Population differentiation in climate sensitivity of resin duct formation during growth resumption in Pinus pinaster

To counteract the effects of herbivores and pathogens, conifers have developed a sophisticated resin-based defensive system. Since defences are costly, trees must continuously accommodate defensive investment throughout plastic responses to environmental stimuli. However, the extent of such responses can differ at the intra-specific level (i.e. genetic variation in plasticity). Here we examined whether and to what extent year-to-year climate fluctuations, an important source of environmental heterogeneity during the trees' life, drive plasticity in defensive allocation of a widespread pine species. Specifically, we quantified interannual variation in resin duct production along a 31-year-period in 174 Pinus pinaster trees of nine range-wide populations grown in two common gardens in Central Spain. We aimed to explore (i) patterns of interannual variation (i.e., temporal plasticity) in resin duct production among populations and sites, (ii) whether such patterns are linked to plastic responses to interannual variation in climate conditions (i.e., climatic plasticity), and (iii) whether plastic responses to climate differ among populations (i.e., genetic variation in plasticity) and sites. We found large interannual plasticity in resin duct production (22.8 % of total variance), with temporal patterns differing among sites and populations. Climate conditions during the early growth period significantly affected the annual differentiation of resin ducts. Particularly, April precipitation had a positive overall effect on resin duct production. Inversely, warmer conditions in April had a negative effect but only in certain populations, which demonstrates genetic variation in climate sensitivity of resin duct formation. Despite significant effects of certain climate variables on annual resin duct production, climate only accounted for a small proportion of the total interannual variation (up to 3.8 % of interannual variation explained by climate factors). This suggests that alternative factors such as trade-offs with growth and temporal variation in biotic and non-climatic abiotic conditions likely contribute to explain interannual fluctuations in defensive investment.     

Local environment prevails over population variations in growth-climate relationships of Pinus pinaster provenances

In view of the projected decrease in precipitation and increase in temperature, a better understanding on growth-climate responses in different populations of tree species is needed to improve and enhance the conservation and management strategies for major forest tree species. In this study, we assessed differences in growth traits (i.e., stem diameter, tree height, and stem radial growth) and analysed climate-growth relationships in five provenances of maritime pine (Pinus pinaster Ait.) grown in four replicated common gardens in Sardinia (Italy). Stem radial growth increased under a positive water balance in late winter and early spring. Conversely, high temperature and low precipitation in summer had a negative impact on stem radial growth. At age 40, none of the considered provenances (Portugal, Corsica, Tuscany, Sardinia-Telti, Sardinia-Limbara) showed a substantial advantage in more than one common garden site for tree height and stem diameter. Nevertheless, differences were found among common garden sites in terms of dendrometric parameters, stem radial growth, and growth-climate responses (including sensitivity to summer drought), suggesting a greater site dependent over tree growth. Although in juvenile stages the Portuguese provenance (in particular) showed greater growth than the Sardinian ones, this study showed that, with tree age, the differences among the five provenances tends to narrow. Therefore, irrespective of the seed source, tree growth patterns and growth-climate responses were similar at age 40. This result can be important for implementing forest management strategies to balance adaptation and mitigation potential of maritime pine plantations in harsh environmental conditions.     

Plasticity of functional traits varies clinally along a rainfall gradient in Eucalyptus tricarpa

Widespread species often occur across a range of climatic conditions, through a combination of local genetic adaptations and phenotypic plasticity. Species with greater phenotypic plasticity are likely to be better positioned to cope with rapid anthropogenic climate changes, while those displaying strong local adaptations might benefit from translocations to assist the movement of adaptive genes as the climate changes. Eucalyptus tricarpa occurs across a climatic gradient in south‐eastern Australia, a region of increasing aridity, and we hypothesized that this species would display local adaptation to climate. We measured morphological and physiological traits reflecting climate responses in nine provenances from sites of 460 to 1040 mm annual rainfall, in their natural habitat and in common gardens near each end of the gradient. Local adaptation was evident in functional traits and differential growth rates in the common gardens. Some traits displayed complex combinations of plasticity and genetic divergence among provenances, including clinal variation in plasticity itself. Provenances from drier locations were more plastic in leaf thickness, whereas leaf size was more plastic in provenances from higher rainfall locations. Leaf density and stomatal physiology (as indicated by δ¹³C and δ¹⁸O) were highly and uniformly plastic. In addition to variation in mean trait values, genetic variation in trait plasticity may play a role in climate adaptation.     

