Growth reactions of Pinus sylvestris L. and Quercus pubescens Willd. to drought years at a xeric site in Valais, Switzerland

In Valais, an inner-Alpine dry valley in Switzerland, low-elevation Scots pine (Pinus sylvestris L.) forests are changing. While pine shows high mortality rates, deciduous species, in particular pubescent oak (Quercus pubescens Willd.), are becoming more abundant. We hypothesise that increasing drought and the species-specific drought tolerance are key factors in these processes. In this study, the growth reaction to drought years of pine and oak growing at a xeric site in Valais was analysed using dendrochronological and wood anatomical methods. Congruent with theoretical expectations, the tree-ring widths of both species, the mean lumen area of earlywood vessels in oak and the number of tracheids in a radial row in pine decreased in response to dry conditions. However, both species also showed reactions deviating from those known from mesic sites: In oak, the mean lumen area of latewood vessels increased in drought years. In pine, in the driest year of the period (1976), the mean radial diameter increased in latewood and decreased only slightly in earlywood. These results emphasises that the process of wood formation and cell functionality at xeric sites is not completely understood yet. Both species seem to have difficulties to adapt the size of their water-conducting cells to strongly reduced water availability in drought years. Additionally, the cell number is strongly reduced. Thus it remains unclear if both species can maintain sufficient water transport under increasingly dry conditions.     

Elevated atmospheric CO2 alters wood production, wood quality and wood strength of Scots pine (Pinus sylvestris L) after three years of enrichment

Scots pine ( Pinus sylvestris L.) trees were grown in open top chambers for three years under ambient and elevated CO₂ concentrations. The trees were aged 3 y at the beginning of the CO₂ exposure, and the effects of the treatment on total stem volume, stem wood biomass, wood quality and wood anatomy were examined at the end of the exposure. The elevated CO₂ treatment lead to a 49% and 38% increase in stem biomass and stem wood volume, respectively. However, no significant effects of the elevated CO₂ treatment on wood density were observed, neither when green wood density was estimated from stem biomass and stem volume, nor when oven-dry wood density was measured on small wood samples. Under elevated CO₂ significantly wider growth rings were observed. The effect of elevated CO₂ on growth ring width was primarily the result of an increase in earlywood width. Wood compression strength decreased under elevated CO₂ conditions, which could be explained by significantly larger tracheids and the increased earlywood band, that has thinner walls and larger cavities. A significant decrease of the number of resin canals in the third growth ring was observed under the elevated treatment; this might indicate that trees produced and contained less resin, which has implications for disease and pest resistance. So, although wood volume yield in Scots pine increased significantly with elevated CO₂ after three years of treatment, wood density remained unchanged, while wood strength decreased. Whilst wood volume and stem biomass production may increase in this major boreal forest tree species, wood quality and resin production might decrease under future elevated CO₂ conditions.     

Wood anatomy and carbon‐isotope discrimination support long‐term hydraulic deterioration as a major cause of drought‐induced dieback

Hydraulic impairment due to xylem embolism and carbon starvation are the two proposed mechanisms explaining drought‐induced forest dieback and tree death. Here, we evaluate the relative role played by these two mechanisms in the long‐term by quantifying wood‐anatomical traits (tracheid size and area of parenchyma rays) and estimating the intrinsic water‐use efficiency (iWUE) from carbon isotopic discrimination. We selected silver fir and Scots pine stands in NE Spain with ongoing dieback processes and compared trees showing contrasting vigour (declining vs nondeclining trees). In both species earlywood tracheids in declining trees showed smaller lumen area with thicker cell wall, inducing a lower theoretical hydraulic conductivity. Parenchyma ray area was similar between the two vigour classes. Wet spring and summer conditions promoted the formation of larger lumen areas, particularly in the case of nondeclining trees. Declining silver firs presented a lower iWUE than conspecific nondeclining trees, but the reverse pattern was observed in Scots pine. The described patterns in wood anatomical traits and iWUE are coherent with a long‐lasting deterioration of the hydraulic system in declining trees prior to their dieback. Retrospective quantifications of lumen area permit to forecast dieback in declining trees 2–5 decades before growth decline started. Wood anatomical traits provide a robust tool to reconstruct the long‐term capacity of trees to withstand drought‐induced dieback.     

