change. However, some species benefit from these changes and expand their distribution. Here we report observations (in 2013 and 2014) of two Euro-Mediterranean bumblebee species: Bombus terrestris for the first time and Bombus lapidarius, north of the Arctic Circle in Fennoscandia.     

Comparison of whole wood and cellulose carbon and oxygen isotope series from Pinus nigra ssp. laricio (Corsica/France)

Stable isotopes in tree rings have widely been used for palaeoclimate reconstructions since tree rings record climatic information at annual resolution. However, various wood components or different parts of an annual tree-ring may differ in their isotopic compositions. Thus, sample preparation and subsequent laboratory analysis are crucial for the isotopic signal retained in the final tree-ring isotope series used for climate reconstruction and must therefore be considered for the interpretation of isotope–climate relationships. This study focuses on wood of Corsican Pine trees (Pinus nigra ssp. laricio) as this tree species allows to reconstruct the long-term climate evolution in the western Mediterranean. In a pilot study, we concentrated on methodological issues of sample preparation techniques in order to evaluate isotope records measured on pooled whole tree-ring cellulose and whole tree-ring bulk wood samples. We analysed 80-year long carbon and oxygen chronologies of Corsican Pine trees growing near the upper tree line on Corsica. Carbon and oxygen isotope records of whole tree-ring bulk wood and whole tree-ring cellulose from a pooled sample of 5 trees were correlated with the climate parameters monthly precipitation, temperature and the self-calibrating Palmer Drought Severity Index (sc-PDSI). Results show that the offsets in carbon and oxygen isotopes of bulk wood and cellulose are not constant over time. Both isotopes correlate with climate parameters from late winter and summer. The carbon and oxygen isotope ratios of cellulose are more sensitive to climatic variables than those of bulk wood. The results of this study imply that extraction of cellulose is a pre-requisite for the reconstruction of high-resolution climate records from stable isotope series of P. nigra ssp. laricio.     

Climate-growth response of Chinese white pine (Pinus armandii) at different age groups in the Baiyunshan National Nature Reserve,central China

Climate-growth response of trees at different age groups is less studied in humid regions of central China. In this study, we divided Pinus armandii ring-width series collected from the Baiyunshan National Nature Reserve of central China into young and old age groups based on the Hierarchical cluster analysis. Chronology statistics indicate that mean sensitivity (M.S.), signal-to-noise ratio (SNR), and expressed population signal (EPS) are higher in the old age group than that in the young age group. Meanwhile, there is are growth difference between the two age groups during their common period 1966–2014. Trees in the old age group exhibit significant decadal (∼10-year) cycles in the 1960s–1980s, while the 2–3-year cycles are more pronounced for the young age group. Correlation analysis between tree-rings and climate factors shows that the old trees generally contain more climatic information and are more sensitive to temperature, precipitation and moisture variability than the young trees, consistent with the chronology statistics. Our findings highlight the importance of considering the “juvenile effect” of young trees on tree-ring based climate reconstructions in the area.     

Late Holocene variability in pelagic fish scales and dinoflagellate cysts along the west coast of Vancouver Island, NE Pacific Ocean

Fish stocks and dinoflagellates are essential components of the marine food chain. Sediment cores from a predominantly anoxic basin in Effingham Inlet, Vancouver Island, British Columbia, archive a late Holocene (500–5300 years BP) record of paleoproductivity in the North American Coastal Upwelling Domain (CUD). We present evidence that late Holocene changes in the dinoflagellate cyst assemblages, sedimentary record, and fish stocks in the northeastern Pacific Ocean fluctuated, at least partially, in accordance with regional and global climate cycles.Principal components analysis (PCA), and trend, wavelet and spectral analyses were used to identify relationships, cycles and trends in sediment grey-scale values, and the abundances of fish scales and dinoflagellate cysts on centennial to millennial time scales. Most observed cycles fluctuated in intensity over time, particularly following transition of the regional climate to a higher rainfall phase that impacted coastal oceanic dynamics 3400 ± 150 years ago. Correlation of the marine paleoproductivity records observed in Effingham Inlet with solar influenced climate proxy cycles observed in the North Atlantic region indicates that solar forcing at different scales might have influenced the climate in the northeast Pacific as well. In particular an 1100- to 1400-year cycle in regional climate is well represented in the fish productivity proxy and sedimentological record. It was also observed that colder water, high-productivity, Selenopemphix nephroides and anchovy-dominated “Anchovy Regime” ecosystems alternate with warmer water, herring-dominated “Herring Regime” ecosystems at millennial time scales. The fish scale record preserved in Effingham Inlet indicates that the NE Pacific is now in transition from an ‘anchovy-’ to a ‘herring’-dominated regime.     

