Environ. Res. Lett. 15 (2020) 124035 https://doi.org/10.1088/1748-9326/abc5e4
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LETTER
City-size bias in knowledge on the effects of urban nature
on people and biodiversity
Dave Kendal1, Monika Egerer2, Jason A Byrne1, Penelope J Jones3, Pauline Marsh4, Caragh G Threlfall5,6,
Gabriella Allegretto1, Haylee Kaplan1, Hanh K D Nguyen1, Sue Pearson7, Abigail Wright1and Emily J Flies8
1School of Technology, Environments and Design, University of Tasmania, Hobart, TAS 7000, Australia
2Department of Ecology, Ecosystem Science/Plant Ecology, Technische Universität Berlin, Rothenburgstr. 12, 12165 Berlin, Germany
3Menzies Institute for Medical Research, University of Tasmania, Hobart, TAS 7000, Australia
4Centre for Rural Health, University of Tasmania, Hobart, TAS 7000, Australia
5School of Life and Environmental Sciences, The University of Sydney, Sydney, NSW 2006, Australia
6School of Ecosystem and Forest Sciences, The University of Melbourne, Parkville, VIC 3010, Australia
7School of Medicine, University of Tasmania, Hobart, 7000 TAS, Australia
8School of Natural Sciences, University of Tasmania, Hobart, 7000 TAS, Australia
E-mail: dav[email protected]
Keywords: Urban nature, health and wellbeing, biodiversity, ecosystem services, urban ecology, small cities, city size
Supplementary material for this article is available online
Abstract
The evidence base for the benefits of urban nature for people and biodiversity is strong. However,
cities are diverse and the social and environmental contexts of cities are likely to influence the
observed effects of urban nature, and the application of evidence to differing contexts. To explore
biases in the evidence base for the effects of urban nature, we text-matched city names in the
abstracts and affiliations of 14 786 journal articles, from separate searches for articles on urban
biodiversity, the health and wellbeing impacts of urban nature, and on urban ecosystem services.
City names were found in 51% of article abstracts and 92% of affiliations. Most large cities were
studied many times over, while only a small proportion of small cities were studied once or twice.
Almost half the cities studied also had an author with an affiliation from that city. Most studies
were from large developed cities, with relatively few studies from Africa and South America in
particular. These biases mean the evidence base for the effects of urban nature on people and on
biodiversity does not adequately represent the lived experience of the 41% of the world’s urban
population who live in small cities, nor the residents of the many rapidly urbanising areas of the
developing world. Care should be taken when extrapolating research findings from large global
cities to smaller cities and cities in the developing world. Future research should encourage
research design focussed on answering research questions rather than city selection by
convenience, disentangle the role of city size from measures of urban intensity (such as population
density or impervious surface cover), avoid gross urban-rural dualisms, and better contextualise
existing research across social and environmental contexts.
1. Introduction
Urban nature underpins the health and wellbeing of
human and non-human life in settlements around
the world (Ives et al 2017, Nilon et al 2017, Zhang
et al 2020). Global policies advocating universal access
to green space (such as the United Nation’s Sustain-
able Development Goals and the New Urban Agenda
(UN Habitat 2016)) and local policies promoting
urban forests and public green spaces are supported
by thousands of studies demonstrating the depend-
ence of biodiversity, ecosystem services and human
health benefits on urban nature. Yet what if this evid-
ence base is skewed? A better understanding of biases
in the literature is needed to identify new research pri-
orities and to generalise existing literature to particu-
lar local contexts.
A substantial and growing body of evidence sug-
gests that urban nature can benefit human health
and wellbeing and biodiversity. City-dwellers with
© 2020 The Author(s). Published by IOP Publishing Ltd
Environ. Res. Lett. 15 (2020) 124035 D Kendal et al
proximity and greater exposure to natural envir-
onments (e.g. parks, gardens, woodlands, rivers
and beaches) experience improved mental, phys-
ical and sociocultural health (Twohig-Bennett and
Jones 2018, Lai et al 2019). Proposed mechanisms
that explain these benefits include opportunities for
physical activity and social contact, better psycho-
logical engagement (Lachowycz and Jones 2013)
and improved microbial exposure (Flies et al 2017,
2018). Parks, streetscapes, gardens and informal
green spaces maintain people’s connection to nat-
ural environments, with flow-on effects for wellbeing
and their support of biodiversity conservation (Miller
and Hobbs 2002, Soga and Gaston 2016, Ives et al
2017). In a rapidly urbanising world, urban nature
also plays a critical role in maintaining biodiversity.
