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Effects of Tree Canopy on Herbaceous Understorey Throughout the Developmental Cycle of a Temperate Mountain Primary Forest

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Forest management is widely considered to have an impact on the understorey plant diversity, which is essential for sustainable forestry and nature conservation. However, contradictions among previous large-scale studies and meta-analyses raised the need for better-designed research. Such research should identify drivers controlling diversity and species composition, quantify the overstorey-understorey relationships and their dynamics in the temperate forests. Two spatial scales (2.25 m2; 314 m2) and stratified random sampling design were used to record understorey vegetation and overstorey and environmental properties along the whole lifecycle of managed Norway spruce (108 years) and European beech (140 years) stands, the most wide-spread mountain forest types in European temperate zone. The dataset also includes primeval fir-beech forests located in the same area. Forest management significantly altered understorey diversity and species composition in both beech and spruce stands. Diversity measures changed considerably over the development of managed stands, exhibiting the rapid decline from species-rich forest clearings to poor stands of 30–40 years, later slowly recovering and reaching the average level of old-growth forests at the age of over 100 years. The impact of management was stronger at the smaller scale. It is caused by the fine-scale character of overstorey-understorey interactions, and it is weakened due to stand structure heterogeneity in larger scales. Competition of overstorey trees was identified as the most important driver of understorey diversity and its temporal dynamics. It was also reflected in the litter amount, which negatively affected diversity especially in the beech forests. In contrast, the light amount was a more important factor in the spruce stands. We conclude that comparisons between datasets that are heterogeneous regarding overstorey age and proportion of development stages, as well as meta-analyses based on such inconsistent studies, can lead to confusing conclusions and improper applications. As a practical implementation, we recommend using overstorey tree density as the most efficient measure for assessment, prediction and managing understorey plant diversity.
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Light is one of the most important drivers of understory vegetation in forests, influencing the patterns of total cover as well as the abundance of individual species. Based on a multi-scale approach, the relationships between the amount and pattern of relative diffuse light and forest understory were studied in an old-growth, temperate mixed forest (Hungary). The recorded vegetation variables were the cover of the vascular understory (herbs, woody seedlings), the bryophyte layer, and some selected vascular understory species. The pattern of light showed aggregations at two scales: 10×10 and 25×25 m. Both vascular understory and bryophyte cover had significant positive correlations with light availability, and their spatial pattern was related to it. The pattern of seedlings displayed the strongest relationships with that of light at a coarser scale (25×25 m) than herbs and bryophytes (10×10 m). At the species level, Festuca heterophylla, Fragaria vesca and Poa nemoralis were characterized as light-demanding herbaceous species (their spatial pattern was congruent with light), Brachypodium sylvaticum and Carex pallescens were transitional, while some species proved to be shade-tolerant (e.g. Ajuga reptans, Dryopteris carthusiana, Viola reichenbachiana). Regarding seedlings, the patterns of Betula pendula, Carpinus betulus, Pinus sylvestris and Quercus petraea were related to the pattern of light. According to our observations, diversity and composition of vascular forest understory and bryophytes were related to heterogeneous light conditions. Forest management should maintain continuous shelter on the stand level; however, smaller gaps are necessary for the survival of light-demanding forest herbs and bryophytes, and larger gaps for tree seedlings.
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The first edition of this book has established itself as one of the leading references on generalized additive models (GAMs), and the only book on the topic to be introductory in nature with a wealth of practical examples and software implementation. It is self-contained, providing the necessary background in linear models, linear mixed models, and generalized linear models (GLMs), before presenting a balanced treatment of the theory and applications of GAMs and related models. The author bases his approach on a framework of penalized regression splines, and while firmly focused on the practical aspects of GAMs, discussions include fairly full explanations of the theory underlying the methods. Use of R software helps explain the theory and illustrates the practical application of the methodology. Each chapter contains an extensive set of exercises, with solutions in an appendix or in the book’s R data package gamair, to enable use as a course text or for self-study.
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Vegetation Ecology, 2nd Edition is a comprehensive, integrated account of plant communities and their environments. Written by leading experts in their field from four continents, the second edition of this book: covers the composition, structure, ecology, dynamics, diversity, biotic interactions and distribution of plant communities, with an emphasis on functional adaptations; reviews modern developments in vegetation ecology in a historical perspective; presents a coherent view on vegetation ecology while integrating population ecology, dispersal biology, soil biology, ecosystem ecology and global change studies; tackles applied aspects of vegetation ecology, including management of communities and invasive species; includes new chapters addressing the classification and mapping of vegetation, and the significance of plant functional types Vegetation Ecology, 2nd Edition is aimed at advanced undergraduates, graduates and researchers and teachers in plant ecology, geography, forestry and nature conservation. Vegetation Ecology takes an integrated, multidisciplinary approach and will be welcomed as an essential reference for plant ecologists the world over.
