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Forests in cities produce goods and generate ecosystem services that improve the well-being of citizens and increase the resilience of cities to shocks.
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FORESTS AND
SUSTAINABLE
CITIES
An internat ional journal of fore stry and forest ind ustries Vol. 69 2018/1
250
ISSN 0041-6436
World Forum on Urban Forests
Mantova, Italy, 28 November–1 December 2018 2018
The rst World Forum on Urban Forests will showcase cities
worldwide that are using urban forestry to provide economic
benets and ecosystem services and to strengthen social cohesion
and public involvement. The Forum will bring together actors from
around the world and across sectors to explore urban forestry
strategies towards a greener, healthier and happier future.
An initiative of FAO, the City of Mantova, the Italian Society of Silviculture and
Forest Ecology, and Politecnico di Milano
More information: www.wfuf2018.com
© BLUEJAYPHOTO
Mantova, Italy, will host the rst World Forum
on Urban Forests in November/December 2018
Editor: A. Sarre
Editorial Advisory Board: I. Buttoud,
P. Csoka, D. Reeb, S. Rose
Emeritus Advisers: J. Ball, I.J. Bourke,
C. Palmberg-Lerche, L. Russo
Regional Advisers: T. Hofer, A.A. Hamid,
J. Meza
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© FAO, 2018
ISBN 978-92-5-130383-2
Contents
Editorial 2
S. Borelli, M. Conigliaro and F. Pineda
Urban forests in the global context 3
P. Calaza, P. Cariñanos, F.J. Escobedo, J. Schwab and G. Tovar
Building green infrastructure and urban landscapes 11
C. Dobbs, A.A. Eleuterio, J.D. Amaya, J. Montoya and D. Kendal
The benets of urban and peri-urban forestry 22
D. J. Nowa k
Improving city forests through assessment, modelling
and monitoring 30
C.C. Konijnendijk, P. Rodbell, F. Salbitano, K. Sayers,
S. Jiménez Villarpando and M. Yokohari
The changing governance of urban forests 37
N. Nagabhatla, E. Springgay and N. Dudley
Forests as nature-based solutions for ensuring urban
water security 43
P. Cariñanos, P. Calaza, J. Hiemstra, D. Pearlmutter and U. Vilhar
The role of urban and peri-urban forests in reducing risks
and managing disasters 53
J. Castro, S. Krajter Ostoić, P. Cariñanos, A. Fini and T. Sitzia
“Edible” urban forests as part of inclusive, sustainable cities 59
C. Y. Ji m
Protecting heritage trees in urban and peri-urban environments 66
FAO Forestry 75
World of Forestry 77
Books 79
Cover: T he Cheonggyecheon promen ade, Seoul,
Republic of Korea. The are a has been restored
in a major urban -renewal project to improve the
downtown environment. Cities ne ed forests
© Nicolas McComber
An internat ional journal of fores try and forest indu stries Vol. 69 2018/1
250
ISSN 0041-6436
EDITORIAL
M
ore than half the world’s population now lives in towns
and cities, and that proportion will continue to grow in
coming decades. If planned and managed well, cities
can be great places to live, but many urban developments cause
environmental havoc – ultimately leading to problems such as
urban “heat islands”, ooding, and air pollution. The cost for
citizens is borne in deteriorating well-being; the costs for the
planet include increased greenhouse gas emissions and other
waste and the degradation of soils and waterways.
Cities need forests. The network of woodlands, groups of trees
and individual trees in a city and on its fringes performs a huge
range of functions – such as regulating climate; storing carbon;
removing air pollutants; reducing the risk of ooding; assisting
in food, energy and water security; and improving the physical
and mental health of citizens. Forests enhance the look of cities
and play important roles in social cohesion; they may even reduce
crime. This, the 250th edition of Unasylva, takes a close look
at urban and peri-urban forestry (UPF) – its benets, pitfalls,
governance and challenges.
In the opening article, Borelli and co-authors describe the essen-
tial role that urban and peri-urban forests must play in meeting
global commitments on sustainable development. The United
Nations and other bodies have long recognized that unplanned
urban growth can drive poverty and inequality and cause social
and environmental problems on a global scale. Most recently, the
Sustainable Development Goals explicitly address the need for
sustainable urban development, aiming to “make cities and human
settlements inclusive, safe, resilient and sustainable”. Forests are
increasingly seen as essential elements of this, and many inter-
national organizations, including FAO, are assisting countries and
local governments to better integrate forests into city governance.
The article by Calaza and co-authors examines the role of UPF
as part of an overall strategy to develop green infrastructure – the
term used to describe the network of green spaces and water
systems delivering multiple economic, social and environmental
values and benets to an area. The article presents international
perspectives on the importance of good design in UPF and
suggests that it can help solve a number of urban problems.
