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Background: Selection of climate-change adapted ecotypes of commercially valuable species to date relies on DNA-assisted screening followed by growth trials. For trees, such trials can take decades, hence any approach that supports focussing on a likely set of candidates may save time and money. We use a non-stationary statistical analysis with spatially varying coefficients to identify ecotypes that indicate first regions of similarly adapted varieties of Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) in North America. For over 70,000 plot-level presence-absences, spatial differences in the survival response to climatic conditions are identified., Results: The spatially-variable coefficient model fits the data substantially better than a stationary, i.e. constant-effect analysis (as measured by AIC to account for differences in model complexity). Also, clustering the model terms identifies several potential ecotypes that could not be derived from clustering climatic conditions itself. Comparing these six identified ecotypes to known genetically diverging regions shows some congruence, as well as some mismatches. However, comparing ecotypes among each other, we find clear differences in their climate niches., Conclusion: While our approach is data-demanding and computationally expensive, with the increasing availability of data on species distributions this may be a useful first screening step during the search for climate-change adapted varieties. With our unsupervised learning approach being explorative, finely resolved genotypic data would be helpful to improve its quantitative validation., (© 2024. The Author(s).)

Climate change is increasing fire activity in the western United States, which has the potential to accelerate climate-induced shifts in vegetation communities. Wildfire can catalyze vegetation change by killing adult trees that could otherwise persist in climate conditions no longer suitable for seedling establishment and survival. Recently documented declines in postfire conifer recruitment in the western United States may be an example of this phenomenon. However, the role of annual climate variation and its interaction with long-term climate trends in driving these changes is poorly resolved. Here we examine the relationship between annual climate and postfire tree regeneration of two dominant, low-elevation conifers (ponderosa pine and Douglas-fir) using annually resolved establishment dates from 2,935 destructively sampled trees from 33 wildfires across four regions in the western United States. We show that regeneration had a nonlinear response to annual climate conditions, with distinct thresholds for recruitment based on vapor pressure deficit, soil moisture, and maximum surface temperature. At dry sites across our study region, seasonal to annual climate conditions over the past 20 years have crossed these thresholds, such that conditions have become increasingly unsuitable for regeneration. High fire severity and low seed availability further reduced the probability of postfire regeneration. Together, our results demonstrate that climate change combined with high severity fire is leading to increasingly fewer opportunities for seedlings to establish after wildfires and may lead to ecosystem transitions in low-elevation ponderosa pine and Douglas-fir forests across the western United States., Competing Interests: The authors declare no conflict of interest.

Statistically downscaled climate change scenarios from four General Circulation Models for two Representative Concentration Pathways (RCP) were applied as inputs to a biogeochemical model, PnET-BGC, to examine potential future dynamics of water, carbon, and nitrogen in an old-growth Douglas-fir forest in the western Cascade Range. Projections show 56% to 77% increases in stomatal conductance throughout the year from 1986-2010 to 2076-2100, and 65% to 104% increases in leaf carbon assimilation between October and June over the same period. However, future dynamics of water and carbon under the RCP scenarios are affected by a 49% to 86% reduction in foliar biomass resulting from severe air temperature and humidity stress to the forest in summer. Important implications of future decreases in foliar biomass include 1) 20% to 71% decreases in annual transpiration which increase soil moisture by 7% to 15% in summer and fall; 2) decreases in photosynthesis by 77% and soil organic matter by 62% under the high radiative forcing scenario; and 3) altered foliar and soil carbon to nitrogen stoichiometry. Potential carbon dioxide fertilization effects on vegetation are projected to 1) amplify decreases in transpiration by 4% to 9% and increases in soil moisture in summer and fall by 1% to 2%; and 2) alleviate decreases in photosynthesis by 4%; while 3) having negligible effects on the dynamics of nitrogen. Our projections suggest that future decrease in transpiration and moderate water holding capacity may mitigate soil moisture stress to the old-growth Douglas-fir forest. Future increases in nitrogen concentration in soil organic matter are projected to alleviate the decrease in net nitrogen mineralization despite a reduction in decomposition of soil organic matter by the end of the century., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In the context of ongoing climatic warming, certain landscapes could be near a tipping point where relatively small changes to their fire regimes or their postfire forest recovery dynamics could bring about extensive forest loss, with associated effects on biodiversity and carbon-cycle feedbacks to climate change. Such concerns are particularly valid in the Klamath Region of northern California and southwestern Oregon, where severe fire initially converts montane conifer forests to systems dominated by broadleaf trees and shrubs. Conifers eventually overtop the competing vegetation, but until they do, these systems could be perpetuated by a cycle of reburning. To assess the vulnerability of conifer forests to increased fire activity and altered forest recovery dynamics in a warmer, drier climate, we characterized vegetation dynamics following severe fire in nine fire years over the last three decades across the climatic aridity gradient of montane conifer forests. Postfire conifer recruitment was limited to a narrow window, with 89% of recruitment in the first 4 years, and height growth tended to decrease as the lag between the fire year and the recruitment year increased. Growth reductions at longer lags were more pronounced at drier sites, where conifers comprised a smaller portion of live woody biomass. An interaction between seed-source availability and climatic aridity drove substantial variation in the density of regenerating conifers. With increasing climatic water deficit, higher propagule pressure (i.e., smaller patch sizes for high-severity fire) was needed to support a given conifer seedling density, which implies that projected future increases in aridity could limit postfire regeneration across a growing portion of the landscape. Under a more severe prospective warming scenario, by the end of the century more than half of the area currently capable of supporting montane conifer forest could become subject to minimal conifer regeneration in even moderate-sized (10s of ha) high-severity patches., (© 2017 John Wiley & Sons Ltd.)

Climatic and land use changes have significant consequences for the distribution of tree species, both through natural dispersal processes and following management prescriptions. Responses to these changes will be expressed most strongly in seedlings near current species range boundaries. In northern temperate forest ecosystems, where changes are already being observed, ectomycorrhizal fungi contribute significantly to successful tree establishment. We hypothesised that communities of fungal symbionts might therefore play a role in facilitating, or limiting, host seedling range expansion. To test this hypothesis, ectomycorrhizal communities of interior Douglas-fir and interior lodgepole pine seedlings were analysed in a common greenhouse environment following growth in five soils collected along an ecosystem gradient. Currently, Douglas-fir's natural distribution encompasses three of the five soils, whereas lodgepole pine's extends much further north. Host filtering was evident amongst the 29 fungal species encountered: 7 were shared, 9 exclusive to Douglas-fir and 13 exclusive to lodgepole pine. Seedlings of both host species formed symbioses with each soil fungal community, thus Douglas-fir did so even where those soils came from outside its current distribution. However, these latter communities displayed significant taxonomic and functional differences to those found within the host distribution, indicative of habitat filtering. In contrast, lodgepole pine fungal communities displayed high functional similarity across the soil gradient. Taxonomic and/or functional shifts in Douglas-fir fungal communities may prove ecologically significant during the predicted northward migration of this species; especially in combination with changes in climate and management operations, such as seed transfer across geographical regions for forestry purposes.