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In this study, two forest sites located in Finland were compared by means of predictions of Gini coefficient (GC) obtained from airborne laser scanning (ALS). We discuss the potential of the proposed method for identifying differences in structural complexity in relation with the management history of forests. The first study site (2200 ha), the Koli National Park (NP), includes areas where human intervention was restricted after 1907, in addition to forests which were protected only after the 1990s. The second study site in the municipality of Kiihtelysvaara (800 ha) has been under intensive management. These are commercial forests which include areas with different types of ownership: a large estate owned by an industrial company together with smaller private properties. We observed that GC predictions may be used to evaluate the effects of management practice on forest structure. Conservation and commercial forests showed significant differences, with the old-protected area of Koli having the highest, and the most intensively managed area in Kiihtelysvaara the lowest GC values. The effect of management history was revealed, as the 1990s' extensions of Koli NP were more similar to unprotected areas than to forests contained within the original borders of the 1907s' state property. Yet, their conservation status for almost two decades has been sufficient for developing significant differences against the outside of the NP. In Kiihtelysvaara, we found significant differences in GC according to the type of ownership. Moreover, the ALS predictions of GC also detected differences near lakeshores, which are driven by limitations on logging governed by Finnish law. Estimating this indicator with ALS remote sensing allowed to observe its spatial distribution and to detect peculiarities which would otherwise be unavailable from field plot sampling. Consequently, the method presented appears to be well suited for monitoring the effects of management practice, as well as verifying its compliance with legal restrictions.
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The problem of testing smooth components of an extended generalized additive model for equality to zero is considered. Confidence intervals for such components exhibit good across-the-function coverage probabilities if based on the approximate result, where f is the vector of evaluated values for the smooth component of interest and V f is the covariance matrix for f according to the Bayesian view of the smoothing process. Based on this result, a Wald-type test of f=0 is proposed. It is shown that care must be taken in selecting the rank used in the test statistic. The method complements previous work by extending applicability beyond the Gaussian case, while considering tests of zero effect rather than testing the parametric hypothesis given by the null space of the component's smoothing penalty. The proposed p-values are routine and efficient to compute from a fitted model, without requiring extra model fits or null distribution simulation.
Article
Testing that random effects are zero is difficult, because the null hypothesis restricts the corresponding variance parameter to the edge of the feasible parameter space. In the context of generalized linear mixed models, this paper exploits the link between random effects and penalized regression to develop a simple test for a zero effect. The idea is to treat the variance components not being tested as fixed at their estimates and then to express the likelihood ratio as a readily computed quadratic form in the predicted values of the random effects. Under the null hypothesis this has the distribution of a weighted sum of squares of independent standard normal random variables. The test can be used with generalized linear mixed models, including those estimated by penalized quasilikelihood.
Article
The Carpathian mountains harbour the largest areas of virgin European beech (Fagus sylvatica L.) forest. Understanding the growth dynamics of European beech under natural conditions without human intervention is crucial for close-to-nature management of beech forests in Europe. In this study we give an insight into the natural disturbance dynamics of the virgin beech forest Uholka, based on a structural analysis and a dendroecological reconstruction of its history. On four circular plots of 0.1ha each, DBH and tree height of all living trees ⩾6cm DBH were measured. Increment cores of all the 164 trees were taken for age estimation and growth pattern analysis. To identify significant growth releases and reconstruct the disturbance history a dendroecological approach, referred to as the boundary line method, was employed. The density of the living trees per plot ranged from 270 to 590 stems per ha and the volume from 525 to 1237m3 per ha. The longest tree-ring series was 451years long, however age estimation methods showed that beech could reach an age of up to 550years. All four plots covered an age span of at least 300years and can be characterised as uneven-aged with continuous tree establishment. Beech can survive long suppression periods of over 100years and shows regularly distributed growth releases over the analysed period (1870–1999). The results suggest that stand dynamics in this forest are driven by periodic small disturbances, while larger events occur only rarely. The high percentage of rotten trees in the upper canopy indicates that individual trees are prone to windbreakage, which promotes these small-scale dynamics.
