Extreme weather events are increasing in frequency and intensity due to global climate change. We hypothesized that tree carbon reserves are crucial for resilience of beech, buffering the source-sink ...imbalance due to late frosts and summer droughts, and that different components of non-structural carbohydrates (NSCs) play specific roles in coping with stressful situations. To assess the compound effects on mature trees of two extreme weather events, first a late frost in spring 2016 and then a drought in summer 2017, we monitored the phenology, radial growth and the dynamics of starch and soluble sugars in a Mediterranean beech forest. A growth reduction of 85% was observed after the spring late frost, yet not after the drought event. We observed a strong impact of late frost on starch, which also affected its dynamic at the beginning of the subsequent vegetative season. In 2017, the increase of soluble sugars, associated with starch hydrolysis, played a crucial role in coping with the severe summer drought. NSCs helped to counteract the negative effects of both events, supporting plant survival and buffering source-sink imbalances under stressful conditions. Our findings indicate a strong trade-off between growth and NSC storage in trees. Overall, our results highlight the key role of NSCs on beech trees response to extreme weather events, confirming the resilience of this species to highly stressful events. These insights are useful for assessing how forests may respond to the potential impacts of climate change on ecosystem processes in the Mediterranean area.
Display omitted
•Ring width samples were collected from Norway spruce and European beech in Central Europe.•Climate–growth interactions were assessed along an altitudinal gradient.•Species-specific ...responses to temperature and water availability depended on altitude.•The climatic sensitivity of the growth of both species showed significant temporal shifts.•Spring temperature and summer drought were the main factors limiting tree growth.
Norway spruce has experienced unprecedented forest declines in recent decades, leading to extensive salvage logging. Currently, because of the conversion of conifer forests into more natural mixed forests in Central Europe, spruce has begun to be replaced, mainly by European beech. The frequently discussed changing climate has a crucial effect on the vitality of both species. To improve our understanding of spruce and beech responses to climate change, including more frequent temperature and drought extremes, we investigated the impact of temporal climate variability on the growth of these species along an elevation gradient. In total, 79 spruce and 90 beech trees were used to build species-specific tree-ring width chronologies representing the altitudinal range in which both species grow (450, 650, 800, and 950m asl) under the conditions of the Czech Republic. The climate–growth relationship indicates strong dependence of spruce and beech tree-ring growth on spring temperature (Mar–May) at all sites and summer (Jun–Aug) water availability at lower altitudes. Significant temporal shifts in the climate–growth relationships of both species indicate an increasing negative effect of summer temperature and positive effect of water availability in summer. The increasing drought and temperature sensitivity of both species suggest a significant impact of the predicted climate change on such forest ecosystems. Discussion emphasizes the current importance of adaptive forest management strategies.
Xylem cavitation resistance is a key physiological trait correlated with species tolerance to extreme drought stresses. Little is known about the genetic variability and phenotypic plasticity of this ...trait in natural tree populations. Here we measured the cavitation resistance of 17 Fagus sylvatica populations representative of the full range of the species in Europe. The trees were grown in three field trials under contrasting climatic conditions. Our findings suggest that the genotypic variability of cavitation resistance is high between genotypes of a given population. By contrast, no significant differences were found for this trait across populations, the mean population cavitation resistance being remarkably constant in each trial. We found a significant site effect and a significant site x population interaction, suggesting that cavitation resistance has a high phenotypic plasticity and that this plasticity is under genetic control. The implications of our findings for beech forest management in a context of climate change are discussed.
Background and Aims Masting, i.e. synchronous but highly variable interannual seed production, is a strong sink for carbon and nutrients. It may, therefore, compete with vegetative growth. It is ...currently unknown whether increased atmospheric CO sub(2) concentrations will affect the carbon balance (or that of other nutrients) between reproduction and vegetative growth of forest species. In this study, reproduction and vegetative growth of shoots of mature beech (Fagus sylvatica) trees grown at ambient and elevated atmospheric CO sub(2) concentrations were quantified. It was hypothesized that within a shoot, fruiting has a negative effect on vegetative growth, and that this effect is ameliorated at increased CO sub(2) concentrations. Methods Reproduction and its competition with leaf and shoot production were examined during two masting events (in 2007 and 2009) in F. sylvatica trees that had been exposed to either ambient or elevated CO sub(2) concentrations (530 mu mol mol super(-1)) for eight consecutive years, between 2000 and 2008. Key Results The number of leaves per shoot and the length of terminal shoots was smaller or shorter in the two masting years compared with the one non-masting year (2008) investigated, but they were unaffected by elevated CO sub(2) concentrations. The dry mass of terminal shoots was approx. 2-fold lower in the masting year (2007) than in the non-masting year in trees growing at ambient CO sub(2) concentrations, but this decline was not observed in trees exposed to elevated CO sub(2) concentrations. In both the CO sub(2) treatments, fruiting significantly decreased nitrogen concentration by 25 % in leaves and xylem tissue of 1- to 3-year-old branches in 2009. Conclusions Our findings indicate that there is competition for resources between reproduction and shoot growth. Elevated CO sub(2) concentrations reduced this competition, indicating effects on the balance of resource allocation between reproduction and vegetative growth in shoots with rising atmospheric CO sub(2) concentrations.
