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Tree establishment practice in towns and cities – Results from a European survey


Abstract and Figures

A working group within the European Union funded COST Action E12, “Urban Forests and Trees”, carried out a survey between 1999 and 2001 to study current tree establishment practice in European towns and cities. An extensive questionnaire requesting information on the urban area, selection of tree species, establishment and aftercare practices and the main damaging factors was sent to tree professionals in urban areas in each of 17 countries.Indicators such as the relationship between the urban population and the number of street trees were used to compare urban areas. While most central European cities have a ratio of 50–80 street trees per 1000 inhabitants, the tree density was as low as 20 street trees per 1000 inhabitants for Nice. Often only a few species are planted and this may give cause for concern, since species diversity is considered an important factor in increasing the resilience of the urban tree population to abiotic and biotic stresses.The planting of larger street trees of 20–30 cm circumference, usually with hessian-wrapped rootballs, is becoming increasingly common practice. However, some countries report the use of mostly bare-rooted stock of much smaller trees (less than 12 cm circumference). Establishment costs for street trees range from less than 200 Euro to over 1500 Euro each. Poor site conditions, and impacts such as utility trenching are considered to be major restrictions to healthy tree life. Vandalism affects up to 30%of newly planted street trees in some towns and cities.Overall, the survey reveals large differences in tree establishment and management practices among European cities. There is a need to provide urban tree managers with guidance on good practice for tree selection and establishment based on empirical information. The survey was a first step towards collecting the necessary urban forest information from across Europe.
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Tree establishment practice in towns and cities –
Results from a European survey
Stephan Pauleit
, Nerys Jones
, Gemma Garcia-Martin
, Jose Luis Garcia-Valdecantos
Louis Marie Rivière5, Laure Vidal-Beaudet6, Monique Bodson7, and Thomas B. Randrup8
CURE – Centre for Urban and Regional Ecology, University of Manchester, Manchester, U.K.
National Urban Forestry Unit, The Science Park, Wolverhampton, U.K.
Dirección General de Investigación – Servicio de Seguimiento, Madrid, Spain
Instituto Tecnológico de Dessarrollo Agrario (ITDA), Consejeria de Medio Ambiente,
Comunidad de Madrid, Madrid, Spain
National Institute for Horticulture (INH), Angers, France
INRA/CR ANGERS, Beaucouze, France
Faculté des sciences agronomiques de Gembloux, Horticulture générale, Gembloux, Belgium
Danish Forest and Landscape Research Institute, Hoersholm, Denmark
Abstract: A working group within the European Union funded COST Action E12, “Urban
Forests and Trees”, carried out a survey between 1999 and 2001 to study current tree es-
tablishment practice in European towns and cities. An extensive questionnaire requesting
information on the urban area, selection of tree species, establishment and aftercare
practices and the main damaging factors was sent to tree professionals in urban areas in
each of 17 countries.
Indicators such as the relationship between the urban population and the number of
street trees were used to compare urban areas. While most central European cities have a
ratio of 50–80 street trees per 1000 inhabitants, the tree density was as low as 20 street
trees per 1000 inhabitants for Nice. Often only a few species are planted and this may
give cause for concern, since species diversity is considered an important factor in in-
creasing the resilience of the urban tree population to abiotic and biotic stresses.
The planting of larger street trees of 20–30 cm circumference, usually with hessian-
wrapped rootballs, is becoming increasingly common practice. However, some countries
report the use of mostly bare-rooted stock of much smaller trees (less than 12 cm circum-
ference). Establishment costs for street trees range from less than 200 Euro to over
1500 Euro each. Poor site conditions, and impacts such as utility trenching are considered
to be major restrictions to healthy tree life. Vandalism affects up to 30% of newly planted
street trees in some towns and cities.
Overall, the survey reveals large differences in tree establishment and management prac-
tices among European cities. There is a need to provide urban tree managers with guid-
ance on good practice for tree selection and establishment based on empirical informa-
tion. The survey was a first step towards collecting the necessary urban forest information
from across Europe.
Key words: Urban forestry, tree management, tree selection, quality standards, tree
planting, street trees, urban woodlands
Urban For. Urban Green.1 (2002): 83–96 1618-8667/02/01/2-83 $ 15.00/0
Address for correspondence: Stephan Pauleit, CURE – Centre for Urban and Regional Ecology, University of Manchester,
Oxford Road, Manchester M13 9PL, U.K. Phone: (+44) 161 275 6895, Fax: (+44) 161 275 6893. E-mail:
© Urban & Fischer Verlag
Urban areas are a challenging environment for trees. In
particular, poor site conditions caused by insufficient
rooting space, soil compaction, use of unsuitable soils,
construction works, and utility trenching, and lack of
tree care create unhealthy conditions for tree life in
towns and cities (Bradshaw et al. 1995; Harris et al.
1999). Monitoring of newly planted trees in the inner
city area of Liverpool (Gilbertson & Bradshaw 1990)
showed that nearly 39% had died within five years of
planting. Therefore, good practice in site preparation,
choice of suitable tree species, selection of quality
trees, as well as intensive tree care during the establish-
ment phase are particularly important for successful
urban tree planting.
An expanding body of European literature is avail-
able on the major damaging factors of urban trees
(e.g. Brod 1990; Bradshaw et al. 1995; Balder et al.
1997), good practice of site preparation (e.g. FLL
1989; Lösken et al. 1997; Couenberg & Reyne 2001)
and tree care (e.g. Drenou 1999; Dujesiefken 1995).
In countries such as Germany, the Netherlands and the
United Kingdom, a set of standards and regulations
have been developed to establish good practice in
these areas.
However, to what extent are good practices adopted
and standards implemented in the day-to-day manage-
ment of the urban tree resource? How advanced are the
practices across Europe and what are their shortcom-
ings? At present, there is no comparative information
available on the practice of tree planting and establish-
ment in European cities and towns. Developing this in-
formation base would enhance the transfer of knowl-
edge and could help towns and cities to improve their
practice of tree establishment and care.
To address these challenges, a working group of the
first European scientific network on ‘Urban forests and
trees’, the EU funded COSTAction E12, carried out a
pilot survey in selected European cities and towns. The
major aim of the survey was to provide a first overview
of current tree establishment practice. Specifically, the
objectives were:
•To develop and test an analytical framework for
comparative assessment of tree establishment and
maintenance practices
•To assess the available information
•To gain a better understanding of both common and
specific challenges of European cities and towns
•To provide an overview of current standards and
eventually identify good practice in tree establish-
ment and maintenance practices.
