European Tree Species Research Articles

Mixed Pyrus pyraster and Sorbus torminalis plantations including companion species enhance high-quality timber production

Wild pear (Pyrus pyraster (L.) Burgsd.) (P) and wild service tree (Sorbus torminalis (L.) Crantz) (S) are sporadic European tree species that are valued for their high-quality timber production. Although mixed plantations including companion species enhance timber quality of several trees, the performance of the association of P and S is not well known. The objective of this study was to assess growth and survival of P and S in pure plantations and in plantations mixed with other companion tree or shrub species in a non-native habitat. To answer the question of whether growth of these species is enhanced by mixtures, specific combinations of the main and companion species were established in central Chile and monitored for a 12-year period after planting. Besides each main species monoculture, five mixtures were tested: Mix1: P+S; Mix2: P+S+ the N-fixing tree Italian alder (Alnus cordata (Loisel.) Duby); and three associations of P and S including shrubs (Mix3: P+S+ Corylus avellana L., Mix4: P+S+ Sambucus ebulus L., and Mix5: P+S+ Sambucus nigra L.). Both P and S presented the highest height growth in Mix2, being 48.6% and 53.4% higher than in the monoculture, respectively. DBH growth was also enhanced in Mix2 for S. Wild service tree, which showed lower growth and survival than P, was more benefited from the mixture including Italian alder than P. Height growth, vigor and survival of the main species were highest in Mix2, even higher than in pure plantations and in Mix1 without companion species. Specific tree associations might increase the probability to obtain high-quality timber of noble species if a timely and adequate management of companion species is provided.

Quercus robur as a Potential Cd Phytostabilizator

Pedunculate oak (Quercus robur L.) is one of the most important forest tree species in Europe, from both economic and ecological perspectives. Several studies indicate the possibility of using different species of the genus Quercus for afforestation of lands affected by industry, including trace-element polluted areas. The main objective of this research was to determine the Cd accumulation patterns of pedunculate oak seedlings subjected to various Cd treatments. Differences in Cd accumulation ability, mineral nutrients concentrations and observed damage upon Cd treatment of plants derived from different regions of origin are discussed. Obtained results suggest the possible use of pedunculate oak in cadmium phytostabilization.

Mycorrhizal symbiosis of alien and invasive tree species

AbstractThe introduction of alien tree species has become a world wide phenomenon over the last centuries and the cultivation of these species is an economically important branch of forestry in many countries. However, the cultivation of alien plant species poses the threat of introducing potentially invasive species, both trees and its mutualistic symbionts, such as mycorrhizal fungi. Mycorrhizal fungi are obligatory symbionts and a key element in the proper development and functioning of trees. It is thought that mycorrhizal fungi may also profoundly influence the invasiveness of alien tree species worldwide, with the proper fungal species acting as a driver to make this invasion possible. Co-invasion of alien trees and its mutualistic symbionts are well-known in the case of pines and co-invading ectomycorrhizal fungi in the southern hemisphere.Invasive tree species constitute a major ecological and economic problem through intense competition and modification of local habitats leading to a decline in biodiversity and potentially threatening many rare, native and endangered species, including fungi. Despite the fundamental role that fungi have in the functioning of forests, the impact alien tree species could have on mycorrhizal fungi in native forest ecosystems has not received much attention.Understanding the relationships between mycorrhizal fungi and alien tree species can allow us to better predict and counter- act alien species invasions, which is necessary in order to maintain biodiversity and preserve native ecosystems. On top of that, climate change could threaten some European tree species and thus free ecological niches for other species, like alien, invasive or potentially invasive trees.

