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Woody vegetation in settlements
Landscape Planning, 14 (1987) 57-78 Elsevier Science Publishers B.V., Amsterdam
57 - Printed
in The Netherlands
WOODY VEGETATION IN SETTLEMENTS
WOLFRAM Gesamthochschule
Kassel, Fachbereich
KUNICK
13, StadtplanunglLandschaftsplanung, (Accepted
for publication
Henschelstr.
2, 03500
Kassel (F.R.G.)
25 April 1986)
ABSTRACT Kunick,
W., 1987.
Woody vegetation
in settlements.
Landscape
Urban Plann.,
14: 57-78.
The woody vegetation in several German cities was analysed and found to consist of a large number of trees and shrubs cultivated in public or private gardens. Many of them are of foreign origin, but are now more or less well adapted to urban soil and climatic conditions. Certain groups of species are characteristic for different city neighbourhoods. Thus, ecological factors as well as social trends influence the species-composition. The number of trees, shrubs and climbers in the cities which are growing spontaneously on different types of derelict land is also considerable. The number of species of foreign origin seems to increase with the increasing size of a city. Some of them are even superior to native species for habitats which are strongly influenced by man.
INTRODUCTION Settlements and areas used for transportation purposes make up 10% of the total land area of the Federal Republic of Germany, corresponding to a total of 24 000 km*. This percentage is, of course, much higher in urban areas. However, the surfaces covered by vegetation (public and private gardens, sites used for agriculture and forestry, urban wasteland, etc.) still account for about 50% of the total area in large cities, according to statistics for the Federal Republic of Germany. Duvigneaud (1975) has reported a similar value for Brussels. The vegetation found on such sites is in part growing spontaneously, in part planted by man. Trees and shrubs play an important role in forming a characteristic landscape, including an urban landscape. They will therefore be the focus of attention in this paper. 0169-2046/87/$03.50
0 1987
Elsevier
Science
Publishers
NATURAL AND HISTORICAL PREREQUISITES FOR TODAY’S COMPOSITION
SPECIES
Were it not for the influence of man, Central Europe would be covered, for the most part, by forests. The species composition of these natural forests would be relatively limited with respect to the numbers of different species, and much less varied than, for example, North American forests, under similar climatic conditions. This is due to the fact that many of the tree species previously occurring in Central Europe became extinct as a result of the Ice Age. They were later unable to re-colonize the region. Human activity has caused on the one hand, the decimation of extensive forest areas, and on the other hand has changed their species composition through various forestry measures. Some tree species such as B.V.
58
the ash and the lime were considered to be sacred in earlier times and were planted at particular sites. Other tree species were encouraged because of their usefulness, whereas still others were suppressed. Under Roman rule, many species were introduced to Central Europe from the Mediterranean area and from the Near East. Beginning in the 16th century, explorers introduced woody plants from foreign lands into European gardens and parks. Dendrology contributed to the satisfaction of the increased and more refined economic and psychological needs of society (Pniower. 1954). The decision to plant trees and to favour certain species does not depend solely on such parameters as the size of a particular piece of land or the composition of the soil. By comparing parks and gardens laid out in different periods, one can observe that these decisions are subject to changes in fashion, and that this continues to the present day. Certain groups of trees characterize the appearance of entire city neighbourhoods. Today, we have at our disposal a wide variety of cultivated trees and shrubs. We should make conscious use of this variety, with an eye to the ecological, economical and historical aspects involved.
TABLE
Actual counts of the numbers of trees found in settlements, with the exception of street trees which are considered separately, are not generally available. However such an inventory has been started in some German cities (e.g. Leitl, 1980: Heinrich, 1982). According to Sukopp (1978), the number of trees on private property has been estimated to be lo-~1 5 times that of the number of street trees. and amounting to 1.5&Z million trees in the city of Berlin (West). The term “urban forest” (Grey and Deneke. 1978) thus does seem to be justifiable. In recent years, the species composition of the tree-stands in urban residential areas and public open spaces in several German cities has been studied on the basis of an analysis of certain areas. Table I lists the most frequent trees, excluding fruit trees, for some of these cities. Less than half of the 44 species which appear in the list are of Central European origin (40.9%1), and some of these are only represented as cultivars. By introducing a large number of foreign trees, as well as by selection and cultivation, man has thus greatly increased the species
1
List of the 25 most frequently
planted
trees in some major German
Origin’
altitude above sea (m) annual temperature annual
rainfall
Species Be&la pendula Picea ornorika
o- 5
(mm)
C. Eur. Med.
cities’
City Bremerhaven’
Average level Average (“Cl Average
THE ACTUAL COMPOSITION OF SPECIES OF PLANTED TREES IN URBAN AREAS
Cologne4
30
Stuttgart5
Karlsruheb
Berlin (West)7
200-400
110
35
X.8 142
9.8 700
9.8 700
>9 630
8.4 517
. .
. <,
. ”
. .
. n
59
TABLE
I (continued)
Origin’
-
Bremerhaven3
Cologne4
Stuttgart5
Karlsruhe6
Berlin (West)’
0 0
0 . + +
. 0 n
. 0 0 t 0 +
o o 0 t 0
t .
. . 0 0 . + t
P. abies Pinus nigra Picea pungens Larix decidua Pinus sylvestris Cedrus atlantica ‘Glauca’
c. Eur. Med. (N. Am.) c. Eur. c. Eur. (Med.)
o . + +
Aesculus hippocastanum Acer platanoides Sorbus aucuparin Acer pseudoplatanus Tilia cordata Carpinus betulus Taxus baccata Acer campestre Quercus robur Fraxinus excelsior Fagus sylvatica (inc. ‘Atropunicea’) Platanus acerifolia Crataegus monogyna ‘Kermesina Plena’
Med. C. Eur. C. Eur. c. Eur. C. Eur. C. Eur. c. Eur. c. Eur. c. Eur. c. Eur. (C. Eur.)
0 + . . 0 0 0 + 0 + I
0 0 0 . + . 0 0 0 + 0
Med. c. Eur.
+ f
0
Prunus serrulata Rex aquifolium Sorbus intermedia
(E. As.) C. Eur. N. Eur.
0 0 +
Robinia pseudoacacia Acer saccharinum Juglans regia Pseudotsuga menziesii Populus nigra ‘Italica’ P. hybrida
N. Am. N. Am. Med. N. Am. (Med.) (N. Am.)
Tsuga canadensis Magnolia soulangeana Prunus pissardii Thuja spp. div. Malus ji’oribunda Chamaecyparis spp. div.
N. Am. (E. As.) (E. As.) (N. Am.) (E. As.) (N. Am.) N. Am. N. Am. N. Am. E. As. (M. Eur.)
Catalpa bignonioides Quercus rubra Acer negundo Ailanthus altissima Salix alba ‘Tristis’
+
0 + 0 +
+ 0
t *
0 t
f
+ +
. +
t 0 0
t + +
t t 0 0
+ t
0 + 0
t
+ 0 + t + + t
’ 0, order l-5; o, order 6-15; +, order 16-25; (), mostly as cultivars. *C. Eur., Central Europe; Med., Mediterranean area; N. Am., North America; E. As., East Asia; N. Eur., Northern Europe; As, Asia; Alp., the Alps. 3 Data from Kunick (1979). 4Data from Kunick (1983b). ‘Data from Kunick (1983a). ’ Data from Kunick and Kleyer (unpublished results, 1984). “Data from: Kunick (1978); Sukopp and Kunick (1976); Drescher and Heim (1978); Drescher and StGhr (1980); Drescher et al. (1981).
60
L1 < 10% j:::::(l
IO - 30 %
a
30 - 70 %
@jjj
> 70%
0 100
Fig. 1. Section of the city of St uttgart; percentage of the area covered by vegetation.
61
Fig. 2. Section of the city of Stuttgart; number of species of planted trees and shrubs.
62
diversity. Trautmann (1973) identified only 22 native trees in the city of Cologne, but in contrast, a study carried out in 1981/82 listed 167 different species (Kunick, 1983b). This increase in species diversity due to human activities is overwhelming. Conifers make up one-third of the most frequent tree-species in all cities. In spite of the fact that the living conditions which they find in cities are extremly adverse and they seldom flourish, conifers are continually being re-planted. The number of species of trees and shrubs per unit area which are planted in gardens and public open spaces generally correlates quite clearly with the percentage
.
Young
of the total area which is covered by vegetation, as seen in Figs. 1 and 2. These figures represent a section of the urban area of Stuttgart. It is the down-town area of a densely built-up valley basin, which rises to the south and north and becomes an area of less closely-set villas and estates. Even where the density of vegetation falls below 10% at least 20 tree and shrub species can usually be found per block. When the density of vegetation is over 70%. 60-100 species are registered. Certain tree species such as the copper beech (Fagus sylvaticu ‘Atropunicea’) or mammoth tree (Sequoia gigalztea) are found
and mlddle
aged
l
Old
,..
lndlviduals
“.
s$xxltaneously
growing
Copper Fig. 3. Distribution of &Stuttgart.
beech
(Fagus
of copper
sy[vatica
‘Atrownicw’)
beech (Fagus sylvatica
‘Atropunicea’)
Mammoth
and mammoth
tree
(SeqLIOia gigantea)
tree (Sequoia
gigunfea)
in a section
of the city
63
only in less densely built-up areas (Fig. 3), whereas the plane tree and the tree of heaven (Ailanthus altissirna) also occur in the downtown area and are even more frequent there than elsewhere (Fig. 4). The birch is the most common tree in all the. citie.s investigated. Of the deciduous trees, the following native Central European species predominate:
(Fraxinus excelsior) (Acer campestre~.
Common ash Field maple
Of the trees which are not native to Central Europe, the most common are two from the ~editerranea1~: Horse chestnut Walnut and two from North America: Silver maple Black locust
tree Fig. 4. Distribution
of &me @Wanus
acerifok)
of heaven
(Aifaniltus
atris.h;t,l
and tree of heaven (Aj~a~r~~s al~~ss~t~a)in a section of the city of Stuttgart.
64
TABLE
II
Street-tree
population
in some major German
cities (56)
City Cologne’
Average altitude above sea level (m) Average annual temperature (“C) Average annual Genus Tilti Acer Quercus AESCUIUS
Robinia Fraxinus Sorbus Betula Populus Crataegus Carpinus Corylus Prunus
’ Data a Data ‘Data 4 Data
from from from from
(mm)
Berlin (West) 3
Karlsruhe’
Augsburg”
30
57
35
110
500
9.8 700
9.0 644
8.4 517
>9 630
8.1 818
39.1 11.3
30.5 16.1 14.5 4.9 3.3 1.1 5.0 3.7 3.2 2.1 2.0 1.1 1.3 0.9
41.7 16.1 7.5 7.1 3.9 1.8 3.5 1.3 3.6 1.8 2.4
1.o
ulmus
Others
rainfall
Hanover’ L
+ + t
2.1
11.5 24.0 9.9 4.4 4.9 1.1 4.9 2.1 7.2 2.1 1.9 7.3 0.9 6.1
31.0 21.0 0.5 7.0 2.0 14.0 2.0 1.0 4.5 4.5 0.5 0.5 1.0 0.5
1.4
3.0
the Municipality. Hester (1982). Sukopp (1978) (+ = no data). Hutter and Miiller (1983).