Materials and methods
An extensive questionnaire was prepared to collect in-
formation on:
The urban context: location and size of the city, en-
vironmental data (climate data, predominating soil
type) to be taken from city statistics.
Tree resources: tree cover, annual number of trees
planted and replanted (average of the last five
years), average costs for planting trees, tree species,
size of planted trees, quality of trees (size, balled or
bare rooted), origin of trees (own nursery, commer-
cial source). Respondents were asked to provide
measured data.
Establishment practice such as stem protection, site
preparation (soil improvements, type of soil used,
application of fertilisers, staking), implementation
of tree planting, planting standards.
Aftercare practice (weeding, irrigation schemes,
pruning, tree preservation regulations). The ques-
tionnaire requested most of the information on estab-
lishment and aftercare techniques in the form of cate-
gorical data, for instance, respondents were asked to
state whether (a) fertilizer was always, sometimes or
never applied to newly planted trees, and (b) how
often it was applied during the year, less than 3 times
per year, 3 times per year to more than 3 times per
year. While record-keeping may well be fragmented
in nature, tree managers are undoubtedly familiar
with practices adopted within their jurisdictions.
Damaging factors: Tree managers were asked to list
major damaging factors such as pests, diseases, van-
dalism and abiotic factors such as use of de-icing salt.
Research needs: Tree managers were asked to list
major needs for research.
Responses on damaging factors and research needs
reflected the knowledge of the tree managers but were
not based on results from empirical studies.
The questionnaire was sent to the five biggest cities
of the 17 participating countries. It was assumed that
the bigger urban areas would be in a better position to
answer the questionnaire, as they were more likely to
have good records on urban trees. This assumption
proved not to be the case and, in the end, some national
co-ordinators decided also to include a few smaller
towns based on personal contacts.
In some countries the questionnaire was first trans-
lated into the national language. Tree managers were
asked to make qualified guesses rather than not answer
the questions in cases where measured data was not
available. As the questionnaire was aimed at local au-
thorities, the question referred only to trees in public
open space. A distinction was made between trees
planted in streets, parks, and in woodlands.
84 S. Pauleit et al.:Tree establishment practice in towns and cities – Results from a European survey
Urban For. Urban Green.1 (2002)
The questionnaires were sent back to the national
members of the COST working group, who agreed on a
standard format for the summary of the survey results
by each national participant. Asmaller group then car-
ried out the comparative analysis of the national sur-
veys using the summary reports and additional infor-
mation provided by the national co-ordinators of the
survey. COST actions only receive funding for meet-
ings of the network, and research activities such as this
survey are not funded. This clearly posed constraints
on the time and resources available for the survey and
the subsequent interpretation of the data. In particular,
it was not possible to interview the urban tree managers
a second time to fill in gaps, reduce inconsistencies be-
tween different cities or to request additional informa-
tion. The data interpretation therefore had to concen-
trate on those topics and urban areas where fairly com-
plete and consistent responses had been provided.
While the working group was aware of the limitations
of this approach, it was considered important to take
advantage of the unique opportunity that COSTAction
E12 provided to undertake such a survey on a pan-Eu-
ropean level.
The following paragraphs contain some of the main re-
sults of the survey. Particular emphasis is placed on
street trees as most data was obtained for this category
and it is also the category for which the most interest-
ing variations between ur-ban areas were observed.
S. Pauleit et al.:Tree establishment practice in towns and cities – Results from a European survey 85
Urban For. Urban Green.1 (2002)
Fig. 1. Location of urban areas
included in the survey (for Slo-
vakia, information from a survey
of 16 urban areas was provided,
however, these are not shown
on the map).
Availability and quality of information
on tree establishment and management practice
Most countries reported results from between three and
five towns and cities (Fig. 1). These were widely spread
across Europe, demonstrating a diverse range of envi-
ronmental, social, economic and cultural circumstances.
For France, a much larger sample of 14 urban areas was
obtained based on thesis research (Charles 2000). The
population of the urban areas ranged from over 3.0 mil-
lion down to 15,000. The majority of the settlements had
a population of 100,000–500,000 (Fig. 2).
Data availability and quality differed greatly. No au-
thority appeared to have a standard protocol for the
monitoring of recently established trees. While only a
few cities returned a complete questionnaire, the major-
ity were able to provide at least part of the requested in-
formation. Statistics on population and surface area of
the local authority were provided in most cases. Data on
the urban tree resource (e.g. proportionate tree cover,
number of street trees), the average costs of street trees,
or the size of trees, on the other hand, were only avail-
able from a much smaller sample (see Figs. 3, 4, 7, 8,
9). While figures appeared to be based on measured
data, the national reports did not contain an assessment
of the methods of measurement nor data accuracy. It
can be assumed that considerable variation exists be-
tween the countries and the urban areas within these.
Reports prepared by members of the working group
followed the same outline, but the results differed due
to the varying availability and quality of the data. This
86 S. Pauleit et al.:Tree establishment practice in towns and cities – Results from a European survey
Urban For. Urban Green.1 (2002)
Fig. 2. Population size of
urban areas (data was
available for N = 70 towns
and cities).
Fig. 3. Relation between
number of street trees and
population (N = 22).
paper relies largely on the summary national reports
and concentrates on those aspects which appeared to
yield particularly interesting information.
The urban forest resource
Data on percentage tree cover for entire cities was only
obtained from eight countries. The data were based on
measured data; however, the questionnaire did not ask
for methods and accuracy of data collection. The per-
centage cover ranged from only 1.5% for Kópavogur,
Iceland, to 62% for Kuopio, Finland. Relating the tree
cover to the population showed an even larger range
from 6895 m2cover per person in Kuopio, Finland, to
20 m2cover per person in Brussels, Belgium, and in
Gouda, Netherlands. To some degree, the tree cover in
urban areas seemed to reflect the general level of
woodland cover in the different countries. This patt
was also found in the USA (Nowak et al. 1996).
cover in urban areas in Iceland, England, the Nether-
lands and Denmark was relatively low, whereas it was
particularly high in the Finnish towns. Even when the
three Finnish towns with the highest tree cover were
excluded, the average tree cover in the remaining four
urban areas was as high as 140 m2cover per person.
This figure compares to 46 m2per person in the five
central European cities, and only 10 m2per person in
the north-western European cities. However, there was
a wide range in every region and the data is certainly
not sufficient to be conclusive.