Urban vegetation enables the persistence of many
plant and animal species (Lepczyk et al 2017, Threl-
fall and Kendal 2018). Threatened species live in cit-
ies, and depend on cities for their survival (Schwartz
et al 2002, Ives et al 2016, Soanes and Lentini 2019).
Urban nature also provides important ecosystem ser-
vices such as cooling, storm water management, food
production and recreation (Bolund and Hunhammar
1999, Dobbs et al 2014, Elmqvist et al 2015).
However, cities are highly diverse in size, function,
character, land use, climate, infrastructure (Robin-
son 2006, Byrne and Houston 2020) and in the pro-
vision of, and demand for, urban nature (Boulton
et al 2018). A city size bias in the literature has been
demonstrated in urban climate solutions (Lamb et al
2019), and the literature suggests that studies of large
cities in developed areas such as New York, Mel-
bourne, Hong Kong, Berlin and London are likely
to be overrepresented (Luederitz et al 2015, Boulton
et al 2018, Filazzola et al 2019, Zhang et al 2020).
Yet almost half the world’s urban population live in
smaller cities of less than 300 000 people (United
Nations 2018), and urbanisation is now predomin-
antly occurring in the developing world (Güneralp
and Seto 2013). This suggests both a city size and geo-
graphic bias that could weaken the utility of the exist-
ing evidence base for most of the world’s cities and
urban dwellers. One of the drivers of bias may be a
correlation between the location of researcher’s insti-
tutions, and the location of cities they study—a phe-
nomena that has been observed for Chinese scholars
in urban ecosystem services research (Luederitz et al
2015).
Urban Scaling research shows that city size (based
on total population) is a critical factor mediating
many entangled economic, social and environmental
facets of urban socio-ecological systems (Bettencourt
and West 2010). City size impacts green space cover-
age, per capita access to green space and vegetation
structure—all drivers of the ecological and human
health benefits urban nature provides (Fuller and
Gaston 2009, Zhao et al 2013, Dobbs et al 2017,
Akuraju et al 2020). City-size affects the health out-
comes associated with urban nature. Larger cities
are associated with higher levels of physical activity
and lower rates of obesity (Bettencourt et al 2007,
Rocha et al 2015). City size also likely affects the
benefits of urban nature for biodiversity. Applying
island biogeography theory to cities suggests biod-
iversity is likely to be affected by city size via differ-
ing rates of species immigration and extinction (Davis
and Glick 1978, Marzluff 2005), and the availabil-
ity and connectivity of habitat. City size is also asso-
ciated with the provision of some urban ecosystem
services. City size is negatively related to total ecosys-
tem service value (Wu et al 2013) and the recreation
potential of vegetation cover (Dobbs et al 2014) (but
not the potential for provisioning ecosystem services:
Larondelle et al 2014). In combination, these findings
strongly suggest that city size will influence the effects
of urban nature through multiple direct and indirect
pathways.
Clearly not all cities in the world have been or
are ever likely to be studied, but biases in the evid-
ence base could significantly undermine the utility of
scientific knowledge informing urban nature policy
for small cities or cities in the developing world (e.g.
Bell and Jayne 2009). In other fields, there is concern
that ‘theoretical generalizations of empirical know-
ledge derived from global cities and metropolises’
have been inappropriately applied to diverse small
cities and towns (van Heur 2010, p 189). There are
important economic, social, environmental and cul-
tural differences in cities around the world that likely
affect both the supply and demand for urban nature
and the benefits it provides. There are radical dif-
ferences in settlement patterns and vastly different
health and biodiversity challenges in different places.
Knowledge generated on urban nature in large cit-
ies will not necessarily apply equally to all cities, and
applying this knowledge may be counterproductive in
some settlements.
Here we aim to quantify evidence of city-size and
geographic biases in the published scientific literature
on the effects of urban nature on people and biod-
iversity by asking:
(a) Are the effects of urban nature more likely to be
studied in large cities than in small cities (city-
size bias)?
(b) Are researchers studying the cities they work in
(academic ‘home’ bias)?
