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Tree species diversity can positively affect numerous forest functions. This is why Scots pine monocultures, widely promoted in Central Europe since the 18th Century, are converted into mixed stands, also with broadleaved species of alien origin. Here we studied the impacts of Northern red oak (Quercus rubra) introduction and forest continuity (ancient vs. recent forests) on bilberry (Vaccinium myrtillus) – a dominant component of the forest understory and very important ecosystem services provider in temperate coniferous (Pinus sylvestris) forests. We measured bilberry cover, density and height of shoots, fruit productivity (number and biomass of berries) as well as biomass of stems and leaves. 2000 bilberry shoots (ramets) were collected in 200 plots located in four types of Scots pine forest in central Poland: recent and ancient forests, with and without Q. rubra. At the individual (ramet) level we found decreased aboveground biomass and fruiting leaf mass fraction of bilberry in recent pine monoculture and in both types of forest with Q. rubra. Presence of Q. rubra also modified the trajectory of the allometric relationship between biomass and height: plants with the same height had lower biomass. At the population level we found a decrease of shoot density, biomass and fruiting, which resulted from effects at the individual shoot level and from lower density. At the ecosystem level these relationships were modified by decreased cover of bilberry in the understory layer and bilberry fruit biomass in recent forests (with and without Q. rubra) and in ancient forest with Q. rubra. Results clearly indicated that V. myrtillus benefited from the continuity of Scots pine forests and declined after Q. rubra introduction. As V. myrtillus serves as shelter and provides food for numerous animal species, decreases in bilberry cover and biomass can have far-reaching consequences for biodiversity and population dynamics of numerous species which occur naturally in Scots pine forests. Results show that it can also result in a decrease in availability of non-wood forest products. Therefore, as part of sustainable forest management, we suggest limiting admixture of invasive Q. rubra (as well as other broadleaved species) into pine monocultures in areas with abundant V. myrtillus cover.

The effective sustainable management of introduced woody species requires understanding of the mechanisms which affect successful colonization in different forest habitats. We studied the spontaneous spread of the alien species – Northern red oak (Quercus rubra) in the Scots pine (Pinus sylvestris) forest located in Poland. We analysed the impacts of seed source distance, presence of and distance from linear structures (public and forest roads) in the landscape, as well as microhabitat diversity, on the distribution of juvenile red oaks. We also studied the effects of types of acorn deposition sites (under shrubs, within clumps of Vaccinium myrtillus, in the open), and ways of seed burial (in moss wefts, in rodent corridors) by animal seed hoarders on seed germination and seedling growth. Field data were collected in six transect lines divided into 3300 plots (1 m2 each). We found that Q. rubra efficiently colonizes Scots pine monoculture. Results of spatially explicit hierarchical generalized linear models showed that distance from acorn sources and occurrence of sparse shrub layers are the most important predictors of Q. rubra ecological success, defined as establishment of juvenile specimens. The presence of roads – potential migration corridors for avian and mammalian acorn consumers/dispersers – favoured non-random red oak spread. The “nurse effect” of native understory components on red oak seed germination and seedling growth was indicated by higher numbers of juvenile specimens as well as by higher proportions of germinated seeds noted under shrubs than in open areas (without shrubs) or within clumps of V. myrtillus. All red oaks developed from seeds buried in compact moss wefts or in spacious caches and corridors created by rodents in the moss layer, which indicated a positive “burial effect”. We conclude that microhabitats make the Scots pine forests very suitable for Q. rubra invasion. Because of the wide distribution of numerous red oak stands in European temperate forests and the presence of numerous oak seed dispersers, the continuous colonization of widespread Scots pine monocultures by Q. rubra must be expected.

