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Landscape and Urban Planning 63 (2003) 197–211

Green plot ratio: an ecological measure forarchitecture and urban planning

Boon Lay Ong∗

Department of Architecture, School of Design and Environment, National University of Singapore,

4 Architecture Drive, Singapore 117566, Singapore

Received 8 January 2002; received in revised form 23 August 2002; accepted 25 August 2002

Abstract

Current research on sustainability of cities has favoured the implementation and conservation of greenery in the urban

context. The benefits of plants are not just environmental but recreational, aesthetic and emotional. The full benefits of plants

and the role they play in the ecology of cities remain to be mapped out but the general significance of plants appears to

be uncontested. This paper proposes a new architectural and planning metric for greenery in cities and buildings. This new

metric, the green plot ratio (GPR), is based on a common biological parameter called the leaf area index (LAI), which is

defined as the single-side leaf area per unit ground area. The green plot ratio is simply the average LAI of the greenery

on site and is presented as a ratio that is similar to the building plot ratio (BPR) currently in use in many cities to control

maximum allowable built-up floor area in a building development. GPR allows more precise regulation of greenery on site

without excluding a corresponding portion of the site from building development. It provides flexibility to the designer whilesimultaneously protecting the green quota in the design. This concept has been applied in a number of design competitions in

which the author has collaborated with colleagues and various architectural practices. It has also been adopted as a planning

requirement by the client authority for one of the competitions for which the author has entered. While seen as a fundamental

and important metric, GPR is not in itself an indicator for all the ecological relationships between plants and cities. A larger

set of related metrics need to be developed.

© 2002 Elsevier Science B.V. All rights reserved.

Keywords: Green plot ratio; Leaf area index; Ecological masterplanning; Plants; Urban landscape

1. Introduction

One of the key components in the planning of sus-

tainable cities, according to current research, is plants

and planted spaces. Whitford et al., 2001 (abstract), in

developing indicators for the ecological performance

of urban areas in the UK noted that “the greatest in-

fluence on ecological performance was the percentage

of green space, particularly of trees.” The fields of

∗ Tel.: +65-874-3536; fax: +65-779-3078.

E-mail address: [email protected] (B.L. Ong).

landscape ecology and urban ecology have emerged

from research to become the primary advocates of ecological design in cities. While a considerable body

of research has been gathered, problems of integration

and common standards remain to be resolved. Leitao

and Ahern (2002), for example, noted that there are

“literally hundreds of metrics developed” and that

these metrics are “frequently strongly correlated,

and may be confounded” (p. 74). They suggested a

reduced list of 7–9 metrics categorised under two

aspects of landscape planning—composition and con-

figuration. According to Pauliet and Duhme (2000),

0169-2046/02/$20.00 © 2002 Elsevier Science B.V. All rights reserved.

P I I : S 0 1 6 9 - 2 0 4 6 ( 0 2 ) 0 0 1 9 1 - 3



198 B.L. Ong / Landscape and Urban Planning 63 (2003) 197–211

urban ecology in Europe is focused mainly on bio-

logical surveys of habitat and autecological studies.

They proposed the phrase urban metabolism to iden-

tify studies developed around notions of exchangeand transfer of energy and matter. Much current work

is centred on natural habitats in the city: the conser-

vation of existing greenery, and the establishment of

new parklands and other forms of planted landscapes.

The emphasis on vegetation is not unfounded.

Attwell (2000) identified three broad areas in which

plants are useful: environmentally, aesthetically and

recreationally. The last two benefits may be consid-

ered to be incidental, although important—we can

obtain our aesthetic and recreational satisfaction in

many ways, not necessarily with plants. It is the en-

vironmental contribution of plants that is important

to the development of sustainability in our cities and

to our future. This aspect, predictably, is the primary

concern of current researchers. Akbari et al. (2001)

identified, among other benefits, climate modification,

carbon sequestration, ozone reduction (and conse-

quently smog reduction), dry deposition of NOx , O3,

and PM10 particulates, improvement in quality of

life, increased value of landed properties, decreased

rainwater runoff, and protection against floods. In a

paper concerned with the implementation of environ-

mental goals, Jensen et al. (2000) also focused on theenvironmental benefits of plants. In this case, their

environmental goal was identified as the potential of

urban green spaces to contribute to organic waste

recycling, surface runoff infiltration, and biodiversity

improvement. Whitford et al. (2001) identified four

performance indicators also linked with green spaces:

climate, hydrology, carbon storage and sequestration,

and biodiversity.