Street trees
A survey of the most common street trees in several cities is shown in Table II. The genera which have traditionally been planted most often are Tilia and Acer, which together account for between 35.5% (in Karlsruhe) and 50% (in Cologne, Berlin (West) and Augsburg) of street trees. The previously common elm trees have nearly disappeared from urban streets, due to Dutch Elm Disease. In 1928, elms accounted for 17% of street trees; by 1975/76 they were reduced to 1.3% (Sukopp, 1978). All the street trees which are still common today are particularly endangered by de-icing salts, as well as by other direct and indirect
traffic influences. An investigation of the street-tree population of Hanover, carried out by Hester (1982) in the summer of 198 1, indicated that more than 13% of the trees were damaged by de-icing salts; in some districts of Hanover about 30% of the street trees were damaged. Species composition public gardens
in difjkrent
types of‘ private or
Different types of neighbourhood or public open space within a single city can be identified on the basis of their typical tree species. Table III presents the results of such a study in Cologne. The present city covers an area of 400 km2
65
TABLE
III
Tree-species frequency)
composition
depending
on urban
land usage (using Cologne
as an example,
and considering
only species with >33%
Land-type Built-up C
T
areas’
Open spaces and cemeteries’
11
R
EP b
c
d
CE
SP b
a
b
c
a
+ + t + + t + +
t t t t + t +
t + t + t + t +
t t t t t + t +
t t t t
+ t + +
t + t t
+ + +
+ t t
t t t t t t
+ + + t t t t t t t
t + + + + + t
a
-
NP
LP
a
b
t t t + t t t
t t t t t
t t t
+ + t t
t + t + t t t t t t t t t t t t
-
Species Betula pendula Acer pseudoplatanus Carpinus betulus Taxus baccata Robinia pseudoacacia Aesculus hippocastanum Platanus acerifolia Populus nigra ‘Italica’
+ + + + + + + +
t + + + +
Pinus nigra Acer saccharinum A. campestre Sorhus aucuparia Fagus sylvatica Acer platanoides Quercus robur Tilia cordata T. platyphyllos Fraxinus excelsior Populus canadensis Ailanthus altissima Quercus rubra Tilia euchlora Prunus avium Acer negundo Pncnus serotina P. padus Sorbus intermedia Pterocarya $-axinifolia Catalpa bignonioides Aesculus carnea Castanea sativa Ulmus minor Alnus glutinosa A. incana Salix alba S. fragilis Prunus mahaleb
+ +
t
Picea abies Pseudotsuga menziesii Larix decidua Pinus strobus P. sylvestris Picea omorika P. pungens
t t t t
t t
t t
t t
t t
t + + + + + t + +
+
t t
+ t + t
+ t t t
+
+ t + t t t
t t
t
+
t t
t t t + + t t + + t + t t t t
t + t t + + + t t t + t
t
+
t t
t t + t
t t t + t t t t
+
t t +
t t +
t + t + t t t
t +
t
t + t
t t t t t t t
t t t t t t t
t t t t t t t
t t t t + t t
t t
t t + t t t t
f + t t t
t
t t t t t
66
TABLE
I11 (continued) Land-type Built-up C
T
Open spaces and cemeteries’
areas’ R
H a
b
c
a
CP b
c
d
cc a
SP b
LP
NP a
b
Species (cant ) Prunus pissardii P. serrulata Ilex aquifolium Cedrus atlantica ‘Glauca’ Chamaecyparis lawsoniana a.0.
+ + + + t
+ +
+ + + +
t
+ + + + +
t t + t t
Fagus sylvatica ‘Atropunicea’ Betula pendula ‘Tristis’ Salix alha ‘Tristis’
t + t
Tsuga canadensis Abies concolor Thuja spp. div. Fagus sylvatica ‘Pendula’ Tilia intermedia
+ + + t t
Juglans regia Crataegus monogyna ‘Kermesina Plena’ Magnolia soulangeana Malus floribunda Cedrus deodara Metasequoia glyptostroboides Salix matsudana ‘Tortuosa’ Ginkgo biloba Liquidambar styraciflua Sorbus aria
+ +
t t
t
+ +
t
+ t t t
t
+ +
t + + + + +
_ ’ Built-up areas: C, densely built-up central areas almost without vegetation; T, old town centres, densely built-up areas with few vegetation components; H, multi-storey housing areas, a = 1920-1940, b = 195OG1970, c = after 1970; R, residential areas with detached and terraced houses, a = before 1918, b = 1920-1940, c = after 1950, d = recently constructed. ’ Open spaces and cemeteries: El’, estate parks; CL, cemeteries, a = older, b = younger (* after 1950); SP, small green places; NP, neighbourhood parks, a = older, b = younger (i- after 1950); LP, large city parks.
and includes a number of settlements which were formerly independent. Residential areas which were built in different periods and which vary in density are grouped around these old settlement centres. If one takes the species listed in Table III into account. it becomes apparent that as well as the tree species common to all types of settlement and public open space (as listed at the top of Table III) certain species-combinations which
are characteristic of a particular land-use type can be observed. The central area of the city, which was destroyed in the war and is now densely built-up (C), has a low species diversity. The area covered by vegetation is minimal, and habitat conditions are extremely adverse. Wherever the proportion of garden area increases, the species diversity rises markedly. Old settlement centres and middle-class resi-
67
dential areas built in the 19th century (T) have front yards and inner gardens which often contain valuable tree stands. Many broad-leaved deciduous trees, in particular those with a large crown volume such as maple, beech, oak or lime, are frequently found here, as well as in public parks. The highest species variety is observed in the gardens of old villas laid out before 1918 (R a) and in old cemeteries (CE a). These sites are characterized by a rich variety of deciduous trees and conifers. Conifers are planted in cemeteries because of their serious, dismal appearance, and in private gardens because, like true “Christmas trees”, they are green in winter and because they avoid the trouble of removing fallen leaves. The standard assortment chosen for more recently laid out private gardens consists of conifers and fruit trees (not included in Table III) and a few small deciduous tree species with showy flowers or especially decorative leaves. This result has been confirmed by similar studies in other cities.
TABLE
Composition of tree species in ruralsettlements
The traditional tree populations of villages is much less clearly differentiated than that of the cities. They are composed for the most part of fruit-tree plantings which often form a large circle around the settlements and integrate them into the surrounding landscape. Nowadays, these orchards are being drastically reduced by the expansion of settlements and changes in agricultural practices. Otherwise, tree stands are generally limited to certain sites, e.g. around churches, taverns and individual farmhouses. Economic conditions limit the establishment of large omamental gardens. The trees planted here are usually taken from the environs of the settlement instead of from nurseries. The most frequent tree species occurring in rural settlements in three different types of landscape are listed in Table IV. The table shows that the spectra of tree species found in these rural settlements generally conform in most cases, but that certain differences due to local con-
IV
The most common
tree species in rural settlements
in three different
types of German
landscape
Type of landscape
Average Average Average
altitude above sea level (m) annual temperature (“C) annual rainfall (mm)
Species Juglans regia Aesculus hippocastanum Tilia spp. div. Fraxinus excelsior Robinia pseudoacaciu Bet& pendula Pices abies Quercus robur
Cologne. Lowlands
Hilly country of Ingolstadt (Bavaria)
south
Swabian-Frankonian forest (Baden- Wiirttemberg)
30 9.8 700
370-450 8.3 650-700
450-550 7-8 900
+ + + t t
+ t + t t t t
+ t + t t t t
68
ditions also arise. It is only recently that the species which are presently favoured in urban ornamental gardens have begun to appear in
TABLE List
these settlements in the course of changing kitchen gardens into omatnental gardens and the modernisation of older village centres.
V
of ornamentalshrubs
and climbers
occurring
in Berlin-Kreuzberg
Origin’
Area investigated No. of blocks
BcrlinKrcuzberp
(km*)
Species Acer ginnala Aesculus parviflora Amelanchier spp. div. Aralia elata Aristolochia durior Aucuba japonica Berbenk thunbergii Berberis, evergreen species (B. gagnepainii, B. julianae a.0.)
Buddleia alternifolia B. davidii Buxus sempervirens Caragana arborescens Cercidiphyllum japonicum Cercis siliquastnrm Chaenomeles japonica a.0 Colu tea arborescens Cornus alba et sericea C. mas C. sanguinea Corylus avellana Co tinus coggygria Cotoneaster spp. div. (C awtifolk, C. bullatus. C. dielsiana, C. franchetti, C multijlon*s) Crataegus monogyna Cytisus praecox Lieu tzia hyhrida ElaeaAmus ankastifolia Guon.vmus alatus E. europaeus E. fortunei Forsythia in tcrmedia ffamamelis spp. div. Hibiscus syriacus Hippophae rhamnoides Ilydrangea macrophylla Juniperus communis J. Chinensis Pfitzeriana J. squamata ‘Meyeri
5 145
L. N. N. E. N. E. E.
As. Am. Am. As. Am. As. As.
28.3 0.7 44.8 2.8 1.4 71.0
11. As.
17.2 5.5 22.1 3.6 17.9 0.7
L. As. C. As. Med. E. As. E. As. Med. I:. As. Med. N. Am. As. Med. c. Eur. c. Eur. Med.
46.9 2.8 42.1 33.8 21.8 41.4 3.4
E. As. c. Eur. Med. b. As.
Med. I;. As. C. Lur. E. As. L. As. N. Am./t. c. As. c. Eur. E. As. c. Lur. 6. As.
As.
33.1 27.6 13.1 35.9 11.7 22.1 22.8 2.1 99.1 0.7
and Stuttgart
(7;) (from
Kunick,
1978 resp. 1983a)
Stuttgart -5 246
19.1 4.5 33.3 8.9 3.7 4.5 43.9
39.4 6.1 29.3 47.8 6.9 3.3 6.1 26.1 0.4 29.7 42.7 32.1 45.1 14.2
18.6 39.6 11.7
39.0 19.9 25.6 36.6 8.5 4.9 17.1 3.3 70.3 4.5 8.5 15.0 36.2 16.7
47.6
39.8
69
TABLE
V (continued) Origin’
Kerria japonica Kolkwitzia amabilis Laburnum anagyroides Ligusti-um ovalifolium L. vulgare Lonicera tatarica L. xylosteum Lycium barbarum Mahonia aquifolium Parthenocissus quinquefoha P. tricuspidata ‘Veitchii Philadelphus coronarius Physocarpus opulifolius Pinus mug0 Polygonum aubertii Prunus laurocerasus P triloba Pvracan tha coccinea Rhamnus cathartica Rhododendron catawbiense Rhus typhina et glabra Ribes alpinum R. sanguineum Rosa canina Salix elaeagnus Sorbaria sorbifolia Spiraea argu ta S. salicifolia S. vanhouttei Stranvaesia davidiana Symphoricarpous rivularis Syringa chinensis S. refrexa S. vulgaris Tamarix spp. div. Viburnum carlesii V. fragrans V. lantana V opulus V rhytidophyllum Weigela hy brida Wisteria sinensis
E. As. E. As. Med. E. As. C. Eur. E. As. c. Eur. Med. N. Am. N. Am. E. As. Med. N. Am. C. Eur. (Alp.) E. As. Med. E. As. Med. c. Eur. N. Am. N. Am. C. Eur. N. Am. c. Eur. C. Eur. E. As. E. As. Med. E. As. E. As. N. Am. Med. E. As. Med. Med. E. As. E. As. c. Eur. C. Eur. E. As. E. As. E. As.