Spoil heaps, resulting from open-pit mining, are deprived of soil cover. A common method of reclamation for such sites is afforestation aimed at creating whole forest ecosystems. Forest stands planted on soilless areas make it possible to determine the effects of different tree taxa on the species composition of flora. The study focused on the vascular species of herb layers in young forest stands formed by Alnus glutinosa, Betula pendula, Pinus sylvestris, Quercus petraea and Robinia pseudoacacia, and mixed stands dominated by Acer pseudoplatanus or Betula pendula. The study included 227 randomly selected plots across the afforested Belchatow Brown Coal Mine spoil heap. Species composition of the herb layer was composed mainly of synanthropic species (over 70%), and was clearly related to the overstory tree species composition of forest stands. TWINSPAN divided sample plots into two groups that developed under the canopy of stands formed by: (1) Betula pendula, Pinus sylvestris or Quercus petraea, or mixed stands with Betula pendula, or (2) Alnus glutinosa or Robinia pseudoacacia, or mixed stands dominated by Acer pseudoplatanus. The first group was dominated by meadow species (25.8%), while the second had higher richness of ruderal (18.6%) and forest-edge species (14.1%). Plant species associated with fertile and moist forest habitats were more frequent in the second group (Alnus-Robinia), whereas species of acidic and dry forests occurred only in the first group (Betula-Pinus). Non-parametric tests on Ellenberg’s indicator values showed that forest stands of Betula-Pinus group created habitat conditions for light-demanding species with low fertility requirements, whereas forest stands of Alnus-Robinia group created habitat conditions for nitrophilous and shade-tolerant plant species. Our data revealed that tree species composition of forest stands is a key factor shaping herb layer conditions and – as a consequence – herb layer species composition despite of initial habitat variability on the spoil heap. These results highlight a key role of forest stand composition in the development of herb layer richness on post-industrial habitats.

Due to the impact of climate change and rising atmospheric carbon dioxide concentrations, assessment of forest carbon pools becomes a crucial task for forest ecology. One of the scientific gaps in this task is the assessment of young tree stands, not included in forest inventories, due to lack of merchantable volume. We aimed to provide a comprehensive set of allometric equations (AEs) and biomass conversion and expansion factors (BCEFs) for young Scots pine tree stands and to develop models of tree stand biomass based on stand features easy-measurable by remote sensing: height and density. We used data collected in 77 tree stands of Scots pine ranging in age from 3 to 20 years in Western and Central Poland, covering forest, post-agricultural and post-industrial sites. Our dataset included 423 sample trees. Our study resulted in collection of 256 site-specific AEs, 12 generalized AEs and equations allowing for dynamic BCEF calculation. Due to lack of BCEF applicability for young trees, we also provided age- and height-dependent functions allowing for precise biomass estimation at the tree-stand level. It was found that tree-stand biomass increased with tree-stand age, height and volume, and decreased with increasing density in the chronosequence. BCEFs decreased with tree-stand age, height and volume and increased with increasing density. Using these relationships we provided stand-level equations based on BCEFs and on tree height – the stand characteristic which is easily obtained from airborne data. These two models did not show a big difference in accuracy. Thus, height-based models are expected to be useful for extensive assessments of young tree stand biomass and carbon sequestration, allowing for better estimation of forest carbon pools. Moreover, our models, in comparison with IPCC guidelines, give more precise values of carbon pools and biomass of young Scots pine tree stands.

Food resources are one of the important components of high quality habitat. One way to better understand the behavioral decisions made by animals to select foraging patches is focusing on the important forest stand structure characteristics. In this study we investigate the relationship between red squirrel habitat preferences, forest characteristics, i.e. distance to forest edge, canopy closure, cover of understory and undergrowth, and estimated cone biomass. We explore for the first time a methodology to predict cone biomass based on allometric equations and the extent to which this parameter affects habitat choice by red squirrels. Using tree measurements to predicted cone biomass at the plot level which is located in a given stand provides a usefulness proxy of food resources and it is not time-consuming compare with the traditional annual cone count. We selected sixty 30-by-30 m plots in mature Norway spruce forest stands where we measured percentage understory cover, percentage undergrowth cover, distance to forest edge, number of Norway spruce trees, diameter at breast height and height of each Norway spruce tree, number of other tree species and percentage of canopy closure. Within each plot, we counted all Norway spruce cones stripped by red squirrels. Results showed that both forest characteristics (i.e. distance to forest edge and canopy closure) and estimated cone biomass were significant predictors of red squirrel feeding signs on Norway spruce. Our study revealed the potential usefulness of cone biomass as a parameter to determine cone productivity of Norway spruce stands. The effects of food abundance and forest stand structure characteristics are crucial for habitat selection by red squirrels. Estimation of cone biomass based on the tree measurement can be useful for predicting potential foraging habitats for red squirrels regardless of the seed year and can be simple to use for conservation practice in order to locate potential sites for protection of this species.