1.1. Environmental benefits of plants

Specific environmental parameters monitored in

research vary. The indicators identified by Whitford

et al. (2001)—climate, hydrology, carbon storage and

sequestration, and biodiversity—provide a convenient

shortlist. To this list may be added one other—

pollution control (ozone reduction, smog control,

dry deposition of NOx and other gases and small

particulates, and organic waste recycling).

Of these, climate amelioration in terms of overall

temperature reduction and subduing the heat-island ef-

fect has been most widely studied. The primary cause

of heat build-up in cities is insulation, the absorption

of solar radiation by roads and buildings in the city

and the storage of this heat in the building materialand its subsequent re-radiation. Akbari et al. (2001)

advocate the use of ‘cool’ surfaces (surfaces with a

high albedo or reflective index) as a remedy but it

can be demonstrated that planted surfaces are more

effective than even high albedo surfaces in reducing

heat build-up. Building materials, however high their

albedo, absorb heat and store it. Even white surfaces

can become as much as 10 ◦C higher than the ambient

temperature (Akbari et al., 2001, p. 298). Plant sur-

faces however, as a result of transpiration, do not rise

more than 4–5 ◦C above the ambient and are some-

times cooler (Jones, 1992).

The effectiveness of vegetation cover in terms of

controlling rainwater runoff is clearly reflected in

studies by Pauliet and Duhme (2000). The data pre-

sented later (Fig. 1) were extracted from Table 2 of

Pauleit and Duhme’s report and show a clear corre-

lation between percentage vegetation coverage and

surface runoff.

Carbon storage and sequestration are directly corre-

lated to plant metabolism, and photosynthesis in par-

ticular. For the purpose of most of the studies sampled

here, the metrics were based on land area coverage.This is calculated either in terms of actual coverage

(m2) or percentage cover, with a distinction sometimes

made between lawn (grass) and ‘trees and bushes.’

Whitford et al. (2001), for example, use percentage

tree cover as the main determinant of both carbon stor-

age and sequestration in their work.

Pollution control (ozone reduction, smog control,

dry deposition of NOx and other gases and small

particulates, and organic waste recycling) involves

both air-borne and water-borne wastes. In the natural

state, as Lovelock (1989) pointed out, the recyclingof animal waste is the primary resource for plants. He

phrases it neatly (p. 26):

I say that only by pollution do we survive. We an-

imals pollute the air with carbon dioxide, and the

vegetation pollutes it with oxygen. The pollution of

one is the meat of another. Gaia (the planet earth)

is more subtle, and, at least until humans appeared,

polluted this region of the solar system with no more

than the gentle warmth of infrared radiation.



B.L. Ong / Landscape and Urban Planning 63 (2003) 197–211 199

Fig. 1. Relationship between surface runoff and percentage vegetation cover (data extracted from Pauliet and Duhme, 2000, Table 2—data

excluded related to railroads and construction sites, which had porous ground but were devoid of vegetation cover, and waterbodies like

lakes, ponds and streams).

It should be noted that the recycling of resourcesbetween animals and plants has kept the planet in rel-

ative ecological balance for millions, if not billions,

of years. The use of plants to recycle our wastes is

thus, interestingly, a re-engagement with the forces of

natural ecology. The problem here is not the act of re-

cycling itself, but the quantity—we need to adjust our

pollution to levels within the processing limits of the

plants we use.

Conversely, Karlik and Winer (2001) studied bio-

genic emissions of plants that contribute to the pro-

duction of ozone and other photochemical compoundsand hence promote pollution rather than reduce it.

These emissions are characteristic of certain plant

species and the amount emitted is linked to leaf

mass.