Species mixing reduces drought susceptibility of Scots pine (Pinus sylvestris L.) and oak (Quercus robur L., Quercus petraea (Matt.) Liebl.) – Site water supply and fertility modify the mixing effect

Tree species mixing has been widely promoted as a promising silvicultural tool for reducing drought stress. However, so far only a limited number of species combinations have been studied in detail, revealing inconsistent results. In this study, we analysed the effect of mixing Scots pine and oak (pedunculate oak and sessile oak) trees on their drought response along a comprehensive ecological gradient across Europe. The objective was to improve our knowledge of general drought response patterns of two fundamental European tree species in mixed versus monospecific stands. We focused on three null hypotheses: (HI) tree drought response does not differ between Scots pine and oak, (HII) tree drought response of Scots pine and oak is not affected by stand composition (mixture versus monoculture) and (HIII) tree drought response of Scots pine and oak in mixtures and monocultures is not modified by tree size or site conditions. To test the hypotheses, we analysed increment cores of Scots pine and oak, sampled in mixed and monospecific stands, covering a wide range of site conditions. We investigated resistance (the ability to maintain growth levels during drought), recovery (the ability to restore a level of growth after drought) and resilience (the capacity to recover to pre-drought growth levels), involving site-specific drought events that occurred between 1976 and 2015. In monocultures, oak showed a higher resistance and resilience than Scots pine, while recovery was lower. Scots pine in mixed stands exhibited a higher resistance, but also a lower recovery compared with Scots pine in monocultures. Mixing increased the resistance and resilience of oak. Ecological factors such as tree size, site water supply and site fertility were found to have significant effects on the drought response. In the case of Scots pine, resistance was increased by tree size, while recovery was lowered. Resistance of oak increased with site water supply. The observed mixing effect on the tree drought response of Scots pine and oak was in some cases modified by the site conditions studied. Positive mixing effects in terms of resistance and resilience of oak increased with site water supply, while the opposite was found regarding recovery. In contrast, site fertility lessened the positive mixing effect on the resistance of Scots pine. We hypothesise that the observed positive mixing effects under drought mainly result from water- and/or light-related species interactions that improve resource availability and uptake according to temporal and spatial variations in environmental conditions.

Particulate matter on foliage of Betula pendula, Quercus robur, and Tilia cordata: deposition and ecophysiology

Trees in urban and industrial areas significantly help to limit the amount of particulate matter (PM) suspended in the air, but PM has a negative impact on their life. The amount of PM gathered on leaves depends on quantity, size, and morphology of leaves and can also be increased by the presence of epicuticular waxes, in which PM can become stuck or immersed. In this study, we determined the ability of PM to accumulate on leaves in relation to the species of tree and PM source. We tested saplings of three common European tree species (Betula pendula, Quercus robur, and Tilia cordata) by experimentally polluting them with PM from different sources (cement, construction, and roadside PM), and then assessing the effects of PM on plant growth and ecophysiology. In all studied species, we have found two types of PM accumulation: a layer on the leaf surface and an in-wax layer. Results showed that the studied species accumulate PM on their leaf blade, reducing the efficiency of its photosynthetic apparatus, which in a broader sense can be considered a reduction in the plants’ normal functioning. Saplings of Q. robur suffered the least, whereas B. pendula (especially photosynthetic rate and conductivity) and T. cordata (especially increase in leader shoot length) exhibited greater negative effects. The foliage of B. pendula collected the most PM, followed by Q. robur, and then T. cordata, regardless of the dust’s source. All tested species showed a tendency for higher wax production when growing under PM pollution stress. We believe that, potentially, B. pendula best enhances the quality of the PM-contaminated environment; however, faster leaf fall, reduced productivity, and worse quality of wood should be considered in urban forest management.

Norway spruce at the trailing edge: the effect of landscape configuration and composition on climate resilience

ContextNorway spruce (Picea abies) is one of the most widespread tree species in Europe’s forests. Due to its high economic value it has been strongly favored by management, especially at the trailing edge of its natural distribution. However, disturbances from wind and bark beetles are increasingly impacting these forests, and their resilience under climate change has been called into question recently.ObjectivesWe quantified the effects of landscape configuration and composition on (1) the risk from natural disturbances, and (2) on the overall resilience of Norway spruce to changing climate at the trailing edge.MethodsWe simulated the dynamics of a 9183 ha forest landscape in Eastern Austria over 190 years. We used the simulation model iLand to experimentally study a wide range of landscape compositions and configurations under five different climate scenarios.ResultsNatural disturbances increased considerably under all future climate scenarios. Dispersing Norway spruce throughout the landscape in mixed stands resulted in the highest levels of climate resilience. Reducing the percentage of Norway spruce on the landscape increased the resilience of the remaining Norway spruce trees, yet landscape configuration generally had a stronger effect on resilience than composition.ConclusionsThe resilience of Norway spruce at the trailing edge of its distribution is challenged by climate change, and considerable efforts are needed to sustain these ecosystems. While currently discussed adaptation measures focus largely on the stand level, we show that modifying landscape composition and configuration can be used to foster Norway spruce resilience while maintaining socio-economically relevant proportions of Norway spruce.