(c) Is there a geographic bias in studies of the effects
of urban nature studies (geographic bias)?
Answering these questions will progress the urban
nature research agenda towards better understand-
ing of how nature associated with human settlements
benefits human and non-human inhabitants across
the spectrum of human settlements globally.
2
Environ. Res. Lett. 15 (2020) 124035 D Kendal et al
Table 1. Search terms used for our three categories of benefits from urban nature.
Search
title
Search terms Records returned
Urban
biodiversity
TITLE-ABS-KEY ((urban OR city OR town OR metropolitan OR
settlement) AND (‘urban ecology’ OR biodiversity))
10 094
Health benefits
of urban nature
TITLE-ABS-KEY ((urban OR city OR town OR metropolitan OR
settlement) AND (greenspace OR (‘green space’) OR garden OR
(‘open space’) OR park) AND (health OR wellbeing))
3929
Urban ecosys-
tem services
TITLE-ABS-KEY ((urban OR city OR town OR metropolitan OR
settlement) AND (‘ecosystem services’)
3992
Table 2. Settlement size allocation to quartiles based on population and corresponding terminology according to key global
organisations.
Quartile Number of
settlements
Population
size
Total population World
bank
UN Habitat UN World
Population
Prospects
Q1 42 281 5000–66 038 741 567 855 Town Urban Cluster Category 6
Q2 5576 66 039–335 414 741 577 575 City Urban Centre Category 6
Q3 1083 335 415–1759 999 741 316 978 City Urban Centre Category 4–5
Q4 165 >1 760 000 741 901 879 City Urban Centre Category 1–3
2. Methods
2.1. Literature on the effects of urban nature
To validate and determine the extent of potential
city-size bias in the literature on the effects of nat-
ural urban environments, we systematically reviewed
three bodies of academic literature:
(a) Urban ecology studies exploring the effects of
natural urban environments on biodiversity
(b) Health studies exploring the effects of natural
urban environments on people’s health and
wellbeing
(c) Ecosystem services studies exploring the ser-
vices and disservices provided by natural urban
environments
We accessed the Scopus bibliometric database API
in October 2019 using the rscopus package in R v3.6
(R. Development Core Team 2010). Separate searches
were conducted on urban ecosystem services, urban
biodiversity and the health benefits of urban nature
(table 1). These results of these searchers were filtered
to exclude records with no abstract (n=262) or that
were not a journal articles (n=1703), and duplic-
ate records returned by multiple searches (n=1265).
Only English language articles were retrieved. The
final list of articles included 14 786 articles, with 8921
from the biodiversity search, 3495 from the health
search, and 3602 from the ecosystem services search.
2.2. City size and geographic data
A global database of 49 115 settlements with a pop-
ulation greater than 5000 residents was obtained
from GeoNames (www.geonames.org/). There is
no universally agreed definition of a ‘city’, nor a
minimum population size required for a settlement to
be considered ‘urban’. We acknowledge that country-
and region-specific thresholds can vary substantially,
and a key challenge is to identify the boundaries of
a city—to define what is urban and what is not—
a decision that is usually made ad-hoc or based on
administrative boundaries. In the absence of universal
standards on these issues, we used a population size of
5000 as a minimum threshold in this study, consist-
ent with thresholds used by global organisations such
as the World Bank (Dijkstra et al 2020) and UN Hab-
itat (Mwaniki 2018). The continent of occurrence of
each city was determined by linking the country in the
GeoNames database to continent using the Natural
Earth country administrative dataset (Natural Earth
2019).
City size analysis often use a hierarchy of settle-
ment sizes to demarcate different settlement types,
although there is no consensus about where size
boundaries begin and end (United Nations 2018,
Lamb et al 2019). In this study, quartiles of urban set-
tlements based on population size were determined so
that each category included approximately the same
number of people (table 2). The quartile of smallest
settlements roughly corresponds to the world bank
classification of town (Dijkstra et al 2020) and the
UN Habitat classification of ‘urban cluster’ (Mwaniki
2018), both 5000–50 000 people. The second quartile
roughly corresponds to the world bank classification
of city (Dijkstra et al 2020) and the UN Habitat classi-
fication of ‘urban centre’ (Mwaniki 2018). In combin-
ation, the bottom two categories fall into the lowest
category of city size as classified by the UN in their
World Urbanization prospect reports, the Q3 cities
map to UN city size categories 4–5 and the Q1 cities
map to UN city size categories 1–3 (United Nations
2018).