Biodiversity is a difficult parameter. While desir-

able, neither a minimum benchmark nor how an ac-

ceptable balance can be achieved manually have yet

been identified. Nature, of course, establishes its own

equilibrium and both enables and requires a high level

of biodiversity to maintain this equilibrium. In the

man-made landscape, it is not clear quantitatively howbiodiversity benefits the human environment. On the

whole, the recommendation is towards greater biodi-

versity and enabling a natural balance as much as pos-

sible. Connections between green patches are useful

in helping animal migration but also increase the risk

of infection and contamination.

It should be noted that the earlier benefits (and dis-

advantages) of plants are dependent primarily on the

extent of leaves or leaf area. In current literature, the

exact species of the plant (with the notable exception

of biogenic emitting plants studied by Karlik andWiner, 2001) and the nature of the landscape (whether

it is a nature reserve or an artificially maintained land-

scape, even agricultural) are generally less critical

than the extent of greenery available. For the purposes

of urban ecological planning, it would appear that

“farmland has much in common with natural ecosys-

tems (Whitford et al., 2001, p. 91).” Such generali-

sations, while patently untrue, are however necessary

and valid when a larger context like cities are being

studied.




Fig. 2. Proposed tropical megacity cooled by plants (source: Tay, 1989).

2. Integration of architecture and greenery

Current literature separates built-up urban areas

from planted landscapes. Underlying the proposals

Fig. 3. An ecological vision of Manhattan greened (source: SITE, Green Architecture and Urbanism, 1990).

set forth by various authors, there is a simple assumed

scenario. The built environment is assumed to be gen-

erally hard and impervious. Against this are planted

landscapes, or greenery, which may be man-made or




wild. The two components—built environment ver-

sus planted landscape—compete for site coverage.

Little distinction is made between the two landscape

typologies—man-made versus wild—except in termsof tree cover. The general recommendation is to en-

courage increased greenery and higher levels of tree

cover and biodiversity.

However, enlightened architects and designers are

looking at ways to incorporate greenery into their de-

signs (Figs. 2 and 3, for example). A new term—

skygardens—has been introduced to refer to planted

landscapes built above the ground: in intermediate

floors of high-rise buildings or at the rooftop (Fig. 4).

How do these new design concepts figure in the met-

rics set-up by current research? Is a roof garden equiv-

Fig. 4. A high-rise residential block designed for the Liuxiancun Ecocity competition which features extensive planting—the entire ground

floor, two skygardens on every three floors which take up two out of a nine-square mandala, and roof garden (GPR = 2:1).

alent to a similar sized garden on the ground? Is a

high-rise building enwrapped by greenery on its roof

as well as facades (Fig. 2) as effective as a mature

tree of similar size? How can we tell? If the incorpo-ration of plants into architecture is somewhat, if not

equally, as effective as greenery on ground, then the

antagonistic face-off between urban ecologists and ar-

chitects/planners/designers may be turned into one of

collaboration.

2.1. Architectural benefits of incorporating

greenery

There are several benefits to incorporating plants

into the building itself. The shade provided by the




plants reduces the cooling load of the building and to

that extent, also helps to reduce the building’s con-

tribution to the urban heat-island effect. Hydrologi-

cal benefits are also derived. Not only do the plantsthemselves capture rain, and the soil on which they

grow help reduce runoff, the remaining rainwater can

be collected for human use within the building. The

plants and growing medium help to sieve and filter

the water so that less of the rain needs to be rejected.

Planted waterbodies can also be designed to help recy-

cle wastewater for reuse within the building. Carbon

storage and sequestration also occur and if harvested

and dried, the plants may be used as fuel. Pollution

control by plants in buildings is not diminished when

compared to greenery planted at ground level. On the

other hand, the capacity of planted spaces in buildings

to support a range of dependent biota is not well estab-

lished. Common wisdom suggests that small animals

are less common the higher the floor is above ground

and that species richness may be reduced because of

isolation of skygardens from the ground.