Dobbs and co-authors use case studies in Australia, Brazil,
Colombia and the United States of America to demonstrate the
benets that urban and peri-urban forests can provide for city
residents. They also discuss some of the challenges that urban
forest planners and managers will need to meet in years to come.
In another article, Nowak sets out a four-step process for assess-
ing, modelling and monitoring urban forest structure, which
can have a profound impact on the benets and costs of urban
and peri-urban forests. This process, says Nowak, enables the
development of local forest management plans that optimize
forest structure to enhance human well-being.
Urban and peri-urban forests are often under pressure from
poor urban development, and better ways of governing them
are needed. According to Konijnendijk and co-authors, diverse
models of urban forest governance are emerging in which local
communities, not-for-prot organizations, municipal authorities
and the private sector all have roles to play in ensuring that the
benets and costs of UPF are shared equitably.
Nagabhatla and co-authors point out that ensuring a sustainable
water supply in cities looms as a major global challenge. They
advocate nature-based solutions, which are actions to protect
and manage ecosystems that both address societal challenges
and provide benets for human well-being and biodiversity.
Forests increase soil inltration, soil water-holding capacity and
groundwater recharge; regulate ows; reduce soil erosion and
sedimentation; and contribute to cloud cover and precipitation
through evapotranspiration. UPF, say the authors, will increas-
ingly be deployed as a cost-effective, nature-based solution for
managing water in cities.
Cariñanos and co-authors examine the role of UPF in reduc-
ing risks and coping with disasters. Poorly managed urban and
peri-urban forests can also create hazards, however, and the
article looks at how these can be handled with the overall aim
of increasing urban resilience to shocks.
The article by Castro and co-authors takes a somewhat different
tack, looking at the role of “food forests” in city sustainability.
It concludes that more work is needed to maximize the potential
of such forests as part of the green infrastructure of cities.
Finally, the article by Jim looks at the cultural role, management
and mismanagement of heritage trees, which are “outstanding”
trees to which societies attach special value. If a city can take
excellent care of its heritage trees, argues Jim, “it can inspire
condence in its capacity to care for all its urban and peri-urban
forests”. The article makes recommendations aimed at mitigat-
ing existing problems in the management of heritage trees and
improving professional practice.
The world will continue to urbanize for decades to come.
Villages will become towns, towns will become cities, and cities
will become megacities. Ensuring that these urban expanses are
both liveable and sustainable is a massive challenge to which
UPF advocates and practitioners must rise. Safeguarding and
sustainably managing forests and other green spaces in cities
will be crucial for the health and well-being of the planet and
its inhabitants. u
3
Unasylva 250, Vol. 69, 2018/1
Cities can lead the way in meeting
the Sustainable Development
Goals and other globally
established objectives by deploying
urban and peri-urban forestry.
number of people living in urban areas
and, overall, 53 per cent of the world’s
urban population (United Nations, 2014).
Managing urbanization poses huge
challenges. Cities can be hubs of socio-
economic development, but the rapid
pace of urban growth and the limited
resources available to accommodate
increasing demand for food and basic
services can also present huge barriers
for the equitability and sustainability of
city development (United Nations, 2016).
Particularly in less-developed countries,
exponential urban population growth has
not been matched by a corresponding
increase in the availability of goods and
services such as clean drinking water,
Urban forests in the global context
S. Borelli, M. Conigliaro and F. Pineda
Simone Borelli, Michela Conigliaro and
Florencia Pineda a re in the Forestr y Policy and
Resources Division, Forest ry Depar tment, FAO.
© SIMONE BORE LLI
Above: A scene in an urban park
in Viterbo, I taly. Urban and peri-
urban fore sts are a crucial pa rt of a
sustainable future for the planet
T
he last century has been charac-
terized by (among other things)
increasing urbanization, with cities
worldwide expanding in both number and
size. For example, the world urban popula-
tion increased from 746 million people
in 1950 to 4 billion in 2015 (more than
a vefold increase), and this growth is
expected to continue in coming decades,
with low- and middle-income countries
projected to more than double and triple
their urban populations, respectively,
by 2050 (United Nations, 2016). Of the
world’s regions, Africa and Asia are
urbanizing fastest: Africa had the highest
urbanization rate of all the regions between
1995 and 2015; and Asia (already home
to 17 megacities1) has by far the largest
1 A megacity is a city with more than 10 million
inhabitants.
Unasylva 250, Vol. 69, 2018/1
4
adequate housing and sanitation, and
energy. In most less-developed countries,
urbanization has translated largely into
unplanned urban expansion accompanied
by unsustainable production and con-
sumption patterns, leading, in turn, to the
overexploitation of natural resources in
and around urban areas. As a result, cities
have become more vulnerable to natural
disasters and to the effects of climate
change, and many urban and peri-urban
communities are highly exposed to food
insecurity and poverty.
