Asymmetric changes of growth and reproductive investment herald altitudinal and latitudinal range shifts of two woody species

Ongoing changes in global climate are altering ecological conditions for many species. The consequences of such changes are typically most evident at the edge of the geographical distribution of a species, where range expansions or contractions may occur. Current demographical status at geographical range limits can help us to predict population trends and their implications for the future distribution of the species. Thus, understanding the comparability of demographical patterns occurring along both altitudinal and latitudinal gradients would be highly informative. In this study, we analyse the differences in the demography of two woody species through altitudinal gradients at their southernmost distribution limit and the consistency of demographical patterns at the treeline across a latitudinal gradient covering the complete distribution range. We focus on Pinus sylvestris and Juniperus communis, assessing their demographical structure (density, age and mortality rate), growth, reproduction investment and damage from herbivory on 53 populations covering the upper, central and lower altitudes as well as the treeline at central latitude and northernmost and southernmost latitudinal distribution limits. For both species, populations at the lowermost altitude presented older age structure, higher mortality, decreased growth and lower reproduction when compared to the upper limit, indicating higher fitness at the treeline. This trend at the treeline was generally maintained through the latitudinal gradient, but with a decreased growth at the northern edge for both species and lower reproduction for P. sylvestris. However, altitudinal and latitudinal transects are not directly comparable as factors other than climate, including herbivore pressure or human management, must be taken into account if we are to understand how to infer latitudinal processes from altitudinal data.     

Assessing forest vulnerability to climate warming using a process‐based model of tree growth: bad prospects for rear‐edges

Growth models can be used to assess forest vulnerability to climate warming. If global warming amplifies water deficit in drought‐prone areas, tree populations located at the driest and southernmost distribution limits (rear‐edges) should be particularly threatened. Here, we address these statements by analyzing and projecting growth responses to climate of three major tree species (silver fir, Abies alba; Scots pine, Pinus sylvestris; and mountain pine, Pinus uncinata) in mountainous areas of NE Spain. This region is subjected to Mediterranean continental conditions, it encompasses wide climatic, topographic and environmental gradients, and, more importantly, it includes rear‐edges of the continuous distributions of these tree species. We used tree‐ring width data from a network of 110 forests in combination with the process‐based Vaganov–Shashkin‐Lite growth model and climate–growth analyses to forecast changes in tree growth during the 21st century. Climatic projections were based on four ensembles CO₂ emission scenarios. Warm and dry conditions during the growing season constrain silver fir and Scots pine growth, particularly at the species rear‐edge. By contrast, growth of high‐elevation mountain pine forests is enhanced by climate warming. The emission scenario (RCP 8.5) corresponding to the most pronounced warming (+1.4 to 4.8 °C) forecasted mean growth reductions of ?10.7% and ?16.4% in silver fir and Scots pine, respectively, after 2050. This indicates that rising temperatures could amplify drought stress and thus constrain the growth of silver fir and Scots pine rear‐edge populations growing at xeric sites. Contrastingly, mountain pine growth is expected to increase by +12.5% due to a longer and warmer growing season. The projections of growth reduction in silver fir and Scots pine portend dieback and a contraction of their species distribution areas through potential local extinctions of the most vulnerable driest rear‐edge stands. Our modeling approach provides accessible tools to evaluate forest vulnerability to warmer conditions.     

Latitudinal and altitudinal diversity patterns and Rapoport effects in north-west European land snails and their causes