BerlirKreuzberg 17.9 15.2 31.9 9.0 77.2 25.5 22.1 10.3 64.8 66.2 33.1 66.9 7.6 54.5 15.9 6.2 18.6 69.0 6.2 36.6 29.7 20.7 40.7 6.9 4.8 1.6 34.5 7.6 79.3 _ 43.4 16.6 0.7 87.6 9.7 0.7 _ 24.8 10.3 18.6 46.9 2.1
Number of species with frequency > 2.5% Other species Total number of species
14 10 84
Origin of species (%) Central Europe Mediterranean area East Asia North America
23.1 23.1 38.5 15.4
’ For abbreviations,
see Table I.
Stuttgart
24.0 23.6 59.3 22.4 61.0 18.3 9.8 3.7 49.2 28.0 38.2 52.8 5.3 42.3 24.4 39.8 16.7 57.3 2.8 36.6 38.6 1.2 32.5 11.0 5.3 2.4 26.9 2.0 37.4 3.7 45.5 13.4 3.7 82.9 19.1 18.3 5.1 29.1 18.7 48.8 42.1 26.4
19 25 104
19.7 18.4 46.1 15.8
70
Planted shrubs and climbers The stands of planted shrubs and climbers (not including berry bushes and small shrubs; the so-called “ground cover”) found in two sections of the built-up urban area of Berlin (West) and Stuttgart were analysed. These 5-km* areas were subdivided into blocks for the purpose of taking this inventory: A total of 112 species (or groups of species) were found for the two cities taken together, 84 of them occurring in Berlin-Kreuzberg and 104 in Stuttgart. There was a high degree of correlation of the variety of tree and shrub species found within the areas studied. Thus, when the available vegetation area increases, the diversity of the tree and shrub layers which together make up the vegetation structure also generally increases. Only in the most recently settled areas, i.e. those settlements which have been built in the past 20 years, has low ground-cover frequently been planted instead of shrubs. With reference to the list of species, the two study areas are very similar. Table V is a compilation of all species registered in at least one of the two areas with a frequency of at least 2.5%. Only about one-fifth of these species are native to Central Europe; this is much less than the number of native tree species (cf. Table I). Most of the favourite ornamental shrubs and those which have been planted in great numbers, such as Forsythia, Lilac, Labumum, Spiraea, Barberry, Firethorn or Oregon Grape are species which have been introduced from the Mediterranean or even from other continents. Ornamental shrubs of East Asian origin clearly predominate in numbers, making up about the same proportion of shrubs as those introduced from North America and the Mediterranean combined. The major differences between Berlin and Stuttgart can be attributed to differences in climatic conditions. Milder winters and higher annual rainfall in Stuttgart allow evergreen
Berberis and Cotoneaster species, cherry laurel,. box and Viburnum to flourish more readily than in Berlin. Oregon grape, firethorn and rhododendron are also often planted in Berlin. However, they do not thrive as well as in Stuttgart. The call for more natural garden landscaping, which has been raised in recent years, has been coupled with the encouragement of more widespread use of native species than has been the case to date. Those who support these efforts tend to overlook the fact that this would result in drastic changes in the features of our gardens. THE ENDANGERING POPULATIONS
OF URBAN TREE
The serious environmental changes taking place in cities pose a threat to tree populations which they are only partially able to withstand. These negative influences are listed in Table VI. Particularly obvious are the adverse effects on street trees, whose life expectancy is drastically reduced. Another factor which threatens the species composition of the urban tree population is the tendency, which has arisen in the last 20 years, not to re-plant the tree species which still characterize the city landscape as extensively as was previously the case - be it on private or on public property. This is the result of an inventory of the tree species composition in different cities, in which the species were registered as belonging to one of three developmental phases (young, middleaged or old). The following trees occur almost entirely as adult specimens: Red horse chestnut Horse chestnut Sycamore Red hawthorn Common
beech
(Aesculus carneu) (Aesculus hippocastanum) (Acer pseudoplatanus) (Crataegus monogyna ‘Kermesina plena’) (Fagus sylvatica)
71
TABLE
VI
Damage’ to tree populations in urban ally and with varying intensity _
agglomerations
(according
to Meyer,
1979).
Air pollution
occurred
both locally
and region-
Habitat Cemetery
Private garden
Open space
Children’s playground
Roadside
l-2 2 2 1 1 7-8
2 l-2 2 1 1 7-8
3 2 2 1 1 9
4 3 2 2 1 12
5 5 4-5 3-5 445 21-25
1
2
2
3
4
5
1
1
1
1
2
5
Park, arboretum Mechanical damage to roots, trunk and crown Soil compaction Cementation Water deficiencies De-icing salts Sum of injuries Resulting restrictions in the choice of species Measures necessary for habitat improvement to compensate for or to avoid injuries ’ 0 = non-existent;
1 = very low; 2 = low; 3 = moderate;
Common ash Walnut Lombardy poplar Weeping willow Lime
4 = high; 5 = very high.
(Fraxinus excelsior) (Juglans regia) (Populus nigra ‘Italica’) (SaZix alba ‘Tristis’) (Tilia spp. div.).
The portion of the total tree population made up by these trees will thus be reduced by natural ageing processes in the coming years, resulting in a great loss in the character of the city landscape. The architectural union of buildings and gardens with specific proportions is disturbed by the removal of trees, which are part of the natural component of such an ensemble. On a larger scale, such disturbances can change the appearance of entire streets or city neighbourhoods. A further cause of change in the tree population is the subdivision of property, leading to increasingly smaller pieces of real estate, which often do not allow for the planting of large trees. An exaggerated sense of neatness, which sees fallen leaves as bothersome refuse, also often plays a role. Thus, among the young trees planted more frequently in recent years,
conifers of the genera Picea, Pinus, Abies and Larix, as well as atlas cedars (Cedrus atlantica ‘Glauca’) predominate and are quite popular, although most of them are barely able to survive under urban conditions, begin to show signs of damage after a few years, and are thus totally unsuitable. It is essential that the public’s awareness be increased with regard to the significance of trees for the characteristic appearance of a city and their contribution to the quality of life in an urban setting. Some first steps in this direction have been made in several German cities in recent years; newspaper articles, public lectures and exhibitions have been used to draw the attention of the general public to these questions. ASPECTS OF THE CHOICE OF SPECIES As seen in the previous sections, the present occurrence of trees and shrubs in our cities consists of a varied mixture of native and foreign species. This development can be explained in terms of time, location and ecol-
ogy, and it always reflects interference by man. As fbrest plunter man influenced the species composition in the oldest parks, which often emerged directly from feudal hunting grounds. They have preserved until the present day a woodland-like flora in terms of the trees and shrubs as well as the undergrowth. In the 20th Century, new afforestations have been undertaken in some urban agglomerations (for example Cologne, the Ruhr area and others) in order to improve the environmental conditions and to create recreational areas. As gardener man laid out parks, cemeteries and gardens to his liking, although fashion always influenced his choice of species. As ecologist man selected species in accordance with specific qualities of the habitat, so that these would grow optimally and require as little management as possible. In view of these varied aspects the following general rules for the choice of species can be drawn up. always bearing in mind that the specific case may require some modifications: (1) In still largely natural fringe areas of a city native species are to be preferred as they grow best, and such woods offer the most appropriate living conditions to the native flora and fauna. For example, over 100 different species of insects live on the native blackthorn, while none at all live on the Asian forsythia. (2) When using alien trees and shrubs, their origin and specific ecological demands must be considered. In the Federal Republic of a number of different climatic Germany, zones have been differentiated where, for example, the danger of frost-damage varies. While it can be assumed that the annual average temperature in the cities is approximately 1-2” higher than in the surrounding countryside, the air humidity is usually lower, which reduces the viability of evergreen species. (3) In urban areas with heavy air pollution, conifers in general can barely survive. Their
use must therefore be avoided as long as the pollution persists. The conifers which survive the best are yew (Taxus baccata), false cypresses (Chamuecypuris spp. div.), Austrian pine (Pinus nigru) and thuja (Thuj~ spp. div.). (4) When renewing the woody vegetation of old parks, cemeteries and gardens, the character of the surroundings and its existing trees and shrubs must be taken into account. On the basis of historical continuity. and also for ecological reasons, fully grown trees show most clearly what will grow best in a specific area. In rural villages, also. there should be strong efforts to increase traditional species instead of making changes at random during re-planting. (5) When laying out new parks, gardens. etc., such considerations are generally of less importance, since new building generally takes place on ground devoid of any vegetation. Here, too, the f.uture character of the area can be predetermined by concentrating on specific “leader” species which are appropriate to the habitat. (6) Special basic requirements have to be met in the vicinity of roads, as they offer difficult conditions for growth. In the Federal Republic of Germany, the Conference of the administration for public gardening is issuing a list of trees especially suited for these conditions. (7) In cases of re-planting in areas of urban rubble or in similar habitats drastically altered by man, the creation of a standardized habitat through top-soil application should be avoided. For such situations, there is a large variety of pioneer species which have developed spontaneously under similar conditions. They consist of both native and foreign species (see Table VIII). WOODY PLANTS SPONTANEOUSLY GROWING IN SETTLEMENTS According to Sukopp (1978), at least 3000 species of woody plants have been introduced
13
into Central Europe since 1500. Several species from the Mediterranean region have been cultivated here much longer than that. Only a relatively small proportion of these species also grow here spontaneously, particularly in cities. Table VII gives data on the origin of the spontaneous woody vegetation of 10 cities. It is apparent that, in general, the proportion of Central European woody plants is higher in smaller cities (about 70%80% of total vegetation) as opposed to larger cities, in which they reach only 50-60s (in Vienna.
TABLE
this figure is less than 50%). Thus, with increasing size of a city, more alien woody plants are found growing wild. The list of species native to an area or found growing spontaneously (Table VIII) includes 114 species from Central Europe, as well as an equal number, 118 to be exact, which are not indigenous to this area. Data on the specific frequency can only be evaluated with certain qualifications, since individual values are difficult to compare due to the variations in the size of the areas studied. The
VII
Origin of the woody
plants growing
Medium-sized
cities (<200
spontaneously
in several cities
000 inhabitants)
Large cities (>500
000 inhabitants)
n
Total (70)
Bremerhaven’ Average
altitude o-5
Average
annual 8.8 Average annual 742 No. of species 59
Origin
Saarloui?
Karlsrub?
above sea level (m) 180110 200 temperature (“C) 9.5 >9 rainfall (mm) 703 630
59
Regensburg4
Augsburg’
330470
500
Duisburg6
20--50
8.1
89
9-10
30
9.8
Stutt&UP
200400 9.8
Berlin (West)9
35
8.4
Vienna”
200
9.5
600
818
750& 800
700
700
577
600700
119
108
110
139
129
139
155
(70) Central Europe 76.4 81.3 Mediterranean 11.9 6.8 East Asia 3.4 1.7 North America 10.2 10.2
56.2
80.7
77.8
73.6
55.4
51.2
59.0
41.7
114
49.1
14.6
11.8
9.3
13.6
12.9
15.5
13.7
20.0
37
15.9
14.6
1.7
4.6
5.5
15.8
19.4
10.8
18.1
49
21.1
5.9
8.3
1.3
15.8
14.0
16.5
14.2
32
13.8
14.6
’ Data ‘Data 3 Data 4 Data ‘Data 6Data ‘Data ‘Data 9Data “Data
Cologne’
from from from from from from from from from from
Kunick (1979). Maas (1983). Kunick and Kleyer (unpublished results, Mergenthaler (1982). Hiemeyer (1978). DiiB and Kutzelnigg (1980). Kunick (1983b). Seybold (1969) and Kunick (1983a). Sukopp et al. (1981). Forstner and Hub1 (1971).