The current planting of economically important timber species, such as Douglas-fir, mainly relies on genetically improved seeds from seed orchards. However, published research on the effects of climate change has largely focused on natural populations. To bridge this gap, data from 80 cooperative second-cycle coastal Douglas-fir progeny tests across eight breeding zones in western Washington and Oregon were analyzed. Climate transfer functions for age-12 growth were derived, showing significant results for the US Pacific Northwest. Region-specific transfer functions (Coast, Inland, and Cascade) displayed stronger correlations. Mean annual temperature and mean coldest month temperature were the most important climatic variables explaining growth. The study found that populations from slightly warmer areas tended to grow better but moving populations from colder to warmer areas by 2 °C (analogous to projected global warming) would result in an 8% genetic loss in age-12 height and a 25% genetic loss in age-12 volume. However, substantial diversity in climatic response was found among full-sib families within large breeding zones, suggesting that breeding and selecting suitable families for future climatic conditions within breeding zones is feasible. The study discusses potential strategies to adapt current breeding programs to address the impacts of future climate change while maintaining high population growth rates in Douglas-fir breeding programs. [ABSTRACT FROM AUTHOR]

Summary: Understanding the genetic basis of how plants defend against pathogens is important to monitor and maintain resilient tree populations. Swiss needle cast (SNC) and Rhabdocline needle cast (RNC) epidemics are responsible for major damage of forest ecosystems in North America.Here we investigate the genetic architecture of tolerance and resistance to needle cast diseases in Douglas‐fir (Pseudotsuga menziesii) caused by two fungal pathogens: SNC caused by Nothophaeocryptopus gaeumannii, and RNC caused by Rhabdocline pseudotsugae.We performed case–control genome‐wide association analyses and found disease resistance and tolerance in Douglas‐fir to be polygenic and under strong selection. We show that stomatal regulation as well as ethylene and jasmonic acid pathways are important for resisting SNC infection, and secondary metabolite pathways play a role in tolerating SNC once the plant is infected. We identify a major transcriptional regulator of plant defense, ERF1, as the top candidate for RNC resistance.Our findings shed light on the highly polygenic architectures underlying fungal disease resistance and tolerance and have important implications for forestry and conservation as the climate changes. [ABSTRACT FROM AUTHOR]

In the face of climate change and associated increases in disturbances, some areas, known as refugia, will remain or become newly habitable for species, while others will be lost. Planning and managing for refugia can support biodiversity and conservation. However, without explicit consideration of justice, planning and management for refugia risks unnecessarily limiting information about local conditions and traditional practices that may be contained in Indigenous knowledges, and causing maladaptive consequences such as exclusion of Indigenous communities from decision-making and from protected areas, with loss of use of traditional plants and animals. The article proposes a new concept, Indigenous refugia, that incorporates three types of justice into existing theories of refugia for conservation in the face of climate change: recognition justice as understanding and respect for Indigenous values, experiences, and knowledges; procedural justice in collaboration and decision-making; and distributional justice as access to species and lands that sustain cultural and social processes. It presents a potential example of Indigenous refugia for the planning and management for climate-vulnerable Douglas-fir in New Mexico in collaboration with Pueblo, Diné (Navajo), Nde (Apache), and other Indigenous peoples with ancestral lands in the area. [ABSTRACT FROM AUTHOR]

Summary: Tree seedlings from populations native to drier regions are often assumed to be more drought tolerant than those from wetter provenances. However, intraspecific variation in drought tolerance has not been well‐characterized despite being critical for developing climate change mitigation and adaptation strategies, and for predicting the effects of drought on forests.We used a large‐scale common garden drought‐to‐death experiment to assess range‐wide variation in drought tolerance, measured by decline of photosynthetic efficiency, growth, and plastic responses to extreme summer drought in seedlings of 73 natural populations of the two main varieties of Douglas‐fir (Pseudotsuga menziesii var. menziesii and var. glauca).Local adaptation to drought was weak in var. glauca and nearly absent in menziesii. Var. glauca showed higher tolerance to drought but slower growth than var. menziesii. Clinal variation in drought tolerance and growth species‐wide was mainly associated with temperature rather than precipitation. A higher degree of plasticity for growth was observed in var. menziesii in response to extreme drought.Genetic variation for drought tolerance in seedlings within varieties is maintained primarily within populations. Selective breeding within populations may facilitate adaptation to drought more than assisted gene flow. [ABSTRACT FROM AUTHOR]

Maximum stand density index (SDIMAX) represents the carrying capacity of a forest stand based on the relationship between the number of trees and their size. Plot‐level inventory data provided through a collaborative network of federal, state, and private forest management groups were utilized to develop SDIMAX models for important Pacific Northwest conifers of western Washington and Oregon, USA. The influence of site‐specific climatic and environmental variables was explored within an ensemble learning model. Future climate projections based on global circulation models under different representative CO2 concentration pathways (RCP 4.5 and RCP 8.5) and timeframes (2050s and 2080s) were utilized in a space‐for‐time substitution to understand potential shifts in modeled SDIMAX. A majority of the region showed decreases in carrying capacity under future climate conditions. Modeled mean SDIMAX decreased 5.4% and 11.4% for Douglas‐fir (Pseudotsuga menziesii (Mirb.) Franco) dominated forests and decreased 6.6% and 8.9% for western hemlock (Tsuga heterophylla (Raf.) Sarg.) and Pacific silver fir (Abies amabilis), dominated forests under the RCP 4.5 in the 2050s and RCP 8.5 in the 2080s, respectively. Projected future conditions often fall outside the range of any contemporary climate profile, resulting in what may be referred to as extramural conditions. Within the study region, 45% and 46% of climate variables included in the final model were extramural for the Douglas‐fir and hemlock models, respectively, under RCP 8.5 in the 2080s. Although extrapolating beyond the range of input data is not appropriate and many unknowns remain regarding future climate projections, these results allow for general interpretations of the direction and magnitude of potential shifts in forest carrying capacity. Recommendations for Resource Managers: These results present forest managers and policy‐makers with the ability to make location‐specific interpretations of potential shifts in forest stand carrying capacity under potential future climate projection scenarios, which show forest communities of the Pacific Northwest may be facing a longer, warmer, droughtier growing season.Across the study region, a majority of the landscape is seeing a downward shift in the modeled maximum carrying capacity under future climate projections.The modeled carrying capacity of mixed species stands appear to be more resilient to projected changes in climate.Planting and thinning to lower densities may provide resilience and capture the projected increases in density‐related mortality.Across all projected future climate scenarios fall into extramural conditions, which are a combination of climatic conditions not currently experienced in the study area. [ABSTRACT FROM AUTHOR]

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), one of the most commercially important tree species in western North America and one of the most valuable timber trees worldwide, was introduced to Europe in 1827. It became a major species for afforestation in Western Europe after WWII, currently grows in 35 countries on over 0.83 million ha and is one of the most widespread non-native tree species across the continent. A lower sensitivity to drought makes Douglas-fir a potential alternative to the more drought-sensitive Norway spruce so its importance in Europe is expected to increase in the future. It is one of the fastest growing conifer species cultivated in Europe, with the largest reported dimensions of 2.3 m in diameter and 67.5 m in height. Pure stands have high productivity (up to 20 m3 ha−1a−1) and production (over 1000 m3 ha−1). The species is generally regenerated by planting (initial stocking density from less than 1000 seedlings ha−1 to more than 4000 ha−1), using seedlings of European provenance derived from seed orchards or certified seed stands. As the range of end-uses of its wood is very wide, the rotation period of Douglas-fir is highly variable and ranges between 40 and 120 years. When the production of large-sized, knot-free timber is targeted, thinnings are always coupled with pruning up to 6 m. There is an increasing interest in growing Douglas-fir in mixtures and managing stands through close-to-nature silviculture, but the species' intermediate shade tolerance means that it is best managed through group selection or shelterwood systems. [ABSTRACT FROM AUTHOR]

Key message: Planting sites that are cooler, with more precipitation, early springs, high TD and hot dry summers reduce bole taper in young Douglas-fir trees. Seed-source climates that are drier, with high TD and low snowfall produce seed-sources with lower taper. Analysis of a 10 year reciprocal transplant study was performed to determine the influence of seed-source and local planting site climates on the bole taper of 8995 Douglas-fir (Pseudotsuga menziesii var. menziesii) trees. Trees were planted at 9 sites across Oregon and Washington, with 120 known families taken from 12 seed-source regions across California, Oregon, and Washington. Diameter at breast height (DBH) ranged from 0.1 to 22.9 cm, with tree ages ranging from 2 year-old seedlings to 12 year-old trees. Changes in Gini coefficients (∆G) of diameters along tree boles, as a surrogate for changes in taper, were modeled as a function of age, site climate, and seed-source climate (Wang et al., in PLoS One 11, 2016) using universal response functions (URF) (Wang et al., in Ecol Appl 20:153–163, 2010). Lower Gini coefficients come from less tapered boles, i.e., more cylindrically shaped boles. There was significant influence on taper from five site climate variables: mean annual temperature (MAT), mean annual precipitation (MAP), beginning of frost-free period (bFFP), difference between minimum and maximum monthly temperatures (TD), and summer heat-moisture index (SHM). These results suggest that cooler years with more precipitation, early springs, large TD and hot dry summers reduce tree taper. There was significant influence on taper from three seed-source climate variables: percent precipitation as snow (PAS), Hargrave's climate moisture deficit (CMD), and TD. These results suggest dry regions with large ranges in monthly temperatures and low snowfall will produce seed-sources with lower Gini coefficients. Projections under future climates using an ensemble model show areas where G estimates are currently highest showed increases in G, while areas with the lowest G estimates decreased. Most of the Douglas-fir region shows declines in Gini coefficients under high emissions scenarios. These predicted changes in taper have direct implications for wood volume and carbon mass estimates of trees under future climates. [ABSTRACT FROM AUTHOR]