Performance of reciprocally sown populations of Senecio vulgaris from ruderal and agricultural habitats

Senecio vulgaris from ruderal habitats may colonise crop fields and persist in the new environment. Persistence may occur through phenotypic plasticity or genetic differentiation. In the presence of genetic variation, differential responses of life history traits to selection may lead to local adaptation. A reciprocal seed transplant experiment was conducted to determine environmental and genetic variation of life history traits in S. vulgaris from ruderal and agricultural habitats, and whether infection by the rust Puccinia lagenophorae is a selection factor in S. vulgaris populations. Emergence, growth and fecundity showed environmental as well as genetic variation, as shown by a significant site and origin effect. However, there was no evidence of local adaptation, as indicated by the absence of significant origin by site interactions. Genetic variation in emerging seedling numbers seems to be important for S. vulgaris, an annual plant which has no means other than seed production for propagation. Seedling survival was solely under environmental control stressing the importance of stochastic events for plant mortality. Most S. vulgaris from ruderal sites showed reduced growth, but still reached reproduction, suggesting that S. vulgaris is following the plastic strategy of a stress tolerator to endure unfavourable environments. Plants at most agricultural sites behaved like r-strategists, exploiting a productive environment for rapid plant growth and maximising reproduction. Emergence, survival, growth and fecundity were higher at the agricultural sites. Infection by the rust occurred at all sites, with the highest incidence at the agricultural sites, and was solely determined by the environment. A higher incidence did not result in an increased disease impact on plant growth and reproduction nor did it affect survival of S. vulgaris. Although the majority of life-history traits studied showed phenotypic and genetic variation, which can both be subject to natural selection, no adaptation of S. vulgaris to its local environment was detected.     

Patterns of Cross-Continental Variation in Tree Seed Mass in the Canadian Boreal Forest

Seed mass is an adaptive trait affecting species distribution, population dynamics and community structure. In widely distributed species, variation in seed mass may reflect both genetic adaptation to local environments and adaptive phenotypic plasticity. Acknowledging the difficulty in separating these two aspects, we examined the causal relationships determining seed mass variation to better understand adaptability and/or plasticity of selected tree species to spatial/climatic variation. A total of 504, 481 and 454 seed collections of black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana Lamb) across the Canadian Boreal Forest, respectively, were selected. Correlation analyses were used to determine how seed mass vary with latitude, longitude, and altitude. Structural Equation Modeling was used to examine how geographic and climatic variables influence seed mass. Climatic factors explained a large portion of the variation in seed mass (34, 14 and 29%, for black spruce, white spruce and jack pine, respectively), indicating species-specific adaptation to long term climate conditions. Higher annual mean temperature and winter precipitation caused greater seed mass in black spruce, but annual precipitation was the controlling factor for white spruce. The combination of factors such as growing season temperature and evapotranspiration, temperature seasonality and annual precipitation together determined seed mass of jack pine. Overall, sites with higher winter temperatures were correlated with larger seeds. Thus, long-term climatic conditions, at least in part, determined spatial variation in seed mass. Black spruce and Jack pine, species with relatively more specific habitat requirements and less plasticity, had more variation in seed mass explained by climate than did the more plastic species white spruce. As traits such as seed mass are related to seedling growth and survival, they potentially influence forest species composition in a changing climate and should be included in future modeling of vegetation shifts.     