Tree rings and ‘El Año del Hambre’ in Mexico

Mexico has a wealth of historical information regarding extreme climate, famine and disease in the colonial period and even in prehispanic times. The recent development of long tree-ring chronologies throughout Mexico now allows comparison between records of past climate and socioeconomic conditions. North American tree-ring data indicate that, for the 3 consecutive years from 1785 to 1787, a major drought occurred across Mexico and the central United States with the most intense conditions extending north from Zacatecas into Texas. This period included the infamous ‘El Año del Hambre,’ one of greatest famines in Mexican history. The tree-ring data are also correlated with maize yield in central Mexico and with the value of Church tithes normally paid with agricultural goods. Drought and crop failure caused the dramatic inflation of crop value and Church tithes in 1786–1787 when tree-ring data indicate that the 1780s drought was most extreme.     

Radial growth response of Populus xjrtyschensis to environmental factors and a century-long reconstruction of summer streamflow for the Tuoshigan River,northwestern China

Broad-leaved tree species have rarely been used in dendroclimatology and dendrohydrology in arid Central Asia. Core samples of Populus xjrtyschensis Ch. Y. Yang were collected along the Tuoshigan River in 2015. Correlation and response analyses indicate that the radial growth of P. xjrtyschensis shows a strong relationship to streamflow and a weak response to climate. We suggest that summer streamflow is a limiting factor for the radial growth of P. xjrtyschensis along the Tuoshigan River. Using tree-ring data from P. xjrtyschensis, we reconstructed the historical summer streamflow of the Tuoshigan River back to 1900. The reconstruction has an adjusted r² of 0.407 (1957–2006). Statistical verification methods and historical documents indicate that the reconstructed series is stable and reliable. The results reveal that the beginning of the 20th century and the end of the 20th century to the present experienced above average streamflow, while the mid-20th century was characterized by a long dry period. The reconstructed streamflow data series revealed 6-yr (99%), 11-yr (95%) and 17–25-yr (99%) cycles. We suggest that variability in summer streamflow of the Tuoshigan River may be related to solar activity and large-scale oscillations in the climate system.     

Geographically partitioned spatial synchrony among cyclic moth populations

Many species of forest lepidopterans exhibit regular population cycles, which culminate in outbreak densities at approximately ten-year intervals. Population peaks and mass outbreaks typically occur synchronously and may lead to extensive forest damages over large geographic areas. Here, we report patterns of spatial synchrony among cyclic autumnal moth ( Epirrita autumnata ) populations across Fennoscandia, as inferred from 24 long-term (10–33 years) data sets. The study provides the first formal analysis of spatial synchrony of this pest species which damages mountain birch ( Betula pubescens ssp. czerepanovii ) forests in the sub Arctic. We detected positive cross-correlations in population growth rates between the time series, indicating overall spatial synchrony. However, we found the strongest degree of synchrony within geographically and climatically distinct regional clusters, into which time series were partitioned using cluster analyses. Within regional clusters, moth populations were exposed to the synchronizing effects of common, spatially autocorrelated environmental conditions, i.e. a Moran effect. Consequently, we conclude that a geographically and climatically restricted Moran effect, perhaps interacting with dispersal, is the most likely explanation for the regionally partitioned pattern of synchrony among autumnal moth populations in Fennoscandia. Our results emphasize that high amounts of environmental variation may result in a clear structuring of spatial synchrony at unexpectedly small scales.     