It is interesting to note that the urban tree cover in
some urban areas in Iceland, England and Denmark
was higher than the respective national average of
woodland cover.
The results should be interpreted carefully as the ad-
ministrative areas can sometimes include just the built-
up areas or may include large parts of the surrounding
countryside. The source of information and the quality
of the data also differed largely.
Parameters such as the number of street trees per in-
habitant indicate the street tree density per population.
Most of the cities had a range of 50–80 street trees per
1000 inhabitants. However, there was a wide variation
between urban areas within a single country (Fig. 3).
While Angers had as many as 100 street trees per 1000
inhabitants, the tree density was as low as 20 for Nice.
Acomparison between geographic regions did not
show any significant difference between urban areas in
western, middle and southern Europe (no data was
available for northern cities and the British Isles). The
two cities with the lowest provision of street trees per
capita were to be found in the Mediterranean.
Finally, it must be emphasised that for a more com-
plete assessment of street tree provision, this assess-
ment would need to be complemented by other infor-
mation to reflect differences in tree cover and quality.
For instance, the number of street trees per capita may
be low in one city, but these trees may be mature, large
and in good condition, whereas in another city, there
may be a large number of young trees of low quality
and life expectancy. This variation is not, however,
recorded in the current dataset. A ratio of street tree
cover per inhabitant would be better suited to reflect
these differences; however, this ratio could not be de-
rived from our data.
Comparing the existing stock of trees with the num-
ber of newly planted trees can show how the tree re-
source is developing (Fig. 4). At the top end of the
S. Pauleit et al.:Tree establishment practice in towns and cities – Results from a European survey 87
Urban For. Urban Green.1 (2002)
Fig. 4. Relation between
newly planted street trees
and the existing street tree
stock (N = 19).
spectrum, in cities such as Athens, Madrid and
Barcelona, the number of newly planted street trees
was just over 4% of the existing stock. In contrast, in
37% of the urban areas for which information was
available new plantings accounted for less than 1% of
the existing stock of street trees.
Balder et al. (1997) estimated the current life ex-
pectancy of street trees in Berlin as being approximate-
ly 60 years but other literature suggests that life ex-
pectancy can be as low as 10 years (Foster & Blaine
1978; Morse 1978). Assuming a higher average life ex-
pectancy of 60 years, the rate of newly planted street
trees would need to exceed 1.7% of the stock in order
to maintain a stable population. This target would only
be met by 10 out of 19 urban areas (Fig. 4). These data
should be treated with caution as it was often not clear
whether planting of new street trees included replace-
ment of established trees. Different methods of ac-
counting could explain why most of the French cities
are at the lower end of the statistics. More information
is needed to illustrate the population dynamics of street
trees. In particular, the quality of street tree planting
and the survival rate need to be known. For instance,
large numbers of small trees planted in streets might
88 S. Pauleit et al.:Tree establishment practice in towns and cities – Results from a European survey
Urban For. Urban Green.1 (2002)
Fig. 5. Replacement rate
of newly planted street
trees during the establish-
ment phase.
Fig. 6. Share of tree
genera and species used
in Italian urban areas
and Dublin, Ireland.
have less impact and a lower chance of survival than a
few bigger trees planted in well-prepared sites. Even
taking this into account, the figures indicate that, in
many cities, there should be real concern about the sus-
tainability of the street tree population.
Low rates of replanting of new street trees during the
establishment phase is one measure of the success of
tree planting. Reliable figures for trees planted in parks
and streets could only be obtained for Denmark, Fin-
land and Iceland (Fig. 5). In all countries the replace-
ment rate is significantly higher in streets than in parks.
The figures clearly indicate the extent of the problem.
For instance, in Danish cities and towns, 220 out of
1000 street trees need to be replaced within the first
10 years.
S. Pauleit et al.:Tree establishment practice in towns and cities – Results from a European survey 89
Urban For. Urban Green.1 (2002)
Fig. 7. Size of average street
trees in cm girth used in Euro-
pean cities and towns
(N = 27) (and/or country where
summary figures were provid-
Tree species and quality
The questionnaire asked for a list of the ten most com-
monly used genera planted in streets, parks and wood-
lands, and their respective frequencies. All countries
provided information on tree species planted, although
in many cases this took the form of a simple list of tree
genera or species where no proportions were given.
The range of tree species that can be used in urban
planting is largely determined by the prevailing climatic
conditions (i.e. winter frost and summer drought) (e.g.
Fig. 6). The survey showed interesting differences be-
tween cities within climatic regions. Some cities used a
much wider range of tree species than others, planting a
wider range of rarer species. For instance Namur, Bel-
gium, listed manna ash (Fraxinus ornus) and narrow-
20 cm circumference size and more. All of the five
central European cities for which this information was
separately available planted street tree sizes of more
than 20 cm circumference. In Brussels even larger trees,
over 30 cm, were reported to be the norm. Urban areas
of the Nordic countries (except Oslo) as well as seven
out of ten Italian and Greek cities reported the use of a
smaller circumference of less than 14 cm.
Italy, Slovenia, Austria, Germany, Norway, Finland
and Iceland reported that street trees were always
balled and burlapped. Similarly, in France, Italy, Nor-
way and Slovenia this was usually the case. In Spain,
approximately 50% of newly planted street trees were
balled and burlapped. In Denmark, the corresponding
figure was only 38%. In Belgium, only Brussels used
balled and burlapped street trees.
Predominantly, street trees were purchased from do-
mestic nurseries and to a lesser degree directly import-
ed from foreign nurseries. Only 13% of the 40 urban
areas where this information was available used trees
predominantly from their own municipal nurseries
(Fig. 8).
In most countries, a more informal, naturalistic ap-
proach to planting in parks was adopted, compared to
that for street tree planting. Small trees, of generally
less than 10 cm circumference, were used. However,
there were some exceptions to this (Belgium, Nether-
lands, Finland and Spain).
For urban woodlands, most countries used forestry
techniques, using very small bare-rooted trees (trans-
plants) planted into unprepared soil, with little fertilisa-
tion or irrigation. An exception to this was Slovenia,
where there was little actual planting, but a great em-
phasis on natural colonisation, to reduce the risk of
using plants of inappropriate provenance. In Spain,
however, significantly larger stock than that used for
conventional afforestation was used, and France re-
ported that in some new afforestation schemes, design-
ers and managers used larger stock for rapid impact.
