Central European Forests Research Articles

Foraging distances, habitat preferences and seasonal colony performance of honeybees in Central European forest landscapes

Abstract Unmanaged forest is considered as native habitat of the Western honeybee Apis mellifera and is assumed to provide important pollen and nectar sources. However, resource supply might be spatially and temporally restricted in managed forests and landscape‐scale studies in European forest regions are currently lacking. Capitalizing on a unique communication behaviour, the waggle dance, we investigated honeybee foraging in a deciduous forest region in southern Germany. We analysed 2022 waggle dances performed by bees of 12 colonies placed in the centre of landscapes with varying degree of forest cover (50%–99% at a 2‐km radius) from March to August 2019, thereby identifying foraging distances and habitat preferences over almost an entire foraging season. By connecting dance information with colony weight recordings, we assessed the role of landscape composition and the contribution of different habitat types to colony weight gain. Foraging distances generally increased with the amount of forest in the surrounding landscape pointing to inferior food resources in the forest. Yet, this effect strongly depended on the season and was more pronounced for pollen than for nectar foraging. Even though colonies in forest‐dominated landscapes had to fly further, colony weight was not significantly affected by forest cover. Compared to expectations based on the proportions of different habitats, colonies foraged more frequently in grassland and cropland than in deciduous and coniferous forests, with late summer being an especially difficult period for pollen foraging in forests. During a phase of colony weight gain in early summer, the use of forests for nectar/honeydew foraging was close to the expectation, highlighting forests as an important complementary source of carbohydrates during short periods of the year. Policy implication. The ecological and economic value of managed forest as habitat for honeybees could be significantly increased by the continuous provision of floral resources, especially for pollen foraging. Therefore, we recommend diversifying forest stands with insect‐pollinated trees, permitting secondary successions in forest gaps, and at larger scales, creating forest landscapes with high habitat diversity. This will not only help native, wild‐living honeybees and beekeepers' colonies residing in forest areas but will also foster social bees in general.

Stand structure of Central European forests matters more than climate for transpiration sensitivity to VPD

Abstract Temperature rise and more severe and frequent droughts will alter forest transpiration, thereby affecting the global water cycle. Yet, tree responses to increased atmospheric vapour pressure deficit (VPD) and reduced soil water content (SWC) are not fully understood due to long‐term tree adjustments to local environmental conditions that modify transpiration responses to short‐term VPD and SWC changes. We analysed sap flux density (SFD) of Fagus sylvatica, Picea abies, Pinus sylvestris and Quercus ilex from 25 sites across Europe to understand how daily variation in SWC affects the sensitivity of SFD to VPD (βVPD) and the maximum SFD (S95). Furthermore, we tested whether long‐term adjustments to site climatic conditions and stand characteristics affect βVPD and S95. The studied species showed contrasting βVPD and S95 with the largest values in F. sylvatica, followed by Q. ilex, which surpassed the two conifers that showed low βVPD and low S95. We observed that βVPD and S95 dropped during days of low SWC in F. sylvatica, P. sylvestris and Q. ilex, but not in P. abies. Both βVPD and S95 were driven by tree height, and the temperature and precipitation at the sites. However, stand basal area was the most important driver of βVPD and S95, explaining 30% of their total variance. Synthesis and applications: A future warmer and drier climate will restrict tree transpiration and thereby heavily affect the soil–plant‐atmosphere coupling. However, the effect of basal area, being the largest driver of tree transpiration sensitivity to vapour pressure deficit across a broad range of conditions, provides the opportunity to pre‐adapt European forests to future climate conditions. While stand thinning can increase the soil water availability for remaining trees, it also increases transpiration sensitivity to high air temperatures and may thereby amplify tree vulnerability to heat and drought.

Forest growth responds more to air pollution than soil acidification.

