Root distribution of under-planted European beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) below the canopy of a mature Norway spruce stand as a function of light

Aboveground and belowground biomass of 15-year-old under-planted European beech seedlings (Fagus sylvatica L.) in Norway spruce stand were studied along a light gradient in three plots, in the northern part of Slovenia. Differences in soil water content, aboveground and fine root biomass distribution were confirmed between studied plots. Light had significant effect on the total biomass, root-shoot ratio (0.388 ± 0.076 under canopy, 0.549 ± 0.042 in the edge, 0.656 ± 0.047 in the open), specific root length (SRL) of fine beech roots (561.9 ± 42.2 under canopy, 664.3 ± 51.2 in the edge, 618.2 ± 72.8 in the open) and specific leaf area in beech, indicating morphological adjustment to shade. However, SRL of beech fine roots indicated no change between plots. The correlation between total aboveground and root biomass and light below the mature stand canopy was higher in the case of diffuse light intensity. Most fine roots of spruce were concentrated in the top (0–20 cm) soil layer. Beech fine roots under canopy and edge conditions were also concentrated in top (0–20 cm) soil layer and exhibited shift downwards to deeper soil horizons in open plot. Root proportion between beech and spruce changed with light toward beech with increasing light intensity for both fine and coarse roots.     

Species proportions by area in mixtures of Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) and European beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.)

Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) dominate many of the European forest stands. Also, mixtures of European beech and Scots pine more or less occur over all European countries, but have been scarcely investigated. The area occupied by each species is of high relevance, especially for growth evaluation and comparison of different species in mixed and monospecific stands. Thus, we studied different methods to describe species proportions and their definition as proportion by area. 25 triplets consisting of mixed and monospecific stands were established across Europe ranging from Lithuania to Spain in northern to southern direction and from Bulgaria to Belgium in eastern to western direction. On stand level, the conclusive method for estimating the species proportion as a fraction of the stand area relates the observed density (tree number or basal area) to its potential. This stand-level estimation makes use of the potential from comparable neighboring monospecific stands or from maximum density lines derived from other data, e.g. forest inventories or permanent observations plots. At tree level, the fraction of the stand area occupied by a species can be derived from the proportions of their crown projection area or of their leaf area. The estimates of the potentials obtained from neighboring monospecific stands, especially in older stands, were poorer than those from the maximum density line depending on the Martonne aridity index. Therefore, the stand-level method in combination with the Martonne aridity index for potential densities can be highly recommended. The species’ proportions estimated with this method are best approximated by the proportions of the species’ leaf areas. In forest practice, the most commonly applied method is an ocular estimation of the proportions by crown projection area. Even though the proportions of pine were calculated here by measuring crown projection areas in the field, we found this method to underestimate the proportion by 25% compared to the stand-level approach.     

Interspecific competition impacts on the morphology and distribution of fine roots in European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.)

Morphology and vertical distribution patterns of spruce and beech live fine roots (diameter ≤2 mm) were studied using a soil core method in three comparable mature stands in the Solling: (1) pure beech, (2) pure spruce and (3) mixed spruce–beech. This study was aimed at determining the effects of interspecific competition on fine root structure and spatial fine root distribution of both species. A vertical stratification of beech and spruce fine root systems was found in the mixed stand due to a shift in beech fine roots from upper to lower soil layers. Moreover, compared to pure beech, a significantly higher specific root length (SRL, P<0.05) and specific surface area (SSA, P<0.05) were found for beech admixed with spruce (pure beech/mixed beech SRL 16.1–23.4 m g⁻¹, SSA 286–367 cm² g⁻¹). Both indicate a flexible ‘foraging’ strategy of beech tending to increase soil exploitation and space sequestration efficiency in soil layers less occupied by competitors. Spruce, in contrast, followed a more conservative strategy keeping the shallow vertical rooting and the root morphology quite constant in both pure and mixed stands (pure spruce/mixed spruce SRL 9.6/7.7 m g⁻¹, P>0.10; SSA 225/212 cm² g⁻¹, P>0.10). Symmetric competition belowground between mixed beech and spruce was observed since live fine roots of both species were under-represented compared to pure stand. However, the higher space sequestration efficiency suggests a higher competitive ability of beech belowground.     