The latitudinal and altitudinal range sizes of north-west European land-snail species increase with increasing latitude/altitude. These Rapoport effects are not caused by northern/high-altitude species with wider latitudinal/altitudinal ranges and southern/low-altitude species with narrower latitudinal/altitudinal ranges, as predicted by the climatic variability hypothesis. They are instead caused mainly by different northern/upper borders of species occurring in the south part of the study area or at low and intermediate altitudes, respectively. This pattern indicates that the observed Rapoport effects are the result mainly of differential northward/upward expansion of species that were restricted to southern/low or intermediate altitude refugia during the glacials. Although all species occurring in a refugium experienced the same climatic conditions, there is stochastic variation in their climatic tolerance. Species with broader climatic tolerance were able to expand farer northwards/upwards postglacial. The altitudinal distribution of species richness in the analysed alpine faunas cannot be explained by the Rapoport-rescue hypothesis, because species richness peaks at intermediate altitudes and because there is no negative correlation between the number of range borders and altitude. The Rapoport-rescue hypothesis alone is probably also insufficient to explain the decrease in species richness with increasing latitude.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 309–323.     

Radial growth response to climate change along the latitudinal range of the world's southernmost conifer in southern South America

Aim

We examined whether and how tree radial‐growth responses to climate have changed for the world's southernmost conifer species throughout its latitudinal distribution following rapid climate change in the second half of the 20th century.

Location

Temperate forests in southern South America.

Methods

New and existing tree‐ring radial growth chronologies representing the entire latitudinal range of Pilgerodendron uviferum were grouped according to latitude and then examined for differences in growth trends and non‐stationarity in growth responses to a drought severity index (scPDSI) over the 1900–1993 AD period and also before and after significant shifts in climate in the 1950s and 1970s.

Results

The radial‐growth response of P. uviferum climate was highly variable across its full latitudinal distribution. There was a long‐term and positive association between radial growth and higher moisture at the northern and southern edges of the distribution of this species and the opposite relationship for the core of its distribution, especially following the climatic shifts of the 1950s and 1970s. In addition, non‐stationarity in moisture‐radial growth relationships was observed in all three latitudinal groups (southern and northern edges and core) for all seasons during the 20th century.

Main conclusions

Climate shifts in southern South America in the 1950s and 1970s resulted in different responses in the mean radial growth of P. uviferum at the southern and northern edges and at the core of its range. Dendroclimatic analyses document that during the first half of the 20th century climate‐growth relationships were relatively similar between the southern and northern range edges but diverged after the 1950s. Our findings imply that simulated projections of climate impacts on tree growth, and by implication on forest ecosystem productivity, derived from models of past climate‐growth relationships need to carefully consider different and non‐stationarity responses along the wide latitudinal distribution of this species.     

Climate warming will reduce growth and survival of Scots pine except in the far north

Tree growth and survival were assessed in 283 populations of Scots pine ( Pinus sylvestris L.) originating from a broad geographic range and grown at 90 common-garden experimental sites across Europe, and in 101 populations grown at 14 sites in North America. Growth and survival were analysed in response to climatic transfer distance, the difference in mean annual temperature (MAT) between the site and the population origin. Differences among populations at each site, and across sites for regional groups of populations, were related to climate transfer distance, but in opposite ways in the northern vs. southern parts of the species range. Climate transfers equivalent to warming by 1–4 °C markedly increased the survival of populations in northern Europe (≥ 62°N, < 2 °C MAT) and modestly increased height growth ≥ 57°N but decreased survival at < 62°N and modestly decreased height growth at < 54°N latitude in Europe. Thus, even modest climate warming will likely influence Scots pine survival and growth, but in distinct ways in different parts of the species range.     

Patterns of Forest Decline and Regeneration Across Scots Pine Populations

To predict future changes in forest ecosystems, it is crucial to understand the complex processes involved in decline of tree species populations and to evaluate the implications for potential vegetation shifts. Here, we study patterns of decline (canopy defoliation and mortality of adults) of four Scots pine populations at the southern edge of its distribution and characterized by different combinations of climate dryness and intensity of past management. General linear and structural equation modeling were used to assess how biotic, abiotic, and management components interacted to explain the spatial variability of Scots pine decline across and within populations. Regeneration patterns of Scots pine and co-occurring oak species were analyzed to assess potential vegetation shifts. Decline trends were related to climatic dryness at the regional scale, but, ultimately, within-population forest structure, local site conditions, and past human legacies could be the main underlying drivers of Scots pine decline. Overall, Scots pine regeneration was negatively related to decline both within and between populations, whereas oak species responded to decline idiosyncratically across populations. Taken together, our results suggest that (1) patterns of decline are the result of processes acting at the plot level that modulate forest responses to local environmental stress and (2) decline of adult Scots pine trees seems not to be compensated by self-recruitment so that the future dynamics of these forest ecosystems are uncertain.     

