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This study aims to identify the ecological factors that drive the survival of Douglas‐fir (Pseudotsuga menziesii [Mirb.] Franco) in Italy, using data from old‐growth experimental stands. A record of 124 Douglas‐fir plantations was compiled from a literature review and ground survey, including 98 Douglas‐fir stands established in the early 20th century. The probability of survival of the species at the surveyed sites was modeled using Species Distribution Models (SDM) with soil and climatic variables as predictors. Pseudo‐absences were also used to balance the proportion of presences and absences in the modeling steps. The best‐fitting models were used to predict the probability of survival of Douglas‐fir stands across the entire country and in the native range of the species to assess the model's goodness of fit. Fitted models performed well with a mean True Skill Statistics (TSS) score of 0.91, suggesting that temperature‐related factors primarily influence the survival of Douglas‐fir stands in Italy. The two most relevant predictors were GDD5 (growing degree‐days above 5°C) and AHM (Annual Heat Moisture), indicating the importance of temperatures and water availability also in the Mediterranean area. A large portion of Italy was predicted to be potentially suitable for Douglas‐fir afforestation or reforestation, mainly across the Apennine Mountains of central Italy. Model projections for the species' native area largely overlap with the range of the coastal variety of Douglas‐fir (P. menziesii var. viridis), supporting the hypothesis that most Douglas‐fir stands in Italy were established using propagation material from this region. The spatial modeling of Douglas‐fir old‐growth stands in Italy demonstrated the relevance of temperatures (GDD5) also in the Mediterranean area and showed a good climate matching between the Italian planting range and the coastal part of Douglas‐fir native range.

Purpose of Review Non-native tree species (NNT) raise a range of different associations and emotions—to many citizens they are just an exotic curiosity in parks, to many conservationists they are an evil to native ecosystems that should be eradicated, to a rising group of foresters they are part of the solution to climate change and an increasing timber demand, and to others they are already daily forestry business. In this review, where we also summarise the findings of the recent COST Action FP1403 (NNEXT) ‘Non-native tree species for European forests: experiences, risks and opportunities’, we highlight opportunities and challenges in the light of climate change, ecological risks and legislative limits of growing non-native tree species in Europe. Recent Findings Few NNT in Europe show invasive behaviour and are listed as prohibited species or as species to be monitored. A larger number of NNT is utilised in productive forestry and forest restoration due to their superior growth, valuable timber properties and good performance under harsh growing conditions. Current species distribution, experiences with success and failures and environmental concerns differ profoundly across Europe, with Western Europe overall revealing higher shares in NNT and showing a stronger interest of forestry related stakeholder groups to continue planting NNT. Summary Many more NNT are already used in forestry than previously thought, but relatively few species have major importance in terms of area, mainly in western European countries. Diversification, mixing and avoidance of invasion in relation to NNT are necessities that are relatively new on the agenda. In contrast, provenance research of major NNT has been going on for many decades and now provides important information for climate change adaptation. Despite the limitations to the use of NNT either through legal restrictions or forest certification that differ considerably across Europe, the careful integration of a range of tested NNT also into future forest management planning shows a high potential for climate change adaptation and mitigation.

Aim: We investigate the effects of the environmental and geographical processes driving growth resilience and recovery in response to drought in Mediterranean Pinus pinaster forests. We explicitly consider how intraspecific variability modulates growth resilience to drought. Location: Western Mediterranean basin. Methods: We analysed tree rings from a large network of 48 forests (836 trees) encompassing wide ecological and climatic gradients, including six provenances. To characterize the major constraints of P. pinaster growth under extremely dry conditions, we simulated growth responses to temperature and soil moisture using a process-based growth model coupled with the quantification of climate–growth relationships. Then, we related growth–resilience indices to provenance and site variables considering different drought events. Results: Pinus pinaster displayed strong variation in growth resilience across its distributional range, but common patterns were found within each provenance. Post-drought resilience increased with elevation and drier conditions but decreased with spring precipitation. Trees from dry sites were less resistant to drought but recovered faster than trees from wet sites. Main conclusions: Resilience strategies differed among tree provenances: wet forests showed higher growth resistance to drought, while dry forests presented faster growth recovery, suggesting different impacts of climate warming on forest productivity. We detected geographically structured resilience patterns corresponding to different provenances, confirming high intraspecific variability in response to drought. This information should be included in species distribution models to simulate forest responses to climate warming and forecasted aridification.