This article outlines the international
response to the urgent need to better
manage urbanization, specically through
the establishment, management and sustain-
able use of urban and peri-urban forests.
URBAN ISSUES IN
THE GLOBAL AGENDA
The international community and the
United Nations have widely acknowledged
that rapid, unplanned urban growth can
drive poverty and inequality, especially in
newly urbanizing countries. As far back
as 1976, the rst Habitat conference (held
in Vancouver, Canada) drew international
attention to the need to consider and discuss
the challenges posed by increasing urbani-
zation. Among other things, it led to the
creation of the United Nations Commission
on Human Settlements – an intergovern
-
mental body – and the United Nations
Centre for Human Settlements, the two
precursors of the United Nations Human
Settlements Programme, commonly known
as UN-Habitat. The second Habitat con-
ference, held in Istanbul, Turkey, in 1996,
ended with the endorsement of the Habitat
Agenda, a policy document containing more
than 100 commitments and 600 recom-
mendations for member countries, setting
a plan of action and urban sustainability
goals for the new millennium.
In 2015, urban sustainable development
was also at the heart of the two main
global development agreements endorsed
by the international community: the 2030
Agenda for Sustainable Development and
the Paris Agreement on climate change.
Building on the Millennium Development
Goals, the 2030 Agenda (which includes
17 Sustainable Development Goals
SDGs) calls on countries to “mobilize
© SIMONE BORE LLI
Participants in
the Habitat III
conference, held
in Quito, Ecuador,
in 2016, enjoy th e
ecosystem services
provided by trees
5
Unasylva 250, Vol. 69, 2018/1
efforts to end all forms of poverty, ght
inequalities and tackle climate change,
while ensuring that no one is left behind”.
The 2030 Agenda recognizes urban
sustainability as a key element for
achieving sustainable development and
includes a specic goal on urban devel-
opment (SDG 11): “make cities and
human settlements inclusive, safe, resil-
ient and sustainable”. About one-third
of the 231 indicators in the SDG Global
Monitoring Framework are related directly
to urban policies with clear impacts on
cities and human settlements and can be
measured at the local level (UN-Habitat,
2017).
The key role of cities in achieving
the sustainability goals set in the Paris
Agreement was recognized at the 22nd
Conference of the Parties to the United
Nations Framework Convention on
Climate Change, held in Marrakech,
Morocco, in 2016. Parties agreed that,
given that cities are the main source of
carbon emissions and contain most of the
human population (UN-Habitat, 2011), the
most important efforts for climate-change
mitigation and adaption will have to be
implemented in urban areas.
The Habitat III conference, held in
Quito, Ecuador, in 2016, put equality
and socio-economic and environmental
sustainability at the heart of discussions
on sustainable urban development. The
main outcome of that conference was the
endorsement of the New Urban Agenda
(NUA), which sets out a global strategy
for addressing urbanization issues in
coming decades. According to the NUA,
cities must develop urban strategies that
are people-centric, helping their citizens
to thrive rather than simply survive. The
NUA is based on three “interlinked”
principles: leave no one behind; ensure
sustainable and inclusive urban economies;
and ensure environmental sustainability.
The NUA builds on the assumption that
well-planned and -managed urbanization
can be a powerful tool for sustainable
development in both developing and
developed countries. It also stresses its
links with the 2030 Agenda and its role
in implementing the latter.
ROLE OF URBAN FORESTS
IN THE NUA AND THE SDGs
The NUA and the SDGs, particularly
SDG 11, highlight the importance of green
spaces in improving living standards in
cities, increasing community cohesion,
improving human wellness and health,
and ensuring sustainable development,
with the text of the NUA echoing the
wording of the SDGs. Thus, countries
commit themselves to the promotion of
safe, inclusive, accessible and green public
spaces (SDG 11) that:
provide urban dwellers with multi-
functional areas designed for social
interaction and inclusion (SDGs 10
and 11);
contribute to human health and well-
being (SDG 3);
promote economic exchange, cultural
expression and dialogue among a
wide diversity of people and cultures
(SDG 8); and
are designed and managed to ensure
human development and build
peaceful, inclusive and participatory
societies (SDGs 10 and 16), as well as
to promote living together, connectiv-
ity and social inclusion.2
© SIMONE BORE LLI
Residents and
tourists in Lju bljana,
Slovenia, enjoy
outdoor leisure time
in the shad e of a
large tree. There
is evidence of an
inverse relationship
betwee n tree
canopy cover and
crime rate s. Green
spaces increase
social cohesion and
provide documented
health benets
2
The NUA addresses the se bu llet poi nts in para-
graphs 13b, 13h, 14c, 37, 38, 51, 53, 65, 67, 71,
100 and 109.
