Trees in the City PDF
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abitat texts PERGAMON PRESS ANNOUNCES A NEW SERIES OF TEXTS HABITAT: A Series of Texts on all Aspects of Human Settlements General Editors: Ira B. Nadel University of British Columbia Cornelia H. Oberlander, Landscape Architect Habitat Texts will examine the environmental, cultural and social dimension of human habitations through a variety of original wide- ranging texts that will be clearly written and visually attractive to students. Planned for use in a variety of classes, from urban studies to geography, history to social studies, Habitat Texts will analyze the dilemma of man's total living condition. References and examples are world wide. Habitat Texts will provide an important introduction to the issues and solutions of human settlement. Each volume in Habitat Texts will have a single focus. TREES IN THE CITY is the first volume in the series; others will center on art, health, transportation and shelter among other topics. The texts combine a historical introduction with a contemporary analysis and practical application. Models, problems and matrices form part of a special feature of every text. Study questions, projects and a Teacher's Manual also accompany the book. Photographs, engravings and original illustrations enhance the design of the text. The terms of our inspection copy service apply to the above books. A complete catalogue of all books in the Pergamon International Library is available on request. TREES IN THE CITY by Ira Bruce Nadel University of British Columbia Cornelia Hahn Oberlander Landscape Architect Lesley R. Böhm Illustrator Pergamon Press New York I Toronto I Oxford / Sydney I Frankfurt / Paris Pergamon Press Offices: U.S.A. Pergamon Press Inc., Maxwell House, Fairview Park, Elmsford, New York 10523, U.S.A. U.K. Pergamon Press Ltd., Headington Hill Hall, Oxford 0X3, OBW, England CANADA Pergamon of Canada, Ltd., 75 The East Mall, Toronto, Ontario M8Z 5WR, Canada AUSTRALIA Pergamon Press (Aust) Pty. Ltd., 19a Boundary Street, Rushcutters Bay, N.S.W. 2011, Australia FRANCE Pergamon Press SARL, 24 rue des Ecoles, 75240 Paris, Cedex 05, France WEST GERMANY Pergamon Press GmbH, 6242 Kronberg/Taunus, Frankfurt-am-Main, West Germany Copyright © 1977 Pergamon Press Inc. Library of Congress Cataloging in Publication Data Nadel, Ira Bruce. Trees in the city. Bibliography: p. 1. Trees in cities. I. Oberlander, Cornelia Hahn, joint author. II. Title. SB436.N25 1977 635.9'77 77-1713 ISBN 0-08-021489-4 ISBN 0-08-021488-6 pbk. All Rights Reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic tape, mechanical, photocopying, recording or otherwise, without permission in writing from the publishers. Book Design by Michael Smacchia Photo Credits: John Kenny, Otto Landauer Printed in the United States of America Basic Concepts of TREES IN THE CITY • Trees play an essential role in man's urban life. • People must become aware of the environ- mental, aesthetic, social and political importance of trees. • Trees need to be integrated with the pattern and function of urban activity. • The design, placement and maintenance of trees on city streets are the responsibility of everyone in the community. I/// Introduction Trees and rocks will teach what thou canst not hear from a master. St. Bernard The oldest living thing in the world is a tree. Even before man could record his history he knew of trees. The Tree of Knowledge and the Tree of Life appear in the Old Testament, and the World Tree, representing the ascent to Heaven, exists in-many primitive religions. Trees have had a central role in the imaginative life of man. Early people believed that a tree stood at the center of the world and connected earth, Heaven and Hell. Buddha became enlightened under a tree and the Norse Sagas recount the power of Yggdrasill, the World Ash with an eagle at the top and a serpent at the bottom. To the Celts, the Oak was sacred; in In the Forum, the busy cen- Germany, it was the Lime tree; in India the ter of Roman life, the sacred fig-tree of Romulus was wor- Fig tree. shipped down to the days of The oldest sanctuaries of man were groves the Empire, and the withering of its trunk was enough to of trees. The Celts named their holy groves spread consternation through Nemi, adapting the Latin Nemus meaning a the city. woodland or grove. The priest of the African Sir James Frazer grove, called the King of the Wood, was The Golden Bough thought to be a personification of the Oak. Before he could be dethroned, it was necessary to break a branch from the Golden Bough (probably mistletoe), symbolic of the end of the King's power. The mystical Hebrew book, the Cabbala, describes the nine emanations / from the central I AM as the branches of a cosmic tree turned upside down and rooted in "the great height." Even holidays honor trees, two of them being Fiesta del Arbol in Spain and Arbor Day in North America. The Tree as Royal Sanctuary At the beginning of his exile after his defeat at the Battle of Worcester on September 3, 1651, Charles II spent 40 days in hiding before escaping to France. His most secure and dramatic location was an Oak tree near Boscobel House Shropshire. Known as the Royal Oak, the tree and the event have become a holiday in England, variously called Royal Oak Day, Oak Apple Day, or Restoration Day. It is celebrated every May 29th, the day of Charles II's birthday and return to London. In addition to their mythic, religious and imaginative significance, trees contribute to man's health on this planet. Without trees the ecology of the earth would be unbalanced, the amount of oxygen would decrease and the natural food and plant chain would be broken. Trees also provide beauty, shade, protection and comfort for man and animals. They introduce a sense of scale. They give a sense of harmony and softness to the man-made To the rapid traveler the number of elms in a town is environment of concrete and steel. the measure of its civility. In our over-populated century, it is Thoreau necessary to return the trees to our streets, to "A Yankee in Canada" humanize the cityscape. This book provides an introduction to that process and a guide to planting trees in city conditions. But what is a tree? The question is more complex than it might 2 TREES IN THE CITY first appear. A tree is a woody plant