A growing body of evidence suggests that climate change is altering the epidemiology of many forest diseases. Nothophaeocryptopus gaeumannii (Rhode) Petrak, an ascomycete native to the Pacific Northwest and the causal agent of the Swiss needle cast (SNC) disease of Douglas-fir [Pseudotsuga menziesii (Mirbel) Franco], is no exception. In the past few decades, changing climatic conditions have coincided with periodic epidemics of SNC in coastal forests and plantations from Southwestern British Columbia (B.C.) to Southwestern Oregon, wherein an increase in the colonization of needles by N. gaeumanii causes carbon starvation, premature needle shedding and a decline in growth. Two major sympatric genetic lineages of N. gaeumannii have been identified in the coastal Pacific Northwest. Past research on these lineages suggests they have different environmental tolerance ranges and may be responsible for some variability in disease severity. In this study, we examined the complex dynamics between biologically pertinent short- and long-term climatic and environmental factors, phylogenetic lineages of N. gaeumannii and the severity patterns of the SNC disease. Firstly, using an ensemble species distribution modeling approach using genetic lineage presences as model inputs, we predicted the probability of occurrence of each lineage throughout the native range of Douglas-fir in the present as well as in 2050 under the “business as usual” (RCP8.5) emissions scenario. Subsequently, we combined these model outputs with short-term climatic and topographic variables and colonization index measurements from monitoring networks across the SNC epidemic area to infer the impacts of climate change on the SNC epidemic. Our results suggest that the current environmental tolerance range of lineage 1 exceeds that of lineage 2, and we expect lineage 1 to expand inland in Washington and Oregon, while we expect lineage 2 will remain relatively constrained to its current range with some slight increases in suitability, particularly in coastal Washington and Oregon. We also found that disease colonization index is associated with the climatic suitability of lineage 1, and that the suitability of the different lineages could impact the vertical patterns of colonization within the crown. We conclude that unabated climate change could cause the SNC epidemic to intensify.

Large trees have disproportionally large competitive advantage in access to light, which has been proposed to increase growth dominance of large trees (e.g., a larger proportion of volume growth than standing volume is in large trees in a stand). Tree growth may also be limited by the availability of other resources besides light. Nutrient deficiency, especially of nitrogen, is considered common among temperate forests including mixedconifer forests of the Inland Northwest of the United States. Data from a long-term forest nutrition study across four Inland Northwest states were analyzed to evaluate nitrogen ( potassium fertilization's effects on growth dominance over an eight-year period following treatment. Our results show that growth dominance varied substantially across plots in each vegetation series and fertilization treatment, and its mean values generally were at minuscule magnitudes, negative, and not significantly different from 0. We propose that this lack of a clear pattern in growth dominance was the result of the mixed-species composition where shade-tolerant species remained in lower crown positions, yet their relative growth kept pace with large trees. Limited moisture availability at dry sites may have hampered the development of growth dominance. Growth dominance also was lowered by mortality observed among relatively large trees. The largely negative growth dominance across fertilization treatments indicated that small trees seem to have maintained higher relative growth rates than large trees, even if absolute growth was higher among large trees. In the case fertilization does improve stand growth, a significant part of this improved growth will be lost in density-dependent mortality over time if not captured through thinning/harvesting. [ABSTRACT FROM AUTHOR]

The contribution of Douglas-fir (Df) to European forests is likely to increase as the species is a potential adaptation option to climate change. In this study, we investigated growth and survival of Df seed sources to fill a knowledge gap regarding recommendations for the future use of Df provenances in Poland. Our experimental test site represents the most continental climate among all Df trials installed in the IUFRO 1966–67 test series in Europe. At this unique single site, we evaluated the performance of 46 Df provenances from North America, and nine local landraces of unknown origin. Repeated measurements of tree diameter, height, and volume were analysed, to age 48, representing integrated responses to geographic and climatic conditions. Significant variation in survival and productivity-related traits were found, with the interior Df provenances performing best, in contrast to previous European reports. The higher survivability and volume of the interior provenances resulted from their superior frost resistance. The low precipitation seasonality at the location of seed origin provided an additional advantage to the trees at the test site. Geographic and climatic factors of seed origin explained most of the variation in productivity (77 and 64%, respectively). The tested landraces exhibited diverse performance, implying that naturalized local seed sources in Poland need improvement and perhaps enrichment with new genetic material from North America, while considering geography and climate. Assisted migration programs should consider the limitations imposed by both frost and drought events in guiding future Df selections for continental climates. Further field testing, early greenhouse screening and DNA testing are also recommended. [ABSTRACT FROM AUTHOR]

Forests are important for biodiversity, timber production and carbon accumulation, but these ecosystem services may be impacted by climate change. Field data collected from individual forest types occurring across a climatic gradient can contribute to forecasting these consequences. We examined how changes in temperature, precipitation and aridity affect ecosystem services in 23 mature Douglas-fir (Pseudotsuga menziesii) forests in nine climatic regions across a 900 km gradient in British Columbia, Canada. Using Canadian National Forest Inventory methodology, we assessed richness and diversity of plant functional groups, site index, and above- and below-ground carbon stocks. As aridity increased, ecosystem-level tree species richness declined on average from four to one species, Douglas-fir site index declined from 30 to 15 m, and ecosystem carbon storage decreased from 565 to 222 Mg ha–1. Tree species richness was positively and herb species richness negatively correlated with carbon storage. Carbon storage by ecosystem compartment was largest in aboveground live tree biomass, declining in the following order: mineral soils > coarse woody debris and dead standing trees > forest floor > small and fine woody debris > understory plants. Mineral soil carbon at depths of 0-15 cm, 15-35 cm, and 35-55 cm increased with increasing mean annual precipitation and decreasing aridity. Our results indicate that as aridity increases and precipitation decreases, tree species richness, site index and carbon storage in existing Douglas-fir forests declines. However, assisted or natural migration of Douglas-fir into more humid regions could be associated with more diverse, productive, carbon-rich forests. This study informs carbon stock vulnerability and provides empirical data essential for carbon stock forecasts.

The forest stands of Douglas-fir [Pseudotsuga menziesii (Mirbel) Franco] and Norway spruce [Picea abies (L.) Karst.] in the South Bohemian uplands (Czech Republic) represent an artificial community of a neophyte (native to North America) and indigenous species (with natural distribution in mountain forests). Ecological characteristics of these two tree species and their response to climatic factors were studied using tree ring analyses and correlation of growth indices for tree-to-tree and between trees and historical parameters of climate (average air temperatures, sum of precipitations and relative air humidity). The two datasets were analysed using multidimensional methods. The ordination analysis shows a considerable difference between both tree species. Growth of both species differed significantly by districts and plots. The effect of climate was studied using correlations as floating time-window. Our results showed that average air temperature had a stronger effect on Douglas-fir growth, for which an increment decrease was found at higher temperatures between May 25th and June 24th. Also, the average maximum air temperature affected the growth of Douglas-fir more strongly than that of Norway spruce. More precipitation was associated with a similar positive effect on the growth of both tree species. Air humidity had a significant effect on growth of both studied tree species and the effect of air humidity was more significant than of distinct precipitation. The combined effects of lack of precipitation and high temperature in vegetation period was the major limiting factor for radial growth. Douglas-fir showed higher productivity (+17.2%) and resistance to climate extremes compared to Norway spruce. Our results suggest that a mixed stand could be more resistant in terms of growth stability than mono-specific stands, as the two studied species exhibited different reaction to climate extremes. Our study further showed that mixed stands with high species diversity had a higher production potential (+13.1%). [ABSTRACT FROM AUTHOR]

