Improving Canberra`s sustainability: why urban tree

Transcription

Improving Canberra's sustainability: why urban tree canopy and other vegetation matters
Dr Jane Tarran
University of Technology Sydney
Senior Lecturer, Environmental Sciences
Program Director, BSc (Urban Ecology)
1.
Overview
This paper imagines how Canberra, the "Bush Capital", can improve its sustainability in a future that
presents challenges in relation to human population growth and climate change, including the supply of
basics such as shelter, energy, water and food, as well as other attributes of a civil society, such as
communication, movement, knowledge and culture. The main aspect under consideration is urban and
suburban vegetation, including both regenerated areas of locally indigenous flora and areas consciously
planted with a range of plants, such as locally indigenous and exotic plants, including food plants. There
is a focus on the components of the urban forest, or the woody plant material, which includes trees,
shrubs and vines, but some comments will also be made on grasses.
The paper starts by looking at early changes in Canberra's landscapes, the development of the garden
city, and some more recent changes in urban trees and vegetation to the present.
The paper then addresses threats to landscape and urban forest sustainability and offers some solutions
in relation to the identified threats. Threats are considered in major areas, such as: (1) a lack of
knowledge about the urban forest and associated lack of vision in supporting and planning for the urban
forest; (2) specific problems for trees arising from existing mature and senescing trees, as well as
problems in retaining existing trees during densification and establishing new trees on lots with larger
house footprints; (3) general competition within city ecosystems for resources needed by trees, such as
space and water, and a lack of integration between green and built infrastructure during planning; (4)
environmental concerns (such as recognition of a lack of urban biodiversity and reduced availability of
pesticides and fertilisers); (5) climate change impacts on the survival of existing trees, particularly mature
trees, and restrictions on tree planting where solar access is required; (6) the availability and cost of a
skilled workforce to maintain trees and landscapes.
At this point, the paper reflects upon urbanisation and the links between people and nature, from both an
individual perspective and a city-wide perspective. Current social attitudes towards nature vary amongst
people and these attitudes will affect the extent to which plants and natural systems are valued and
encouraged within cities.
The paper then explains why urban tree canopy and other vegetation matters, to both people and the
urban ecosystem, and how trees and other vegetation can help make Canberra sustainable. Whilst there
has been some discussion of the benefits of urban forests and urban green amongst parks and tree
professionals, many of the messages are yet to reach key decision-makers involved in planning or,
indeed, the general community. Contributions towards sustainability are discussed in four major areas:
(1) environmental and ecological, including human comfort, energy budgets for buildings, mitigation of
urban heat islands, air quality improvements, carbon dioxide uptake and stormwater and catchment
benefits; (2) aesthetic and visual; (3) social and psychological, with a focus on the restorative power of
"green nature"; and (4) economic benefits to business.
Urban tree canopy and other vegetation are generally valued for their aesthetic and visual contributions to
the city; indeed, these are often the main reasons that initial plantings are undertaken when a new city or
suburb is established. A focus on these values, however, contributes to a perception that "green
infrastructure" in cities is much less important than built infrastructure. Similarly, locally native vegetation
may be retained initially, but is often sacrificed when a city expands. We are now entering a period of
urbanisation where "the city" and "nature" are being examined together, in the field of urban ecology, and
there is a much stronger focus on the function of city ecosystems rather than simply on appearance. This
should see urban tree canopy and other vegetation receive a higher priority for their functional
contributions to the city and its people.
Dr Jane Tarran / UTS / ACT PLA Bush Capital Workshop / 7 April 2009 / Improving Canberra's sustainability: Why
urban tree canopy and other vegetation matters
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Research into the critical roles played by urban tree canopy and other vegetation in environmental,
ecological, social and psychological aspects of urban living and city function is a relatively recent
phenomenon, with most research having taken place over the last 20 years or so. Armed with this new
knowledge about the environmental and social benefits of urban trees and other vegetation, especially in
relation to city sustainability, it is important to move forward in three key areas. Firstly, these broader
benefits need to be promoted and marketed more widely, especially to key decision-makers, planners and
the general community. Secondly, it is essential to plan proactively for the incorporation of urban forests
and other urban vegetation into the fabric of the city. It is important not to regress by losing beneficial
vegetation that currently exists or by taking planning approaches in future developments that "design out"
the possibilities of having vegetation, especially trees, in the areas where people live, work and play.
Thirdly, it is essential that adequate resources are provided to maintain and extend urban green.
This paper was prepared in response to an invitation from the Australian Capital Territory Planning and
Land Authority (ACT PLA) to consider sustainability issues related to Canberra as the "Bush Capital". The
focus requested for this paper was the vegetation itself, especially the urban forest (and urban green more
generally), in relation to the benefits of plants, including trees, to Canberra's future sustainability. The
background I bring to this paper is some 20 years professional experience as a plant scientist,
researching plants and landscapes in and around urban areas, chiefly Sydney, but with observations
elsewhere in Australia (including in Canberra over this period) and overseas. In my work with urban
vegetation and its management, I have explored a wide range of plants and plant communities in urban
areas, including street trees, formal and informal parks, home gardens, remnant bushland undergoing
regeneration and revegetation projects, using locally indigenous species. In preparing this paper, I have
reviewed, in addition to the literature dealing with urban vegetation, various relevant websites (e.g. ACT
Commissioner for Sustainability and the Environment, ACT Natural Resource Management Council and
ACT Territory and Municipal Services) and the document "Sustainable Future Objectives" in which drivers
of change are considered in relation to the built form, urban ecology and the community.
This paper is linked to the powerpoint presentation of the same name delivered at the ACT PLA
Sustainable Future "Bush Capital" Workshop (no. 4) on 7 April 2009. It is useful to read both documents
together, especially for the pictorial material included in the powerpoint presentation.
2.
Vegetation focus
The vegetation focus for this paper relates to the vegetation of urban and suburban areas. These are the
areas where people live, work and play - that is, the areas in which people come into contact with plants in
their daily lives. These areas therefore encompass public and private areas, such as government,
institutional, residential, commercial, industrial and open space areas, including streets. Also included are
areas of regenerated bushland, where plants of the locally indigenous flora are encouraged back into the
landscape. Other consciously planted areas may have plant species from various sources - exotic
species from other continents, "native" species from elsewhere in Australia (or exotic Australian species)
and locally indigenous species. The plants are established over time, for various reasons, and perform a
range of functions in addition to those intended. Food plants in urban and suburban areas are also
included.
There is a particular focus on what is known as the "urban forest" - that is, all the trees and shrubs in and
around urban areas (Miller, 1997), including street trees, park and garden trees and shrubs, as well as
bushland. The urban forest occurs on both public and private land and includes woody plants that have
been planted intentionally as well as trees remaining from previously forested areas, either singly or in
small groups, or within a more extensive bushland remnant. The urban forest is managed for the
physiological, sociological, economic and aesthetic benefits it provides (Helms, 1998).
Over time, there has been a change in our focus from individual trees (or avenues) to the urban forest.
The focus on individual trees is associated with issues such as tree species selection, planting,
establishment and maintenance through to maturity. Whilst not abandoning the recognition of the
importance of individual trees, we have come to focus more on our populations of urban trees, or the
urban forest.
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At its most basic level, the urban forest is measured by the canopy cover percentage of the total area.
With a focus on trees more than on shrubs (Konijnendijk & Randrup, 2002), another measure of the urban
forest is the number of trees. More detailed descriptions of the urban forest include information on tree
species distribution and composition, community diversity and abundance, distribution of tree sizes and
ages, tree health and other parameters.
