The paper analyzes the results of 26 years (1996-2021) of phenological observations of the vegetative organs of European beech (
L.) in the Western Carpathians. It evaluates the influence of the ...heterogeneity of this territory, including relief and elevation, based on climatic-geographical types.
Phenological stages, including leaf unfolding, full leaves, leaf coloring, and leaf fall, were monitored at 40 phenological stations across eight elevation zones. The study assesses trends in the occurrence of phenological stages, the length of the growing season, and phenological elevation gradients.
The results indicate a statistically significant earlier onset of spring phenological phases and delay in autumn phases, resulting in an average extension of the beech growing season by 12 days. Our findings confirm that the lengthening of the growing season due to warming, as an expression of climate change, is predominantly attributed to the warming in the spring months. The detected delayed onset of autumn phenophases was not due to warming in the autumn months, but other environmental factors influence it. The trend of elongation of the growing season (p<0.01) is observed in all elevation zones, with a less significant trend observed only in zones around 400 and 600 m a.s.l, signaling changes in environmental conditions across most of the elevation spectrum. Moreover, the heterogeneity of climatic-geographical types within each elevation zone increases the variability in the duration of the growing season for sites with similar elevations. By extending the growing season, it is assumed that the beech area will be changed to locations with optimal environmental conditions, especially in terms of adverse climatic events (late spring frosts, drought) during the growing season. The phenological elevation gradients reveal an earlier onset of 2.2 days per 100 m for spring phenophases and a delay of 1.1-2.9 days per 100 m for autumn phenophases.
These findings highlight the specific environmental conditions of European beech in the Western Carpathians and their potential for anticipating changes in its original area. Additionally, these observations can aid in forecasting the further development of phenological manifestations related to climate change.
The research presented herein explores soil organic carbon concentration (SOCC) under monodominant primeval forests of European beech trees and their association with parent material on a regional ...scale. Soil sampling to a maximum depth of 0.8 m was conducted in six localities in the West, East, and South Carpathians, Eastern Albanides, and Central Apennines, situated on different parent materials. Samples were analysed for SOCC by the dry combustion method. The average SOCC values representing individual localities ranged from 12.5 g kg−1 to 154.8 g kg−1 with a 99.7% coefficient of variation. SOCC association with climatic variables and forest stand volume data available from the literature were assessed by a Pearson correlation coefficient. Differences in SOCC among localities caused by site conditions were treated as a fixed factor in Welch’s ANOVA and found to be significant (p < 0.05) in the majority of cases. The associations between SOCC and climatic variables or stand volume were nonsignificant or perturbed. Since they validly explained less than 10% of the overall SOCC variance, the results of multiple comparison tests were assessed and interpreted in view of distinct parent materials.
Covering large parts of Europe, Norway spruce (Picea abies L Karst.) plays an important role in the adaptation strategy of forest services to future climate change. Although dendroecology can provide ...valuable information on the past relationships between tree growth and climate, most previous studies were biased towards species-specific distribution limits, where old individuals grow slowly under extreme conditions. In the present study, we investigated the growth variability and climate sensitivity of 2851 Norway spruce trees along longitudinal (E 12–26°), latitudinal (N 45–51°), and elevation (118–1591 m a.s.l.) gradients in central-eastern Europe. We reveal that summer weather significantly affects the radial growth of spruce trees, but the effects strongly vary along biogeographical gradients. Extreme summer heatwaves in 2000 and 2003 reduced the growth rates by 10–35%, most pronounced in the southern Carpathians. In contrast to the population in the Czech Republic, climate warming induced a synchronous decline in the growth rates across biogeographical gradients in the Carpathian arc. By demonstrating the increased vulnerability of Norway spruce under warmer climate conditions, we recommended that the forest services and conservation managers replace or admix monocultures of this species with more drought-resilient mixtures including fir, beech and other broadleaved species.
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•Major summer heatwaves synchronized growth reactions across biogeographic gradients.•Populations in southern latitudes and lower elevations are more vulnerable to drought.•Spruce has strongly suffered from climate warming and environmental pollution.•Spruce monospecific forests should be admixed with better-adapted species.