In forests, mycorrhizal fungi regulate carbon (C) and nitrogen (N) dynamics. We evaluated the interplay among ectomycorrhizas (ECM), ecosystem C fluxes, tree productivity, C and N exchange and ...isotopic fractionation along the soil‐ECM‐plant continuum in a Mediterranean beech forest. From bud break to leaf shedding, we monitored: net ecosystem exchange (NEE, a measure of the net exchange of C between an ecosystem and the atmosphere), leaf area index, stem growth, N concentration, δ13C and δ15N in rhizosphere soil, ectomycorrhizal fine root tips (ERT), ECM‐free fine root portions (NCR) and leaves. Seasonal changes in ERT relative biomass were strictly related to NEE and mimicked those detected in the radial growth. The analysis of δ13C in ERT, leaves and NCR highlighted the impact of canopy photosynthesis on ERT development and an asynchronous seasonal C allocation strategy between ERT and NCR at the root tips level. Concerning N, δ15N of leaves was negatively related to that of ERT and dependent on seasonal 15N differences between ERT and NCR. Our results unravel a synchronous C allocation towards ERT and tree stem driven by the increasing NEE in spring‐early summer. Moreover, they highlighted a phenology‐dependent 15N fractionation during N transfer from ECM to their hosts. This evidence, obtained in mature beech trees under natural conditions, may improve the knowledge of Mediterranean forests functionality.
Summary Statement
The natural abundances of C and N stable isotopes along the soil‐ectomycorrhiza‐plant continuum in mature Fagus sylvatica trees revealed the key role of ectomycorrhizae in regulating source‐sink relationships and the close interchange between biogeochemical cycles in forest ecosystem.
In the context of global decline in old‐growth forest, historical ecology is a valuable tool to derive insights into vegetation legacies and dynamics and develop new conservation and restoration ...strategies. In this cross‐disciplinary study, we integrate palynology (Lago del Pesce record), history, dendrochronology, and historical and contemporary land cover maps to assess drivers of vegetation change over the last millennium in a Mediterranean mountain forest (Pollino National Park, southern Italy) and discuss implications in conservation ecology. The study site hosts a remnant beech–fir (Fagus sylvatica–Abies alba) mixed forest, a priority habitat for biodiversity conservation in Europe. In the 10th century, the pollen record showed an open environment that was quickly colonized by silver fir when sociopolitical instabilities reduced anthropogenic pressures in mountain forests. The highest forest cover and biomass was reached between the 14th and the 17th centuries following land abandonment due to recurring plague pandemics. This rewilding process is also reflected in the recruitment history of Bosnian pine (Pinus heldreichii) in the subalpine elevation belt. Our results show that human impacts have been one of the main drivers of silver fir population contraction in the last centuries in the Mediterranean, and that the removal of direct human pressure led to ecosystem renovation. Since 1910, the Rubbio State Forest has locally protected and restored the mixed beech–fir forest. The institutions in 1972 for the Rubbio Natural Reserve and in 1993 for Pollino National Park have guaranteed the survival of the silver fir population, demonstrating the effectiveness of targeted conservation and restoration policies despite a warming climate. Monitoring silver fir populations can measure the effectiveness of conservation measures. In the last decades, the abandonment of rural environments (rewilding) along the mountains of southern Italy has reduced the pressure on ecosystems, thus boosting forest expansion. However, after four decades of natural regeneration and increasing biomass, pollen influx and forest composition are still far from the natural attributes of the medieval forest ecosystem. We conclude that long‐term forest planning encouraging limited direct human disturbance will lead toward rewilding and renovation of carbon‐rich and highly biodiverse Mediterranean old‐growth forests, which will be more resistant and resilient to future climate change.