Swiss needle cast (SNC), caused by Nothophaeocryptopus gaeumannii , is a foliage disease of Douglas-fir (Pseudotsuga menziesii), that reduces growth in native stands and exotic plantations worldwide. An outbreak of SNC began in coastal Oregon in the mid-1990s and has persisted since that time. Here we review the current state of knowledge after 24 years of research and monitoring, with a focus on Oregon, although the disease is significant in coastal Washington and has recently emerged in southwestern British Columbia. We present new insights into SNC distribution, landscape patterns, disease epidemiology and ecology, host-pathogen interactions, trophic and hydrologic influences, and the challenges of Douglas-fir plantation management in the presence of the disease. In Oregon, the SNC outbreak has remained geographically contained but has intensified. Finally, we consider the implications of climate change and other recently emerged foliage diseases on the future of Douglas-fir plantation management. [ABSTRACT FROM AUTHOR]

A central challenge in global change research is the projection of the future behavior of a system based upon past observations. Tree‐ring data have been used increasingly over the last decade to project tree growth and forest ecosystem vulnerability under future climate conditions. But how can the response of tree growth to past climate variation predict the future, when the future does not look like the past? Space‐for‐time substitution (SFTS) is one way to overcome the problem of extrapolation: the response at a given location in a warmer future is assumed to follow the response at a warmer location today. Here we evaluated an SFTS approach to projecting future growth of Douglas‐fir (Pseudotsuga menziesii), a species that occupies an exceptionally large environmental space in North America. We fit a hierarchical mixed‐effects model to capture ring‐width variability in response to spatial and temporal variation in climate. We found opposing gradients for productivity and climate sensitivity with highest growth rates and weakest response to interannual climate variation in the mesic coastal part of Douglas‐fir's range; narrower rings and stronger climate sensitivity occurred across the semi‐arid interior. Ring‐width response to spatial versus temporal temperature variation was opposite in sign, suggesting that spatial variation in productivity, caused by local adaptation and other slow processes, cannot be used to anticipate changes in productivity caused by rapid climate change. We thus substituted only climate sensitivities when projecting future tree growth. Growth declines were projected across much of Douglas‐fir's distribution, with largest relative decreases in the semiarid U.S. Interior West and smallest in the mesic Pacific Northwest. We further highlight the strengths of mixed‐effects modeling for reviving a conceptual cornerstone of dendroecology, Cook's 1987 aggregate growth model, and the great potential to use tree‐ring networks and results as a calibration target for next‐generation vegetation models. [ABSTRACT FROM AUTHOR]

Few studies have quantified intraspecific variation of hydraulic functional traits in conifers across elevation gradients that include range boundaries. In the Intermountain West, USA, the lower elevational limit of forests (lower treeline) is generally assumed to be caused by water limitations to growth and water relations, yet few studies directly show this. To test this assumption, we measured changes in a suite of traits that characterize drought tolerance such as drought-induced hydraulic vulnerability, hydraulic transport capacity and morphological traits in branch tips and branches of Douglas-fir (Pseudotsuga menziesii var. glauca (Mirb.) Franco) along a 400-m elevation gradient in southeastern Idaho that included lower treeline. As elevation decreased, vulnerability to hydraulic dysfunction and maximum conductivity both decreased in branches; some hydraulic safety–efficiency trade-offs were evident. In branch tips, the water potential at the turgor loss point decreased, while maximum conductance increased with decreasing elevation, highlighting that branch-tip-level responses to less moisture availability accompanied by warmer temperatures might not be coordinated with branch responses. As the range boundary was approached, we did not observe non-linear changes in parameters among sites or increased variance within sites, which current ecological hypotheses on range limits suggest. Our results indicate that there is substantial plasticity in hydraulic functional traits in branch tips and branches of Douglas-fir, although the direction of the trends along the elevation gradient sometimes differed between organs. Such plasticity may mitigate the negative impacts of future drought on Douglas-fir productivity, slowing shifts in its range that are expected to occur with climate change. [ABSTRACT FROM AUTHOR]

Maps of the growth potential for the non-native coastal Douglas-fır (Pseudotsuga menziesii var. menziesii) are presented for Austria and Germany. The regional growth potentials were derived using a site-sensitive statistical model which determines productivity as the dominant-height at age 60 (SI60). The model was calibrated using data from 28 Douglas-fır stands in Austria and Germany growing on silicate and carbonate bedrock. The model is based on non-linear relationships between SI60 and ten climatic, soil physical and soil chemical parameters. Model predictions were calculated for a 1 km x 1 km grid for Austria and Germany. The results revealed that the Northern Alpine foothills in southern Germany are an area with a particularly high growth potential under current climatic conditions (mean 1970-2000). Applying two climate change scenarios (RCP 4.5 and RCP 8.5) to assess the future productivity of Douglas-fır, we see that the changing growth conditions will have a positive impact on Douglas-fır growth at higher altitudes, whereas the productivity may decline in areas where the current growing conditions are dry and highly productive. [ABSTRACT FROM AUTHOR]

Highlights • Maximum stand density index is not invariant to site climate and topographic position. • Presence of deep, surficial volcanic ash mantles (Andisols) significantly increases maximum stand density index. • Mixed species stands were shown to have higher maximum density frontiers relative to pure species stands. Abstract Density management is a key silvicultural tool for developing management prescriptions that maintain and enhance forest health and productivity, particularly in droughty, fire-prone ecosystems of the Inland Northwest, USA. Within this context, understanding the role of species mixing, climate, topography, and soil properties on maximum stand density is critical for predicting forest stand response to management given a suite of site characteristics and species composition. We assembled a dataset from public and private land management organizations that allowed us to test the role of ecological variables on modifying maximum stand density frontiers. Maximum stand density frontier models were built for selected conifer species using stochastic frontier regression. The influence of species mixing was assessed by including as a covariate basal area proportion of the three conifer species of interest in this study: Pinus ponderosa var. ponderosa , Pseudotsuga menziesii var. glauca , and Abies grandis var. idahoensis. A single, parsimonious model was found to fit each species, with variable coefficients reflecting species adaptation to varying abiotic site factors across the region. Site factors that increased maximum density included cool, moist conditions, soils containing volcanic ash over coarse-textured bedrock, and high tree-species diversity. These observations correspond to regional silvicultural guidance, thereby providing both a site-sensitive, quantitative maximum density measure for mixed species stands, and a tool for evaluating the effect of climate scenarios on future stand carrying capacity. [ABSTRACT FROM AUTHOR]

Old trees (defined here as ≥ 150 years old) can be rare in many forests because of past timber harvest, uncharacteristically severe wildfires, and - increasingly - climate change. Old trees provide unique structural, ecological, scientific, and aesthetic values missing in forests containing only younger trees. Here we compile crossdated ages from over 10,000 living and dead trees sampled in montane forests of the central Rocky Mountains in Colorado and southern Wyoming, USA, to examine changes in age structure of the oldest trees since Euro-American settlement and to provide guidelines to aid in identification of old trees for retention during ecological restoration treatments. Eroded stumps (containing only heartwood) were found in over 93% of 179 randomly sampled plots. Number of stumps found in each plot was proportional to reconstructed historical (1860 C.E.) stand basal area. The regional median date of maximum plot tree recruitment was over 150 years older when including stumps versus only living trees, suggesting that if all those harvested trees had survived to the present, the ages of oldest trees would be substantially greater than it is today. However, the regional median age of oldest trees in 1860 before harvesting was not different from the median age of oldest living trees in the current forest (246 vs. 248 years), which alternatively suggests that the regional population of oldest trees has recovered to near historical levels in the time since early Euro-American harvests. Each living tree at the time of sampling was assigned to one of three potential age classes based on a subjective assessment of tree morphology: old (likely ≤ 150 years old), young (likely <150 years old), or transitional (containing a mixture of young and old tree characteristics). Trees assigned to the old and young morphology categories were classified correctly 88% to 96% of the time depending on species as confirmed by their crossdated ages. Regression tree analysis revealed that tree diameter at breast height was not as reliable a predictor of tree age as were morphological characteristics. A measure of site productivity was a significant variable to use to separate transitional morphology trees into old and young age classes, but classification accuracy was not high because of large variability in ages of these trees. Our results suggest that residual live old trees in the current forest, although perhaps not rare compared to historical age distributions, should be retained during restoration treatments, and that using simple morphological and environmental criteria to identify old trees is more reliable than tree size alone. [ABSTRACT FROM AUTHOR]