Growth responses to climate and drought at the southernmost European limit of Mediterranean Pinus pinaster forests

Climate warming and increasing aridity may negatively impact forest productivity across southern Europe. A better understanding of growth responses to climate and drought in southernmost populations could provide insight on the vulnerability of those forests to aridification. Here we investigate growth responses to climate and drought in nine Pinus pinaster (maritime pine) stands situated in Andalusia, southern Europe. The effect of climatic variables (temperatures and precipitation) and drought on radial growth was studied using dendrochronology along biogeographic and ecological gradients. We analyzed old native stands with non-tapped and resin-tapped trees mixed, showing their usefulness in dendroclimatic studies. Our results indicate a high plasticity in the growth responses of maritime pine to climate and drought, suggesting that site aridity modulated these responses. The positive growth responses to spring precipitation and the negative responses to summer drought were stronger in the more xeric inland sites than in wet coastal ones, in particular from the 1980s onwards. The characterization of tree species’ responses to climate at the southern or dry limits in relation to site conditions allows improving conservation strategies in drought-prone forest ecosystems.     

Know your limits? Climate extremes impact the range of Scots pine in unexpected places

Background and Aims Although extreme climatic events such as drought are known to modify forest dynamics by triggering tree dieback, the impact of extreme cold events, especially at the low-latitude margin (‘rear edge’) of species distributional ranges, has received little attention. The aim of this study was to examine the impact of one such extreme cold event on a population of Scots pine (Pinus sylvestris) along the species’ European southern rear-edge range limit and to determine how such events can be incorporated into species distribution models (SDMs).Methods A combination of dendrochronology and field observation was used to quantify how an extreme cold event in 2001 in eastern Spain affected growth, needle loss and mortality of Scots pine. Long-term European climatic data sets were used to contextualize the severity of the 2001 event, and an SDM for Scots pine in Europe was used to predict climatic range limits.Key Results The 2001 winter reached record minimum temperatures (equivalent to the maximum European-wide diurnal ranges) and, for trees already stressed by a preceding dry summer and autumn, this caused dieback and large-scale mortality. Needle loss and mortality were particularly evident in south-facing sites, where post-event recovery was greatly reduced. The SDM predicted European Scots pine distribution mainly on the basis of responses to maximum and minimum monthly temperatures, but in comparison with this the observed effects of the 2001 cold event at the southerly edge of the range limit were unforeseen.Conclusions The results suggest that in order to better forecast how anthropogenic climate change might affect future forest distributions, distribution modelling techniques such as SDMs must incorporate climatic extremes. For Scots pine, this study shows that the effects of cold extremes should be included across the entire distribution margin, including the southern ‘rear edge’, in order to avoid biased predictions based solely on warmer climatic scenarios.     

Plasticity in Dendroclimatic Response across the Distribution Range of Aleppo Pine (Pinus halepensis)

