Psychological Impact
of Nature

Many
of the ways in which living walls positively impact our urban environment are
through subconscious psychological impacts, improving the overall quality of
the day to day life of urbanites. Through this section I will assess the impact
through two sections, health and stress and attention and productivity in the
workplace.

Health and Stress

The
idea that the presence of nature in daily life “is psychologically healthful is
very old.” (Ulrich 1979) Although the visual impact of the beauty of nature is
clear to see, the deeper lying psychological benefits are not so obvious. There
is a wealth of evidence that living in urban centres where crowding, noise and
air pollution are prevalent is stress provoking in large groups of people
(Cohen et al, 1986) however more recent studies have also examined exactly to
what extent the surrounding environment can increase the rate of stress
reduction and improve people’s overall happiness. In Ulrich. et al’s (1991)
experiment, subjects experiencing a level of stress were given audible and
visual stimuli of being in a range of environments (pedestrian mall, traffic
and natural settings among others.) Measurements were taken to determine stress
levels, such as heart rate and muscle tension, alongside questionnaire
responses by the test subjects to calculate an overall numerical value of their
stress level. After various time periods measurements were taken to determine
current stress level, despite the pedestrian mall and traffic situations giving
very similar stress relieving results, “recovery from stress was much faster
and more complete when subjects were exposed to the natural settings.”
Furthermore, in just a 5-7-minute exposure the reduction of stress from a
natural environment was far greater than that of an urban environment. In day
to day life this is the equivalent of the walk to a tube station or the initial
journey out of work, a known stressor, journeys often made through built urban
areas where traffic and pedestrian noise are prominent. The benefits of the
introduction of living walls, proving a natural environment through views and
sound of plants and the attracted wildlife, therefore may well act to reduce
stress within the working population of cities.

The
psychological benefits of surrounding nature are not limited to stress
reduction, various studies suggest that there is a strong correlation between
nature and physical health. Kaplan & Kaplan discuss the positive effect
that having a good view out of a window to nature is a significant factor in
the speed of recovery of patients in rehabilitation wards at hospitals. Whilst
Moore (1981) proves there is a dramatic relationship between inmates use of the
healthcare facilities at large federal prisons and the view inmates have from
their cell, with views facing out to surrounding nature seeking the least care.

 

Three systems for
living and green walls

Not
only do living and green walls have psychological benefits when brought into
cities, they have significant impacts on the environmental conditions as well.
Using three different systems of vertical planting I will consider the
positives and negatives of each against a series of criteria based on the work of
Wood, A. et al (2014.) These are as follows;

            Reduction of the Urban Heat Island
Effect

            Improvement of Air Quality

            Noise Reduction

            Biodiversity

            Storm Water Management

Trellis
System

This
system uses evenly spaced planters attached to the existing façade or
structure, must be masonry or concrete, with a trellis bridging the gap between
each planter box. Evergreen climbers such as Hedera Helix and Vitis (Perini, K.
et al. 2011) grow between boxes forming a living wall. Nutrients and water are
supplied by tubes running to each planter box, this is computer controlled to
ensure the plants grow in optimum conditions.

 

 

 

Felt Hydroponic System

This system uses felt rather than soil
as the growing medium for the plants roots, all nutrients and water are drip
fed at various levels throughout the felt to supply the plants with all they
need to grow. Any waste water runs through the felt and is collected at the
bottom to be reused. This system allows any plant to grow, as the nutrients are
controlled, this means a variety of plants can be grown to create a diverse
living wall, preferably those most common in the surrounding natural
environment to attract insects and create an area of biodiversity.

 

 

 

 

Planter Living Wall
System

This system works in a very
similar way to a felt hydroponic system however the growing planters are filled
with soil into which the plants are planted. Although there is soil in the
planters’ nutrients and water are supplied and monitored by an irrigation
system to allow the plants to grow in their optimal conditions. Any plants can
be used within this system however indigenous ones are preferable.