Xylem traits of peatland Scots pines reveal a complex climatic signal: A study in the Eastern Italian Alps

Long-term climate reconstructions are frequently based on tree-ring high-resolution proxies extracted from subfossil peatland trees. Peatlands are peculiar ecosystems characterized by high moisture in the upper soil part which creates a harsh living environment for trees. The climate mostly indirectly influences tree growth determining seasonal variations in the water table level. Within this framework, the aim of this study was to investigate climate responses of trees (Pinus sylvestris L.) growing inside and outside a Southern Alpine peat bog, by using tree-ring and wood anatomical traits (e.g. tracheid number and dimension, cell-wall thickness). Our results showed differences in the xylem structure and climate signal recorded by peatland and mineral soil trees. Peatland trees were characterized by narrow rings and tracheids with thinner cell wall. Summer temperature and precipitation were the major drivers of xylem formation in peatland trees. At intra-annual level wood anatomical traits revealed a complex within-ring signal during the growing season. The multi-parameters approach together with the high-resolution gained by using tree-ring sectors allowed us to obtain new detailed information on the xylem development of peatland trees and climate drivers that influenced it.     

Assessing cross-datable distinct annual growth rings in non-native Pinus kesiya Royle ex Gordon in Zambia

The response of non-native forest plantation trees to climate change remains poorly understood.We hypothesized that precipitation and temperature modulate tree-ring width chronology at each site and that higher tree growth is exhibited at remote sites than sites near copper mines. This study investigates if the annual tree-ring boundaries in non-native Pinus kesiya Royle ex Gordon in Zambia are distinct, cross-datable, and coherent with climate signal. We collected increment cores from live trees and climate data near and further away from emission sources and developed site tree-ring width chronologies. Based on cross-dating and chronology building statistics (i.e., ESP > 0.85; Glk > 0.6 and series inter-correlation > 0.4), P. kesiya posses cross-datable distinct annual growth ring boundaries that exhibited a high climate signal at both sites. The tree-ring width chronology was positively modulated by precipitation and negatively by solar radiation and temperature. The dry season precipitation was the limiting factor for the growth of P. kesiya. The predicted decrease in dry season precipitation and increase in temperature and solar radiation may reduce tree growth of P. kesiya, reduce productivity, and extend the rotation age. The mean ring width in P. kesiya was not significantly (p = 0.296) different between sites. However, the mean basal area increment at the site near the emission source (Ichimpe) was significantly (p < 0.001) higher than at the remote site (Chati), suggesting site-specific influences that require investigation. We recommend evaluating the causes and consequences of tree growth variation between sites and their relation to environmental variation, including microclimate, soils, and pollution. In this regard, an assessment of site-specific ring-width chronology and tree growth variation in this study directly contributes to an improved understanding of non-native P. kesiya ecology, and it offers the potential to study trees' responses to edaphic and climatic factors. Knowing these responses deepens our understanding of non-native pine tree growth in the face of climate change, given the significant role of tropical forests in the global carbon cycle.     

Tree-ring width based streamflow reconstruction for the Kaidu River originating from the central Tianshan Mountains since A.D. 1700

In this study, a 310-year pSeptember–August record of streamflow (where p denotes a month from the previous year) for the Kaidu River was reconstructed based on tree-ring-width from 137 Schrenk spruces (Picea schrenkiana). Spatial correlation showed that this streamflow reconstruction contains local hydroclimatic signals that approximately overlap the Kaidu River watershed. A comparison between the streamflow reconstruction for the Kaidu River and five tree-ring-based hydrological reconstructions for the surrounding areas revealed similar variations in the low-frequency domain. The results of comparison analyses between this reconstruction and other hydrological reconstructions indicated that the hydrological characteristics of the Kaidu River in the 1910s (the driest decade for the Kaidu River in the last 310 years), and the increasing trend of streamflow that began in the 1980s, might have occurred in other areas of the Tianshan Mountains and covered an even larger area. Furthermore, the highest and lowest values of this reconstructed streamflow series capture five flood or snowfall events (1803, 1804, 1836, 1923, and 1959) and six drought events (1894, 1916, 1917, 1918, 1931, and 1944) that were noted in historical documents. The 10.8- and 3.5–5.4-year cycles of this reconstruction coincided with the observed data and other tree-ring based hydrometeorological reconstructions, and revealed the possible influences of solar activity and the atmosphere–ocean system.     