Dendroclimatology of sugar maple (Acer saccharum): Climate-growth response in a late-successional species

Sugar maple (Acer saccharum) is a shade-tolerant, late successional dominant species in the North American eastern deciduous forest. The objective of this study was to quantify the relationship between climate and radial growth in sugar maple and to identify spatial and temporal patterns in dendroclimatic response. We used a combination of archived sugar maple tree-ring chronologies and newly sampled sites to calculate dendroclimatic response of sugar maple at 13 sites in the United States and Canada. At all sites, sugar maple growth was significantly correlated to monthly temperature, precipitation, or Palmer Drought Severity Index. However, there were no generalizable patterns in sugar maple’s growth response to climate. Individual sites had unique dendroclimatic responses with respect to: a) which climatic variables were correlated to radial growth; b) what months had significant correlations between climate and radial growth; and c) what years had significant correlations between climate and radial growth. The individualistic dendroclimatic response of sugar maple appears to reflect a plastic response of the species to changes in climate perhaps related to its status as a strong competitor in late-successional forests. This ability to survive a wide range of environmental conditions may bode well for the species persistence under variable future climatic conditions. It also points to the need for more research on late-successional species in examining forest response to potential climate change scenarios because these species may be more resilient than early-successional species.     

Environmental heterogeneity and neighbourhood interference modulate the individual response of Juniperus thurifera tree-ring growth to climate

Individual variation of tree-ring growth response to climate and heterogeneity of the local environment are usually neglected in dendrochronological research. Even if there is evidence showing that individual responsiveness to climate may depend on intrinsic traits such as tree age, size or sex, its modulation by the local heterogeneity of extrinsic factors has been less studied. Using an extensive, strictly regular sampling scheme across a 3300 ha woodland, we assessed the individual variation of tree-ring growth responses to climate in 100 Juniperus thurifera L. trees. The climatic response was evaluated by bootstrapped correlations of both population- and individual-based tree-ring chronologies with monthly records of precipitation, cloudiness, minimum and maximum temperatures. We studied also the influence of extrinsic abiotic (elevation, slope, heat load, tree location) and biotic (competition from neighbouring trees) factors on the individual growth variation and its climatic response. At a population level, growth was controlled by February–March precipitation, April minimum temperature, and June water stress. A significant proportion of individuals did not respond to those variables, but were sensitive to others not relevant at the population level. Inter-annual growth variation was strongly modulated by competition, whereas trees under lower competition levels, in eastern and warmer areas, were the most responsive to climate. The individual climatic response was, at least partially, modulated by the local heterogeneity of extrinsic factors. By considering environmental heterogeneity and neighbourhood interference we can identify the spectrum of site-dependent climatic responses in a population, which in turn will enable more realistic predictions of tree responses to ongoing climate change.     

Variation in radial growth of Pinus cooperi in response to climatic signals across an elevational gradient

Climate change could modify the biogeography of many forest species. Elevational gradients have been documented as strategic sites to better understand tree growth response to regional climate variables. Pinus cooperi Blanco is one of the most important species in Northern Mexico. However, little is known concerning effects of climate responses on growth of this species. We used tree data records to compare the influence of precipitation and temperature on radial growth among P. cooperi populations across a mountain landscape at elevation gradient. Correlation and regression analysis of the regional growth–climate relationships showed that radial growth was correlated with previous winter conditions at most sites along the gradient. Wet and cold winters were positively associated with radial growth. Although our results showed significant climate influences on tree radial growth, other site factors also may have affected growth–climate responses. The results support the idea that climate change influences P. cooperi growth.     

Genetic Delineation of Local Provenance in Persoonia longifolia: Implications for Seed Sourcing for Ecological Restoration

Restoration of diverse native plant communities typically requires the collection of large amounts of seed. Thus, practitioners often struggle to find adequate supplies near project sites and need to know from how far they can collect without compromising restoration success—how far does local provenance extend? We addressed this issue by assessing genetic variation within, and differentiation among, 12 potential seed source populations of Persoonia longifolia, a key component of the jarrah forest of Western Australia. An analysis of molecular variance of 66 polymorphic amplified fragment length polymorphism markers partitioned 92% of the total genetic variation within populations and 8% among populations, indicating relatively weak but statistically significant population genetic differentiation. Ordination of these genetic data showed marked west/east and north/south gradients. Pairwise population genetic dissimilarity was correlated with both geographic distance and environmental distance derived from five climate variables. However, partial Mantel tests showed that the relationship between genetic and geographic distance was not independent of environmental distance, suggesting a non‐neutral signature in these markers. Bayesian outlier analysis identified two markers, and spatial analysis method tests identified highly significant associations between these two markers and three environmental variables. Frequency differences at these markers across populations suggested the possibility of climatically adapted provenances. The global significance value from analyses of similarities for these two markers correlated to a general provenance distance of 47 km, in contrast to a threshold of 60 km for the complete dataset. Guidelines for seed sourcing that consider these population genetic data should lead to more effective ecological restoration with this species.     