• Drought intensity and frequency are increasing under global warming, with soil water availability now being a major factor limiting tree growth in circumboreal forests. Still, the adaptive capacity of trees in the face of future climatic regimes remains poorly documented. • Using 1481 annually resolved tree-ring series from 29-yr-old trees, we evaluated the drought sensitivity of 43 white spruce (Picea glauca (Moench) Voss) populations established in a common garden experiment. • We show that genetic variation among populations in response to drought plays a significant role in growth resilience. Local genetic adaptation allowed populations from drier geographical origins to grow better, as indicated by higher resilience to extreme drought events, compared with populations from more humid geographical origins. The substantial genetic variation found for growth resilience highlights the possibility of selecting for drought resilience in boreal conifers. • As a major research outcome, we showed that adaptive genetic variation in response to changing local conditions can shape drought vulnerability at the intraspecific level. Our findings have wide implications for forest ecosystem management and conservation.

Purpose of Review Despite the rapidly increasing use of resilience indices to analyze responses of trees and forests to disturbance events, there is so far no common framework to apply and interpret these indices for different purposes. Therefore, this review aims to identify and discuss various shortcomings and pitfalls of commonly used resilience indices and to develop recommendations for a more robust and standardized procedure with a particular emphasis on drought events. Recent Findings Growth-based resilience indices for drought responses of trees are widely used but some important drawbacks and limitations related to their application may lead to spurious results or misinterpretation of observed patterns. The limitations include (a) the inconsistency regarding the selection and characterization of drought events and the climatic conditions in the pre- and post-drought period and (b) the calculation procedure of growth-based resilience indices. Summary We discuss alternative options for metrics, which, when used in concert, can provide a more comprehensive understanding of drought responses in cases where common growth-based resilience indices are likely to fail. In addition, we propose a new analytical framework, the “line of full resilience,” that integrates the three most commonly used resilience indices and show how this framework can be used for comparative drought tolerance assessments such as rankings of different tree species or treatments. The suggested approach could be used to harmonize quantifications of tree growth resilience to drought and it may thus facilitate systematic reviews and development of the urgently needed evidence base to identify suitable management options or tree species and provenances to adapt forests for changing climatic conditions.

Non-native forest tree species have been introduced in Europe since the 16th century, but only in the second half of the 20th century the significance of the seed source origin for their economic use was recognized, resulting in the establishment of numerous provenance trials at a national, regional, European and International level, as those led by IUFRO. Breeding programs have also been launched in the continent for the most economically important species. Aim of this work is the formulation of provenance recommendations for planting of five non-native tree species in Europe (Douglas fir, grand fir, Sitka spruce, lodgepole pine and black locust), based on the information obtained from twenty countries, in the frame of the EU FP-1403 NNEXT Cost Action. The survey revealed that official and non-official national recommendations, based on provenance research results, have been elaborated and followed at a different level and extend for the above five species, but only for Douglas fir recommendations exist in almost all the participating to the survey countries. The compilation of provenance recommendations across Europe for each species is presented in the current work. Besides the recommended introduced seed sources, European seed sources are also preferred for planting, due to ease of access and high availability of forest reproductive material. European breeding programs yielding genetic material of high productivity and quality constitute currently the seed source of choice for several species and countries. Consolidation of trial data obtained across countries will allow the joint analysis that is urgently needed to draw solid conclusions, and will facilitate the development of ‘Universal-Response-Functions’ for the species of interest, rendering possible the identification of the genetic material suitable for global change. New provenance trial series that will test seed sources from the entire climatic range of the species, established in sites falling within and outside the environmental envelopes of their natural ranges, are urgently needed to pinpoint and understand the species-specific climate constraints, as well as to correlate functional traits to the seed origin and the environmental conditions of the test sites, so that the selection of suitable forest reproductive material of non-native tree species in the face of climate change can be feasible.

Local adaptation in tree species has been documented through a long history of common garden experiments where functional traits (height, bud phenology) are used as proxies for fitness. However, the ability to identify genes or genomic regions related to adaptation to climate requires the evaluation of traits that precisely reflect how and when climate exerts selective constraints. We combine dendroecology with association genetics to establish a link between genotypes, phenotypes and interannual climatic fluctuations. We illustrate this approach by examining individual tree responses embedded in the annual rings of 233 Pinus strobus trees growing in a common garden experiment representing 38 populations from the majority of its range. We found that interannual variability in growth was affected by low temperatures during spring and autumn, and by summer heat and drought. Among-population variation in climatic sensitivity was significantly correlated with the mean annual temperature of the provenance, suggesting local adaptation. Genotype–phenotype associations using these new tree-ring phenotypes validated nine candidate genes identified in a previous genetic–environment association study. Combining dendroecology with association genetics allowed us to assess tree vulnerability to past climate at fine temporal scales and provides avenues for future genomic studies on functional adaptation in forest trees.