Urban forestry emerged in the USA in the 1960s from traditional forestry, as foresters sought to engage
with urban residents, at a time when traditional forestry was receiving more attention from urban dwellers,
including those from the growing environmental movement (Miller, 1997). The USDA Forest Service set
up a network of research ecologists across the USA in the 1980s and the 1990 Farm Bill provided funds
for tree planting, education and research. A significant achievement was the Chicago Urban Forest
Climate Project (McPherson et al., 1994) which demonstrated the range and extent of environmental
benefits associated with the urban forest and provided a model for research in other cities. Canberra was
probably the first city in Australia to embrace urban forestry, no doubt because of its early history of urban
tree planting and links between forestry at CSIRO, ANU and forestry groups overseas, particularly in the
USA.
The conceptual shift from a focus on individual trees to the urban forest as a whole appears to occur when
trees start to die or need replacement. The disastrous losses of urban elm trees in the Northern
Hemisphere as a result of Dutch elm disease undoubtedly hastened the adoption of urban forestry in the
USA. In a similar way, we are beginning to see, in Canberra and elsewhere in Australia, some of our
early and significant plantings of landscape trees reaching the end of their lives and entering senescence
or dying, often as a result of additional environmental stress, such as lack of water or attack by fungal root
pathogens.
The urban forest, however, is much more than canopy area and numbers of trees. Similarly, the remnant
grassland and bushland are much more than measures of area and condition. Vegetated areas can be
regarded as the "natural capital" of Canberra or the principal of an investment in trees and bushland that
keeps providing returns, year after year, as benefits to people and their environment. The urban forest
also constitutes a window into the soul of a city (McPherson, 1998a) - it reflects the values, lifestyle
preferences and aspirations of past and present residents, and it is the legacy that current generations
leave for future generations.
The urban forest is also recognised as a key contributor to high quality urban environments. In fact, it is a
slide of Canberra from Mt Ainslie, across to Parliament House, that I most frequently show to illustrate the
achievement of an outstanding urban forest - one that has been well-planned and well-resourced.
Canberra's urban forest rates highly by world standards in terms of number of trees per capita (Banks &
Brack, 2003), which is about 1.3, compared with 0.4-0.5 for cities in the USA in the 1980s and 1990s.
Unfortunately, however, urban forests are often taken for granted, overlooked, or under threat, despite the
fact that they are quietly working full-time to make cities more livable (McPherson & Simpson, 2003). For
example, it is disturbing to see, from aerial photos of some of the newer Canberra suburbs, such as
Gunghalin, that space is not available for trees on house lots containing houses with large footprints.
The ACT also has significant areas of natural vegetation with more than half the territory protected in
conservation reserves (ACT Natural Resource Management Council, 2008). Nevertheless, there are
some 39 plant and animal species and two ecological communities that are either vulnerable or
endangered, with the at-risk groups occurring mostly in the lowland open woodland and grassland areas
where the city is located and rural activities occur. Of particular concern to these threatened species and
communities are the effects of urban expansion, fragmentation and pest plants and animals.
Plants, and especially large trees, have another critical role to play in 21st century cities, including
Canberra, in that they are the most conspicuous element of nature in a city, co-existing with built
infrastructure and people. They also support other elements of nature, such as urban fauna. In fact, in
the relatively new field of urban ecology, where ecological models developed in natural areas are applied
to urban areas (Lord et al., 2003), the city itself is viewed as an ecosystem - a new type of ecosystem,
created by humans specifically for dwelling (McIntyre et al., 2000).
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For a city to be sustainable into the future, the functioning of the city, both ecologically and socially, will be
of prime importance, rather than just the city's appearance (Platt, 2004). To support this approach, there
needs to be a stronger appreciation by people of the role of nature and its functions in urban areas, the
establishment of links between humans and nature in urban areas and the development of new strategies
to restore ecological services (Daily, 1997) in urban areas. Urban forests and other vegetation, therefore,
form the basis of this recognition of the importance of nature in urban areas.
3.
Canberra's landscapes over time
3.1
From Garden City to the Bush Capital
Canberra appears to be unique in Australia in that it is the only city whose design arose out of an
international competition and whose entire subsequent development has been continuously based on a
plan (Fitzgerald, 1987). Obviously, if the plan and its implementation are appropriate, both at the start and
as the plan evolves, you can achieve the best possible outcomes.
Also unlike many other Australian cities, Canberra is fortunate in having very good documentation of some
aspects of its landscapes, particularly urban tree planting, thanks to conscientious early record keeping
during three major periods of landscape establishment as identified by Banks and Brack (2003). These
periods were led by Charles Weston (1913-1926), by Lindsay Pryor (post-World War Two until 1958) and
by the National Capital Development Commission (NCDC) and its successors (period 1958-present). It is
worthwhile noting the early emphasis on trees, since this has influenced landscape directions and
community attitudes to a significant extent. These tree records have provided the basis for analysis by
forestry associated academics from the Australian National University (e.g. Banks & Brack, 2003; Brack,
2002; Gilbert & Brack, 2007). As well, there are books on trees in Canberra for the general community
(e.g. Pryor, 1962; Edwards, 1979). It would appear that extensive documentation continues to this day, as
indicated by the contents of government-related websites (e.g. see ACT Natural Resource Management
Council, 2008; ACT Commissioner for Sustainability and the Environment, 2008; Department of Territory
and Municipal Services, 2006a & 2007).
Planning for Canberra's future urban landscapes began in 1911 on the site that had been grazing land in
the southern tablelands of New South Wales. It was described by Banks and Brack (2003), with a forestry
background, as " ... essentially a treeless, wind-swept and dusty valley divided by the Molonglo River,
surrounded by forested hill crests and back-dropped with the Snowy Mountains." By 2003, it was
described as "... a city of over 300,000 people living in a well-treed and spacious environment" and " ... a
magnificent example of what can be achieved with holistic landscape planning."
Canberra today is described as a city in a forest or "The Bush Capital". The city and suburbs were
imposed on, but now remain interspersed with, open grass and land with trees ('the bush") (ACT Natural
Resource Management Council, 2008). Nowadays, the "bush" is seen to include all the natural assets of
the ACT - the upland forests, woodlands and grasslands, soils, waterways and the biodiversity in its
landscapes, including urban ones.
One component of the forest of Canberra is the urban forest - the trees and shrubs (or woody plant
material) in and around urban areas, on public and private land, including plantings and bushland
remnants. The urban forest was planned from the start, with trees to be planted in streets, parks and
gardens to reinforce the design (e.g. to mark land axes) and to ameliorate the adverse environmental
conditions of the grazed sheep paddocks, like wind and dust (Banks & Brack, 2003). Trees were also
seen as improving the barren landscape view. Whilst the urban forest is a natural asset, it does not
necessarily involve planting tree and shrub species that are locally indigenous to the area, deriving from
the forests and woodlands nor planting designs that might mimic the structure of these vegetation
communities.
In the first major establishment period (1913-1926), Weston undertook street plantings in the first suburbs,
as well as Telopea and Haig Parks, with formal arrangements focussing on the optimal presentation of
individual species, in the gardenesque tradition of his training (Banks & Brack, 2003). He also carried out
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major reafforestation projects on adjacent hills (e.g. Mt Ainslie), using native trees, and established trial
afforestation projects outside the city using exotic pines and cork oak to test these species in the local
environment.
In the second major establishment period (post-World War Two to 1958), Pryor renewed the planting
program, with massed plantings in informal arrangements, particularly filling spaces between major
buildings (Banks & Brack, 2003). He expanded the species used to over 100 species, but continued the
focus on exotic species. Streets continued to be planted with single species and new species were
trialled in both streets and arboreta. The National Botanic Gardens, devoted to native flora, were also
established at this time.