Beyond this, plants in high-rise buildings also help

to humanise the building and give tenants a stronger

emotional relationship to the ground. If well tended

and healthy, plants and greenery are generally aesthet-

ically pleasing to most people. For some, the space

and opportunity to garden in high-rise buildings mayalso be welcome.

2.2. The need for a greenery metric

The strategic position of greenery in sustainability

argues for a common metric. A common metric is im-

portant if research findings and empirical data are to be

shared and compared. Experience gained from various

projects can then be more easily consolidated and ap-

plied to new projects. Data developed by different re-

searchers can contribute to a common knowledge base.The selected metric must meet rigorous standards and

broad applicability. Current correlation between envi-

ronmental benefits and land coverage is coarse and at

best, indicative. Current parameters also assume exist-

ing typological configurations which may not be ap-

plicable with new ecological building alternatives.

The present paper proposes a green metric that

does not presuppose typical configurations of land

and building. The proposed metric is based on a bi-

ological parameter—leaf area index (LAI)—that is

currently used to monitor the ecological health of

natural ecosystems and to mathematically model and

predict plant metabolic processes. As such, it can be

used to quantify planning metrics in biological terms.Being in common use in the biological sciences, it

provides a useful link between planners, ecologists

and scientists.

3. Green plot ratio (GPR) and leaf area index

(LAI)

In the literature reviewed, the primary metric for

greenery is land cover. This metric is sometimes fur-

ther delineated into lawns and shrubs-and-trees. The

present paper proposes that a more scientific and ac-curate metric be adopted. Most, if not all, of the ben-

efits gained from plants result from plant metabolic

processes. These processes include photosynthesis,

evapotranspiration, respiration and uptake of minerals

from the air and ground. The extent to which plants

engage in these processes is directly related to the

amount of green matter, usually found in the leaves of

the plant (see Jones, 1992, for example, for a detailed

account of plant metabolism). Even dry deposition

of pollutants and particulates depend on the total leaf

area of the plant and its leaf characteristics.

The total leaf area of a plant is indicated, in biolog-ical science, by the LAI. The present paper provides

a summarised account of LAI in current application

and proposes an equivalent planning metric called the

green plot ratio (GPR), for urban planning. GPR is

defined as the average LAI of the greenery on site.

3.1. LAI—a metric for greenery

LAI is related to a range of ecological processes

like photosynthesis, transpiration and metabolism.

These plant processes in turn enable the predictionof net primary production, rates of energy exchange

between plants and the atmosphere, rates of future

growth and yield, and the monitoring of changes in

canopy structure due to pollution and climate change.

The ability to estimate LAI is therefore a valuable

tool in modelling the ecological processes occurring

within a forest and in predicting ecosystem responses.

Actual plant productivity is dependent on chlorophyll

concentration, stomatal density and other physiolog-

ical and environmental factors.




In biological science, LAI is defined as the single-

side leaf area per unit ground area. It is a dimensionless

number. At a simplistic level, LAI can be considered

simply as the ratio of leaves to ground covered. How-ever, in so far as chlorophyll and stomata concentra-

tion differs from plant to plant and influences the light

absorption ability of the individual plant, LAI is more

accurately understood in terms of its ‘green’ content

rather than leaf area alone. This is reflected in the in-

direct methods of measuring LAI, e.g. measurements

of canopy transmittance or remote sensing techniques.

These indirect methods measure the intensity of light

transmittance or absorption rather than leaf area. As

might be expected, LAI values from different methods

vary.

Indicative LAI for various biomes are available.

