Tree populations usually show adaptations to their local environments as a result of natural selection. As climates change, populations can become locally maladapted and decline in fitness. Evaluating the expected degree of genetic maladaptation due to climate change will allow forest managers to assess forest vulnerability, and develop strategies to preserve forest health and productivity. We studied potential genetic maladaptation to future climates in three major European tree species, Norway spruce (Picea abies), silver fir (Abies alba), and European beech (Fagus sylvatica). A common garden experiment was conducted to evaluate the quantitative genetic variation in growth and phenology of seedlings from 77 to 92 native populations of each species from across Switzerland. We used multivariate genecological models to associate population variation with past seed source climates, and to estimate relative risk of maladaptation to current and future climates based on key phenotypic traits and three regional climate projections within the A1B scenario. Current risks from climate change were similar to average risks from current seed transfer practices. For all three climate models, future risks increased in spruce and beech until the end of the century, but remained low in fir. Largest average risks associated with climate projections for the period 2061–2090 were found for spruce seedling height (0.64), and for beech bud break and leaf senescence (0.52 and 0.46). Future risks for spruce were high across Switzerland. However, areas of high risk were also found in drought-prone regions for beech and in the southern Alps for fir. Genetic maladaptation to future climates is likely to become a problem for spruce and beech by the end of this century, but probably not for fir. Consequently, forest management strategies should be adjusted in the study area for spruce and beech to maintain productive and healthy forests in the future.
Recent vulnerability assessments, conducted in diverse regions in the northwestern United States, indicate that many commonalities exist with respect to projected vulnerabilities to climate change. Dry forests are projected to have significant changes in distribution and abundance of species, partially in response to higher temperature and lower soil moisture, but mostly in response to projected increases in extreme events and disturbances—drought, wildfire, and insect outbreaks. Wildfire and mountain pine beetles have caused extensive mortality across millions of hectares in this region during the past decade, and wildfire area burned is projected to increase 200%–300% by mid-21st century. Science–management partnerships associated with recent assessments have identified an extensive list of adaptation options, including both strategies (general planning) and tactics (on-the-ground projects). Most of the options focus on increasing resilience to disturbances and on reducing current stressors to resource conditions. Adaptation options are generally similar across the biogeographically diverse region covered by assessments, suggesting that there may be a limit on the number of feasible responses to climate change. Federal agencies in the northwestern United States are now using these assessments and adaptation approaches to inform sustainable resource management and planning, mostly through fine tuning of existing practices and policies.
Species’ differences in the stringency of stomatal control of plant water potential represent a continuum of isohydric to anisohydric behaviours. However, little is known about how quasi-steady-state stomatal regulation of water potential may relate to dynamic behaviour of stomata and photosynthetic gas exchange in species operating at different positions along this continuum. Here, we evaluated kinetics of light-induced stomatal opening, activation of photosynthesis and features of quasi-steady-state photosynthetic gas exchange in 10 woody species selected to represent different degrees of anisohydry. Based on a previously developed proxy for the degree of anisohydry, species’ leaf water potentials at turgor loss, we found consistent trends in photosynthetic gas exchange traits across a spectrum of isohydry to anisohydry. More anisohydric species had faster kinetics of stomatal opening and activation of photosynthesis, and these kinetics were closely coordinated within species. Quasi-steady-state stomatal conductance and measures of photosynthetic capacity and performance were also greater in more anisohydric species. Intrinsic water-use efficiency estimated from leaf gas exchange and stable carbon isotope ratios was lowest in the most anisohydric species. In comparisons between gas exchange traits, species rankings were highly consistent, leading to species-independent scaling relationships over the range of isohydry to anisohydry observed.
1. In temperate ecosystems, freeze-thaw events are an important environmental stress that can induce severe xylem embolism (i.e. clogging of conduits by air bubbles) in overwintering organs of trees. However, no comparative studies of different adaptive strategies among sympatric tree species for coping with winter embolism have examined the potential role of the presence or absence of embolism refilling by positive xylem pressure. 2. We evaluated the degree of winter embolism and hydraulic architecture traits in 22 deciduous angiosperm tree species typical of temperate forest sites in NE China. Co-occurring trees growing in a local botanical garden were used to minimize variation caused by differences in proximal environmental conditions and to ensure that interspecific variation reflected genetic differences between species. 3. Four functional groups with potentially different strategies for coping with winter embolism were compared: positive xylem pressure- generating species (PXP) that are all diffuse-porous, except a semi-ring-porous species, large (LDP) and small (SDP) statured diffuse-porous tree species that are unable to generate positive xylem pressure, and ring-porous species (RP). 4. The PXP group exhibited nearly full recovery from winter embolism in contrast to the other three groups, which showed persistent and relatively high degrees of hydraulic dysfunction during the subsequent growing season. The absence of a functional trade-off between hydraulic efficiency and safety against freeze-thaw-induced embolism in the PXP group and the presence of a trade-off in the other three groups, suggests that the ability to generate root or stem pressure for embolism refilling may partially free some temperate tree species from adaptive constraints imposed by winter embolism formation. 5. Efficient winter embolism reversal by positive pressure in PXP species did not distinguish them from their non-xylem pressure-generating LDP counterparts in terms of various measures of xylem hydraulic efficiency during the growing season. Divergence in the ability to refill winter embolism through generation of positive xylem pressure implies a series of functional trade-offs that may partially explain the co-existence of these two types of temperate tree species.
Landscape exposure to multiple stressors can pose risks to human health, biodiversity, and ecosystem services. Attempts to study, control, or mitigate these stressors can strain public and private budgets. An interdisciplinary team of Pacific Northwest Research Station and Oregon State University scientists created maps of the conterminous United States that indicate landscape exposure to concentrated wildfire potential, insects and disease risk, urban and exurban development, and climate change. The maps, which show where these stressors might occur and overlap, provide a valuable resource for regional and national land use, land management, and policymaking efforts by helping to guide resource prioritization.
The researchers identified locations where each stressor is more prevalent on the landscape relative to other locations, and then combined future climate projections from 30 separate global circulation models to establish a climate change metric. The climate change metric represents when the average annual temperature is projected to permanently depart from the prevailing climate of the past century under a “business as usual” scenario. The goal was to identify large contiguous areas of stress exposure—locations that may be vulnerable to ecological and social disruption.
This information has been used in Oregon, for example, to inform discussions about urban expansion and fire risk around the City of Bend.