The forests of central Europe have undergone remarkable transitions in the past 40 years as air quality has improved dramatically. Retrospective analysis of Norway spruce (Picea abies) tree rings in the Czech Republic shows that air pollution (e.g. SO2 concentrations, high acidic deposition to the forest canopy) plays a dominant role in driving forest health. Extensive soil acidification occurred in the highly polluted "Black Triangle" in Central Europe, and upper mineral soils are still acidified. In contrast, acidic atmospheric deposition declined by 80% and atmospheric SO2 concentration by 90% between the late 1980s and 2010s. In this study we oserved that annual tree ring width (TRW) declined in the 1970s and subsequently recovered in the 1990s, tracking SO2 concentrations closely. Furthermore, recovery of TRW was similar in unlimed and limed stands. Despite large increases in soil base saturation, as well as soil pH, as a result of repeated liming starting in 1981, TRW growth was similar in limed and unlimed plots. TRW recovery was interrupted in 1996 when highly acidic rime (originating from more pronounced decline of alkaline dust than SO2 from local power plants) injured the spruce canopy, but recovered soon to the pre-episode growth. Across the long-term site history, changes in soil chemistry (pH, base saturation, Bc/Al soil solution ratio) cannot explain observed changes in TRW at the two study sites where we tracked soil chemistry. Instead, statistically significant recovery in TRW is linked to the trajectory of annual SO2 concentrations or sulfur deposition at all three stands.

Qualitative and Quantitative Changes in Soil Organic Compounds in Central European Oak Forests with Different Annual Average Precipitation

The various climate scenarios consistently predict warming and drying of forests in Hungary. Soils play a significant role in the long-term sequestration of atmospheric CO2, while in other cases they can also become net carbon emitters. Therefore, it is important to know what can be expected regarding future changes in the carbon storage capacity of soils in forests. We used precipitation gradient studies to solve this problem, using a type of “space–time” substitution. In this research, we primarily examined the quality parameters of soil organic matter (SOM) to investigate how climate change transforms the ratio of the main SOM compound groups in soils. For our studies, we applied elemental and 13C and 15N isotopic ratio analysis, NMR analysis, FT-IR spectra analysis, thermogravimetric and differential thermal analyses to measure SOM chemistry in samples from different oak forests with contrasting mean annual precipitation from Central Europe. Our results showed that soil organic carbon (SOC) was lower in soils of humid forests due to the enhanced decomposition processes and the leaching of Ca, which stabilizes SOM; however, in particular, the amount of easily degradable SOM compounds (e.g., thermolabile SOM, O-alkyl carbon, carboxylic and carbonyl carbon) decreased. In dry forest soils, the amount of recalcitrant SOM (e.g., thermostable SOM, alkyl carbon, aromatic and phenolic carbon and organo–mineral complexes stabilized by Ca increased, but the amount of easily degradable SOM increased further. The main conclusion of our study is that SOC can increase in forests that become drier, compensating somewhat for the decrease in forest plant biomass.

Habitat and tree species identity shape aboveground and belowground fungal communities in central European forests.

Trees interact with fungi in mutualistic, saprotrophic, and pathogenic relationships. With their extensive aboveground and belowground structures, trees provide diverse habitats for fungi. Thus, tree species identity is an important driver of fungal community composition in forests. Here we investigate how forest habitat (bark surface vs. soil) and tree species identity (deciduous vs. coniferous) affect fungal communities in two Central European forests. We assess differences and interactions between fungal communities associated with bark surfaces and soil, in forest plots dominated either by Fagus sylvatica, Picea abies, or Pinus sylvestris in two study regions in southwestern and northeastern Germany. ITS metabarcoding yielded 3,357 fungal amplicon sequence variants (ASVs) in the northern and 6,088 in the southern region. Overall, soil communities were 4.7 times more diverse than bark communities. Habitat type explained 48-69% of the variation in alpha diversity, while tree species identity explained >1-3%. NMDS ordinations showed that habitat type and host tree species structured the fungal communities. Overall, few fungal taxa were shared between habitats, or between tree species, but the shared taxa were highly abundant. Network analyses, based on co-occurrence patterns, indicate that aboveground and belowground communities form distinct subnetworks. Our study suggests that habitat (bark versus soil) and tree species identity are important factors structuring fungal communities in temperate European forests. The aboveground (bark-associated) fungal community is currently poorly known, including a high proportion of reads assigned to "unknown Ascomycota" or "unknown Dothideomycetes." The role of bark as a habitat and reservoir of unique fungal diversity in forests has been underestimated.