Article
A renewed interest in natural gap dynamics has developed from a recent focus on sustainable forestry in Europe. To improve our understanding of the role of a canopy opening on the physical environment in a natural forest, a case study was undertaken in and around a gap in a semi-natural, beech-dominated (Fagus sylvatica L.) forest. Spatial and temporal variations in photosynthetically active irradiance (IP), soil and air temperature (TS and TA) and soil water content (SWC) were studied until the third growing season after natural formation of the gap.IP was highest in the northern part of the gap and in the adjacent forest, particularly around mid-summer and on sunny days, when IP was predominantly direct. Total IP in the southern part of the gap and along gap edges declined by about 19.6% from the first to the second year after gap formation, possibly due to growth of canopy and sub-canopy trees. Maximum and mean TS were generally highest in the southern central part of the gap, and in late spring and summer also under the closed canopy east of the gap. The insulating effect of dense regeneration could to some extent explain the spatial variation of TS, though this was not tested directly. SWC in the gap was near field capacity and generally higher than that under the closed canopy during summer. A decrease in SWC from the first to the second year after gap formation may have been attributed to released edge trees, although water use by the dense regeneration could not be ruled out.In general, the effect of this small irregular gap on light, soil and air temperature, and soil moisture was influenced by the considerable microsite variation. Furthermore, growth of regeneration and edge trees, resulting in increased interception, shading and water extraction by roots, may have modified the gap effect seen as early as the second year after gap formation.
Article
Temperate-zone forests have been shaped by fire, wind and grazing over thousands of years. This book provides a major contribution to the study of their dynamics by considering three important themes: • The combined influence of wind, fire and herbivory on the successional trajectories and structural characteristics of forests • The interaction of deciduous and evergreen tree species to form mosaics which, in turn, influence the environment and disturbance regime • The significance of temporal and spatial scale with regard to the overall impact of disturbances These themes are explored via case studies from the forests in the Lake States of the USA (Minnesota, Wisconsin and Michigan) where the presence of large primary forest remnants provides a unique opportunity to study the long-term dynamics of near-boreal, pine and hardwood-hemlock forests. The comparability of these forests to forests in other temperate zones allows generalizations to be made that may apply more widely.
Article
Where natural production capacity permits, modern silvicultural management in Central Europe frequently aims at the development of mixed broadleaved stands, instead of pure European beech (Fagus sylvatica) stands. It is crucial to study the effects of these tree-layer diversity variations on herb-layer vegetation, since herb-layer vegetation contributes significantly to ecosystem functioning in forests. In Hainich National Park (Thuringia, Germany), we conducted observational research in deciduous stands to investigate whether herb-layer diversity was related to canopy-layer diversity, and to ascertain possible causal mechanisms. We found that herb-layer vegetation of deciduous forest stands rich in canopy species appeared to be more diverse than herb-layer vegetation of beech-dominated stands. We surmise that herbaceous understorey diversity was indirectly influenced by canopy tree species through the medium of the altered environmental factors soil pH and litter layer thickness. Apparently, lower beech proportion had a more profound effect than the number of secondary tree species. There were no correlations between herb-layer diversity and light transmissibility of the canopy layer, indicating that the light factor was not crucial for herb-layer diversity. At least for the Hainich research sites, our results indicated that small-scale light and soil heterogeneity is insignificant for herb-layer diversity. We found several herb-layer species whose occurrence was particularly correlated with tree-layer diversity and environmental factors. Remarkably, all species positively correlated with soil pH were important for the phytosociological classification of the research sites. Beech-dominated research sites showed high tree-layer volumes, whereas research sites with high tree-layer diversity tended to feature lower tree-layer volumes. These findings could be the result of differing former silvicultural systems and varying soil clay contents affecting tree species composition. In contrast, herb-layer biomass was positively correlated with tree-layer diversity. Herb-layer productivity might be promoted in more diverse research sites by increased nutrient supply and base saturation. It is also possible that greater beech proportion interfered with herb-layer productivity. However, herb-layer biomass was also positively correlated with herb-layer diversity. Hence, our study hints that positive diversity-functioning relationships might occur in the herb-layer of the deciduous forest under investigation.
Article
Bell System Technical Journal, also pp. 623-656 (October)
Article
Changes to vegetation and soil were assessed in primeval forests of the Eastern Carpathians after a period of 59–68 years. We hypothesized that forest ecosystems were acidified through the long-distance transport of air pollutants. A total of 141 relevés and 20 soil profiles that had been studied in 1938 in spruce- and beech-dominated forests along an altitudinal gradient ranging from 1085–1575 m a.s.l. were re-surveyed from 1997 to 2006. Relevés were analyzed using multidimensional statistics and plant community characteristics (Shannon–Wiener’s index, equitability, fidelity, Ellenberg indication values – EIV); soil reaction and sorption complex properties were analyzed in soils.