Tree litter decomposition on disturbed post-mining sites has been mainly studied within successional gradients, whereas almost no results were shown from afforested spoil heaps. Litterfall and its decomposition rate are considered the most important ecological processes for soil restoration during stand development on such initial forest habitats. These processes allow development of a functional ecosystem and productive forest stands. Moreover, the pedogenesis process on such “soilless”’ habitats can be significantly improved and accelerated by tree species selection during afforestation. The main aim of the study was to determine litter decomposition rates of nine tree species used for afforestation of a lignite mine spoil heap. We assumed that leaf litter decomposition rates would differ among tree species studied and that the site conditions would significantly influence this process. Our study was conducted on the spoil heap of the lignite open cast mine in Belchatow, central Poland. We studied leaf litter decomposition of Alnus glutinosa, Betula pendula, Pinus sylvestris, Quercus robur, Q. rubra and Robinia pseudoacacia in pure stands of these species (home stands), and litter decomposition of Acer pseudoplatanus, A. glutinosa, Fagus sylvatica, Prunus serotina, Q. rubra, and R. pseudoacacia in Scots pine stands. We used the litterbag method. The experiments lasted for three years and the samples were collected every three months. Leaf litter decomposition calculated for home stands after three years of decomposition was 94.4% of the initial leaf mass for A. glutinosa, 70.9% for R. pseudoacacia, 70.1% for P. sylvestris, 68.3% for B. pendula, 66.9% for Q. rubra and 61.5% for Q. robur. In Scots pine stands, after three years of the experiment, 92.3% of the initial leaf mass decomposed for P. serotina, 85.7% for A. glutinosa, 83.5% for A. pseudoplatanus, 65.2% for R. pseudoacacia, 50.9% for Q. rubra and 40.1% for F. sylvatica. A. glutinosa, R. pseudoacacia and Q. rubra leaves decomposed significantly faster in home stands than in Scots pine stands. Site aspect significantly influenced litter decomposition of the species studied, with higher rates mostly on the western slope. Our study revealed that the decision on tree species used for afforestation might shorten the period needed for soil restoration and achievement of sustainability of novel ecosystems. Proper selection of main and admixture tree species for afforestation of the post-mining sites might reduce the renewal period of the soilless and newly created habitats, which may provide noticeable ecological and economical effects during stand management.

Forest stand biomass or carbon storage in the biomass may be estimated by conversion of the trees volume since roughly 50% of tree biomass is carbon. There is a need to find biomass conversion and expansion factors (BCEFs) for young stands, because those established for older ones may not be relevant due to changes in biomass allocation patterns over stand age and development phases. We developed BCEFs for above- and belowground biomass components of young silver birch stands as separate functions of stand age or variables that reflect growth conditions and the biological status of trees, i.e. top height (H100), mean height (Hg), base diameter (D0), quadratic mean diameter at breast height (Dg) or stand volume (V). Data were collected on 120 pure birch stands that regenerated naturally on post-agricultural lands in Poland. We determined BCEFs based on the stem volume and dry biomass of above- and belowground components. We applied segmented linear regression (SLR) to develop equations for BCEF determination for each of the pre-determined age classes using (a) fixed break points (FBP) found with the Ward method and (b) estimated break points (EBP) derived based on the best fit of regression models during piecewise regression estimation. We found that the use of SLR and non-linear regression (NR) approaches produced similar results in terms of quality of fit. However, non-linear parameter estimates are more efficient than linear ones, as NR seems to be more frequently used and easier to process using existing statistical tools, but at the same time the SLR provides biological interpretation of results (i.e. the point where BCEF value stabilizes and beyond which stand features do not influence BCEF). The largest difference between EBP and FBP occurs for stems, and the smallest for roots. For total biomass and all biomass components except stem, BCEFs are very high for the youngest, shortest and thinnest trees and hence stands with low volume. Their values decrease along with age, height, diameter and volume towards the EBPs. For individuals older, taller, thicker and with higher volume than EBP, there is no influence of age, H100, Hg, D0, Dg and V on BCEF values. We confirmed that H100 might be a good biomass predictor for young birch stands, which is important because measuring tree height is not as time consuming as tree diameter measurements, particularly for young and very dense stands, and this parameter can be obtained from remote sensing technology.

Six juvenile Sitka spruce ( Picea sitchensis (Bong.) Carr) clones were grown in monoclonal (pure) and polyclonal mixtures (mixed) in a field experiment to assess effects of clonal diversity on above- and below-ground growth, biomass partitioning and fine root morphology. Shoot height and root collar diameter were measured twice annually and after the second year 48 clones were destructively harvested. Fine roots were divided into 10 diameter classes, for each of which morphological characteristics were calculated from digitized images. Competitive interactions arising from deployment type were found to significantly increase fine root surface area in mixed plots and fine root length in pure plots for two fine root diameter classes for some clones. Competitive interactions were also found to significantly alter relationships between above- and below-ground variables and reduce the strength and significance of relationships among root traits in mixed plots. Significant inter-clonal variation for many above- and below-ground parameters was also observed. The two most productive clones, in terms of height and diameter growth, differed significantly in biomass partitioning suggesting that a high degree of variation occurs among Sitka spruce clones, which may affect stand productivity and uniformity.