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•Size-asymmetric and inter-specific competition drove tree growth in mixtures.•Tree growth and size of Scots pine was higher in mixtures compared to monocultures.•Drought drove tree ...growth for both species, but temperature only affects pine.•Weather conditions modified inter-specific tree competition for both species.•Growth reduction of Norway spruce in mixtures may be offset by faster Scots pine growth.
Mixed forests are suggested as a strategic adaptation of forest management to climate change. Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) are tree species of high economic and ecological value for European forestry. Both species coexist naturally in a large part of their distributions but there is a lack of knowledge on the ecological functioning of mixtures of these species and how to manage such stands. This paper analyses these species’ intra- and inter-specific competition, including size-symmetric vs. size-asymmetric competition, and explore the effect of weather conditions on tree growth and competition. We studied basal area growth at tree level for Scots pine and Norway spruce in mixed versus pure stands in 22 triplets of fully-stocked plots along a broad range of ecological conditions across Europe. Stand inventory and increment cores provided insights into how species mixing modifies tree growth compared with neighbouring pure stands. Five different competition indices, weather variables and their interactions were included and checked in basal area growth models using a linear mixed model approach. Interspecific size-asymmetric competition strongly influenced growth for both tree species, and was modulated by weather conditions. However, species height stratification in mixed stands resulted in a greater tree basal area growth of Scots pine (10.5 cm2 year−1) than in pure stands (9.3 cm2 year−1), as this species occupies the upper canopy layer. Scots pine growth depended on temperature and drought, whereas Norway spruce growth was influenced only by drought. Interspecific site-asymmetric competition increased in cold winters for Scots pine, and decreased after a drought year for Norway spruce. Although mixtures of these species may reduce tree size for Norway spruce, our results suggest that this could be offset by faster growth in Scots pine. How inter-specific competition and weather conditions alter tree growth may have strong implications for the management of Scots pine-Norway spruce mixtures along the rotation period into the ongoing climate change scenario.
•Mixtures showed a significantly higher basal area increment than monocultures.•Transgressive overyielding was detected in 35% of the sites and degressive underyielding in 15%•Higher stratification ...was found in mixed-species stands with a strong effect on productivity.•Site conditions have a limited impact on productivity.
Mixed-species stands have been found to be more productive than would be expected from the performance of their component species in monocultures due to facilitation and complementarity between species, although these interactions depend on the combination of species present. Our study focuses on monospecific and mixed-species stands of Scots pine and Norway spruce using 20 triplets established in nine countries along a climatic gradient across Europe. Differences in mean tree and stand characteristics, productivity and stand structure were assessed. Basal area increment in mixed stands was 8% higher than expected while volume increment was only 2% greater. Scots pine trees growing in mixed-species stands showed 11% larger quadratic mean diameter, 7% larger dominant diameter, 17% higher basal area and 25% higher stand volume than trees growing in monospecific stands. Norway spruce showed only a non-significant tendency to lower mean values of diameters, heights, basal area, as well standing volume in mixtures than monocultures. Stand structure indices differed between mixed stands and monocultures of Scots pine showing a greater stratification in mixed-species stands. Furthermore, the studied morphological traits showed little variability for trees growing in monospecific stands, except for diameter at breast height, crown length and crown length ratio. For trees growing in mixed stands, all the morphological traits of the trees were identified as different. Some of these morphological traits were associated with relative productivity. Nevertheless, relative productivity in mixed-species stands was not related to site conditions.
Climate change is increasing the severity and frequency of droughts around the globe, leading to tree mortality that reduces production and provision of other ecosystem services. Recent studies show ...that growth of mixed stands may be more resilient to drought than pure stands. The two most economically important and widely distributed tree species in Europe are Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.), but little is known about their susceptibility to drought when coexist.
This paper analyses the resilience (resistance, recovery rate and recovery time) at individual‐tree level using a network of tree‐ring collections from 22 sites along a climatic gradient from central Europe to Scandinavia. We aimed to identify differences in growth following drought between the two species and between mixed and pure stands, and how environmental variables (climate, topography and site location) and tree characteristics influence them.
We found that both the timing and duration of drought drive the different responses between species and compositions. Norway spruce showed higher vulnerability to summer drought, with both lower resistance and a longer recovery time than Scots pine. Mixtures provided higher drought resistance for both species compared to pure stands, but the benefit decreases with the duration of the drought. Especially climate sensitive and old trees in climatically marginal sites were more affected by drought stress.