Patterns of Differentiation in Wiregrass (Aristida beyrichiana): Implications for Restoration Efforts

Aristida beyrichiana (wiregrass) is increasingly being planted in restoration projects across the southeastern coastal plain, with little focus on genetic differences among populations across the region. Local and regional population differentiation for establishment and growth traits were examined in common garden and reciprocal transplant experiments. Seeds from up to 20 plants from each of seven populations were collected in northern and central Florida sites that encompassed gradients of soils, hydrology, and temperature. Reciprocal seed transplants using three of the common garden populations were conducted in two consecutive years. In the common garden, significant population differences were seen in seed weight, seedling emergence and survival, tiller height, number of tillers, the relationship between tiller number and tiller height, and flowering. Variation among maternal families was seen in tiller number and in the relationship between tiller number and tiller height. The reciprocal transplant study did not detect either local adaptation to sites of origin or consistent superiority of one source population or planting site in seedling establishment. These results suggest that the probability of seedling establishment is primarily dependent on environmental conditions rather than genetic differences. Genetic variation for traits related to fitness (e.g., tiller number) may be retained within populations because phenotypically plastic growth responses of seedlings to environmental variation buffer genetic variation against the action of selection. But despite the lack of evidence for genetic influences on initial establishment in wiregrass, our common garden study suggests genetic differences among populations. This result, when combined with previous results indicating local adaptation in later life stages of wiregrass, suggests that restoration efforts involving this species should use local seed sources from sites with similar soil and hydrological conditions.     

How far is it to your local? A survey on local provenance use in New South Wales

Summary The decision as to where to source seed is one of the most critical in restoration projects. Locally collected seed is often recommended, or even contractually required, because it is assumed to be adapted to local conditions and therefore result in superior survival and growth rates, conferring a greater probability of restoration success. The perceived advantages, which include retaining the genetic ‘integrity’ of the site, are centred around the avoidance of outbreeding depression and hybridization. These traditional reasons for using locally collected seed need to be reconsidered in the light of rapidly changing climatic and other environmental conditions; plants that are locally adapted now may not be locally adapted in future. Understanding the current usage of local provenance is pivotal to discussions on its appropriateness under climate change. We present the results of a survey of restoration practitioners in New South Wales on attitudes and practices in relation to the use of local provenance. We found that whilst the majority of practitioners preferentially use local provenance seeds, the actual definition of local provenance varied amongst respondents. Whilst 80% of participants believe that projections of future climate change are relevant to restoration projects, there is an apparent reluctance to actively manage for this eventuality. However, many respondents are in favour of a review of seed‐sourcing policy/guidelines to allow for the inclusion of non‐local provenance material. Implications of the survey for potential changes to guidelines to better prepare for anticipated changing conditions are discussed.     

The climatic drivers of primary Picea forest growth along the Carpathian arc are changing under rising temperatures