Reduction of the Urban
Heat Island Effect

An
urban heat island is the effect which causes the temperature of a dense urban
centre to be higher than that of the surrounding suburbs. Caused by the
increased density of heat sources such as vehicles, people, buildings and
pollution and amplified by the narrow street canyons of buildings. The hard
concrete, asphalt and steel and glass facades which make up cities all act to
reflect thermal energy rather than absorb it. (ARUP, 2016) This reflection
causes an exponential rise in temperature, buildings get hotter and thus
require more mechanical cooling, which in turn creates a greater volume exhaust
heat. It has been measured that at night time the UHI effect can cause cities
to be up to 12°C warmer at night than the surrounding area. (Wood, A, et al.
2014) However various studies have shown how the use of plants as living or
green walls within these narrow street canyons can lower the effects of the UHI
in a variety of ways. In the most basic way plants act to shade hard surfaces
of buildings, this stops the surfaces reflecting thermal energy back into the
street, as well as reducing any heat absorption into the building, therefore
lowering the requirement for mechanical cooling. Furthermore evotranspiration1
causes heat to be taken away from buildings and street canyons by evaporation,
contributing to an overall lowering of the surrounding air temperature. Each of
the living wall systems are suited to different plant species, I will consider
three species, suited to a specific system, to conclude which system has the
highest potential for UHI reduction. (Cameron, 2014)

            Urban Heat Island Reduction with
Trellis System

The
trellis system is best suited to climbing plants, which, planted in evenly
spaced trellises, grow up mesh perpendicular to the buildings surfaces. Hedera
Helix2 is
an evergreen climbing ivy capable of growing up to 12m tall and 4m wide. The
densely packed leaves provide a strong shading effect on the wall behind. Few
plants or trellises are required due to the plants size. Hedera gave results of
cooling a brick wall’s surface by 7.3°C.

            Urban Heat Island Reduction with
Felt Hydroponic System

Using
data compiled by Mazzali, U, et al. (2013) a felt hydroponic system showed
excellent results for reducing the heat flux of a wall, that is the thermal
energy emitted from the wall. An identical wall was measured both bare and
covered with the results showing a wide range in temperature difference,
between 5°C and 20°C. However, the heat flux, caused not only by the absorption
properties of the felt but the evotranspiration and absorption coefficient of
the vegetation, was reduced by between 70 and 80%. Stachys Byzantia, a
perennial evergreen shrub suited to drier conditions which could be allowed by
the high level of control of the irrigation system, a shrub with densely packed
leaves growing no larger than 0.5m tall and 1m wide. The dense leaves not only
provide high levels of shading but through evapotranspiration3
the temperature of the wall is reduced by 7.6°C.

 

            Urban Heat Island reduction with
Planter System

Mazzali,
U et a’sl (2013) study also considered the way a planter system reduced the
heat flux on an exposed wall. Although the system did reduce thermal emittance
it did so to a far lesser extent, reducing the wall at most by 12°C even on the
hottest days. Prunus Laurocerasus is well suited to the planter system due to
the shrubs larger size, growing up to 4m tall and 4m wide, the shrub would need
pruning to maintain a constant size. This evergreen, like the Stachys Bzantia,
reduced the temperature of the wall through not only shading but
evapotranspiration however only recording an average temperature reduction of
6.3°C.

 

In
conclusion, to reduce the temperature of a wall in a temperate environment and
help reduce the UHI effect all three systems ‘significantly reduced the wall
temperature.’ (Cameron, 2014) However the felt hydroponic system reduced the
temperature by the greatest amount, mostly in part to it using both solar
shading, reducing the incident solar radiation on the wall in the first place,
as well as evapotranspiration removing thermal energy from the air surrounding
the plant.

 

Improvement of Air
Quality

Air
quality in areas of high population density is highly polluted due to the
combination of “dust, pollen, factory emissions, soot, smoke and motor vehicle
emissions.” (Arup, 2016) This combination of toxins and pollutants has negative
health effects on every single inhabitant of a city, with WHO4
reporting 7 million deaths worldwide, all attributed to poor air quality, in
just 2012 alone. With more drivers on the roads than ever before5
(Department for Transport, 2017) and 7bn people forecast to live in cities by
the end of the century (Arup, 2016) this is not an issue which can be resolved
without significant intervention or change. Numerous studies have revealed the
positive effect plants and vegetation have on the air quality of a localised
area through biofiltration6
(Loh, 2008) and the ability of plants to sequester carbon dioxide and produce
oxygen in its place through photosynthesis. (Wood et al. 2014.) Although living
walls are not the only way to introduce plant species and areas of green space
into a city, land is at a premium and largely unavailable for areas of park
land, whereas the total vertical area of a city, using building facades, is
considerably greater than land area. Furthermore, the positive effects of green
space on pollution and carbon dioxide levels are localised to the plant matter,
bring vegetation onto busy streets and residential areas will allow
improvements in the air quality of the street canyon, where people spend the
majority of their time. Different plant species are better at each aspect of
improving the quality of air around them; pine species such as Pinus Sylvestris
and Pinus Mugo (ARUP, 2016) are suited to catching high volumes of particulate
matter such as dust, pollen and soot, due to the large surface area afforded by
their needles, whereas it has been discovered that the soil and root zone of
the plant are where the highest proportion of volatile organic compounds are
removed. (NASA, 1989) The most efficient sequesters of carbon are trees,
however these are not possible to introduce into a retrofitted living wall and
as such the best plants to use are local ones which will thrive in their
habitat.