3
Environ. Res. Lett. 15 (2020) 124035 D Kendal et al
Figure 1. The proportion of cities mentioned in (a) all abstracts and affiliations and (b) abstracts returned by searches on urban
biodiversity, urban ecosystem services and health benefits of nature, in each settlement size bin.
2.3. Data analysis
Text matching of city names with article meta-data
was used to (1) identify article abstracts mentioning
city names (study city), and (2) the city/cities of the
institutions the authors were affiliated with (author
city). Text was matched automatically using a cus-
tom R script to identify city names in abstracts and
in author affiliations.
For each settlement size quartile, and for both
study cities and author cities, the total number of
articles mentioning the city, the proportion of cities
in the quartile that were mentioned, and the average
number of times each city was mentioned was cal-
culated. The total number of publications and num-
ber of publications per 20 million inhabitants was
determined for each continent.
2.4. Data cleaning and validation
City names that are also common words were
excluded from the text matching (see supplement-
ary material stacks.iop.org/ERL/15/124035/mmedia
appendix 1). City names that were commonly con-
fused with other names (states, regions, rivers,
people) were refined using exclusion or inclusion cri-
teria (see supplementary material appendix 2). The
327 non-unique city names, referring to 1190 unique
cities, that were found regularly in abstracts (>3 men-
tions) were qualified using exclusion or inclusion
criteria (see supplementary material appendix 3).
Abstracts were cleaned to remove copyright notices
that included city names (see supplementary mater-
ial appendix 4).
To check the validity of the automated city name
matching, 100 articles were randomly selected, and
the abstracts were manually checked for false positives
(city identified but no city name in the abstract) and
false negatives (city in abstract not identified via auto-
mated text matching). This found 82% of abstracts
were correctly coded, which was considered accept-
able for the purposes of this study. There were 74
cities identified in the abstracts, 11 of which were
false positives and 132 city names in the abstracts
were not identified by the analysis. False positives
were mainly caused by confusion with author names,
province/state names and names of rivers and lakes.
False negatives were largely caused by variation in
spelling or the settlement having a population of less
than 5000 people, and therefore not included in the
master list of cities used in this study.
3. Results
A total of 7529 article abstracts were identified as con-
taining at least one city name (51% of all articles),
and 1778 articles mentioned more than one city name
(with one abstract mentioning 25 cities). Cities were
identified from author affiliations in 92% of articles.
3.1. City-size bias
An analysis of abstracts and affiliations shows that
large cities are much better represented in the
literature than smaller settlements (figure 1(a)). A
minority of small cities have been studied (3% of the
smallest quartile of settlements and 18% of Q2 cit-
ies), compared with a majority of large cities (85% of
Q1 cities and 49% of Q3 cities). As these are quartiles
based on population, this means that the smaller set-
tlements where half the world’s population live have
been rarely studied. A similar pattern was observed
in author affiliations; most large cities are mentioned
in affiliations but only a tiny minority of small cit-
ies are mentioned. These biases are most pronounced
4
Environ. Res. Lett. 15 (2020) 124035 D Kendal et al
Figure 2. The average number of times each city is mentioned in (a) abstracts and affiliations and (b) abstracts returned by
searches on urban biodiversity, urban ecosystem services and health benefits of nature, in each settlement size bin (95%
confidence intervals are shown).
in studies of urban ecosystem services (figure 1(b)),
although the same patterns were observed in studies
of urban biodiversity and the health impacts of urban
nature.
As well as large cities being more likely to be stud-
ied, large cities were also likely to have been more
studied more often (figure 2(a)). Cities in the largest
quartile were the subject of 25 studies on average,
while smallest two quartiles of cities were studied only
once or twice. Authors were also more likely to be
affiliated with institutions in large cities (figure 2(b)).
Q4 cities had an average of over 50 mentions in affil-
iations per city while small cities had fewer than 5.
There was a great deal of variation in patterns of
repetition across different search categories, making
trends difficult to discern.
3.2. Academic ‘home’ city bias
Researchers are often writing about the cities in which
they are working, with 45% of cities mentioned in
abstracts also listed in the affiliation of one of the
authors of the article. There was a strong correlation
(Pearson r=0.84) between the overall number of
authors with an affiliation from a city, and the num-
ber of article abstracts mentioning that city.