Douglas-fir forests of the coastal Pacific Northwest experience yearly summer droughts; however, the variation in shallow soil available water supply throughout the region is not well understood nor is the effect of future climate change. Soil moisture sensors were installed in 60 Douglas-fir plantation forests over 6 years. Stands were grouped by physiographic regions to describe differences in climate and available water supply. Monthly available water supply (MAWS) (0-50 cm) was calculated as the average daily available moisture content. MAWS was modeled using monthly climate variables, and the equation was then used to predict the change in MAWS due to mild, moderate, and severe climate change predictions. Regional monthly air temperature and precipitation were strongly predictive of MAWS. Mild to severe climate change are predicted to decrease yearly available water supply by 8% to 19%, while summer available water supply will decrease from 25% to 72%. The greatest decreases due to climate change will be found in the coastal regions of Washington and Oregon due to greater negative effects of temperature on available water supply. Climate change, especially the most severe predictions, was shown to have a sizeable effect on shallow soil available water supply in coastal Douglas-fir forests. [ABSTRACT FROM AUTHOR]

Forest disturbance regimes are beginning to show evidence of climate-mediated changes, such as increasing severity of droughts and insect outbreaks. We review the major insects and pathogens affecting the disturbance regime for coastal Douglas-fir forests in western Oregon and Washington State, USA, and ask how future climate changes may influence their role in disturbance ecology. Although the physiological constraints of light, temperature, and moisture largely control tree growth, episodic and chronic disturbances interacting with biological factors have substantial impacts on the structure and functioning of forest ecosystems in this region. Understanding insect and disease interactions is critical to predicting forest response to climate change and the consequences for ecosystem services, such as timber, clean water, fish and wildlife. We focused on future predictions for warmer wetter winters, hotter drier summers, and elevated atmospheric CO 2 to hypothesize the response of Douglas-fir forests to the major insects and diseases influencing this forest type: Douglas-fir beetle, Swiss needle cast, black stain root disease, and laminated root rot. We hypothesize that (1) Douglas-fir beetle and black stain root disease could become more prevalent with increasing, fire, temperature stress, and moisture stress, (2) future impacts of Swiss needle cast are difficult to predict due to uncertainties in May-July leaf wetness, but warmer winters could contribute to intensification at higher elevations, and (3) laminated root rot will be influenced primarily by forest management, rather than climatic change. Furthermore, these biotic disturbance agents interact in complex ways that are poorly understood. Consequently, to inform management decisions, insect and disease influences on disturbance regimes must be characterized specifically by forest type and region in order to accurately capture these interactions in light of future climate-mediated changes. [ABSTRACT FROM AUTHOR]

Warmer temperatures associated with climate change have the potential to accelerate litter decay and subsequently release large amounts of carbon stored in soils. Condensed tannins are widespread secondary metabolites, which accumulate to high concentrations in many woody plants and play key roles in forest soil nutrient cycles. Future elevated atmospheric CO concentrations are predicted to reduce nitrogen content and increase tannin concentrations in plant tissues, thus reducing litter quality for microbial communities and slowing decomposition rates. How the distinct condensed tannin fractions (water-soluble, acetone:MeOH-soluble and solvent-insoluble) impact soil processes, has not been investigated. We tested the impact of condensed tannin and nitrogen concentrations on decay rates of poplar and Douglas-fir litter at sites spanning temperature and moisture gradients in coastal rainshadow forests in British Columbia, Canada. The three condensed tannin fractions were quantified using recent improvements on the butanol-HCl assay. Decay was assessed based on carbon remaining, while changes in litter chemistry were primarily observed using two methods for proximate chemical analyses. After 0.6 and 1 year of decay, more carbon remained in poplar litter with high, compared to low, condensed tannin concentrations. By contrast, more carbon remained in Douglas fir litter than poplar litter during this period, despite lower condensed tannin concentrations. Rapid early decay was especially attributed to loss of soluble compounds, including water-soluble condensed tannins. Water-insoluble condensed tannin fractions, which were transformed to acid-unhydrolyzable residues over time, were associated with reduced carbon loss in high condensed tannin litter. [ABSTRACT FROM AUTHOR]

The occurrence of endophytic fungi, hosted by living tissues of forest trees seems to be a common phenomenon. Numerous studies show that these colonists are mostly symptomless or even live in a symbiotic relationship to the host plant. Our investigations on Douglas-fir and Rhabdocline needlecast show that Rhabdocline pseudotsugae (Sydow), which has been described exclusively as an obligatory needle pathogen up to now, is able to persist symptomless in different types of plant tissues and therefore an endophytic lifestyle has to be assumed. Whether this lifestyle is part of the infection strategy of the fungus is still unclear. However, examples of other wood associated fungi lead us to the hypothesis that environmental such as climate conditions are able to trigger the phenomenon of changing from a mutualist to a virulent parasite.

Abstract In recent years, increased wildfire activity and climate change have raised concern among scientists and land managers regarding current and future vegetation patterns in post‐burn landscapes. We surveyed conifer regeneration 8–15 years after fire in six burn areas in the lower montane zone of the Colorado Front Range. We sampled across a broad range of elevations, aspects, and fire severities and found that densities of ponderosa pine (Pinus ponderosa) and Douglas‐fir (Pseudotsuga menziesii) are generally low, although areas of abundant regeneration do occur. Conifer regeneration was most limited in xeric settings, including more southerly aspects and elevations closer to lower treeline. Additionally, fewer juvenile conifers occurred at greater distances from mature, live trees indicating that seed source as well as topoclimatic setting limits post‐fire tree regeneration. Projecting the extent of future forest cover is uncertain due to the possibility of future pulses of tree establishment and unknown depletion rates of existing seedling populations. However, current patterns of post‐fire seedling establishment suggest that vegetation composition and structure may differ notably from historic patterns and that lower density stands and even non‐forested communities may persist in some areas of these burns long after fire, especially in xeric settings or where no nearby seed source remains.

• Douglas-fir water stress was driven by elevated vapor pressure deficit. • Elevated VPD reduced GPP more than decreased rainfall during the growing season. • Decreasing spring rainfall did not significantly alter deep soil water content. Understanding how trees respond to drought is critical to understanding forest sensitivity to global climate change, which can help inform forest policy and management decisions. However, mechanisms governing carbon fixation and water fluxes in response to increased temperatures and water limitation in regions with Mediterranean climates, with wet winters and dry summers, remain only partially understood. We tested the effect of increased vapor pressure deficit (VPD) and decreased rainfall on water and carbon fluxes of Douglas-fir (Pseudotsuga menziesii) trees using the Soil-Plant-Atmosphere model (SPA). We simulated a 50-year-old Douglas-fir stand on the western slopes of the Cascade Mountains in Oregon, USA. Simulation results showed that increasing the daily maximum VPD by 0.25–2.5 kPa during the summer increased cumulative transpiration by 1–3% and decreased cumulative gross primary production by 3–25%. In contrast, decreasing rainfall by 10–100% during the spring and summer decreased cumulative transpiration by 2–16% and decreased cumulative gross primary production by 0.5–4%. Transpiration was highly sensitive to decreases in rainfall, especially in late spring and early summer but much less sensitive to increases in maximum daily VPD. In contrast, gross primary productivity was much more sensitive to VPD, with summertime increases in VPD having a 5- to 6-fold greater effect on gross primary productivity than did decreasing the rainfall. These results suggested that temperature increases expected from climate change in combination with increases in VPD are likely to reduce forest productivity regardless of soil moisture availability. [ABSTRACT FROM AUTHOR]