Scurlock et al. (2001) provides a summary of selected

biomes which is helpful in determining the corre-

sponding LAI of urban greenery (Table 1). It may be

noted that the LAI of various biomes range from about

1 to 2 for grasslands and 6 to 8 for plantations and

wetlands. Shrubs have a mean LAI of 2 but depend-

ing on the density of cover, can be expected to rise to

about 4. The data in Table 1 may be used as indicative

values, in lieu of actual measurements, of urban green-

ery. It is reasonable, for example, to assume that turf

Table 1

Statistical distribution of leaf area index by biome, for the data set “Global Leaf Area Index Data from Field Measurements, 1932–2000”

Biome Original data Data after IQR analysis

Number of

observations

Mean Standard

deviation

Minimum Maximum Number of

outliers

removed

Mean Standard

deviation

Minimum Maximum

All 931 5.23 4.08 0.002 47.0 53 4.51 2.52 0.002 12.1

Forest/BoDBL 58 2.64 1.03 0.28 6.0 5 2.58 0.73 0.6 4.0

Forest/BoENL 94 3.50 3.34 0.48 21.6 8 2.65 1.31 0.48 6.21

Crops 88 4.22 3.29 0.2 20.3 5 3.62 2.06 0.2 8.7

Desert 6 1.31 0.85 0.59 2.84 0 1.31 0.85 0.59 2.84

Grassland 28 2.50 2.98 0.29 15.4 3 1.71 1.19 0.29 5.0Plantation 77 8.72 4.32 1.55 18.0 0 8.72 4.32 1.55 18.0

Shrub 5 2.08 1.58 0.4 4.5 0 2.08 1.58 0.4 4.5

Forest/BoTeDNL 17 4.63 2.37 0.5 8.5 0 4.63 2.37 0.5 8.5

Forest/TeDBL 187 5.12 1.84 0.4 16.0 3 5.06 1.60 1.1 8.8

Forest/TeEBL 58 5.82 2.57 0.8 12.5 1 5.70 2.43 0.8 11.6

Forest/TeENL 215 6.70 5.95 0.002 47.0 16 5.47 3.37 0.002 15.0

Forest/TrDBL 18 3.92 2.53 0.6 8.9 0 3.92 2.53 0.6 8.9

Forest/TrEBL 61 4.90 1.95 1.48 12.3 1 4.78 1.70 1.48 8.0

Tundra 13 2.69 2.39 0.18 7.2 2 1.88 1.47 0.18 5.3

Wetlands 6 6.34 2.29 2.50 8.4 0 6.34 2.29 2.5 8.4

Preliminary analysis by Asner and co-workers, May 2000 (source: Scurlock et al., 2001).

or grass will have an LAI of 1, herbal gardens or small

bushes may have an LAI of 3 and highly wooded and

densely populated landscapes with trees may reach an

LAI of 6.

3.2. Methods for measuring LAI

Several methods for measuring LAI exist. On the

whole, current research in determining LAI (Martens

et al., 1993; Wilkinson, 1991; Peper and McPherson,

1998; Gower et al., 1999; Green and Clark, 2000) us-

ing destructive and/or non-destructive methods have

been conducted on forest canopies, orchards and agri-

cultural row crops rather than single trees or in the

urban context. Peper and McPherson’s (1998) work

is distinctive in that their research was orientated to-

wards the determination of LAI values of single trees

in urban conditions and pertain more directly to this

current paper.

The methods of measuring LAI can be divided into

two main categories: destructive and direct methods;

and non-destructive and indirect methods. The direct

methods essentially involve physically calculating the

average area of individual leaves taken from a plant

or parts of a tree and then extrapolating to the stand

or the entire tree. Indirect methods in general involve




determining light transmittance values through the

plant canopy and remote sensing measurements of

Earth’s albedo; that is in effect a measure of the

canopy’s absorption instead of its transmittance.

3.2.1. Direct measurement

Direct estimates of LAI are obtained either by total

harvesting or by partial harvesting. With partial har-

vesting, the application of suitable allometric equa-

tions can extrapolate the harvested data to the whole

tree or stand. These allometric equations are not only

species specific but also site specific as plant growth

and leaf composition are strongly influenced by nu-

merous environmental and ecological factors.

3.2.2. Canopy transmittanceThe estimation of LAI using linear canopy mea-

surements is based on the Beer-Lambert law. The

Beer-Lambert law assumes that light is attenuated

exponentially as it passes through the canopy in ac-

cordance to the extinction coefficient, k . The light

below the canopy, Qi , is related to the light above the

canopy, Q0, and LAI, by the relationship.