3.3. Geographic bias
There was a clear geographic bias in the dataset (fig-
ure 3). Most studies were from Asia (in the developed
cities of Beijing =296, Shanghai =104, Singa-
pore =83, Hong Kong =81), Europe (Berlin =106,
London =103, Barcelona =77, Rome =74) and
North America (New York =238, Chicago =95,
Figure 3. The total number of mentions in abstracts of
cities on different continents, and by population (per 20
million human inhabitants).
Phoenix =77, Baltimore =73). The relatively few
studies from Africa (Cape Town =67) and South
America (S˜
ao Paulo =118, Rio de Janeiro =65)
also tended to be from more developed or larger cit-
ies. On a per capita-basis, cities in Oceania (Australia
and New Zealand) had a relatively low urban popula-
tion but were the subject of a disproportionately high
number of studies (Melbourne =119, Sydney =103).
Conversely, cities in Asia and Africa that are home
to much of the world’s expanding urban populations
were poorly represented.
5
Environ. Res. Lett. 15 (2020) 124035 D Kendal et al
4. Discussion
4.1. Key findings
There are biases in the published research on the
effects of urban nature on people and biodiversity.
First, bias towards the study of larger cities, which
are studied many (~25) times over, while small to
mid-sized cities are rarely studied at all. The most
studied cities (Beijing, New York, Melbourne, Ber-
lin, London and Shanghai) all have populations over
3 million people—consistent with in topic-specific
reviews (Luederitz et al 2015, Filazzola et al 2019)
and the quantified bias observed in climate solutions
research (Lamb et al 2019). The methods used in
this study have not captured studies where the city
name is not included in the abstract, a likely scenario
with some multi-city reviews such as meta-analysis or
other big data studies. However, our findings likely
capture a majority of primary research on the bene-
fits of urban nature for people and biodiversity, as city
names were found in more than half the abstracts ana-
lysed.
Currently, 41% of the world’s urban population
live in cities of less than 300 000 people (United
Nations 2018). Current research on the effects of
urban nature does not adequately capture the lived
experience of the almost half the world’s urban dwell-
ers. Further reducing the diversity of cities studied is a
bias of convenience; many studies are being conduc-
ted in cities where researchers work, consistent with
findings at the country level by Luederitz et al (2015).
Cities are complex social-ecological systems and hav-
ing more studies per city allows greater diversity and
depth in research topics. In small cities, fewer stud-
ies per city means less knowledge of different taxo-
nomic groups and trophic levels, different classes of
disease and diverse health and wellbeing pathways,
and diverse ecosystem services and disservices. Lar-
ger research institutions in larger cities are more
likely to have a greater number of researchers with
more diverse research expertise, reinforcing the bias
towards the increased extent and scope of research in
large cities.
Geographically, rapid urbanisation is occurring
across Asia, Africa and South America, but this review
shows that there is comparatively little research on
how urban nature can benefit developing cities in
these locales (particularly outside a few large cities
in Asia: Luederitz et al 2015, Lamb et al 2019, and
as this review shows, in South America) This study
only included English-language articles, and it is likely
that articles in other languages would better represent
South America, Africa and Asia. Yet the studies pub-
lished in English and analysed here make an import-
ant contribution to global knowledge of the benefits
of urban nature.
4.2. Does city size matter?
These biases will be important only if city size
or geography influence the benefits derived from
urban nature. There are several ways that city size
could influence the mechanisms thought to under-
pin the benefits of urban nature. Firstly, smaller cities
may facilitate easier access to extra-urban nature for
humans (e.g. for recreation and physical activity) and
non-humans (e.g. for foraging and habitat) which in
turn affects the usage and importance of intra-urban
nature. Island Biogeography theory provides a use-
ful framework for thinking about connection of cities
with extra-urban landscapes (Davis and Glick 1978),
suggesting that movement of species (and humans)
between urban and extra-urban areas will decrease
in larger cities. This idea could be extended to the
movement of other phenomena such as wildfire and
both beneficial and nuisance animals (e.g. locusts,
pademelons, deer).
