Summary1. This account presents information on all aspects of the biology of Fagus sylvatica L. that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation. 2. Fagus sylvatica (Beech) is a large usually single-stemmed deciduous tree native to south-east England but now growing over almost the whole of the British Isles, often planted as a forestry tree on all but the wettest soils. It forms extensive woodlands, where it is dominant over a large altitudinal range, competing primarily with Quercus robur. The outcome of this competition is determined by local soil and climatic conditions leading to a gradation into oak woodlands. It is monoecious, wind-pollinated and notable for its periodic large seed numbers (mast years); seed is dispersed by birds and mammals but mostly drops below the parent tree. 3. Fagus sylvatica is hardy, very shade tolerant, casts a deep shade and is fairly resistant to browsing but susceptible to spring frosts. 4. Due to its shallow rooting and intensive rather than extensive mode of soil water exploitation, it is also susceptible to drought, and this is likely to be the main factor controlling its expected response to climate change. 5. Fagus sylvatica is facing few conservation problems, and indeed, its range is currently expanding into central Europe. However, in the face of climate change, its range is likely to contract from its extremes in all but the north, and Phytophthora diseases may become more serious.

The population dynamics of Betula pubescens and Picea abies in a boreal forest near Kvikkjokk, northern Sweden, are governed by a process of storm gap regeneration similar to the gap regeneration described for boreo-nemoral forests. Cumulative age distribution curves, interpreted as static survivorship curves, lead to a simple theory of differential survival based on properties of the species, i.e. shade tolerance and relative growth rate. The theory is sustained by diameter and height distributions and by the spatial distributions of logs and of trees in different life-phases. Species of the field and ground layers respond differentially to gap formation and the ensuing successional stages. Browsing by moose (Alces alces) may prevent tree species, mainly Sorbus aucuparia, Betula pubescens and Pinus sylvestris, from developing into a tree layer. The regeneration ability for tree species growing in a stand at 460 m a.s.1, is limited compared with the regeneration at 330 m a.s.l., and typical storm gap formation involving more than one tree seems to occur rarely if at all, while overthrown trees with exposed rootplates are uncommon. Spruce at 460 m a.s.1, shows also a lower growth rate and a lower height/diameter ratio compared to the lower situated stands.

One of the sites (Plot III) used by Sernander (1936) in developing the 'storm-gap theory' of cyclic change in Picea abiest forests on unstable soils has been located in Fiby urskog, near U ppsala. Re-mapping has facilitated calculation of the time elapsing between the fall of the trunk and its complete disintegration, which varies according to individual circumstances: the original estimate of90 years proves something of an over-estimate.The results confirm the validity of the storm-gap theory; indicating that the size of gaps is often increased by further· falls in subsequent years and that dwarf trees play an important role in regrowth. Small spruce saplings are concentrated on boulders and logs, where they are less vulnerable to competition from the field layer. Few occur where the shade is deep.

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SUMMARYAn experiment simulating defoliation at three levels of severity was conducted on 196 young oaks in a plot at Wolverhampton.In comparison with control plants, defoliation caused (1) earlier production of growth spurts (which are normal in undefoliated trees) and formation of more lateral branches, which were susceptible to winter frost damage; (2) production of more abundant, smaller leaves; (3) reduced diameters of main stems, from which can be calculated growth rates, varying with both defoliation treatment and growing conditions over the year, and returning to normal values as soon as defoliation ceased; (4) formation throughout the season of xylem of early wood type having a lower proportion of xylem fibres.With light defoliation, most of these responses were scarcely apparent, but with more severe defoliation, morphological effects dominated. The most noticeable effects of total defoliation were low growth rates and effects on wood anatomy.The results suggest that substantial natural defoliation could cause failure of regeneration, although in unshaded plots of young trees leaf loss results in retarded growth rather than death.