Spatial patterns and genetic structures within beech populations (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) of forked and non-forked individuals

Analyses of distribution patterns and genetic structures of forest stands can address distinct family structures and provide insights into the association of genetic and phenotypic variation patterns. In this study, point pattern analysis and spatial autocorrelation were used to examine the spatial and genetic structures in two naturally generated beech stands, which differ in age, trunk morphology, and stand management. Significant tree clumping was observed at distances up to 20 m in the young forest stand, whereas dispersion at distances under 10 m was observed in the old stand. The spatial analysis based on Ripley’s k function of the two different groups of trees showed that the non-forked trees match in both stands the spatial pattern of all trees while the forked were randomly distributed. Additionally, according to the bivariate analysis, forked trees in both stands were randomly distributed as related to non-forked tree positions. Finally, Moran’s I values were not very high, though significant genetic autocorrelation was identified at distances up to 20 m in the young stand, suggesting the existence of distinct family structures. However, no significant genetic structuring was observed in the old stand. Our findings suggest that spatial genetic patterns are impacted by stand age, environmental factors and human activities. The spatial distribution of forked trees was not clearly associated to family structures. Random effects and also micro-environmental variation could be additional factors explaining forking of beech individuals.     

Predicting tree regeneration in <Emphasis Type="Italic">Picea abies</Emphasis> snag stands

A bark beetle (Ips typographus) infestation caused the death of almost all Norway spruce (Picea abies) trees in a mountain forest in the Swiss Alps. We developed a tree regeneration model, ‘RegSnag’ (=REGeneration in a SNAG stand), to project the future amount and height of tree regeneration in these snag stands. The model combines a height-class structured tree module with a microsite-based module of snag decay and ground-vegetation succession. Microsite-specific rates of germination, mortality and height growth were modelled for four tree species (Picea abies, Sorbus aucuparia, Acer pseudoplatanus and Betula pendula) in eight height classes (from seedlings to saplings 5 m tall) and on 26 microsite types (e.g. moss, grass). Model tests with independent field data from 8 years after the Picea die-back demonstrated that microsites had a considerable effect on the development of tree regeneration on both the montane and the subalpine level. With microsite-specific parameters, the height and frequency of Picea in each microsite could be simulated more accurately than without considering microsite effects (e.g. bias of 8 vs. 119 saplings ha⁻¹ on the montane level). Results of simulations 40 years into the future suggest that about 330–930 Picea saplings per ha out of those that germinated in 1994 and 1996 will reach a height of 5 m within 30–35 years after Picea die-back. This is due to differences in seed inflow and browsing intensities. Picea and not Betula or Sorbus trees will replace the current herbaceous vegetation in these snag stands.     

Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis> L.) regeneration and growth of understory trees under single-tree selection silviculture in Finland

This study presents empirical data on regeneration and growth of understory trees and constructs simple models for predicting these characteristics at various stand structure and post-thinning standing volume levels. The field experiment was established on a grass/herb mineral soil site in central Finland. Regeneration and understory tree growth data were collected from 24 Norway spruce (Picea abies L.)-dominated mixed substands. Seedlings with heights from 5 to 130 cm were measured in 1996 and 2007. In addition, the annual height growth of Norway spruce seedlings was measured in 2007. The spatial pattern of the substands varied from clustered to regular with a decreasing standing volume. Stand complexity was uniform across the range of standing volume. In the 2007 survey, the amount of Norway spruce regeneration increased from approximately 400 to 5,000 seedlings ha⁻¹ when the post-thinning standing volume level was reduced from 230 to 90 m³ ha⁻¹, respectively. Nearly no seedlings were found when the standing volume was over 300 m³ ha⁻¹. The annual diameter increment in Norway spruce understory (dbh < 5 cm) trees decreased, on the average, from 2.3 to 0.3 mm with an increase in the standing volume level from 90 to 340 m³ ha⁻¹, respectively; their height growth showed also a decreasing trend when the standing volume increased. The results indicated that a post-thinning standing volume lower than 150 m³ ha⁻¹ with a regular overstory spatial structure provides a suitable environment for regeneration and growth of Norway spruce understory trees in the studied forest type.     