In the third major establishment period (1958-present), which saw Canberra's population increase and
new development expand into valleys based on the Y-plan, fundamental changes occurred in landscape
design and preferred tree species (Banks & Brack, 2003). Street trees were now planted using multiple
species per street and in an irregular manner, to give an informal feel, rather than the previous single
species in a regular, formal planting pattern. As well, Australian native plants, especially eucalypts, were
used much more extensively, with limited used of exotic species (although there has been a recent return
to a more equal use of native and exotic). Banks and Brack (2003) claim that the use of eucalypts, and
their visual blending with the adjacent hill top eucalypt forests, led to the term "The Bush Capital". Some
recent trends include a loss of tree density and species planted in the newest suburbs, outsourcing of field
operations and provision of nursery stock, and a reduction in the diversity of species used (Banks &
Brack, 2003).
3.2
Natural vegetation of the area
There was, however, another landscape in the area of Canberra - the one from pre-grazing days. The
Botanist Lindsay Pryor (1962) describes it as treeless, grassland vegetation in the valley of the present
city area. Eucalypt woodlands adjoined the grassland and there were areas of open forest as well. Both
the Natural Temperate Grassland and the Yellow Box / Red Gum Grassy Woodland are today listed as
endangered ecological communities, largely as a result of clearing for agriculture followed by urban
expansion (ACT Natural Resource Management Council, 2008).
It appears that, in recent times, the locally indigenous vegetation communities, especially the lowland
woodlands and grasslands, have come to the fore in the thinking about Canberra's landscapes and their
future. There is a recognition that these natural assets are a limited resource and should not be
automatically sacrificed to build new suburbs (ACT NRM Council, 2008). Whilst over 50% of land use in
the ACT is protected in conservation reserves, it is the potential loss of particular ecological communities
and plant and animal species, close to where people live and work, that drives the urge to protect them.
In the ACT, some 39 plant and animal species and two ecological communities are either vulnerable or
endangered (ACT Natural Resource Management Council, 2008).
Unlike the situation for the trees of the urban forest, it is noted that there is "only limited information on the
underlying trends in ecosystem health and condition" (ACT Natural Resource Management Council,
2008), presumably as a result of their more recent recognition.
There appears to be a dynamic and passionate community of people involved in the care of bushland,
including grasslands, in and near Canberra, based on recent annual reports in The Scribby Gum
newsletter (Ning, 2008). Nevertheless, it is not clear whether this interest extends to the broader
population of Canberra. It may be that many local residents are so impressed by the conversion of the
former grazed paddocks to the leafy and well-treed national capital, as exemplified by the terms "Garden
City" and "Bush Capital", that they are not necessarily as familiar with the pre-European natural vegetation
that was removed to make way for Canberra.
Whilst there is some information on the original vegetation of Canberra, including bushland and
grasslands, much of this is scattered across the web in electronic form and not easy to synthesise into a
meaninngful story about the past, present and possible future of vegetation in Canberra and the ACT. In
this regard, user-friendly publications, like those available for Sydney as a whole (Benson & Howell, 1990)
or at a finer scale for local areas, such as along the Cooks River catchment in Sydney (Benson et al.,
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1999), allow people to learn about the original natural vegetation of their neighbourhoods, by providing
maps (down to street level in the case of the latter publication) of the original native vegetation of the
entire area. Descriptions of nearby remnant vegetation and underlying soils, species lists and
descriptions of plant appearance also help people to use locally native species for revegetation projects in
previously cleared areas, including on house blocks if residents wish to use species that are already
adapted to local conditions of soil and climate, including water availability. In fact, the use of locally native
species in waterwise and drought-friendly gardening practices can avoid problems of new bushland
weeds developing when similarly adapted but exotic plants from other locations are used. Books like
these, directed towards the general public and with the vegetation story embedded within a broader
history of change, help establish a personal connection to the land and its original native vegetation. It
could be argued that a small booklet like this could help raise awareness amongst more of the local
community as to the special values of the locally indigenous grasslands and other bushland.
3.3
An alternative view of Canberra's landscape
A further observation on Canberra's urban forest was made by Bruce Mackenzie on overlooking the city of
Canberra in the autumn of 1969, from the top of Red Hill, northwards along the axis of Northbourne
Avenue (Mackenzie, 1996). As someone who had a strong appreciation of the natural environment,
through numerous visits to wild places, he described his "revelation on Red Hill" as he saw before him "...
an alien landscape, albeit laid out like a grand tapestry of rich detail, colour and texture ... patterned and
disciplined with consummate skill. I felt offended whenever the special qualities of the native landscape
are wasted or worse, humiliated - in this instance even with the best will in the world and with such
indisputable competence." He concluded that the bush might be retained, but always in the background.
In arguing the case for a design ethos driven by the intrinsic nature of Australian landscape systems, but
also embodying design excellence and functional effectiveness, Mackenzie (1996) stressed that one of
the underlying foundations was sustainability, based as it was on Australian landforms, soils and flora. He
believed that this kind of landscape could be strong enough to absorb gardenesque landscapes of
suburbia. Seddon (1972 & 1979), similarly, had noted the importance of understanding and working with
what was locally distinctive (in geology, landform, soil, hydrology, natural vegetation and cultural
landscape) in order to achieve local identity and sustainability. In 1996, Mackenzie observed, in the
almost 30 years since his "revelation on Red Hill", that the developed landscape of Canberra had taken a
significant directional change and that it now had the colours, scents and textures of a created Australianinspired landscape, in a mix with exotic materials.
Two of the best-known, created landscapes in Canberra are the Sculpture Garden at the National Gallery
of Australia and the Garden of Australian Dreams at the National Museum of Australia - two vastly
different gardens, but indicative of the debate that occurs around landscape-making in Australia. The
springtime festival, Floriade, is also part of Canberra's "landscape". It is worthwhile remembering that
these public landscapes engage with visitors, including the local community, and help to shape their ideas
of appropriate landscapes for Canberra. Perhaps the landscapes of the natural grasslands and bushland
are less promoted, and less well-recognised, by the majority of the local population.
4.
Threats to landscape and urban forest sustainability and some solutions
Sustainability for the ACT Government "is about providing for people, protecting our place and creating
prosperity - now and into the future" (Department of Territory and Municipal Services, 2006b). To achieve
this, it is important to protect and enhance the Earth's life support systems. Sustainability recognises the
interdependence of social, economic and environmental well-being and aims to be based on equity and
fairness.
Sustainability, as it applies to the vegetation component of Canberra, the "Bush Capital", should consider
the full range of vegetated areas •
vegetation of governmental, residential, commercial and industrial areas
•
vegetation of urban "open space"
•
broadacre
•
rural
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•
•
•
•
hills, ridges and buffer areas
river corridors
mountains and bushland
plantation forestry
This paper will focus on the first two areas, particularly in relation to the urban forest of woody plants in
and around where people live, work and play. It will also touch on buffer areas and bushland nearby (but
not the more distant nature conservation areas).
