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

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


An essential guide to every species of tree found in the British Isles – outside of arboretumsThis easy-to-use guide covers the 360 species of tree that are found in Britain & Ireland. Each species is covered in detail with information on how to identify, whether from a leaf, twig, bark or whole tree, plus extra information on where the tree grows (including a map), how high they grow, what uses it is put to and history.Every species is also comprehensively illustrated with photographs of every useful feature – bark, leaf, seed, flower, twig and whole tree.Sample identification section:Silver Birch Betula pendula (Betulaceae) height to 26mA slender, fast-growing deciduous tree with a narrow, tapering crown when young and growing vigorously. Older trees acquire a weeping habit, especially if growing in an open, uncrowded situation.




















COPYRIGHT (#ulink_e80b1aca-5df3-5fff-8f0c-c0a96b703eb6)


HarperCollinsPublishers Ltd.

1 London Bridge Street

London SE1 9GF

The Collins website address is: http://www.harpercollins.co.uk (http://www.harpercollins.co.uk).

Collins is a registered trademark of HarperCollinsPublishers Ltd.

First published in 2007

Text © 2007 Paul Sterry

Photographs © Individual photographers as indicated in the picture credits

Paul Sterry asserts his moral right to be identified as the author of this work.

All rights reserved under International and Pan-American Copyright Conventions. By payment of the required fees, you have been granted the nonexclusive, nontransferable right to access and read the text of this e-book on-screen. No part of this text may be reproduced, transmitted, downloaded, decompiled, reverse-engineered, or stored in or introduced into any information storage and retrieval system, in any form or by any means, whether electronic or mechanical, now known or hereafter invented, without the express written permission of HarperCollins e-books.

A catalogue record for this book is available from the British Library.

Source ISBN: 9780007211777

Ebook Edition © MARCH 2015 ISBN: 9780008144593

Version: 2015-04-22

Colour reproduction by Nature Photographers Ltd

HarperCollinsPublishers has made every reasonable effort to ensure that any picture content and written content in this ebook has been included or removed in accordance with the contractual and technological constraints in operation at the time of publication.




DEDICATION (#ulink_e787005c-d56c-5e46-b691-496d9497e21b)


The book is dedicated to the memory of Bramley Frith.




CONTENTS


Cover (#uec6544f0-cdf8-5770-91f0-43e00e2f3519)

Title Page (#u52321872-d945-5735-88bf-bdc8f02cd288)

Copyright (#ulink_b4f43c9b-90a0-5441-9ddf-7997e86ede72)

Dedication (#ulink_424eaf2f-822a-5738-8238-a83c8fc8cb8c)

Introduction (#ulink_50771edb-c26d-5b58-a3c6-d8b2b567eeec)

How to Use this Book (#ulink_c79cc358-e193-5b21-b3d6-bd004eb0a417)

Glossary (#ulink_18aa40df-d251-5fee-ad99-67e1fbebfea4)

Basic Tree Biology (#ulink_533a57ab-7744-55cb-b7a1-c52eefd18d2b)

What is a Tree? (#ulink_7eacddeb-aaea-51ec-aa99-c6faaf2183cd)

Tree and Shrub Families in Britain and Ireland (#ulink_30ddb860-b3b4-57fa-9d07-d75f056f4756)

Identifying Trees (#ulink_e1bb28ac-c2d2-5f17-9ef5-c29b278fb4c5)

The Life Cycle of a Tree (#ulink_f6efea17-8ffe-5e61-aff8-7c007d4abfc8)

Growth Rings and Ageing a Tree in the Field (#ulink_780a1f94-b2b3-5ae4-ab86-1cc35d867b3c)

The Ecology of Trees and Woodland (#ulink_13d76421-9bea-52b3-bad9-3e294ea97167)

Fungi, Trees and Woodland (#ulink_cb925825-a45f-5e80-8356-6904de3c484f)

Galls (#ulink_5da539c6-4283-5e0e-9009-cb0516d408ea)

Mosses, Liverworts and Lichens (#ulink_c6f1c56f-ef88-5d07-ad01-634c7833fdec)

Hedgerows (#ulink_e813b8c5-0d3b-5642-820a-c838a718e159)