Regenerating oak seedlings by different methods impacts taproot architecture, root-to-shoot allometry and, potentially, soil water use and plant growth under water limitations. In the present study, Quercus robur (L.) seedlings regenerated by four different methods – sowing (acorn-sown seedlings), sowing followed by shoot clipping (coppiced), sowing followed by root-pruning (root-pruned), and container planting with the root plug intact (containerized) – were subjected to four water-shortage regimes – full watering and 75, 50, and 25% of full watering. These treatments were used to test the hypotheses that root morphology, anatomy and biochemistry varied among regeneration methods, and, thus, differentially affected plant responses to water-shortages. For most traits, the response to water shortage of acorn-sown and containerized seedlings was similar, and opposite to that of coppiced and root-pruned seedlings. Water shortage did not change tree allocation to total root biomass among regeneration methods but altered the partitioning between absorptive and structural roots within the root system. Acorn-sown and containerized seedlings produced more pioneer roots, and coppiced and root–pruned seedlings more highly-branched fine roots with greater specific root length and specific root surface area under greater water shortage. Thus, acorn-sown and containerized oaks appeared to be primed for water foraging, and coppiced and root-pruned oaks for water absorption efficiency in response to water shortage. Water shortage caused a reduction in nonstructural carbohydrate concentrations in fine roots of acorn-sown and containerized seedlings and in the taproot of coppiced and root-pruned seedlings. Results generally indicated that seedling response to water limitation depended on the regeneration method, highlighting the importance of root–to–shoot allometry, taproot development, and carbon reserve mobilization for plant functioning under water shortage. Acorn-sown and containerized oaks seedlings might be more suitable for forest regeneration in sites characterized by severe water shortage periods. The reduction of taproot starch reserves under strong water shortage may render root-pruned oak trees more susceptible to topsoil water deficit than acorn-sown trees. This work contributes to understand drought acclimation and to identify the most adequate forestry regeneration practices to adapt forest ecosystems to ongoing climatic changes.

Despite different levels of complexity among biomass models, it is unclear how much patterns of biomass production and allocation differ between mountain and lowland forests, and how much neglecting this difference biases carbon pool estimations. To address this question, we studied chronosequences of 24 Fagus sylvatica and 24 Picea abies stands in Poland, located both in lowlands and highlands (12 stands of each species per category). We cut and weighted 192 sample trees, and we measured carbon content in wood, bark, branches and leaves. We also developed allometric tree- and stand-level models of biomass and carbon mass. Using log-transformed linear models we checked the effect sizes of elevation category (lowland and highland) on estimate output. We found small, statistically insignificant differences in biomass allocation patterns, carbon content and allometric trajectories in trees between lowland and highland stands. Tree-level allometric models without elevation category had higher accuracy than models including elevation category and explained 96.8–99.8% of biomass variability. Biomass and carbon stock of species studied was positively correlated with stand volume, age, basal area and height, and negatively with stand density. However, the differences between lowlands and highlands were low and did not exceed 38 Mg ha−1 (for P. abies foliage biomass, with model root mean squared error of 37.638 Mg ha−1). Our results revealed transferability of models developed using lowland and highland populations of the studied species. This will increase confidence in methods used to estimate carbon pools.

Specific leaf area (SLA, leaf area to dry mass ratio) is a widely used functional trait in functional ecology. In most studies, SLA is collected by compiling large databases. However, standardized protocols of data collection include only measurements from the sunny side of the crown. We investigated interspecific SLA variability among 179 woody species in common garden conditions of Kornik Arboretum (W Poland). Then, we quantified the differences in SLA measurements between sunny and shaded parts of the crowns of those species. On average, shade leaves had 43.3% higher SLA than sun leaves. Including differentiation between sun and shade measurements explained an additional 12.2% of SLA variability (in total 95.2% explained by species, family and canopy position). In conclusion, intra-canopy SLA variation can result in providing lower SLA values in databases while following the standardized data collection protocols. Here, we contribute to improved understanding of the importance of SLA variability in the context of its wide use in mechanistic and physiological modelling of ecosystem functioning.