Article
1. Atmospheric nitrogen (N) deposition is expected to change forest understorey plant community composition and diversity, but results of experimental addition studies and observational studies are not yet conclusive. A shortcoming of observational studies, which are generally based on resurveys or sampling along large deposition gradients, is the occurrence of temporal or spatial confounding factors. 2. We were able to assess the contribution of N deposition versus other ecological drivers on forest understorey plant communities by combining a temporal and spatial approach. Data from 1205 (semi-)permanent vegetation plots taken from 23 rigorously selected understorey resurvey studies along a large deposition gradient across deciduous temperate forest in Europe were compiled and related to various local and regional driving factors, including the rate of atmospheric N deposition, the change in large herbivore densities and the change in canopy cover and composition. 3. Although no directional change in species richness occurred, there was considerable floristic turnover in the understorey plant community and a shift in species composition towards more shade-tolerant and nutrient-demanding species. However, atmospheric N deposition was not important in explaining the observed eutrophication signal. This signal seemed mainly related to a shift towards a denser canopy cover and a changed canopy species composition with a higher share of species with more easily decomposed litter. 4. Synthesis. Our multi-site approach clearly demonstrates that one should be cautious when drawing conclusions about the impact of atmospheric N deposition based on the interpretation of plant community shifts in single sites or regions due to other, concurrent, ecological changes. Even though the effects of chronically increased N deposition on the forest plant communities are apparently obscured by the effects of canopy changes, the accumulated N might still have a significant impact. However, more research is needed to assess whether this N time bomb will indeed explode when canopies will open up again.
Article
Question We were interested if and how variation in frequency and/or size of disturbances affect the dynamics of a montane old‐growth forest in Central Europe. Location The forest, co‐dominated by Fagus sylvatica, Picea abies and Abies alba , is located in Lower Austria and represents one of the few sizable virgin forests in Central Europe. Methods We extracted cores from 100 trees using systematic grid sampling (grid cell size 10 m × 10 m) on each of four 1‐ha plots distributed across the old‐growth remnant of 300 ha. We inferred disturbance events from rapid early growth and release events. For defining release criteria, we applied the boundary line method. We investigated the spatial structure of current age and gap distributions and past disturbance events in grid cells, using a pair density statistic. Results The disturbance histories indicate decades with peaks and also extended periods without disturbance. Some peaks occurred synchronously at three of the four plots (1910s, 1930s, 1960s and 1980s). Peaks and gaps in the disturbance chronologies widely agreed with peaks and gaps in the age distributions. Most disturbance events during single decades showed a random spatial distribution. Conclusions There is considerable variation in disturbance frequency and/or severity over time. Most disturbance events will rather thin the stand than clear larger areas at once. Following scattered disturbance two pathways occur: (1) gap expansion leading to creation of larger gaps, and (2) gap closure by lateral encroachment or by subcanopy trees growing into the canopy.
Article
Tree species composition is a primary attribute of forest ecosystems, and is often manipulated by silvicultural practices. Forest management to diversify tree species is now being promoted to favor biodiversity. To assess the soundness of this policy we reviewed and analyzed the literature on the relationship between tree species composition and floristic diversity, including the mechanisms involved therein. Coniferous forests generally provide less diversified vascular understories than broadleaved forests. At the tree species scale, there are not enough reports to draw firm conclusions on the effect of any particular species. Mixing of deciduous and coniferous tree species generally affects understory diversity, but in almost all cases maximum diversity is observed in one of the pure stands, not in mixed stands. Understory vegetation is influenced by overstory composition and structure through modifications of resource availability (light, water and soil nutrients) and other effects, such as physical characteristics of the litter layer. Overstory light transmittance and diverse properties of forest litter are factors that have been most fully studied to date, but other factors such as throughfall water quantity and chemistry may also play a role. While the relative importance of mechanisms that account for the effect of overstory on understory biodiversity has often been discussed, these mechanisms have rarely been the subject of formal experiments. Overall, varying management practices and site attributes make it difficult to generalize results. They combine with the effects of tree species in influencing understory vegetation diversity, but they have been rarely considered. Future research is needed to gain a better understanding of the relationship between overstory and understory diversity and establish general laws.
Article
Understanding the mechanisms that control vegetation development beneath canopy gaps is of major importance for a nature-based management of European beech forests. We studied the herb layer vegetation beneath 56 canopy gaps of various sizes (116–1410 m2) in near-natural beech forest stands of the Kellerwald-Edersee National Park, Germany. Three objectives were pursued: (i) to compare the patterns of species number and species composition caused by different gap sizes and light conditions with those found in North America, (ii) to investigate the impact of herbivory by ungulates on gap vegetation and (iii) to assess establishment from a persistent seed bank and zoochorous seed dispersal as potential pathways for gap colonisation. Herbivory intensity was determined for each gap as the proportion of browsed terminal shoots of beech saplings. The mean Ellenberg indicator value for light was used as a measure for light availability in gaps. The data were analysed by a variation partitioning approach using multiple regression and redundancy analysis.Species number increased with gap size and light availability. Herbivory caused a reduction of competition by tree regeneration and was therefore responsible for higher species numbers, too. Species composition was relatively homogenous but significantly determined by gap size, light availability and herbivory. With more favourable light conditions, an increasing proportion of generalist species occurred within gaps. By means of two dispersal traits, it is shown that these species may use both pathways, a persistent seed bank or transportation by ungulates, to colonise gaps.