Size-dependent responses to summer drought in Scots pine, Norway spruce and common oak

In this study, we provide a detailed analysis of tree growth and water status in relation to climate of three major species of forest trees in lower regions of Bavaria, Southern Germany: Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and common oak (Quercus robur). Tree-ring chronologies and latewood δ¹³C were used to derive measures for drought reaction across trees of different dimensions: growth reduction associated with drought years, long-term growth/climate relations and stomatal control on photosynthesis. For Scots pine, growth/climate relations indicated a stronger limitation of radial growth by high summer temperatures and low summer precipitation in smaller trees in contrast to larger trees. This is corroborated by a stronger stomatal control on photosynthesis for smaller pine trees under average conditions. In dry years, however, larger pine trees exhibited stronger growth reductions. For Norway spruce, a significantly stronger correlation of tree-ring width with summer temperatures and summer precipitation was found for larger trees. Additionally, for Norway spruce there is evidence for a change in competition mode from size-asymmetric competition under conditions with sufficient soil water supply to a more size-symmetric competition under dry conditions. Smaller oak trees showed a weaker stomatal control on photosynthesis under both dry and average conditions, which is also reflected by a significantly faster recovery of tree-ring growth after extreme drought events in smaller oak trees. The observed patterns are discussed in the context of the limitation-caused matter partitioning hypothesis and possible species-specific ontogenetic modifications.     

Wood borer performance and wood characteristics of drought‐stressed Scots pine seedlings

Four‐year‐old Scots pine [Pinus sylvestris L. (Pinaceae)] seedlings were exposed to medium and severe drought stress for two consecutive years. The anatomical properties of drought‐stressed Scots pine wood and their impact on the performance of destructive wood boring early instars of Hylotrupes bajulus L. (Coleoptera: Cerambycidae) were studied. Drought stress significantly decreased diameter of earlywood tracheids in both growing years and diameter of latewood tracheids after the second growing season only. Cell lumen area was significantly decreased by both medium and severe drought stress compared to well‐watered controls. In addition, area of cell lumen was significantly smaller in severe drought than in medium drought treatment. The drought stress marginally increased the number of resin canals in the wood, but did not affect the size of resin canals either in wood or bark. The relative growth rate of xylophagous H. bajulus neonatal larvae was not significantly affected by drought stress during the 106‐day feeding period on Scots pine wood blocks. The results show that although water availability was an important factor affecting the development and anatomy of wood cells, observed changes in wood characteristics did not affect the performance of early instars feeding on wood processed from drought‐stressed young Scots pine seedlings.     

How needle phenology indicates the changes of xylem cell formation during drought stress in Pinus sylvestris L.

Temperature, water availability and photoperiod are the primary drivers of tree phenological processes. However, there is lack of information how the spring temperature and summer drought affect phenology of both cambium and needles. We evaluated the interplay between xylem and needle development of mature Scots pine trees in three consecutive years differing in the spring temperatures and onset and duration of summer drought. Cambial activity began on the day of a year (DOY) 83–87, while the bud break occurred on DOY 113–119, when also the secondary cell wall of tracheids started its formation. While the timing of bud break correlated with the sum of effective temperatures, the beginning of cambial zone activity did not. The needles were fully unfolded around DOY 170, which corresponded to the transition between earlywood and latewood tracheids. Summer drought did not affect needle development, but it changed the rate of production and morphology of latewood tracheids. Latewood tracheids from the year 2015 when the drought was longest (i.e. until the second half of August in 2015 compared to the duration from June until the middle of July in the two other years) were 32% narrower and they had 34% thinner cell walls than in 2014 and 2016. The improvement of tree water status in July resulted in the formation of intra-annual density fluctuations (IADF). The interplay between needle and cambium phenology provided an insight into how the tree allocates the resources with varying temperature and soil water availability.     

Climatic control of intra- and inter-annual wood-formation dynamics of Scots pine in northern Finland