We investigated the variability of the climate-growth relationship of Aleppo pine across its distribution range in the Mediterranean Basin. We constructed a network of tree-ring index chronologies from 63 sites across the region. Correlation function analysis identified the relationships of tree-ring index to climate factors for each site. We also estimated the dominant climatic gradients of the region using principal component analysis of monthly, seasonal, and annual mean temperature and total precipitation from 1,068 climatic gridpoints. Variation in ring width index was primarily related to precipitation and secondarily to temperature. However, we found that the dendroclimatic relationship depended on the position of the site along the climatic gradient. In the southern part of the distribution range, where temperature was generally higher and precipitation lower than the regional average, reduced growth was also associated with warm and dry conditions. In the northern part, where the average temperature was lower and the precipitation more abundant than the regional average, reduced growth was associated with cool conditions. Thus, our study highlights the substantial plasticity of Aleppo pine in response to different climatic conditions. These results do not resolve the source of response variability as being due to either genetic variation in provenance, to phenotypic plasticity, or a combination of factors. However, as current growth responses to inter-annual climate variability vary spatially across existing climate gradients, future climate-growth relationships will also likely be determined by differential adaptation and/or acclimation responses to spatial climatic variation. The contribution of local adaptation and/or phenotypic plasticity across populations to the persistence of species under global warming could be decisive for prediction of climate change impacts across populations. In this sense, a more complex forest dynamics modeling approach that includes the contribution of genetic variation and phenotypic plasticity can improve the reliability of the ecological inferences derived from the climate-growth relationships.     

Importance of abiotic stress as a range-limit determinant for European plants: insights from species responses to climatic gradients

Aim We examined whether species occurrences are primarily limited by physiological tolerance in the abiotically more stressful end of climatic gradients (the asymmetric abiotic stress limitation (AASL) hypothesis) and the geographical predictions of this hypothesis: abiotic stress mainly determines upper‐latitudinal and upper‐altitudinal species range limits, and the importance of abiotic stress for these range limits increases the further northwards and upwards a species occurs. Location Europe and the Swiss Alps. Methods The AASL hypothesis predicts that species have skewed responses to climatic gradients, with a steep decline towards the more stressful conditions. Based on presence–absence data we examined the shape of plant species responses (measured as probability of occurrence) along three climatic gradients across latitudes in Europe (1577 species) and altitudes in the Swiss Alps (284 species) using Huisman–Olff–Fresco, generalized linear and generalized additive models. Results We found that almost half of the species from Europe and one‐third from the Swiss Alps showed responses consistent with the predictions of the AASL hypothesis. Cold temperatures and a short growing season seemed to determine the upper‐latitudinal and upper‐altitudinal range limits of up to one‐third of the species, while drought provided an important constraint at lower‐latitudinal range limits for up to one‐fifth of the species. We found a biome‐dependent influence of abiotic stress and no clear support for abiotic stress as a stronger upper range‐limit determinant for species with higher latitudinal and altitudinal distributions. However, the overall influence of climate as a range‐limit determinant increased with latitude. Main conclusions Our results support the AASL hypothesis for almost half of the studied species, and suggest that temperature‐related stress controls the upper‐latitudinal and upper‐altitudinal range limits of a large proportion of these species, while other factors including drought stress may be important at the lower range limits.     

Nutrient conservation increases with latitude of origin in European<Emphasis Type="Italic"> Pinus sylvestris</Emphasis> populations

Nutrient availability varies across climatic gradients, yet intraspecific adaptation across such gradients in plant traits related to internal cycling and nutrient resorption remains poorly understood. We examined nutrient resorption among six Scots pine (Pinus sylvestris L.) populations of wide-ranging origin grown under common-garden conditions in Poland. These results were compared with mass-based needle N and P for 195 Scots pine stands throughout the species' European range. At the common site, green needle N (r(2)=0.81, P=0.01) and P (r(2)=0.58, P=0.08) concentration increased with increasing latitude of population origin. Resorption efficiency (the proportion of the leaf nutrient pool resorbed during senescence) of N and P of Scots pine populations increased with the latitude of seed origin (r(2) > or = 0.67, P < or = 0.05). The greater resorption efficiency of more northerly populations led to lower concentrations of N and P in senescent leaves (higher resorption proficiency) than populations originating from low latitudes. The direction of change in these traits indicates potential adaptation of populations from northern, colder habitats to more efficient internal nutrient cycling. For native Scots pine stands, results showed greater nutrient conservation in situ in cold-adapted northern populations, via extended needle longevity (from 2 to 3 years at 50 degrees N to 7 years at 70 degrees N), and greater resorption efficiency and proficiency, with their greater resorption efficiency and proficiency having genotypic roots demonstrated in the common-garden experiment. However, for native Scots pine stands, green needle N decreased with increasing latitude (r(2)=0.83, P=0.0002), and P was stable other than decreasing above 62 degrees N. Hence, the genotypic tendency towards maintenance of higher nutrient concentrations in green foliage and effective nutrient resorption, demonstrated by northern populations in the common garden, did not entirely compensate for presumed nutrient availability limitations along the in situ latitudinal temperature gradient.     

