PLANT FOR LIFE
Briefing Report 17: November 2008
Ross Cameron and Jane Taylor
University of Reading
The Benefits of Green Space
Social, Physiological and Psychological Benefits
Field surveys in Switzerland assessed the restorative effects of visiting an urban forest and a
city park (Hansmann et al., 2007). Respondents rated their headaches, level of stress, and how
balanced they felt both prior to visiting the outdoor location and at the time of being interviewed
(1-2 hours later). Suffering from headaches and stress decreased significantly, and feeling wellbalanced increased significantly. The recovery ratio for stress was 87%, and the reduction in
headaches was 52%, in terms of possible improvements on a five-point rating. (It should be
noted though, that only a small sample size - 15 people was used in the headache data - 14 of
which claimed their headache had reduced after a period of time in the greenspace). With
respect to feeling well-balanced, the observed changes amounted to 40% of the possible
enhancement. The authors state the positive effects increased with length of visit, and
individuals practising sports (e.g., jogging, biking, playing ball) showed significantly higher
improvements than those engaged in less strenuous activities (e.g., taking a walk or relaxing).
A couple of drawbacks of this research was that it only interviewed people who had voluntarily
visited the park, and the questions were often based on hypothetical situations – e.g. ‘what
activity would you recommend to a friend suffering from stress’?
In a rather unusual paper, Groenewegen et al., (2006) fail to present any results themselves,
but discuss a methodology for assessing the benefits of green space. Nevertheless, there is a
comprehensive and informative review of the literature. The authors state:
“Exposure to green space consists of direct physical exposure and the psychological processes
through which exposure influences health and well-being. These psychological processes will
be developed, using theories about stress and restoration Van den Berg (2003). Restorative
effects can be achieved by merely looking at nature or natural elements, indicating that the
aesthetic experience of nature may play a role in this mechanism. Besides providing relief from
stress, an aesthetically attractive living environment may also improve well-being by enhancing
satisfaction, attachment, and a sense of responsibility. Related to stress reduction, (American)
evidence suggests that exposure to natural environments may reduce feelings of anger,
frustration and aggression (e.g. Kuo and Sullivan, 2001a). In turn, this may enhance feelings of
social safety, and even reduce actual rates of aggressive behaviour and criminal activity (Kuo
and Sullivan, 2001b). Physical exposure to cleaner air may play a role also. Traffic density
seems to be the most important source of polluted air in the direct vicinity, while the overall
level of air pollution is rather constant in the Netherlands (Hoek et al., 2002).
A behavioural mechanism will be developed, using sociological theories about life style,
combining structural aspects (socio economic status) and opportunities (availability, social
integration) and choices people make (behaviour) (Ganzeboom 1988; Joosten, 1995). Natural
environments are perceived as more attractive than built environments. Because of this, green
areas may stimulate residents to undertake healthy physical activities such as walking or
cycling or to choose these activities as a mode of transport, and to spend more time in them
(Taylor et al., 1998). Attractive green areas in the neighbourhood may serve as a focal point of
tacit coordination for positive informal social interaction, strengthening social ties and thereby
social cohesion (Kweon et al., 1998). Social cohesion by itself is thought to have a positive
effect on well-being and feelings of safety. It is important to distinguish the effect of green
space from that of population density or urbanicity, which has an established relationship with
(mental) health (Verheij, 1996).
Apart from these causal mechanisms, part of the effect may be the result of selection. Selective
migration to or retention in particular living environments might explain part of the relationship
between green space in people's living environment and their health. Direct selection occurs,
when people's well-being influences their chances of living in a favourable environment;
indirect selection, when people with certain characteristics, such as a high income, that are
related to well-being can afford to live in a favourable environment (Verheij, 1999). Migration
flows in general are related to such socio-demographic characteristics as age, income and
education (Heins, 2002). Consequently, indirect selection might play a role in explaining
relationships between the amount of green space in people's living environment and health and
well-being. It is therefore important to take into account and control for the possibility of
selection.”
Groenewegen et al. (2006) go on to state that some of the questions posed above, will be
answered in three projects.
“The first project will establish the strength of the relationships between green space and
health, well-being, and feelings of safety. Recent epidemiological research by our team has
shown a relationship between a green living environment and perceived health indicators in a
large population sample (De Vries et al., 2003). This was the first study in the general
population, showing that this relationship was not exclusive to extreme and controlled settings.
People living in greener areas tend to perceive their physical and mental health status as better
than their counterparts living in less green areas (controlling for socio-economic and
demographic spatial clustering). Whether such a positive relationship will also be found when
looking at other health indicators is not known. The same applies to people's feelings of safety,
which could even be negatively influenced by the presence of green space in one's living
environment (because the lack of social control may turn urban green spaces into 'hot spot'for
criminal activities).
