Forests exchange large amounts of CO2 with the atmosphere and can influence and be influenced by atmospheric CO2. There has been a recent proliferation of literature on the effects of atmospheric CO2 on forest trees. More than 300 studies of trees on five different continents have been published in the last five years. These include an increasing number of field studies with a long‐term focus and involving CO2×stress or environment interactions. The recent data on long‐term effects of elevated atmospheric CO2 on trees indicate a potential for a persistent enhancement of tree growth for several years, although the only relevant long‐term datasets currently available are for juvenile trees. The current literature indicates a significantly larger average long‐term biomass increment under elevated CO2 for conifers (130%) than for deciduous trees (49%) in studies not involving stress components. However, stimulation of photosynthesis by elevated CO2 in long‐term studies was similar for conifers (62%) and deciduous trees (53%). Recent studies indicate that elevated CO2 causes a more persistent stimulation of biomass increment and photosynthesis than previously expected. Results of seedling studies, however, might not be applicable to other stages of tree development because of complications of age‐dependent and size‐dependent shifts in physiology and carbon allocation, which are accelerated by elevated CO2. In addition, there are many possible avenues to down‐regulation, making the predicted canopy CO2 exchange and growth of mature trees and forests in a CO2‐rich atmosphere uncertain. Although, physiological down‐regulation of photosynthetic rates has been documented in field situations, it is rarely large enough to offset entirely photosynthetic gains in elevated CO2. A persistent growth stimulation of individual mature trees has been demonstrated although this effect is more uncertain in trees in natural stands. Resource interactions can both constrain tree responses to elevated CO2 and be altered by them. Although drought can reduce gas‐exchange rates and offset the benefits of elevated CO2, even in well watered trees, stomatal conductance is remarkably less responsive to elevated CO2 than in herbaceous species. Stomata of a number of tree species have been demonstrated to be unresponsive to elevated CO2. We conclude that positive effects of CO2 on leaf area can be at least as important in determining canopy transpiration as negative, direct effects of CO2 on stomatal aperture. With respect to nutrition, elevated CO2 has the potential to alter tree–soil interactions that might influence future changes in ecosystem productivity. There is continued evidence that in most cases nutrient limitations diminish growth and photosynthetic responses to elevated CO2 at least to some degree, and that elevated CO2 can accelerate the appearance of nutrient limitations with increasing time of treatment. In many studies, tree biomass responses to CO2 are artefacts in the sense that they are merely responses to CO2‐induced changes in...

Although trees have responded to global warming in the past -to temperatures higher than they are now -the rate of change predicted in the 21st century is likely to be unprecedented. Greenhouse gas emissions could cause a 3 -6 ° C increase in mean land surface temperature at high and temperate latitudes. Despite this, few experiments have isolated the effects of temperature for this scenario on trees and forests. This review focuses on tree and forest responses at boreal and temperate latitudes, ranging from the cellular to the ecosystem level. Adaptation to varying temperatures revolves around the trade-off between utilizing the full growing season and minimizing frost damage through proper timing of hardening in autumn and dehardening in spring. But the evolutionary change in these traits must be sufficiently rapid to compensate for the temperature changes. Many species have a positive response to increased temperature -but how close are we to the optima? Management is critical for a positive response of forest growth to a warmer climate, and selection of the best species for the new conditions will be of vital importance.

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Background: The New Nordic Diet (NND) was designed by gastronomic, nutritional, and environmental specialists to be a palatable, healthy, and sustainable diet containing 35% less meat than the Average Danish Diet (ADD); more whole-grain products, nuts, fruit, and vegetables; locally grown food in season; and .75% organic produce. The environmental impact of the 2 diets was compared based on 16 impact categories, which were monetized to evaluate the overall socioeconomic effect of a shift from an ADD to an NND. Objective: The objective was to determine whether this diet shift can be an effective tool in environmental protection. Design: The 3 features by which this diet shift affects the environmentcomposition, transport (import), and type of production (organic/ conventional)-were separately investigated by using life cycle assessment. Results: When both diet composition and transport were taken into account, the NND reduced the environmental impact relative to the ADD measured by all 16 impact categories. The socioeconomic savings related to this diet shift was €266/person per year, or 32% of the overall environmental cost of the ADD. When the actual 8% content of organic produce in the ADD and the 84% content of organic produce in the investigated recipe-based NND were also taken into account, the NND reduced the environmental impact relative to the ADD measured by only 10 of the 16 impact categories whereas 6 were increased. The socioeconomic savings related to the diet shift were lowered to €42/person per year, or 5% of the overall environmental cost of the ADD. Conclusion: Reducing the content of meat and excluding most longdistance imports were of substantial environmental and socioeconomic advantage to the NND when compared with the ADD, whereas including high amounts of organic produce was a disadvantage.

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Growth responses of two provenances of European beech (Fagus sylvatica) were studied. The seedlings were grown in closed‐top chambers at four temperature regimes (−2.9 °C below ambient, ambient, +2.3 °C and +4.8 °C above ambient) in combination with two CO2 partial pressures (40 Pa and 74 Pa). Growth was followed by making destructive harvests c. every 25 d from germination in early June to senescence in late September. Allocation patterns were significantly affected by the temperature regimes. However, changes in dry matter allocation and morphology associated with the different treatments at a given time were mostly a result of differences in tree size. Temperature regimes only had a significant effect on the relative growth rate, RGR, at the beginning of the experiment. In contrast to temperature, high [CO2] increased RGR throughout the experiment when compared with plants of equal size. As the trees increased in size net assimilation rate, NAR, decreased but the effect of [CO2] on both NAR and RGR had a tendency to increase. Increases in NAR caused by elevated [CO2] were partly counteracted by reductions in the leaf area ratio, LAR. Reductions in LAR were caused by concomitant reductions in specific leaf area, SLA, whereas the level of [CO2] did not significantly affect leaf weight ratio, LWR, nor other dry weight ratios. The interactions between temperature and [CO2] are highly dependent on whether they are expressed as instantaneous values for plants at a common age or instantaneous values at a common size (and thereby extracting the effects of ontogenetic drift). When comparing instantaneous values at common sizes, the positive effect of [CO2] on RGR increased with plant size in every temperature regime. This also occurred in every temperature regime when comparing plants of equal age but the response to [CO2] was less. The effect of [CO2] on RGR was dependent on growth temperature. The positive effects of elevated [CO2] on RGR were less than the positive effect on photosynthesis. The two provenances did not differ significantly in the response of RGR to [CO2] which is in agreement with measurements of photosynthesis.