Winter Twigs (#ulink_e5a46e81-9aab-59b4-821a-3e04e11431fc)

Comparing Leaves of Common Trees and Shrubs (#ulink_6762c2a4-e660-599f-ae1a-13b1a1c1ed75)

Comparing the Bark of Common Trees and Shrubs (#ulink_b616d2ef-f0f0-5cce-aa24-42051749089e)

Fruits and Seeds (#ulink_48061bb0-4d2d-596c-9af4-faceba0fbfba)

History of Woodland Management (#ulink_c3ce6680-4ce2-5ac2-af8c-35cd62da215b)

Traditional Timber Uses (#ulink_b36e5aeb-248f-5ed9-b4f0-1bc86e2c8439)

How to Use an Oak Tree (#ulink_b6845960-8e75-5ef7-b932-1a899a2bc758)

Recognising Timber (#ulink_0f59f386-b01d-5386-8565-f62cc503d9f8)

Places to Visit (#ulink_75c98475-65dd-5f08-a709-bcc1291a6cc3)

Conservation (#ulink_3082a024-34ef-5104-9658-fa070000e2a7)

Species Descriptions (#ulink_91259e85-02ab-5ec3-bb38-eb82b42ec91c)

Keep Reading (#u5ce1992b-c9d8-5ca2-a7a9-b02fa72659c0)

Further Reading (#ulink_d3ba0b3c-afe2-5bd0-83fb-8bffd92bc220)

Index (#ulink_009f4c1c-663a-5b80-8121-0d3884080b51)

About the Publisher (#ulink_2e580fc4-e03f-5ff7-a1ca-988893ce8436)





INTRODUCTION (#ulink_bf6bfcea-268e-5649-b562-da1c25c4ed7c)


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 (#ulink_9d949b51-4008-528f-aeac-883948f87ff0)


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.




GLOSSARY (#ulink_e1842a90-6df3-51f6-a446-b07ca48d0549)


Achene – one-seeded dry fruit that does not split.

Acute – sharply pointed.

Alien – introduced by man from another part of the world.

Alternate – not opposite.

Anther – pollen-bearing tip of the stamen.

Auricle – one of a pair of lobes at the base of a leaf.

Axil – angle between the upper surface of a leaf, or its stalk, and the stem on which it is carried.

Berry – fleshy, soft-coated fruit containing several seeds.

Bract – modified, often scale-like leaf found at the base of flower stalks in some species.

Calcareous – containing calcium, the source typically being chalk or limestone.

Calyx – outer part of a flower, comprising the sepals.

Capsule – dry fruit that splits to liberate its seeds.

Catkin – hanging spike of tiny flowers.

Clasping – descriptive of leaf bases that have backward-pointing lobes which wrap around the stem.

Compound – (of leaves) divided into a number of leaflets.

Cordate – heart-shaped at the base.

Corolla – the collective term for the petals.

Cultivar – plant variety created by cultivation.

Deciduous – plant whose leaves fall in autumn.

Dentate – toothed.

Dioecious – having male and female flowers on separate plants.

Drupe – succulent or spongy fruit, usually with a hard-coated single seed.

Entire – (of leaves) with an untoothed margin.

Fruits – the seeds of a plant and their associated structures.

Glabrous – lacking hairs.

Globose – spherical or globular.

Hybrid – plant derived from the cross-fertilisation of two different species.

Inflorescence – the flowering structure in its entirety, including bracts.

Introduced – not native to the region.

Involucre – ring of bracts surrounding a flower or flowers.

Lanceolate – narrow and lance-shaped.

Leaflet – leaf-like segment or lobe of a leaf.

Lenticel – breathing pore on a fruit, shoot or trunk.

Linear – slender and parallel-sided.

Lobe – a division of a leaf.

Midrib – the central vein of a leaf.

Native – occurring naturally in the region and not known to have been introduced.

Oblong – (of leaves) with sides at least partly parallel.

Obtuse – (of leaves) blunt-tipped.

Opposite – (usually of leaves) arising in opposite pairs on the stem.

Oval – leaf shape.

Ovary – structure containing the ovules, or immature seeds.