Boreal forests are highly sensitive to climate and human impacts and therefore suitable as biological indicator for environmental changes. In this context, our study was aimed at getting deeper insight into the climate-dependence of the onset, intensity and end of wood formation of Scots pine during the growing season.We monitored the intra-annual growth dynamics of, on average, 42-year-old Scots pine trees over five consecutive years, 2000-2004, at two sites located 80 and 300 km south of the tree line in northern Finland. For that purpose, the cambium of the trees was weekly wounded with a pin and the resulting wound tissue, microscopically detectable in transverse thin-sections through the newly built wood, was taken as a time marker. During this 5-year study period, the intra-annual wood formation at the southern site was mainly positively associated with summer temperature. However, at the northern site such an association was either entirely missing or negative. At both sites, two thirds of the radial growth was produced within only 4 weeks from mid-June to mid-July, independent of whether the growing season started earlier or later.Moreover, we measured the widths of all tree rings from bark to pith (inter-annual growth) of the same study trees and assembled them to 51-year long tree-ring site chronologies. Since 1999, these two site chronologies - after having run fairly parallel over the preceding decades - were running in divergent directions thus corroborating our results derived from the intra-annual climate/growth analysis. Whereas the chronology of the southern site follows the average temperature of May and July very closely from 1961 up to 2004, the chronology of the northern site follows the July temperature, but only up to 1998, and from 1999 to 2004 is running just opposite to the distinctly rising July temperature. During the same period, there was - unlike in the years before - nearly no snow cover in May at the northern site, whereas at the southern site there was no change of the normally existing slight snow cover in May. This deviating weather situation may have led to a temperature-induced, temporary drought stress for the Scots pines at the northern site.     

Dating lightning: Dendrochronological and magnetic analyses of lightning scars

Lightning impacts on forests and trees are still understudied from a tree-ring perspective. Lighting causes direct and indirect damages on forests and trees. Trees struck by lightning can show a growth reduction and lightning storms also trigger wildfires in seasonally dry areas such as Mediterranean mountains. Here we combined dendroecological and magnetic analyses to reconstruct and assess the impact of lightning on radial growth and the magnetic properties of wood in Scots pine (Pinus sylvestris) and Black pine (Pinus nigra) in two sites with a high density of lightning impacts located in eastern Spain. We dated several lightning scars, particularly in Scots pine, formed during 1982, when a wildfire was initiated by lightning during a dry summer storm. Growth was reduced during the year when the scar was formed in both pine species, albeit this effect could be masked or amplified by other disturbances (drought, outbreaks). However, despite that short-term growth reduction scarred trees showed higher growth rates than non-scarred trees in the case of Scots pine. The intensity of magnetization did not significantly differ in wood produced before and after the lightning scar was formed. This could be due to multiple lightning hits in the same or nearby stands affecting the magnetization of wood. Wood magnetic properties should be further explored as proxies of lightning impacts in sites where scars are not formed and tree-ring information is limited such as tropical forests. Further cross-disciplinary research is required to assess the impacts of lightning on tree growth and magnetism.     

Light rings in Chinese pine (Pinus tabulaeformis) in semiarid areas of north China and their palaeo-climatological potential

Light rings in conifer trees are characterized by a light-coloured, narrow latewood band of thin-walled tracheids. Most reports on light rings have been for subarctic and subalpine regions, and little is known about their occurrence in semiarid areas. Dendrochronological methods were used to date the occurrence of light rings in Chinese pine (Pinus tabulaeformis) in the semiarid region of north China. The anatomical and chemical characteristics and the potential environmental controls of their formation were investigated. Light rings in Chinese pine were dated to the year of their formation. The wall thickness and lumen diameter of the wood cells of light rings and reference rings were distinctly different. However, the configuration of the light-ring latewood cell walls was normal, although they were thinner than average, and their lignification had been completed normally. The climate characteristics that result in light-ring formation appear to be ongoing severe drought from the previous autumn to July of the current year in conjunction with a warm summer, suggesting that light rings can be used as indicators for past drought events.     

What tree rings can tell us about the competition between trees and lianas? A case study based on growth,anatomy, density,and carbon accumulation

In tropical forest, landscape fragmentation and the consequent degradation of disturbed forests increase the incidence of light and dry hot winds, causing a disturbance on natural regeneration. Under these conditions, lianas (woody vines) development is stimulated instead of other species, which are more suited to mature forest and under less influence of the edge effect. For this, lianas colonization is an important variable for assessing the disturbance level of a forest. In this context, it becomes important to understand the nature of the competitive relationships between hyper-abundant lianas and ring growth of the host trees. Here, we selected trees with occupation or absence of lianas from two tropical species – Pinus caribaea var. hondurensis (Caribbean pine) and Tectona grandis (teak) – localized in a semideciduous forest fragment in southeastern Brazil, aiming to compare growth, climatic response, anatomy (vessels and intra-annual density fluctuations), wood density and carbon, by tree-ring analysis. The results showed that the lianas caused a change in tree-ring anatomy of host trees in last 10 years, mainly. We observed that trees occupied by lianas had a decrease the radial growth and carbon in the two species, an increase of the vessels size in teak and a decrease of the IADF frequency in Caribbean pine. In teak, the climate-tree relationship indicated that trees with lianas had lower response to rainfall and higher response to temperature in the summer (rainy and hottest period); in Caribbean pine, we observed that trees with lianas had a 2-month delay in the radial growth response to rainfall in the dry season. In the teak group, we observed that host trees had higher wood density values than liana-free tree in the outer rings, and the opposite was showed for pine. These findings show that tree-ring growth of host trees are a strong bioindicator of forest disturbance caused by aggressive colonization of lianas. We believe that these methods are applicable to future studies relating to the effects of habitat fragmentation and forest degradation on biodiversity and ecosystem services, particularly in the context of global climate change.     

