Table Of Contentabitat 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
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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
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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