Climate is a major environmental factor affecting the phenotype of trees and is also a critical agent of natural selection that has molded among-population genetic variation. Population response functions describe the environmental effect of planting site climates on the performance of a single population, whereas transfer functions describe among-population genetic variation molded by natural selection for climate. Although these approaches are widely used to predict the responses of trees to climate change, both have limitations. We present a novel approach that integrates both genetic and environmental effects into a single \"universal response function\" (URF) to better predict the influence of climate on phenotypes. Using a large lodgepole pine (Pinus contorta Dougl. ex Loud.) field transplant experiment composed of 140 populations planted on 62 sites to demonstrate the methodology, we show that the URF makes full use of data from provenance trials to: (1) improve predictions of climate change impacts on phenotypes; (2) reduce the size and cost of future provenance trials without compromising predictive power; (3) more fully exploit existing, less comprehensive provenance tests; (4) quantify and compare environmental and genetic effects of climate on population performance; and (5) predict the performance of any population growing in any climate. Finally, we discuss how the last attribute allows the URF to be used as a mechanistic model to predict population and species ranges for the future and to guide assisted migration of seed for reforestation, restoration, or afforestation and genetic conservation in a changing climate.

Geographic variation in trees has been investigated since the mid‐18th century. Similar patterns of clinal variation have been observed along latitudinal and elevational gradients in common garden experiments for many temperate and boreal species. These studies convinced forest managers that a ‘local is best’ seed source policy was usually safest for reforestation. In recent decades, experimental design, phenotyping methods, climatic data and statistical analyses have improved greatly and refined but not radically changed knowledge of clines. The maintenance of local adaptation despite high gene flow suggests selection for local adaptation to climate is strong. Concerns over maladaptation resulting from climate change have motivated many new genecological and population genomics studies; however, few jurisdictions have implemented assisted gene flow (AGF), the translocation of pre‐adapted individuals to facilitate adaptation of planted forests to climate change. Here, we provide evidence that temperate tree species show clines along climatic gradients sufficiently similar for average patterns or climate models to guide AGF in the absence of species‐specific knowledge. Composite provenancing of multiple seed sources can be used to increase diversity and buffer against future climate uncertainty. New knowledge will continue to refine and improve AGF as climates warm further.

Street trees are public resources planted in a municipality’s right-of-way and are a considerable component of urban forests throughout the world. Street trees provide numerous benefits to people. However, many metropolitan areas have a poor understanding of the value of street trees to wildlife, which presents a gap in our knowledge of conservation in urban ecosystems. Greater Los Angeles (LA) is a global city harboring one of the most diverse and extensive urban forests on the planet. The vast majority of the urban forest is nonnative in geographic origin, planted throughout LA following the influx of irrigated water in the early 1900s. In addition to its extensive urban forest, LA is home to a high diversity of birds, which utilize the metropolis throughout the annual cycle. The cover of the urban forest, and likely street trees, varies dramatically across a socioeconomic gradient. However, it is unknown how this variability influences avian communities. To understand the importance of street trees to urban avifauna, we documented foraging behavior by birds on native and nonnative street trees across a socioeconomic gradient throughout LA. Affluent communities harbored a unique composition of street trees, including denser and larger trees than lower-income communities, which in turn, attracted nearly five times the density of feeding birds. Foraging birds strongly preferred two native street-tree species as feeding substrates, the coast live oak (Quercus agrifolia) and the California sycamore (Platanus racemosa), and a handful of nonnative tree species, including the Chinese elm (Ulmus parvifolia), the carrotwood (Cupaniopsis anacardioides), and the southern live oak (Quercus virginiana), in greater proportion than their availability throughout the cityscape (two to three times their availability). Eighty-three percent of street-tree species (n = 108, total) were used in a lower proportion than their availability by feeding birds, and nearly all were nonnative in origin. Our findings highlight the positive influence of street trees on urban avifauna. In particular, our results suggest that improved street-tree management in lower-income communities would likely positively benefit birds. Further, our study provides support for the high value of native street-tree species and select nonnative species as important habitat for feeding birds.