The Holocene history of Fagus

Historical and contemporary factors shaping genetic variation in Fagus:
An overview

How do morphological and physiological traits determine the characteristics of individual beech trees?

Trees, including beech and many other species, have important functions that make their own lives possible and that help to maintain stable environmental conditions around them.  Trees have a conspicuous characteristic three-dimensional branching structure within which their functions take place.  Both function and structure are important for understanding the ecology of trees.  However, researchers have often focused on only one of these when modeling trees, and the resultant models are morphological branching models or physiological process-based models.
   Recently, functional-structural tree models have been developed that represent both the three-dimensional structures and functions of trees.  Behind the development of functional-structural tree models lies the fact that the functions and structures of trees are tightly interrelated.  For example, light interception and photosynthesis by leaves in the crown are determined by the structure of the crown (mutual shading), and the development of crown structure depends largely on the amount of photosynthesis in the crown.  The functional-structural tree models should reproduce the realistic behavior of trees in computer simulations and predict their performance under various environmental conditions.  They should also increase our understanding of the ecology of individual trees.  We can conduct various “what if” experiments by modifying certain components of tree functions and structures in the models and evaluate the relative importance of the traits in question.
   This review summarizes the important features of functional-structural tree models, and functional-structural models developed for beech trees.  We also present a new model for beech saplings with which we evaluate the importance of shoot structure, phenology, and the vertical gradient of light intensity in determining shade tolerance.

Beech regeneration research: ecology and silvicultural aspects

   Many (all?) species of Fagus epitomize shade tolerant, heavy seeded climax species of the northern hemisphere. The genus globally is the subject of long-standing regeneration ecology research, and more recently the focus of studies into effects of environmental changes on regeneration issues. In addition, current forest management gives a high priority to beech silviculture, as it is an important part of a commercially oriented and nature-based forestry in many parts of the world.
  Given the importance of beech (Fagus sylvatica) under unmanaged conditions in Central Europe, re-introduction of beech is often seen as a method to enrich pure and artificially established conifer stands for biodiversity. Also, the natural regeneration process leads to a new trend of nature based (close to nature silviculture) forest management in the Caspian forests, which is derived from experiments in the virgin oriental beech (Fagus orientalis) stands.
   This synthesis provides a comprehensive overview about recent regeneration research into the genus Fagus, and applications in silviculture for beech forests. It includes information about the life cycle of beech species, and masting events. It gives particular attention to regional differences in flowering and seed maturation, and to seed predation by insects, birds and mammals. Evidence also suggests that the frequency of masting has increased in European beech (Fagus sylvatica) within the last 30 years. Interest in far reaching dispersal of beech by animals is increased due to near-to-nature management practices. However, some beech species regenerate vegetatively, (e.g. Fagus engleriana, Fagus japonica, and Fagus grandifolia), which may increase their competitive ability and abundance. Particularly for Fagus grandifolia, much information has become available about negative effects of beech root suckers on the regeneration of other broadleaved species. So are findings about the loss of American beech as a large-diameter tree in regions of North America affected by beech bark disease. In addition, research into the disturbance regime of beech and beech-dominated forests (e.g. of Fagus sylvatica, Fagus orientalis and Fagus crenata) has improved our understanding about the role of gaps and gap sizes in natural forest dynamics, and about competition processes during seedling and sapling stages of pure and mixed regeneration. Other research has addressed impacts of browsing on regeneration dynamics in pure and mixed forests, and the role of herb, grass, and bamboo competition in combination with damage by voles, mice, and other herbivores. Applied research has also explored advance planting and seeding techniques to reintroduce Fagus sylvatica into coniferous stands of central Europe.

Crop-Tree-Oriented versus Whole-Stand Silviculture of Beech:
Growth, Yield and Quality

Across Europe there is a large variety of silvicultural systems for European beech (Fagus sylvatica L.). Two fundamental categories of growth control are implemented in forest management: Single tree silviculture, where all silvicultural activities are based upon a limited number of crop trees selected at an early stage in tree development and on the other side silvicultural systems where growth and yield of the whole stand is optimised.
   This review critically summarizes both approaches and analyses their impact on tree and stand growth, wood quality traits like branchiness and red heart wood and on stem quality. In addition we used own long-term growth and yield plots from Germany and France observed over up to 35 years to analyse the effects of a single-tree-oriented and a stand-wise thinning on growth of European beech.
  An economic analysis of crop-tree-oriented versus whole-stand silviculture on these plots reveals some superiority of the former when considering the timber assortment of the removed and remaining trees, and the production value. The crop trees of the crop-tree thinning had - compared to their homologues from the stand-wise thinnings - higher shares of above-average stem quality. This reflects the higher quality requirements of crop-tree selection as well as the higher stem diameters of the dominant trees. Furthermore, the overall timber assortment of the crop-tree thinned stands compared to the stand-wise thinned stands had higher shares of large-dimension timber within both the total amount of removed trees, and the trees remaining at the last measurements. Finally, production value of plots where crop-tree thinning has been applied was higher compared to whole-stand silviculture, both with and without considering the time-related occurrence of the harvested timber.

How will Fagus respond to climate change?
Modelling its geographic distribution, phenotypic plasticity and adaptive capacity

Profound changes in the geographic distribution of European beech (Fagus sylvatica L.) are projected both by advanced process-based and statistical modelling techniques. However, some authors argue that beech has high phenotypic plasticity that allows it to withstand large environmental fluctuations during their life time. In addition, from a genetic point of view it is argued that adaptation to climate change is possible because European beech has high within population genetic diversity and because gene flow of pollen is found to take place over large distances thereby exchanging favorable genetic variants between isolated stands. Other authors argue on the contrary that: trees are unable to adapt because the rate of climate change is high relative to the longevity of individual trees; trees may not have adequate genetic diversity to adapt to the changing environmental conditions; and trees may not be able to disperse to newly available habitat to match the rate of global change as the landscape trees have to cross is highly fragmented.
   In this review we present an overview of the modelling principles of both the process-based- and the statistical forecasting approaches and analyse the environmental causes in combination of the modelled features of beech resulting in the prediced loss of large parts of its current distribution. From an ecophysiological point of view we present the potential of beech to respond to environmental changes by phenotypic plasticity. Finally, from a genetic point of view we analyse the available evidence on the adaptitive capacity of beech to respond to global change.