Climate is a strong predictor of the geographic distribution of tree species, and thus climate change may trigger shifts in the distribution of a tree species and/or its demographic structure. In the ...study, we aim to comprehensively compare the distributions of four life stages of European beech (Fagus sylvatica) (i.e., regeneration, recruitment, young trees and mature trees) in forests in Slovenia, Central Europe, which are characterized by strong gradients of elevation (ELV), temperature (TEMP) and precipitation (PREC) to detect possible shifts in distribution and demography. Beech life stages were surveyed on 3366 plots. To depict disparities between ELV, TEMP and PREC distributions of beech life stages, we applied several non-parametric methods: basic statistical tests to study differences in medians, means, and 1st and 9th deciles; generalized additive models to study shifts in the optimum; and extreme value analysis to study shifts at the trailing and leading edges. A substantial shift in juvenile beech stages upward and toward colder sites was detected. However, the shift was not uniform along the distributions; the most significant shift was detected at the leading edge of ELV (+73 m) and TEMP (−2.6 °C), but surprisingly there was no beech movement identified at the trailing edge. The observed shift may be a result of the interplay between climate change, high spatial variability in microclimate, unexceptional droughts in the recent past, changes in forest use and possible limitations in the migration ability of beech and its adaptation capacity.
The role of forests in mitigating climate change by acting as a carbon sink is becoming increasingly important. Forest management practices can either positively or negatively affect the ability of ...forests to mitigate climate change. The objectives of our study were to: (a) investigate the effects of natural disturbances on long-term carbon sequestration dynamics in forests and (b) identify opportunities to adapt current forest management practices to increase carbon sequestration in forests. The study focused on mixed mountain forests in the Slovenian Alps, dominated by Norway spruce, and used the SLOMATRIX model to simulate forest development. Three forest management scenarios were simulated: (1) no management, (2) business-as-usual and (3) an optimized scenario maximizing carbon sequestration in forests while achieving the required harvest. Our results indicate that both forest management practices and natural disturbances have an impact on carbon sequestration dynamics. Optimizing harvests resulted in changes in the diameter structure and species composition of the harvested trees. Although natural disturbances can hinder the mitigation of climate change impacts, they can also catalyze forest adaptation to climate change and reduce the time required to reach carbon equilibrium.
Questions
What is the long‐term impact of deer browsing on the diversity of the herbaceous layer and tree species regeneration? Which parameters of regeneration of the tree species regeneration and ...the herbaceous layer best indicate browsing impact?
Study site
Dinaric Mountains, Slovenia.
Methods
We studied the long‐term impact of red deer on mixed temperate forests by comparing the tree species regeneration and herbaceous layer vegetation under two treatments: deer present, no deer. We analyzed the regeneration of trees older than one year up to a diameter at breast height of 10 cm (categorized into five height classes) and the cover abundance of plant species in the herbaceous layer (<50 cm).
Results
There were no significant differences between the treatments in the number of tree species regeneration. Browsing impact on the most abundant tree species—European beech, silver fir and sycamore—varied, indicating differences in palatability. When deer were present, the number of silver fir regenerating was significantly lower in all height classes, and regeneration of European beech specimens shorter than 50 cm was more abundant, while for sycamore shorter seedlings (<20 cm) were more abundant, and regeneration of taller specimens (≥50 cm) was significantly less abundant. The reduction of tree species diversity during natural regeneration is evident. There were no significant differences between the treatments in the number and diversity of plant species in the herbaceous layer; however, the abundance of 13 plant species differed significantly between the treatments. Deer reduce the density of tree species saplings due to long‐term browsing and thus indirectly increase tree species diversity in the regeneration up to 20 cm in height and plant species diversity in the herbaceous layer.
Conclusions
We documented the direct and indirect impact of deer on the diversity of tree species regeneration, but only found an indirect influence on the diversity of the herbaceous layer. The height structure of palatable tree species regeneration appears to be the most appropriate indicator of browsing impact. The observed browsing impact leads to the complete dominance of European beech in the tree species composition of forest stands.
Naturally regenerating tree species showed different, size‐dependent responses to the impact of red deer. Deer prevented recruitment of palatable tree species above the browse layer. No plant species in the herbaceous layer went locally extinct because of deer; however, deer influenced the abundance of some plant species. Deer indirectly increased plant species diversity in the herbaceous layer by reducing the density of tree saplings.
•Soil is a stronger driver of forest productivity than climate or topography.•Stand and tree growth rates differ significantly between soil units.•The soil unit is a more important variable in tree ...growth than in stand growth.•Most tree species exhibit the highest and the lowest growth on different soil units.•Most of the studied tree species grow most poorly on calcareous Leptosols.
