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•Short- and long-term climate responses were investigated for mixed and pure stands.•Triplet experimental setup enables the specific analysis of mixing effects.•Douglas-fir benefits ...from mixtures, but at the expense of European beech.•Mixing effect results from complementary phenology.•Tree size, competition and limitation of the stands influence the sensitivity.
Due to possible positive and compensatory interaction between species, mixed stands are a commonly accepted silvicultural response to reduce risks arising from climate change. Nonetheless, only a few species combinations have been studied more detailed so far revealing variable mixing effects. Here, we analyze the effect of the mixture of Douglas fir and European beech with regard to the species-specific climate sensitivity of growth. We focus on three hypotheses: (i) Species-specific long term growing performance and climate sensitivity do not differ between monocultures and mixed stands, (ii) species-specific growth reactions to severe drought events do not differ between monocultures and mixed species stands and (iii) species-specific growth reactions on severe drought events are not influenced by differing ecological growing conditions.
To scrutinize the hypothesis we analyzed tree cores from both species taken from pure and mixed stands covering different site conditions and age classes. Tree ring characteristics were used to analyze the differences in climate related long-term growth responses in pure and mixed stands. Short-term responses were investigated by growth reaction indices on individual tree and stand level involving drought events during the years 1950–2010. Linear mixed models were applied to detect effects of ecological co-variables on the indices.
Results reveal that Douglas-fir in mixed stands exhibit a significant improved growing performance compared to pure stands. European beech seems to react indifferently concerning its performance in mixture compared to pure stands.
Differences in drought stress resistance and growth recovery time mainly arose between the species. Douglas-fir showed a significantly lower resistance and required more time to reach again its initial growth level compared to European beech. In mixture we found a trend that Douglas-fir growth recovery time is shortened and extended for European beech.
The analysis along the ecological gradients showed that base-limited soils systems are more drought-tolerant during drought events. Lower basal area as a proxy for reduced stand competition decreased the relative growth loss by drought.
We hypothesize that mainly spatial differentiation in height trigger enhanced diameter growth of Douglas-fir in mixture. Temporal differentiation expressed by deferred phenology attenuates climate sensitivity of this conifer. We conclude that in mixed Douglas-fir and European beech stands the former species is stabilized against climatic impacts. On the contrary, climate sensitivity of European beech is increased.
•The first repeated terrestrial canopy gap inventory in a Eur. beech virgin forest.•We found a significant decrease in gap fraction and changes in gap size pattern.•High rates of gap closure were ...found that strongly dominated over gap formation.•There was a shift in the dominant gap filling process with increasing gap size.•Gaps released a heterogeneously structured understory and promoted its height growth.
Canopy gaps play a crucial role for forest dynamics processes, as they largely determine light transmission to lower canopy strata, thereby controlling the turnover of tree individuals in the stand. Even though their functional importance is undisputed, quantitative data on the rate of gap creation and gap closure, and the temporal change in gap size distribution patterns in temperate virgin forests are scarce. We used a repeated inventory (line-intercept sampling) of gap size frequency and fraction in a virgin beech (Fagus sylvatica) forest in the Slovakian Carpathians over a 10-year interval (2003–2013) to test the hypotheses that (i) disturbance intensity and thus gap creation and gap closure rate change only little over time, (ii) gaps persist or even expand, until they are filled primarily by vertical ingrowth of trees from lower strata, and (iii) gap creation promotes the height growth of released saplings and sub-canopy trees. In the 2003 and 2013 inventories, 37 and 30 gaps >20 m2 size were mapped along a total of 3217 m transect line investigated. The large majority of gaps was <100 m2 in size; large gaps >500 m2 were very rare. Gap fraction decreased significantly from 13.6% in 2003 to 8.2% in 2013 (associated with a reduction in mean gap size from 261 to 96 m2), indicating considerable variation in disturbance intensity in the past decades. Before 2003, both large gaps (probably caused by wind throw) and small gaps (from dying trees) have been formed, while only small gaps developed in the period 2003–2013. Small gaps were closed within a few years through rapid horizontal canopy expansion of neighboring beech trees, while vertical gap filling through ingrowth of lower canopy layers and regeneration was the dominant process in larger gaps. Saplings and trees in lower canopy layers formed a heterogeneous understory in large parts of recently formed gaps and responded to this process with increased height growth. We conclude that, despite considerable variation in disturbance intensity over time, this beech virgin forest responds to gap formation with high resilience through rapid lateral canopy expansion in small gaps and ingrowth of saplings and sub-dominant tree layers in larger gaps.