Linking increasing drought stress to Scots pine mortality and bark beetle infestations

In the dry Swiss Rhone Valley, Scots pine forests have experienced increased mortality in recent years. It has commonly been assumed that drought events and bark beetles fostered the decline, however, whether bark beetle outbreaks increased in recent years and whether they can be linked to drought stress or increasing temperature has never been studied. In our study, we correlated time series of drought indices from long-term climate stations, 11-year mortality trends from a long-term research plot, and mortality probabilities modeled from tree rings (as an indicator of tree vitality) with documented occurrences of various bark beetle species and a buprestid beetle, using regional Forest Service reports from 1902 to 2003 and advisory cases of the Swiss Forest Protection Service (SFPS) from 1984 to 2005. We compared the historical findings with measured beetle emergence from a 4-year tree felling and breeding chamber experiment. The documented beetle-related pine mortality cases increased dramatically in the 1990s, both in the forest reports and the advisory cases. The incidents of beetle-related pine mortality correlated positively with spring and summer temperature, and with the tree-ring based mortality index, but not with the drought index. The number of advisory cases, on the other hand, correlated slightly with summer drought index and temperature, but very highly with tree-ring-based mortality index. The tree-ring-based mortality index and observed tree mortality increased in years following drought. This was confirmed by the beetle emergences from felled trees. Following dry summers, more than twice as many trees were colonized by beetles than following wet summers. We conclude that increased temperatures in the Swiss Rhone Valley have likely weakened Scots pines and favored phloeophagous beetle population growth. Beetles contributed to the increased pine mortality following summer drought. Among the factors not addressed in this study, changed forest use may have also contributed to increased beetle populations and Scots pine mortality, whereas air pollution seems to be of lesser importance.     

Nine Years of Irrigation Cause Vegetation and Fine Root Shifts in a Water-Limited Pine Forest

Scots pines (Pinus sylvestris L.) in the inner-Alpine dry valleys of Switzerland have suffered from increased mortality during the past decades, which has been caused by longer and more frequent dry periods. In addition, a proceeding replacement of Scots pines by pubescent oaks (Quercus pubescens Willd.) has been observed. In 2003, an irrigation experiment was performed to track changes by reducing drought pressure on the natural pine forest. After nine years of irrigation, we observed major adaptations in the vegetation and shifts in Scots pine fine root abundance and structure. Irrigation permitted new plant species to assemble and promote canopy closure with a subsequent loss of herb and moss coverage. Fine root dry weight increased under irrigation and fine roots had a tendency to elongate. Structural composition of fine roots remained unaffected by irrigation, expressing preserved proportions of cellulose, lignin and phenolic substances. A shift to a more negative δ¹³C signal in the fine root C indicates an increased photosynthetic activity in irrigated pine trees. Using radiocarbon (¹⁴C) measurement, a reduced mean age of the fine roots in irrigated plots was revealed. The reason for this is either an increase in newly produced fine roots, supported by the increase in fine root biomass, or a reduced lifespan of fine roots which corresponds to an enhanced turnover rate. Overall, the responses belowground to irrigation are less conspicuous than the more rapid adaptations aboveground. Lagged and conservative adaptations of tree roots with decadal lifespans are challenging to detect, hence demanding for long-term surveys. Investigations concerning fine root turnover rate and degradation processes under a changing climate are crucial for a complete understanding of C cycling.     