Density of natural regeneration of black cherry ( Padus serotina ) depends on distance from the propagule source. Ecological success of this species is higher in coniferous than deciduous forests. The main aim of this study was to assess the interaction between the distance from propagule source and tree stand type (coniferous, deciduous and mixed) on occurrence and density of natural regeneration of black cherry. The study was conducted on 202 experimental plots in Rogow Arboretum (Central Poland), consisting of plantations of alien and native tree species, growing on potential habitats of fertile deciduous forest. The density of natural regeneration was measured in four height classes: 0–0.5 m, 0.5–2 m, 2–5 m and over 5 m. Natural regeneration of black cherry occurred on 79 of the 202 plots, and its density varied from 0 to 25,660 ind. ha −1 . The mean density of black cherry was statistically significantly higher ( p −1 ) than in deciduous (138.3 ± 48.3 ind. ha −1 ) and mixed (29.3 ± 12.3 ind. ha −1 ) stands. There was also a negative relationship between distance from propagule source (stand of P. serotina established in 1932 in the central part of the Arboretum) and density of natural black cherry regeneration ( R 2 = 0.19, p p p P. serotina invasion.

Oaks play an important role in forest ecosystems and are of great economic value. Therefore, the increasing frequency of oak decline incidents in recent decades is of outstanding interest to foresters and researchers in many fields. Despite the general agreement that drought is of major importance in oak decline, very little attention has been devoted to the condition of root systems during drought. In this paper we tested whether cutting the taproot of oak seedlings, a common forest nursery practice, or coppicing, a common management strategy, play a pivotal role in drought-related weakening of oak plantations. Using dendrochronological methods we analyzed whether Quercus robur stands originating from acorns sown directly in the ground, planted seedlings and coppice managed stands differ in response to drought. All studied stands have shown growth depression as a result of prolonged drought conditions. However, stands originating from direct seeding were less severely affected than those from planted seedlings and stands regrown from sprouts after coppicing. In addition, stands established by direct acorns sowing were characterized by lower 13 C/ 12 C isotope ratios ( δ 13 C) in wood, indicating better access to water during its deficit. Therefore, it is likely that intact taproot systems of trees developed from direct seeding are able to reach deeper levels of ground water, and as a result oaks are able to cope more effectively with the difficulties created by prolonged drought conditions. Our study has indicated that common forestry practices may exacerbate drought stress in oak stands, which is considered a major factor causing or predisposing oak decline.

The North-American Northern red oak (Quercus rubra L.) introduced to European forests over 200 years ago, spreads spontaneously in various types of forest ecosystems. At the same time the retreat of native pedunculate oak (Q. robur L.) has been observed. We aimed to recognize the extent of natural regeneration and recruitment of pedunculate (PO) and red oak (RO) in managed forests (central Poland) on sites typical of oak-pine mixed forest, as well as to identify habitat conditions which favour the occurrence of native oak and spread of the alien oak. The abundance and heights of juveniles of both oaks, as well as the impacts of the canopy, nurse and burial effects, on distribution and occurrence of oak specimens were studied on 1000 study plots (1 m2 each), in two transects crossing the Scots pine-pedunculate oak forest (POF) and the Scots pine-northern red oak forest (ROF). We revealed an advantage of introduced RO over native PO in natural regeneration, recruitment and spread. However, we did not find direct (interspecific) competition between PO and RO recruits. RO predominance over PO resulted from more effective colonization of empty niches by the alien oak in POF (suitable for both species), and the abundant establishment of RO seedlings and saplings within ROF. In contrast, PO was not able to re-colonize ROF. The regeneration of RO was microsite-limited in ROF gaps in the regeneration phase (probably due to site moisture deficiency) and under closed RO canopy in the recruitment phase (due to low light availability), and microsite-favoured under mature tree crowns due to the burial effect of the litter layer (and higher light availability under heterogeneous canopy). In POF, RO regeneration was microsite-favoured due to the burial effect of a dense moss layer and the nurse effect of shrubs, including conspecifics. PO regeneration was also microsite-favoured due to the burial effect of the moss layer, but its recruitment was herbivore-limited there (due to browsing). The co-occurrence of PO and RO specimens, both in POF and ROF, resulted from forest community structure, oak ecology and behaviour of acorn dispersers. Because the native PO is at a disadvantage in its native range caused by a lower share of mature trees in forested areas, strong impacts of fungal pathogens and high pressure by insects and large herbivores (also noted in our study), the introduced oak is able to become a serious competitor.