Site preparation and planting techniques
In Netherlands, Belgium, Austria, Germany and France
standards and regulations covered the quality of nurs-
ery stock, preparation of planting sites, establishment
techniques and aftercare techniques. The standards
were sometimes national, but could be complemented
or modified at a local level. In France, in each city the
requirements for plant quality, soil preparation, type of
material added to the soil were recorded in a tree man-
agement book (‘cahiers de charges’). The survey re-
vealed that Greece, Spain, Croatia, Slovenia and Ice-
land lacked any standards and regulations.
The size of the standard planting pit used in streets
ranged from 1 m3to 10 m3per tree. Where figures for
leaved ash (F. angustifolia) as the fourth and fifth most
frequently planted tree species. In Brugge, Belgium,
southern hackberry (Celtis australis) was the second
most common species.
Awide range of species were used in central and
north west European countries. However, only 3–5
genera usually accounted for 50–70% of all street trees
planted. Among the most popular genera were lime,
maple, plane, horse chestnut, oak and ash (Tilia sp.,
Males sp., Platanus, sp., Aescules sp., Quercus sp. and
Fraxinus sp.). Often, in northern Europe, a single
species or even single clones, will be used almost ex-
clusively in a single local authority. For instance, lime
(Tilia x vulgaris ‘Pallida’) accounted for 70% of the
newly planted street trees in Oslo. In Reykjavik, as
much as 90% of the new street tree planting consisted
of a single poplar species (Populus trichocarpa).
Cities and towns in southern Europe overall used a
wide range of species. Cities in the Mediterranean also
differed through the use of frost-sensi
tive genera and
species such as Citrus ssp. or palms.Plane (Platanus x
acerifolium) was among the most frequently planted tree
species. Holm oak (Quercus ilex), black locust (Robinia
pseudacacia), hackberry (Celtis australis, C. occidenta-
lis), Japanese pagoda tree (Sophora japonica), Albizzia
julibrissin, mulberry (Morus sp.), poplar (Populus sp.)
and elm (Ulmus sp.) were other popular tree species for
Mediterranean streets.
In parks and woodlands, the species used varied ac-
cording to climate, but there was a high preponderance
of Tilia, Quercus, Acer, Alnus, Fraxinus and Fagus in
most park planting. In some cases, e.g. Iceland, a
greater variety of species was used in parks than in
street planting.
The size of street trees used differed widely (Fig. 7).
Overall only one third of the urban areas used trees of
90 S. Pauleit et al.:Tree establishment practice in towns and cities – Results from a European survey
Urban For. Urban Green.1 (2002)
Fig. 8. Share of street trees purchased from commercial
nurseries (N = 40).
the surface area of standard tree pits were given, these
could be as small as 0.5 m by 0.5 m.
The survey showed that many local authorities used
specially prepared soils for street tree planting. Local
authorities were conscious of the need to use appropri-
ate substrates for street trees. A wide variety of local
soil mixes was used, which seemed to be based on per-
sonal experience of the tree managers rather than on
findings from research. Fertilisers were also widely ap-
plied at the time of planting but rarely afterwards. The
application of mycorrhizae as a means of improving
tree establishment was rarely practised; only two
French cities experimented with this technique. Newly
planted trees were usually irrigated for up to three
Weeds were removed mechanically in cities in Aus-
tria, Belgium, Denmark, Greece, Germany, Nether-
lands, Norway and Slovenia. Finland, France, Iceland,
Ireland and Spain reported both mechanical and chemi-
cal weeding. In Croatia and the UK it seems that weed
control is mostly chemical. Some countries – Austria,
Belgium, Denmark, and Norway – also used mulching
to control weeds.
Pruning was a standard procedure in most countries,
though newly planted street trees were not always
pruned in Ireland, and Norway stated that new street
trees were not pruned at all. Newly planted street trees
were usually staked and often protected against me-
chanical damage, e.g. from cars.
Establishment costs
Table 1 gives an overview of the overall costs of street
tree planting. The costs show the different quality of
street trees used, the level of site preparation but impor-
tantly also different levels of labour costs. Figures may
not be directly comparable but they do, nonetheless,
give a broad indication of the level of investment into
new street tree planting. On average, costs ranged from
less than 250 Euro in Slovenia, the United Kingdom
and Spain to over 1000 Euro in France, Denmark, Ger-
many, Finland, and Norway.
The per capita expenditure for new street tree plant-
ing also differed largely between urban areas (Fig. 9).
While 26% of the cities and towns for which this infor-
mation could be computed invested more than 2 Euro
S. Pauleit et al.:Tree establishment practice in towns and cities – Results from a European survey 91
Urban For. Urban Green.1 (2002)
Table 1. Average costs for new street tree plantings in Euro
per tree
Average costs Range Average costs
for new of costs by categories
street tree
(Euro per tree) 1) (Euro per tree)1)
Spain 13 13
Slovenia <100 <100 250 Euro
UK 120 50–190
Italy 350 284–413
Austria 600 470–727 >250–1000
Belgium 770 40–1500
France 1250 200–2300
Denmark 1375 750–2000 >1000–2000
Germany 1450 500–2400
Finland 1670 1667–1681
Norway 3750 2500–5000 > 2000
1) overall costs including acquisition of trees and site prepara-
Fig. 9. Annual per-capita
expenditure for new street
tree plantings (N = 27).
per capita per year into new street tree plantings, 44%
spent less than 0.5 Euro. In part, these differences may
be attributed to different levels of general costs of liv-
ing and labour across Europe. Yet, there can be also
large differences between urban areas within a single
country where differences in costs of living and labour
should not vary to a large degree. In France, at the
upper end, Angers spent over 2 Euro per capita where-
as, at the lower end, Nice spent less than 0.5 Euro.
There is no relation between the per capita spending
for street trees and the size of the urban areas. Howev-
er, there seems to be a clear geographic trend as cities
and towns in northern Europe spend on average
4.0 Euro per capita per year (n = 5), central Europe
1.5 Euro per capita per year (n = 15), whereas southern
European cities and towns on average spend only 0.4
Euro per capita per year (n = 7). The results for north-
ern Europe are biased by a high figure for one relative-
ly small town (Kuopio: 11.5 Euro). However, even if
Kuopio is left out, the average per-capita expenditure
for Nordic cities is 1.7 Euro per capita, i.e. higher than
in the rest of Europe.