Whilst the landscape setting of Canberra is one of its characteristics, there are various threats to its
sustainability •
lack of understanding of the benefits of urban vegetation, including trees, and limited monetary
quantification of these benefits or benefit:cost analyses
•
lack of powerful and articulate lobbyists for urban vegetation, including trees, and vegetation
specialists able to engage with other professionals operating in the urban environment
•
planning yet to fully embrace urban ecology, and recognise urban ecosystems as interactions
between organisms, including humans, and the biophysical environment - planning yet to focus on
the function of nature in urban areas rather than just appearance
•
maintenance requirements of many mature trees, as the oldest planted trees approach 100 years
(Banks & Brack, 2003)
•
planning for and ultimate replacement of trees reaching the end of their lifespans
•
retaining existing trees or establishing new trees in inner areas undergoing densification
•
establishing new trees in new suburbs which often show changing house-building preferences
•
competition for water amongst various user groups
•
competition for space generally with built infrastructure, which is usually given priority, and a lack of
integration of "green infrastructure" and "built infrastructure" at the planning stage
•
potentially reduced availability of pesticides (because of concerns with environmental and human
toxicity) and fertilisers (because of nutrient enrichment of waterways) that may be needed by some
existing plants
•
temperature- and moisture-related environmental changes associated with climate change - higher
temperatures, increased winds in summer months and drier average seasonal conditions
•
increased frequency of extreme weather events including storms
•
increased risk of bushfire
•
solar access for photovoltaic and solar hot water panels
•
cost and availability of human labour to maintain trees and landscapes
•
reliance on volunteer labour for bush regeneration and inadequate recognition of their contribution to
the common good
Some solutions to the various threats to landscape and urban forest sustainability can be identified and
are described below, grouped under the threats noted in the headings.
(1) Lack of vision and knowledge regarding the urban forest
There is substantial research, mainly overseas and especially in the USA, regarding the benefits of the
urban forest, including quantification of these benefits. These benefits are applicable to Canberra and can
be promoted, but local research, in addition to that carried out by Brack (2002), would also be worthwhile.
Landscape and urban forest issues need to be embedded in all planning, including that of new suburban
development and redevelopment, so that the landscape advantages that Canberra currently enjoys are
not diluted over time. Given the concentration of educational and research institutions in Canberra, it
would be possible to undertake long term urban ecological research in the city along the lines of the Long
Term Ecological Research (LTER) Network (US Long Term Ecological Research Network, 2004)
established in the USA, where, for the first time in 1997, two new LTER sites were established in urban
ecosystems, as opposed to all the previous sites which had been in "natural" ecosystems (Parris, 2004).
(2) Current and future problems for trees
It is important that existing research which models Canberra's tree populations over time (Banks et al.,
1999; Banks & Brack, 2003) is continued, so that workloads and required resources can be estimated.
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Whilst those in charge of tree species selection in Canberra have constantly evaluated tree performance
and refined their recommended species lists (Department of Territory and Municipal Services, 2006a), it
will be even more important, in a future dealing with climate change, to understand the climatic tolerances
of species and not recommend or use species at their limits. In relation to densification, it is important to
plan for tree canopy as part of densification and to re-examine building codes that "design out" places for
trees. In a hotter future, and with much more expensive energy required to provide air-conditioning, there
may well be a return to tree shade as a cost-effective option for cooling houses and low-rise apartment
buildings. In fact, for the latter, a maximum building height equivalent to tree canopy level (3-4 storeys)
provides visual buffering and shade potential. High-rise apartment buildings are unable to make use of
tree canopy as a shading strategy in summer.
(3) Competition within city ecosystems
Trees and other vegetation compete with various user groups for water (if reliant on other than natural
rainfall) and with built infrastructure for space. Some solutions regarding water use can be found in the
selection of species, including locally indigenous species, that have their water requirements met by the
local rainfall, as well as the use of Water Sensitive Urban Design and Xeriscape® principles. In
embracing waterwise gardening, it is important for homeowners and managers of public landscapes to
recognise that any exotic plant adapted to survive in a certain environment, without additional inputs of
water and/or nutrients, may become a weed when transferred to a similar environment elsewhere. If trees
are retained in areas undergoing redevelopment, it is important to provide conditions, especially around
the tree root zone, that are as stable as possible to prolong the life of the trees.
(4)
Environmental concerns
An emerging issue in city ecosystems is the lack of urban biodiversity and a lack of connectivity between
bushland remnants. Increased use of locally indigenous species and vegetation communities would
provide a base for local biodiversity and would avoid the problem of exotic species becoming
environmental weeds, displacing locally native plants elsewhere. The promotion of "bush gardening" to
homeowners, using locally indigenous plants appropriate to site soils and aspects, would have the dual
benefits of increasing biodiversity and saving water. In this regard, the publication of the booklet referred
to previously in section 3.2 would be of enormous educational and inspirational value. Similarly, the ready
availability of locally indigenous plants of known provenance is important to the success of a strategy such
as this.
Another environmental concern relates to possible future limitations on the use of pesticides and fertilisers
in landscapes and gardens, for reasons of human and environmental toxicity associated with the former
and nutrient enrichment of waterways with the latter. It may be that, in the future, species selection will
rely more heavily on plants that can grow in the Canberra area without the protection provided by the use
of pesticides and without the additional nutrients provided by fertilisers.
(5) Climate change
Climate change is likely to see plant survival affected by higher temperatures, increased winds in summer,
and dryer average seasonal conditions, as well as by more frequent extreme weather events (such as
storms) and bushfires. As well, it is likely that solar access will become more important, as an energy
saving strategy. Some solutions to the threats posed by climate change to vegetation include refining
species selection so that plants are not used at the limits of their climatic tolerances, continuing the tree
hazard management systems that are in place, researching tree survival after storms to provide
information to refine future species selection and reviewing and developing bushfire planning procedures
and requirements for protection zones at suburban-bushland interfaces. As regards the provision of solar
access, it is important to model future tree canopies near buildings so that north-facing areas are kept
free. As well, it is likely that exotic deciduous trees will continue to be recommended and used near
buildings, since there are few, if any, local deciduous tree species (Correy, 1992).
(6) Workforce issues
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Workforce issues impacting on the sustainability of the landscape and urban forest in Canberra include
the cost and availability of a skilled workforce to maintain trees and landscapes and the reliance on
volunteer labour for bush regeneration, with inadequate recognition of the contribution made by these
volunteers to the common good. It may be that both entry-level and professional training needs to be
expanded in targeted areas, given anecdotal information on reduced education taking place in
horticulture, agriculture and related areas. For some members of the aging population, however, certain
tasks within landscape maintenance and bush regeneration may be undertaken, with concomitant benefits
of exercise, social contact and reduction of depression. It has been found that ecological restoration
carried out by volunteers yields psychological benefits, including an overall sense of satisfaction from
restoration and a variety of specific satisfactions (Miles et al., 1998). For volunteers engaged in such
activities, which contribute to environmental sustainability in Canberra, incentives, including rate rebates,
could be considered, similar to those given for water and energy savings. In one sense, not providing
such incentives or rebates sends out a message that the sustainability of the landscape and its vegetation
is less important than sustainability in water and energy.
5.
People, urbanisation and links to nature
For some time now, humans have been undertaking a large scale planetary experiment, removing
vegetation in some areas and making cities, all the while increasing their population such that Homo
sapiens is now the dominant species on earth, particularly in terms of resource use and modification of the
land (Vitousek et al., 1997). For a range of reasons, people have sought to maintain or introduce
vegetation into their cities (Miller, 1997). Whether for food, or ornament, or to improve recreational
spaces, we have planted trees and other plants in the belief that they make better places in which to live
and work.
Our responses to nature and trees probably occur at both subconscious and conscious levels. E.O.
Wilson uses the term "biophilia" to describe our subconscious connection to the rest of life and suggests
that it has its basis in human evolution (Miller, 1997). Biophilia refers to both positive and negative
responses to elements of the natural world that had survival value to our evolutionary predecessors e.g.
our preference for savanna-like parkland (a positive) and our fear of spiders and snakes (a negative).