Climatic constraints on tree growth mediate an important link between terrestrial and atmospheric carbon pools. Tree rings provide valuable information on climate‐driven growth patterns, but existing data tend to be biased toward older trees on climatically extreme sites. Understanding climate change responses of biogeographic regions requires data that integrate spatial variability in growing conditions and forest structure. We analyzed both temporal (c. 1901–2010) and spatial variation in radial growth patterns in 9,876 trees from fragments of primary Picea abies forests spanning the latitudinal and altitudinal extent of the Carpathian arc. Growth was positively correlated with summer temperatures and spring moisture availability throughout the entire region. However, important seasonal variation in climate responses occurred along geospatial gradients. At northern sites, winter precipitation and October temperatures of the year preceding ring formation were positively correlated with ring width. In contrast, trees at the southern extent of the Carpathians responded negatively to warm and dry conditions in autumn of the year preceding ring formation. An assessment of regional synchronization in radial growth variability showed temporal fluctuations throughout the 20th century linked to the onset of moisture limitation in southern landscapes. Since the beginning of the study period, differences between high and low elevations in the temperature sensitivity of tree growth generally declined, while moisture sensitivity increased at lower elevations. Growth trend analyses demonstrated changes in absolute tree growth rates linked to climatic change, with basal area increments in northern landscapes and lower altitudes responding positively to recent warming. Tree growth has predominantly increased with rising temperatures in the Carpathians, accompanied by early indicators that portions of the mountain range are transitioning from temperature to moisture limitation. Continued warming will alleviate large‐scale temperature constraints on tree growth, giving increasing weight to local drivers that are more challenging to predict.     

Scots pine plantations growth adaptation to climate warming in locations at the southernmost distribution limit of the species

Under the current climate change conjuncture, understanding the forest plantations capacity of acclimation to warming and increased drought stress is crucial for forest managers. To get some understanding of their adaptability, plantations of similar provenance but located in climatically contrasting sites can be compared. Here we study the growth dynamics and their relationship with climate and drought in two Scots pine (Pinus sylvestris L.) plantations located in the center (Sierra de Guadarrama, wetter site) and south (Sierra Nevada, drier site) of Spain, the latter situated at the southernmost distribution limit of the species. Our objectives are to quantify the trends in radial growth of these plantations, to quantify the influence of climate on growth, and to project the plantations growth as a function of forecasted climate. Results reveal that the plantations from the drier site show lower, and less responsive to climate, growth and greater resilience than those from the wetter site. Furthermore, if the current climate-growth relationships continue in the future, these plantations would maintain the current limited growth rate during the 21st century. On the contrary, plantations from the wetter site show higher growth rate and more resistance to drought, and they are projected to increase growth under the warmer conditions forecasted for the 21st century. Our study shows that plantations in drier sites may have a great capacity to acclimate to local climate conditions and would not be negatively impacted by the projected climate warming.     

Aridity promotes differences in proline and phytohormone levels in <Emphasis Type="Italic">Pinus pinaster</Emphasis> populations from contrasting environments

We analysed proline, abscisic acid, (ABA), jasmonic acid (JA), indole acetic acid (IAA) and salicylic acid (SA) accumulation after summer drought at two Pinus pinaster provenance-progeny trial sites. The aim of the study was to evaluate P. pinaster phenotypic plasticity and intraspecific variation in the endogenous concentrations of these metabolites and to determine the best stress indicators for family and population discrimination. The environmental effect was remarkable, as striking differences between the sites were obtained for all indicators except for SA, which was unaffected by the environmental conditions. The levels of proline, ABA and IAA were higher in the xeric than in the mesic site. In contrast, JA was higher in the mesic site. The higher variation displayed at the family level led to family differences for all parameters and sites. Differences in proline and ABA between populations were exclusively found in the xeric site, where the population from the wet climate showed higher accumulation. This study provides evidence for differentiation among P. pinaster populations and families in their plastic responses to drought and highlights the importance of considering intraspecific variability when evaluating biochemical stress indicators in environmental studies.     

Adaptation and plasticity in aboveground allometry variation of four pine species along environmental gradients