Leaf area of beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) from different stands in eastern Austria studied by randomized branch sampling

Few tree size/leaf area correlations have been produced for hardwoods, where the extrapolation from individual branches to the whole tree is less straightforward than in conifers with more regular branching patterns. We used randomized branch sampling to estimate leaf area of European beech (Fagus sylvatica L.) trees of different stands, ages and areas in Austria. Cross-sectional areas (CSA) predicted 87–92% of leaf area variation, the best predictor being the sum of branch CSA. Leaf area was somewhat better correlated with CSA at breast height than at the base of the crown, and using sapwood instead of total CSA made little difference. While there was no effect of growth area, a stepwise regression model showed that dominant trees in pole-stage had, for unclear reasons, significantly higher leaf area/CSA relationships. A comparison with regressions produced from smaller beech trees in other parts of Europe suggests that the leaf area/basal area regression is generally valid for beech in central Europe.     

Oak (<Emphasis Type="Italic">Quercus robur</Emphasis> L.) regeneration as a response to natural dynamics of stands in European hemiboreal zone

The oak (Quercus robur L.) regeneration intensity was assessed in the core area of the Białowieża National Park (BNP) in Poland with respect to the selected ecological factors. The emphasis was placed on the response of oak regeneration to disturbances, including the large-scale dieback of spruce stands. Defining their effect could help predicting the role of oak in naturally developing lowland forest ecosystems in the European hemiboreal zone. The results of the study challenge the opinion that the ‘lime-oak-hornbeam forest’ is a ‘climax’ community, confirming a very poor regeneration represented by only two saplings taller than 0.5 m per hectare. By contrast, in spruce-dominated communities, from 49 to 848 taller saplings per hectare were found. The occurrence of saplings was associated with discontinuous canopy of late seral stage of stands, as well as with large gaps. Most of the best quality grown-up oak saplings developed in the immediate neighbourhood of spruce logs. The results of the research indicate that ‘lime-oak-hornbeam forest’ (Tilio-Carpinetum) should be rather perceived as a transient community, evolved from relict, culturally modified, oak woodlands. Because spruce had become a dominating species only after abandoning in mid-1800s the historical regime of anthropogenic disturbances (involving frequent forest fires), the observed phenomena related to the disintegration of spruce stands had probably no precedent over the last 500 years. To confirm whether the massive decline of spruce stands will finally result in the successful establishment of the new canopy oak generation, both in Białowieża and other forests of hemiboreal zone, further research is needed.     

Climate change impacts on stand structure and competitive interactions in a southern Swedish spruce–beech forest

It is believed that European beech (Fagus sylvatica L.) will increase its competitive ability at its northern range margin in Scandinavia due to climate change. In mixed old-growth forests of beech and Norway spruce (Picea abies (L.) Karst.) at Siggaboda nature reserve (southern Sweden), stand structure characteristics were sequentially recorded in the years 2004, 2005 and 2007 as well as growth in stem diameter using tree-coring analyses. Using these measurements, we studied the effects on stand dynamics of an extreme storm event (2005 “Gudrun” hurricane), drought and heat (mid-summer 2006, spring 2007) and subsequent bark beetle attacks on spruce (growing season 2007), overlaid with warming tendencies. The storm, which caused disastrous damage in many stands nearby, had comparatively little impact on the structure of the spruce–beech stand. All together, only 32 trees (19 spruces, 10 beeches, 3 other species) per hectare were thrown or broken mainly in the leeward direction (NE) or impacted by secondary damage by uprooted neighbour trees; this represents 7% of the total tree number and 11% of the growing stock. Diameter and height structure did not change significantly. However, the 2006 drought and the 2007 attack of biotic agents changed the stand structure and composition strongly due to the death of about 19% of the dominating older spruce trees that accounted for 35% of total stand volume. This resulted in a considerable increase in beech’s contribution to stem number (4% increase) and wood volume of the living stand (7% increase). A comparison of diameter growth of beech and spruce during the periods 1894–1949 and 1950–2005 showed a distinct decrease in growth superiority of spruce during the last 50 years. These results support the idea of a northward migration of European beech as a nemoral tree species in Sweden, due to a higher tolerance to the abiotic and biotic threats accompanying climate change and an increased competitive ability compared to boreal tree species Norway spruce.     