Latitude and altitude differentially shape life history trajectories between the sexes in non-anadromous brown trout

We used two different approaches involving two organizational levels and spatial scales to explore altitudinal and latitudinal variation in life histories of non-anadromous brown trout Salmo trutta. First, we studied the factors influencing the maturation of individuals from populations in northern Spain. Second, we explored the effects of altitude (range 40–1,340 m) and latitude (range 40.6–61.7°N) on longevity, maximum length, length and age at maturity, and fecundity, comparing Spanish and Norwegian populations. Individual maturation was determined by length, age, and sex, and at a given size and age individuals were more likely to mature at higher altitudes. Brown trout lived longer but attained smaller sizes at higher latitudes. Both males and females matured at an older age with increasing latitude, but latitude affected their life-history strategies differentially. Males matured at smaller sizes with increasing latitude and altitude, which may indicate that their maturation threshold depends on the growth potentiality of the river since they compete with other males from the same population. The opposite effects were detected in females. Since female fecundity increases strongly with size there may be a size below which maturation has strong fitness costs. Brown trout are extraordinarily plastic, allowing persistence in a wide variety of environments. In the context of climate change, latitudinally based studies are important to predict potential effects of climate change, especially at the southern edge of species distribution.     

Latitudinal gradients in butterfly population variability are influenced by landscape heterogeneity

The variability of populations over time is positively associated with their risk of local extinction. Previous work has shown that populations at the high‐latitude boundary of species’ ranges show higher inter‐annual variability, consistent with increased sensitivity and exposure to adverse climatic conditions. However, patterns of population variability at both high‐ and low‐latitude species range boundaries have not yet been concurrently examined. Here, we assess the inter‐annual population variability of 28 butterfly species between 1994 and 2009 at 351 and 18 sites in the United Kingdom and Catalonia, Spain, respectively. Local population variability is examined with respect to the position of the species’ bioclimatic envelopes (i.e. whether the population falls within areas of the ‘core’ climatic suitability or is a climatically ‘marginal’ population), and in relation to local landscape heterogeneity, which may influence these range location – population dynamic relationships. We found that butterfly species consistently show latitudinal gradients in population variability, with increased variability in the more northerly UK. This pattern is even more marked for southerly distributed species with ‘marginal’ climatic suitability in the UK but ‘core’ climatic suitability in Catalonia. In addition, local landscape heterogeneity did influence these range location – population dynamic relationships. Habitat heterogeneity was associated with dampened population dynamics, especially for populations in the UK. Our results suggest that promoting habitat heterogeneity may promote the persistence of populations at high‐latitude range boundaries, which may potentially aid northwards expansion under climate warming. We did not find evidence that population variability increases towards southern range boundaries. Sample sizes for this region were low, but there was tentative evidence, in line with previous ecological theory, that local landscape heterogeneity may promote persistence in these retracting low‐latitude range boundary populations.     