Secondly, the composition and structure of urban
nature, and therefore its functions and benefits, is
likely to change with city size (Hahs and Mcdon-
nell 2006). Gradient studies have shown that urban
nature changes along gradients of human population
density, proportion of sealed surfaces, and distance
from the urban edge (Hahs and Mcdonnell 2006).
This gradient has been shown to have implications for
biodiversity and health. For example, emerging evid-
ence suggests that environmental microbiomes are
shaping human health and wellbeing, and the micro-
biomes of urban green spaces almost certainly differ
with city size (Laforest-Lapointe et al 2017, Flies et al
2017,2019,2020, Murray et al 2020). Many studies
show the effects of levels of urbanisation on verteb-
rate biodiversity (e.g. Mckinney 2008).
Lastly, and perhaps most importantly, the effects
of urban nature are highly context dependent, medi-
ated by a diversity of geographical, ecological and
socio-cultural factors (Luederitz et al 2015). Settle-
ment patterns in these areas are radically different to
the developed world. More than a billion urban resid-
ents live in informal settlements (slums) in the devel-
oping world, where urban densities are higher, san-
itation and infrastructure are often substandard or
missing. ‘Nature’ occurs more frequently in informal
green spaces and where human-environment interac-
tions are different (Boulton et al 2018). Urban eco-
system disservices are also likely to be different in
developing countries, and the negative effects of urb-
anisation on people’s health and wellbeing and on
biodiversity conservation have been little studied out-
side global cities (Von Döhren and Haase 2015, Lai
et al 2019). Evidence that is generated in a large global
city may be irrelevant, or even counterproductive if
applied in a different social-ecological context. There
is a risk that evidence generated in the narrow con-
6
Environ. Res. Lett. 15 (2020) 124035 D Kendal et al
text of large global cities may lead to normative beliefs
about the role of all nature in all cities, without appro-
priate consideration of local context. For example,
zoonotic diseases in tropical cities may be spread
through some kinds of urban greening interventions
promoted in Western cities. Increasing urban forest
cover is often unquestioned as a policy goal, yet in
some places, like those subject to wildfire, this could
have harmful consequences (Moskwa et al 2018).
While some research has observed scaling effects
in urban nature e.g. that larger cities have proportion-
ally less green space (Fuller and Gaston 2009, Akur-
aju et al 2020), these scaling effects are not laws, and
different effects may be observed on different collec-
tions of cities (Cebrat and Sobczy´
nski 2016, Chang
et al 2018). In fact, while large cities tend to follow
urban scaling models closely, small cities are diverse
and can display a great deal of heteroscedasticity in
urban indicator data (Sarkar 2019). A critique of scal-
ing analyses highlights that the urban functions of
small cities are the result of complex intersections
of many factors, and must be understood ‘in place’
(Waitt and Gibson 2009).
4.3. Towards an urban nature research agenda for
all urban dwellers
‘Without incorporating the study of small cities more
fully into urban research, we shall fail in the task of
understanding cities in their diversity, their connected-
ness and their distinctiveness.’ (Bell and Jayne 2009,
p 696). We extend this to call to the study of urban
nature and its effects on human and non-human life.
4.3.1. Addressing city size and geographic biases
One pathway to this goal is for researchers to care-
fully consider the design of their research, and to
study cities that can best answer their research ques-
tions rather than those conveniently accessible (i.e.
where they live, work or study). There are many good
reasons for studying local cities including knowledge
of cultural, socio-economic and historical context
and potential pathways to impact and engagement.
However, research design may be improved and bet-
ter answer research questions by explicitly consider-
ing different cities or extending a study to compare
multiple cities. Recognising that researchers will con-
tinue to ‘oversample’ the cities they work in, collab-
orations between researchers that span institutions
in different cities, between institutions in developing
and developed countries, and leverage networks of
cities (e.g. ICLEI) may facilitate the study of a greater
diversity of cities.
4.3.2. Moving beyond urbanisation gradients
While gradient studies have contributed much to our
understanding of nature in urban systems, studying
mechanisms rather than level of urbanisation may
further develop knowledge. Many gradient studies of
urban biodiversity and ecosystem services use pop-
ulation density as a measure of urbanisation (e.g.