Synthesis. Promoting Scots pine and mixed forests is a promising strategy for adapting European forests to climate change. However, if future droughts become longer, the advantage of mixed stands could disappear which would be especially negative for Norway spruce.
Mixtures of Scots pine and Norway spruce provided higher drought resistance for both species compared to pure stands, but the benefit decreases with drought duration. Norway spruce showed higher vulnerability to summer drought, with both lower resistance and a longer recovery time. Promoting Scots pine and mixed forests is a promising strategy for adapting European forests to climate change.
A random intercept for each triplet and year for Quercus robur and Quercus petraea (top) and Pinus sylvestris (bottom) showing the inter-annual variation in diameter increment on different sites at ...the logarithmic scale in mm.
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•Tree growth reactions to climate are highly site-specific within a bioclimatic zone.•Local (micro)-site conditions outweigh large-scale climatic patterns.•Tree growth reactions to climate are dependent on relative tree size.•Growth sharply declines with increasing potential evapotranspiration in June.•Species identity and mixture effects clearly differ between years at the same site.
Quercus robur/Quercus petraea and Pinus sylvestris are widely distributed and economically important tree species in Europe co-occurring on mesotrophic, xeric and mesic sites. Increasing dry conditions may reduce their growth, but growth reductions may be modified by mixture, competition and site conditions. The annual diameter growth in monospecific and mixed stands along an ecological gradient with mean annual temperatures ranging from 5.5 °C to 11.5 °C was investigated in this study. On 36 triplets (108 plots), trees were cored and the year-ring series were cross-dated, resulting in year-ring series of 785 and 804 trees for Q. spp. and P. sylvestris, respectively. A generalized additive model with a logarithmic link was fit to the data with random effects for the intercept at the triplet, year and tree level and a random slope for the covariate age for each tree; the Tweedie-distribution was used. The final model explained 87 % of the total variation in diameter increment for both tree species. Significant covariates were age, climate variables (long-term mean, monthly), local competition variables, relative dbh, mixture, stand structure and interactions thereof. Tree growth declined with age and local density and increased with social position. It was positively influenced by mixture and structural diversity (Gini coefficient); mixture effects were significant for P. sylvestris only. The influence of potential evapotranspiration (PET) in spring and autumn on tree growth was positive and non-linear, whereas tree growth sharply decreased with increasing PET in June, which proved to be the most influential month on tree growth along the whole ecological gradient. Interactions of PET with tree social position (relative dbh) were significant in July and September for Q. spp. and in April for P. sylvestris. Interactions of climate with density or mixture were not significant. Climatic effects found agree well with previous results from intra-annual growth studies and indicate that the model captures the causal factors for tree growth well. Furthermore, the interaction between climate and relative dbh might indicate a longer growth duration for trees of higher social classes. Analysis of random effects across time and space showed highly dynamic patterns, with competitive advantages changing annually between species and spatial patterns showing no large-scale trends but pointing to the prevalence of local site factors. In mixed-species stands, the tree species have the same competitivity in the long-term, which is modified by climate each year. Climate warming will shift the competitive advantages, but the direction will be highly site-specific.
The increasing disturbances in monocultures around the world are testimony to their instability under global change. Many studies have claimed that temporal stability of productivity increases with ...species richness, although the ecological fundamentals have mainly been investigated through diversity experiments. To adequately manage forest ecosystems, it is necessary to have a comprehensive understanding of the effect of mixing species on the temporal stability of productivity and the way in which it is influenced by climate conditions across large geographical areas.
Here, we used a unique dataset of 261 stands combining pure and two‐species mixtures of four relevant tree species over a wide range of climate conditions in Europe to examine the effect of species mixing on the level and temporal stability of productivity. Structural equation modelling was employed to further explore the direct and indirect influence of climate, overyielding, species asynchrony and additive effect (i.e. temporal stability expected from the species growth in monospecific stands) on temporal stability in mixed forests.