Plant species aboveground allometry can be viewed as a functional trait that reflects the evolutionary trade‐off between above‐ and belowground resources. In forest trees, allometry is related to productivity and resilience in different environments, and it is tightly connected with a compromise between efficiency‐safety and competitive ability. A better understanding on how this trait varies within and across species is critical to determine the potential of a species/population to perform along environmental gradients. We followed a hierarchical framework to assess tree height‐diameter allometry variation within and across four common European Pinus species. Tree height‐diameter allometry variation was a function of solely genetic components –approximated by either population effects or clinal geographic responses of the population's site of origin– and differential genetic plastic responses –approximated by the interaction between populations and two climatic variables of the growing sites (temperature and precipitation)–. Our results suggest that, at the species level, climate of the growing sites set the tree height‐diameter allometry of xeric and mesic species (Pinus halepensis, P. pinaster and P. nigra) apart from the boreal species (P. sylvestris), suggesting a weak signal of their phylogenies in the tree height‐diameter allometry variation. Moreover, accounting for interpopulation variability within species for the four pine species aided to: (1) detect genetic differences among populations in allometry variation, which in P. nigra and P. pinaster were linked to gene pools –genetic diversity measurements–; (2) reveal the presence of differential genetic variation in plastic responses along two climatic gradients in tree allometry variation. In P. sylvestris and P. nigra, genetic variation was the result of adaptive patterns to climate, while in P. pinaster and P. halepensis, this signal was either weaker or absent, respectively; and (3) detect local adaptation in the exponent of the tree height‐diameter allometry relationship in two of the four species (P. sylvestris and P. nigra), as it was a function of populations' latitude and altitude variables. Our findings suggest that the four species have been subjected to different historical and climatic constraints that might have driven their aboveground allometry and promoted different life strategies.     

A bridge too far: cold and pathogen constraints to assisted migration of riparian forests

Assisted migration of warm‐adapted genotypes to currently cooler climates may reduce maladaptation from future climate change. Few assisted migration trials have considered limitations of the cooler climates and pathogens currently present at transplant sites. This is especially important to consider in riparian ecosystems that are priority targets for restoration in the western United States as they harbor diverse communities. In an effort to validate assisted migration as an effective strategy for mediating the negative impacts of climate change, we used a provenance trial with replicated genotypes from 19 populations of the foundation riparian tree species, Fremont cottonwood (Populus fremontii), transplanted to a cold site to test for genetic variation in growth, mortality, and resistance to shoot blight fungi (Venturia sp.). Populations from cool sites had up to 4 times faster growth, 3 times higher survival, and 8 times higher resistance to Venturia than populations from warm sites, providing evidence of local adaptation to both climate and pathogenic fungi. Budburst phenology and shoot blight were correlated with frost damage, subsequent shrub‐form architecture, and mortality. While climate change models predict 6°C increases, plants transferred distances of 6°C at this time would not perform well; an intermediate transfer distance of less than 3°C would avoid maladaptation to the current environment during assisted migration. Thus, multiple and intermediate transfer phases to supplement local genetic variation will likely be necessary for effective assisted migration to accommodate current environments and large changes in climate.     

Survival and growth patterns of white spruce (Picea glauca [Moench] Voss) rangewide provenances and their implications for climate change adaptation

Intraspecific assisted migration (ISAM) through seed transfer during artificial forest regeneration has been suggested as an adaptation strategy to enhance forest resilience and productivity under future climate. In this study, we assessed the risks and benefits of ISAM in white spruce based on long‐term and multilocation, rangewide provenance test data. Our results indicate that the adaptive capacity and growth potential of white spruce varied considerably among 245 range‐wide provenances sampled across North America; however, the results revealed that local populations could be outperformed by nonlocal ones. Provenances originating from south‐central Ontario and southwestern Québec, Canada, close to the southern edge of the species' natural distribution, demonstrated superior growth in more northerly environments compared with local populations and performed much better than populations from western Canada and Alaska, United States. During the 19–28 years between planting and measurement, the southern provenances have not been more susceptible to freezing damage compared with local populations, indicating they have the potential to be used now for the reforestation of more northerly planting sites; based on changing temperature, these seed sources potentially could maintain or increase white spruce productivity at or above historical levels at northern sites. A universal response function (URF), which uses climatic variables to predict provenance performance across field trials, indicated a relatively weak relationship between provenance performance and the climate at provenance origin. Consequently, the URF from this study did not provide information useful to ISAM. The ecological and economic importance of conserving white spruce genetic resources in south‐central Ontario and southwestern Québec for use in ISAM is discussed.     

Relationship between climate and growth of two North African varieties of Pinus pinaster Arn.

