The approaches to modifying the biodiversity value of buildings and sealed surfaces in urban areas. including an analysis of the wider environmental value of biodiversity and its importance in tackling issues such as air pollution, climate change, and human health.
By Paul Michael Reynolds
1.0 Introduction
The urban environment differs
from the rural environment significantly in both its biotic and abiotic
features. This is primarily to do with the general unnatural construction of
urban areas which forces the majority of natural processes to be obstructed,
stopped or changed to some degree, for example the changing of the natural
hydrological cycle with increased surface run-off of rain due to masses of
impermeable surface (Gills et al., 2007).
Since urbanisation began there has been little consideration given to the
biodiversity value of urban areas along with the potential for urban areas to
be improved through “greening”/the use of green infrastructure (by greening I
refer to the process of making the urban environment more natural/utilising
natural processes as a means of improving urban areas biotic and abiotic
functions to help combat climate change, improve human health and reduce
pollution). However, the Third Assessment Report (TAR) of the Intergovernmental
Panel on Climate Change (IPCC) has essentially linked human activity to causing
global environment change and that this will continue to cause further change
in the earth’s climate leading to increased average temperatures and sea level
rises for a long time to come (IPCC 2001). The revelations about climate change
and it’s potential effects upon the planet have bought the impacts of the urban
environment on climate change (i.e emissions from urban areas) into mainstream
science but also more importantly how the urban environment can be changed to
both help reduce emissions and to also reduce the impacts that climate change
will have on urban environments (i.e temperature rises and decreased
precipitation in the UK) and the humans that dwell within.
Green infrastructure has a
variety of definitions to different people depending on your profession but for
the purposes of this work it is an interconnected
network of green space that conserves
natural ecosystem values and functions and provides associated benefits to
human populations (Benedict& McMahon 2002) further to this definition I
will add buildings, pavements, roads that have/can be modified to be greener. It
is this green infrastructure that needs to be utilised as a means of “greening”
urban areas. According to Planning Policy Statement 9 (PPS9) local authorities
should aim to maintain green space networks and protect them from development
or where possible integrate the two (Anonymous 2005). So according to planning
guidelines developments within the urban environment should already be seeking
ways to integrate green space i.e green roofs into their design thus creating a
means for species to disperse and live across the urban environment.
2.0 Approaches to modifying the biodiversity value of buildings and sealed surfaces in Urban Areas
There are a variety of methods
for modifying buildings and the urban area in general to help increase the
biodiversity value of such areas as well as creating a positive effect on the
local environment which in turn can help negate the impact of climate change on
urban areas as well as reduce pollution and improve human health both mental
and physical.
2.1 Green Roofs and Walls
Urban areas produce a greater
quantity of rainwater run-off than their rural equivalents for example a
typical city block generates more than five times as much run off than a wooded
area of the same size (USEPA 2003) this is due to a greater percentage of
impermeable surfaces that prevent water from permeating into the ground or
being evapotranspired by vegetation (VanWoert, et al 2004 & Gills et al 2007)
the majority of studies on green roofs are focused upon this particular aspect
(Liptan 2003) which is indeed one of the
key benefits of green roofs in an urban environment with the majority of
studies concluding that a vegetated roof is far more efficient at absorbing
(thus reducing) rainwater flow as well as slowing down the time it takes to
reach ground flow (Liu & Minor 2005). Not only do green roofs absorb and
slow down water flow but they also filter out the pollutants that often get
washed into watercourses from urban environments according to Graham & Kim 2003,
who also concluded that if every building in Vancouver had a green roof fitted
then over the next 50 years the overall health of the watershed could be
restored to natural conditions. Although this conclusion was obtained through
modelling it serves as a good example of the potential benefits to adapting
urban areas to have green roofs and it would be interesting to see a similar
study of other major cities throughout the world to see if the same principle
still applies. One of the main reasons green roofs are so useful in creating
green space within an urban environment is land is both expensive and hard to
come by within the confines of an urban area thus roofs offer a cheaper and
easier approach to the problem (Mentens, Raes, Hermy 2005). Carter and Keller (2008) explain that there
are two main types of green roof one termed extensive and the other intensive.