Unasylva 250, Vol. 69, 2018/1
6
Urban forests, social cohesion and
human health
If properly planned and managed,
urban and peri-urban forests – dened
as “networks or systems comprising all
woodlands, groups of trees, and individual
trees located in and around urban areas”
(FAO, 2016) – can make valuable contribu-
tions to the quality of urban green spaces.
In Baltimore, United States of America,
for example, a strong inverse association
was observed between crime rates and
tree-canopy cover (adjusting for many
confounding factors); this association was
true for both public and private lands but
was strongest for public lands that were
accessible to all (Troy, Grove and O’Neil-
Dunnea, 2012). A study on the collective
efcacy3 of various urban features found
that parks are considered community
assets. They bring people in surrounding
areas to common places to participate in
leisure activities – at times when people
are most likely to be open to what they
see around them and more receptive to
others because they are pursuing recrea-
tion together and sharing common spaces
(Cohen, Inagami and Finch, 2008).
Another study, in the Netherlands
(Maas et al., 2009), found, after adjust-
ing for socio-economic and demographic
characteristics, that less green space in
people’s living environment coincided
with feelings of loneliness and with a
perceived shortage of social support.
Overall, information collected through
interviews showed that people with more
green space in their living environments
felt healthier, had experienced fewer health
complaints in the previous 14 days, and
had a lower self-rated propensity for psy-
chiatric morbidity than those with less
access to green areas. The study also
found that the relationship between green
space and health indicators was strongest
and most consistent for the percentage
of green space within a 1-km radius of
people’s homes. A report by The Nature
Conservancy (2017) considered that, given
the increasingly well-documented benets
of urban and peri-urban forests for human
health, “there is a strong business case for
more investment in urban trees”; thus, “the
health sector (whether public or private
institutions) could supply some nancial
resources that help partially pay for activi-
ties in the urban forestry sector.
Socio-economic development
In the NUA, green spaces are no longer
viewed simply as aesthetic features
in landscapes but as drivers of socio-
economic development that can be
leveraged to increase socio-economic
value, including by increasing property
values, facilitating business and public and
private investments, and providing liveli-
hood opportunities for all (SDGs 8 and 10).
Hedonic models used to determine the
effects of green spaces and urban and peri-
urban forests on house sale prices have
found, for example, that the presence of
green spaces within 80–100 m of a home
increases its price by 7 percent (Conway
et al., 2010). Wolf (2003) used contingent
valuation methods to assess correlations
between variations in urban forest char-
acter and shopper behaviour in a number
of cities in the United States of America,
nding that consumers were 9–12 percent
more likely to make their purchases in
shopping districts that had trees than in
comparable districts without trees.
Environmental benets
In line with SDG 13 (climate action) and
SDG 15 (life on land), the NUA calls for
the sustainable management of natural
resources in cities and human settlements
in a manner that protects and improves
urban ecosystems and their ecosystem
services, reduces greenhouse gas emis
-
sions and air pollution, and promotes
disaster risk management. Urban and
peri-urban forests and trees help mitigate
climate change by directly capturing
and storing atmospheric carbon dioxide.
Also, trees provide shade and reduce wind
speeds, thereby indirectly lowering carbon
emissions by reducing the need for air con-
ditioning and heating and thereby cutting
emissions from power plants (Nowak et al.,
2013). Shaded surfaces can be 11–25 °C
cooler than the peak temperatures of
unshaded materials (Akbari et al., 1997);
shading, therefore, can extend the useful
life of street pavement by as much as ten
years, thus reducing emissions associated
with petroleum-intensive materials and the
operation of heavy equipment required
to repave roads and haul away waste
(McPherson and Muchnick, 2005).
Urban areas are generally warmer than
their surroundings – typically by 1–2 °C
but by as much as 10 °C in certain climatic
conditions (Bristow, Blackie and Brown,
2012; Kovats and Akhtar, 2008). Urban
and peri-urban forests can reduce this
“heat island” effect by providing shade
and reducing urban albedo (the fraction
of solar radiation reected back into the
environment) and by cooling through
evapotranspiration (Romero-Lankao and
Gratz, 2008; Nowak et al., 2010).
People in urban areas face many poten-
tial climate-related risks, such as the
increased incidence and severity of storms
and ooding. Urban trees can contribute
to stormwater management in a number of
ways. Stormwater run-off can be reduced
by the evaporation of rainfall intercepted
by tree canopies and through transpiration,
and stormwater quality can be improved
by the retention of pollutants in soils and
plants (Stovin, Jorgensen and Clayden,
2008). Reducing stormwater ows also
reduces the risk of hazardous combined
sewer overows (Fazio, 2010).
By increasing social cohesion, urban and
peri-urban forests can hel