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Trees have evolved to time flowering to maximize outcrossing, minimize exposure to damaging frosts, and synchronize development with soil moisture and nutrient availability. Understanding the environmental cues that influence the timing of reproductive budburst will be important for predicting how flowering phenology of trees will change with a changing climate, and aid in the time-sensitive management of seed orchards. We examined how temperature influenced the timing of female flowering of coastal Douglas-fir with over 4500 flowering observations of trees from 12 sites across western Oregon and Washington. We predicted flowering dates by modifying chilling and forcing effectiveness functions from a model of vegetative budburst of Douglas-fir. We also examined whether genetic variation in Douglas-fir influenced the relationships between chilling and forcing accumulations using flowering observations from two common-garden experiments with trees from 60 populations from a diverse range of climates. Our reproductive budburst model predicted the day of flowering within an average of five days of the observed flowering dates across all sites and years. Fewer hours of forcing temperatures were required for flowering on sites that had experienced high chilling. Warmer temperatures in the future will likely result in earlier flowering on sites which currently have high chilling; however, sites which currently experience low chilling may display no change or possibly even a delay in flowering. Douglas-fir genotypes from different geographic regions flowered in the same order from year to year in common gardens, indicating that both temperature and genetic variation influence flowering. Genetic variation in flowering dates was more strongly related to summer drought of seed source locations than to cold winters. Knowledge of the environmental cues and genetic variation in timing of flowering can help predict how future changes in temperature under various climate models could change flowering time across the range of coastal Douglas-fir. [ABSTRACT FROM AUTHOR]

Global climate change may detrimentally affect future generations of numerous forest tree species, hampering their long-term sustainability if appropriate evolutionary responses remain lacking. To face these novel threats, conservation biologists are in need of a thorough understanding and identification of adaptive variation in key fitness traits. We here provide an elaborate synthesis of pre-existing and novel analyses of an association mapping, genecological and landscape genomic study integrating genotypic, environmental and phenotypic data to gain insights into the genetic basis of cold-hardiness adaptation in coastal Douglas-fir ( Pseudotsuga menziesii var. menziesii). Data were collected across part of the natural range for a total of 643 individuals. A landscape genomic approach revealed 28 putative non-neutral genes, although a variance partitioning analysis indicated only moderate power of this gene set in explaining cold-hardiness-related phenotypic variation, and suggests many important genes await discovery. Integrating these results within the entire phenotype-genotype-environment spectrum allowed us to delineate the six most promising candidate genes under selection. By combining genomic, phenotypic and environmental data, this study attempts to gain insights in the genetic basis of key adaptations, which may ultimately aid forestry managers to establish resilient ecosystems in face of future climate change. [ABSTRACT FROM AUTHOR]

Under climate change, the reduction of frost risk, onset of warm temperatures and depletion of soil moisture are all likely to occur earlier in the year in many temperate regions. The resilience of tree species will depend on their ability to track these changes in climate with shifts in phenology that lead to earlier growth initiation in the spring. Exposure to warm temperatures ('forcing') typically triggers growth initiation, but many trees also require exposure to cool temperatures ('chilling') while dormant to readily initiate growth in the spring. If warming increases forcing and decreases chilling, climate change could maintain, advance or delay growth initiation phenology relative to the onset of favorable conditions. We modeled the timing of height- and diameter-growth initiation in coast Douglas-fir (an ecologically and economically vital tree in western North America) to determine whether changes in phenology are likely to track changes in climate using data from field-based and controlled-environment studies, which included conditions warmer than those currently experienced in the tree's range. For high latitude and elevation portions of the tree's range, our models predicted that warming will lead to earlier growth initiation and allow trees to track changes in the onset of the warm but still moist conditions that favor growth, generally without substantially greater exposure to frost. In contrast, toward lower latitude and elevation range limits, the models predicted that warming will lead to delayed growth initiation relative to changes in climate due to reduced chilling, with trees failing to capture favorable conditions in the earlier parts of the spring. This maladaptive response to climate change was more prevalent for diameter-growth initiation than height-growth initiation. The decoupling of growth initiation with the onset of favorable climatic conditions could reduce the resilience of coast Douglas-fir to climate change at the warm edges of its distribution. [ABSTRACT FROM AUTHOR]