The second project focuses on the urban environment. Green space is scarcer in urban areas
and access to it might be more skewed. Several studies have demonstrated positive
relationships between the presence of greenery in urban neighborhoods and residents'health,
well-being, and social safety (De Vries et al., 2003; Kaplan, 2001; Kuo and Sullivan, 2001a and
2001b; Grahn and Stigsdotter, 2003). These relationships have been explained mostly through
the mechanism of stress reduction. Indeed, there is some evidence that exposure to local
greenery in an urban context may reduce stress and mental fatigue. For example, Honeyman
(1992) found that stressed participants who viewed images of vegetated urban scenes showed
the highest levels of stress reduction, even higher than those viewing countryside, while those
viewing barren urban scenes exhibited an increase in stress levels. However, besides stress
reduction, there may be other mechanisms underlying beneficial effects of local greenery, in
particular increased physical activity and improved social cohesion.
The third project focuses on the micro geographic scale. Being also located in an urban
environment, it studies people with and without an allotment garden. There is a long history of
the use of gardens to improve psychological well-being and physical health (Cooper and
Barnes, 1999). However, few studies have systematically investigated the health benefits of
gardens in general, and allotment gardens in particular. Allotment gardens originated at the
turn of the 20th century and have known revivals during and after the two world wars to
increase supplies of fresh foods (Wiltshire and Azuma, 2000). Today, food production is only
one of the many functions of allotment gardens. These gardens are now generally assumed to
contribute to a wide array of public health and lifestyle issues (Twiss et al., 2003). Beneficial
effects of allotment gardens have been attributed to various factors, including enhanced
physical activities, reduced levels of stress and mental fatigue, and a better social and cultural
integration (Armstrong, 2000; Philips and Wielers, 2001). Several studies have investigated
physical activities associated with gardening (Blair et al., 1991; Ford et al., 1991). In one study
among elderly men in The Netherlands, participants spent a greater amount of time per week
doing gardening than doing other activities such as walking or cycling (Carspersen, et al.,
1991). Gardening activities have typically been related to specific health benefits such as
reduced cholesterol levels (Pahor et al., 1994). But there is some evidence that activities on
allotment gardens may also contribute to health and well-being in a more general way (Milligan,
et al., 2004). When they are asked to describe their reasons for participating in an allotment
garden, people often refer to the stress reducing effects of gardening (Milligan, et al., 2004). It
has been suggested that in addition to promoting physical activity and reducing stress,
allotment gardens may also help to establish a sense of social and cultural integration among
gardeners (Schmelzkopf, 1995). Especially for older people, allotment gardens may provide a
supportive environment that combats social isolation and contributes to the development of
their social networks (Milligan, et al., 2004).”
Economic Value of Green Space
Green space provision is proceeding apace in many Chinese cities, and Chen and Jim (2008)
claim that cost–benefit analyses are needed to justify the level of investment and the use of
public funds. Their paper assessed the use of urban green spaces in the new Zhuhai city in
south China, and employed the contingent valuation method to estimate the non-market leisure
value of an ambitious new urban greening project. A questionnaire of 850 randomly chosen
households was conducted. Some 65.7% of respondents used public green spaces for leisure
frequently, but young residents aged 20–30 were less frequent users. Chen and Jim (2008)
considered that the traditional wholesome functions provided by green spaces, such as
relaxation, quiet and discourse with nature, might not appeal to younger people. More active
and exciting leisure pursuits, such as visiting pubs and wildland exploration, were preferred by
young residents (Ma and Zhang, 2004; Liu, 2006). This result differs from work in the USA
where household gardens in western cities tend to encourage older residents to stay at home,
and the gregarious recreational opportunities in urban parks tended to attract young patrons
(Payne et al., 2002).
The new greening project in China was strongly supported for its leisure and ecological values.
A logit regression model indicated that household income and bid amount would affect
individual willingness-to-pay (WTP). The mean WTP was RMB161.84 (about US $23) per
household per year, translated into an aggregate leisure value of RMB12.3 million per year
($1.75m). The net present value is projected to be RMB32.94 million (US $4.7m), but this
relates to a discounted benefit–cost ratio of 0.88 when other benefits are excluded. By
comparison, conservative estimate of the leisure value of urban forests in parks and recreation
areas in the USA exceeds $2 billion per year (based on travel cost method by Dwyer et al.,
1992). Similarly, the analysis of street and park trees in California yielded benefit–cost ratios at
1.85:1 in Modesto and 1.52:1 in Santa Monica (McPherson and Simpson, 2002). The Finnish
national parks demonstrated leisure benefits (€32 million per year) exceeding the annual
maintenance expenditures by a large margin (about €13 million) (Huhtala, 2004). Other studies
furnished data for urban greening projects (McPherson, 1994; Pepper et al., 2005), and
facilitated natural resource management based on consumer satisfaction (Peterson and
Loomis, 2000; Huhtala, 2004). A recent study in Guangzhou, China, found average WTP for
recreation-amenity services at RMB18.04/person/month (US $2.6) (Jim and Chen, 2006).
Overall Chen and Jim (2008) suggest the findings confirmed community support for the Zhuhai
project, although the preferred payment method was via donation, rather than entry fee or
taxation.
A report has recently been published (Anon 2008) highlighting the value of green space to the
economy
of
Philadelphia
(USA).