1984).
TABLE VIII List of trees, shrubs Species
of Central
and climbers European
growing
origin,
spontaneously
occurring
European
Abies alba Alnus incana Berberis vulgaris Bet& carpathica B. pubescens Coronilla emerus Cotoneaster integerrima Cytisus nigricans Daphne mezereum Juniperus communis .I. sabina Larix decidua Lonicera caprifolium L. nigra L. periclymenum Myrica gale Picea abies Pinus mug0 spp. Populus canescens Potentilla fruticosa
frequency
(local; common)
Quercus petraea Q. robur Ribes nigrum R. rubrum R. uva-crispa Rosa canina Rubus caesius R. fruticosus R. idaeus Salix alba S. caprea S. cinerea S. fragilis S. purpurea S. rubens S. triandra S. viminalis Sambucus nigra S. racemosa Sarothamnus scoparius Sorbus aucuparia
Betula pendula Carpinus betulus Clematis vitalba Cornus sanguinea Corylus avellana Crataegus laevigata C monogyna Euonymus europaeus Fagus sylvatica Frangula alnus Fraxinus excelsior Hedera helix Hippophae rhamnoides Ilex aquifolium Ligustrum vulgare Lonicera xylosteum Pinus sylvestris Populus alba P. n&a P. tremula Prunus avium P. domestica P. mahaleb P. padus P. spinosa of Central
cities (cf. Table VII)
in 6 or more cities with medium-to-high
Acer campestre A. platanoides A. pseudoplatanus Alnus glutinosa
Species
in 10 different
Taxus baccata Tilia cordata T. platyphyllos Ulmus glabra U. minor Viburnum lantana I/. opulus
and North
European
origin,
occurring
Prunus fncticosa Rhamnus cathartica Ribes alpinum Rosa agrestis R. arvensis R. coriifolia R. corymbifera R. elliptica R. gallica Rosa jundzillii R. majalis R. micrantha R. obtusifolia R. pendulina R. pimpinellifolia R. rubiginosa R. tomentosa R. villosa R. uosagiaca Salix aurita
in 5 or less cities with low frequency
(rare)
TABLE
VIII (continued)
Species of Central
European
and North
S. dapnoides S. elaeagnus S. hippophaefolia S. myrsinifolia S. pentandra S. repens S. smithiana Sambucus nigra ‘Laciniata’ Sorbus aria Species
N N
N N
N N
N
N
N N
occurring
in 5 or more cities with low frequency
origin
American
N N
N N N
N
N N N N
Laburnum anagyroides Lycium barbarum Malus domestica Mespilus germanica Philadelphus coronarius Pinus nigra Platanus acerifolia Prunus cerasus P laurocerasus Pyracan tha coccinea Pyrus communis Quercus cerris Sorbus domestica Spiraea salicifolia Staphylea pinnata Syringa vulgaris Tamarix parviflora T ramosissima
origin
Acer negundo A. saccharinurn Amelanchier lamarckii Amorpha jiucticosa Catalpa bignonioides Celtis occiden talis Chamaecyparis lawsoniana Cornus sericea Crataegus prunifolia Fraxinus pennsylvanica Gleditsia triacanthos Gymnocladus dioicus Juglans nigra Mahonia aquifolium Parthenocissus quinquefolia Philadelphus pubescens
Species
N
of North
origin,
S. danubialis S. graeca S. in termedia S. torminalis Ulex europaeus lh’mus hollandica U. laevis Vitis vinifera
Acer monspessulanum A. tataricum Aesculus hippocastanum Buxus sempervirens Castanea sativa Cercis siliquastrum Clematis viticella Colutea arborescens Cornus mas Corylus colurna C maxima Cydonia o blonga Elaeagnus angustifolia Euonymus verrucosa Ficus carica Fraxinus angustifolia F. ornus Juglans regia
Species N
of Mediterranean
American
N
N
N
Physocarpus opulifolius Pinus stro bus Populus canadensis Prunus serotina Pseudotsuga menziesii Ptelea trifoliata Quercus palustris Q. rubra Rhus typhina Ribes aureum R. sanguineurn Robinia pseudoacacia Rubus odoratus Symphoricarpus rivularis Thuja occidentalis
of East Asian origin
Acer ginnala Ailanthus altissima Berberis gagnepainii B. julianae
B. thunbergii Buddleia davidii Caragana arborescens C. frutex
(rare) (coni.)
76
TABLE
VIII (continued)
Species of East Asian origin (cont.) Caryopteris incana Chaenorneles japonica Citrus aurantium Cornus alba Cotoneaster acutifolius C. bullatus C franchetii C. horizontalis C. lucida C. multiflorus C. salicifolius Deutzia hybrida Forsythia suspensa F. viridissima Ginkgo hiloba Hydrangea macrophylla Kerria japonica Koelreuteria paniculata Kolkwitzia amabilis Ligustrum ovalifolium Lonicera maackii
most common cities are:
common
Elder Goat willow Bramble Dewberry Traveller’s joy Hazel Dog rose
N
native
Sycamore Birch Wild cherry Common ash Norway maple The most
N
species
L. pileata I,. tatarica Lycium chinense Morus alba M nigra Parthenocissus tricuspidata Paulownia tomentosa Polygonum aubertii Prunus armeniaca P. cerasifera P. persica Pterocarya fraxinifolia Rose multiflora R. rugosa Sophora japonica Sorbaria sorbifolia S. tomen tosa Thuja orien talis Viburnum rhytidophyllum Weigela hybrida Zelkova serrata
found
in all
(Acer pseudoplatanus) (Betula pendula) (Pru72us avium) (Fraxinus excelsior) (Acer platanoides) native
shrub
species
are:
(Sambucus nigra) (Salix caprea) (Rubus fruticosus) (Rubus caesius) (Clematis vitalba) (Corylus avellana) (Rosa canina)
Only a few of these species are ever deliberately planted (cf. Tables I and V). Of the non-native woody plants listed, only 27 can be considered to be at least locally naturalized outside the cities, as determined
by Trautmann (1976) and Lohmeyer (1976). These are marked in Table VIII with an “N”. Most of these species have their origin in the Mediterranean area, which is geographically and culturally closest to Central Europe. Only eight species from North America and four from East Asia have become fully established to date. More detailed descriptions are available for some of these species, e.g. Rohkia pseudoacacia (Kohler and Sukopp. 1963). Ailanthus altissima (Bbcker and Kowarik, 1982) and Buddleia davidii (Kunick. 1970). In the cities, as well as the afore-mentioned plants. the following species occur more or less regularly, although not always in great numbers: Walnut Apple Lilac Horse chestnut Pear Barbary
wolfberry
(Juglans regia) (Malus domestica) (Syringa vulgaris) (Aesculus hippocastarzum) (Pyrus communis) (Lycium barbarum)
II
Sweet chestnut Laburnum Bladder senna Dwarf cherry Plane
(Castanea sativa) (Laburnum anagyroides) (Colutea arborescens) (Prunus cerasus) (Platanus acerifolia j
shrubs on woodland edges around the city of Erlangen. However, most of these species are unable to penetrate the forests. In the innercity they are. nevertheless, some of the species best adapted to the environment. REFERENCES
The species listed above are from the Mediterranean. whereas the following ones originated in North America: Rum cherry Red oak Snowberry Virginia creeper Box elder Sumac Oregon grape Red osier
(Prunes serotina) (Quercus rubra) (Symphoricarpos rivularis ) (Parthenocissus quinquefolia) (A cer negwzdo) (R hus tvphina > (Mahonia aquifolium > (Cornus sericea)
With regard to the ecological concentration of distribution, it is clear that native Central European species dominate on sites which are rich in nutrients and humus, but which are not far removed from their original natural state. This is the case in gardens, parks and cemeteries. where maple and elder-thickets develop particularly well. Adventitious woody plants, in contrast: profit especially from habitats which have been strongly influenced by man. Such habitats make up a significant portion of the surface area of large cities? e.g. building-rubble sites and unused railway tracks. Robinia, Buddleia and Ailanthus can develop large stands on such sites, as has been reported in various studies from several different cities (e.g. Sukopp et al., 1979). Adventitious woody plants also try to move out from the inner-city and become established in the city environs, as shown by a study conducted by Asmus (198 l), in which he found 70 different ornamental trees and
U., 1981. Der Einfluss von NutzungsEnderung und Ziergtiten auf die Florenrusammensetzung stadtnaher Forste in Erlangen. Ber. Bayer. Bot. Ges. Erforsch. Heim. Flora, 52: 117-121. Biicker, R. and Kowarik, I., 1982. Der Giitterbaum in Berlin (West). Berl. Naturschutzbl., 26: 4-9. Drescher, B. and Heim, P., 1978. GehSlzbesttide in Altbaugebieten. Untersuchungsgebiet Leopoldplatz, Nord. .4smus,
Techn. Univ. Berlin, Institut dkologie, Berlin. Drcscher, B. and Stiihr, M., 1980. Untersuchung des Gehijlzbestandes der Onkel-Tom-Siedlung in Bezirk Zehlendorf von Berlin. Techn. Universitlt Berlin, Institut Gkologie, Berlin. Drescher, B., Mohrmann, R. and Stern, S., 1981. Untersuchung des Gehijlzbestandes der Hufeisensiedlung in Berlin-Britz. Techn. Univ. Berlin, Institut ckologie, Berlin. Diill, R. and Kutzelnigg, H., 1980. Punktkartenflora von Duisburg und Umgebung. Westdeutscher Verlag, Opladen. Duvigneaud, P., 1975. L’bcosysti.me Bruxelles. In: P. Duvigneaud et S. Denayer-de Smet, L’CcosystZme urbain. Application & l’agglomtration bruxelloise, Bruxelles, pp. 16-m33. Forstner, W. and Hiibl, IX., 1971. Ruderal-, Segetal- und Adventivflora von Wien. Verlag Notring, Wien. Grey, G.W. and Deneke, F.J., 1978. Urban forestry. Wiley, Chichestcr. Heinrich, W., 1982. BLume in der Stadt ~ Betrachtungen und Erhebungen in Jena. Beitr. Phytotaxon., 10: 83121. Hiemcycr, F., 1978. Flora von Augsburg. Ber. Naturwissensch. Verein ftir Schwaben, Augsburg. Hijster, H.R., 1982. Streusalzschiden an Strassenbaumen. Landschaft + Stadt, 14: 63-11. Huttcr, S. and MiiIler, N., 1983. Zustandserfassung der Baume an Strassen und Platzen in Augsburg. Teil 11: Gesamtstadt. Stadt Augsburg, Gartenamt. Kohler, A. and Sukopp, H., 1963. uber die GehGlzentwicklung auf Berliner Triimmerstandorten. Ber. Dtsch. Bot. Ges., 76: 389-406. Kunick, W., 1970. Dcr Schmetterlingsstrauch (Buddleia davidii Franch.) in Berlin. Berl. Naturschutzbl., 14: 1-4. Kunick, W., 1978. Stadtbiotopkartierung Berlin. I. Kreuzberg-Nord. Techn. Univ., Berlin, Institut Gkologie, Berlin. Kunick, W., 1979. Vegetationskundlich gische Untersuchungen im Gebiet Stadt Bremerhaven, Gartenbauamt.
~ landschaftsijkoloder Stadt Bremerhaven.