Both life‐history plasticity and local adaptation will shape range‐wide responses to climate warming in the tundra plant Silene acaulis

Many predictions of how climate change will impact biodiversity have focused on range shifts using species‐wide climate tolerances, an approach that ignores the demographic mechanisms that enable species to attain broad geographic distributions. But these mechanisms matter, as responses to climate change could fundamentally differ depending on the contributions of life‐history plasticity vs. local adaptation to species‐wide climate tolerances. In particular, if local adaptation to climate is strong, populations across a species’ range—not only those at the trailing range edge—could decline sharply with global climate change. Indeed, faster rates of climate change in many high latitude regions could combine with local adaptation to generate sharper declines well away from trailing edges. Combining 15 years of demographic data from field populations across North America with growth chamber warming experiments, we show that growth and survival in a widespread tundra plant show compensatory responses to warming throughout the species’ latitudinal range, buffering overall performance across a range of temperatures. However, populations also differ in their temperature responses, consistent with adaptation to local climate, especially growing season temperature. In particular, warming begins to negatively impact plant growth at cooler temperatures for plants from colder, northern populations than for those from warmer, southern populations, both in the field and in growth chambers. Furthermore, the individuals and maternal families with the fastest growth also have the lowest water use efficiency at all temperatures, suggesting that a trade‐off between growth and water use efficiency could further constrain responses to forecasted warming and drying. Taken together, these results suggest that populations throughout species’ ranges could be at risk of decline with continued climate change, and that the focus on trailing edge populations risks overlooking the largest potential impacts of climate change on species’ abundance and distribution.     

Leap frog in slow motion: Divergent responses of tree species and life stages to climatic warming in Great Basin subalpine forests

In response to climate warming, subalpine treelines are expected to move up in elevation since treelines are generally controlled by growing season temperature. Where treeline is advancing, dispersal differences and early life stage environmental tolerances are likely to affect how species expand their ranges. Species with an establishment advantage will colonize newly available habitat first, potentially excluding species that have slower establishment rates. Using a network of plots across five mountain ranges, we described patterns of upslope elevational range shift for the two dominant Great Basin subalpine species, limber pine and Great Basin bristlecone pine. We found that the Great Basin treeline for these species is expanding upslope with a mean vertical elevation shift of 19.1 m since 1950, which is lower than what we might expect based on temperature increases alone. The largest advances were on limber pine‐dominated granitic soils, on west aspects, and at lower latitudes. Bristlecone pine juveniles establishing above treeline share some environmental associations with bristlecone adults. Limber pine above‐treeline juveniles, in contrast, are prevalent across environmental conditions and share few environmental associations with limber pine adults. Strikingly, limber pine is establishing above treeline throughout the region without regard to site characteristic such as soil type, slope, aspect, or soil texture. Although limber pine is often rare at treeline where it coexists with bristlecone pine, limber pine juveniles dominate above treeline even on calcareous soils that are core bristlecone pine habitat. Limber pine is successfully “leap‐frogging” over bristlecone pine, probably because of its strong dispersal advantage and broader tolerances for establishment. This early‐stage dominance indicates the potential for the species composition of treeline to change in response to climate change. More broadly, it shows how species differences in dispersal and establishment may result in future communities with very different specific composition.     

Impact of the climatic scenario of global warming on the growth of trees

The climatic impact on tree radial growth resulting from an atmospheric CO2 doubling was studied for 24 populations of five tree species in the French Alps and the French Mediterranean area. The Arpege AGCM, which predicts a 3 degrees C increase in mean temperature and a light increase of precipitation, is used to estimate the climatic perturbation. The method is based on the integration of estimated climate in an empirical tree-ring to climate model, involving artificial neural networks. Only a few populations are sensitive to the climatic change; all are located on the boundaries of their ecological area and can be divided in two groups. The first one is composed of high altitude populations which show a growth increase induced by the warmer climate during the growing season. The second one, composed of a single Mediterranean Scots pine population, reacts with a severe growth reduction induced by the stronger water stress in summer.     