Amphibian decline in a Central European forest and the importance of woody debris for population persistence

Achieving an understanding of species’ temporal and spatial abundance patterns is a prerequisite for proper conservation and management decisions. Little is known of the ecological indicators of census size or biomass of terrestrial amphibian communities and historical estimates of population size are rare. Here we took advantage of abundance and biomass data collected in 1967/1968 for a leaf-litter amphibian community in Niepołomice Forest (NF) in south-central Poland. Using the same technique (removal sampling), we censused the amphibian community of this forest 50 years later (2016/2017), spatially matching a subset of current plots with the historical sampling sites. Averaged over all plots, we revealed at least a fourfold decline in amphibian abundance from 2817 ± 776 individuals/ha in 1967 to 674 ± 508 individuals/ha currently, paralleled by a decline in biomass from roughly 15.5 ± 1.7 to 3.8 ± 3.1 kg/ha. The decline was more striking (over 15-fold) for current plots placed in the same forest division as the historical plots (mean counts of 157 ± 103 individuals/ha corresponding in biomass to 1.0 ± 0.5 kg/ha). We also recorded a change in species composition between surveys, and propose that conversion of aquatic habitat and forest succession have decreased amphibian diversity and abundance in NF. Further, we estimated densities of anuran amphibians in forest plots differing in management regime and local habitat characteristics for contemporary plots (all historical plots were placed in managed forest). We found that unmanaged, old growth forest plots with coarse woody debris on the forest floor held on average twice as many anurans compared to plots in managed stands. Average body condition of the most common species, Rana temporaria, measured as a scaled mass index, was enhanced in plots situated in old growth forest. Our findings suggest that the preservation of old growth forests containing coarse woody debris may boost anuran abundance, biomass and body condition, and has the potential to buffer against long-term demographic decline. Moreover, the retention of deadwood could be a means of increasing the conservation potential of managed forests for terrestrial amphibian communities.

Non-native Douglas fir promotes epigeal spider density, but has a mixed effect on functional diversity

With climate change altering ecosystems worldwide, forest management in Europe is increasingly relying on more adaptable non-native tree species, such as Douglas fir (Pseudotsuga menziesii). However, the ecological consequences of the increased utilization of Douglas fir on arthropod diversity and ecosystem functioning are not fully known. Here we assessed how non-native Douglas fir as well as large- and small-scale differences in the environmental context, affect epigeal spider abundance, biomass, taxonomic and functional diversity, and community structure in Central European forests. Our study sites were divided into two regions with large differences in environmental conditions, with seven replicates of five stand types, including monocultures of native European beech (Fagus sylvatica), non-native Douglas fir and native Norway spruce (Picea abies), as well as two-species mixtures of European beech and each of the conifers. Contrary to our expectations, Douglas fir promoted small-scale spider diversity, and abundance and biomass (activity density). On the other hand, it decreased spider functional divergence and altered spider community structure. Microhabitat characteristics had opposing effects on spider diversity and activity density, with more open stands harboring a more diverse but less abundant spider community. Overall, our findings suggest that increasing Douglas fir utilization at the expense of Norway spruce does not necessarily decrease the diversity of epigeal arthropods and may even promote local spider diversity and activity density. However, care needs to be taken in terms of biodiversity conservation because typical forest spider species and their functional divergence were more strongly associated with native beech than with coniferous stands.