The success of conifers over much of the world's terrestrial surface is largely attributable to their tolerance to cold stress (i.e., cold hardiness). Due to an increase in climate variability, climate change may reduce conifer cold hardiness, which in turn could impact ecosystem functioning and productivity in conifer-dominated forests. The expression of cold hardiness is a product of environmental cues (E), genetic differentiation (G), and their interaction (G × E), although few studies have considered all components together. To better understand and manage for the impacts of climate change on conifer cold hardiness, we conducted a common garden experiment replicated in three test environments (cool, moderate, and warm) using 35 populations of coast Douglas-fir ( Pseudotsuga menziesii var. menziesii) to test the hypotheses: (i) cool-temperature cues in fall are necessary to trigger cold hardening, (ii) there is large genetic variation among populations in cold hardiness that can be predicted from seed-source climate variables, (iii) observed differences among populations in cold hardiness in situ are dependent on effective environmental cues, and (iv) movement of seed sources from warmer to cooler climates will increase risk to cold injury. During fall 2012, we visually assessed cold damage of bud, needle, and stem tissues following artificial freeze tests. Cool-temperature cues (e.g., degree hours below 2 °C) at the test sites were associated with cold hardening, which were minimal at the moderate test site owing to mild fall temperatures. Populations differed 3-fold in cold hardiness, with winter minimum temperatures and fall frost dates as strong seed-source climate predictors of cold hardiness, and with summer temperatures and aridity as secondary predictors. Seed-source movement resulted in only modest increases in cold damage. Our findings indicate that increased fall temperatures delay cold hardening, warmer/drier summers confer a degree of cold hardiness, and seed-source movement from warmer to cooler climates may be a viable option for adapting coniferous forest to future climate. [ABSTRACT FROM AUTHOR]

Highlights: [•] We model the climate niche of Pinus ponderosa and Pseudotsuga menziesii varieties. [•] Classification errors were less than 5% and were mostly false positives. [•] Niche space was mapped for the decade surrounding 2060 using GCM ensemble output. [•] Projected impacts were more severe for P. ponderosa than for P. menziesii. [•] Projections were dire for the varieties occurring in Mexico. [Copyright &y& Elsevier]

Models to predict budburst and other phenological events in plants are needed to forecast how climate change may impact ecosystems and for the development of mitigation strategies. Differences among genotypes are important to predicting phenological events in species that show strong clinal variation in adaptive traits. We present a model that incorporates the effects of temperature and differences among genotypes to predict the timing of budburst of coast Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco). The main components of the model are (i) functions to calculate the accumulation of chilling units (CU) and forcing units (FU) during dormancy and (ii) a function defining the combinations of CU and FU needed for budburst (the possibility line). The possibility line was fit to data from 59 populations subjected to eight different winter environments. Differences among populations were incorporated into the possibility line using population coefficients that vary the FU required for budburst. Correlations among the population coefficients and variables describing local environments supported the hypothesis that genetic variation in budburst is largely an adaptation to summer drought. The new model can be used to test potential seed transfers as a strategy to mitigate some of the effects of climate change. On a besoin de modèles capables de prédire le débourrement ainsi que d'autres événements d'ordre phénologique chez les plantes pour prévoir les effets néfastes des changements climatiques sur les écosystèmes et pour élaborer des stratégies visant à atténuer ces effets. Les différences génotypiques sont importantes pour prédire les événements d'ordre phénologique chez les espèces dont les traits adaptatifs sont soumis à une forte variation clinale. Nous présentons un modèle qui intègre les effets de la température et les différences entre les génotypes pour prédire le moment du débourrement chez le douglas de Menzies typique (Pseudotsuga menziesii var. menziesii (Mirb.) Franco). Les principaux éléments du modèle sont (i) des fonctions pour calculer l'accumulation des unités de froid et des unités de forçage durant la période de dormance et (ii) une fonction qui définit les combinaisons d'unités de froid et de forçage nécessaires pour le débourrement (ligne des possibilités). La ligne des possibilités a été ajustée aux données de 59 populations soumises à huit sortes de conditions hivernales différentes. Les différences entre les populations ont été intégrées dans la ligne des possibilités sous forme de coefficients de population qui font varier les unités de forçage requises pour le débourrement. Les corrélations entre les coefficients de population et les variables qui décrivent les conditions environnementales locales supportent l'hypothèse selon laquelle la variation génétique associée au débourrement est en grande partie une adaptation à la sécheresse estivale. Le nouveau modèle peut être utilisé pour tester les transferts potentiels de graines en tant que stratégie pour minimiser certains des effets des changements climatiques. [ABSTRACT FROM AUTHOR]