Ovoid – egg-shaped.

Palmate – (of leaves) with finger-like lobes arising from the same point.

Pedicel – stalk of an individual flower.

Perianth – collective name for a flower’s petals and sepals.

Petals – inner segments of a flower, often colourful.

Petiole – leaf stalk.

Pinnate – (of leaves) with opposite pairs of leaflets and a terminal one.

Pod – elongated fruit, often almost cylindrical, seen in pea family members.

Pollen – tiny grains that contain male sex cells, produced by a flower’s anthers.

Pubescent – with soft, downy hairs.

Rachis – main stalk of a compound leaf or stem of an inflorescence or array of fruits.

Reflexed – bent back at an angle of more than 90 degrees.

Sepal – outer, usually less colourful, segments of a flower.

Stamen – male part of the flower, comprising anther and filament.

Stigma – receptive surface of the female part of a flower, to which pollen adheres.

Style – an element of the female part of the flower, sitting on the ovary and supporting the stigma.

Tepal – perianth segment when petals and sepals are not identifiably separable.

Tomentose – covered in cottony hairs.

Whorl – several leaves or branches arising from the same point on a stem.





BASIC TREE BIOLOGY (#ulink_c97061c9-42b8-5152-865e-59840f60b6dd)


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. (#u4cc36f64-8c98-5a86-937e-184ebd4d571a)).




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 alsopp (#u4431f9d4-c879-493c-861b-983cad1c0f5a).).






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.




LEAVES


Leaves are among the most conspicuous and distinctive features of any tree. They grow in a huge variety of shapes, sizes, colours and combinations and are usually the best feature for identifying the tree because of their unique structure. Leaves may vary from one species to another but they all perform the same vital function as the principal producers of food for the tree.

The first pair of leaves to emerge from the seed are simple, and bear no resemblance to the true leaves of the tree; they are derived from the seed’s food store. They are green, however, and supply the tiny seedling with its first food made from sunlight energy. Once the seedling has begun to produce leaves that are miniature versions of its true leaves, growth can begin very rapidly. Tiny seedlings are vulnerable to grazing, trampling, drought and competition, so very few survive.






Recently germinated oak seedling.






A plant’s leaves are its powerhouse, trapping energy from sunlight and converting it into basic food.

Leaves are basically thin layers of living tissue with the ability to trap light energy and use this to convert the raw materials of water and carbon dioxide into a simple sugar. This reaction, known as photosynthesis, is arguably the most important chemical reaction in the world, for it is the basis of all other food production. Animals do not have the ability to convert these simple materials into food; they have to rely on plants to do it for them. The simple sugar produced in the leaves is glucose, and this can be formed into a variety of other important materials, particularly starch, which many plants store, or pack into their seeds. A vital by-product of this reaction is oxygen, the gas essential for the respiration of all members of the animal kingdom. This explains the vital role of trees in the ecosystem: they are major consumers of carbon dioxide, one of the so-called ‘greenhouse gases’; and they are major producers of oxygen, the gas we need for our respiration. They are also major producers of food for much of the animal kingdom.

Contained within a leaf are numerous specialised cells. Some are concerned with the transport of materials in and out of the leaf, some are the vital energy-trapping cells that utilise sunlight, and others are concerned with the regulation of water movements. The cells that trap light-energy contain a light-absorbing pigment called chlorophyll, which gives leaves their green colour. Other pigments of different colours may be present in varying amounts, and it is this variety that gives leaves of different trees their own subtle shade of green. Without the green chlorophyll or other light-absorbing pigments, leaves would be unable to perform their important function, and also, if deprived of light, they would be unable to manufacture the tree’s food.

Leaves arrange themselves in such a way to absorb the maximum amount of sunlight, so spreading canopies or trees growing taller than their neighbours, are both ways in which trees maximise the light-gathering power of their leaves. Some leaves have paler patches that lack green chlorophyll; these are known as variegated leaves and certain trees, such as some cultivars of the Highclere hollies, regularly produce green-and-yellow leaves. If the leaves were completely lacking in chlorophyll they would be unable to manufacture food for the tree; the small areas of green tissue in the leaf produce all the food needed by the whole leaf.