78
Kunick, W., 1983a. Pilotstudie Stadtbiotopkartierung Stuttgart. Beih. Veroff. Naturschutz Landschaftspflege Bad.Wiirtt., 36: 1-139. Kunick, W., 1983b. Landschaftsokologische Grundlagen. Teil 3. Biotopkartierung. Stadt Koln, Griinflachenamt. Leitl, U., 1980. Der Baumkataster Koln. Gartenamt, 29: 707.-717. Lohmeyer, W., 1976. Verwilderte Zier- und Nutzgeholze als Neuheimische (Agriophyfen) unter besonderer Beriicksichtigung ihrer Vorkommen am Mittelrhein. Nat. Land., 51: 2755283. Maas, S., 1983. Die Flora von Saarlouis. Abh. Delattinia, 13: l-108. Mergenthaler, O., 1982. Verbreitungsatlas zur Flora von Kegensburg. Hoppea, 40: l- 297. Meyer, F.H., 1979. Schadliche Umwelteinfliisse auf Strassenb&me in Ballungsgebieten. In: H. Grzimek and H. Weinzierl (Editors), Die griine Stadt - Naturschutz in der Grosstadt. Deutsche Naturschutzakademic, Miinchen, pp. 19937. Pniower, G., 1954. iibcr die Entwicklungsgeschichte und landeskulturelle Bedeutung der Dendrologie. In: Kulturbund zur demokratischen Erneuerung Deutschlands (ed.), Gcholzkunde und Landeskultur. Urania, Leipzig/Jena, pp. 13-141.
Seybold, S., 1969. Flora von Stuttgart. Uhler, Stuttgart. Sukopp, H., 1978. Gehijlzarten und -vegetation Berlins. Mitt. Dtsch. Dendrol. Ges., 70: 7 ~21. Sukopp. H. and Kunick, W., 1976. ekologische Analyst mit landschaftsokologischen Sanierungsund Nutzungsvorschlagen der H&tinge und des Vorlandes entlang des Havelufcrs siidlich des Imchenplatzes in Berlin Spandau, Ortsteil Kladow. Senator Bau- und Wohnungswesen, Berlin. Sukopp. II., Blume. H.P. and Kunick, W., 1979. The soil, flora and vegetation of Berlin’s waste lands. In: l.c. Laurie (Editor), Nature in Cities. Wiley, Chichestcr, pp. 1155132. Sukopp, lI., Auhagen, A., Henncrt, W., Backer, R., Hennig, U., Kunick, W., Kutzschkau, H.. Schneider, C., Scholz, H. and Zimmermann, F., 1981. Liste dcr wildwachsenden Farn- und Blhtenpfhanzcn van Berlin (West). Landesbeauftragter fir Naturschutz Landschaftsptlcge, Berlin. Trautmann, W., 1973. Vegctationskarte dcr Bundearepublik Deutschland 1: 200 000 ~ Potentiellc natiirliche Vegetation -~ Blatt cc 5502 Koln. Schr. Reihc Vegetationskundc, 6: l-172. Trautmann, W., 1976. Veranderungcn der Geholzflora und Waldvegctation in jiingerer Zcit. Schr. Rcihc Vegctationskundc, 10: 91-108.
57 - Printed
in The Netherlands
WOODY VEGETATION IN SETTLEMENTS
WOLFRAM Gesamthochschule
Kassel, Fachbereich
KUNICK
13, StadtplanunglLandschaftsplanung, (Accepted
for publication
Henschelstr.
2, 03500
Kassel (F.R.G.)
25 April 1986)
ABSTRACT Kunick,
W., 1987.
Woody vegetation
in settlements.
Landscape
Urban Plann.,
14: 57-78.
The woody vegetation in several German cities was analysed and found to consist of a large number of trees and shrubs cultivated in public or private gardens. Many of them are of foreign origin, but are now more or less well adapted to urban soil and climatic conditions. Certain groups of species are characteristic for different city neighbourhoods. Thus, ecological factors as well as social trends influence the species-composition. The number of trees, shrubs and climbers in the cities which are growing spontaneously on different types of derelict land is also considerable. The number of species of foreign origin seems to increase with the increasing size of a city. Some of them are even superior to native species for habitats which are strongly influenced by man.
INTRODUCTION Settlements and areas used for transportation purposes make up 10% of the total land area of the Federal Republic of Germany, corresponding to a total of 24 000 km*. This percentage is, of course, much higher in urban areas. However, the surfaces covered by vegetation (public and private gardens, sites used for agriculture and forestry, urban wasteland, etc.) still account for about 50% of the total area in large cities, according to statistics for the Federal Republic of Germany. Duvigneaud (1975) has reported a similar value for Brussels. The vegetation found on such sites is in part growing spontaneously, in part planted by man. Trees and shrubs play an important role in forming a characteristic landscape, including an urban landscape. They will therefore be the focus of attention in this paper. 0169-2046/87/$03.50
0 1987
Elsevier
Science
Publishers
NATURAL AND HISTORICAL PREREQUISITES FOR TODAY’S COMPOSITION
SPECIES
Were it not for the influence of man, Central Europe would be covered, for the most part, by forests. The species composition of these natural forests would be relatively limited with respect to the numbers of different species, and much less varied than, for example, North American forests, under similar climatic conditions. This is due to the fact that many of the tree species previously occurring in Central Europe became extinct as a result of the Ice Age. They were later unable to re-colonize the region. Human activity has caused on the one hand, the decimation of extensive forest areas, and on the other hand has changed their species composition through various forestry measures. Some tree species such as B.V.
58
the ash and the lime were considered to be sacred in earlier times and were planted at particular sites. Other tree species were encouraged because of their usefulness, whereas still others were suppressed. Under Roman rule, many species were introduced to Central Europe from the Mediterranean area and from the Near East. Beginning in the 16th century, explorers introduced woody plants from foreign lands into European gardens and parks. Dendrology contributed to the satisfaction of the increased and more refined economic and psychological needs of society (Pniower. 1954). The decision to plant trees and to favour certain species does not depend solely on such parameters as the size of a particular piece of land or the composition of the soil. By comparing parks and gardens laid out in different periods, one can observe that these decisions are subject to changes in fashion, and that this continues to the present day. Certain groups of trees characterize the appearance of entire city neighbourhoods. Today, we have at our disposal a wide variety of cultivated trees and shrubs. We should make conscious use of this variety, with an eye to the ecological, economical and historical aspects involved.
TABLE
Actual counts of the numbers of trees found in settlements, with the exception of street trees which are considered separately, are not generally available. However such an inventory has been started in some German cities (e.g. Leitl, 1980: Heinrich, 1982). According to Sukopp (1978), the number of trees on private property has been estimated to be lo-~1 5 times that of the number of street trees. and amounting to 1.5&Z million trees in the city of Berlin (West). The term “urban forest” (Grey and Deneke. 1978) thus does seem to be justifiable. In recent years, the species composition of the tree-stands in urban residential areas and public open spaces in several German cities has been studied on the basis of an analysis of certain areas. Table I lists the most frequent trees, excluding fruit trees, for some of these cities. Less than half of the 44 species which appear in the list are of Central European origin (40.9%1), and some of these are only represented as cultivars. By introducing a large number of foreign trees, as well as by selection and cultivation, man has thus greatly increased the species
1
List of the 25 most frequently
planted
trees in some major German
Origin’
altitude above sea (m) annual temperature annual
rainfall
Species Be&la pendula Picea ornorika
o- 5
(mm)
C. Eur. Med.
cities’
City Bremerhaven’
Average level Average (“Cl Average
THE ACTUAL COMPOSITION OF SPECIES OF PLANTED TREES IN URBAN AREAS
Cologne4
30
Stuttgart5
Karlsruheb
Berlin (West)7
200-400
110
35
X.8 142
9.8 700
9.8 700
>9 630
8.4 517
. .
. <,
. ”
. .
. n
59
TABLE
I (continued)
Origin’
-
Bremerhaven3
Cologne4
Stuttgart5
Karlsruhe6
Berlin (West)’
0 0
0 . + +
. 0 n
. 0 0 t 0 +
o o 0 t 0
t .
. . 0 0 . + t
P. abies Pinus nigra Picea pungens Larix decidua Pinus sylvestris Cedrus atlantica ‘Glauca’
c. Eur. Med. (N. Am.) c. Eur. c. Eur. (Med.)
o . + +
Aesculus hippocastanum Acer platanoides Sorbus aucuparin Acer pseudoplatanus Tilia cordata Carpinus betulus Taxus baccata Acer campestre Quercus robur Fraxinus excelsior Fagus sylvatica (inc. ‘Atropunicea’) Platanus acerifolia Crataegus monogyna ‘Kermesina Plena’
Med. C. Eur. C. Eur. c. Eur. C. Eur. C. Eur. c. Eur. c. Eur. c. Eur. c. Eur. (C. Eur.)
0 + . . 0 0 0 + 0 + I
0 0 0 . + . 0 0 0 + 0
Med. c. Eur.
+ f
0
Prunus serrulata Rex aquifolium Sorbus intermedia
(E. As.) C. Eur. N. Eur.
0 0 +
Robinia pseudoacacia Acer saccharinum Juglans regia Pseudotsuga menziesii Populus nigra ‘Italica’ P. hybrida
N. Am. N. Am. Med. N. Am. (Med.) (N. Am.)
Tsuga canadensis Magnolia soulangeana Prunus pissardii Thuja spp. div. Malus ji’oribunda Chamaecyparis spp. div.
N. Am. (E. As.) (E. As.) (N. Am.) (E. As.) (N. Am.) N. Am. N. Am. N. Am. E. As. (M. Eur.)
Catalpa bignonioides Quercus rubra Acer negundo Ailanthus altissima Salix alba ‘Tristis’
+
0 + 0 +
+ 0
t *
0 t
f
+ +
. +
t 0 0
t + +
t t 0 0
+ t
0 + 0
t
+ 0 + t + + t
’ 0, order l-5; o, order 6-15; +, order 16-25; (), mostly as cultivars. *C. Eur., Central Europe; Med., Mediterranean area; N. Am., North America; E. As., East Asia; N. Eur., Northern Europe; As, Asia; Alp., the Alps. 3 Data from Kunick (1979). 4Data from Kunick (1983b). ‘Data from Kunick (1983a). ’ Data from Kunick and Kleyer (unpublished results, 1984). “Data from: Kunick (1978); Sukopp and Kunick (1976); Drescher and Heim (1978); Drescher and StGhr (1980); Drescher et al. (1981).
60
L1 < 10% j:::::(l
IO - 30 %
a
30 - 70 %
@jjj
> 70%
0 100
Fig. 1. Section of the city of St uttgart; percentage of the area covered by vegetation.
61
Fig. 2. Section of the city of Stuttgart; number of species of planted trees and shrubs.
62
diversity. Trautmann (1973) identified only 22 native trees in the city of Cologne, but in contrast, a study carried out in 1981/82 listed 167 different species (Kunick, 1983b). This increase in species diversity due to human activities is overwhelming. Conifers make up one-third of the most frequent tree-species in all cities. In spite of the fact that the living conditions which they find in cities are extremly adverse and they seldom flourish, conifers are continually being re-planted. The number of species of trees and shrubs per unit area which are planted in gardens and public open spaces generally correlates quite clearly with the percentage
.