We determined the size of differences in stand and tree growth in semi-natural forests with respect to 16 reference soil groups. The forest area of Slovenia (11.8 thousand km2) was used as the study area, and reference soil units were derived from the national soil map at a 1:25,000 scale consisting of 10,781 polygons with an average size of 117.95 ha. Stand growth was defined as periodic stand basal area increment, while the growth of Norway spruce, silver fir, Scots pine, European beech and sessile oak trees was estimated by the periodic diameter increment of 238,349 dominant trees on 67,061 permanent sampling plots. A linear fixed-effects model and linear mixed-effect models were used for studying stand and tree growth in different site, stand and tree conditions. The soil unit was the dummy variable with Dystric Cambisols set as the reference category. Soil contributed 4.3 % to the explained variability of basal area increment and 4–27 % to the explained variability of the diameter increment of the five tree species. Soil was a stronger driver of stand and tree growth than climate or topography. Stand and tree species production rate on soil units was in the interval of −28 % to +5 % and −47 % to +14 % of that on the reference soil unit, respectively. Stand growth was the highest on Eutric Gleysols and the lowest on Histosols, and tree species generally exhibited the highest and the lowest growth rates on different soil units. We suggest that soil should be considered in growth models and studied interrelatedly with climatic, site and stand variables.
With the advent of global warming, forests are becoming an increasingly important carbon sink that can mitigate the negative effects of climate change. An understanding of the carbon dynamics of ...forests is, therefore, crucial to implement appropriate forest management strategies and to meet the expectations of the Paris Agreement with respect to international reporting schemes. One of the most frequently used models for simulating the dynamics of carbon stocks in forests is the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3). We applied this model in our study to evaluate the effects of harvesting on the carbon sink dynamics in Slovenian forests. Five harvesting scenarios were defined: (1) business as usual (BAU), (2) harvesting in line with current forest management plans (PLAN), (3) more frequent natural hazards (HAZ), (4) high harvest (HH) and (5) low harvest (LH). The simulated forest carbon dynamics revealed important differences between the harvesting scenarios. Relative to the base year of 2014, by 2050 the carbon stock in above-ground biomass is projected to increase by 28.4% (LH), 19% (BAU), 10% (PLAN), 6.5% (HAZ) and 1.2% (HH). Slovenian forests can be expected to be a carbon sink until harvesting exceeds approximately 9 million m3 annually, which is close to the calculated total annual volume increase. Our results are also important in terms of Forest Reference Levels (FRL), which will take place in European Union (EU) member states in the period 2021–2025. For Slovenia, the FRL was set to −3270.2 Gg CO2 eq/year, meaning that the total timber harvested should not exceed 6 million m3 annually.
Abstract
In northern temperate forests, ice storms are a common disturbance agent, though climate change may alter their occurrence patterns. Their impact on forest ecosystems is complex, as they ...influence both structure and processes. In 2014, an ice storm of high intensity and large spatial extent occurred in Slovenia, Central Europe, which enabled a detailed study of ice damage to individual trees across a broader spatial scale. Pre- and post-ice storm measurement data on 11 414 trees on 960 permanent plots were used to examine ice damage patterns on trees in the disturbed forest area (~8700 km2) to determine the predictors of ice damage to trees and to investigate the relative susceptibility of eight groups of tree species in mixed Central European forests. We used a novel approach to modelling ice-storm intensity across the region based on measured data on air temperature, precipitation amount and duration, precipitation intensity and wind speed. The ice storm damaged 31 percent of the analysed trees; high variability in the damage rate was observed across the disturbed area. For the tree species, a susceptibility to ice damage index (SI) ranging between 0 (no damage) and 1 (complete damage) was calculated based on terrestrial assessment of trees. Tree species differed significantly in susceptibility to ice damage: Abies alba (SI = 0.14) and Quercus sp. (SI = 0.11) were rather resistant; Picea abies, Fagus sylvatica and Acer sp. (SI = 0.23–0.28) were moderately to very susceptible; and Pinus sp. (SI = 0.62) was extremely susceptible to ice damage. Eight predictors and three interactions were included in an ordinal logistic regression model of tree damage: ice damage on trees depends mainly on ice-storm intensity, elevation and tree species, whilst tree dbh and social status, tree size and tree species diversity indices and slope were relatively less important. Our study illustrates the complexity of damage patterns on trees due to ice storms and the significance of ice-storm intensity and tree species as predictors when modelling ice damage on individual trees.