Aboveground biomass and nutrient allocation in an age-sequence of <Emphasis Type="Italic">Larix olgensis</Emphasis> plantations

Biomass and nutrient (N, P, K, Ca, Mg) stock in various aboveground tree components (stemwood, stembark, branches and leaves) were quantified in an age sequence of pure Larix olgensis planta- tions (20, 35, 53 and 69 years old) in Northeast China. The results show that the aboveground biomass allocation in various tree components was in the order of stemwood (62%-83%), branches (9%-21%), stembark (7%-11%) and leaves (1%-6%) for all stands. The proportion of stemwood biomass to total aboveground biomass increased whereas that of other tree components decreased consistently with stand age from 20 to 53 years old, but kept relatively constant with stand age from 53 and 69 years old. The nutrient allocation in various tree components generally followed the same pattern as the biomass allocation (i.e. stemwood > branches > stembark > leaves). The proportion of nutrient stock in leaves to total aboveground nutrient stock decreased consistently with increasing stand age, while that in stemwood increased with stand age from 20 to 53 years old but then decreased from 53 to 69 years old. The rate of nutrient removal for stands was estimated at different stand ages under different logging schemes, showing that the rate of nutrient removal would be unchanged when the rotation length was shortened to 20 years by the harvest of stem only, but greatly increased by the harvest of total aboveground biomass. The rate of nutrient removal would be a considerable reduction for all elements by debarking, especially for Ca.     

Spatial pattern of beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) and oak (<Emphasis Type="Italic">Quercus pubescens</Emphasis> Mill.) seedlings in natural pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) woodlands

Spatial pattern of recruitment is an important factor influencing population dynamics of plant communities. The spatial pattern is determined by seed dispersal and by the spatial variability of germination and initial survival. In the process of forest expansion following farmland abandonment, mid- and late-successional species are often dispersed in pioneer forests by birds. This could result in an aggregated spatial pattern of seeds that could influence the dynamics of these species in mixed pioneer forests. In the sub-Mediterranean area, mid- and late-successional species such as Quercus pubescens (downy oak) and Fagus sylvatica (European beech) are expected to replace pioneer Pinus species. Using a point sampling method we demonstrated that beech and oak seedlings (height <2 m) have a clumped distribution in the understorey of pine. This could result from an aggregated dispersal by jays (dispersal effect) or from preferential recruitment in particular habitats (habitat effect). To test these hypotheses we proposed a statistical analysis of spatial patterns of regeneration of beech and oak. Ground cover variables (i.e. cover by rock outcrops, herbs, box shrubs, mosses or pine) did not differ significantly around seedlings as compared with random sample plots. Likewise, clumped seedlings had growth similar to isolated seedlings, thus refuting the hypothesis of preferential location in the most favourable microsites. Aggregated dispersal seems to be involved in the process of regeneration. Since beech and oak seedlings have contrasting ecological demands, we discuss the implication of this pattern for the replacement dynamics of pine by these species.     

A non-linear model to predict crown recession of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis> [L.] Karst.) in Austria

In this study, a non-linear model was developed that predicts the five-year change of height to crown base (HCB) of Norway spruce (Picea abies [L.] Karst.). Data were available from the Austrian National Forest Inventory and comprised 2,419 trees from 1,637 permanent sample plots measured during 1981 and 2002. The dynamic model explained 36% of the variation in the observed change of HCB. It is well behaved and meets biological expectations. Based on five independent data sets, the predictive ability of the new dynamic model was compared to an already existing static crown ratio model. For this comparison, the models were applied as follows: the new ∆ HCB model was used to predict the change in HCB directly. For the semi-dynamic method, the static model was applied at the end and at the start of the growth period to obtain two estimates of HCB. The difference of these two estimates was then added to the initial HCB. For the static method, the model was only applied at the end of the prediction period to obtain the new estimate of HCB. Except for one plot, the new ∆ HCB model yielded the smallest BIAS and the highest precision, followed by the semi-dynamic and the static method. Because the independent data sets cover a broad range of age classes and thinning regimes, the validation results also indicate that the new ∆ HCB is robust and the effect of stand management is adequately represented.     

Modelling the risks of natural stand closure release with ageing in pure beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis>) and spruce (<Emphasis Type="Italic">Picea abies</Emphasis>) stands

• Background  

In the development of pure beech and pure spruce pristine forests, we assume there should be a continuous transition from full stocking to successive disintegration and, finally, total replacement of the first generational wave at the end of its lifetime, dependent on mortality due to overcrowding as well as ageing, leading newly recruited cohorts to grow up from below.     

Towards a DNA marker assisted seed source identification: a pilot study in European beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.)