According to their description extensive Green roofs are lightweight and
designed to be easily fitted onto existing roofs as they contain only a thin
growing media of approximately 2-6 inches and typically support small drought
resistant plants while intensive green roofs are generally more extravagant
with growing media depths exceeding 6 inches and supporting a great range of
plant life although they are more expensive and cost more to maintain. So in
many urban areas when it comes to retrofitting green roofs it is the extensive
green roofs that will be most practical for the majority of buildings with new
developments (or those with more money to spend on retrofitting) taking on the
intensive green roofs. Dunnett and Kingsbury (2004) point out that in some
European countries it is a legal requirement to build green roofs as a matter
of getting planning permission in the first place something which one would
assume in the current climate should be the norm in most countries especially
the UK however there is little literature on how this could be implemented in
the UK. Green roofs and walls are proven to reduce the Urban Heat Island (UHI)
effect significantly (Woodruff 2009, Takebayashi & Moriyama 2007, Kumar
& Kaushik 2005, Lazzarin, Castellotti & Busato 2005) as they are able
to hold water and thus remove heat through evaporation as well as reflect some
heat energy as well (Takebayashi & Moriyama 2007) whereas standard urban
roofs often constructed of cement absorb heat and radiate it heating the air
around it throughout the day and night causing the UHI effect whereby Urban
areas remain hotter than their rural counterparts (Landsberg 1981). A lot of
the work published on the Urban Climate and ways to mitigate such effects as
the UHI prove that green roofs and walls are the best option (Woodruff 2009, Takebayashi
& Moriyama 2007, Kumar & Kaushik 2005, Lazzarin, Castellotti & Busato
2005, Benedict & McMahon 2002, Gills,S.et
al 2007, Liptan 2003, Liu & Minor 2005).
Green Walls can be created in a variety of ways from the use of climbing plants to actively climb up (and attach themselves) the building, specialist wall garden systems and trellising (which can be bother free standing or attached to the wall). There is little in regards to literature on green walls directly however they are often covered in literature on green walls as essentially they complete the same services in principle with the addition of green walls being used indoors although they are designed differently. There are two types of green wall- Green Facades and Living Walls. Green facades generally involve climbing plants either on the wall themselves or attached to special screens/trellising. Whereas living walls are more complex structures that involve vegetated panels being attached to a wall usually in blocks and due to their vertical nature are watered from the top either by hand or through irrigation systems, when built indoors these can improve the air flow and quality within a building (Woodruff 2009). Dunnet and Kingsbury (2004) describe modular wall systems which follow the same principle as above with plants in blocks stacked one on top of the other to form a wall.
Green Walls can be created in a variety of ways from the use of climbing plants to actively climb up (and attach themselves) the building, specialist wall garden systems and trellising (which can be bother free standing or attached to the wall). There is little in regards to literature on green walls directly however they are often covered in literature on green walls as essentially they complete the same services in principle with the addition of green walls being used indoors although they are designed differently. There are two types of green wall- Green Facades and Living Walls. Green facades generally involve climbing plants either on the wall themselves or attached to special screens/trellising. Whereas living walls are more complex structures that involve vegetated panels being attached to a wall usually in blocks and due to their vertical nature are watered from the top either by hand or through irrigation systems, when built indoors these can improve the air flow and quality within a building (Woodruff 2009). Dunnet and Kingsbury (2004) describe modular wall systems which follow the same principle as above with plants in blocks stacked one on top of the other to form a wall.
A by product of the research into
green roofs (and walls) and their enforcement in some parts of Europe has shown
that they can offer habitat compensation for rare and endangered species
affected by land use changes providing they are built correctly (Brenneisen
2006). Miller (2005) provides an example of this whereby a city hall in Chicago
has a green roof that consists of over 20,000 individual plants made up of over
150 different species over a 2000M2 area which in-turn has been
colonised by a diverse array of native invertebrates and birds thus proving
that a green roofs value is not just in controlling the urban hydrological and
heat energy cycles but also in their biodiversity value.