We showed that by adding only one tree species to monocultures, the level (overyielding: +6%) and stability (temporal stability: +12%) of stand growth increased significantly. We identified the key effect of temperature on destabilizing stand growth, which may be mitigated by mixing species. We further confirmed asynchrony as the main driver of temporal stability in mixed stands, through both the additive effect and species interactions, which modify between‐species asynchrony in mixtures in comparison to monocultures.
Synthesis and applications. This study highlights the emergent properties associated with mixing two species, which result in resource efficient and temporally stable production systems. We reveal the negative impact of mean temperature on temporal stability of forest productivity and how the stabilizing effect of mixing two species can counterbalance this impact. The overyielding and temporal stability of growth addressed in this paper are essential for ecosystem services closely linked with the level and rhythm of forest growth. Our results underline that mixing two species can be a realistic and effective nature‐based climate solution, which could contribute towards meeting EU climate target policies.
Resumen
Las cada vez más frecuentes perturbaciones en masas forestales monoespecíficas en todo el mundo, son una muestra de su inestabilidad bajo el cambio climático. Numerosos estudios indican que la estabilidad temporal de la productividad aumenta con la riqueza de especies, aunque los fundamentos ecológicos de esta relación se han estudiado principalmente en experimentos de diversidad de especies. Para una gestión adecuada de los ecosistemas forestales, es necesaria una mejor comprensión del efecto de la mezcla de especies en la estabilidad temporal de la productividad y de cómo esta se ve modificada por las condiciones climáticas.
En este trabajo usamos una base de datos única de 261 masas monoespecíficas y mixtas de dos especies a largo de un amplio rango de condiciones climáticas para examinar el efecto de la mezcla de especies en el nivel y estabilidad temporal de la productividad. Las mezclas estudiadas son combinaciones de dos especies entre cuatro de las especies forestales más relevantes en Europa. Se utilizan modelos de ecuaciones estructurales para explorar la influencia directa e indirecta del clima, el mayor crecimiento en mixtas que en puras (overyielding), la asincronía entre especies y el efecto aditivo (estabilidad temporal esperada según el crecimiento de las dos especies en las masas puras) en la estabilidad temporal en masas mixtas.
Los resultados muestran que añadiendo solo una especie a las masas monoespecíficas el nivel (overyielding: +6%) y la estabilidad temporal (+12%) del crecimiento aumentan significativamente. Se ha identificado que la temperatura tiene un efecto clave en la desestabilización del crecimiento, que puede ser mitigado en parte por la mezcla de especies. Se confirma que la asincronía, a través del efecto aditivo y de la interacción de especies (que modifica la asincronía entre especies en masas mixtas con respecto a la de las masas monoespecíficas), es el principal factor que explica la mayor estabilidad temporal en masas mixtas.
Síntesis y aplicaciones. Este estudio revela las propiedades emergentes asociadas a la mezcla de dos especies, que resultan en sistemas de producción eficientes y estables. Se identifica el impacto negativo de las temperaturas en la estabilidad temporal de la productividad y cómo el efecto estabilizador de la mezcla de dos especies puede contrarrestar este impacto. El nivel y la estabilidad temporal del crecimiento estudiados en este trabajo son fundamentales en los servicios ecosistémicos ligados al nivel y el ritmo del crecimiento forestal. Los resultados subrayan que la mezcla de dos especies puede ser una realista y efectiva solución climática basada en la naturaleza, que contribuya a cumplir los objetivos climáticos de la EU.
This study highlights the emergent properties associated with mixing two‐species, which result in resource efficient and temporally stable production systems. We reveal the negative impact of mean temperature on temporal stability of forest productivity and how the stabilizing effect of mixing two species can counterbalance this impact. The overyielding and temporal stability of growth addressed in this paper are essential for ecosystem services closely linked with the level and rhythm of forest growth. Our results underline that mixing two species can be a realistic and effective nature‐based climate solution, which could contribute towards meeting EU climate target policies.
•The study based on 90 mature Scots pine stands along a productivity gradient across Europe.•Growth partitioning became more asymmetric and structuring with increasing site quality.•Mortality ...eliminated predominantly small trees with increasing site quality.•We found the highest size variation on poor sites and the lowest on rich sites.•As a result stand structure became more homogeneous with increasing site quality.