with a trunk and a crown at the top. It differs from a shrub by its height and single trunk. The roots of a tree take water from the soil, pass it through the trunk to the leaves where it evaporates in the air. As a perennial plant, at least 15 feet tall or more at maturity, it has a single stem, several inches in diameter and a well-developed crown at the top. Whatever the description, the process that occurs within a tree is the same. Minerals in the water are absorbed through the small fibrous roots, convert themselves into food- starches and sugars-and by means of sunlight, create chlorophyll which gives the green appearance to the leaves. The three fundamental components of a tree system are its roots, trunk and leaves. Roots spread radially from a tree trunk, but rarely to a depth greater than four feet. A rich soil creates a shallow root system; a dry soil encourages a deep root system since the moisture is further down in the soil. The root hairs at the end of the roots take up the minerals in solution from the soil. This is the life line of the tree, bringing food into its trunk. Trees, being sturdy, can withstand the loss of as much as half of their root system, but it remains the central life support system of the tree. A balance must always be kept between the amount of water evaporated through the leaves and that taken in by the roots. In the city, damage to the root system is almost inevitable during the transplanting of trees. The pavement around the base of a tree, even with several feet of dirt around it, compacts the soil above the roots and prevents oxygen and bacteria from entering the root system. This action retards growth. It is INTRODUCTION 3 Section of Tree Trunk Summer Spring Summer Spring cambium 2nd year xylem 1st year xylem phloem pith ray pith cork essential to remember that trees grow up by growing down. They cannot get any higher unless the root system enlarges. To ensure proper aeration of the roots and adequate watering and seepage, cast-iron grates or pave- ment with soil joints (stones or bricks laid together) are placed around the base of city trees. They form interesting patterns as they CORK circle the trunk and the famous Parisian cast- The outer bark, actually iron grate is perhaps the best known. waterproof tissue derived from cork cambium. The trunk of a tree transports the minerals absorbed by the roots to the leaves where they are converted into food. A cross-section of a PHLOEM trunk reveals three components: the protective Food conducting tissues of the tree. bark, the thin green tissue called the cambium, and the concentric circles of sapwood. CAMBIUM 1. Bark protects the tree from the drying Principal layer of tissue be- action of the sun and wind, as well as tween the phloem (inner insects. As the cylinder of cambium grows, bark) and xylem (wood). Responsible for annual rings the bark cracks and forms characteristic of wood. patterns—peeling on Birch trees, mottling on Sycamores. 4 TREES IN THE CITY The cambium produces the sapwood which is the circulation system of a tree; it carries raw materials to the leaves and then moves the manufactured food to various parts of the tree. In winter the sapwood returns the food to the trunk for storage. PITH RAY The cambium produces its own protective A lateral extension of the pith. covering, bark. If a cut is made horizontally on a tree and pierces the cambium, it will kill the tree. A vertical slice, avoiding the XYLEM cambium, will not be fatal. It is essential, The vascular tissue that trans- ports water and minerals; en- particularly with city trees, that they be free larges yearly. from nicks, abrasions or damage that might be caused by workmen, pedestrians or vehicles. The leaf is the lungs and stomach of a tree. PITH Internal tissue located in cen- It traps sunlight and, through chlorophyll, ter of trunk. manufactures food from the minerals absorbed by the roots. Tiny breathing pores called lenticels exist in the leaf and evaporate mois- ture during the manufacturing process. They take carbon dioxide from the air, using it with the sunlight.and minerals in the creation of starches and sugars required for the growth of the tree. Lenticels are also needed for transpira- tion, the evaporation of water through the leaves. The dust, smoke, pollutants and heat of a city can clog the lenticels, or breathing pores, however, and make the survival of the tree difficult. For a tree to flourish it needs light, soil, and water. More than anything else, water effects the form, growth and structure of a tree. Large trees can evaporate as much as 300 gallons of water per day through their leaf system. Street trees need particular care with respect to water since they are cut off from natural INTRODUCTION 5 supplies of ground and surface water. Soil, composed of minerals, decayed vege- table matter (humus), bacteria and water, holds minerals and oxygen in solution. Differ- ent soils contain these ingredients in different proportions; each tree species has a different soil preference. In the city, where soil is often neglected or non-existent, attention must be paid to the character and needs of street plantings. Also, inadequate light on city trees caused by high buildings, signs, or underground obstructions retard the growth of trees, Dogwood, Beech and Hemlock can grow in the shade, but Birch, Poplar, Pine and Willow require full light. Heat requirements of trees determine their hardiness and influence the amount of evaporation from the leaves. The most important quality in selecting street trees is their suitability to the conditions of the area. Can they survive on the street you are planting? This is the central question in designing a street with trees. Design Problem 1 The Parks Board of a large city wants to plant trees around an underground subway station located in the financial district. Large office buildings sur- round the station which also has a bus stop directly in front of it. The area available for tree planting on either side of the entrance of the station is 10 feet wide, 20 feet deep. 1. What facts should be considered in choosing trees? 2. How will the noise, vibrations, heat, and traffic affect the life of the trees? 3. Why is it worth the trouble and expense to plant trees at this site? 6 TREES IN THE CITY
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