Collins Complete Guide to British Trees: A Photographic Guide to every common species

INTRODUCTION

Trees and shrubs are such a feature of the British scene that many people take them for granted. However, imagine what the landscape (not to mention the parks and gardens) of Great Britain and Ireland would be like without them and you can begin to appreciate their significance. Indeed, in many ways it is our trees and shrubs, more than other living things, that help define what we think of as the British countryside.

Native tree species have an ecological significance that goes beyond their individual presence. The role they play in the ecology of our native woodlands particularly fascinates me, perhaps more than their appearance. So I make no apologies for this book being biased in favour of native species. However, introduced trees and shrubs also have a role to play in today’s world. Some are widely naturalised, many soften our otherwise often brutal urban landscapes and still more are familiar and valued features of mature gardens. Consequently, I have included a wide range of familiar planted species, along with a selection of more unusual or exotic trees and shrubs mostly associated with collections and arboreta.

Whether planted or growing in the wild, the Common Beech produces autumn colours that cannot fail to lift the spirits.

Known best for its colourful berries, the Rowan is widely planted in urban settings and is a welcome sight in autumn.

My personal interest in trees and shrubs extends beyond enjoyment of trees for their own sake and their role in our ecology. I am also fascinated by the uses of timber and tree products in woodland crafts and traditional practices. Sections of the book reflect this interest.

THE REGION COVERED BY THIS BOOK

The region covered by the book comprises the whole of mainland England, Wales, Scotland and Ireland, as well as offshore islands including the Shetlands, the Orkneys, the Hebrides, the Isle of Man, the Isles of Scilly and the Channel Islands.

THE CHOICE OF SPECIES

The coverage of the book is restricted mainly to what most people understand to be trees and larger shrubs; the former are usually defined as single-boled plants with a trunk that exceeds 5m, while shrubs are typically multi-stemmed. However, for the sake of completeness, and as a minor self-indulgence, I have also included native members of tree groups such as willows and birches that should not qualify for inclusion, in the strict sense, on the grounds that they are too small.

Complete British Trees will enable amateur naturalists to identify all native and widely naturalised tree and shrub species found growing wild in the British countryside. With an eye to the exotic, it also allows naturalists and gardeners alike to identify ornamentally planted trees, and to anticipate what any given specimen tree will look like if bought and planted. I hope that the range of popular garden species included in the book helps in this regard.

HOW TO USE THIS BOOK

The book has been designed so that the text and photographs for each species are on facing pages. A system of labelling clearly identifies each tree or shrub. The text complements the information conveyed by the photographs. By and large, the order in which species appear in the main section of the book roughly follows standard botanical classification. However, because parts of the field are in a state of flux, the order may differ slightly from that found in other guides, past, present or future.

SPECIES DESCRIPTIONS

At the start of each species description the most commonly used and current English name is given. My primary source of reference for this, and for scientific names, has been Clive Stace’s New Flora of the British Isles. Essentially this covers native and widely naturalised British species. For non-native garden trees and shrubs I have followed the naming employed by Owen Johnson in Collins’ Tree Guide.

The English name of each plant is followed by its scientific name, which comprises the genus name followed by the specific name. In a few instances, where this is pertinent, reference is made (either in the species heading or in the main body of the text) to a further subdivision: subspecies. Some cultivated trees and shrubs are known best, or sometimes exclusively, by their cultivar name, so where this helps with recognition I have included it; some hybrid trees and shrubs are now known only by their horticultural names.

The text has been written in as concise a manner as possible. Each description begins with a summary of the tree or shrub. To avoid potential ambiguities, the following subheadings break up the rest of each species description: BARK; BRANCHES (occasionally SHOOTS); LEAVES; REPRODUCTIVE PARTS; STATUS AND DISTRIBUTION; COMMENTS. Not all these headings are used for every species. Within the sections dealing with plant parts, colour, shape and size are described; these tend to be more constant, and hence are more useful for identification, than the overall size of the tree or shrub.

MAPS

The maps provide invaluable information about the distribution and occurrence of species in the region, but obviously they are only relevant in the case of native species and widely naturalised ones. Magenta has been used to represent the range of native species while cyan denotes the occurrence of naturalised alien trees or shrubs; the intensity of the colour gives an indication of a species’ abundance in a given area. In compiling the maps, I have made reference to a number of sources, including An Atlas of the Wild Flowers of Britain and Northern Europe, various county floras, the New Atlas of the British and Irish Flora and my own notes. The maps represent the current ranges of trees and shrubs in the region in general terms. Please bear in mind that, given the size of the maps, small and isolated populations will not necessarily be featured. Furthermore, the ranges of many species (particularly invasive introduced species and declining native trees and shrubs) are likely to change as the years go by.

Map coloration helps distinguish between the native and introduced distributions of species such as the Scots Pine.

PHOTOGRAPHS

Great care has gone into the selection of photographs for this book and in many cases the images have been taken specifically for this project. Preference was given to photographs that serve both to illustrate key identification features of a species and to emphasise its beauty. In many instances, smaller inset photographs illustrate features useful for identification that are not shown clearly by the main image.