Young
of the total area which is covered by vegetation, as seen in Figs. 1 and 2. These figures represent a section of the urban area of Stuttgart. It is the down-town area of a densely built-up valley basin, which rises to the south and north and becomes an area of less closely-set villas and estates. Even where the density of vegetation falls below 10% at least 20 tree and shrub species can usually be found per block. When the density of vegetation is over 70%. 60-100 species are registered. Certain tree species such as the copper beech (Fagus sylvaticu ‘Atropunicea’) or mammoth tree (Sequoia gigalztea) are found
and mlddle
aged
l
Old
,..
lndlviduals
“.
s$xxltaneously
growing
Copper Fig. 3. Distribution of &Stuttgart.
beech
(Fagus
of copper
sy[vatica
‘Atrownicw’)
beech (Fagus sylvatica
‘Atropunicea’)
Mammoth
and mammoth
tree
(SeqLIOia gigantea)
tree (Sequoia
gigunfea)
in a section
of the city
63
only in less densely built-up areas (Fig. 3), whereas the plane tree and the tree of heaven (Ailanthus altissirna) also occur in the downtown area and are even more frequent there than elsewhere (Fig. 4). The birch is the most common tree in all the. citie.s investigated. Of the deciduous trees, the following native Central European species predominate:
(Fraxinus excelsior) (Acer campestre~.
Common ash Field maple
Of the trees which are not native to Central Europe, the most common are two from the ~editerranea1~: Horse chestnut Walnut and two from North America: Silver maple Black locust
tree Fig. 4. Distribution
of &me @Wanus
acerifok)
of heaven
(Aifaniltus
atris.h;t,l
and tree of heaven (Aj~a~r~~s al~~ss~t~a)in a section of the city of Stuttgart.
64
TABLE
II
Street-tree
population
in some major German
cities (56)
City Cologne’
Average altitude above sea level (m) Average annual temperature (“C) Average annual Genus Tilti Acer Quercus AESCUIUS
Robinia Fraxinus Sorbus Betula Populus Crataegus Carpinus Corylus Prunus
’ Data a Data ‘Data 4 Data
from from from from
(mm)
Berlin (West) 3
Karlsruhe’
Augsburg”
30
57
35
110
500
9.8 700
9.0 644
8.4 517
>9 630
8.1 818
39.1 11.3
30.5 16.1 14.5 4.9 3.3 1.1 5.0 3.7 3.2 2.1 2.0 1.1 1.3 0.9
41.7 16.1 7.5 7.1 3.9 1.8 3.5 1.3 3.6 1.8 2.4
1.o
ulmus
Others
rainfall
Hanover’ L
+ + t
2.1
11.5 24.0 9.9 4.4 4.9 1.1 4.9 2.1 7.2 2.1 1.9 7.3 0.9 6.1
31.0 21.0 0.5 7.0 2.0 14.0 2.0 1.0 4.5 4.5 0.5 0.5 1.0 0.5
1.4
3.0
the Municipality. Hester (1982). Sukopp (1978) (+ = no data). Hutter and Miiller (1983).
Street trees
A survey of the most common street trees in several cities is shown in Table II. The genera which have traditionally been planted most often are Tilia and Acer, which together account for between 35.5% (in Karlsruhe) and 50% (in Cologne, Berlin (West) and Augsburg) of street trees. The previously common elm trees have nearly disappeared from urban streets, due to Dutch Elm Disease. In 1928, elms accounted for 17% of street trees; by 1975/76 they were reduced to 1.3% (Sukopp, 1978). All the street trees which are still common today are particularly endangered by de-icing salts, as well as by other direct and indirect
traffic influences. An investigation of the street-tree population of Hanover, carried out by Hester (1982) in the summer of 198 1, indicated that more than 13% of the trees were damaged by de-icing salts; in some districts of Hanover about 30% of the street trees were damaged. Species composition public gardens
in difjkrent
types of‘ private or
Different types of neighbourhood or public open space within a single city can be identified on the basis of their typical tree species. Table III presents the results of such a study in Cologne. The present city covers an area of 400 km2
65
TABLE
III
Tree-species frequency)
composition
depending
on urban
land usage (using Cologne
as an example,
and considering
only species with >33%
Land-type Built-up C
T
areas’
Open spaces and cemeteries’
11
R
EP b
c
d
CE
SP b
a
b
c
a
+ + t + + t + +
t t t t + t +
t + t + t + t +
t t t t t + t +
t t t t
+ t + +
t + t t
+ + +
+ t t
t t t t t t
+ + + t t t t t t t
t + + + + + t
a
-
NP
LP
a
b
t t t + t t t
t t t t t
t t t
+ + t t
t + t + t t t t t t t t t t t t
-
Species Betula pendula Acer pseudoplatanus Carpinus betulus Taxus baccata Robinia pseudoacacia Aesculus hippocastanum Platanus acerifolia Populus nigra ‘Italica’
+ + + + + + + +
t + + + +
Pinus nigra Acer saccharinum A. campestre Sorhus aucuparia Fagus sylvatica Acer platanoides Quercus robur Tilia cordata T. platyphyllos Fraxinus excelsior Populus canadensis Ailanthus altissima Quercus rubra Tilia euchlora Prunus avium Acer negundo Pncnus serotina P. padus Sorbus intermedia Pterocarya $-axinifolia Catalpa bignonioides Aesculus carnea Castanea sativa Ulmus minor Alnus glutinosa A. incana Salix alba S. fragilis Prunus mahaleb
+ +
t
Picea abies Pseudotsuga menziesii Larix decidua Pinus strobus P. sylvestris Picea omorika P. pungens
t t t t
t t
t t
t t
t t
t + + + + + t + +
+
t t
+ t + t
+ t t t
+
+ t + t t t
t t
t
+
t t
t t t + + t t + + t + t t t t
t + t t + + + t t t + t
t
+
t t
t t + t
t t t + t t t t
+
t t +
t t +
t + t + t t t
t +
t
t + t
t t t t t t t
t t t t t t t
t t t t t t t
t t t t + t t
t t
t t + t t t t
f + t t t
t
t t t t t
66
TABLE
I11 (continued) Land-type Built-up C
T
Open spaces and cemeteries’
areas’ R
H a
b
c
a
CP b
c
d
cc a
SP b
LP
NP a
b
Species (cant ) Prunus pissardii P. serrulata Ilex aquifolium Cedrus atlantica ‘Glauca’ Chamaecyparis lawsoniana a.0.
+ + + + t
+ +
+ + + +
t
+ + + + +
t t + t t
Fagus sylvatica ‘Atropunicea’ Betula pendula ‘Tristis’ Salix alha ‘Tristis’
t + t
Tsuga canadensis Abies concolor Thuja spp. div. Fagus sylvatica ‘Pendula’ Tilia intermedia
+ + + t t
Juglans regia Crataegus monogyna ‘Kermesina Plena’ Magnolia soulangeana Malus floribunda Cedrus deodara Metasequoia glyptostroboides Salix matsudana ‘Tortuosa’ Ginkgo biloba Liquidambar styraciflua Sorbus aria
+ +
t t
t
+ +
t
+ t t t
t
+ +
t + + + + +
_ ’ Built-up areas: C, densely built-up central areas almost without vegetation; T, old town centres, densely built-up areas with few vegetation components; H, multi-storey housing areas, a = 1920-1940, b = 195OG1970, c = after 1970; R, residential areas with detached and terraced houses, a = before 1918, b = 1920-1940, c = after 1950, d = recently constructed. ’ Open spaces and cemeteries: El’, estate parks; CL, cemeteries, a = older, b = younger (* after 1950); SP, small green places; NP, neighbourhood parks, a = older, b = younger (i- after 1950); LP, large city parks.
and includes a number of settlements which were formerly independent. Residential areas which were built in different periods and which vary in density are grouped around these old settlement centres. If one takes the species listed in Table III into account. it becomes apparent that as well as the tree species common to all types of settlement and public open space (as listed at the top of Table III) certain species-combinations which
are characteristic of a particular land-use type can be observed. The central area of the city, which was destroyed in the war and is now densely built-up (C), has a low species diversity. The area covered by vegetation is minimal, and habitat conditions are extremely adverse. Wherever the proportion of garden area increases, the species diversity rises markedly. Old settlement centres and middle-class resi-
67
dential areas built in the 19th century (T) have front yards and inner gardens which often contain valuable tree stands. Many broad-leaved deciduous trees, in particular those with a large crown volume such as maple, beech, oak or lime, are frequently found here, as well as in public parks. The highest species variety is observed in the gardens of old villas laid out before 1918 (R a) and in old cemeteries (CE a). These sites are characterized by a rich variety of deciduous trees and conifers. Conifers are planted in cemeteries because of their serious, dismal appearance, and in private gardens because, like true “Christmas trees”, they are green in winter and because they avoid the trouble of removing fallen leaves. The standard assortment chosen for more recently laid out private gardens consists of conifers and fruit trees (not included in Table III) and a few small deciduous tree species with showy flowers or especially decorative leaves. This result has been confirmed by similar studies in other cities.
TABLE
Composition of tree species in ruralsettlements
The traditional tree populations of villages is much less clearly differentiated than that of the cities. They are composed for the most part of fruit-tree plantings which often form a large circle around the settlements and integrate them into the surrounding landscape. Nowadays, these orchards are being drastically reduced by the expansion of settlements and changes in agricultural practices. Otherwise, tree stands are generally limited to certain sites, e.g. around churches, taverns and individual farmhouses. Economic conditions limit the establishment of large omamental gardens. The trees planted here are usually taken from the environs of the settlement instead of from nurseries. The most frequent tree species occurring in rural settlements in three different types of landscape are listed in Table IV. The table shows that the spectra of tree species found in these rural settlements generally conform in most cases, but that certain differences due to local con-
IV
The most common
tree species in rural settlements
in three different
types of German
landscape
Type of landscape
Average Average Average
altitude above sea level (m) annual temperature (“C) annual rainfall (mm)
Species Juglans regia Aesculus hippocastanum Tilia spp. div. Fraxinus excelsior Robinia pseudoacaciu Bet& pendula Pices abies Quercus robur
Cologne. Lowlands
Hilly country of Ingolstadt (Bavaria)
south
Swabian-Frankonian forest (Baden- Wiirttemberg)
30 9.8 700
370-450 8.3 650-700
450-550 7-8 900
+ + + t t
+ t + t t t t
+ t + t t t t
68
ditions also arise. It is only recently that the species which are presently favoured in urban ornamental gardens have begun to appear in
TABLE List
these settlements in the course of changing kitchen gardens into omatnental gardens and the modernisation of older village centres.
V
of ornamentalshrubs
and climbers
occurring
in Berlin-Kreuzberg
Origin’
Area investigated No. of blocks
BcrlinKrcuzberp
(km*)
Species Acer ginnala Aesculus parviflora Amelanchier spp. div. Aralia elata Aristolochia durior Aucuba japonica Berbenk thunbergii Berberis, evergreen species (B. gagnepainii, B. julianae a.0.)
Buddleia alternifolia B. davidii Buxus sempervirens Caragana arborescens Cercidiphyllum japonicum Cercis siliquastnrm Chaenomeles japonica a.0 Colu tea arborescens Cornus alba et sericea C. mas C. sanguinea Corylus avellana Co tinus coggygria Cotoneaster spp. div. (C awtifolk, C. bullatus. C. dielsiana, C. franchetti, C multijlon*s) Crataegus monogyna Cytisus praecox Lieu tzia hyhrida ElaeaAmus ankastifolia Guon.vmus alatus E. europaeus E. fortunei Forsythia in tcrmedia ffamamelis spp. div. Hibiscus syriacus Hippophae rhamnoides Ilydrangea macrophylla Juniperus communis J. Chinensis Pfitzeriana J. squamata ‘Meyeri
5 145
L. N. N. E. N. E. E.
As. Am. Am. As. Am. As. As.