Fast response of Scots pine to improved water availability reflected in tree‐ring width and δ13C

Drought‐induced forest decline, like the Scots pine mortality in inner‐Alpine valleys, will gain in importance as the frequency and severity of drought events are expected to increase. To understand how chronic drought affects tree growth and tree‐ring δ¹³C values, we studied mature Scots pine in an irrigation experiment in an inner‐Alpine valley. Tree growth and isotope analyses were carried out at the annual and seasonal scale. At the seasonal scale, maximum δ¹³C values were measured after the hottest and driest period of the year, and were associated with decreasing growth rates. Inter‐annual δ¹³C values in early‐ and latewood showed a strong correlation with annual climatic conditions and an immediate decrease as a response to irrigation. This indicates a tight coupling between wood formation and the freshly produced assimilates for trees exposed to chronic drought. This rapid appearance of the isotopic signal is a strong indication for an immediate and direct transfer of newly synthesized assimilates for biomass production. The fast appearance and the distinct isotopic signal suggest a low availability of old stored carbohydrates. If this was a sign for C‐storage depletion, an increasing mortality could be expected when stressors increase the need for carbohydrate for defence, repair or regeneration.     

Drought as an Inciting Mortality Factor in Scots Pine Stands of the Valais, Switzerland

During the 20th century, high mortality rates of Scots pine (Pinus silvestris L.) have been observed over large areas in the Rhône valley (Valais, Switzerland) and in other dry valleys of the European Alps. In this study, we evaluated drought as a possible inciting factor of Scots pine decline in the Valais. Averaged tree-ring widths, standardized tree-ring series, and estimated annual mortality risks were related to a drought index. Correlations between drought indices and standardized tree-ring series from 11 sites showed a moderate association. Several drought years and drought periods could be detected since 1864 that coincided with decreased growth. Although single, extreme drought years had generally a short-term, reversible effect on tree growth, multi-year drought initiated prolonged growth decreases that increased a tree’s long-term risk of death. Tree death occurred generally several years or even decades after the drought. In conclusion, drought has a limiting effect on tree growth and acts as a bottleneck event in triggering Scots pine decline in the Valais.     

Daily dynamics in xylem cell radial growth of Scots pine (Pinus sylvestris L.)

Daily dynamics of radial cell expansion during wood formation within the stems of 25-year-old Scots pine trees (Pinus sylvestris L.), growing in field conditions, were studied. The samples of forming wood layers were extracted 4 times per day for 3 days. Possible variations in the growth on different sides of the stem, duration of cell development in radial cell expansion phase and dynamics of cell growth in this phase were taken into account. The perimeters of tracheid cross-sections as a reflection of primary cell wall growth were the criterion of growth in a radial direction. For the evaluation of growing cell perimeters a special system for digital processing and image analysis of tracheid cross-sections of the forming wood was used. Growth rate for certain time intervals was estimated by the change in the relation of the perimeter of each observed cell in each of ten tracheid rows in each of 12 trees to the perimeter of the xylem cell of the same row before the expansion. Temporal differences in average values of the relations were estimated by Analyses of Variance. The existence of daily dynamics of Scots pine xylem cell radial growth has been proved. Intensive growth of pine tracheids has been shown to occur at any time of the day and to depend on the temperature regime of the day and the night as well as water supply of stem tissues. Moreover, reliable differences (P = 0.95) in the increment of cell walls during tracheid radial expansion have been found. Pulsing changes of the water potentials both of the cell and the apoplast, as the reason for the fluctuations of radial cell growth rate, were discussed.     

The impact of the 2003 summer drought on the intra-annual growth pattern of beech (Fagus sylvatica L.) and oak (Quercus robur L.) on a dry site in the Netherlands

Climate change is expected to result in more extreme weather conditions over large parts of Europe, such as the prolonged drought of 2003. As water supply is critical for tree growth on many sites in North-Western Europe, such droughts will affect growth, species competition, and forest dynamics. To be able to assess the susceptibility of tree species to climate change, it is necessary to understand growth responses to climate, at a high temporal resolution. We therefore studied the intra-annual growth dynamics of three beech trees (Fagus sylvatica L.) and five oak trees (Quercus robur L.) growing on a sandy site in the east of the Netherlands for 2 years: 2003 (oak and beech) and 2004 (oak). Microcores were taken at 2-week intervals from the end of April until the end of October. Intra-annual tree-ring formation was compared with prior and contemporary records of precipitation and temperature from a nearby weather station.The results indicate that oak and beech reacted differently to the summer drought in 2003. During the drought, wood formation in both species ceased, but in beech, it recovered after the drought. The causes of species-specific differences in intra-annual wood formation are discussed in the context of susceptibility to drought.     