Tratalos et al 2007, Luck et al 2009, Peng et al 2017,
Moreira et al 2019, Łopucki et al 2020). This focus
on population density could confound understand-
ing of alternative mechanisms, such urban scaling
effects from total population, environmental context
or local habitat characteristics. A greater use of com-
parative studies across different cities could improve
understanding of these factors (Mcdonnell and Hahs
2009) and also reveal how interactions between biod-
iversity and human health vary between cities. The
study of urban teleconnections could lead to better
understand the processes underpinning movement of
species, people, technology and culture between dif-
ferent spatially discreet urban, peri-urban and rural
areas (Seto et al 2012).
4.3.3. Avoiding gross urban-rural dualisms
We cannot assume that the benefits of nature will be
the same in smaller urban contexts as in large cities.
Much of literature surrounding the effects of urban
nature is grounded in gross rural-urban and natural-
built environment dualisms which fail to reflect the
diversity of urban environments and the permeabil-
ity of contemporary urban/peri-urban/rural intersec-
tions (Tornaghi and Dehaene 2020). In Australia, the
disease burden rate in the most rural areas is 1.4 times
the rate in major cities (Australian Institute of Health
and Welfare 2019) despite extensive access to natural
environments. Health benefits derived from nature
may be different in smaller cities than in large cit-
ies, and the health inequities that occur in rural areas
may extend to into smaller urban settlements. Redu-
cing the big-city bias in urban health, biodiversity and
ecosystem service literature that we have revealed here
is needed to better understand nuances, complex-
ity and normative thinking in the benefits of urban
nature.
4.3.4. Contextualising existing research
Care must be taken when generalising findings from
large cities to small cities, or across cultural or devel-
opment contexts. Scientific findings and evidence
from Stockholm, London or New York may not
be easily generalisable to Hobart, Puntas Arenas or
C`
a Mau. For example, education level rather than
income has been shown to drive patterns of veget-
ation diversity and cover in small cities in south-
eastern Australia (Luck et al 2009, Kendal et al 2012).
In rapidly growing cities in Africa, Asia and South
America, urban nature may be more important as a
source of firewood, fresh food, medicines and cultural
practices (e.g. Kaoma and Shackleton 2014) than
in Western cities. Different values towards nature,
such as wood gathering and subsistence activities in
African settlements or the sacredness of some trees in
7
Environ. Res. Lett. 15 (2020) 124035 D Kendal et al
Indian cities (Jaganmohan et al 2018), will likely pro-
duce different urban ecologies, and applying Western
norms and ideas about nature to such places, without
studying them, will produce ethnocentric biases. Care
should be taken when generalizing findings to a par-
ticular city to ensure comparisons are made with
an adequate and representative sample of cities. In
quantitative generalisations, weights could be applied
to help correct biases in the evidence base. City man-
agers need information on urban biodiversity man-
agement that can be taken and applied to their own
city social, cultural and environmental context.
5. Conclusion
There is strong evidence base of the many positive
effects of urban nature on biodiversity, ecosystem ser-
vices and human health. However, several import-
ant biases exist in the literature that raise questions
about the utility of this literature as an evidence base
for urban policy in the diverse cities that exist in the
world. There is an over-representation of studies in
the large cities where research institutions are located,
and a lack of studies in small cities and in develop-
ing areas. Urban scaling effects are likely, the results of
studies in big cities should not be blindly translated to
small and regional city contexts. In the coming dec-
ades, small to mid-size cities will remain important
sites of human existence and human-nature interac-
tions. Diversifying the sites of urban nature studies
and a greater emphasis on multi-city research part-
nerships should lead to a more robust evidence-
base, and more effective application of urban nature
research and in cities around the world.
Acknowledgments
The work was supported by the University of Tas-
mania through a Visiting Scholars program awar-
ded to CGT, and a Research Enhancement Program
grant awarded to EJF from the College of Science and
Engineering.
DK receives support from Australian Research
Council Linkage grants (LP160100439 and
LP160100780).
CGT is supported by the Clean Air and Urban
Landscapes Hub, funded by the Australian Gov-
ernment’s National Environmental Science Program,
and the Australian Research Council via a DECRA
(DE 200101226).
PJJ is supported by the Department of Health,
Tasmanian Government
Data availability statement
All data that support the findings of this study are
included within the article (and any supplementary
information files).
ORCID iDs
Monika Egerer https://orcid.org/0000-0002-3304-
0725
Gabriella Allegretto https://orcid.org/0000-0002-
5384-3699
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