Where given, the costs for park plantings varied a
great deal from 0.3 Euro/tree for a UK city, where an
urban woodland approach was adopted within the park
to 2500 Euro/tree (Finland, where, presumably, indi-
vidual specimen trees were planted). For woodland
plantings, costs varied from 0.3 Euro/tree (UK) to 213
Euro/tree (Italy). Many countries reported low costs of
1–2 Euro/tree.
Main challenges for the establishment and main-
tenance of urban trees
The results showed that there was widespread agree-
ment over the main factors of tree damage. While the
ranking differed, abiotic causes of tree damage such as
the use of de-icing salt, poor site conditions (lack of
92 S. Pauleit et al.:Tree establishment practice in towns and cities – Results from a European survey
Urban For. Urban Green.1 (2002)
Fig. 10. Level of vandalism on
trees in European urban areas by
rooting space etc.) and utility trenching were consid-
ered major restrictions to healthy tree life in all coun-
tries involved (Table 2).
The extensive use of de-icing salt is widespread, ex-
cept in the Mediterranean area, and this is a well-known
cause of serious damage to urban trees (e.g. Brod 1990;
Dobson 1991). In some cities special protective mea-
sures were taken. These included the use of kerbstones
and protective walls around trees (Austria, Denmark and
France), the use of straw mats (Denmark), increasing the
planting distances from roads (Austria, Netherlands and
Denmark) or drainage (Norway). The use of de-icing
salt was prohibited on pedestrian walkways in cities in
Austria and Germany, and efforts were made to reduce
the salt application by precision dosage. For France,
summer pruning, while the trees are in leaf, was report-
ed as a means of removing salt from the tree. No data
was obtained on the effectiveness of these measures.
Air pollution was frequently mentioned as a major
problem, but the extent of damage was not quantified
anywhere. The frequent listing of air pollution was
somewhat surprising, as this is probably no longer a
major damaging factor for trees in urban areas
(QUARG 1996). Other factors such as drought (e.g.
Kjellgren & Clark 1993, Kopinga 1989) or frost dam-
age were also listed, but the extent of these problems
was not quantifiable (Table 2). The selection of species
adapted to the urban environment and the quality of
planting were considered to be major challenges for the
successful establishment of trees.
Avariety of pests and diseases were reported to affect
urban trees in woodlands. Insects were cited in almost
every case: aphids, mites and scale insects. In some
countries (Croatia, Finland, Italy, Slovenia, Slovakia,
Austria and Belgium) the species were recorded, but in
others, there was only reference to broad groups of
pests and diseases. Spain, Norway, Iceland, Finland and
Slovakia provided information on specific diseases,
with Anthracnose, Oidium and Dutch elm disease (Cer-
atocystus ulmi) being problems common to all.
Quantitative information on the extent and severity
of pests and diseases could not be obtained. The most
detailed results were recorded in the Netherlands,
where towns and cities are particularly worried about
the effects of Dutch elm disease. Aphids and scales
were listed as the most common pests.
Horse chestnut leaf miner (Cameraria ohridella) is
considered a severe problem in some countries (Aus-
tria, Belgium). In particular plane (Platanus ssp.) was
reported to be severely affected by a number of pests in
the Mediterranean, where it is often the predominant
tree in streets and squares.
The most interesting result from this section is prob-
ably the level of vandalism reported. In the UK, up to
30% of newly planted trees were reported to be van-
dalised, whereas in central European cities levels of
vandalism were below 5%. As can be seen from Fig. 7
and 10, in countries where the maximum level of van-
dalised trees is high, smaller trees are usually planted.
Thus, there seems to be a relation between the overall
level of investment in new tree planting and the level of
Few specific problems were noted for parks and
woodlands: these included disease and fire in Greece,
pollution in Belgium and vandalism in Belgium, Ire-
land and the UK.
S. Pauleit et al.:Tree establishment practice in towns and cities – Results from a European survey 93
Urban For. Urban Green.1 (2002)
Table 2. Main challenges for tree life in urban areas mentioned by respondents
Soil De-icing Air Vandalis m Drought Elevated summer Frost
salt pollution temperatures damage
Greece X X X X
Spain X X X
France X X
Croatia X X
Slovenia X X X X
Slovakia X X X
Austria X X X X
Germany X X X X
The Netherlands X X X
Belgium X X X
U.K. X X X
Ireland X X
Denmark X X X
Finland X X X
Norway X X
Iceland X X X
Finally, the lack of quantitative information on the
status of urban trees and all of the aspects listed above,
and the lack of information on management practices
and costs were noted as major obstacles to the adoption
of better approaches to urban tree establishment and
Discussion and conclusions
This is the first time that information on tree establish-
ment and maintenance practice has been gathered in a
pan-European survey of cities and towns. The survey
included 17 countries and nearly 100 towns and cities,
and therefore should give a broad picture of the current
situation of tree establishment and management prac-
tice across Europe. The survey concentrated on larger
urban areas, and may not be representative for smaller
towns, but it did cover a range of different urban situa-
The data needs to be treated with caution as it is
probably collected in different ways and is based on
different sources of information, despite the use of a
common questionnaire. Statistics on urban population
and city surface area were given in most national re-
ports. Data on tree and woodland cover, the number of
trees, etc. were only available from a smaller sample of
urban areas and are probably less accurate. Some ques-
tions were interpreted in quite different ways by the re-
spondents due to the lack of clear definitions. For in-
stance, ‘replacement’ plantings were understood by
some as replacement of the overall stock of trees and
by others just as replacement of the newly planted trees
during the establishment phase. Not all of the variables
included in the survey proved to be useful for the as-
sessment of establishment and maintenance practice.
In particular, more detailed information would have
been required on maintenance practices (weeding, irri-
gation, staking, pruning, etc.) to be able to really com-
pare these practices between urban areas. Data inter-
pretation would have also clearly benefited from all na-
tional delegates providing the raw data instead of a
summary report.
In retrospect, adopting a more rigorous framework
for data collection and interpretation would have
helped to improve the results. However, one of the
main purposes of the survey was to test the approach
and to learn from the results. Thus, the results should
be considered as a first indication of the current state of
tree establishment and management practice, to stimu-
late discussion and hopefully lead to more extensive re-
search in this field.
Given these limitations, the survey has already yield-
ed a number of interesting results which were hitherto
unavailable. Most significant of all, the survey showed
the wide difference in tree establishment and mainte-
nance practices such as:
The level of provision of trees
The investment into tree establishment and mainte-
Site preparation and
Selection of tree species.