•Terrestrial laser scanning (TLS) was applied on a unique drought stress experiment.•The approach revealed three-dimensional change of tree shape due to drought stress.•Drought stress led to smaller ...crown size and lower height growth.•Competition and drought resulted in crowns that were less rough and more compact.•TLS may enable efficient tree vitality monitoring.
Due to climate change, the occurrence of drought events with essential effects on trees will arise. The impact of severe drought stress on trees’ vitality with regard to growth has often been analysed using traditional, easy-to-measure variables, such as diameter at breast height (d1.3). Another commonly used tree-vitality indicator is crown transparency, which is not directly measurable and has to be determined qualitatively by well-trained field experts. In this study, we focused on tree dimensions, as potential vitality indicators, that are difficult to measure. The new approach for the efficient monitoring of tree vitality introduced here revealed three-dimensional change of tree shape due to drought stress.
The unique drought stress experiment “Kranzberg Forest Roof Experiment” (KROOF) was used as a basis for scanning and analysing the growth of Norway spruce (Picea abies (L.) H. Karst.) and European beech (Fagus sylvatica L.) under progressively limiting water reserves. Before the start of the experiment in the winter of 2012/2013, terrestrial laser scanning (TLS) was performed and repeated in the winter of 2018/2019. One sample of 21 trees was trenched and roofed (treatment), while additional 26 trees served as untreated reference (control). Using the TLS-point clouds of the two subsequent surveys, structural tree modifications within the 6-year period can be directly visualised, computed and linked to drought stress.
Drought stress led to significantly smaller crown size and lower height growth for both tree species. The crowns of Norway spruce trees increased significantly in transparency and roughness. In addition, high competition combined with drought stress significantly reduced the roughness and increased the compactness of the crown. The periodic annual change in crown projection area (paccpa) as well as the periodic annual height increment (paiheight) differed significantly between control and treatment for both tree species. Under drought conditions, paccpa changed by –0.74 m2 yr−1 and –0.42 m2 yr−1 for spruce and beech trees respectively, whereas the control trees showed a growth of 0.17 m2 yr−1 and 0.62 m2 yr−1 respectively. This means that crowns became considerably smaller under dry conditions. Under drought, the paiheight was 0.09 m yr−1 less for spruce and 0.17 m yr−1 less for beech compared with normal growing conditions. The periodic annual change in crown roughness (pacroughness) was −9.5% yr−1 if local competition increased by one.
Our results show that TLS can offer new opportunities for identifying structural features in trees. Iterative TLS-surveys may extend existing measuring campaigns on common long-term experimental plots, in order to analyse general changes or monitor tree vitality.
Fagus sylvatica is one of the most representative trees of the European deciduous broadleaved forests, yet the impact of changing climatic conditions and anthropogenic pressures (anthromes) on its ...presence and distribution in the coastal and lowland areas of the Mediterranean Basin has long been overlooked.
Here, we first analysed the local forest composition in two different time intervals (350–300 Before Current Era, BCE and 150–100 BCE) using charred wood remains from the Etruscan site of Cetamura (Tuscany, central Italy). Additionally, we reviewed all the relevant publications and the wood/charcoal data obtained from anthracological analysis in F. sylvatica, focusing on samples that date back to 4000 years before present, to better understand the drivers of beech presence and distribution during the Late Holocene (LH) in the Italian Peninsula. Then, we combined charcoal and spatial analyses to test the distribution of beech woodland at low elevation during LH in Italy and to evaluate the effect of climate change and/or anthrome on the disappearance of F. sylvatica from the lowlands.