Qi = Q0 e−kLAI (1)

The canopy is assumed to be randomly dispersed

both in this instance and also in the use of hemi-spherical photography described later. This assump-

tion is not true in fact as canopies can be observed

Fig. 5. Hemispheric photograph used in the determination of LAI of a mulberry tree (source: Peper and McPherson, 1998).

to be distributed into clumps rather than smoothly

homogeneous, randomly distributed volumes. How-

ever, the assumption is a necessary simplification

that enables mathematical manipulation of collecteddata.

3.2.3. Hemispheric and other photographic methods

The use of hemispherical photography in estimating

LAI relies on the fact that tree canopies are unevenly

distributed (Fig. 5) and therefore gaps exist through

which unattenuated solar penetration may be assumed.

The light intensity of other user-defined partitions of

the canopy is then compared against this and averaged

to obtain an average solar beam penetration (Peper

and McPherson, 1998). The values obtained produce

estimates of LAI, leaf distribution, mean foliage incli-

nation, transmission coefficients for diffuse and radi-

ation penetration, and extinction coefficient.

Peper and McPherson (1998) also reported using a

photographic method of determining LAI using tree

profiles. These are pictures of trees taken on elevation

(Fig. 6). For greater accuracy, additional photographs

are taken from different angles—Peper and McPher-

son used two photographs at positions perpendicular

to one another.

3.2.4. Remote sensingRemote sensing using satellite images is based on a

discovered linear relationship between the normalised




Fig. 6. Elevational photograph used in the determination of LAI (source: Peper and McPherson, 1998).

difference vegetation index (NDVI) and LAI (Green

and Clark, 2000). NDVI is calculated using values

of red and infra-red bands of satellite photographs—

between 666.5 and 752.8 nm. A regression formula

Fig. 7. Thematic map of leaf area index (LAI) for mangroves on the

north-west of South Caicos Island (source: Green and Clark, 2000).

linking NDVI values and LAI is then used to derive

an LAI thematic map (Fig. 7).

4. Green plot ratio explained

The concept of a green plot ratio is developed by

combining the concepts of LAI and building plot ratio

(BPR). BPR is defined as the ratio of gross liveable

(or rentable) area and the site area. A site with a BPR

of 2:1 can have a building that has a total useable

floor area twice that of the site. The distribution of

this floor area can be in the form of a two storey high

building which covers the site entirely, a building that

is four-storeys high which covers only half of the site,

or permutations of various kinds. As the site coverage

reduces, the building can be taller and have additionalfloors. Most skyscrapers, which may be 20 or more

storeys high, are designed within a BPR of much less,

perhaps 6:1 or 8:1.

If we were to consider a lawn (Fig. 8), i.e. a patch

of ground covered with grass—we may imagine that

the ratio of grass to the ground is roughly 1:1. The

LAI in this case is 1 and the corresponding green plot

ratio is 1:1. A closer inspection will reveal that it is

actually more but for the sake of discussion, the figure

is close enough.




Fig. 8. Allocated green plot ratio (GPR) values based on ground cover (the values are rounded from data summarised by Scurlock et al.,

2001; Table 1 above).

If this patch of ground were to be covered instead by

a clump of bushes, the total surface area of leaves ex-

posed to the sun may be expected to be more. Leaves

are translucent and leaves within a canopy are able

to tap the transmitted light through the upper layer of

leaves. Current research (e.g. Deshmukh, 1986; Jones,

1992; Scurlock et al., 2001—see Table 1 above) sug-gests that a reasonable figure for this is about 3:1. That

is, the total area of leaves exposed to the sun is about

three times that of the area of the ground itself.

If the ground is covered instead with full grown

trees, with a dense canopy and closely planted individ-

ual trees, the ratio would be yet higher—6:1 or even

10:1. From Table 1, a more reasonable ratio for the

most heavily planted landscape would be 6:1.