28.3 0.7 44.8 2.8 1.4 71.0
11. As.
17.2 5.5 22.1 3.6 17.9 0.7
L. As. C. As. Med. E. As. E. As. Med. I:. As. Med. N. Am. As. Med. c. Eur. c. Eur. Med.
46.9 2.8 42.1 33.8 21.8 41.4 3.4
E. As. c. Eur. Med. b. As.
Med. I;. As. C. Lur. E. As. L. As. N. Am./t. c. As. c. Eur. E. As. c. Lur. 6. As.
As.
33.1 27.6 13.1 35.9 11.7 22.1 22.8 2.1 99.1 0.7
and Stuttgart
(7;) (from
Kunick,
1978 resp. 1983a)
Stuttgart -5 246
19.1 4.5 33.3 8.9 3.7 4.5 43.9
39.4 6.1 29.3 47.8 6.9 3.3 6.1 26.1 0.4 29.7 42.7 32.1 45.1 14.2
18.6 39.6 11.7
39.0 19.9 25.6 36.6 8.5 4.9 17.1 3.3 70.3 4.5 8.5 15.0 36.2 16.7
47.6
39.8
69
TABLE
V (continued) Origin’
Kerria japonica Kolkwitzia amabilis Laburnum anagyroides Ligusti-um ovalifolium L. vulgare Lonicera tatarica L. xylosteum Lycium barbarum Mahonia aquifolium Parthenocissus quinquefoha P. tricuspidata ‘Veitchii Philadelphus coronarius Physocarpus opulifolius Pinus mug0 Polygonum aubertii Prunus laurocerasus P triloba Pvracan tha coccinea Rhamnus cathartica Rhododendron catawbiense Rhus typhina et glabra Ribes alpinum R. sanguineum Rosa canina Salix elaeagnus Sorbaria sorbifolia Spiraea argu ta S. salicifolia S. vanhouttei Stranvaesia davidiana Symphoricarpous rivularis Syringa chinensis S. refrexa S. vulgaris Tamarix spp. div. Viburnum carlesii V. fragrans V. lantana V opulus V rhytidophyllum Weigela hy brida Wisteria sinensis
E. As. E. As. Med. E. As. C. Eur. E. As. c. Eur. Med. N. Am. N. Am. E. As. Med. N. Am. C. Eur. (Alp.) E. As. Med. E. As. Med. c. Eur. N. Am. N. Am. C. Eur. N. Am. c. Eur. C. Eur. E. As. E. As. Med. E. As. E. As. N. Am. Med. E. As. Med. Med. E. As. E. As. c. Eur. C. Eur. E. As. E. As. E. As.
BerlirKreuzberg 17.9 15.2 31.9 9.0 77.2 25.5 22.1 10.3 64.8 66.2 33.1 66.9 7.6 54.5 15.9 6.2 18.6 69.0 6.2 36.6 29.7 20.7 40.7 6.9 4.8 1.6 34.5 7.6 79.3 _ 43.4 16.6 0.7 87.6 9.7 0.7 _ 24.8 10.3 18.6 46.9 2.1
Number of species with frequency > 2.5% Other species Total number of species
14 10 84
Origin of species (%) Central Europe Mediterranean area East Asia North America
23.1 23.1 38.5 15.4
’ For abbreviations,
see Table I.
Stuttgart
24.0 23.6 59.3 22.4 61.0 18.3 9.8 3.7 49.2 28.0 38.2 52.8 5.3 42.3 24.4 39.8 16.7 57.3 2.8 36.6 38.6 1.2 32.5 11.0 5.3 2.4 26.9 2.0 37.4 3.7 45.5 13.4 3.7 82.9 19.1 18.3 5.1 29.1 18.7 48.8 42.1 26.4
19 25 104
19.7 18.4 46.1 15.8
70
Planted shrubs and climbers The stands of planted shrubs and climbers (not including berry bushes and small shrubs; the so-called “ground cover”) found in two sections of the built-up urban area of Berlin (West) and Stuttgart were analysed. These 5-km* areas were subdivided into blocks for the purpose of taking this inventory: A total of 112 species (or groups of species) were found for the two cities taken together, 84 of them occurring in Berlin-Kreuzberg and 104 in Stuttgart. There was a high degree of correlation of the variety of tree and shrub species found within the areas studied. Thus, when the available vegetation area increases, the diversity of the tree and shrub layers which together make up the vegetation structure also generally increases. Only in the most recently settled areas, i.e. those settlements which have been built in the past 20 years, has low ground-cover frequently been planted instead of shrubs. With reference to the list of species, the two study areas are very similar. Table V is a compilation of all species registered in at least one of the two areas with a frequency of at least 2.5%. Only about one-fifth of these species are native to Central Europe; this is much less than the number of native tree species (cf. Table I). Most of the favourite ornamental shrubs and those which have been planted in great numbers, such as Forsythia, Lilac, Labumum, Spiraea, Barberry, Firethorn or Oregon Grape are species which have been introduced from the Mediterranean or even from other continents. Ornamental shrubs of East Asian origin clearly predominate in numbers, making up about the same proportion of shrubs as those introduced from North America and the Mediterranean combined. The major differences between Berlin and Stuttgart can be attributed to differences in climatic conditions. Milder winters and higher annual rainfall in Stuttgart allow evergreen
Berberis and Cotoneaster species, cherry laurel,. box and Viburnum to flourish more readily than in Berlin. Oregon grape, firethorn and rhododendron are also often planted in Berlin. However, they do not thrive as well as in Stuttgart. The call for more natural garden landscaping, which has been raised in recent years, has been coupled with the encouragement of more widespread use of native species than has been the case to date. Those who support these efforts tend to overlook the fact that this would result in drastic changes in the features of our gardens. THE ENDANGERING POPULATIONS
OF URBAN TREE
The serious environmental changes taking place in cities pose a threat to tree populations which they are only partially able to withstand. These negative influences are listed in Table VI. Particularly obvious are the adverse effects on street trees, whose life expectancy is drastically reduced. Another factor which threatens the species composition of the urban tree population is the tendency, which has arisen in the last 20 years, not to re-plant the tree species which still characterize the city landscape as extensively as was previously the case - be it on private or on public property. This is the result of an inventory of the tree species composition in different cities, in which the species were registered as belonging to one of three developmental phases (young, middleaged or old). The following trees occur almost entirely as adult specimens: Red horse chestnut Horse chestnut Sycamore Red hawthorn Common
beech
(Aesculus carneu) (Aesculus hippocastanum) (Acer pseudoplatanus) (Crataegus monogyna ‘Kermesina plena’) (Fagus sylvatica)
71
TABLE
VI
Damage’ to tree populations in urban ally and with varying intensity _
agglomerations
(according
to Meyer,
1979).
Air pollution
occurred
both locally
and region-
Habitat Cemetery
Private garden
Open space
Children’s playground
Roadside
l-2 2 2 1 1 7-8
2 l-2 2 1 1 7-8
3 2 2 1 1 9
4 3 2 2 1 12
5 5 4-5 3-5 445 21-25
1
2
2
3
4
5
1
1
1
1
2
5
Park, arboretum Mechanical damage to roots, trunk and crown Soil compaction Cementation Water deficiencies De-icing salts Sum of injuries Resulting restrictions in the choice of species Measures necessary for habitat improvement to compensate for or to avoid injuries ’ 0 = non-existent;
1 = very low; 2 = low; 3 = moderate;
Common ash Walnut Lombardy poplar Weeping willow Lime
4 = high; 5 = very high.
(Fraxinus excelsior) (Juglans regia) (Populus nigra ‘Italica’) (SaZix alba ‘Tristis’) (Tilia spp. div.).
The portion of the total tree population made up by these trees will thus be reduced by natural ageing processes in the coming years, resulting in a great loss in the character of the city landscape. The architectural union of buildings and gardens with specific proportions is disturbed by the removal of trees, which are part of the natural component of such an ensemble. On a larger scale, such disturbances can change the appearance of entire streets or city neighbourhoods. A further cause of change in the tree population is the subdivision of property, leading to increasingly smaller pieces of real estate, which often do not allow for the planting of large trees. An exaggerated sense of neatness, which sees fallen leaves as bothersome refuse, also often plays a role. Thus, among the young trees planted more frequently in recent years,
conifers of the genera Picea, Pinus, Abies and Larix, as well as atlas cedars (Cedrus atlantica ‘Glauca’) predominate and are quite popular, although most of them are barely able to survive under urban conditions, begin to show signs of damage after a few years, and are thus totally unsuitable. It is essential that the public’s awareness be increased with regard to the significance of trees for the characteristic appearance of a city and their contribution to the quality of life in an urban setting. Some first steps in this direction have been made in several German cities in recent years; newspaper articles, public lectures and exhibitions have been used to draw the attention of the general public to these questions. ASPECTS OF THE CHOICE OF SPECIES As seen in the previous sections, the present occurrence of trees and shrubs in our cities consists of a varied mixture of native and foreign species. This development can be explained in terms of time, location and ecol-
ogy, and it always reflects interference by man. As fbrest plunter man influenced the species composition in the oldest parks, which often emerged directly from feudal hunting grounds. They have preserved until the present day a woodland-like flora in terms of the trees and shrubs as well as the undergrowth. In the 20th Century, new afforestations have been undertaken in some urban agglomerations (for example Cologne, the Ruhr area and others) in order to improve the environmental conditions and to create recreational areas. As gardener man laid out parks, cemeteries and gardens to his liking, although fashion always influenced his choice of species. As ecologist man selected species in accordance with specific qualities of the habitat, so that these would grow optimally and require as little management as possible. In view of these varied aspects the following general rules for the choice of species can be drawn up. always bearing in mind that the specific case may require some modifications: (1) In still largely natural fringe areas of a city native species are to be preferred as they grow best, and such woods offer the most appropriate living conditions to the native flora and fauna. For example, over 100 different species of insects live on the native blackthorn, while none at all live on the Asian forsythia. (2) When using alien trees and shrubs, their origin and specific ecological demands must be considered. In the Federal Republic of a number of different climatic Germany, zones have been differentiated where, for example, the danger of frost-damage varies. While it can be assumed that the annual average temperature in the cities is approximately 1-2” higher than in the surrounding countryside, the air humidity is usually lower, which reduces the viability of evergreen species. (3) In urban areas with heavy air pollution, conifers in general can barely survive. Their
use must therefore be avoided as long as the pollution persists. The conifers which survive the best are yew (Taxus baccata), false cypresses (Chamuecypuris spp. div.), Austrian pine (Pinus nigru) and thuja (Thuj~ spp. div.). (4) When renewing the woody vegetation of old parks, cemeteries and gardens, the character of the surroundings and its existing trees and shrubs must be taken into account. On the basis of historical continuity. and also for ecological reasons, fully grown trees show most clearly what will grow best in a specific area. In rural villages, also. there should be strong efforts to increase traditional species instead of making changes at random during re-planting. (5) When laying out new parks, gardens. etc., such considerations are generally of less importance, since new building generally takes place on ground devoid of any vegetation. Here, too, the f.uture character of the area can be predetermined by concentrating on specific “leader” species which are appropriate to the habitat. (6) Special basic requirements have to be met in the vicinity of roads, as they offer difficult conditions for growth. In the Federal Republic of Germany, the Conference of the administration for public gardening is issuing a list of trees especially suited for these conditions. (7) In cases of re-planting in areas of urban rubble or in similar habitats drastically altered by man, the creation of a standardized habitat through top-soil application should be avoided. For such situations, there is a large variety of pioneer species which have developed spontaneously under similar conditions. They consist of both native and foreign species (see Table VIII). WOODY PLANTS SPONTANEOUSLY GROWING IN SETTLEMENTS According to Sukopp (1978), at least 3000 species of woody plants have been introduced
13
into Central Europe since 1500. Several species from the Mediterranean region have been cultivated here much longer than that. Only a relatively small proportion of these species also grow here spontaneously, particularly in cities. Table VII gives data on the origin of the spontaneous woody vegetation of 10 cities. It is apparent that, in general, the proportion of Central European woody plants is higher in smaller cities (about 70%80% of total vegetation) as opposed to larger cities, in which they reach only 50-60s (in Vienna.