 NEDLAW ORCHIDS AND BROMLIADS CO2 AT NIGHT?!

WOOD
2014?

Noise Reduction

Cities are commonly areas of
high noise pollution7
and with increasing evidence that long term exposure to high levels of
environmental noise above certain levels can have physical and mental
implications (Stansfeld, 2016) it is imperative that governments act to reduce
this pollution. WHO suggests nightly noise levels of 40dB (WHO, 2010) with the
average environmental noise level in London currently at 60dB, reaching over
75dB along busy roads (London Noise Survey, 2005) (WEBSITE?!) the population is
at risk of a number of long term health problems. Although the most commonly
known problem of noise pollution is the annoyance of it and how this then
disrupts daily activities, feelings, thoughts, sleep and rest, experiments have
shown the direct relationship of long term exposure to Furthermore, the
stressing effect can cause attention disruption and in school aged children
just a 5dB increase of aircraft noise over a period of time is associated with
a 2-month delay in reading age in the UK (Basner, 2013)(Babisch, 2003) as well
as tests suggesting that “at least one million healthy life years are lost
every year from traffic related noise” in western Europe. (WHO, 2011)

Noise
pollution is mostly caused by traffic within street canyons of urban centres,
physically hard environments with tarmacked roads, paved pavements and
concrete, metal and glass buildings. (Davis et al. 2016) These materials are
however also acoustically hard, reflecting and reverberating noises only adding
to the amplification of overall sound level. To reduce this amplification
effect and therefore lower the total volume of environmental noise green walls
can be used. The vegetation is able to “reduce noise levels by reflecting,
refracting as well as absorbing acoustic energy.” (Ambius, 2018) Trees and
planted boarders are currently used to muffle the noise of traffic, but this
still leaves enormous areas of building facades able to reflect and thus
amplify the traffic sounds, furthermore this large area provides a great opportunity
to deaden environmental noise by retrofitting living walls. “Green facades can
reduce sound levels from emergent and traffic noises by up to 10dB(A).” (ARUP,
2016) However this muffling and reduction in sound reflection is not entirely
due to the vegetation itself, Azkorra et al. and Davis et al.’s reports independently
discuss the way in which green facades absorb sound energy, concluding that the
main absorber is the substrate soil rather than the leaves or plant matter.
Therefore, the best applicable living wall is the Planter System, due to the
high volume of soil as the trellis system only has minimal planting beds and
the felt hydroponic system has none. (Azkorra et al., 2015) (Davis et al.,
2017) The best plants to use are densely planted shrubs or ferns (ibid) where mechanical
vibrations of plant elements, caused by the sound waves, dissipate sound by converting
sound energy to heat. (Azkorra et al., 2015) Soil works to destructively
interfere with sound waves through ground dip, vegetation in the substrate soil
is acoustically porous due to plant litter and root interference, resulting in
an absorption of lower sound frequencies below 1kHz, (Nilsson, 2015) such as
that of traffic at around 0.6 kHz. (Azkorra et al., 2015)

 

1
Evotranspiration – process by which water is transferred from the land to the
atmosphere by evaporation from plants by transpiration. Similar to the way in
which sweat takes heat from an animal’s body.

2
Known as Common Ivy

3
Evapotranspiration – The sum of evaporation and a plant’s transpiration from
the Earth. Removes heat as water turns to water vapour.

4
World Health Organisation

5
“January to March 2017 saw the highest number

of new registrations ever recorded in the first

quarter, in Great Britain, at 959,000”

6
Plants act as filters, air passing over leaves and plant matter interacts with
micro-organisms growing there which act to degrade a pollutant,

7
Unwanted noise

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