Planting tree species that are well adapted to local ecological conditions guarantees the success and sustainability of forest restoration. The aim of this study was to investigate the acclimation of two varieties of Pinus pinaster (var. renoui from Tunisia and var. maghrebiana from Morocco), to the ecological conditions of the Kroumirie Mountains in northwest of Tunisia. Tree growth performance (diameter at 1.30 m [DBH], ring widths and total height) and climate–growth responses over the period 1970–2013 were evaluated for two varieties. The trees used in this study were from pine variety and provenance trials growing in common garden in Souiniet (21 trees per variety). Significant difference in height growth rate, DBH and ring widths was found between the two varieties. The Maghrebiana variety had the highest survival and mean radial growth rates. The mean sensitivity to climate was the same in two varieties. A significant negative correlation between May precipitation and radial growth was found for var. maghrebiana. Both varieties showed a significant negative correlation between May and June temperatures and radial growth. January–February temperatures had a positive influence on ring width. The Maghrebiana variety appears well acclimatised so it is expected to ensure more successful restoration of Kroumirie Mountains.     

Tree species from contrasting hydrological niches show divergent growth and water-use efficiency

Tree species occupy different hydrological niches and climate warming may affect tree performance in those niches through increased drought stress. However, the effects of climate warming on growth, carbon and water fluxes would differ depending on species’ hydrological niche. Species from wet sites should show a lower growth dependence on precipitation and also lower intrinsic water-use efficiency (WUEi), as compared with species from dry sites which should improve more the WUEi. We test these ideas by comparing radial-growth rates (basal-area increment), climate- and drought-growth associations and WUEi of hackberry (Celtis australis) vs. Aleppo pine (Pinus halepensis) and maritime pine (Pinus pinaster) in two Mediterranean sites located in Spain. Species are subjected to similar regional climate conditions in each site but occupy contrasting local hydrological niches (hackberry in wet sites and pines in dry sites). Climate is warming in both study sites and drought-avoiding pines are responding by showing higher growth rates and improved WUEi. We also found a similar growth dependency on winter-spring precipitation and summer drought of all species and sites and comparable WUEi values and trends, excepting in hackberry from southern Spain which grew more, and showed a higher growth resistance to drought and lower and more stable WUEi values. Variables inferred from tree rings as growth rates and WUEi allow characterizing the hydrological niche of tree species, which may be contingent on site conditions and climate warming.     

Visualising the environmental preferences of Pinus tecunumanii populations

A network of 92 pedigreed ex situ conservation plantings of Pinus tecunumanii, established as replicated progeny within provenance trials, is used to present a principal components-based analysis that illustrates the climatic preferences of 23 populations from the species’ native range. This meta-analysis quantifies changes in the relative productivity, assessed as individual-tree volume, of populations across climatic gradients and associates the preference of a population with increased volume production along the climatic gradient. Clustering and ordination on the matrix containing estimates of change in productivity for each population summarise differentials in productivity associated with climatic gradients. The preference of populations along principal components therefore reflects the adaptive profiles of populations, which may be used with breeding-value estimates from routine genetic evaluations to assist with the development of deployment populations targeting different environments. As well, the approach may be used to test whether the preference of a population, estimated as population loadings for growth differentials, is affected by the climate in the native range of the population. This relationship may be interpreted as an estimate of how much local climate shapes the adaptive profiles of populations. The amount and seasonality of precipitation most clearly differentiate the adaptive profiles of populations, with less variation in the population responses explained by temperature differentiation. As expected from type-B correlation estimates, most populations exhibited small changes in relative productivity across climatic gradients. However, patterns of similarities in adaptive profiles among populations were evident using spatial orientation to display population responses to the climatic variables experienced in the provenance trials. Clustering and ordination of population responses derived from empirical data served to identify populations that responded positively or negatively to climatic variables; this information may help guide conservation genetics efforts, direct the deployment of germplasm, or identify seed sources that are sensitive to changes in climatic variables. Linking response patterns to the climatic data from the native range of each population indicated little effect of local climate shaping adaptive profiles.