AIMS: We investigated N₂O emissions from stems of Fraxinus angustifolia and Fagus sylvatica, hypothesizing that trees emit N₂O through the stem via diffusion out of the transpiration stream. METHODS: ...We used static chambers fixed at different heights of the stem to estimate N₂O stem effluxes. Chambers were also used for monitoring soil N₂O emissions. To stimulate soil N₂O production and stem N₂O emissions we fertilized the soil. RESULTS: Before soil fertilization, stem N₂O emissions were at most 2 μg N₂O-N m⁻² bark h⁻¹. After fertilization, stem and soil emissions were linearly correlated; stem emissions decreased linearly with increasing height. Stems of Fagus sylvatica emitted up to 80 μg N₂O-N m⁻² bark h⁻¹ at 20 cm above soil level; at 200 cm, stem N₂O emissions were below detection limit. Fraxinus angustifolia stem N₂O emissions reached 35 μg N₂O-N m⁻² bark h⁻¹ after soil fertilization. CONCLUSIONS: Stem N₂O emissions in upland trees occur even without aerenchyma, associated with xylem water transport. However, stem N₂O emissions represented only 1–3 % of total (soil + stem) N₂O emissions at the forest level. If this holds for other forest ecosystems, stem N₂O emissions would be a minor pathway of N₂O loss from terrestrial ecosystems into the atmosphere.
Forest management aims for productive and stable forests that continuously provide ecosystem goods and services, including balancing nutrient fluxes. Increasing heat and frequent droughts in ...temperate European forests make the introduction of non-native Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) an increasingly relevant climate change adaptation strategy, particularly as an admixture to native tree species, such as European beech (Fagus sylvatica L.). Douglas fir can alter biogeochemical processes in forest soils, potentially leading to an excess of nitrogen in the ecosystem, but the biotic and abiotic controls of this effect need further examination (species interactions, soil type). Here we studied nitrate leaching on plots of two contrasting textures (southern loamy and northern sandy site) planted with either pure Douglas fir, pure Norway spruce (Picea abies L. Karst.), pure European beech or a mixture of beech with either of the conifers. We used P80 suction lysimeters at 5 and 60 cm soil depth and collected soil solution over two continuous years to estimate nitrate leaching risks. We found highest concentrations of nitrate in soil solution in lower soil layers under Douglas fir (29.14 mg/L), which corroborates the findings of some studies conducted in pure stands. Comparisons of concentrations below the litter layer and below the main rooting zone implied that accumulation and microbial production of nitrate is taking place under Douglas fir. In Douglas fir-beech mixed stands, however, we found sustained significantly lower nitrate concentrations in soil solution below the main rooting zone (1.68 mg/L), implying a mixture effect. Furthermore, site played a key role in controlling nitrate concentrations in soil solution under Douglas fir on sites with finer soil texture and a lower C:N ratio. Elevated nitrate concentrations were associated with a P-limitation found in the trees, which likely caused reduced nitrate uptake. We discuss the results with regards to throughfall, litter, soil and microbial characteristics. We conclude that increased nitrate concentrations under Douglas fir stands may pose a relatively higher nitrate leaching risk than Norway spruce and a considerably higher risk compared to beech stands. However, the low susceptibility to leaching under beech stands seems to be a strong effect trait in mixtures, diminishing the high leaching potential Douglas fir induces on some sites. Low leaching potential is key to sustaining adequate nutrition in temperate forests and reducing pollution of groundwater. Our findings strongly urge forestry experts to carefully assess site conditions and foster mixtures with European beech when planting Douglas fir.
•Tree species affect nitrogen cycling; Douglas fir can increase nitrate concentrations in soil solution, posing a risk for nitrate leaching.•When mixed with European beech, nitrate concentrations remain low.•On sandy, poorer sites, nitrate leaching was much lower than on loamy sites.•P-limitation of Douglas fir caused reduced N uptake, leading to N accumulation in soil solution.•Nitrate production by microorganisms was likely stimulated under Douglas fir.
Aim of study: Although beech (Fagus sylvatica L.) forests in north-western Spain constitute c.a. 40% of the total area occupied by the species in the whole country, no growth or yield studies have ...been carried out regarding these forests. The specific objective of this study was to elaborate yield tables and stand density management diagrams for the beech forests. Area of study: Asturias and León provinces (NW Spain). Material and methods: Sample plots (n=112) were established in natural beech forests, and 60 dominant trees were felled for sampling. The Asturias Government Forest Service provided data on another 351 felled trees. Yield tables and stand density management diagrams (SDMDs) were elaborated to estimate tree volume and biomass in the study area for the first time. Main results: These forests are more productive than expected. Although they are currently not managed for forestry purposes, they could be managed again in the future and the tools are now available for this purpose. Research highlights: The study generates new user-friendly tools to manage beech forests in northwestern Spain. These tools will also enable simulations to be conducted to determine the potential carbon storage or the capacity of the stands to sequester atmospheric carbon.
PDF