Annual precipitation in Liancheng, China, since 1777 AD derived from tree rings of Chinese pine (Pinus tabulaeformis Carr.)

Precipitation from the previous August to the current June over the last 232 years in Liancheng, China, was reconstructed by a transfer function based on the correlation between tree-ring widths and local meteorological data. The explained variance was 45.3 %, and fluctuations on both annual and decadal scales were captured. Wet periods with precipitation above the 232-year mean occurred from 1777 to 1785, 1802 to 1818, 1844 to 1861, 1889 to 1922 and 1939 to 1960. Dry periods (precipitation below the mean) occurred from 1786 to 1801, 1819 to 1843, 1862 to 1888 and 1923 to 1938. The reconstruction compares well with a tree-ring-based precipitation reconstruction at Mt. Xinglong; both of them showed the well-known severe drought in the late 1920s. The rainfall series also shows highly synchronous decreasing trends since the 1940s, suggesting that precipitation related to the East Asian summer monsoon at these two sites has decreased by large spatial and temporal (decadal) scales. Power spectrum analysis of the reconstruction showed remarkable 21.82-, 3.48-, 3.12-, 3.08- and 2.31-year cycles for the past 232 years; the 22-year cycle corresponds to the solar cycle and is expressed widely in tree ring/precipitation reconstructions on the China Loess Plateau. This may suggest a solar influence on the precipitation variations on the Loess Plateau, although the mechanisms are not well understood.     

El Niño and related monsoon drought signals in 523-year-long ring width records of teak (Tectona grandis L.F.) trees from south India

We present a 523-year (A.D. 1481–2003) tree-ring width index chronology of Teak (Tectona grandis L.F.) from Kerala, Southern India, prepared from three forest sites. Dendroclimatological investigations indicate a significant positive relationship between the tree-ring index series and Indian summer monsoon rainfall (ISMR) and related global parameters like the Southern Oscillation Index (SOI). A higher frequency of occurrence of low tree growth is observed in years of deficient Indian monsoon rainfall (droughts) associated with El Niño since the late 18th century. Prior to that time, many low tree growth years are detected during known El Niño events, probably related to deficient Indian monsoon rainfall. The general relationship between ISMR and El Niño is known to be negative and the spatial correlations between our Kerala tree-ring chronology and sea surface temperatures (SSTs) over the Niño regions follow similar patterns as those for ISMR. This relationship indicates strong ENSO-related monsoon signals in the tree-ring records. These tree-ring chronologies with a high degree of sensitivity to monsoon climate are useful tools to understand the vagaries of monsoon rainfall prior to the period of recorded data.     

Climatic factors controlling Pinus sylvestris radial growth along a transect of increasing continentality in southern Siberia

The forest-steppe ecotone in southern Siberia is characterized by a strong dependence of tree growth on summer drought, which is expected to increase under ongoing climate change, with potential consequences for regional and global water and carbon cycles. Since climate conditions control tree secondary growth throughout the growing season, it is assumed that climate change will differently impact the formation of particular tree-ring sectors.In this study, we evaluated spatiotemporal trends in Pinus sylvestris L. tree-ring traits: tree-ring (RW), earlywood (EW) and latewood (LW) widths, as well as their climate response in order to understand potential reactions of P. sylvestris radial growth to climate change along a 4900 km longitudinal transect of increasing continentality in southern Siberia.Results indicated an increasing tree radial growth from the West to the East along the transect. Tree-ring parameters were sensitive to drought, showing a temporal delay in the climatic signals of LW (summer) relative to EW (spring). Climate control of tree growth was stronger at the western site, while it was alleviated over time in eastern sites.This study highlighted the wide plasticity of P. sylvestris to thrive within a wide range of climatic conditions, also suggesting that future drought, as predicted by climate change simulations, will potentially impact P. sylvestris growth differently along the studied gradient, being more susceptible at the western sites due to the current growth limitation.