We collected 1383 charcoal fragments in Cetamura belonging to 21 woody taxa, with F. sylvatica being the most abundant species (28 %), followed by other broadleaved trees. We identified 25 sites in the Italian Peninsula with beech charcoals in the last 4000 years. Our spatial analyses showed a marked decrease in habitat suitability of F. sylvatica from LH to the present (ca. 48 %), particularly in the lowlands (0–300 m above sea level, a.s.l.) and in areas included between 300-600 m a.s.l. with a subsequent shift upwards of the beech woodland of ca. 200 m from the past to the present. In the lowland areas, where F. sylvatica has disappeared, anthrome alone and climate + anthorme had a main effect on beech distribution whitin 0-50 m a.s.l., while the climate from 50 to 300 m a.s.l. Furthermore, climate affect also the beech distrinution in the areas >300 m a.s.l., while climate + anthrome and antrhome alone were mainly focused on the lowland areas.
Our results highlight the advantage of combining different approaches, such as charcoal analysis and spatial analyses, to explore biogeographic questions about the past and current distribution of F. sylvatica, with important implications for today's forest management and conservation policies.
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•Fagus sylvatica inhabited the Italian Peninsula lowlands in the late Holocene.•Climate and anthropogenic pressure affected the loss of F. sylvatica from the Italian Peninsula lowlands.•The climate had an effect on the beech disappearance in Italy mainly in the innermost areas included between 50 - 300 m a.s.l.•Anthropogenic pressure mostly affected the loss of beech in lowland areas placed at 0-50 m a.s.l.
Ongoing climate warming is increasing evapotranspiration, a process that reduces plant-available water and aggravates the impact of extreme droughts during the growing season. Such an exceptional hot ...drought occurred in Central Europe in 2018 and caused widespread defoliation in mid-summer in European beech (Fagus sylvatica L.) forests.
Here, we recorded crown damage in 2021 in nine mature even-aged beech-dominated stands in northwestern Switzerland along a crown damage severity gradient (low, medium, high) and analyzed tree-ring widths of 21 mature trees per stand. We aimed at identifying predisposing factors responsible for differences in crown damage across and within stands such as tree growth characteristics (average growth rates and year-to-year variability) and site-level variables (mean canopy height, soil properties).
We found that stand-level crown damage severity was strongly related to soil water availability, inferred from tree canopy height and plant available soil water storage capacity (AWC). Trees were shorter in drier stands, had higher year-to-year variability in radial growth, and showed higher growth sensitivity to moisture conditions of previous late summer than trees growing on soils with sufficient AWC, indicating that radial growth in these forests is principally limited by soil water availability. Within-stand variation of post-drought crown damage corresponded to growth rate and tree size (diameter at breast height, DBH), i.e., smaller and slower-growing trees that face more competition, were associated with increased crown damage after the 2018 drought. These findings point to tree vigor before the extreme 2018 drought (long-term relative growth rate) as an important driver of damage severity within and across stands. Our results suggest that European beech is less likely to be able to cope with future climate change-induced extreme droughts on shallow soils with limited water retention capacity.
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•Across stands, crown damage severity increased with decreasing water availability.•Trees growing in drier sites were shorter and their growth was more sensitive to climate.•Within stands, slower-growing trees under increased competition showed more damage.•We identified previous tree vigor as a driver of damage severity within and across stands.
•Forest management strongly affected the presence of specialist species.•Accounting only for species richness may provide biased information for conservation.•Functional approach is promising for ...better-informed conservation planning.•Lists of conservation-relevant species are effective for understudied groups.•A multi-taxon framework is needed for guiding conservation action.
We investigated the consistency between richness and trait-based diversity metrics in capturing the effects of management-related habitat factors on biodiversity. The choice of biodiversity metrics can substantially affect the evaluation of conservation tools. However, the relative sensitivity of different metrics is not well investigated, especially in a multi-taxon framework.
European beech forests in Denmark.
We studied 20 beech stands comprising four management types (from intensively managed to long unmanaged stands). We analyzed how management-related environmental variables were reflected in the measure of: (i) species richness, (ii) number of conservation-relevant species (red-listed species and old-growth forest indicators) and (iii) functional diversity targeting five organism groups with different habitat requirements, i.e. vascular plants, epiphytic lichens and bryophytes, saproxylic fungi and breeding birds.