The green plot ratio has been defined earlier as

the average LAI of the greenery on the site. It can

also be equivalently defined as the ratio of the totalsingle-side leaf area of the planted landscape to the

plot or site area. Its value is effectively the same as

the average LAI but expressed as a ratio rather than a

single figure to reflect the normal practice for calcu-

lating maximum allowable floor area in architectural

and planning practice. GPR is a more reasonable

indication of the effectiveness of the greenery on a

site than current metrics based on the extent of site

coverage because it is directly related to the amount

of photosynthetically active leaves on site.

4.1. The ecological value of GPR

Since GPR replicates the conventional planning in-

strument of BPR, it is easily understood by the design

and planning professions while maintaining a direct

correlation to scientific measures. In practice, GPR is

specified as a ratio applied to the whole site.Because of this, GPR enables the designer to off-

set areas of low LAI values with areas of high LAI

values. The specification of GPR is useful in various

ways. Firstly, it enables urban planners to specify a

minimum acceptable degree of ecological responsive-

ness without restricting or predetermining the design

proposal. Secondly, it provides designers greater flex-

ibility in terms of design options since it is a targeted

degree of green composition that is specified rather

than land cover. Thirdly, it is consistent with current

practices of measuring the ecological health of natu-ral ecosystems using remote sensing technology, and

can therefore be a similar indicator of the ecological

health of urban areas. Finally, it is possible to include

urban environments in a global audit of the planet’s

ecological health using satellites and remote sensing

technology.

The use of GPR carries some caveats. GPR alone

cannot indicate species richness on site. Leitao and

Ahern (2002), for example, have provided a more de-

tailed discussion of applicable metrics in a broader




ecological context. The determination of which set of

metrics should finally be used lies outside the scope

of the present paper. Issues to be answered include the

definition of urban ecology, not as a broad field encom-passing various research directions, but as a planning

and design target with quantifiable criteria to be met

and regulated. While additional ecological criteria are

needed, they do not, however, replace the usefulness

of GPR but complement it. It is argued here that GPR,

and its correlate LAI, are metrics fundamental to the

development of this larger set of ecological metrics.

4.2. Application in architecture and urban

planning

GPR has been applied by the author to a number

of design proposals. GPR can be applied as an urban

tool, for masterplanning, as well as an architectural

design tool, for individual buildings. The determina-

tion of suitable GPR may take one of three possible

Fig. 9. Masterplan of Liuxiancun Ecocity showing the central nature reserve and ecologically designed high-rise housing in the corresponding

terrain.

options. It can reflect the desired degree of greenery

from the viewpoint of the planners and/or users. In this

case, the GPR will be an arbitrary number to be settled

by negotiation—on social, aesthetic and environmen-tal grounds. The GPR value can also be determined

on the grounds of anticipated use of the site. For ex-

ample, it is more difficult to achieve a high GPR in

an industrial or commercial site than in a residential

or recreational site. Until suitable designs and tech-

nologies are developed, this is likely to be the most

common method of determination. Finally, the GPR

value can also be determined in terms of ecology—

either in terms of the current LAI of the site before

development, in terms of restoration of the green-

ery on site to reflect a specific period historically, or

as part of an ecological masterplan requiring specific

LAI values for greenery at various sites. The author

prefers the last option and has applied it in two design

competitions in which he has participated in recent

years.




4.2.1. Liuxiancun ecocity, Shenzhen, China

The design entry for Liuxiancun new town (Foo and

Ong, 1999) was a collaboration between the author,

Dr. Foo Ah Fong, Archurban Architects and Planners,and CESMA (a subsidiary of the Housing and De-

velopment Board, Singapore). Although not required

within the brief, the approach taken was to implement

ecological measures as fundamentally and as exten-

sively as possible. The strategies adopted included

bioclimatic design, conservation of natural landscapes,

energy conservation, intelligent building design, and

extensive greenery. A key strategy was to incorpo-

rate skygardens—gardens incorporated into high-rise

buildings above ground level. In the prototypical

high-rise housing design (Fig. 4) that was proposed,

the first level of accommodation was raised 3 storeys

above the ground to enable light penetration into the

entire ground floor. This allowed the ground floor or

void deck under the building to be extensively land-

scaped. There were two skygardens every three floors

which took up two of the nine square mandala upon

which the plan was based. The roof was also greened.