Genetic variation in fall cold damage in coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) was measured by exposing excised branches of seedlings from 666 source locations grown in a common garden to freezing temperatures in a programmable freezer. Considerable variation was found among populations in fall cold hardiness of stems, needles, and buds compared with bud burst, bud set, and biomass growth after 2 years. Variation in fall cold hardiness was strongly correlated (r = 0.67) with cold-season temperatures of the source environment. Large population differences corresponding with environmental gradients are evidence that natural selection has been important in determining genetic variation in fall cold hardiness, much more so than in traits of bud burst (a surrogate for spring cold hardiness), bud set, and growth. Seed movement guidelines and breeding zones may be more restrictive when considering genetic variation in fall cold hardiness compared with growth, phenology, or spring cold hardiness. A regional stratification system based on ecoregions with latitudinal and elevational divisions, and roughly corresponding with breeding zones used in Oregon and Washington, appeared to be adequate for minimizing population differences within regions for growth and phenology, but perhaps not fall cold hardiness. Although cold hardiness varied among populations, within-population and within-region variation is sufficiently large that responses to natural or artificial selection may be readily achieved. [ABSTRACT FROM AUTHOR]

• Background and Aims Genecological knowledge is important for understanding evolutionary processes and for managing genetic resources. Previous studies of coastal Douglas fir (Pseudotsuga menziesii var. menziesii) have been inconclusive with respect to geographical patterns of variation, due in part to limited sample intensity and geographical and climatic representation. This study describes and maps patterns of genetic variation in adaptive traits in coastal Douglas fir in western Oregon and Washington, USA.• Methods Traits of growth, phenology and partitioning were measured in seedlings of 1338 parents from 1048 locations grown in common gardens. Relations between traits and environments of seed sources were explored using regressions and canonical correlation analysis. Maps of genetic variation as related to the environment were developed using a geographical information system (GIS).• Key Results Populations differed considerably for adaptive traits, in particular for bud phenology and emergence. Variation in bud-set, emergence and growth was strongly related to elevation and cool-season temperatures. Variation in bud-burst and partitioning to stem diameter versus height was related to latitude and summer drought. Seedlings from the east side of the Washington Cascades were considerably smaller, set bud later and burst bud earlier than populations from the west side.• Conclusions Winter temperatures and frost dates are of overriding importance to the adaptation of Douglas fir to Pacific Northwest environments. Summer drought is of less importance. Maps generated using canonical correlation analysis and GIS allow easy visualization of a complex array of traits as related to a complex array of environments. The composite traits derived from canonical correlation analysis show two different patterns of variation associated with different gradients of cool-season temperatures and summer drought. The difference in growth and phenology between the westside and eastside Washington Cascades is hypothesized to be a consequence of the presence of interior variety (P. menziessii var. glauca) on the eastside. [ABSTRACT FROM AUTHOR]

Tree improvement programs have generally relied on testing families in open light environments. With increased interest in multiaged silvicultural systems, some people have questioned whether families selected in the open are appropriate for planting in the shade. We grew Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) families from two climatically distinct seed sources for 2 years under four levels of shade. The response to shade differed for several traits between the two populations and among families within populations. The magnitude of variation associated with the interaction, however, was small compared with the overall effects of genetic selection or of shade. Families selected based on performance in an open light environment resulted in nearly the same response to selection when grown under shade as families selected based on performance in the shade. We conclude that seedlings from families selected in an open light environment are appropriate for use in the low-light environments of alternative silvicultural systems and that use of such genetically selected stock may compensate for the less favorable growing conditions. Genetic selection may contribute importantly to meeting multiple objectives, including the production of significant amounts of wood as well as the efficient and timely creation of large stand structures neededfor other forest values. [ABSTRACT FROM AUTHOR]

Adaptation to cold is one of the greatest challenges to forest trees. This process is highly synchronized with environmental cues relating to photoperiod and temperature. Here, we use a candidate gene-based approach to search for genetic associations between 384 single-nucleotide polymorphism (SNP) markers from 117 candidate genes and 21 cold-hardiness related traits. A general linear model approach, including population structure estimates as covariates, was implemented for each marker-trait pair. We discovered 30 highly significant genetic associations [false discovery rate (FDR) Q < 0.101 across 12 candidate genes and 10 of the 21 traits. We also detected a set of 7 markers that had elevated levels of differentiation between sampling sites situated across the Cascade crest in northeastern Washington. Marker effects were small (r2 < 0.05) and within the range of those published previously for forest trees. The derived SNP allele, as measured by a comparison to a recently diverged sister species, typically affected the phenotype in away consistent with cold hardiness. The majority of markerswere characterized as having largely nonadditive modes of gene action, especially underdominance in the case of cold-tolerance related phenotypes. We place these results in the context of trade-offs between the abilities to grow longer and to avoid fall cold damage, as well as putative epigenetic effects. These associations provide insight into the genetic components of complex traits in coastal Douglas fir, as well as highlight the need for landscape genetic approaches to the detection of adaptive genetic diversity. [ABSTRACT FROM AUTHOR]