Some of the results showed geographic patterns
which illustrate the overall different standard of tree es-
tablishment and maintenance practice in European
countries. For instance, the expenditure on tree estab-
lishment was on average higher in the Nordic countries
and in central Europe. It was quite low in the Mediter-
ranean countries, the United Kingdom, Ireland and Ice-
land. The results from the survey suggest that there is a
relationship between the level of investment into trees
and the amount of vandalism, which was particularly
high in the UK and Ireland. Tree condition and survival
are also certainly related to the expenditure on trees.
There seems to be a clear need to promote the wider
implementation of state-of-the-art practices e.g. from
research on the preparation of soils, on the design of
planting pit or on the selection of tree species (e.g.
Balder et al. 1997; Balder 1998; Bradshaw et al. 1995;
FLL 1989). Further study would be required to explore
in more detail the links between the success of new tree
planting and tree establishment practice. Urban tree
surveys based on a common methodology might prove
very helpful in developing regionally based lists of rec-
ommended tree species (Duhme & Pauleit 2000). The
need for more information on these issues was also
consistently mentioned by the questionnaire respon-
Overall, the survey showed that there is a huge in-
formation deficit. Socio-demographic and economic
data is usually easily available in every country and
municipality. However, information on land use, and
particularly on greenspace and the urban tree resource
is quite limited. For instance, data could not be ob-
tained on the relationship between the level of existing
tree stock and the rate of new planting. This means,
that in most cases there is a lack of knowledge about
the dynamics of the tree population – whether it is sta-
ble increasing or decreasing. There is a particular need
for more research on:
The total urban forest resource (greenspace and tree
cover, age composition). Geographical information
systems based approaches such as the inventory of
trees in urban land use or morphology types (see
LUC 1993; Pauleit & Duhme 2000) have proven to
be well suited to the establishment of a comparative
database on the extent and distribution of the urban
forest. Digital image processing offers hope to easi-
94 S. Pauleit et al.:Tree establishment practice in towns and cities – Results from a European survey
Urban For. Urban Green.1 (2002)
ly produce cover maps for GIS. At present, there is
only limited information available on the specific
functions of urban trees for recreation, aesthetic
quality, environmental protection and nature conser-
vation. Most studies in this field have been under-
taken in the USA, most notably, the extensive study
of Chicago’s urban forest (McPherson et al. 1994).
Similar approaches to assess the different benefits of
urban forests systematically are still unavailable in
Europe (Pauleit & Duhme 2000; Whitford et al.
Survival and dynamics of urban trees, including
quantitative information on damaging factors and
their ranking. Tree surveys are often one-off efforts,
whereas monitoring over a period of time is required
to provide local authorities with detailed informa-
tion on the condition of the urban tree population.
Success of tree establishment and maintenance prac-
tices and techniques. The survey showed that there
is an almost complete lack of information on the
success of tree establishment, and how this relates to
site factors, tree species, etc. Without this informa-
tion, it is difficult to make progress towards more
successful tree establishment and maintenance prac-
Tree establishment schemes and standards. The
adoption of standards and regulations could be an
effective means of improving the quality of tree se-
lection, planting and maintenance practice. Wider
dissemination of information on standards and good
practice could help other countries to develop and
improve their own tree establishment and mainte-
nance standards.
This pilot survey was the first attempt to collect this
information from across Europe. The EU funded
COSTAction E12 ‘Urban Forests and Treesprovided
an excellent opportunity to initiate this effort. Howev-
er, this initial study has illuminated the need for a more
rigorous pan-European study. Such a study should be
based on a sample of case studies representative for
urban situations across Europe. The results of this
study would be useful to assess the current state-of-
practice of urban tree management. Moreover, such a
study could initiate establishment of an information
network between European towns and cities to enhance
transfer of knowledge on good practice of urban tree
management and successfully address the challenges
urban trees are facing in the urban environment.
Acknowledgements. We would like to thank the anonymous
reviewers and Christine Carr for their constructive comments
which greatly helped to improve the paper.
While the authors are entirely responsible for the content of
this paper, its preparation would not have been possible with-
out the contribution of other members of COST Action E12,
Working Group 2 undertaking this survey, preparing national
reports and discussing the results during various COST meet-
ings. Many thanks therefore go to Per Anker Pedersen, Chris-
tos Apostolidis, Thorarinn Benedikz, Zelimir Borzan, Robert
Brus, Els Couenberg, Mary Forrest, Jos Koolen, Leena Lin-
den, G. Malamidis, Viera Paganova, Johann Palsson, Anna de
Rogatis, Kaj Rolf, Arne Saeboe, Gabor Schmidt, Monika
Sieghardt, Richard Siwecki, Jan Supuka, and Jos van Slyck-
en. It was a great experience for all of us to participate in this
pan-European network.
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Received: July 1, 2002
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96 S. Pauleit et al.:Tree establishment practice in towns and cities – Results from a European survey
Urban For. Urban Green.1 (2002)
... Some studies have revealed that the main function of UGAs in Granada is the improvement of citizens well-being by providing spaces for socialising, relaxing or exercising (Adinolfi et al., 2014), which is corroborated by the main families present in such areas, with a high aesthetic value usually incorporated as ornamentals in flower beds, low hedges or thematic collections (i.e. rose gardens, aromatic plants) (Franco et al., 2006). In contrast, tree-lined streets are often dominated by gymnosperms or broad-leaved deciduous plants with high ecological plasticity and adapted to urban microclimate conditions (Pauleit et al., 2002). Although there may be diversity in the pollination strategy of this group, anemophily is the main strategy of such over-represented genera in urban areas such as Platanus, Cupressus, Quercus, Acer or Pinus (Pauleit et al., 2002). ...
... In contrast, tree-lined streets are often dominated by gymnosperms or broad-leaved deciduous plants with high ecological plasticity and adapted to urban microclimate conditions (Pauleit et al., 2002). Although there may be diversity in the pollination strategy of this group, anemophily is the main strategy of such over-represented genera in urban areas such as Platanus, Cupressus, Quercus, Acer or Pinus (Pauleit et al., 2002). Their role as pollination ES suppliers is minimised, being more relevant their disservice as sources of allergen emission (Cariñanos et al., 2021(Cariñanos et al., , 2016. ...