2.2 Sustainable Urban Drainage
In 21st Century
society sustainability is at the top of the agenda as resources become more
expensive, space more limited and demands for services higher. The old methods
of urban drainage are largely accepted to be outdated, destructive and wasteful
(Ashley et al 2004). Drainage was
originally created in urban areas to transport all excess waters (both polluted
and non polluted) as swiftly and efficiently as possible out of the urban area
into receiving waters i.e rivers to avoid flooding within the urban area (Boller
1997) however as the climate changes and the population grows the old methods
of bringing drinking water into urban areas and removing excess water/sewage
are becoming more costly and technical which is where Sustainable Urban
Drainage Systems (SUDS) come into play as a natural and cost effective method
to both reducing the treatment cost and time of waste water and slowing the run
off of water out of urban areas giving time for pollutants to be removed as
well as reducing the risk of flooding of the receiving waters. Changes in the
law both EU and domestic now require sustainability and environmental
protection to be at the top of the list in regards to planning with specific
legislation aimed at water and it’s treatment along with acceptable levels of
pollutants within waterways and surrounding coastal waters (Ashley et al 2004) The EC Water Framework
Directive (2000/60/EC) being the primary piece of legislation which is ensuring
that European nations set up legislation to ensure the above. Mansell (2003)
lists the main advantages of SUDS as being able to enhance water quality,
provide aquatic habitats for flora and fauna within the urban environment and
aid in recharging natural ground water levels, he also points out that for
these reasons SUDS are becoming more and more common in new developments.
However, Mitchell (2005) points out that much of the pollution entering
waterways from urban areas comes from existing developments thus even though
the integration of SUDS with new developments was a good thing it would not
have an effect upon the pollution already coming from existing areas and due to
a lack of research on the implementation of SUDS into existing built up areas it
was a problem.
The purpose of SUDS are to act as
a means to emulate the natural hydrological cycle and preserve natural drainage
patterns (Parkinson & Mark 2005) which in-turn brings benefits to the urban
environment such as reduced risk of flooding.
One basic form of sustainable
urban drainage is in the form of permeable pavements that is rather than having
the standard cement/paving block pavements within the urban area (which allow
for very little- to no water penetration). A study by the Environmental and
Resources Institute (2007) tested standard asphalt surface against permeable
pavement in regards to water permeation and subsequent peak flow times with the
results showing that the permeable pavement delayed the onset of runoff by 2.4
hours on average and decreased the total peak flow by 83%. This is a phenomenal
reduction in the overall volume of water which shows that permeable pavements
could significantly aid in urban hydrological control. The Environmental and
Water Resources Institute (2007) also found that the permeable pavements
reduced pollutant mass by 58-96% depending on the pollutant which is an
important feature of permeable pavements for the increasing of water quality
leaving urban areas into rivers etc. Roesner et al (2001) discuss the use of detention ponds as a means of both
controlling water volume leaving an urban area and also as a means of removing
pollutants before it leaves the site as the pond fills with water it naturally
prevents the water moving on down the system immediately with the vegetation
both within and around the pond responsible for removing pollutants such as
heavy metals (wetlands and swales also serve the same purpose) and taking up
some of the water to be lost through evapotranspiration thus reducing the
overall water volume. Ellis et al (2002)
expand upon the use of such methods of SUDS to include the added benefits to
local biodiversity increasing the numbers of aquatic invertebrates, flora and
associated fauna both terrestrial and aquatic.
An example of technology used as part of SUDS Diagram by Greenfix Soil Stabilisationand Erosion Control Ltd
2.3 Urban trees
Trees within the urban environment play a key role both
aesthetically and for maintaining the microclimate found within urban areas.