(See
http://www.tpl.org/content_documents/PhilaParkValueReport.pdf). Not all beneficial factors
could be calculated, but relating certain aspects to economic equivalents was a useful process
for defining value. These were influences on clean air, clean water, direct use, tourism, health,
property values and community cohesion. A range of formulae were used to define value in
each case. The summary of the data suggested that the economic value p.a. could be broken
down to:
Values:
Tax from increased property value = $18m
Tax from increased tourism = $5.2m
Stormwater management = $6m
Air pollution mitigation = $1.5m
Community cohesion = $8.6m
Direct use = $1,076m
Health value = $ 69m
Property value increase = $688.8m
Profit from tourism = $40.2m
Research from Spain (Castellón) focussed on how the provision of greenspace influences the
value of property. Morancho (2002) analysed the link between housing prices and urban green
area using the hedonic technique as methodological approach. With the hedonic technique the
value is indirectly obtained through the influence exercised by the environment on the market
price of another goods product. A representative sample of the current real estate market in
this city was selected. The data set contained the sale price and other key features of 810
residential dwellings. Together with conventional determinants of housing prices (size, number
of rooms, age, etc.) certain environmental factors were included such as proximity to a green
area, its size and the existence or absence of views of a garden or a public park.
Results show housing size to be the most relevant variable on price. As far as the hedonic
variables are concerned, there is an inverse relationship between the selling price of the
dwelling and its distance from a green urban area. As far as environmental variables are
concerned, only the distance from a green area was significant. According to the estimates
obtained, every 100 m further away from a green area means a drop of 300,000 pesetas
approximately (€1800) in the housing price. Hence, its proximity to the green area was more
relevant than its size. Although the distance effect can be considered as modest, the author
claims it has important policy implications for urban planning since it seems to indicate that
provision of numerous small green areas throughout the city is more appropriate than a few
vast parks. In the final analysis, large park areas should be created and planned as
complements to small landscaped gardened areas.
Similar studies in Turkey came to slightly different conclusions. Yilmaz et al., (2007) determined
if parks and playgrounds had any economical effect on the house prices in the city of Erzurum.
The correlation between parks and playgrounds and house prices was analysed by using the
hedonic pricing method. With this aim, in three different sites (e.g. the city centre, Yenisehir and
Dadaskent districts), the prices and distances from nearby parks and playgrounds of the
residences were detected. Hedonic pricing method indicated that the most significant factors
affecting the prices of the houses in the city of Erzurum are those related to the features of the
residences. However, playgrounds were effective on house prices but park areas did not have
significant effect on house prices.
Benefits of Green Space and Contact with Nature
Urban public greenspaces form the arena of many people's daily contact with nature and such
contact has measurable physical and psychological benefits. Fuller et al., (2007) state that that
these psychological benefits increase with the species richness of urban greenspaces.
Moreover, they suggest that greenspace users can more or less accurately perceive species
richness depending on the taxonomic group in question (birds, insects, plants etc.). These
results indicate that successful management of urban greenspaces should emphasize
biological complexity to enhance human well-being in addition to biodiversity conservation. The
authors acknowledge that people may be appreciating the more diverse landscapes directly,
but rather under-emphasize this point compared to the landscape being a precursor for species
richness; i.e. the more variable and interesting landscapes may be having a direct benefit on
human perceptions rather than an indirect one through biodiversity!
Alien Plant Species
Whilst there is little doubt about the benefits from urban green space and natural areas within
cities, the quality and composition of such space has received less attention claims
McConnachie et al., (2008). These authors claim that without proper management, such
spaces may become refuges for alien species planted by officials, or alien invasive species that
thrive in disturbed sites. According to Pysek (1998), the occurrence of indigenous and alien
species in urban flora follows different patterns of dispersal between cities. Understanding the
behaviour of alien species across cities is vital. This is because the cities act as immigration
sources from which the alien species can disperse into the surrounding landscape (Pysek,
1998; Alston and Richardson, 2006). Invading vegetation is believed to be the second largest
threat to biodiversity, after direct habitat destruction (Cowling and Hilton-Taylor, 1994; IUCN,
2000; Alston and Richardson, 2006). Hence, greater understanding of their extent and
dynamics in urban green spaces is required. McConnachie et al. (2008) based their work on
green space within South African urban areas.
McConnachie et al. (2008) found that that mean woody species richness per green space was
low (4.9 woody species per sampled green space). (In contrast to other studies on urban
species richness). Clearly, they state, very little natural thicket vegetation remains in the public
greens spaces of the towns studied. An explanation for this low species richness at the town
level could be that of biotic homogenisation, where only a few plant species are thriving in the
conditions in the sampled towns. A large proportion (48.7%) of the green spaces sampled in
the study had less than 20 woody plants per green space. A common trend encountered was
that the distribution of woody plants was unevenly distributed in favour of the more wealthy
areas within a town. Fewer woody plants were present in the poorer townships. In order to
improve the ecosystem functioning and human benefits of the existing green spaces, the
restoration of green spaces by planting of woody plants needs to be advocated within the local
municipalities (Ruiz-Jaen and Aide, 2006). In terms of the woody plant species encountered by
McConnachie et al. (2008), the proportion of alien species was considered high.
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Campaign financed with aid from the European Union