Plain species richness at stand level was generally misleading, as it did not capture changes in the number of conservation relevant species with changes in management-related environmental variables. The interpretation of functional responses was most informative for the better known vascular plants, while responses were more fragmented for the other organism groups. Overall, however, functional responses were consistent with a loss of specialization and progressive simplification of species assemblages from long-unmanaged to intensively managed stands.
Our findings suggest that the occurrence of conservation-relevant species is a sound and relevant metric for planning and evaluating conservation actions, especially for less studied organism groups (e.g., saproxylic fungi and epiphytes). The functional approach is promising, but presupposes the availability of databases of relevant traits.
•Fagus orientalis was introduced to a northern German forest stand ca. 100 years ago.•F. orientalis hybridizes with autochthonous F. sylvatica in the introduced range.•Both species can act as pollen ...and seed parent.•The necessity and suitability for assisted gene flow management should carefully be evaluated.
Fagus sylvatica L., one of the most common Central European deciduous tree species, is one of the species globally suffering from changing and stressful environmental conditions. It has shown symptoms of crown damage, a reduction in growth and increased mortality following recent severe droughts. Fagus orientalis Lipsky, a closely related species with higher drought tolerance, originates from southeastern Europe, Turkey, the Greater Caucasus region, and the Hyrcanian forest. For Germany, F. orientalis has been proposed as an alternative to F. sylvatica by translocation of pre-adapted planting material as a tool to mitigate negative effects of climate change in certain locations. This approach can be beneficial but might also harbor risks.
We studied admixtures between the two beech species and the direction of gene flow, taking advantage of F. orientalis trees planted over 100 years ago in the forest district of Memsen, Germany. Additionally, we used a range-wide dataset of F. sylvatica and F. orientalis provenances to determine the origin of the introduced trees. Using a combination of nuclear microsatellites and one chloroplast marker with species-specific variants, we showed that interspecific gene flow was going in both directions. In most cases, F. sylvatica was the pollen donor, likely due to its greater abundance and production of vast amounts of pollen. The planted trees from Memsen originated from the Greater Caucasus region and showed strong genetic divergence from German F. sylvatica populations, clearly differing in leaf morphological traits. In the future, the suitability of different provenances for the mitigation of climate change impacts should be carefully assessed by testing gene flow patterns as well as hybrid performance in additional stands and in comparison to F. sylvatica provenances from southern Europe.
•We calibrated the 3-PG model for Fagus sylvatica applying a Bayesian approach.•Model and climate change uncertainty affected significantly forest productivity.•Increasing thinning intensity appeared ...as the most robust management option.•Disregarding model, climate and economic uncertainty may lead to risky decisions.
To assess the long-term impacts of forest management interventions under climate change, process-based models, which allow to predict transient dynamics under environmental change, are arguably the most suitable tools available. A challenge for using these models for management decisions, however, is their higher parametric uncertainty, which propagates to predictions and thus into the decision-making process. Here, we demonstrate how this problem can be addressed through Bayesian inference. We first conduct a Bayesian calibration to generate an estimate of posterior parametric uncertainty for the process-based forest growth model 3-PG for Fagus sylvatica. The calibration uses data from twelve sites in Germany, together with a robust (Student’s t) error model. We then propagate the estimated uncertainty together with economic uncertainty to forest productivity and Land Expectation Value (LEV), allowing us to evaluate alternative management regimes under climate change. Our results demonstrate that parametric and economic uncertainty have strong impacts on the variation of predicted forest productivity and profitability. Management regimes with increased thinning intensity were overall most robust to economic, climate change and parametric model uncertainty. We conclude that estimating and propagating economic and model uncertainty is crucial for developing robust adaptive management strategies for forests under climate change.
•Current tree growth was modulated by the ecological memory of the past tree development.•Age, stem, and crown size only insufficiently reflected the trees' past.•Subdominant social position in the ...past was beneficial for tree growth at present.•Past progressive and smooth growth trajectories increased present tree growth.•Information about the trees' past growth pattern significantly improved growth prediction.
