Urban Forestry in Tropical Cities
Lecture for Master of Urban Design Studio on 27 September 2006
Ismail Said, Faculty of Built Environment, UTM
A. Objective
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To give awareness on the role of forest and greenway for city planning and development
B. What is Urban Forestry?

Trees of varied characteristics, height, canopy and flowering habit, form the greenery of
urban areas.

Urban greenery can be classified as (1) greenway, (2) green corridor, (3) greenbelt, (4) largescale park, and (5) natural reserve. For example, greenway may compose of a variety of
native and adapted tree species planted in linear way such as along roadway or drainage way
(see Figure 1). A good example would be the East Coast Parkway in Singapore which is lined
with mixture of palms and large shade trees that provide a continuous character of greenway.
Large-scale park as the Central Park in New York is a greenery with matured tree species.
Perhaps, the alun-alun known as Simpang Lima in Semarang would become an urban forest if
it is planted with indigenous tree species such as Leguminosae, Dipterocarpus, Barringtonia
and a variety of palms such as Arenga, Areca and Cocos.

Therefore, urban forestry can be established in urban when roadway, drainage way and open
spaces are planted with trees of varied species.
C. Uses of Forest in Cities
The forest provides three major uses: (1) Engineering, (2) Architecture, (3) Climate Control and (4)
Aesthetic and emotional well-being
1. Engineering

Erosion control: Foliage reduces the impact of rain and surface runoff. Roots of vegetation
bind the soil particles and slowly release the excess water.
Runoff erosion is classified 4 ways: sheet erosion, rill erosion, gully, erosion and slip erosion.

Acoustical control: Plants absorb sound. The vibrations of sound waves are absorbed by
leaves, branches and twigs of trees. The effectiveness of trees and shrubs as acoustic
absorption directly depended on (1) density of foliage, and (2) depth of vegetative screen. For
example, distances of 75 feet or more should be available for planting between the noise
sources and the area to be protected. For the most effective screening of highway noise, the
planting width should be from 25 to 35 feet. For maximum effectiveness a planting consists
of both trees and shrubs, since the shrubs are not high enough nor the trees branched low
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enough to the ground. As such plants reduced noise by 7 decibels per 100-foot width of
planting.

Atmospheric purification
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Plants cleanse the air by the process of photosynthesis that is absorbing carbon
dioxide and releasing oxygen.
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The leaves, branches and pubescence (hairs) on the leaves trap air-borne particles.
The particles are then washed away by the rain and fall to the ground. This is why the
greener is the city the lesser amount of dust in its atmosphere.
o
Air washing: Growing tree transpire a considerable amount of water. A thick foliage
tree loses 75 to 100 gallons of water in a hot day. A mature orchard transpires as
much as 600 tons of water per acre per day. Plants transpire large amounts of water
into the air, and cause water to form through the guttation process on their leaves,
enabling them to act as air cleaners.
 Glare and reflection control
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Plants screen, blunt, or soften glare and reflection. The degree to which they can do
this depends upon their height, density and location.
o
Control of glare from reflection ranges from almost complete stoppage of light, to a
minor filtering and diffusion, by placing plants between the light source and the
viewer.
2. Architecture

The architectural use of plants recognizes that plants have a potential to achieve a given
form, texture, color, and size. These characteristics are dynamic, that is, changing
seasonally and yearly. Tembusu (Fragrea fragrans) blooms in April adding fragrance to
the air. Young leaves of ironwood (Mesua ferrea) turn its canopy reddish which adds
colorful character to the city scene. Hence, trees are view filtration adding beauty to the
city scenery.

Plants are able to form walls, canopies or floors in the landscape. The are able to
articulate, define, enclose or delimit exterior space either by themselves or in conjunction
with other architectural components.

Design reinforcement
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Direction
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Sequential movement
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Invitation
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Enframement
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Subdivision
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Screening
3. Climate Control

The four major elements of climate which affect human comfort are air temperature, solar
radiation, air movement and humidity.

In the tropics, the comfort zone is from 220 to 280 C. Staying under a shade tree enables us to
attain this zone because the foliage of the tree filters much of the sunlight to reach the
ground. Additionally, a breeze adds to the feeling of comfort because it circulates the
humidity which is always high.

Temperature control: This control linked directly to solar radiation control, wind control and
precipitation control.


Radiant heat transfer has been categorized as 5 types:

direct shortwave radiation from the sun

diffused shortwave radiation from the sky vault

shortwave radiation reflected from the surrounding terrain

longwave radiation from the heated ground and nearby objects

outgoing longwave radiation exchange from building to sky
Trees, shrubs, groundcovers and grass are among the best exterior solar radiation control
devices. The control includes:

Shading

Intercepting reflected radiation

Reflecting: Dark green foliage and small-leafed plants with pubescent
surfaces greatly decrease solar reflection reflectivity. The foliage also
absorbs the heat and provides insulation.

Trees control wind by obstructing, deflecting and filtering. For example, obstructing means
reducing the windspeed by increasing the resistance of windflow. Rows of trees become a
shelter belt and windbreak which break the prevailing winds.

Wind is one of the most important climatic elements in urban planning, since dispersion of air
pollution and human comfort are largely dependent on it.

Trees intercept rain, soak the water in their foliage, store the water in their roots and gradually
release the water to stream for human consumption.
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4. Aesthetic Values and Emotional Well-being

Since the dawn of time, human has innate relationships with plants including source of food
and shelter, and stimulate senses.

Food: Tall fruit trees such as Kasai, Mango, Breadfruit, Durian, Tamarind and Eugenias and
palms such as Arenga and Cocos provide fruit for human and animal consumptions.

Shelter: Large shade trees such as Angsana and Raintree provide resting and breeding place
for small mammals, birds and insects. Many epiphytes grow on these trees that provide more
shelter for frogs and lizards. A family hornbill is known to take refuge at the Singapore
greenways, and its population is growing.

Color, texture, form and fragrance of trees stimulate our senses. People may be fascinated to
view the following elements:

o
open greenery composed of a variety of tree forms and gradation of greens
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flowering trees such as Delonix regia and Cassia fistula
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overarching trees such as Raintrees
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tall slender palms such as Areca
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bold trunk palms such as Cabbage palm
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conical foliage tree such as Meninjau
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perhaps, the shadow patterns of tree canopy
99% of human time on this Earth involves directly with plants as hunters and food gatherers.
Hence, our attachment towards the plant and the climatic factors is built in our gene.
Discussion questions
1. Why landscape of towns and cities in developing countries such as Malaysia, Thailand and
Malaysia is lack of continuous greenway system?
2. How could cities in such developing countries create large park like the New York’s Central
Park?
3. Who should play the dominant role to plan and develop greenway with forest, indigenous
species in towns and cities in your country
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