Conifers and non-native tree species shift trophic niches of generalist arthropod predators in Central European beech forests

BackgroundFunctional diversity is vital for forest ecosystem resilience in times of climate-induced forest diebacks. Admixing drought resistant non-native Douglas fir, as a partial replacement of climate-sensitive Norway spruce, to native beech forests in Europe appears promising for forest management, but possible consequences for associated biota and ecosystem functioning are poorly understood. To better link forest management and functional diversity of associated biota, we investigated the trophic niches (∆13C, ∆15N) of epigeic generalist predators (spiders and ground beetles) in mixed and pure stands of European beech, Norway spruce and non-native Douglas fir in north-west Germany. We assessed the multidimensional niche structure of arthropod predator communities using community-based isotopic metrics.ResultsWhilst arthropod ∆13C differed most between beech (high ∆13C) and coniferous stands (low ∆13C), ∆15N was lowest in non-native Douglas fir. Tree mixtures mitigated these effects. Further, conifers increased isotopic ranges and isotopic richness, which is linked to higher canopy openness and herb complexity. Isotopic divergence of ground beetles decreased with Douglas fir presence, and isotopic evenness of spiders in Douglas fir stands was lower in loamy sites with higher precipitation than in sandy, drier sites.ConclusionsWe conclude that tree species and particularly non-native trees alter the trophic niche structure of generalist arthropod predators. Resource use and feeding niche breadth in non-native Douglas fir and native spruce differed significantly from native beech, with more decomposer-fueled and narrower feeding niches in beech stands (∆13C, isotopic ranges and richness). Arthropod predators in non-native Douglas fir, however, had shorter (∆15N) and simplified (isotopic divergence) food chains compared to native forest stands; especially under beneficial abiotic conditions (isotopic evenness). These findings indicate potential adverse effects of Douglas fir on functional diversity of generalist arthropod predators. As tree mixtures mitigated differences between beech and conifers, mixed stands including (non-native) conifers constitute a promising compromise between economic and conservational interests.

Bark Beetle Attacks Reduce Survival of Wood Ant Nests

Central European coniferous forests are facing the most significant bark beetle outbreak in history. The consequence is the creation of large clearings, which are associated with changes in environmental parameters. We studied how these changes affected the survival of wood ant nests. Specifically, we monitored the relationship between mound occurrence, tree coverage, and the coverage and height of vegetation on ant mounds. We found that wood ant nests were less likely to survive (39% decline) in bark beetle-affected forests than in unaffected forests. The Formica rufa species was more affected than F. polyctena. The bark beetle attack was significantly positively correlated with increases in understory vegetation cover and height. Several factors may explain the negative effects of bark beetles on wood ants. The removal of trees subsequently increased the amount of light on ground vegetation. The support of understory vegetation growth on ant mounds cast shadows on the nests and disrupted nest thermoregulation. Additionally, the bark beetle attack may have been associated with a loss of food resources for wood ants. Our results showed that early (small-scale) management intervention against the spread of bark beetles is the preferred method for maintaining the ant population in conifer forests prone to bark beetle attacks.

Phytophthora species cause sudden and severe decline of naturally regenerated European beech (Fagus sylvatica) seedlings