The growth of forest trees under given environmental conditions is assumed to depend mainly on their age, stem and crown size, and competitive position in the stand. The current stem and crown size are commonly recognized as adequate proxy markers for the tree's ecological memory of the past. In contrast, tree ring structure, crown whorl morphology, or other biographical patterns are rarely used for predicting growth. Here, we asked how the latter affect tree growth.
Our main hypothesis was that the growth in the longer past significantly co-determines the present growth. To test this hypothesis we derived metrics which quantify the social position, course of growth, and annual variation of trees in their past. We further selected variables for quantifying the trees' present stem and crown size and competitive status. Finally, we selected the approximately 200-years-old thinning experiment in European beech (Fagus sylvatica L.) Fabrikschleichach 15 in South Germany as our study object because it provided all required information.
To examine the dependency of the current growth on the present growing conditions and the past tree development more closely, we applied linear mixed models. They revealed that (i) trees with similar age, size, crown and competitive status at present grew better if they were subdominant in the past. (ii) Ceteris paribus, slow starting trees with progressive growth trajectories were associated with higher growth than quick starting trees with degressive growth trajectories. (iii) Trees with lower interannual variations of growth in the past had significantly higher growth rates at present than trees with higher interannual variations of growth in the past. (iv) Including information about the trees' past reduced the RSME of the diameter growth model by 17–27% and increased the R2 by 15–30%. Thus, the diameter growth model could achieve R2 values of 0.76–0.79. (v) The contribution of past information for estimating present growth was higher in periods without thinning.
We suggest that in the analysed European beech stands, even at parity of stem diameter or crown size, different courses of growth created different internal stem structures and crown morphologies. Such past structural and morphological formations may affect the tree's light interception and hydraulic conduction. These differences in structure may cause specific differences in the present tree functioning and growth. Of course these findings based on only one long-term experiment should not yet be generalized. However, the revealed relationship between the past and present growth deserves further investigations. We discuss the relevance of the ecological memory embedded in the past growth and in the tree ring pattern. We stress the consequences of the ecological memory for the monitoring, inventory, and modelling of tree growth and its implications for the development of silvicultural prescriptions.
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•Growth trend analysis in dry-marginal populations of 5 tree species in SE Europe.•Declining growth in Fagus and Tilia due to a deteriorating climate water balance.•Stable growth of ...the 3 Quercus species despite increasing climatic aridity.•Results suggest future species shifts from beech to oak in a warming climate.•Admixing oaks will make silviculture less susceptible to climate warming.
Global warming and increasing drought severity are exposing temperate forests to increasing stress, challenging silvicultural decision making. Growth analyses in marginal tree populations at drought-induced range limits may provide valuable information on tree species’ adaptive potentials and species-specific climate turning points. We studied the climate sensitivity and resilience to drought of radial growth, and long-term growth trends of mesic and rear-edge populations of Fagus sylvatica in comparison to three oak species (Quercus petraea, Q. frainetto, Q. cerris) and Tilia tomentosa in natural ecotones from mesic beech to xeric oak forests along three elevation transects in western Romania. Radial growth of all species was positively influenced by summer precipitation and low drought intensity, and negatively by high summer temperatures. The basal area increment (BAI) of F. sylvatica and T. tomentosa has declined in the last 10–20 years with warming and a deterioration of the summer water balance, while the three Quercus species maintained stable growth rates, though at lower BAI levels, suggesting a negative relationship between mean BAI and drought resistance among the five species. Growth reductions during three severe drought events (2000, 2003, 2012) were stronger, and growth resilience lower, in F. sylvatica and T. tomentosa than in the Quercus species, pointing at a thermal limit of beech at June–August temperatures of 20–21 °C. As the climate of the studied ecotones is similar to the predicted climate at colline/submontane elevation in Central Europe in about 50 years, a decline in beech growth and vitality is likely also in drought-affected regions in the distribution centre with future warming. Our results demonstrate that choosing stress-tolerant Q. petraea (as well as Q. frainetto and Q. cerris) instead of more productive timber species is a relatively safe option for Central European forestry in a warmer climate.
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