At the conscious level, urban ecologists are now studying the role of nature and its functions in urban
areas and more people are recognising the importance of nature as we attempt to develop ecologically
sustainable cities for the 21st century (Platt, 2004). For example, where previously there were exotic
kikuyu grass lawns near a concrete stormwater drain, there may now be a small wetland around a reshaped water body, created using appropriate locally native plant species in zones from the water up to
higher levels. The concept of "ecological services" provided by nature to human society was developed
by the biologists Paul Ehrlich and Gretchen Daily (Daily, 1997) and these services, provided in both rural
and urban settings, have helped to reinforce the idea that cities and nature are not mutually exclusive.
Current social attitudes held by an urban society towards nature are seen as a continuum of values,
involving both subconscious and conscious components (Miller, 1997). They are reflected in the following
five groups, which are likely to be present in Canberra, as elsewhere *
people with a love of and dependency on nature - people in this group must live in nature and draw
subsistence from it; this group includes remaining hunter-gatherer societies and individuals who seek
to live in wilderness areas
*
people who seek renewal in nature - many city dwellers reflect this attitude, by renewing themselves
spiritually through periodic contact with nature, whilst spending most of their lives in urban areas at
urban tasks
*
people who prefer tamed nature - this group includes people who are satisfied by occasional contact
with nature, but prefer the tamed nature of yards, high density camping grounds, or motorised
outdoor recreation
*
nature neutrals - people who have no interest in nature and are quite comfortable in areas devoid of
nature; nature does not matter to them
*
nature haters - people who see nature as messy or threatening or in conflict with their lifestyle and in
need of control by humans
9
As well as these general attitudes to nature, there is some evidence that the cultural background and
landscape history of people affects their perceptions of particular plants and plant groupings, such as the
urban forest (e.g. see Fraser & Kenney, 2000) and that socio-economic status influences the types of
plants used in residential gardens, such that higher incomes are associated with a greater presence of
trees (e.g. see Kirkpatrick et al., 2007).
Another aspect of our relationship with nature, and a rather disturbing one, is a recently recognised
condition known as "plant blindness" (Moss Warner, 2004), with the symptoms of *
the inability to see or notice plants in one's environment
*
the inability to recognise the importance of plants in the biosphere and in human affairs
*
the inability to appreciate the aesthetic and biological features of plants
*
the anthopocentric ranking of plants as inferior to animals, so that plants are believed to be not
worthy of human consideration
People with "plant blindness" are probably "nature neutrals". It is possible that this is a growing group of
people, as societies become more urbanised, housing types change, indoor recreation increases and
people have less and less contact with nature in their daily lives.
As we enter the 21st century, we are confronted with a paradox - never has the role and function of nature
in cities been more important, especially to city sustainability, but this is occurring at a time when we have
more people in urban areas who are more out of touch with nature, blind to it or actively "hate" it. Whilst
many people will respond to unusual or spectacular plants, the challenge is to help them to understand
the critical importance of the "everyday" plants in their urban surroundings.
6.
How the urban forest can help make Canberra sustainable
The urban forest and other vegetation can help make Canberra sustainable by providing benefits in four
major areas: (1) environmental and ecological; (2) aesthetic and visual; (3) social and psychological; and
(4) economic. Whilst the trees of the urban forest, and particularly large trees with substantial canopies
and biomass, are critical to the provision of environmental and ecological benefits, both trees and other
vegetation (shrubs, ground covers, vines, grasses and food plants) can contribute to benefits in the other
three areas.
6.1
Environmental and ecological benefits
Environmental and ecological benefits of urban forests are evident in several different areas - in climate
effects and increased human comfort, contributions to building energy budgets, mitigation of the Urban
Heat Island effect, improvements in air quality, carbon dioxide sequestration and catchment benefits.
6.1.1
Climate effects and human comfort
The urban forest provides shade in summer, for people and their cars, as well as for surfaces (e.g. walls,
footpaths and roads) that reradiate heat. By providing both direct and indirect shade in summer, human
comfort is increased. Shading can protect asphalt pavements and reduce repair costs (McPherson &
Muchnick, 2005).
Urban vegetation in general, and trees in particular, can effectively reduce air temperatures during hot
summer days, by shading and transpirational cooling. Such transpirational cooling (evapotranspiration) is
the reason that trees have been called "nature's air conditioners" (Grey & Deneke, 1986), with one tree
being equivalent to 5 room air conditioners running 20 hours/day. Cooler surface temperatures, which are
related to air temperatures, are found in urban areas where there is greater vegetation cover, with a
o
reduction of up to 8 C recorded in one study (Pauleit & Duhme, 2000).
Trees can also act as windbreaks to reduce cold winter winds and so offer benefits to both people and
buildings (Miller, 1997).
10
6.1.2
Energy budgets for buildings and cities
Well-placed trees can reduce building energy use (McPherson, 2004). Summer cooling of buildings via
shading and transpirational cooling can reduce air-conditioning needs. Trees can reduce the wind speed
and cooling effects of winter winds, reducing the need for heating.
Trees can intercept up to 90% of summer solar energy and thus provide substantial reductions in interior
temperatures (Heisler, 1986). Air-conditioning energy savings as high as 80% have been measured, but
savings of 25%-50% are more common and are found in both dry and humid locations (Meier,
o
1990/1991). A 5% increase in canopy cover can reduce summertime air temperatures by 1-2 C
(McPherson & Rowntree, 1993), but energy efficient landscaping will be different for different climatic
regions. For Canberra, the requirement for shade in summer coupled with solar penetration in winter will
see continued use of deciduous trees combined with thoughtful location of evergreen trees to allow sun in
winter where required. Reductions in peak cooling demand of 2-10% also occur with strategically planted
shade trees (Simpson & McPherson, 1996).
Scaling up of energy savings from buildings to cities can yield potentially very large savings. This has
been recognised by cities in the USA through the development of partnerships for tree planting involving
citizens, Energy Utilities, Environmental Protection Authorities, plant nurseries and government agencies.
These partnerships are designed to save energy and delay the need for new power stations (McPherson
& Rowntree, 1993; Simpson & McPherson, 1996; McPherson & Simpson, 2003; Harris et al., 2004).
6.1.3
Building energy budgets scaled up for states
For some time, California has been actively pursuing peak load reduction strategies to cope with
population increases (McPherson & Simpson, 2003). The existing urban forest reduces annual air
conditioning energy use by 2.5% (worth US$490 million) and peak load use by 10% (worth US$780
million). Planting 50 million new shade trees, strategically placed to offer the most energy savings (e.g. to
the west of buildings) could, over 15 years, reduce cooling energy use by 1.1% (saving US$3.6 billion)
and peak load demand by 4.5% (saving $7.6 billion). These new shade trees would be planted on 1/5 of
the empty sites identified as having shade potential. This strategy was found to be cost-effective,
providing savings equivalent to seven 100-megawatt power plants.
6.1.4
Mitigation of the Urban Heat Island
Cities are Urban Heat Islands (UHI), with the central city being the hottest and lower temperatures being
recorded progressively through suburban to rural areas (US EPA, 2009). Temperature differences of
o
more than 5 C have been observed between city centres and more vegetated suburban areas (Mizuno et
al., 1990/1991). The high temperatures in the central city areas result from less vegetation (which limits
the cooling effect achieved by evaporation of moisture from plants and soil), more buildings, asphalt and
concrete (which absorb solar radiation and emit long long-wave radiation that heats the atmosphere) and
high energy use (emitted as waste heat). Urban areas have also become warmer over the last 50 years,
o
increasing by 0.8 C/decade in the USA (McPherson & Rowntree, 1993). Electricity demand increases by
o
3-4% per C increase in temperature. The UHI effect also causes increases in carbon dioxide emissions,
water demand, ozone levels and human discomfort and disease.