AbstractNatural tree regeneration is a fundamental process in forest ecosystems ensuring the persistence and resilience of forest stands. Research on natural regeneration of European beech (Fagus sylvatica) in Central European forests has mainly focused on the impacts of abiotic processes, while little is known about the impact of pathogens. The aim of this study was to isolate Phytophthora species and identify the role that they may play in the decline of beech seedlings in Poland. A total of 1192 Phytophthora isolates were obtained from 300 symptomatic beech seedlings (60 seedlings from each of five stands): 638 isolates from seedlings exhibiting above‐ground symptoms and 554 isolates from seedlings that had roots with damping‐off symptoms. Based on morphological and molecular identification, the isolated species were Phytophthora cactorum, P. × cambivora, P. europaea, P. gonapodyides, P. plurivora and P. pseudosyringae. P. cactorum, P. × cambivora, P. europaea and P. plurivora were the most frequently isolated species from both above‐ and below‐ground organs. P. cactorum, P. × cambivora and P. plurivora were the most pathogenic species in the pathogenicity trials and caused 100% seedling mortality within 14 days of inoculation of the above‐ground organs. One single isolate of P. europaea was similarly pathogenic. P. gonapodyides, and P. pseudosyringae induced seedling mortality after inoculation of the cotyledons but not the roots. Our results demonstrate that Phytophthora may play an important role in reduction of naturally regenerated European beech seedlings.

The vertical form of the common ivy Hedera helix L. is associated with diverse and semi-natural forests in Central European highlands

Understanding the role of epiphytic vegetation and other microhabitats created by plants (hereafter lianas) developing on the surrounding ones is crucial for understanding the functioning of forest communities. Despite the observed increase in the biomass of lianas, the factors connected with forest plant communities determining their occurrence have not been investigated in a temperate zone. This research concerns the determinants of vertical form of the common ivy Hedera helix L. occurrence in highland forests in Central Europe. We established 69 pairs of sites, which consisted of areas inhabited by the vertical form of ivy and control areas (hereafter non-ivy plots). The sites with ivy were characterized by a higher volume (488 m3 ha-1 ± 251 SD vs. 411 m3 ha-1 ± 186 SD), a higher amount of deadwood (34 m3 ha-1 ± 39 SD vs. 23 m3 ha-1 ± 29 SD), and a higher tree species richness (8.0 species/ha ± 2.2 SD vs. 6.8 species/ha ± 2.14 SD) than non-ivy plots. The presence of vertical form of ivy was mainly influenced by a large share of alder in the stand and a higher diversity of trees and shrubs. Moreover, the number of large ivy vines increased with the presence of veteran trees. The presence of gaps was not conducive to the occurrence of large vines. The northern exposure and the presence of deadwood had a positive effect on the number of vines per tree. Our results contribute to the knowledge about variables influencing the occurrence and development of ivy vertical form in forests. The obtained results indicate that ivy requires diverse forests with a mix of trees and numerous veteran ones, which makes this species a good candidate as an indicator of forest habitat quality. We suggest that the common ivy should be protected within its native range and forest patches containing dense ivy vines should be excluded from silviculture.

The Soil Environment of Abandoned Charcoal Kiln Platforms in a Low-Altitude Central European Forest

This study examines the soil environment of eight charcoal kiln platforms and the neighboring soil in Czech and Bohemian low-altitude forest stands. Both mixed and undisturbed soil samples were used to assess the hydrophysical soil properties, nutrient content, cation exchange capacity, enzyme activity, and soil active carbon content, while soil color, stoniness, root density, and horizon thickness were estimated in the field. Charcoal-rich horizons had high total organic carbon concentrations and total nitrogen content (about 150% and 40% higher than in the organomineral horizons of the control plot, respectively), with total carbon stocks being higher than those in neighboring forest soils. Fine root density was highest in the charcoal-rich horizons, encouraged by high soil porosity, aeration, and favorable chemical properties. Enzyme group activity differed between individual soil horizons and kiln and control plots, with depolymerization enzyme activity highest in charcoal-rich horizons and humification enzyme activity highest in mineral horizons. Phosphatase, chitinase, and phenoloxidase activity were highest in charcoal-rich horizons, while β-glucosidase activity remained similar across horizons. After long-term abandonment, kiln sites shift from inhospitable sites to localized hotspots for plant and microbial growth, having more favorable physical, enzymatic, and chemical soil properties than the surrounding areas. This study confirmed that kiln production platforms act as microhabitat hotspots, also providing information on a wide spectrum of soil properties linked with soil microorganisms and root growth.