Flux-Based Ozone Risk Assessment for a Plant Injury Index (PII) in Three European Cool-Temperate Deciduous Tree Species

This study investigated visible foliar ozone (O3) injury in three deciduous tree species with different growth patterns (indeterminate, Alnus glutinosa (L.) Gaertn.; intermediate, Sorbus aucuparia L.; and determinate, Vaccinium myrtillus L.) from May to August 2018. Ozone effects on the timing of injury onset and a plant injury index (PII) were investigated using two O3 indices, i.e., AOT40 (accumulative O3 exposure over 40 ppb during daylight hours) and PODY (phytotoxic O3 dose above a flux threshold of Y nmol m−2 s−1). A new parameterization for PODY estimation was developed for each species. Measurements were carried out in an O3 free-air controlled exposure (FACE) experiment with three levels of O3 treatment (ambient, AA; 1.5 × AA; and 2.0 × AA). Injury onset was found in May at 2.0 × AA in all three species and the timing of the onset was determined by the amount of stomatal O3 uptake. It required 4.0 mmol m−2 POD0 and 5.5 to 9.0 ppm·h AOT40. As a result, A. glutinosa with high stomatal conductance (gs) showed the earliest emergence of O3 visible injury among the three species. After the onset, O3 visible injury expanded to the plant level as confirmed by increased PII values. In A. glutinosa with indeterminate growth pattern, a new leaf formation alleviated the expansion of O3 visible injury at the plant level. V. myrtillus showed a dramatic increase of PII from June to July due to higher sensitivity to O3 in its flowering and fruiting stage. Ozone impacts on PII were better explained by the flux-based index, PODY, as compared with the exposure-based index, AOT40. The critical levels (CLs) corresponding to PII = 5 were 8.1 mmol m−2 POD7 in A. glutinosa, 22 mmol m−2 POD0 in S. aucuparia, and 5.8 mmol m−2 POD1 in V. myrtillus. The results highlight that the CLs for PII are species-specific. Establishing species-specific O3 flux-effect relationships should be key for a quantitative O3 risk assessment.

The GenTree Dendroecological Collection, tree-ring and wood density data from seven tree species across Europe

The dataset presented here was collected by the GenTree project (EU-Horizon 2020), which aims to improve the use of forest genetic resources across Europe by better understanding how trees adapt to their local environment. This dataset of individual tree-core characteristics including ring-width series and whole-core wood density was collected for seven ecologically and economically important European tree species: silver birch (Betula pendula), European beech (Fagus sylvatica), Norway spruce (Picea abies), European black poplar (Populus nigra), maritime pine (Pinus pinaster), Scots pine (Pinus sylvestris), and sessile oak (Quercus petraea). Tree-ring width measurements were obtained from 3600 trees in 142 populations and whole-core wood density was measured for 3098 trees in 125 populations. This dataset covers most of the geographical and climatic range occupied by the selected species. The potential use of it will be highly valuable for assessing ecological and evolutionary responses to environmental conditions as well as for model development and parameterization, to predict adaptability under climate change scenarios.