The hotter central city areas are a problem not only for city workers but, increasingly, for city residents as
more people are encouraged to live closer to the city centre in areas which have been targeted for
densification in Canberra. In fact, if existing tree canopy in suburbs near the city is lost, and provision is
not made for future canopy during densification, problems with urban heat could well be exacerbated.
Urban trees and other urban vegetation can reduce the UHI effect by using solar energy to evaporate
water from leaves and reducing building energy demands. Increasing the tree cover by 25% in
Sacramento (California) and Phoenix (Arizona) is calculated to decrease mid-summer temperatures by 3o
6 C (Miller, 1997, pp. 63-65).
In a recent project, National Aeronautics and Space Administration (NASA) researchers in the USA
investigated the urban heat island effect in New York City with the aid of a computer-based regional
11
climate model. They measured ways to reduce urban heat island effects by using light-coloured surfaces
that reflect sunlight, planting "urban forests" including vegetation at street level and creating "living roofs"
on top of buildings. In making recommendations to policy-makers, they noted that "... vegetation is a
powerful cooling mechanism. It appears to be the most effective tool to reduce surface temperatures."
(NASA, 2006).
6.1.5
Air quality improvement
Most urban air masses are chronically polluted, with problems compounded by temperature inversions
(Miller, 1997, pp. 65-68). Major air pollutants (Nowak, 1994) include particulates which have been
associated with respiratory diseases (asthma), cardiopulmonary diseases, and cancer. Other pollutants
are gases, either released directly or synthesised.
Trees remove air pollutants and improve air quality (McPherson, 2004; Grey & Deneke, 1986) since they
intercept particulates on their surfaces, absorb gases through stomates in leaves, lower air temperatures
(and hence reduce ozone levels and power plant emissions), shade parking lots (and hence reduce
hydrocarbon emissions from cars) and release oxygen through photosynthesis. In Sacramento, the urban
forest removes 1,457 tonnes of pollutants annually (ozone, particulates <10µm, nitrogen dioxide and
sulfur dioxide), with a value of US$28,763,000 (Scott et al., 1998).
6.1.6
Carbon dioxide uptake and storage by trees
The concentration of carbon dioxide (CO2) in the earth's atmosphere has been increasing since the
industrial age, accompanied by global warming which is expected to have several adverse effects. Urban
forests are important storage sites for carbon dioxide, with the amount stored being proportional to
biomass - that is, bigger trees with more canopy and larger trunks store more CO2 (McPherson, 1998b).
Urban forests also reduce atmospheric CO2 by reducing the demand for air conditioning and heating,
thereby reducing power plant emissions. Sacramento County's urban forest provides, each year, a net
removal of 304,200 tonnes of CO2, worth US$3.3 million (McPherson, 1998b).
6.1.7
Stormwater and catchment benefits
Urban forests provide catchment benefits by reducing problems associated with urban stormwater runoff
which is of concern because of its quantity and pollutants. Trees act as mini-reservoirs - they intercept
precipitation, store it on surfaces, slow its descent to the soil and assist infiltration (McPherson, 2004). In
Sacramento County, the urban forest intercepts 11% of the annual rainfall, with greater interception in the
suburbs than the city (Xiao et al., 1998).
6.1.8
Benefits of Canberra's trees in publicly managed areas
Continuing research into the publicly managed urban forest in Canberra, involving about 400,000 planted
trees, Brack (2002) estimated that these trees had a combined value of US$20-67 million over a 5-year
period (2008-2012) based on their contributions to reduction in energy consumption, pollution mitigation,
hydrology amelioration and carbon sequestration. This value does not include trees on private lands and
naturally regenerated lands and so is likely to underestimate the environmental value of Canberra's entire
urban forest. As well, this study did not include values attributable to landscape and aesthetic
contributions to Canberra.
6.2
Aesthetic and visual benefits
Aesthetic and visual benefits of urban trees and other urban green are well described (Miller, 1997) and
understood by many people. Plants are used to define spaces in landscapes and to provide contrasting
enclosed and open spaces. Plants appear as walls, ceilings and floors. With different forms, colours and
textures, plants provide interest through diversity but can also create unity out of visual chaos, using
repeated elements, such as street trees. Plants are often called upon to soften the urban harshness
associated with buildings and pavements, and they provide foregrounds and backgrounds to buildings and
other landscape elements. Plants are able to provide privacy, enhance desirable views and screen
12
undesirable ones. By attracting birds and other wildlife, plants remind us of other animals that share the
planet and our urban areas. Plants can reinforce the local character of an area and evoke special feelings
in us, by their appearance, their sounds and their scents. Seasonal changes in plants and their steady
growth link people to yearly cycles and the passing of time.
6.3
Social and psychological benefits of the urban forest: the restorative power of nature
Rachel and Stephen Kaplan have been studying the relationship between people and nature (in its
broadest sense) for over 25 years (Kaplan et al., 1998). In particular, they have studied the way the
natural environment can foster well-being and can enhance people's ability to function effectively.
Nature, in their research, includes a variety of outdoor settings, often nearby, that are encountered
everyday and that have substantial amounts of vegetation e.g. parks, open spaces, street trees and
backyard gardens. They can be small or large, visible through the window or more distant, and carefully
managed or neglected.
Their research and that of others has shown that people generally do indeed prefer natural environments
to other settings and that people experience benefits other than the mere fact of enjoyment. In particular,
they have found that nature has the power to be restorative and calming, to allow people to recover from
mental fatigue which results from our attempts to manage vast amounts of information. Symptoms of
mental fatigue include difficulty in focusing, risk-taking activity, impatience and irritability. Nature allows
people to become comfortable, civil and effective once again.
They note that it is not just the sensational or extraordinary landscapes that are important and deserve
respect and protection. They recognise the importance of ordinary, close-at-hand landscapes. Whilst
these landscapes may not be famous or spectacular, they are the places that nourish people on a daily
basis.
6.3.1
Case studies involving the restorative power of nature
Some specific examples of the restorative power of nature include the following.
One of the best known studies into the restorative power of nature was described by Roger Ulrich (1984)
who examined the restorative effect of natural views (trees) on surgical patients in a hospital. He found
that patients recovering after abdominal surgery had different recovery experiences, depending on
whether they were in a room with a window view of a natural setting or of a brick building wall. Those who
looked out on a small stand of deciduous trees *
had shorter post-operative hospital stays
*
received fewer negative evaluative comments in nurses' notes
*
took fewer potent analgesics
If window views of plants could shorten postoperative hospital stays by the 8.5% reported in Ulrich's study,
the annual health cost savings in the USA would total several hundred million dollars (Ulrich, 1986).
Moore (1981) found that the use of health services by prisoners was significantly lower if the prisoners
had views of nature (farmland) from their cells, rather than views of the prison interior.
Rachel Kaplan and Steven Kaplan carried out studies on nearby nature and the workplace (Kaplan et al.,
1988; Kaplan, 1993), in recognition of the fact that most daytime hours for many people are spent at work.
They found that nearby nature, even when only viewed from the window, had a substantial beneficial
effect in the work setting, affecting job satisfaction and well-being.