Influence of altitude on local adaptation in upland tree species from central Argentina

• Steep climatic gradients boost morphological and physiological adjustments in plants, with consequences on performance. The three principal woody species of the Sierras Grandes Mountains of central Argentina have marked differences in sapling performance along their altitudinal distribution. We hypothesize that the steep gradient of climatic conditions across the species’ altitudinal distribution promotes trait differences between populations of different altitudes that are inherited by the following generation.
• Seeds from different altitudes were exposed to three temperature regimes to assess differential germination responses. Saplings were then transplanted to a greenhouse to assess possible variations in attributes and performance after 18 months.
• The three species showed differences in germination responses to temperature among altitudes and/or in sapling attributes and performance. In Maytenus boaria and Escallonia cordobensis, germination success was higher under high temperatures for the highest‐altitude, whereas lower temperatures boosted germination of the lowest altitudes. Polylepis australis showed no differences in germination among temperature treatments. In the greenhouse, saplings of the three species from intermediate altitudes showed high performance, whereas the upper and lower populations seemed to be adjusted to tolerating more stressful conditions (i.e., lower temperatures at the upper end and water stress at the lower end), showing lower performance toward both altitudinal limits.
• These patterns agree with those described for saplings growing under field conditions, suggesting adjustments in response to environmental changes undergone by populations along the altitudinal range. The marked adjustments of populations to the local environment suggest a potentially high impact of climatic change on species distribution.

     

Growth and resilience responses of Scots pine to extreme droughts across Europe depend on predrought growth conditions

Global climate change is expected to further raise the frequency and severity of extreme events, such as droughts. The effects of extreme droughts on trees are difficult to disentangle given the inherent complexity of drought events (frequency, severity, duration, and timing during the growing season). Besides, drought effects might be modulated by trees’ phenotypic variability, which is, in turn, affected by long‐term local selective pressures and management legacies. Here we investigated the magnitude and the temporal changes of tree‐level resilience (i.e., resistance, recovery, and resilience) to extreme droughts. Moreover, we assessed the tree‐, site‐, and drought‐related factors and their interactions driving the tree‐level resilience to extreme droughts. We used a tree‐ring network of the widely distributed Scots pine (Pinus sylvestris) along a 2,800 km latitudinal gradient from southern Spain to northern Germany. We found that the resilience to extreme drought decreased in mid‐elevation and low productivity sites from 1980–1999 to 2000–2011 likely due to more frequent and severe droughts in the later period. Our study showed that the impact of drought on tree‐level resilience was not dependent on its latitudinal location, but rather on the type of sites trees were growing at and on their growth performances (i.e., magnitude and variability of growth) during the predrought period. We found significant interactive effects between drought duration and tree growth prior to drought, suggesting that Scots pine trees with higher magnitude and variability of growth in the long term are more vulnerable to long and severe droughts. Moreover, our results indicate that Scots pine trees that experienced more frequent droughts over the long‐term were less resistant to extreme droughts. We, therefore, conclude that the physiological resilience to extreme droughts might be constrained by their growth prior to drought, and that more frequent and longer drought periods may overstrain their potential for acclimation.     

Altitudinal and seasonal variation in microsatellite allele frequencies of Drosophila buzzatii

Variation in climate, particularly temperature, is known to affect the genetic composition of populations. Although there have been many studies of latitudinal variation, comparisons of populations across altitudes or seasons, particularly for animal species, are less common. Here, we study genetic variation (microsatellite markers) in populations of Drosophila buzzatii collected along altitudinal gradients and in different seasons. We found no differences in genetic variation between 2 years or between seasons within years. However, there were numerous cases of significant associations between allele frequencies or expected heterozygosities and altitude, with more than half showing nonlinear relationships. While these associations indicate possible selection and local altitudinal adaptation, direct tests gave strong evidence for selection affecting two loci and weaker evidence for five other loci. Two loci that are located within an inversion (including the one with strongest evidence for selection) show a linear increase in genetic diversity with altitude, likely due to thermal selection. Parallel associations with altitude here and with latitude in Australian populations indicate that selection is operating on chromosomal regions marked by some of the loci.