Multiangular spectra of tree bark for common boreal tree species in Europe

Despite the importance of spectral properties of woody tree structures, they are seldom represented in research related to forests, remote sensing, and reflectance modeling. This study presents a novel imaging multiangular measurement set-up that utilizes a mobile handheld hyperspectral camera (Specim IQ, 400–1000 nm), and can measure stem bark spectra in a controlled laboratory setting. We measured multiangular reflectance spectra of silver birch ( Roth), Scots pine ( L.) and Norway spruce ( (L.) Karst.) stem bark, and demonstrated the potential of using bark spectra in identifying tree species using a Support Vector Machine (SVM) based approach. Intraspecific reflectance variability was the lowest in visible (400–700 nm), and the highest in near-infrared (700–1000 nm) wavelength regions. Interspecific variation was the largest in the red, red-edge and near-infrared spectral bands. Spatial variation of reflectance along the tree height and different sides of the stem (north and south) were found. Both birch and pine had increased reflectance in the forward-scattering directions for visible to near-infrared wavelength regions, whilst spruce displayed the same only for the visible wavelength region. In addition, spruce had increased reflectance in the backward-scattering directions. In spite of the intraspecific variations, SVM could identify tree species with 88.8% overall accuracy when using pixel-specific spectra, and with 97.2% overall accuracy when using mean spectra per image. Based on our results it is possible to identify common boreal tree species based on their stem bark spectra using images from mobile hyperspectral cameras.Betula pendulaPinus sylvestrisPicea abies

Range margin populations show high climate adaptation lags in European trees.

How populations of long-living species respond to climate change depends on phenotypic plasticity and local adaptation processes. Marginal populations are expected to have lags in adaptation (i.e. differences between the climatic optimum that maximizes population fitness and the local climate) because they receive pre-adapted alleles from core populations preventing them from reaching a local optimum in their climatically marginal habitat. Yet, whether adaptation lags in marginal populations are a common feature across phylogenetically and ecologically different species and how lags can change with climate change remain unexplored. To test for range-wide patterns of phenotypic variation and adaptation lags of populations to climate, we (a) built model ensembles of tree height accounting for the climate of population origin and the climate of the site for 706 populations monitored in 97 common garden experiments covering the range of six European forest tree species; (b) estimated populations' adaptation lags as the differences between the climatic optimum that maximizes tree height and the climate of the origin of each population; (c) identified adaptation lag patterns for populations coming from the warm/dry and cold/wet margins and from the distribution core of each species range. We found that (a) phenotypic variation is driven by either temperature or precipitation; (b) adaptation lags are consistently higher in climatic margin populations (cold/warm, dry/wet) than in core populations; (c) predictions for future warmer climates suggest adaptation lags would decrease in cold margin populations, slightly increasing tree height, while adaptation lags would increase in core and warm margin populations, sharply decreasing tree height. Our results suggest that warm margin populations are the most vulnerable to climate change, but understanding how these populations can cope with future climates depend on whether other fitness-related traits could show similar adaptation lag patterns.

Mining ecophysiological responses of European beech ecosystems to drought

The most accurate understanding of forest functioning during drought is crucial to improve the forecast of future forest productivity. Here we investigate the ecophysiological responses (i.e. primary production, evapotranspiration and water use efficiency) of European beech to drought events with the ecosystem model MuSICA, using as benchmark the observed fluxes at the experimental forest Hesse (France). We show that MuSICA is able to realistically simulate observed drought-induced limitations. Subsequently we use simulation experiments to provide: (1) a quantification of the reduction of ecosystem fluxes during the 2003 drought, (2) a partitioning of heat stress and water limitations during droughts, (3) an analysis of the impact of specific drought trajectories, and (4) an evaluation of the potential impact of projected climate change on the studied forest and (5) over the beech distributional range. Our results show that the 2003 drought resulted in a 17% reduction of annual gross primary production and in a 21% reduction of evapotranspiration at Hesse. The studied forest ecosystem is mostly sensitive to negative precipitation anomalies (82% of the reduced forest productivity in 2003) and almost insensitive to heat stress due to high temperatures (16%). Moreover, we show that the ecosystem fluxes are limited more by fast drought onsets in the early growing season (June–July) than by onsets later in the season. Deciphering the impact of future climate change on beech productivity is complicated by large uncertainties in projected future precipitation and in the severity of extreme dry years. Drastic reduction of ecosystem fluxes is only predicted with climate projections that show marked reductions in precipitation. However, increased CO2 fertilization in the future will counterbalance negative drought impacts. This modelling-based study improves our understanding of the functioning of an emblematic European tree species during extreme events and informs on potential future forest responses to projected climate change.