Questions Do functional traits explain individual tree species' responses to environmental filters and dispersal limitations following stand-replacing fire? Can post-fire conditions initiate alternate trajectories of community assembly? Location Glacier National Park, Montana, USA. Methods We characterized the species composition of tree re-establishment following nine recent fires in the lower subalpine zone of Glacier National Park, a region with multiple co-dominant tree species that has experienced extensive fire in recent decades. We used GLMMs to describe individual species' responses to spatial and temporal heterogeneity of post-fire conditions and seed availability, and used multivariate approaches to examine whether post-fire conditions can initiate alternate trajectories of forest community assembly. Results Post-fire regeneration responses were strongly species-dependent and consistent with functional trait differences. We found that there was a brief opportunity for establishment during the first several years after fire, during which tree recruitment for all species was contingent upon the availability of nearby seeds and the occurrence of favourable weather conditions. There was a remarkable amount of compositional change following fire, and the majority of our study sites transitioned from a mixed forest to a tree assemblage dominated by a single species. Conclusions Differential species-specific responses to climate and disturbance can initiate alternate trajectories of community assembly, triggering substantial changes in forest composition. The composition of post-fire tree assemblages reflects the differential responses of individual species to climate and disturbance, providing support for the interacting role of dispersal and environmental filtering in shaping post-disturbance communities and highlighting the importance of incorporating functional traits into predictive models of ecosystem dynamics. [ABSTRACT FROM AUTHOR]

In recent years, increased wildfire activity and climate change have raised concern among scientists and land managers regarding current and future vegetation patterns in post-burn landscapes. We surveyed conifer regeneration 8-15 years after fire in six burn areas in the lower montane zone of the Colorado Front Range. We sampled across a broad range of elevations, aspects, and fire severities and found that densities of ponderosa pine ( Pinus ponderosa) and Douglas-fir ( Pseudotsuga menziesii) are generally low, although areas of abundant regeneration do occur. Conifer regeneration was most limited in xeric settings, including more southerly aspects and elevations closer to lower treeline. Additionally, fewer juvenile conifers occurred at greater distances from mature, live trees indicating that seed source as well as topoclimatic setting limits post-fire tree regeneration. Projecting the extent of future forest cover is uncertain due to the possibility of future pulses of tree establishment and unknown depletion rates of existing seedling populations. However, current patterns of post-fire seedling establishment suggest that vegetation composition and structure may differ notably from historic patterns and that lower density stands and even non-forested communities may persist in some areas of these burns long after fire, especially in xeric settings or where no nearby seed source remains. [ABSTRACT FROM AUTHOR]

Recommendations on suitable seed sources for reforestation are usually model based and include uncertainties arising from model assumptions, parameter estimation, and future climate scenarios. Due to the long-lived nature of forests, such uncertainties need to be considered when developing guidance for managers and policy makers. We evaluate the uncertainties and apply our recently developed genetically based models, Universal Response Functions (URFs) in Austria and Germany. The URFs predict growth performance (dominant height and basal area at age 24) of Douglas-fir ( Pseudotsuga menziesii [Mirbel] Franco) populations, as a function of both environmental and genetic factors. We evaluated the URFs by comparing the predicted height growth performances with observations from independent provenance trial data across Europe. Also, the sensitivity of the URF variables and the overall model uncertainty were estimated and compared to the uncertainty due to climate change projections. Model evaluation suggests that the URFs perform better in Central and Southeastern Europe compared to maritime Western Europe. Summer drought and mean annual temperature of planting sites were the most sensitive variables of the models, whereas the mean annual temperature of seed origin was the least sensitive. Model uncertainty increased with mean annual temperature of the planting site. Uncertainty due to projected future climate was found to be higher than the model uncertainty. The URFs predicted that provenance regions of southwest Germany and southeast Austria below 1500 m altitude will be suitable, whereas Pannonian east of Austria will become less suitable for growing Douglas-fir in future. Current seed stands in North America providing planting materials for Europe under the legal framework of the Organization for Economic Cooperation and Development shall continue to provide the most suitable seed material also in the future. [ABSTRACT FROM AUTHOR]

Drought-caused tree dieback is an issue around the world as climates change and many areas become dryer and hotter. A drought from 1998-2004 resulted in a significant tree dieback event in many of the wooded areas in portions of the Jemez Mountains and the adjacent Pajarito Plateau in northern New Mexico. The objectives of this study were to evaluate and quantify the differences in tree mortality before and after a recent drought in ponderosa pine and spruce-fir ecosystems, and to assess the effect of mechanical thinning on ponderosa pine mortality. Significant increases in mortality were observed in the unthinned ponderosa pine ecosystem. Mortality varied significantly between species and within size classes. Mechanical thinning of ponderosa pines reduced overstory mortality to non-significant levels. A lack of rainfall, snowfall, and increases in daily minimum temperature contributed most to the mortality. Adaptive management, including the use of thinning activities, appear to moderate the impact of climate change on ponderosa pine forests in this region, increasing the long-term health of the ecosystem. The impact of climate change on the spruce-fir ecosystems may accelerate successional changes. [ABSTRACT FROM AUTHOR]

To accurately predict how ecosystems will respond to climate change - and how management actions can influence such responses - scientists and managers need a better understanding of how and when biotic interactions modify climate-growth relationships. However, current research has largely ignored the role of competition in modulating climate-growth relationships of mature trees. In this study, we assessed the effect of competition on tree responses to drought and interannual climate variability as well as linkages between climate sensitivity and morphological characteristics of the stem wood., We sampled 10 sites in north-eastern Washington, USA, and used dendroecology to quantify responses of Douglas-fir ( Pseudotsuga menziesii) to drought and climate variability. Tree-ring series were converted to basal area increment series, and the effects of competition on climate-growth relationships were assessed at the tree and site levels using a combination of correlation analyses and linear mixed-effects models., Competition did not affect tree responses to extreme drought. When soil moisture was below average, tree growth was tightly coupled to climate variability for all trees, regardless of their competitive status. However, in wet years, competition had a pronounced, positive effect on climate sensitivity of growth., Trees with more competition from neighbours exhibited a significantly higher proportion of sapwood area in latewood (a morphological trait associated with greater drought resistance)., Synthesis. Our results suggest that a tree's ability to cope with environmental variability is driven not just by the proximate effects of neighbours on resource availability, but also by phenotypic plasticity and long-term adaptations to competitive stress (such as changes in carbon allocation). Findings have important implications for individual-tree and stand-level growth models and may help managers better understand how their activities will modify tree responses to climate change. [ABSTRACT FROM AUTHOR]

Forests near the lower limit of montane tree cover are expected to be particularly vulnerable to warming climate, potentially converting to non-forest for prolonged periods if affected by canopy-removing disturbances. Such disturbance-catalyzed shifts are by nature stochastic, offering few opportunities to test these predictions. We capitalized on a landmark event exemplary of recent large disturbances--the 1988 wildfires in Yellowstone National Park (USA)--to investigate long-term (24-yr) regeneration dynamics in Douglas-fir (Pseudotsuga menziesii var. glauca) forests, which compose the lower treeline yet have received little study. We tested the hypothesis that, under current conditions (warmest decades in last 6000 yr), dry lower-margin stands are less apt to attain self-replacement than adjacent, but more mesic, stands farther from the ecotone. Mesic sites characterized by dense forests prefire regenerated robustly regardless of burn severity, even in large high-severity patches, whereas dry sites did so only if nearby seed sources survived (i.e., small patch size or moderate burn severity). Regeneration continued over two decades, peaking between ~5 and 15 yr, with mesic stands continuing regenerating beyond 15 yr to a greater degree than dry stands. Self-replacement of stands by 24 yr postfire was nearly universal in mesic stands, variable but common in dry stands not adjacent to the lower ecotone, and uncommon in dry stands near the ecotone--particularly if burned at high severity. Whether the lack of regeneration in ecotonal stands is categorically directional with warming climate or part of a long-term cycle is unresolved, but we estimate that the 1988 fires converted > 4000 ha of lower-montane forest to grass/sage steppe for at least several decades, possibly indefinitely given current trends in climate. These data support the notion that climate-driven shifts in vegetation cover are likely to occur in punctuated fashion with disturbances, with relatively abrupt implications for montane forest cover, biogeography, and ecosystem function. [ABSTRACT FROM AUTHOR]