Variation in reproduction and growth in declining Scots pine populations

Disentangling how variation in reproduction and growth is linked in plants across different ecological scales, and how allocation rules change in response to stress are fundamental aspects of life history theory. Although it is known that reproductive allocation is an allometric process and that environmental conditions can influence demographic traits, patterns of variation in vegetative and reproductive functions across and within individuals of tree species suffering drought-induced decline have rarely been documented. In this study we use Scots pine (Pinus sylvestris L.) as a model species to explore patterns of variation in cone production and growth in two declining populations at the southern edge of its distribution. A Bayesian approach was used to assess how these demographic traits vary as a function of drought effects and competition and covary across different ecological scales. The allometric trajectories relating tree size with cone production and growth differed along gradients of drought impacts and biotic interactions. Although reproduction and growth increased with tree size, cone production reached a maximum at intermediate sized trees and stabilized or decreased at larger sizes. Drought stress effects (defoliation at the tree level and overall decline at the plot level) and competition for resources reduced cone production and growth. Our results also showed differential effects of defoliation on cone production depending on tree size, with stronger effects on larger individuals. After accounting for these effects, much of the variation of demographic traits and correlations among them occurred at small ecological scales across individuals (i.e. within plots) and within individuals across years. This resulted in covariations between demographic traits among nearby individuals and within individuals through time, suggesting a consistent advantage in resource acquisition of some individuals within plots, and trade-offs between growth and cone production within trees across years. In conclusion, this study reports that drought-induced forest decline is associated with lower growth and cone production in Scots pine, which could contribute to explain the long-term impacts of drought in southern populations of this species and, in particular, its low regeneration capacity after severe drought.     

Long- and short-term impacts of a defoliating moth plus mistletoe on tree growth,wood anatomy and water-use efficiency

Climate warming and biotic stressors are expected to reduce tree radial growth and performance at short and long time scales. However, the impacts of different biotic stressors on performance throughout a tree’s life are largely understudied. Here we assessed the effects of a past nun moth (Lymantria dispar) outbreak and related defoliation on Scots pine (Pinus sylvestris) trees, which were later severely infested by the hemiparasite mistletoe (Viscum album subsp. austriacum). We compared the responses of trees severely infested or not infested by mistletoe in a wet vs. a dry site to quantify the relative importance of biotic stressors under different climate conditions. We used dendrochronology to quantify: long- and short-term changes in radial growth (resilience), differences in wood anatomy during the outbreak, and recent changes in intrinsic water-use efficiency (WUEi). The outbreak caused a sharp growth reduction in 1953 (50% decrease in basal area increment –BAI) and the formation of tracheids of small transversal lumen diameter (33% decrease in diameter). Recent mistletoe infestation caused a difference in growth between infested and non-infested trees lasting 34 and 21 years in the wet and dry sites, respectively. Growth (BAI) decreased more steeply in severely infested than in non-infested trees, the post-drought resilience decreased in severely infested trees, and the WUEi increased, particularly in the dry site. The BAI of severely infested trees was more negatively impacted by warm and dry conditions during the growing season than in non-infested trees, particularly in the dry site. Tree rings recorded historical effects of biotic stressors (L. monacha outbreak), which may constrain responses to recent stressors (mistletoe).     

Stand- and tree-level determinants of the drought response of Scots pine radial growth

Characterizing the responses of key tree species to extreme climatic events may provide important information for predicting future forest responses to increased climatic variability. Here we aimed at determining which tree- and stand-level attributes were more closely associated with the effect of a severe drought on the radial growth of Scots pine, both in terms of immediate impact and recovery after the drought event. Our dataset included tree-ring series from 393 plots located close to the dry limit of the species range. Time series analysis and mixed-effects models were used to study the growth of each tree and its detailed response to a severe drought event that occurred in 1986. Our results showed that the radial growth responses of Scots pine were determined primarily by tree-level characteristics, such as age and previous growth rate, and secondarily by stand basal area and species richness, whereas local climate had a relatively minor effect. Fast-growing trees were more severely affected by the drought and retained proportionally lower growth rates up to three years after the episode. In absolute terms, however, fast-growing trees performed better both during and after the event. Older trees were found to be less resilient to drought. The effect of stand basal area and species richness indicated that competition for resources worsened the effects of drought, and suggested that the effect of interspecific competition may be particularly detrimental during the drought year.