Extent, distribution and origin of non-native forest tree species in Europe

ABSTRACTThe management of non-native tree species in European forests has a long history, but the information on the current number and geographic distribution of these species in European forests is incomplete and scattered across various datasets. This study aims to perform an inventory of the most frequent non-native tree species growing in European forests and analyse their current extent, geographic distribution and geographic origin. Our results show that at least 150 non-native tree species are currently growing in European forests and provenance trials. The genera represented by largest number of species are Eucalyptus, Pinus, Acacia and Abies. Species growing at the largest areas are Robinia pseudoacacia (2.44 million ha), Eucalyptus globulus (1.46 million ha), Picea sitchensis (1.16 million ha) and Pseudotsuga menziesii (0.83 million ha). In total, non-native tree species in Europe are found in an area of approximately 8.54 million ha, or 4.0% of the European forest area, and the five most abundant species account for up to 77% of this area. The largest number of these 150 species were introduced from North America (71), followed by Asia (45) and Australia (20). North American species occupy by far the largest area.

Contrasting resistance and resilience to extreme drought and late spring frost in five major European tree species.

Extreme climate events (ECEs) such as severe droughts, heat waves, and late spring frosts are rare but exert a paramount role in shaping tree species distributions. The frequency of such ECEs is expected to increase with climate warming, threatening the sustainability of temperate forests. Here, we analyzed 2,844 tree-ring width series of five dominant European tree species from 104 Swiss sites ranging from 400 to 2,200m a.s.l. for the period 1930-2016. We found that (a) the broadleaved oak and beech are sensitive to late frosts that strongly reduce current year growth; however, tree growth is highly resilient and fully recovers within 2years; (b) radial growth of the conifers larch and spruce is strongly and enduringly reduced by spring droughts-these species are the least resistant and resilient to droughts; (c) oak, silver fir, and to a lower extent beech, show higher resistance and resilience to spring droughts and seem therefore better adapted to the future climate. Our results allow a robust comparison of the tree growth responses to drought and spring frost across large climatic gradients and provide striking evidence that the growth of some of the most abundant and economically important European tree species will be increasingly limited by climate warming. These results could serve for supporting species selection to maintain the sustainability of forest ecosystem services under the expected increase in ECEs.

Characterization of differential throughfall drop size distributions beneath European beech and Norway spruce

AbstractForest canopies present irregular surfaces that alter both the quantity and spatiotemporal variability of precipitation inputs. The drop size distribution (DSD) of rainfall varies with rainfall event characteristics and is altered substantially by the forest stand properties. Yet, the influence of two major European tree species, European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. Karst), on throughfall DSD is largely unknown. In order to assess the impact of these two species with differing canopy structures on throughfall DSD, two optical disdrometers, one above and one below the canopy of each European beech and Norway spruce, measured DSD of both incident rainfall and throughfall over 2 months at a 10‐s resolution. Fractions of different throughfall categories were analysed for single‐precipitation events of different intensities. While penetrating the canopies, clear shifts in drop size and temporal distributions of incoming rainfall were observed. Beech and spruce, however, had different DSD, behaved differently in their effect on diameter volume percentiles as well as width of drop spectrum. The maximum drop sizes under beech were higher than under spruce. The mean ± standard deviation of the median volume drops size (D50) over all rain events was 2.7 ± 0.28 mm for beech and 0.80 ± 0.04 mm for spruce, respectively. In general, there was a high‐DSD variability within events indicating varying amounts of the different throughfall fractions. These findings help to better understand the effects of different tree species on rainfall partitioning processes and small‐scale variations in subcanopy rainfall inputs, thereby demonstrating the need for further research in high‐resolution spatial and temporal properties of rainfall and throughfall.

Root-Associated Microbial Communities of Abies nordmanniana: Insights Into Interactions of Microbial Communities With Antioxidative Enzymes and Plant Growth.