Tree and stand growth differ among soil classes in semi-natural forests in central Europe

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.

Long-term changes in soil composition in unmanaged central European mountain spruce forests after decreased acidic deposition and a bark beetle outbreak

We studied the effect of tree mortality on nutrient concentrations and pools in soils of two unmanaged mountain forest catchments (Plešné, PL; and Čertovo, CT; Czech Republic) recovering from acidification due to decreasing acidic atmospheric deposition since the late 1980s. Both catchments were situated at similar elevation, and before a bark beetle outbreak were covered by healthy mature Norway spruce (Picea abies) forests. However, differing bedrock [granite (PL) vs mica-schist and quartzite (CT)] resulted in lower concentrations of base cations (except for magnesium), but higher concentrations of aluminium and iron oxyhydroxides in the CT soils, enabling higher phosphorus (P) accumulation. Despite these differences, soils were similarly acidic, with pHH2O from 3.5 to 4.3 and cation exchange capacity (CEC) dominated by exchangeable protons (H+ex) and aluminium in both catchments in 2000. In the PL catchment, >75 % of mature spruce trees died after a bark beetle infestation between 2004 and 2008, and all dead biomass was left on site. Forest damage in the CT catchment was minor. Soil concentrations and pools of exchangeable calcium (Ca2+ex), magnesium (Mg2+ex), potassium (K+ex), and H+ex were tightly related to concentrations of organic carbon (C). Following the tree dieback in the PL catchment, we observed significant (p < 0.05) increases in (1) concentrations and pools of Ca2+ex, Mg2+ex, and K+ex, (2) base saturation (from 30 to ∼ 40 %), (3) CEC:C ratios (i.e., CEC of soil organic carbon), (4) pHH2O, (5) mineral P forms, and (6) total nitrogen (N) in the upper (O and A) soil horizons. Similar changes were less pronounced or negligible in the less impacted CT soils. The elevated litterfall after tree dieback, resulting in the increased input of base cations to forest floor and increased CEC of soil organic C, played a more important role in the decreasing acidity of the PL soils than the continuing decrease in acidic deposition.

Post-fire forest floor succession in a Central European temperate forest depends on organic matter input from recovering vegetation rather than on pyrogenic carbon input from fire

The predicted global increase in the frequency, severity, and intensity of forest fires includes Central Europe, which is not currently considered as a wildfire hotspot. Because of this, a detailed knowledge of long-term post-fire forest floor succession is essential for understanding the role of wildfires in Central European temperate forests. In this study, we used a space-for-time substitution approach and exploited a unique opportunity to observe successional changes in the physical, chemical, and microbial properties of the forest floor in coniferous forest stands on a chronosequence up to 110 years after fire. In addition, we assessed whether the depletion of organic matter (OM) and input of pyrogenic carbon (pyC) have significant effects on the post-fire forest floor succession. The bulk density (+174 %), pH (+4 %), and dissolved phosphorus content (+500 %) increased, whereas the water holding capacity (−51 %), content of total organic carbon and total nitrogen (−50 %), total phosphorus (−40 %), dissolved organic carbon (−23 %), microbial respiration and biomass (−60 %), and the abundance of fungi (−65 %) and bacteria (−45 %) decreased shortly after the fire event and then gradually decreased or increased, respectively, relative to the pre-disturbance state. The post-fire forest floor succession was largely dependent on changes in the OM content rather than the pyC content, and thus was dependent on vegetation recovery. The time needed to recover to the pre-disturbance state was <110 years for physical and chemical properties and < 45 years for microbial properties. These times closely correspond to previous studies focusing on the recovery of forest floor properties in different climate zones, suggesting that the times needed for forest vegetation and forest floor properties to recover to the pre-disturbance state are similar across climate zones.