Douglas-fir ( Pseudotsuga menziesii var. menziesii (Mirb.) Franco) growth in the Pacific Northwest is affected by climatic, edaphic factors and Swiss needle cast (SNC) disease. We examine Douglas-fir growth responses to temperature, dewpoint deficit (DPD), soil moisture, and SNC using time series intervention analysis of intra-annual tree-ring width data collected at nine forest stands in western Oregon, USA. Air temperature, previous-year DPD and SNC and their interactions were the primary factors influencing tree growth at all sites, whereas other key seasonal climatic factors limiting growth varied by site. Winter temperature was more important at high elevation cool sites, whereas summer temperature was more important at warm and dry sites. Growth rate increased with summer temperature to an optimum ( T opt ) then decreased at higher temperatures. At drier sites, temperature and water affected growth interactively such that T opt decreased with decreasing summer soil moisture. With increasing temperature due to climate change, growth rates increased at high elevation sites and declined at mid-elevation inland sites since ∼1990. Growth response to climate and SNC are confounded at all sites. We conclude that as temperature rises and precipitation patterns shift toward wetter winters and drier summers, Douglas-fir will experience greater temperature and water stress and an increase in severity of SNC. [ABSTRACT FROM AUTHOR]

This paper documents the capability of the ARW/WRF regional climate model to regionalize near-surface atmospheric variables at high resolution (8 km) over Burgundy (northeastern France) from daily to interannual timescales. To that purpose, a 20-year continuous simulation (1989-2008) was carried out. The WRF model driven by ERA-Interim reanalyses was compared to in situ observations and a mesoscale atmospheric analyses system (SAFRAN) for five near-surface variables: precipitation, air temperature, wind speed, relative humidity and solar radiation, the last four variables being used for the calculation of potential evapotranspiration (ET). Results show a significant improvement upon ERA-Interim. This is due to a good skill of the model to reproduce the spatial distribution for all weather variables, in spite of a slight over-estimation of precipitation amounts mostly during the summer convective season, and wind speed during winter. As compared to the Météo-France observations, WRF also improves upon SAFRAN analyses, which partly fail at showing realistic spatial distributions for wind speed, relative humidity and solar radiation-the latter being strongly underestimated. The SAFRAN ET is thus highly under-estimated too. WRF ET is in better agreement with observations In order to evaluate WRF's capability to simulate a reliable ET, the water balance of thirty Douglas-fir stands was computed using a process-based model. Three soil water deficit indexes corresponding to the sum of the daily deviations between the relative extractible water and a critical value of 40 % below which the low soil water content affects tree growth, were calculated using the nearest weather station, SAFRAN analyses weather data, or by merging observation and WRF weather variables. Correlations between Douglas-fir growth and the three estimated soil water deficit indexes show similar results. These results showed through the ET estimation and the relation between mean annual SWDI and Douglas-fir growth index that the main difficulties of the WRF model to simulate soil water deficit is mainly attributable to its precipitation biases. In contrast, the low discrepancies between WRF and observations for air temperature, wind speed, relative humidity and solar radiation make then usable for the water balance and ET computation. [ABSTRACT FROM AUTHOR]

Determining appropriate actions to create or maintain landscapes resilient to climate change is challenging because of uncertainty associated with potential effects of climate change and their interactions with land management. We used a set of climate-informed state-and-transition models to explore the effects of management and natural disturbances on vegetation composition and structure under different future climates. Models were run for dry forests of central Oregon under a fire suppression scenario (i.e., no management other than the continued suppression of wildfires) and an active management scenario characterized by light to moderate thinning from below and some prescribed fire, planting, and salvage logging. Without climate change, area in dry province forest types remained constant. With climate change, dry mixed-conifer forests increased in area (by an average of 21-26% by 2100), and moist mixed-conifer forests decreased in area (by an average of 36-60% by 2100), under both management scenarios. Average area in dry mixed-conifer forests varied little by management scenario, but potential decreases in the moist mixed-conifer forest were lower with active management. With changing climate in the dry province of central Oregon, our results suggest the likelihood of sustaining current levels of dense, moist mixed-conifer forests with large-diameter, old trees is low (less than a 10% chance) irrespective of management scenario; an opposite trend was observed under no climate change simulations. However, results also suggest active management within the dry and moist mixed-conifer forests that creates less dense forest conditions can increase the persistence of larger-diameter, older trees across the landscape. Owing to projected increases in wildfire, our results also suggest future distributions of tree structures will differ from the present. Overall, our projections indicate proactive management can increase forest resilience and sustain some societal values, particularly in drier forest types. However, opportunities to create more disturbance-adapted systems are finite, all values likely cannot be sustained at current levels, and levels of resilience success will likely vary by dry province forest type. Land managers planning for a future without climate change may be assuming a future that is unlikely to exist. [ABSTRACT FROM AUTHOR]

Context: Since the 2003 drought and heat wave, there have been many reports of Douglas-fir decline and dieback in France. Given the climate change that is predicted, more frequent drought episodes could induce recurrent decline processes. The nature and background of this threat requires a careful assessment. Aims: The objectives of this study were: (1) to test the hypothesis that the major climate hazard that accounts for the decline in Douglas-fir growth is drought, and (2) to identify the main vulnerability factors involved. Methods: Decline and recovery of radial growth were quantified of Douglas-fir in two particularly affected regions with a dendroecological approach; 899 trees were sampled on 58 plots. Mean climate data, ecological and dendrometric stand characteristics were tested in order to identify potential vulnerability factors Results: A clear relationship was evidenced between growth and soil water deficit. A severe decline of radial growth was induced by the 2003 drought and was maintained during subsequent years due to recurrent drought episodes. Growth recovery at the stand level was enhanced by soil nutrient fertility. Conclusion: Radial growth of Douglas-fir is clearly driven by the intensity of drought. In a context of climate change, an adaptive silvicultural strategy is required in order to cope with more frequent drought events. To mitigate the frequency and the intensity of water shortage episodes, site selection must take into account not only local climate characteristic but also soil properties like maximum extractable water content. Soil nitrogen fertility was found to play a key role for an efficient recovery of radial growth after drought episodes and thus must be preserved. [ABSTRACT FROM AUTHOR]

Highlights: [•] Climate change will impact reforestation strategies. [•] We assess impacts to Pinus ponderosa and Pseudotsuga menziesii varieties. [•] Few populations should remain adapted to the 2060 climate of their provenance. [•] High proportions of forested lands will need species or climatype conversion. [•] Conservation programs of P. menziesii in Mexico are of urgent need. [Copyright &y& Elsevier]

Characteristics of annual rings are reliable indicators of growth and wood quality in trees. The main objective of our study was to model the variation in annual ring attributes due to intensive silviculture and inherent regional differences in climate and site across a wide geographic range of Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco). Ring specific gravity and ring width of Douglas-fir were examined at five long-term Levels-Of-Growing-Stock (LOGS) installations, three in the US and two in Canada, covering a latitudinal gradient between 43°N and 50°N. At each location, increment cores were collected from replicated plots with three levels of stocking: control (unthinned), lightly thinned (70% basal area retention), and heavily thinned (30% basal area retention). X-ray densitometry analysis provided ring specific gravity and width profiles for 5676 rings from 134 trees. The reduction of stand density through repeated entries resulted in decreased ring specific gravity and increased ring width. A four-parameter mixed-effects logistic model was used to predict ring specific gravity using cambial age, stand density (as number of stems per hectare), and two climatic variables: average temperature from March to May and total precipitation from April to August. A three-parameter mixed-effects logistic model was used to predict ring width using cambial age, stand density (as stand density index), and total climatic moisture deficit of June and July. Both models indicated significant site differences that were included in the models through indicator variables. Ring specific gravity increased slightly with increasing average temperature from March to May and decreasing total precipitation from April to August. Predictions of ring specific gravity of Douglas-fir appear to be more sensitive to changes in temperature compared with changes in precipitation. [ABSTRACT FROM AUTHOR]