There are now many studies indicating that vegetation aids in the recovery from mental fatigue (see Kuo &
Sullivan, 2001a, p.347), providing enhanced cognitive functioning as measured by both self-report and
performance on objective tests. Vegetation in these studies is represented by contact with nature in a
variety of forms - community parks, window views and interior plants, as well as more natural areas.
13
Steven Kaplan (1995) proposed, in his Attention Restoration Theory, that contact with nature can renew
the resource underlying our capacity to direct attention by providing elements that are effortlessly
engaging or involve our involuntary attention. It is believed that this gives our directed attention (or
voluntary attention) a chance to rest and helps overcome the mental fatigue associated with continued
directed attention.
In residential settings, views of nature have been linked to (see Faber Taylor et al., 2002) *
residential satisfaction (Kaplan, 1985)
*
enhanced well-being (Kaplan, 2001)
*
more effective patterns of coping (Kuo, 2001)
*
greater day-to-day effectiveness (Tennessen & Cimprich, 1995)
Even views of nature from the roadside, while driving, may be important in stress recovery and protection
from further stress. A study by Parsons et al. (1998), involving drivers viewing four different types of
drives (forest/rural, golf and treed residential, a mix of residential and commercial with fairly substantial
vegetation, and urban with commercial buildings, signs and billboards), found that drivers viewing the
nature-dominated drives recovered more quickly from stress and coped better with further stress than
drivers viewing building-dominated drives.
In a study of the well-being of children in poor urban environments, Wells (2000) found that the nearby
natural environment plays a far more significant role than had previously been recognised. By examining
the cognitive functioning (i.e. attentional capacities) of 17 children initially in poor housing and the same
children after they moved to better housing with more natural resources, Wells found that children whose
homes improved the most in terms of greenness following relocation also tended to have the highest
levels of cognitive functioning following the move.
Urban forests and parks have been found to be areas that serve as refuges for privacy, away from home
and work environments (Hammitt, 2002). People visiting these areas for privacy stated that the most
important benefit they obtained was the opportunity for "reflective thought". The most important reasons
for visiting these urban forest and park areas were to be away from crowded places and daily routines of
work and home, as well as to go to a place of peace and quiet.
6.3.2
Social and psychological benefits of the urban forest - the research of Frances Kuo,
Andrea Faber Taylor, William Sullivan and others
At the University of Illinois Landscape and Human Health Laboratory (LHHL) [previously the HumanEnvironment Research Laboratory (HERL)], Frances Kuo, Andrea Faber Taylor, William Sullivan and
others are studying how residents of inner city areas respond to trees and other vegetation and how the
physical and psychological health of individuals and communities can improve when nearby nature and
natural views are present (Landscape and Human Health Laboratory (LHHL), 2009). Their research has
built upon other work carried out by USDA Forest Service researchers, including social scientists (Dwyer
et al., 1991 & 1992), and Charles Lewis (Lewis, 1996).
As a result of extensive research, Kuo (2001) suggests that nature may be an essential component of a fit
human habitat, given the apparent effects of nature on blood pressure, heart rate, mood, day-to-day
effectiveness, social behaviour, cognitive functioning and work performance. She goes on to say that
"Regular contact with nature may be as important to our psychological and social health as the regular
consumption of fruit and vegetables is to our physical health."
Practical application of their research has resulted in recommendations that *
people should spend time in green, natural settings to relax and revive the ability to concentrate on
challenging tasks
*
trees should be planted and maintained near homes, schools, work sites and other places where
concentration and mental energy were needed most
*
indoors, time should be spent in places where there is a green view from the window and desks at
work and school should be arranged to provide a green view
*
green spaces should be created, especially in inner city neighbourhoods
14
Their research supporting these recommendations is summarised in the following six themes, using the
titles provided by the Landscape and Human Health Laboratory (2009).
(1)
Canopy and Crime: Green Streets, not Mean Streets
In a study of a Chicago public housing development, involving 98 apartment buildings over two years, it
was found that apartment buildings surrounded by trees and greenery were dramatically safer than
buildings without green. Higher levels of greenery reduced total crimes by 52% (Kuo & Sullivan, 2001a).
The greener the surroundings, the fewer were the crimes against people (down by 56%) and property
(down by 48%). It is believed that greenery helps by *
reducing aggression, since people feel more relaxed
*
bringing people together outdoors, which increases surveillance
*
indicating that a building is cared for by its residents, and that they watch over it and each other
Tall trees and open, grassy areas with low shrubs and flowers that preserve visibility are recommended as
potential crime deterrents. It was recognised by the authors that criminals can use dense vegetation like
shrubs to conceal their activities and that such vegetation that blocks views can sometimes evoke fear
and fear of crimes (Talbot & Kaplan, 1984). However, not all greenery blocks views.
(2)
Vegetation and Violence or Cooler in the Shade: Aggression and Violence are Reduced
with Nature Nearby
In a study of the relationship between the outdoor environment and family violence in an inner city public
housing project, involving 145 residents, it was found that families with trees and greenery in their
immediate outdoor surroundings had safer domestic environments than families in buildings barren of
nature (Kuo & Sullivan, 2001b). Levels of mental fatigue were also higher in buildings devoid of nature,
and aggression accompanied this mental fatigue.
It appears that exposure to trees and greenery reduces mental fatigue and associated feelings of
irritability, thereby helping people to concentrate and become both more able and willing to deal with
problems thoughtfully and less aggressively.
(3)
Kids and Concentration or Go Out and Play: Nature Adds up for ADD Kids
A study of 96 children in the 7-12 age group, formally diagnosed with Attention Deficit Disorder (ADD), has
found that the symptoms of children with ADD are relieved after contact with nature and that the greener
the setting, the greater is the relief (Faber Taylor et al., 2001). By comparison, activities indoors such as
watching TV, or outdoors in paved, non-green areas, leave ADD children functioning worse. Children with
ADD have chronic difficulty paying attention and focusing on tasks. They are impulsive, prone to
outbursts and sometimes aggressive. Often their behaviour results in family conflict, peer rejection and
academic failure. The information also applies to Attention Deficit Hyperactive Disorder (ADHD) which is
a broader diagnostic term under which a child can be diagnosed as predominantly inattentive (attention
deficit), or inattentive and hyperactive/impulsive; only inattention was examined in this study, not
hyperactivity.
It is thought that children, like adults, become fatigued from concentration on schoolwork and structured
activities; to refresh and renew their voluntary attention, the use of involuntary attention helps, such as by
contact with nature.
It was recommended that, before beginning activities that demand attention, like school or homework,
children should go out and play in a green yard or park. Furthermore, it was suggested that recess in
schools should be taken in green schoolyards.
Further studies have supported these original findings. In a subsequent nationwide survey (Kuo & Faber
Taylor, 2004), using parents' ratings of the after effects of 49 common after-school and weekend activities
on children's symptoms, green outdoor activities reduced symptoms significantly more than did activities
conducted in other settings (e.g. indoors or in a built outdoors setting) even when activities were matched
15
across settings (e.g. reading in each setting). Another study (Faber Taylor & Kuo, 2009) found that
children professionally diagnosed with ADHD concentrated better after a 20-minute walk in the park than
after a downtown walk or a neighbourhood walk of similar length.
(4)
Girls and Greenery: Views of Green Help Girls Succeed
A study of 169 inner city children (about 8-12 years old) in a Chicago public housing development (12 16storey buildings, floors 2, 3 & 4 - Robert Taylor Homes) (Faber Taylor et al., 2002) found that the greener
and more natural a girl's view from home, the better she scores on tests of self-discipline (including tests
of concentration, impulse inhibition and delay of gratification). The greater a girl's self-discipline, the better
she is able to avoid dangerous, unhealthy or problem behaviours and behave in ways that foster life
success. (For boys, who typically spend less time playing in and around their homes, view from home
showed no relationship to self-discipline.)