Chances and Limitations of Mixed Oak Regeneration under Continuous Canopy Cover—Evidence from Long-Term Observations

Traditionally, due to its light ecology, oak is regenerated on clear cuts or areas where the crown coverage is heavily reduced. Thus, the regeneration phase is relatively short. Recently, selective long-term regeneration phases avoiding large gaps in the canopy but fostering mixed-species stands have been advocated as being more in keeping with close-to-nature forestry in Central European forests. However, examples of the successful regeneration of oak in mixtures following this type of regeneration are largely missing. Here, we report the results of long-term experiments located in three different forest types, where oak was long-term regenerated under different mixing and canopy cover situations. The observation periods reached from 26 to 36 years. We focused on the dynamics of stem number reduction, as well as the height and biomass development of oaks and their interaction with interspecific competition and canopy density. The probability of oaks occurring in the regeneration basically decreased over the duration of the regeneration period. Despite this, considerable regeneration biomass growth could be observed, especially in the case of the lower standing volume of the mature stand. The development of beech as the main competitor is scarcely slowed down by the canopy cover compared to oak. Increasing canopy cover noticeably impeded oak regeneration in the considered mixed stands. The model results suggest that a reduction in competition within the regeneration by lowering the proportion of beech below 30% enhanced the success of oak regeneration in the long run even in small patches. The productivity of the remaining stand was primarily driven by standing volume. However, a negative trend of its productivity emerged with high regeneration biomasses. The study results show that small-scale oak regeneration with prolonged regeneration duration is possible in principle. However, oak regeneration requires active and continuous silvicultural assistance, which has to be adjusted to the specific site conditions.

Higher spring phenological sensitivity to forcing temperatures of Asian compared to European tree species under low and high pre-chilling conditions

Winter chilling, spring forcing temperature and photoperiod are the most important drivers explaining the spatial and temporal variability of spring phenology in temperate trees. However, how these factors interact with each other on dormancy release and spring budburst date remains unclear and varies greatly depending on species. Our knowledge is also limited as to whether heat accumulation of forcing temperatures that trigger bud break in spring is a linear or non-linear process. Here, we aimed at experimentally quantifying the effect of chilling, forcing, photoperiod and their interactions on the budburst dates of nine different temperate tree species from East Asia (near Beijing, China) and Central Europe (near Zurich, Switzerland), including six phylogenetically related species (same genus). We conducted a full factorial experiment in climate chambers using two chilling (low and high, i.e., 0 vs. 56 days at 2°C after sampling at the end of December), four forcing (5, 10, 15, and 20°C), and two photoperiod (8 vs. 16 h) treatments simultaneously in Beijing and Zurich. We found that species growing near Beijing responded more readily to forcing conditions than species of the same genus growing near Zurich regardless of chilling treatment. Budburst timing of most species but European beech was marginally, if at all, affected by photoperiod. Furthermore, our results suggest that linear heat accumulation, as commonly used with the growing degree hours (GDH) model, could result in accurate prediction of budburst date depending on the temperature threshold used as a basis for heat accumulation. Our results also demonstrate the important role of chilling in shaping the sensitivity and rate of forcing accumulation to trigger budburst and suggest that species-specific sigmoid relationship for accumulating heat that accounts for prior chilling exposure may yield better predictions of budburst dates. Our results suggest that deciduous trees may have adapted their chilling and forcing requirements in regards to the predictability of winter-spring transition and late spring frosts. A less predictable winter-spring transition, as observed in Central Europe, could have driven species evolution towards higher chilling and forcing requirements compared to species growing in a more predictable climate of Northeastern Asia. Our cross-continental experiment therefore suggests that the spring phenology of East Asian species is tighter coupled to spring forcing temperature than Central European forests.