The widespread European forest tree Fagus sylvatica L. is of great importance for forest management. However, information about seed dispersal is still very rare, though important for harvesting strategies and later on seed source identification. We refined a DNA fingerprinting method for beech nut shells in order to directly assign dispersed seeds to their mother trees. A pilot study was conducted in two beech stands in Germany where leaves of the adult trees and the exocarp of dispersed seeds were fingerprinted at six nSSR loci. While one stand was randomly analysed for adults and dispersed seeds the other was systematically investigated following common harvesting procedures. Imitating the typical net harvesting strategy, seeds were collected beneath 19 adult trees. Exocarp genotyping revealed that on average three different mother trees contributed to a sample of five or six seeds collected beneath a single adult tree. Of the identified mother trees most were located within a radius of 15 m from the sampling point. The repeated pattern of seed dispersal within a short distance constitutes the basis for a straightforward strategy for the assignment of seed lots to a seed source stand. This strategy is based on the matching of individual genotypes without the necessity for a full inventory of the putative source stand. Additionally, we provide allelic ladders of five nSSR loci for standardization among laboratories.     

Estimation of stand attributes in <Emphasis Type="Italic">Cryptomeria japonica</Emphasis> and <Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis> stands using QuickBird panchromatic data

This study aims to estimate stand density and stand volume in Cryptomeria japonica and Chamaecyparis obtusa stands from high-resolution satellite data and verify the reliability and uncertainty of the data. Sixty circular sample plots of 0.04 ha each were established. Their stand densities were estimated from the number of tree crowns derived from high-resolution satellite data using the watershed method. Stand densities derived from field surveys in the sample plots were compared with those obtained from high-resolution satellite data by stand age class. As a result, there was a positive correlation between them for sample plots of 41 years of age and over (R = 0.82); however, there was no correlation between them for sample plots of 40 years and under. Individual diameters at breast height (DBH) were estimated from crown areas obtained from high-resolution satellite data for the two species. Using the estimated DBH, individual tree heights were predicted from the height–diameter curves. Stand volumes were estimated from the sum of individual volumes, which were derived from volume formulas having two variables, i.e., DBH and height. Stand volumes derived from the field survey were compared with those obtained from high-resolution satellite data. The correlation coefficient between them for stands of 41 years of age and over was 0.78.     

Stem taper functions for maritime pine (<Emphasis Type="Italic">Pinus pinaster</Emphasis> Ait.) in Galicia (Northwestern Spain)

A total of 31 taper functions from 3 different groups of models (single, segmented and variable-form taper functions) were fitted to diameter-height data from 203 Pinus pinaster trees sampled across even-aged stands in Galicia (northwestern Spain). Most of the taper functions analyzed showed problems of multicollinearity as indicated by the condition number. A second-order autoregressive CAR(2) error process was incorporated into the models to minimize the effect of autocorrelation inherent in the longitudinal data used, and to provide valid tests of significance for model parameter estimates. In general, variable-form taper functions provided the most accurate predictions. The flexibility and predictive performance of the variable-form model developed by Kozak (For Chron 80(4):507–515, 2004) indicated its usefulness for estimating diameter at a specific height, merchantable volume, and total volume of Maritime pine in the study area.     

Ectomycorrhizal communities within beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) forests that naturally regenerate from clear-cutting in northern Spain

The objectives of the work described here were to evaluate the diversity of ectomycorrhizal (ECM) fungi within Spanish beech (Fagus sylvatica L.) forests subjected to clear-cutting and natural regeneration and to elucidate the extent to which the carbohydrate concentration in roots of trees of different ages and sizes is related to ECM colonization. The study concerned an unmanaged forest, a stand clear-cut in 1996 and another clear-cut in 2001. ECM colonization of beech roots showed seasonal dynamics in the disturbed areas, but the percentage of roots colonized by ECM was not always related to the accumulation of non-structural carbohydrates. The composition of ECM communities differed between different stands and 40% of ECM morphotypes only occurred in disturbed ecosystems. However, comparable numbers of different ECM morphotypes (24, 25) were found in the three beech stands. This finding indicates that ECM diversity was quite high and similar within disturbed and unmanaged areas. This finding suggests that (1) ECM diversity was not affected by the size and age of trees and (2) the potential of ECM inocula remained high within clear-cut areas. Consequently, the introduction of ECM inocula by silvicultural practices would not be needed to improve the regeneration of clear-cut areas described in our study.