All leaves have tiny pores in their surface (normally just the lower surface) called stomata. These allow water to evaporate into the atmosphere. To some extent the tree can regulate the opening and closing of these stomata, but during daylight hours, when the tree is trapping sunlight, they will be open, allowing water out and also allowing the circulation of the gases involved in photosynthesis. This can lead to problems for trees growing in hot, dry areas, or in well-drained soils where little ground water is available. In order to allow the essential gases to circulate, and at the same time minimising water loss, many leaves have become reduced in size, such as the needles of firs and pines, or have thick waxy upper surfaces such as the glossy green leaves of hollies and magnolias. This reduces water loss to a minimum without impeding photosynthesis.

The great variety of leaf shapes and sizes is an indication of the variety of ways in which trees can cope with environmental conditions. Some trees grow in areas where water is at a premium, so they have small leaves, to cut down on water loss through their thin skins. Some grow in shady conditions, so they may have larger leaves that can trap the maximum amount of light energy. Some trees are subject to grazing by animals, so their leaves are spiny or prickly, or protected on tough, thorny stems.

Beech






OVAL AND ENTIRE

Hornbeam






ELLIPTICAL AND TOOTHED

Small-leaved Lime






CORDATE

Red Oak






LOBED

Horse-chestnut






PALMATE

White Ash






COMPOUND

Yew






NEEDLE-LIKE

Scots Pine






WITH PAIRED NEEDLES

Leaf types.






Deciduous trees, such as Horse-chestnut, produce fresh leaves each spring, which burst forth from buds.






Autumn leaf colour is spectacular in many maple species: as chlorophyll and other pigments are withdrawn, remaining red pigments prevail.

Evergreen trees do not lose all their leaves at the end of every growing season; most leaves remain on the tree through the winter, although there is always some loss and some replacement. In many of the pines, for example, the needles will remain on the tree for about 3 years. As the shoot grows longer each year, a new set of needles grows on the tip of the lengthening shoot. The older needles, finding themselves further and further away from the tip, gradually fall off. Small leaf scars remain, and these are quite distinctive in some species and may be a useful aid to identification. Broadleaved trees such as Holly also replace their leaves gradually so there is always some leaf-fall, but plenty of green foliage remains on the tree.

Deciduous trees generally shed all their leaves at the end of the growing season, before the onset of winter. Many of them produce spectacular displays of colour before the leaves finally fall. These colour changes are the result of the gradual withdrawal back into the tree of all the useful materials in the leaf; as the various pigments are removed the leaf itself changes colour until finally a corky layer, called the abscission layer, grows at the base of the petiole or leaf stalk. This seals off the shoot and when the leaf finally falls, a scar is left through which mould spores and other harmful materials are unable to pass. The twigs of Horse-chestnut have very distinctive leaf scars that look like tiny horseshoes. If these are examined carefully through a hand-lens, the sealed-off ends of the vessels that conducted materials in and out of the leaves can clearly be seen.

There may be as many as 250,000 leaves on a mature oak tree, whilst a large spruce probably has 10 times as many, in the form of needles. The oak’s leaves will be shed at the end of the growing season, adding to the rich accumulation on the ground beneath it, whilst the spruce’s needles will be shed and replaced gradually, each individual needle remaining on the tree for about 4 years.




REPRODUCTION


Trees normally produce flowers when they are several years old. Beech, for example, produces its first flowers at around 30 years old, repeating the process each spring for the next 200 years if it remains healthy. Some trees, such as apples or oaks, have years in which they produce a large crop of fruits or seeds, followed by other years with hardly any, whilst other species, such as some maples, produce a good seed crop year after year.






Even a slight breeze will liberate pollen from the male catkins of Hazel






Carry it to female flowers.

Some trees and shrubs produce conspicuous flowers to attract pollinating insects, something that, in ornamental trees, we also find attractive. Honey Bees are particularly important pollinators, but numerous other insects visit the flowers for nectar and pollen. Many flowering trees have also long been prized by gardeners for their scent.