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... Despite the high compactness and density of the city and the low number of green urban areas per inhabitant (7.0 m 2 /inhabitant on average in the entire city), Barcelona has a large number of street trees (157,636 trees), with 95 trees per 1000 inhabitants, which is well above the average range of other European cities (50-80 trees per 1000 inhabitants) (Pauleit et al., 2002;Baró et al., 2019). Moreover, the municipal government has a complete inventory of all the street trees and palm trees updated every 4 months, including information such as geographic coordinates, species name and other structural and health condition variables (available in https:// ...
Street trees are an important driver of street microclimate through shading and transpirative cooling, which are key mechanisms for improving thermal comfort in urban areas. Urban canopy models (UCM) with integrated trees are useful tools because they represent the impacts of street trees on neighborhood-scale climate, resolving the interactions between buildings, trees and the atmosphere. In this study, we present the results of a measurement campaign where vehicle transects were completed along two similar parallel streets of Barcelona with different tree densities, recording upward and downward radiation fluxes, air temperature and humidity at street level. These observations are used to evaluate and improve the multi-layer UCM Building Effect Parameterization with Trees (BEP-Tree). Prior simulations of the model revealed insufficient heat exchange between the canyon surfaces and the air at the lowest vertical levels inside the deep canyons, which we solve by including turbulent buoyancy driven wind velocity in the model. Air temperatures are on average 1.3 °C higher in the street with sparser trees when wind direction is perpendicular to the streets. The BEP-Tree simulations demonstrate good agreement with the observations in terms of temperature and radiation, and capture the diurnal evolution of temperature and radiation between the two streets.
... All this information can promote urban tree management and planning, responding to different goals of the administration such as species planting, arboricultural management, risk control, and people and traffic safety (Östberg et al., 2018). After all, the arboreal vegetation which is present in the studied urban parks, consists of the typical very fast-growing species usually used in European cities (Pauleit et al., 2002;Bayer et al., 2018) and, thus, we believe that our study has a wider applicability without the need for major re-adjustments. ...
Urban trees are a fundamental and key component of urban green areas, however, they are subject to several stresses which can compromise their mechanical integrity through the development of defects such as wood decay. In this study, we evaluated the structural health state of trees in four urban parks in the city of Mytilene, Greece, using structural traits of the trees, their trunk surface temperature distribution as recorded using infrared thermography, and spatial statistics both at single tree and at park level. We developed thermal indices by analyzing data from 334 trees belonging to three main species (Robinia pseudoacacia, Morus alba and Melia azedarach). We estimated temperature spatial dependence across each tree trunk using Moran's I index, while statistically significant spatial clusters were assessed using local spatial autocorrelation statistics. Relationships between tree traits, thermal, and spatial indices were established using linear and logistic regression models. Finally, we used the Getis-Ord Gi* statistic for the identification of risky tree hotspots and we applied the kriging geostatistical procedure for mapping of such hotspots. Our results have shown that the thermal and spatial indices can sufficiently predict different types of structural defect, and to identify hotspots of risky trees and their spatial extent. This approach can successfully contribute to tree risk assessment for a more effective urban park management.
... Kühn et al., 2006), a big proportion of that diversity in case of woody species is due to planting non-native specieson average 59% in our sampled UGSs (Supplementary Table S2). The proportion of native and non-native species and predominance of the abundance of native species in our sample are in line with previous research from other urban areas (Crosby et al., 2021;Pauleit et al., 2002). ...
Urban green spaces (UGSs) are important elements of urban landscapes. Woody vegetation is a key component of UGSs, providing many socio-ecological benefits such as habitat provision and human well-being. Knowing plant diversity and vegetation configuration that underpin urban ecosystem processes and functions is critical to maximize nature contributions to city dwellers. Here, we present a well-replicated multi-city study showing a detailed description of taxonomic and structural diversity of woody vegetation in 225 UGSs distributed across seven European cities along a NE-SW gradient. Our aim was to understand how UGSs attributes, including size and fragmentation, influence woody vegetation features. A total of 418 woody species belonging to 76 families were identified. UGS size displayed weak positive correlations with woody species richness, but a strong negative correlation with woody species density. Alien woody species were abundant in all cities (from 40% of all species recorded in Antwerp to 64% in Lisbon and Zurich). Among the native tree species we found a predominance of Pinus spp. in southern cities and Acer spp. in cooler climates. On average, tree canopies extent was 56% of UGSs. This paper provides insights on the plant diversity and woody vegetation composition in UGSs of different size, climate and urban planning history. Our results encourage and contribute to future urban ecology studies involving different taxa and ecosystem services as well as support effective urban planning and management practices.
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Trees are integral components of the urban environment and smart city missions to accelerate the aesthetic and ecological values of urban life. Directly or indirectly trees provide numerous benefits and ameliorate the living quality of urban residents. Trees absorb CO 2 , release O 2 , filter air pollutants, reduce urban heat island, reduce noise and improve water infiltration to ground and reduce runoff, besides the direct ecosystem services, food security, environmental security, and health security. Although trees are vital for urban sustainability, there are increasing incidences of tree vandalism worldwide, and therefore trees are unable to contribute their services and become victims of vandalisation. This chapter highlights the benefits of urban trees, and incidences of tree vandalism in cities, identifying criteria for tree vandalism. Study shows that urban tree vandalism is mostly in trees neighbouring individual houses and properties across trees, followed in trees having higher utility. Based on the reviewed literature, the top five criteria have been identified each for three broad categories, and suggest some solutions to reduce tree vandalism. If the urban planner and government authority choose ‘right trees in right location’, with other initiatives like adopting a tree, memory tree, awareness campaign, and reward to informers, etc., the cases of vandalism can be minimised and urban trees can contribute sustainably to several decades with changing climate in future.
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Une taille mal pratiquée peut être considérée comme ce qu’il y a de plus dommageable pour un arbre. C’est pourquoi le métier d’arboriste-grimpeur ne s’improvise pas. Il requiert une très bonne aptitude physique, la maîtrise du grimper et des compétences sans cesse actualisées en biologie de l’arbre. Le concept des quatre barrières du CODIT, les termes de réitération et de suppléant, ou encore la distinction entre une fourche maîtresse et une fourche accidentelle sont le b.a.-ba du métier. Mais il ne suffit pas de savoir tailler, encore faut-il, pour atteindre son objectif, savoir pourquoi on le fait ! Partant du principe que la taille ne doit pas être systématique mais doit résulter d’une démarche méthodique, l’ouvrage, bâti autour d’études de cas suffisamment précises pour ne pas être dangereusement généralisées, ne vous enferme pas dans une théorie mais vous aide à respecter les arbres. L’auteur vous propose des méthodes de raisonnement adaptées à la diversité des cas rencontrés sur le terrain ainsi qu’un vocabulaire simplifié, avec un glossaire de plus de 170 termes. L’ouvrage analyse en outre les caractéristiques de nombreuses essences et donne une vision dynamique de la taille au cours du temps en tirant les leçons d’arbres taillés voici 5 ou 10 ans. C’est une autre vision de la taille qui vous est offerte avec ce nouveau manuel, indispensable à tous les gestionnaires d’arbres et praticiens. Largement illustré de photos et de nombreux dessins techniques, il aura sa place entre les mains et dans les bibliothèques de tous ceux dont l’arbre est le métier ou la passion. Cet ouvrage désormais classique vient de faire l’objet d’une réactualisation et relecture attentive de Christophe Drénou, auteur primé et spécialiste de la biologie et de l’architecture des arbres.