BASIC TREE BIOLOGY

In many ways, trees and shrubs are no different from other flowering plants – they just happen to be bigger. They all grow, produce leaves, flowers and fruits in order to reproduce, and compete with other forms of life in the struggle to survive. The following is a basic review of the biology of trees and shrubs, which will help any reader unfamiliar with the subject to gain a better understanding of these fascinating organisms.

WOODY TISSUE

The principal way in which a tree or shrub differs from other, herbaceous, members of its family is its ability to produce woody tissue; this serves to conduct materials around the plant, and leads to the production of permanent shoots. In the case of perennial herbaceous plants, the shoots die back at the end of each growing season, or in the case of annuals, the whole plant dies and a new generation arises from seeds formed by the previous generation.

Trees and shrubs have an important layer of cells enclosing shoots, buds and roots, called the cambium layer. This is an active layer that is constantly producing new cells on its inner and outer surfaces. Cells that grow on the inside of the cambium develop into woody tissue or xylem; this conducts water from the roots to the shoots, buds and leaves. Eventually it forms the bulk of the trunk and branches of the tree as a new layer is laid down each year. Cells that grow on the outside of the cambium form the conductive tissue, known as phloem, that carries sugars from the leaves down to the roots. This vital layer must not be damaged. If a complete ring of this tissue is cut away from the trunk of a tree the roots will be deprived of nourishment from the leaves and the tree will eventually die.

A cross section through a Pedunculate Oak trunk reveals its many layers.

ANNUAL RINGS

When the tree begins to grow vigorously in the spring it forms large conductive cells that allow sap to flow freely through the trunk. As the season advances, cells produced by the cambium layer become smaller, with thicker walls for support, so they give a more dense appearance. In winter, cell production slows down and then ceases for a while; come the spring, however, there is a sudden burst of cell production and large cells are produced once more. The new growth of large cells immediately next to the thinner layer of dense cells gives the appearance of a ring. By examining a cut stump it is possible to count the rings and therefore discover the age of the tree, and also to find out which were the best growing seasons (see pp.).

BARK

The bark is an important part of a tree, protecting the vital growing layers of cells below from varying environmental conditions. It is produced by a layer of cambium cells and grows to accommodate the increasing girth of the tree. It may be thin and papery, smooth and shiny, or thick and deeply furrowed. Each type of bark is matched to the tree’s environment, so tree species that are subject to heat and strong sunlight in their native ranges have a thicker bark than those that come from cooler, humid climates (see also pp.).

Himalayan Birch bark is relatively thin and peels readily.

while Pyrenean Oak bark is thick and corky.

ROOTS

The first part of a tree to emerge from a seed is a tiny root whose first function is to draw up water and dissolved minerals from the soil. In the case of most of our tree species, successful germination is dependent upon this first root making contact with a species-specific symbiotic fungal partner, a relationship that continues for the rest of the tree’s life. This relationship is discussed in more detail on p. 34. From this simple start the tiny root will grow and divide, eventually forming a large network of powerful roots, side-branches and fine root hairs that spread out in all directions around the base of the trunk. The main roots will be woody and very strong, but their many branches terminate in fine root hairs that are only a few cells long; these have thin, permeable walls through which will pass all the water and minerals needed for the survival and growth of the tree. Although the sturdy roots strengthened with woody tissue help anchor the tree in the ground, it is the millions of fine root hairs that keep the tree alive by supplying it with water and nutrients. These fine root hairs are very short-lived, being constantly replaced as the main roots grow through the soil.

The root system of a large, mature tree does not penetrate far down into the soil. The most useful supply of dissolved nutrients for the tree lies in the shallow layer of topsoil and the adjacent sub-soil, so it is more beneficial if the roots spread outwards through this layer rather than penetrate to a great depth into a rather sterile and hostile layer. A 50mtall tree will probably have a spread of smaller branching roots all around the bole, the extent approximately equal to the spread of the branches or, sometimes, to the height of the tree. The proximity of other trees, the nature of the soil, and the presence of obstacles like rocks or river banks will all influence the final extent of the root system, however. This knowledge of the spread of the roots is useful when planning where to plant large trees that may damage drains or the foundations of buildings when they reach maturity, and it should also be borne in mind when digging ditches or ponds near large trees.

Spreading Beech roots.

In order to be able to function at all, roots require a supply of nutrients from the leaves, so within the root system there is a two-way traffic of water and minerals up from the soil to the leaves, and dissolved sugars and other nutrients down from the leaves.

The root hairs are living cells that require oxygen in order to be able to carry out respiration. They give off carbon dioxide as a waste gas, so they need access to air in the soil to allow these gases to circulate. Most trees, and most land plants, cannot grow in completely waterlogged soils and those that do have special adaptations for survival.

A number of trees, especially members of the Fabaceae, such as the Honey Locust, have many rounded nodules on the roots that contain colonies of nitrogen-fixing bacteria. These are able to use gaseous nitrogen and turn it into compounds vital to the growth of the plants.