Urban trees are often chosen for their beauty but also have value in shading,
cooling the local climate, removing green house gases (Dwyer et al 1991, Akbari 2002) and also
removing toxic particulates out of the air. Nowak (1994) and Nowak (2006) state
that tree transpiration and canopies can affect air temperature, radiation,
wind speed, relative humidity, and turbulence, all of which are essential in
determining the microclimate of urban areas and can indeed serve in their own
right to reduce pollution levels. The effect of shading by Urban trees means
that air conditioning demand is reduced which combined with their action of
absorbing carbon dioxide makes them a very good tool in the fight against
climate change thus delaying global warming (Akbari 2002). Urban trees and
forests do not only serve as a natural means to control climate and air quality
but also act as habitat islands and corridors allowing species to live in and
move around (and in some cases into and out of) urban areas promoting
biodiversity (Carreiro 2008). Trees often get a large amount of public support
as well primarily for their beauty but also for their aforementioned properties
in shading etc and a study conducted by Lohr et al (2004) which involved a survey backed up this view and added
that any potential problems envisaged by urban trees were not believed to
justify not having the trees and these views have been echoed in various other
surveys (Westphal 1993, Austin 2002 and Sommer et al. 1994)
An example of trees within the urban environment photograph taken by the USDA
2.4 Urban Green spaces
Urban green spaces can include cemeteries,
parks, allotments and gardens all of which can act to improve urban
environments both aesthetically and from a biodiversity and pollution control
perspective. Green spaces of a good quality increase the urban environment life
and ultimately contribute to legislative goals in regards to pollution
controls, air quality, quality of life (human) and sustainability (Enhancing
Urban Green Space 2005/6 and Miller & Patassini 2005). Urban green spaces
tend to be valued for their intrinsic nature (Miller & Patassini 2005) however
they are also of an economic value as they make the city more attractive (thus
bring in more tourists, people wanting to live and work etc) and through their
effects of reducing pollution and increasing human health. Maas et al (2006) concluded that the
percentage of greenspace in people’s living environment had a positive
correlation with the perceived general health of residents which in turn of
course means people are less likely to be ill and take time off of work further
strengthening the economic argument for green space rather than it just being a
matter of aesthetics this was also backed up by Takano.T, Nakamura.K and
Watanabe.M (2002) who also concluded that the availability of green space
increased the longevity and health of senior citizens. An increase in green
space also aids in physical activity (walking, running, cycling etc) of those
living nearby within urban areas which further supports Maas et al (2006) and Takano.T, Nakamura.K
and Watanabe.M (2002) assessment of people’s general well being in association
with green space. Green spaces and parks also have value in regards to
education, naturalist activities, wildlife habitat and community gardens
(Roseland and Connelly 2005). As a wildlife habitat just like urban trees and
forests they can act as habitat islands and corridors allowing species to move
between other islands and in some cases both into and out of the urban area
(Roseland and Connelly 2005).
3.0 Conclusion.
The biodiversity of urban areas
is of the upmost importance in the 21st Century as the population in
urban areas increases along with the impacts of climate change threatening the
very nature of life in these areas (Savard, Clergeau & Mennechez 2000). To
increase the biodiversity value of urban areas is to increase the use of: green
roofs and walls, sustainable urban drainage, urban trees/forests and green
space in general such as cemeteries, parks and allotments (Benedict &
McMahon. 2002). This will in-turn bring a wealth of benefits to the urban
environment (Roseland and Connelly 2005) by decreasing energy costs for example
properly positioned trees can reduce energy bills by up to 25% (Department of
Energy 1995), reducing the urban heat island effect through the use of green
roofs/walls, urban forests etc, decreasing water demand through the use of
sustainable drainage and water use as well as by planting native species
adapted to local climates, increase the absorption of pollutants through
particulate entrapment by trees and uptake by vegetation and increase urban
wildlife habitats (Roseland and Connelly 2005). The studies mentioned earlier
by Maas et al (2006) and Takano.T,
Nakamura.K and Watanabe.M (2002) prove a positive correlation between access to
greenspace as well as it’s quantity within urban environments and increased
health/longevity of those who live within the urban environment. This of course
is also aided by the fact that the very greenspace that encourages physical
exercise also helps to remove pollutants from the air (Dwyer et al 1991, Akbari 2002, Nowak 1994
& 2006) which also includes carbon dioxide and other greenhouse gases
attributed to Climate Change (Akbari 2002, Nowak 1994 & 2006, IPCC 2001,
Gills et a, 2007). The majority of
the research literature on green infrastructure is found from the year 2000
onwards as climate change and sustainability have really entered the mainstream
and it has become even more apparent how important it is going to be as a tool
in dealing with the consequences of climate change. As is evident from the
literature increasing biodiversity through green infrastructure in urban areas
is both economically and practically viable as well as ultimately essential to
the future of mans habitation en masse in artificial urban environments.
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