Many trees are pollinated by the wind. Their flowers are less conspicuous, often taking the form of catkins, which are pendulous and usually open before the leaves so that nothing impedes the free movement of the pollen grains. Wind-pollinated flowers normally have flowers of separate sexes, the males usually being larger and more abundant. Many wind-pollinated trees are such prolific producers of pollen that on warm breezy days in spring clouds of pollen can sometimes be seen blowing from the trees.

Conifer flowers are either male or female, and borne on the same or different trees. There are no petals, but some of the flowers are still quite colourful and decorative. Male flowers are short-lived, falling off after they have released clouds of pollen, but the female flowers, often covered with brightly coloured scales, remain on the tree after pollination and develop into cones containing the seeds. They rely on the wind for pollination and also for seed dispersal. A few close relatives of the conifers, such as the yews, produce fleshy fruits instead of cones.






Mature cones open and close in response to temperature and humidity, releasing seeds in hot, dry conditions.

The flowers of broadleaved trees and shrubs are usually hermaphrodite, containing both male and female parts, but there are a number of exceptions. Both sexes usually have petals in some form or other and they may also be scented. Small flowers are often grouped together in larger clusters to help attract pollinating insects. Some are wind-pollinated and open early in the year before the leaves, but insect-pollinated flowers usually open in spring and summer when more insects are active.

The fruits of trees and shrubs are much more varied than the cones of the conifers. They range from tiny papery seeds with wings, through nuts and berries, to large succulent fruits in a variety of shapes and colours. Edible fruits are designed to assist dispersal of the seeds by animals and many are delicious to the human palate.






Hawthorn flowers are an attractive sight in spring and are irresistible to pollinating insects.






HAZEL – NUTS






CRAB APPLE – FLESHY FRUIT






SYCAMORE – WINGED SEEDS






GUELDER-ROSE – BERRIES

The fruits of broadleaved trees and shrubs come in a range of shapes and size, including winged seeds, hard-cased nuts, luscious berries and juicy fruits.




WHAT IS A TREE? (#ulink_8a944caf-1030-5678-bef8-0b1ecd3d6e36)


Nobody could have any doubt that a mature Wellingtonia or an ancient, spreading Pedunculate Oak is a tree, but would a prostrate Juniper, or a Creeping Willow, also qualify, or are they merely shrubs? One feature common to both trees and shrubs is that their stems increase in thickness each year by the laying down of internal layers of woody tissue in the form of concentric rings. This secondary thickening builds up year by year to increase the diameter of the stem and gives a permanent record of the age of the tree or shrub.

Trees are generally considered to have a single main stem of 5m or more in height with a branching crown above this, whereas shrubs may have numerous stems arising at ground level and may not normally reach the height of a tree. Both trees and sizeable shrubs are covered in this book but the distinction is not always clear. Individuals of the same species may become trees or form shrubs, depending on the circumstances in which they are growing, or their management. Hazel, for example, forms a multi-stemmed shrub in response to coppicing, or cutting back to the rootstock; each time this is done, new shoots arise from the rootstock and the Hazel regenerates. If this cutting back does not take place, it can grow as a medium-sized tree on a single stem.

Trees do not belong to a single family of plants; many plant families are represented, and some, like the Fabaceae and Rosaceae, also include many herbaceous plants and shrubs as well as large trees.

The plant kingdom is divided into two main classes, the Gymnosperms and the Angiosperms. The most primitive of the two classes is the Gymnosperms, the name meaning ‘naked seeds’; the ovule is borne on a bract and not enclosed in a seedpod or case. This class includes the Maidenhair Tree, a very primitive tree, and all the conifers, or cone-bearing trees.

The name Angiosperm means ‘hidden seeds’ and refers to the way the seeds are contained inside an ovary, a structure that may later develop into a seedpod or fruit. This large class includes many well-known plant families, some of which are mostly made up of herbaceous plants, and some of which are mostly composed of trees. The Limes (Tiliaceae) and Elms (Ulmaceae), for example, are mostly trees, whilst trees feature in only one of many genera in the Foxglove family (Scrophulariaceae). All of our garden and wild flowers, bulbs, palms and the grasses and cereals are Angiosperms.






With their massive trunks, there is no mistaking that these Common Beeches are indeed trees.





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