The individual buildings achieved a GPR of about 2:1.

Fig. 10. Planted and naturally ventilated basement carpark. The plants provide visual relief, aesthetics, and environmental benefits as well

as reduce the need for mechanical ventilation and artificial lighting.

Sixty percent of the site was conserved and returned

to nature (Fig. 9). This portion of the site was origi-

nally a quarry and was, at the time of the competition,

open for commercial exploitation. It was mountainousand was, for high-rise buildings, expensive to build

upon. On the other hand, it had a scenic topography

and good potential for development as a nature reserve.

Our proposal, by conserving this part of the site, not

only reduced the cost of construction (we built only on

flat terrain and 60% of the site did not require any civil

work), the value of the project was also increased by

introducing a nature reserve within easy access. A sell-

ing point of the project was that there would be a view

from any apartment of this landscape, and there will be

a garden just outside the front door. The GPR for the

conserved part of the site was set at maximum—6:1.

A key innovation was to design an underground car

park which would be ventilated by large landscaped

openings which opened to the sky (Fig. 10). This

proposal would save costs and energy consumption

required for artificial ventilation as well as provide

natural lighting, ventilation and other environmental

advantages arising from the plants.




Fig. 12. Planted design for proposed residential apartments for Bouna Vista competition entry. Note the planting on the roof, facades,

central spaces and at ground level. It is anticipated that the final green coverage will meet a GPR of 1:1.

adopted by the organisers, Jurong Town Corporation,

and will be applied in the final development of the

project—now renamed 1 North.

5. Conclusion

One of the primary strategies in the greening of

the built environment is the incorporation of trees and

plants. There are several benefits to increasing theamount of greenery in cities—environmentally, aes-

thetically, and recreationally. Current research not only

supports the argument that plants are an important in-

gredient in balancing the polluting effects of cities, but

also found plants to be aesthetically and emotionally

beneficial. In fact, it is not the beneficial significance

of plants that is surprising but the ability of modern

society to camouflage our dependence on plants. Paper

alone accounts for nearly half of the global appetite

for wood and together with the use of hardwoods for

furniture and building construction, is responsible for

much of the destruction of natural forests and habitat

in the world today. Most of our medicine, clothing,

furniture, flooring and building material come directly

from plants. Of course, we still rely on plants for food,

as do the animals we eat. Similarly, the oxygen in the

air we breathe still comes entirely from plants. Plants

are also responsible for the cleanliness of the water in

our rivers, streams and other natural waterbodies—to

the degree that these waterbodies are clean and havenot been polluted by our industries.

A proper, and future, strategy for a sustainable city

must not only include plants but be more precise in

channelling plants towards balancing what Pauliet and

Duhme (2000) have called urban metabolism. Better

technology will be needed to increase the efficiency of

cities and reduce their pollution levels, but it is likely

that all the best efforts will not be enough if the role of

plants in the sustainability of cities is not recognised.

To do this, cities will need to be described in ecological




terms such that the ecological impact of cities on the

global environment can be identified and monitored.

Within cities themselves, ecological processes of cities

cannot be separated into industrial and natural systemsbut the two will need to be resolved and integrated.

Both human needs and the need to maintain nature’s

equilibrium will have to be met concurrently—not just

globally but within the urban context.

The green plot ratio, or GPR, proposed here is a

small, but hopefully, useful step towards enabling this

development of a future strategy for sustainability in

our cities. Based on a biological parameter, LAI, cur-

rently used to monitor the metabolic rate of agricul-

tural fields and the overall ecological impact of natural

ecosystems, GPR bridges the fields of ecology, bio-

logical science and urban planning. The concept has

been used in two projects involving the author and is

currently being considered for regulatory adoption in

Singapore.

Acknowledgements

The work presented is a culmination of collabora-

tion with colleagues, architects and planners over the

last few years. In particular, the contribution and sup-

port of the Department of Architecture, Dr. Foo Ah

Fong, Archurban Architects and Planners, CESMA,

Design Vista and Jurong Town Corporation are gladly

acknowledged.

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