We studied the impacts of site, stand and tree variables on the diameter growth of beech trees (
Fagus
sylvatica
L.) on carbonate bedrock and examined to what extent the regional diameter growth ...model can be used at the forest type level. Based on 12,193 permanent sampling plots (500 m
2
each) with 94,770 beech trees, we first developed a linear mixed-effect model of the periodic diameter increment at the regional level (Dinaric region, Slovenia, 1.7 thousand km
2
). Subsequently, we parametrized the model for five forest types within the region (submontane, thermophilous, montane, upper montane and subalpine) and used a homogeneity-of-slopes model to test whether the covariates have different effects in the five forest types. The regional model suggested the positive impact of tree diameter (nonlinear), tree diameter diversity, mean diurnal temperature range and mean annual temperature and the negative impact of basal area, proportion of beech, inclination, rockiness and annual amount of precipitation. Stand basal area and the proportion of beech contributed > 50% of the total explained diameter increment variability, followed by tree diameter (44%), topographic (3%) and climatic variables (< 2%). The regional model was well transferable to forest types; the only variable with a significantly different effect in forest types was tree diameter. However, models at the forest type level differed with respect to the slopes and significance of several predictors, wherein coefficients for some predictors were even of opposite sign. Not all predictors from the regional model were included in the forest type models if predictor selection and model parameterization were performed independently for each forest type. Our study suggests that some growth characteristics of beech can be detected at the regional level only, while analyses at the forest type level can reveal significant differences in beech growth response to tree, stand and environmental variables.
•The suggested procedure enables estimation of tree species composition alteration.•The alteration was primarily the result of past land use and forest management.•The alteration decreased along the ...gradients of rockiness, inclination and elevation.•Greater alteration appeared in areas closer to forest edge.•The alteration increased the susceptibility of forest stands to natural disturbances.
The alteration of natural tree species composition is defined as the deviation of the current tree species composition from that of the natural state. It can be used as a measure of human influence on forest vegetation, and thus as an indicator of the naturalness of forest vegetation. The aim of the study was to develop a standard procedure for estimating the alteration of natural tree species composition, to explain factors driving alteration and to examine its significance for susceptibility of forest stands to natural disturbances. The alteration of natural tree species composition was estimated for the Dinaric region (5556km2, Slovenia) by the Robič Index of Dissimilarity (RID), ranging from 0 (completely natural) to 100 (completely altered). The index was calculated on the compartment level (24ha each on average) with data on current and potential natural forest vegetation. The influence of human activities on tree species alteration was examined by using topographic and accessibility variables. The susceptibility of forest stands to natural disturbances was analysed with data on sanitary felling. In the study area, the natural tree species composition of forest stands is moderately preserved; the average value of RID was 50.05, ranging from 1.76 to 100, and the coefficient of variation was 0.49. The alteration of the natural tree species composition of forest stands is primarily the result of forest management and past land use, conditioned either by topography or accessibility of forests. The degree of alteration of tree species composition decreased along the gradients of rockiness, inclination and elevation. A greater degree of alteration appeared on the slopes of intermediate and south facing aspects than on north facing slopes, and in areas that were closer to the forest edge. A higher level of alteration significantly increases the susceptibility of forest stands to natural disturbances. The procedure represents a novel approach in modelling the alteration (naturalness) of tree species composition of forest vegetation. It is applicable at different spatial scales and fosters an understanding of the patterns of tree species composition under the influence of human activity across forest landscapes.
In the Dinaric Mountains, the future of silver fir and Norway spruce appears to be uncertain, especially given the threat of climate change to both species and browsing pressure on fir. Stand ...development of mixed Dinaric mountain forest in Slovenia was simulated for the period 2010–2110 using the ForClim model to explore the prospects of both target species under five management scenarios (business-as-usual, no management, single-tree selection, fir conservation and exclusion of browsing) and three climate scenarios (current climate and two climate change scenarios). Simulations under the current climate revealed a decrease in fir proportion from 53% in 2010 to 14–37% in 2110, while the proportion of spruce remained relatively constant (13% in 2010 and 9–13% in 2110). Climate change may intensify the decline of both species along an elevation gradient. An upward shift was projected for fir in the observed period; in low-elevation stands (600–800 m a.s.l.), fir could almost disappear, while at high elevations (1050–1400 m a.s.l.), our simulations projected an increase in the proportion of both fir and spruce. No single management strategy proved to be significantly beneficial for either species. The most promising strategies were the fir conservation-oriented scenario and the exclusion of browsing; large ungulates strongly impacted the development of fir, but not that of spruce. Forest management affords different options for maintaining both species, but its capacity to prevent fir decline under climate change and high browsing pressure is limited. Concurrent measures of wildlife management and silviculture should be applied to maintain conifers in the studied forests.
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