Abies nordmanniana is a major Christmas tree species in Europe, but their uneven and prolonged growth slows down their production. By a 16S and 18S rRNA gene amplicon sequencing approach, we performed a characterization of root-associated bacterial and fungal communities for three-year-old A. nordmanniana plants collected from two nurseries in Denmark and Germany and displaying different growth patterns (small versus tall plants). Proteobacteria had the highest relative abundance at both sampling sites and plant sizes, and Ascomycota was the most abundant fungal phylum. At the order level, Acidobacteriales, Actinomycetales, Burkholderiales, Rhizobiales, and Xanthomonadales represented the bacterial core microbiome of A. nordmanniana, independently of the sampling site or plant size, while the fungal core microbiome included members of the Agaricales, Hypocreales, and Pezizales. Principal Coordinate Analysis indicated that both bacterial and fungal communities clustered according to the sampling site pointing to the significance of soil characteristics and climatic conditions for the composition of root-associated microbial communities. Major differences between communities from tall and small plants were a dominance of the potential pathogen Fusarium (Hypocreales) in the small plants from Germany, while Agaricales, that includes reported beneficial ectomycorrhizal fungi, dominated in the tall plants. An evaluation of plant root antioxidative enzyme profiles showed higher levels of the antioxidative enzymes ascorbate peroxidase, peroxidase, and superoxide dismutase in small plants compared to tall plants. We suggest that the higher antioxidative enzyme activities combined with the growth arrest phenotype indicate higher oxidative stress levels in the small plants. Additionally, the correlations between the relative abundances of specific taxa of the microbiome with the plant antioxidative enzyme profiles were established. The main result was that many more bacterial taxa correlated positively than negatively with one or more antioxidative enzyme activity. This may suggest that the ability of bacteria to increase plant antioxidative enzyme defenses is widespread.

Weather and trade-offs between growth and reproduction regulate fruit production in European forests

Some tree species have a highly variable year-to-year pattern of reproduction which has repercussions for the entire ecosystem. Links between meteorological variability, fruit production and crown cover, and trade-offs between reproduction and vegetative growth, remain elusive, despite a long history of research. We explored how meteorological conditions determined variations in fruit production and crown cover and how remotely sensed vegetation indices, such as the enhanced vegetation index (EVI), may be used to characterize the fluctuations in fruit production. We used data for fruit production from six European tree species (Abies alba, Picea abies, Pseudotsuga menziesii, Fagus sylvatica, Quercus petraea and Q. robur) growing in monospecific stands, EVI and seasonal meteorological variables (precipitation and temperature) for 2002–2010. Weather accounted for fruit production better than EVI. Deciduous trees were more responsive to weather than evergreens, most notably to different seasonal temperatures, which were positively correlated mainly with crown cover and fruit production in deciduous species. Our results also suggested different patterns of relationships between fruit production, crown cover and weather, indicating different strategies of resource management. These patterns indicated a possible internal trade-off in evergreens, with resources allocated to either growth or reproduction. In contrast, in deciduous species we found no evidence for such a trade-off between vegetative growth and reproduction.

Differential impacts of soil microbes on native and co‐occurring invasive tree species

AbstractThe Janzen‐Connell effect is often generated by interactions between trees and soil microbes while the enemy release hypothesis states that invasive species are released from regulation by natural enemies. Thus, the strength of the Janzen‐Connell effect could differ between native vs. nonnative plants. We tested this hypothesis with congeneric pairs of invasive and native tree species in Europe: boxelder (Acer negundo) vs. Norway maple (A. platanoides), and Northern red oak (Quercus rubra) vs. pedunculate oak (Q. robur). We conducted greenhouse experiments using soil sterilization treatments, field experiments on distance‐dependent germination, and field surveys of early life stages of the focal species. Greenhouse and field experiments demonstrated patterns consistent with Janzen‐Connell effect that is most likely caused by negative distance dependence in seed germination and stem growth which was found in both genera of the native, but not the invasive trees. Soil sterilization experiments suggested that these effects are driven by interactions with soil biota. Field surveys revealed the Janzen‐Connell pattern in the distribution of seedlings and saplings of the native, but not the invasive Acer species. Our findings indicate that weakened Janzen‐Connell effect might contribute to successful invasions of certain nonnative plant species.