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It is well known that urbanisation has many deleterious ecological effects. These may be mitigated by good urban design but the first step in doing this is to quantify them. This paper describes four simple ecological performance indicators which quantify the effects of urbanisation on surface temperature, hydrology, carbon storage and sequestration, and biodiversity. They have been developed and customised from recent studies, are simple to use, and require a minimum of input information; the only major inputs needed are the percentages of the different surface covers.The indicators were tested by applying them to four urban areas of Merseyside, UK, of contrasting affluence. The results showed that the greatest influence on ecological performance was the percentage of greenspace, particularly of trees. The affluent areas had lower temperatures, less run-off, more stored carbon, and higher diversity, largely because they had more open area and woodland cover. These results suggest that the indicators could be a useful planning tool, facilitating the comparison of existing urban areas, and helping to predict the ecological impact of new developments. However, the indicators also suggest that compact cities with good regional performance will inevitably have poorer performance locally, because of a lack of greenspace. The performance indicators could determine the potential of possible means of amelioration such as the use of roof gardens or permeable paving.
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Measurement of city tree cover can aid in urban vegetation planning, management, and research by revealing characteristics of vegetation across a city. Urban tree cover in the United States ranges from 0.4% in Lancaster, California, to 55% in Baton Rouge, Louisiana. Two important factors that affect the amount of urban tree cover are the natural environment and land use. Urban tree cover is highest in cities that developed in naturally forested areas (31%), followed by grassland cities (19%) and desert cities (10%), but showed wide variation based on individual city characteristics. Tree cover ranged from 15 to 55% for cities in forested areas, 5 to 39% for those in grassland areas, and 0.4 to 26% for cities developed in desert regions. Park and residential lands along with vacant lands in forested areas generally have the highest tree cover among different land uses. Methods of measuring urban tree cover are presented as are planning and management implications of tree-cover data.
Chapter 1 describes the early investigations that led to the recognition of salt as a cause of street tree death, and outlines the current situation in Britain. The symptoms of salt damage are described. Data on foliar concentrations of chloride and sodium associated with leaf symptoms are summarised. In Chapter 2 the methods used for evaluating salt tolerance are described and the mechanisms of salt tolerance are outlined. A comprehensive list of woody plants with their reported salt tolerance rankings is presented. The mechanisms of salt toxicity are described in Chapter 3, and the relative importance of osmotic and specific ion effects in the development of injury symptoms are discussed. The methods that are being used, or could be used, to reduce de-icing salt damage to trees are evaluated in Chapter 4. (See also 92L/05279). -from Author
The results of regular monitoring of the survival over three years of newly planted trees and older stands in inner city Liverpool show that nearly 23 per cent had died three years after planting and a further 16 died in the following two years. Detailed per cent analysis using cohort lifetables suggests that failure in the first few years after planting results from a failure to establish properly so that the trees die from drought stress. Death is exacerbated by poor management and design practices, in particular weed competition. The survival of replacements is worse than that of the original plantings. Combining data for new and older stands together suggests that the half life of inner city trees in Liverpool is ten to fifteen years.
A geographic information system (GIS) was de- veloped and applied to assess the spatial pattern and envi- ronmental functions of the urban forest in the city of Munich. Urban land cover types were delineated as the un- derlying spatial units, characterized by physical and land- use attributes such as the percentage cover of built-on land and vegetation. The urban forest was described as the cover of trees and shrubs and the maximum age of trees. The survey was coupled with statistical databases and environ- mental data such as a habitat survey and thermal infrared photography. Trees and shrubs covered approximately 5,400 ha (13,300 ac) of land, or 18% of Munich's surface area. The spatial pattern of the urban forest was closely linked with the general zoning of different land use and building density. The relationship between cover, size, and age of woody vegetation and the incidence of woodland indicator birds was used to assess the role of the urban forest for urban nature conservation, and potential habitat links of closely neighboring woodlands were identified by means of the GIS. Furthermore, it was shown that the ur- ban forest can effectively reduce air temperatures during hot summer days. Specific urban forestry programs and quantitative targets were proposed for urban zones. These would increase the forest cover to 22% of the city's surface area. An estimate for the overall costs for the establishment of the additional forest areas is given.
Growth and water relations of 10-year-old sweet gum (Liquidambar styraciflua L.) street trees were studied in sites with low and high potential evapotranspiration to determine how these differences are integrated by growth and water relations over time. The trees were located in the parking strip between the curb and sidewalk at a partially vegetated urban park and an urban plaza in Seattle, Washington. Crown size, and seasonal and diurnal stomatal conductance and water potential, as well as diurnal air temperature and humidity, were measured over 2 growing seasons. Yearly trunk growth since transplanting was measured from increment cores. Vapor pressure deficits and air temperatures averaged 18% greater at the plaza, but whole-tree water loss appeared to be much lower than the park trees due to more restricted stomatal conductance and crown size. In addition, yearly diameter increment declined progressively once the plaza trees were established in the existing soil several years after transplanting. Lower water potential in the plaza trees indicated greater internal moisture deficits than the park trees, and tissue analysis revealed lower nutritional status, particularly nitrogen. A manipulative study of water and fertilizer to several additional plaza trees showed an interaction between water and nutrient deficiencies in the coarse and shallow soil that apparently limited growth. Furthermore, soil limitations probably interacted with paved surface conditions over time by reducing nutrient recycling from leaf litter, and generating higher vapor pressure deficits that would contribute to prolonged stomatal closure. Restricted growth and water relations status of the plaza trees represented an equilibrium between chronic high-resource demand above ground and limited below ground.