A process-based forest growth model, 3-PG (Physiological Principles Predicting Growth), parameterized with values of soil properties constrained by satellite-derived estimates of maximum leaf area index (LAImax), was run for Douglas-fir (Pseudotsuga menziesii) to contrast the extent to which site growth potential might vary across western North America between a cool, wet period (1950-1975) and a more recent, generally warmer and drier one (2000-2009). LAImax represents a surrogate for overall site growth potential, as demonstrated from a strong correlation between the two variables, with the latter based on the culmination of mean annual increment estimates made at 3356 ground-based U.S. Forest Service survey plots across the states of Oregon and Washington. Results indicate that since 2000, predicted LAImax has decreased more than 20% in portions of the Southwest USA and for much of the forested area in western Alberta. Similar percentage increases in LAImax were predicted for parts of British Columbia, Idaho and Montana. The modeling analysis included an assessment of changes in seasonal constraints on gross primary production (GPP). A general reduction in limitations caused by spring frost occurred across the entire study area. This has led to a longer growing season, along with notable increases in summer evaporative demand and soil drought for much of the study area away from the maritime influence of the Pacific Ocean. [ABSTRACT FROM AUTHOR]

Abstract: We examined radial growth rates of locally co-occurring Douglas-fir (PSME –Pseudotsuga menziesii var. glauca) and ponderosa pine (PIPO –Pinus ponderosa var. ponderosa) trees growing within the Northern Rockies to determine if there are differential growth and climatic responses between these species and whether these responses are consistent among topographically and climatologically diverse sites. We developed standardized tree-ring chronologies from seven sites, with each site a matched pair of PSME and PIPO. For each chronology we examined the climate response of radial growth by comparing the standardized ring widths to a suite of climatic variables. We examined temporal changes by comparing 1905–1950 and post-1950 growth rates and climatic conditions. Both conifers experience increased radial growth post-1950. A combination of spring/summer moisture conditions related positively to radial growth and the primary climatic drivers were consistent both between species and within the region. The primary climatic drivers of radial growth remain unchanged during the last century or have trended toward drier conditions unfavorable for growth. We conclude that increases in standardized radial growth rates are unlikely climatically-driven. Other potential vectors of radial growth change, such as atmospheric CO2 enrichment, have affected these co-occurring species on a largely equal basis and positively. [Copyright &y& Elsevier]

Abstract: Many of the world''s forests are likely to face multiple stresses under a rapidly changing climate. Understanding the impact of climate change on tree species suitability is therefore crucial for forest management planning and policy development. We use the Douglas-fir and spruce (white spruce, Engelmann spruce, and interior spruce) forests of British Columbia as a case study. The impact of projected climate change on these forests was assessed using flexible bioclimatic envelope models appropriate for areas with sparse species locations records. Analysis of the model results focused on quantifying uncertainty due to differences between global climate models, emissions scenarios, and spatial resolution of climate data. To this end, future suitability was modelled using downscaled climate data from a collection of 10 climate projections that sampled across nine different global climate models and three different emissions scenarios (A2, A1B, and B1). All projections indicate a rapid shift in suitability for both spruce and Douglas-fir to higher elevations and latitudes relative to their current range. However, significant differences exist between the projections with regard to the pace, extent, and fine-scale details of these changes. This research was conducted as part of a collaborative interdisciplinary assessment involving both scientists and resource managers. [Copyright &y& Elsevier]

Abstract: There is increasing interest in actively managing forests to increase their resilience to climate-related changes. Although forest managers rely heavily on the use of silvicultural treatments that manipulate stand structure and stand dynamics to modify responses to climate change, few studies have directly assessed the effects of stand structure or canopy position on climate–growth relationships – or examined how this relationship may vary among species or across environmental gradients. In this study, we analyzed variability in tree-ring series from 15 low-elevation stands in northeastern Washington (USA) using time series analysis and linear mixed effects models. Our objective was to assess the relative influences of species (Pinus ponderosa vs. Pseudotsuga menziesii), crown class (dominant vs. intermediate), and habitat type (Xeric vs. Dry-Mesic) on the climate responses of mature trees in unmanaged forests. We found that climate–growth relationships varied significantly between canopy classes and across habitat types but that these effects were highly species-specific. For P. menziesii, growth responses to temperature and precipitation did not vary between canopy classes. For P. ponderosa, however, regression coefficients for the relationship between temperature and radial growth were nearly twice as large for dominant trees compared to intermediate trees, and 84% of dominant trees were significantly influenced by precipitation, compared to only 62% of intermediate trees. In contrast, habitat-type did not significantly affect the climate responses of P. ponderosa, but did affect responses of P. menziesii. For example, for P. menziesii only 51% of trees in Dry-Mesic sites, were significantly affected by drought (PDSI), compared to 93% in Xeric sites. A better understanding of the relationship between climate sensitivity, species-specific hydraulic strategies, and stand dynamics is crucial for accurately predicting tree responses to climate change and designing forest treatments that will effectively reduce the climatic vulnerability of key forest species and habitats. Results may assist managers with understanding how altering stand dynamics will differentially affect climate-responses of individual species. [Copyright &y& Elsevier]

Ectomycorrhizal (EM) networks are hypothesized to facilitate regeneration under abiotic stress. We tested the role of networks in interactions between P. menziesii var. glauca trees and conspecific seedlings along a climatic moisture gradient to: (1) determine the effects of climatic factors on network facilitation of Pseudotsuga menziesii (Mirb.) Franco var. glauca (Mayr) seedling establishment, (2) infer the changing importance of P. menziesii var. glauca parent trees in conspecific regeneration with climate, and (3) parse the competitive from facilitative effects of P. menziesii var. glauca trees on seedlings. When drought conditions were greatest, seedling growth increased when seedlings could form a network with trees in the absence of root competition, but was reduced when unable to form a network. Survival was maximized when seedlings were able to form a network in the absence of root competition. Seedling stem natural abundance δC increased with drought due to increasing water use efficiency, but was unaffected by distance from tree or network potential. We conclude that P. menziesii seedlings may benefit from the presence of established P. menziesii trees when growing under climatic drought, but that this benefit is contingent upon the establishment of an EM network prior to the onset of summer drought. These results suggest that networks are an important mechanism for EM plants establishing in a pattern consistent with the stress-gradient hypothesis, and therefore the importance of EM networks to facilitation in regeneration of EM trees is expected to increase with drought. [ABSTRACT FROM AUTHOR]

The article discusses phylogeography. It states that phylogeography is the study of micro and macro evolutionary process that contributes the lineage divergence, species and biodiversity with the genetic data within the geographical distributions of organisms. It highlights the phylegeographical analysis of Gugger et al on the biotic responses of Mexican Douglas fir population to climatic change and to the conservation of genetic diversity.

Abstract: Effective adaptation of forest management practices to climate change will require a good understanding of the ecological and climatic factors influencing tree sensitivities and responses to climate. Using tree-ring data collected from 33 stands of mature interior Douglas-fir (Pseudotsuga menziesii var. glauca) spanning a wide climatic range in British Columbia (BC), Canada, we present an approach combining high-resolution spatiotemporal climate data with traditional dendroecological analyses to quantify relationships between population climate–growth sensitivity and provenance (i.e., seed-source origin) climate. Key results showed that Douglas-fir climate–growth sensitivities were strongly linked to provenance climate and varied in coherent patterns across climatic gradients. Climate–growth sensitivities and responses were sometimes opposite between provenances from disparate climates. Perhaps most importantly, our results showed that Douglas-fir productivity across most of its range was sensitive to moisture limitations, and this sensitivity increased strongly with decreasing provenance mean annual precipitation and increasing heat-moisture index. Using geographic information systems, we visualize the link between provenance mean annual precipitation and climatic sensitivity of Douglas-fir across BC to identify “high risk” populations. By understanding the link between biological responses and climate, forest managers may be able to spatially identify sensitive populations using spatiotemporal climate data. [ABSTRACT FROM AUTHOR]