TABLE
this figure is less than 50%). Thus, with increasing size of a city, more alien woody plants are found growing wild. The list of species native to an area or found growing spontaneously (Table VIII) includes 114 species from Central Europe, as well as an equal number, 118 to be exact, which are not indigenous to this area. Data on the specific frequency can only be evaluated with certain qualifications, since individual values are difficult to compare due to the variations in the size of the areas studied. The
VII
Origin of the woody
plants growing
Medium-sized
cities (<200
spontaneously
in several cities
000 inhabitants)
Large cities (>500
000 inhabitants)
n
Total (70)
Bremerhaven’ Average
altitude o-5
Average
annual 8.8 Average annual 742 No. of species 59
Origin
Saarloui?
Karlsrub?
above sea level (m) 180110 200 temperature (“C) 9.5 >9 rainfall (mm) 703 630
59
Regensburg4
Augsburg’
330470
500
Duisburg6
20--50
8.1
89
9-10
30
9.8
Stutt&UP
200400 9.8
Berlin (West)9
35
8.4
Vienna”
200
9.5
600
818
750& 800
700
700
577
600700
119
108
110
139
129
139
155
(70) Central Europe 76.4 81.3 Mediterranean 11.9 6.8 East Asia 3.4 1.7 North America 10.2 10.2
56.2
80.7
77.8
73.6
55.4
51.2
59.0
41.7
114
49.1
14.6
11.8
9.3
13.6
12.9
15.5
13.7
20.0
37
15.9
14.6
1.7
4.6
5.5
15.8
19.4
10.8
18.1
49
21.1
5.9
8.3
1.3
15.8
14.0
16.5
14.2
32
13.8
14.6
’ Data ‘Data 3 Data 4 Data ‘Data 6Data ‘Data ‘Data 9Data “Data
Cologne’
from from from from from from from from from from
Kunick (1979). Maas (1983). Kunick and Kleyer (unpublished results, Mergenthaler (1982). Hiemeyer (1978). DiiB and Kutzelnigg (1980). Kunick (1983b). Seybold (1969) and Kunick (1983a). Sukopp et al. (1981). Forstner and Hub1 (1971).
1984).
TABLE VIII List of trees, shrubs Species
of Central
and climbers European
growing
origin,
spontaneously
occurring
European
Abies alba Alnus incana Berberis vulgaris Bet& carpathica B. pubescens Coronilla emerus Cotoneaster integerrima Cytisus nigricans Daphne mezereum Juniperus communis .I. sabina Larix decidua Lonicera caprifolium L. nigra L. periclymenum Myrica gale Picea abies Pinus mug0 spp. Populus canescens Potentilla fruticosa
frequency
(local; common)
Quercus petraea Q. robur Ribes nigrum R. rubrum R. uva-crispa Rosa canina Rubus caesius R. fruticosus R. idaeus Salix alba S. caprea S. cinerea S. fragilis S. purpurea S. rubens S. triandra S. viminalis Sambucus nigra S. racemosa Sarothamnus scoparius Sorbus aucuparia
Betula pendula Carpinus betulus Clematis vitalba Cornus sanguinea Corylus avellana Crataegus laevigata C monogyna Euonymus europaeus Fagus sylvatica Frangula alnus Fraxinus excelsior Hedera helix Hippophae rhamnoides Ilex aquifolium Ligustrum vulgare Lonicera xylosteum Pinus sylvestris Populus alba P. n&a P. tremula Prunus avium P. domestica P. mahaleb P. padus P. spinosa of Central
cities (cf. Table VII)
in 6 or more cities with medium-to-high
Acer campestre A. platanoides A. pseudoplatanus Alnus glutinosa
Species
in 10 different
Taxus baccata Tilia cordata T. platyphyllos Ulmus glabra U. minor Viburnum lantana I/. opulus
and North
European
origin,
occurring
Prunus fncticosa Rhamnus cathartica Ribes alpinum Rosa agrestis R. arvensis R. coriifolia R. corymbifera R. elliptica R. gallica Rosa jundzillii R. majalis R. micrantha R. obtusifolia R. pendulina R. pimpinellifolia R. rubiginosa R. tomentosa R. villosa R. uosagiaca Salix aurita
in 5 or less cities with low frequency
(rare)
TABLE
VIII (continued)
Species of Central
European
and North
S. dapnoides S. elaeagnus S. hippophaefolia S. myrsinifolia S. pentandra S. repens S. smithiana Sambucus nigra ‘Laciniata’ Sorbus aria Species
N N
N N
N N
N
N
N N
occurring
in 5 or more cities with low frequency
origin
American
N N
N N N
N
N N N N
Laburnum anagyroides Lycium barbarum Malus domestica Mespilus germanica Philadelphus coronarius Pinus nigra Platanus acerifolia Prunus cerasus P laurocerasus Pyracan tha coccinea Pyrus communis Quercus cerris Sorbus domestica Spiraea salicifolia Staphylea pinnata Syringa vulgaris Tamarix parviflora T ramosissima
origin
Acer negundo A. saccharinurn Amelanchier lamarckii Amorpha jiucticosa Catalpa bignonioides Celtis occiden talis Chamaecyparis lawsoniana Cornus sericea Crataegus prunifolia Fraxinus pennsylvanica Gleditsia triacanthos Gymnocladus dioicus Juglans nigra Mahonia aquifolium Parthenocissus quinquefolia Philadelphus pubescens
Species
N
of North
origin,
S. danubialis S. graeca S. in termedia S. torminalis Ulex europaeus lh’mus hollandica U. laevis Vitis vinifera
Acer monspessulanum A. tataricum Aesculus hippocastanum Buxus sempervirens Castanea sativa Cercis siliquastrum Clematis viticella Colutea arborescens Cornus mas Corylus colurna C maxima Cydonia o blonga Elaeagnus angustifolia Euonymus verrucosa Ficus carica Fraxinus angustifolia F. ornus Juglans regia
Species N
of Mediterranean
American
N
N
N
Physocarpus opulifolius Pinus stro bus Populus canadensis Prunus serotina Pseudotsuga menziesii Ptelea trifoliata Quercus palustris Q. rubra Rhus typhina Ribes aureum R. sanguineurn Robinia pseudoacacia Rubus odoratus Symphoricarpus rivularis Thuja occidentalis
of East Asian origin
Acer ginnala Ailanthus altissima Berberis gagnepainii B. julianae
B. thunbergii Buddleia davidii Caragana arborescens C. frutex
(rare) (coni.)
76
TABLE
VIII (continued)
Species of East Asian origin (cont.) Caryopteris incana Chaenorneles japonica Citrus aurantium Cornus alba Cotoneaster acutifolius C. bullatus C franchetii C. horizontalis C. lucida C. multiflorus C. salicifolius Deutzia hybrida Forsythia suspensa F. viridissima Ginkgo hiloba Hydrangea macrophylla Kerria japonica Koelreuteria paniculata Kolkwitzia amabilis Ligustrum ovalifolium Lonicera maackii
most common cities are:
common
Elder Goat willow Bramble Dewberry Traveller’s joy Hazel Dog rose
N
native
Sycamore Birch Wild cherry Common ash Norway maple The most
N
species
L. pileata I,. tatarica Lycium chinense Morus alba M nigra Parthenocissus tricuspidata Paulownia tomentosa Polygonum aubertii Prunus armeniaca P. cerasifera P. persica Pterocarya fraxinifolia Rose multiflora R. rugosa Sophora japonica Sorbaria sorbifolia S. tomen tosa Thuja orien talis Viburnum rhytidophyllum Weigela hybrida Zelkova serrata
found
in all
(Acer pseudoplatanus) (Betula pendula) (Pru72us avium) (Fraxinus excelsior) (Acer platanoides) native
shrub
species
are:
(Sambucus nigra) (Salix caprea) (Rubus fruticosus) (Rubus caesius) (Clematis vitalba) (Corylus avellana) (Rosa canina)
Only a few of these species are ever deliberately planted (cf. Tables I and V). Of the non-native woody plants listed, only 27 can be considered to be at least locally naturalized outside the cities, as determined
by Trautmann (1976) and Lohmeyer (1976). These are marked in Table VIII with an “N”. Most of these species have their origin in the Mediterranean area, which is geographically and culturally closest to Central Europe. Only eight species from North America and four from East Asia have become fully established to date. More detailed descriptions are available for some of these species, e.g. Rohkia pseudoacacia (Kohler and Sukopp. 1963). Ailanthus altissima (Bbcker and Kowarik, 1982) and Buddleia davidii (Kunick. 1970). In the cities, as well as the afore-mentioned plants. the following species occur more or less regularly, although not always in great numbers: Walnut Apple Lilac Horse chestnut Pear Barbary
wolfberry
(Juglans regia) (Malus domestica) (Syringa vulgaris) (Aesculus hippocastarzum) (Pyrus communis) (Lycium barbarum)
II
Sweet chestnut Laburnum Bladder senna Dwarf cherry Plane
(Castanea sativa) (Laburnum anagyroides) (Colutea arborescens) (Prunus cerasus) (Platanus acerifolia j
shrubs on woodland edges around the city of Erlangen. However, most of these species are unable to penetrate the forests. In the innercity they are. nevertheless, some of the species best adapted to the environment. REFERENCES
The species listed above are from the Mediterranean. whereas the following ones originated in North America: Rum cherry Red oak Snowberry Virginia creeper Box elder Sumac Oregon grape Red osier
(Prunes serotina) (Quercus rubra) (Symphoricarpos rivularis ) (Parthenocissus quinquefolia) (A cer negwzdo) (R hus tvphina > (Mahonia aquifolium > (Cornus sericea)
With regard to the ecological concentration of distribution, it is clear that native Central European species dominate on sites which are rich in nutrients and humus, but which are not far removed from their original natural state. This is the case in gardens, parks and cemeteries. where maple and elder-thickets develop particularly well. Adventitious woody plants, in contrast: profit especially from habitats which have been strongly influenced by man. Such habitats make up a significant portion of the surface area of large cities? e.g. building-rubble sites and unused railway tracks. Robinia, Buddleia and Ailanthus can develop large stands on such sites, as has been reported in various studies from several different cities (e.g. Sukopp et al., 1979). Adventitious woody plants also try to move out from the inner-city and become established in the city environs, as shown by a study conducted by Asmus (198 l), in which he found 70 different ornamental trees and
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