Heterogeneity of structure can increase mechanical stability, stress resistance and resilience, biodiversity and many other functions and services of forest stands. That is why many silvicultural measures aim at enhancing structural diversity. However, the effectiveness and potential of structuring may depend on the site conditions. Here, we revealed how the stand structure is determined by site quality and results from site-dependent partitioning of growth and mortality among the trees. We based our study on 90 mature, even-aged, fully stocked monocultures of Scots pine (Pinus sylvestris L.) sampled in 21 countries along a productivity gradient across Europe. A mini-simulation study further analyzed the site-dependency of the interplay between growth and mortality and the resulting stand structure. The overarching hypothesis was that the stand structure changes with site quality and results from the site-dependent asymmetry of competition and mortality.
First, we show that Scots pine stands structure across Europe become more homogeneous with increasing site quality. The coefficient of variation and Gini coefficient of stem diameter and tree height continuously decreased, whereas Stand Density Index and stand basal area increased with site index.
Second, we reveal a site-dependency of the growth distribution among the trees and the mortality. With increasing site index, the asymmetry of both competition and growth distribution increased and suggested, at first glance, an increase in stand heterogeneity. However, with increasing site index, mortality eliminates mainly small instead of all-sized trees, cancels the size variation and reduces the structural heterogeneity.
Third, we modelled the site-dependent interplay between growth partitioning and mortality. By scenario runs for different site conditions, we can show how the site-dependent structure at the stand level emerges from the asymmetric competition and mortality at the tree level and how the interplay changes with increasing site quality across Europe.
Our most interesting finding was that the growth partitioning became more asymmetric and structuring with increasing site quality, but that the mortality eliminated predominantly small trees, reduced their size variation and thus reversed the impact of site quality on the structure. Finally, the reverse effects of mode of growth partitioning and mortality on the stand structure resulted in the highest size variation on poor sites and decreased structural heterogeneity with increasing site quality. Since our results indicate where heterogeneous structures need silviculture interventions and where they emerge naturally, we conclude that these findings may improve system understanding and modelling and guide forest management aiming at structurally rich forests.
•Patterns of mixing effects on pine/beech growth-climate relationships were analyzed across Europe.•Tree growth-climate relationships were driven by the regional climate conditions.•Differences in ...climate-growth relationships between pure and mixed beech stands were evidenced in the driest climates.•On average, mixing had no significant effect on resistance to drought events.•Growth reduction during drought events was lower in mixed compared to pure pine stands in sites with higher water balance in autumn.
Increasing species diversity is considered a promising strategy to mitigate the negative impacts of global change on forests. However, the interactions between regional climate conditions and species-mixing effects on climate-growth relationships and drought resistance remain poorly documented.
In this study, we investigated the patterns of species-mixing effects over a large gradient of environmental conditions throughout Europe for European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.), two species with contrasted ecological traits. We hypothesized that across large geographical scales, the difference of climate-growth relationships and drought resistance between pure and mixed stands would be dependent on regional climate. We used tree ring chronologies derived from 1143 beech and 1164 pine trees sampled in 30 study sites, each composed of one mixed stand of beech and pine and of the two corresponding pure stands located in similar site conditions. For each site and stand, we used Bootstrapped Correlation Coefficients (BCCs) on standardized chronologies and growth reduction during drought years on raw chronologies to analyze the difference in climate-tree growth relationships and resistance to drought between pure and mixed stands.
We found consistent large-scale spatial patterns of climate-growth relationships. Those patterns were similar for both species. With the exception of the driest climates where pure and mixed beech stands tended to display differences in growth correlation with the main climatic drivers, the mixing effects on the BCCs were highly variable, resulting in the lack of a coherent response to mixing. No consistent species-mixing effect on drought resistance was found within and across climate zones. On average, mixing had no significant effect on drought resistance for neither species, yet it increased pine resistance in sites with higher climatic water balance in autumn. Also, beech and pine most often differed in the timing of their drought response within similar sites, irrespective of the regional climate, which might increase the temporal stability of growth in mixed compared to pure stands.
Our results showed that the impact of species mixing on tree response to climate did not strongly differ between groups of sites with distinct climate characteristics and climate-growth relationships, indicating the interacting influences of species identity, stand characteristics, drought events characteristics as well as local site conditions.
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