It was recommended that girls should be encouraged to study or play in rooms with a view of nature, and
also to play outdoors in green spaces and have recess in green schoolyards, which may be especially
helpful for renewing children's concentration. It was also suggested that the practice of constructing
treeless residential developments might have important unintended costs (Faber Taylor et al., 2002).
(5)
Neighbours and Nature or Nice to See You: How Trees Build a Neighbourhood
In an observational study of 59 common outdoor spaces of a large public housing development in
Chicago, Illinois, it was found that the more trees and grass present, the more those spaces were used by
residents (Sullivan et al., 2004). This created more opportunities for informal social interaction.
Compared to residents living near barren spaces, residents closer to green spaces enjoyed more social
activities, had more visitors, knew more of their neighbours and had stronger feelings of belonging.
It was suggested that the results from this study of a profoundly poor neighbourhood could be generalised
to other neighbourhoods that are not poor - that strong social ties are important for a variety of reasons
(e.g. building consensus on values and norms, monitoring neighbourhood activity and intervening if
problem behaviours occur and defending their neighbourhoods against crime). It was also thought to be
worth investigating in otherwise barren, new housing developments.
In another study using interviews with 145 (female) residents of 28 high-rise buildings of a large public
housing development in Chicago, Illinois, it was found that the presence of trees and grass supported
common space use and informal social contact among neighbours (Kuo et al., 1998).
(6)
Plants and Poverty or Green Relief: Trees Ease Poverty in Inner City Neighbourhoods
In a study of 145 urban public housing residents randomly assigned to buildings with and without nearby
nature, attentional functioning (via attentional testing) and effectiveness in managing major life issues (via
self-reporting in structured interviews) were compared (Kuo, 2001). When trees and greenery were
immediately outside their apartments, inner city residents coped better with the demands of living in
poverty, felt more hopeful about the future, and managed their most important problems more effectively.
Kuo made the comment - "It is striking that the presence of a few trees and some grass outside a 16storey apartment building could have any measurable effect on its inhabitants' functioning. It is all the
more surprising that such a modest dose of nature could enhance an individual's capacity to manage the
most important issues in her life, with an effect size comparable to that of major factors such as health and
age."
6.4
Economic benefits of the urban forest to business: property values and business districts
Whilst it has been known for some time that residential property values benefit from tree cover or the
presence of parks nearby, research has begun into the economic benefits to business that flow from
urban forests (Wolf, 2003). A substantial study in New York (Bisco Werner et al., undated) found that the
urban forest was important for the economics of districts and the stability of nearby communities. Trees
16
made good business sense in terms of market identity, customer preference, lower vacancy rates and
providing a competitive edge. Urban trees also improved the quality of life.
7.
Other urban green
Although the focus of much of the research into the benefits of urban vegetation has involved urban trees
and forests, it is important to consider other places for plants in urban ecosystems. Such plants can be
found growing not in the natural ground or soil, but rather in creative adaptations with built infrastructure.
The importance of other urban green is that it may help overcome "plant blindness" in urban dwellers and
cause them to reflect on the role of plants, including trees, in urban ecosystems.
Opportunities for other urban green are likely to be explored in the future in the following ways *
roof gardens, which may or may not have human access - such gardens can offer multiple
environmental benefits
*
vertical gardens and wall gardens - these gardens offer the opportunity for green, when space is
limited
*
interior plantscapes - the use of a few or many indoor plants can improve indoor air quality by
removing volatile organic compounds (VOCs) (Wood et al., 2006); this, in turn, has implications for
improved human health and productivity
*
community gardens - these gardens can help establish links between people in a community as well
as re-establishing links between people and nature, including food production
*
hydroponics - food production using hydroponic systems is common at the fringes of urban areas,
and may well increase within urban areas in the future
8.
Sustainability of the Bush Capital - the urban forest and other vegetation
The wide range of benefits associated with the urban forest makes it clear that urban trees belong in
cities, alongside people, buildings, roads and other infrastructure. Whilst aesthetic and visual benefits are
important, recent research has revealed a wealth of environmental, ecological, social, psychological and
economic benefits associated with the urban forest. Whilst there are technological alternatives to trees for
achieving environmental benefits in cities, benefit:cost analyses indicate the value of trees (McPherson &
Simpson, 2002), especially given their provision of simultaneous benefits in several areas. As regards
social and psychological benefits, it may be that our attachment to nature is so deep that urban nature is
essential and not easily substituted.
By virtue of thoughtful planning and ongoing commitment, Canberra is fortunate in having developed a
world-class urban forest. It is important that planning changes already occurring (and foreshadowed) to
deal with a growing population do not compromise this urban forest, especially during densification. The
urban forest is critical to both environmental and social sustainability. It therefore needs to be retained
and enhanced. This does not preclude changes to forest structure and species selection to cope with
climate change.
Despite this recognition of the multiple benefits provided by urban trees, a major impediment to effective
funding of urban forests derives from the fact that the benefits provided by trees are almost pure public
goods (Bisco Werner et al., undated) - that is, trees provide benefits that may be enjoyed by anyone and
the cost to produce the benefits is the same no matter how many people receive them. These qualities
mean that the economic market will discount or ignore the value of trees. Once a tree is planted, it is
virtually impossible to charge people for its environmental, aesthetic or symbolic benefits.
The environmental and social benefits of the urban forest are highly relevant to the emerging area of
research into urban ecology, which brings together the natural sciences (or biologically based ecology)
and the social sciences (or social aspects of humans). Sustainable cities of the future will have, at their
core, a healthy environment and a health community of urban dwellers. Urban ecology has emerged at a
critical time in the process of global urbanisation.
17
The urban forest has a special role to play in urban ecology, since trees are the most conspicuous
element of nature in cities. They are highly symbolic of green, healthy, liveable cities. Whilst they evoke
strong responses, both positive and negative, from many people, there may be an increasing number of
people who are "blind" to their existence and importance. Yet recent research has indicated that urban
trees and other urban green may be essential to our social, psychological and spiritual well-being.
To maximise the benefits from urban trees, we need to market the importance of the urban forest more
widely to decision-makers and the public, and in more creative ways, so that urban trees are seen as a
normal part of the planning of city infrastructure and quality space is made availabl for them. Furthermore,
resources are needed for their establishment and maintenance, as for any other infrastructure. To guide
the development of urban forestry and urban ecology in Canberra, it is essential to undertake much more
local research into these areas than has been the case to date.
It is also important to recognise the contributions of other vegetation to the future sustainability of
Canberra, especially the locally indigenous vegetation communities such as lowland woodlands and
grasslands. These ecological communities are under threat from urban impacts, including expansion.
Conservation of these communities is important in its own right. These communities, however, offer the
additional benefit of natural plant resources that could be used more widely in Canberra's open space
areas, both public and private, being already adapted to local conditions of soil and climate, including
natural water availability. Whilst there are dynamic and passionate groups of people who know about and
love these plants, serious consideration should be given to publicising them more widely, in a user-friendly
format, such as a small booklet, combined with more extensive promotion of both natural areas and
landscapes reconstructed using these plants. It is inevitable that locally indigenous plant resources will
play an increasingly important role in and around Canberra, assisting adaptation to climate and enhancing
urban biodiversity, including connectivity, in both private and public areas.
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This paper is linked to the powerpoint presentation of the same name delivered at the ACT PLA
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documents together.
22

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