Phytogeographic Characteristics of Montane Coniferous Forests of the Central Balkan Peninsula (SE Europe)

We investigated taxonomic and endemic richness, patterns of spatial distribution, cenotic and spatial diversification, and chorological and life form spectra of montane coniferous forests in the central part of the Balkan Peninsula. We collected information on 1435 taxa (1351 at the level of species and 84 subspecies) with 65,289 species-occurrence data, published in 1930 original plots with a total area of about 215 ha in the analysis. All statistical analyses (univariate and multivariate) were performed on binary matrices prepared for different levels of analysis. Our main results showed that the montane coniferous forests of the central Balkan Peninsula represent very species-rich vegetation. At the same time, the high proportion of endemics indicated that the montane coniferous forests of the central Balkan Peninsula differ significantly from Central European and boreal forests of a similar type. Furthermore, we found that there were regional differences in the species composition of the coniferous forests of the Balkan Peninsula, and that the primary centers of floristic richness are located in the area of the central and continental Dinarides. This latter finding suggested that the true centers of the richness of European coniferous forests are located south of the Limestone Alps-Western Dinarides-Carpathian Foothills line in Romania, which used to be considered the center of the richness of the coniferous forests in Europe.

Fire-induced changes in soil properties depend on age and type of forests

Abstract Wildfires affect different physical, chemical, and hydraulic soil properties, and the magnitude of their effects varies depending on intrinsic soil properties and wildfire characteristics. The objectives of this study are: to estimate the impact of heating temperature (50–900°C) on the properties of sandy soil (Arenosol) taken in 1) coniferous forests (Scots pine Pinus sylvestris) of different ages (30 and 100 years); and 2) coniferous (Scots pine Pinus sylvestris) and deciduous (alder Alnus glutinosa) forests of the same age (30 years). The forests are located in the central part of the Borská nížina lowland (western Slovakia), and the properties treated were soil organic carbon content (SOC), pH, and soil water repellency (measured in terms of water drop penetration time, WDPT). It was found that the impact of heating temperature on the properties of sandy soil is great and depends on both the age and type of forest. The SOC value decreased unevenly with temperature in all three soils, and it was higher in the 30-year-old deciduous forest soil than in the 30-year-old coniferous forest soil. The value of pH increased monotonously with temperature from 200 °C, and it was higher in 30-year-old coniferous forest soil than in the 100-year-old coniferous forest soil. SOC and WDPT in the 100-year-old coniferous forest soil were higher than SOC and WDPT in the 30-year-old coniferous forest soil. Results obtained (decrease in SOC, disappearance of SWR after heating to 400 °C, and increase in pH from heating temperature 200 °C) bring important information for post-fire vegetation restoration and post-fire management of Central European forests established on sandy soil.

Longhorn beetles and predatory clerid beetles attracted to a blend of longhorn beetle pheromone compounds in a Central European oak forest (Coleoptera: Cerambycidae, Cleridae)

A blend of longhorn beetle pheromones was tested as a generic attractant in a Central European oak forest. Overall, 20 cerambycid species totalling 1250 specimens were captured using two trap types. More adults of Phymatodes testaceus and Leiopus nebulosus nebulosus were attracted to pheromone-baited traps compared to solvent controls. Significant numbers of four other species were caught by panel traps but not funnel traps. For the cerambycine Pyrrhidium sanguineum, significantly more beetles were caught in treatment traps than controls. For the cerambycine Anaglyptus mysticus, lepturines Cortodera humeralis and Rhagium sycophanta, the numbers of beetles caught in treatment or control traps were similar, indicating no attraction to the lure blend. Adults of a predatory clerid beetle Clerus mutillarius were caught in significantly larger numbers by both baited trap types in comparison to controls, totalling 1514 specimens. Antennae of both sexes of C. mutillarius showed responses to 3-hydroxyhexan-2-one and 2-methylbutan-1-ol, and males also responded to syn-2,3-hexanediol. Strong attraction of C. mutillarius suggests eavesdropping on the pheromones of cerambycids and that such attractant baits, without traps, might be used to manipulate the local population density of predators in a push-pull biological control program.