The Effect of Non-Native Black Pine (Pinus nigra J. F. Arnold) Plantations on Environmental Conditions and Undergrowth Diversity

The cover of introduced tree species in Europe has recently increased, due to several factors. Attempts to understand the impact of non-native edificator trees on the environmental conditions and diversity of undergrowth have so far been limited to a few studies. In this paper, we analyse the effect of one of the most commonly planted non-native tree species–black pine (Pinus nigra J. F. Arnold) in the Carpathian-Pannonian region, north of the border of its native occurrence. The objectives of our study were to determine the following: (i) How does black pine, as a non-native edificator, change the forest structure and environmental conditions in comparison to those of native communities? (ii) How does black pine change the species composition of undergrowth in comparison to that of native communities? (iii) Which factors are associated with the impact of black pine on diversity? To answer these questions, we used the twin plot method, sampling two neighbouring plots with the same environmental conditions in which one plot of the pair is in a forest with native tree species composition and the second plot is in a planted non-native Pinus nigra plantation. We found that in forests dominated by the non-native black pine, (a) the tree canopy is significantly more open; (b) the cover of the shrub layer is significantly higher; (c) the needles of black pine form a significantly thicker litter layer and (d) the cover of the herb layer is significantly lower than that in the native forest. (e) Black pine plays a vital role in modifying local climate by altering air temperature and humidity; (f) there were no significant differences in the soil pH between black pine plantations and native forests; (g) the plantations of black pine cause changes in diversity at both the species and the community level and (h) the dissimilarity between black pine plantations and neighbouring native forests decreases at higher altitudes.

Leaf Nutrients and Macroinvertebrates Control Litter Mixing Effects on Decomposition in Temperate Streams

Plant litter decomposition is an essential ecosystem function in temperate streams. Both riparian vegetation and decomposer communities are major determinants of the decomposition efficiency and the interactions occurring within litter mixtures. However, the extent to which such litter mixture interactions are affected by combined shifts in litter traits and decomposer community is not well understood. We used leaf litter from 10 European tree species in order to study litter decomposition and litter mixture effects occurring in two-species litter mixtures in a temperate forested stream of northwestern France. The study distinguished between (1) decomposition involving microorganisms alone or together with invertebrates, and (2) decomposition involving litter mixtures of similar or dissimilar nutrient content. Increasing mean litter nutrient concentration favored both microbial activity and litter decomposition rate. Surprisingly, the highest litter mixture effects occurred in mixtures containing two nutrient-rich litters and occurred mainly in macroinvertebrate presence. Both the “mass ratio hypothesis,” expressed as the community-weighted mean traits (TraitCWM), and the “niche complementarity hypothesis,” expressed as the functional dissimilarity of litter traits (TraitFD), contributed to explain litter mixture effects. However, TraitCWM was found to be a better predictor than TraitFD. Finally, when evaluating the individual contributions of litter nutrients, calcium and magnesium appeared as important drivers of litter mixture effects. Our findings suggest that the mass ratio hypothesis overrules the niche complementarity hypothesis as a driver of litter diversity effects. Our study highlights the key importance of macroinvertebrates and of leaf nutrients, such as Ca and Mg, which are often neglected in decomposition studies in streams.

Tree and stand level estimations of Abies alba Mill. aboveground biomass

Key messageWe provided a complete set of tree- and stand-level models for biomass and carbon content of silver firAbies alba. This allows for better characterization of forest carbon pools in Central Europe than previously published models. The best predictor of biomass at the stand level is stand volume, and the worst are stand basal area and density.ContextAmong European forest-forming tree species with high economic and ecological significance, Abies alba Mill. is the least characterized in terms of biomass production.AimsTo provide a comprehensive set of tree- and stand-level models for A. alba biomass and carbon stock. We hypothesized that (among tree stand characteristics) volume will be the best predictor of tree stand biomass.MethodsWe studied a chronosequence of 12 A. alba tree stands in southern Poland (8–115 years old). We measured tree stand structures, and we destructively sampled aboveground biomass of 96 sample trees (0.0–63.9 cm diameter at breast height). We provided tree-level models, biomass conversion and expansion factors (BCEFs) and biomass models based on forest stand characteristics.ResultsWe developed general and site-specific tree-level biomass models. For stand-level models, we found that the best predictor of biomass was stand volume, while the worst were stand basal area and density.ConclusionOur models performed better than other published models, allowing for more reliable biomass predictions. Models based on volume are useful in biomass predictions and may be used in large-scale inventories.