Introduction - Bukit Timah Nature Reserve

The interior of the Bukit Timah Nature Reserve

Singapore has an all year round humid equatorial climate and due to this climate, our forest is evergreen as the trees do not undergo seasonal changes. Bukit Timah Nature Reserve is the only primary virgin forest left in Singapore. The forest interior is basically made up of three layers which includes the highest layer (emergents), the lower layer and the forest floor. It also occupies 164 ha with a primary forest of about 70 ha. But what is most special about Bukit Timah Nature Reserve is that it lies in the heart of a city unlike larger plots of forests which are normally stituated in remote areas.

BTNR is covered with soil derived from granite parent material of the Rengam Series. (Ausafur Rahman 1991) and according to Swan(1988), the variation in soil depth had a large influence on variation in plant distributions in the Bukit Timah forest. The dominant tree families found in the reserve are Shorea curtisii (Dipterocarpaceae) and Koompassia malaccensis (Fabaceae). Timber from the Dipterocarpaceae tree family is also known as the commercial hardwood timber. Other characteristic trees also include Dyera costulata (Jelutong).

In this photo journal, we will explore how plants in the Bukit Timah Nature Reserve adapt to its tropical rainforest environment.

How do trees adapt?

In rain forests, trees adapt by growing taller to compete for sunlight. After the trees grow sufficiently tall, its trunk will begin to thicken to support its height. Therefore, older trees tend to be taller and thick as opposed to younger trees that tend to be thinner.

Picture of Helmi standing by the side of a huge tree

Younger trees are opportunists. They adapt to the unforgiving environment by remaining constantly vigilant. A young tree is always ready to take over the position of an older tree should it collapse.

It is equally interesting to note that the mortality rate found in Bukit Timah is among the higher values recorded for tropical rainforest (Swaine et al. 1987). One of the reasons that constitute to the high mortality rate may be due to depth of anchorage of roots. Organic minerals and nutrients are normally found on the top layer of the soil, and most of the trees adapt by having shallow roots to gain access to these nutrient. Thus, they can collapse easily during thunderstorms due to the lack of root support.

Picture 1 - Thick buttress roots

Picture 2 - Developing buttress roots

Trees in tropical rainforest usually adapt to the wet soils by growing buttress roots. The root system spreads horizontally at the ground level and it also helps the tree to balance in the shallow rainforest soil. Furthermore, buttressing helps the roots to spread out more effectively to obtain the nutrients that are usually found in the top soil layers.

Wind dispersed seeds

Wind dispersal is a feature that some tall trees in the rainforest use to adapt to the environment. Seeds are sometimes endowed with certain structures for the wind to carry it away from the parent tree to another habitat. This serves to reduce competition for limited resources found in the rainforest.


How do Epiphytes adapt?

Most ferns are leafy plants that grow in damp areas under the forest canopy. Unlike most plants, where the adult plant grows from a seed, ferns reproduce from spores.

Stag's Horn Fern

The Stag's Horn Fern adapts by producing "nest leaves" that grows together to form a basket . Its upper leaves edge out like fingers to trap fallen leaves of other plants. When the "nest leaves" die, it wither and curl inwards to grip the dead leaves as well as the previous set of "nest leaves", while the new "nest leaves" form outside, trapping yet more fallen leaves. The humus (highly nutritous soil material) formed from these rotting leaves provide nutrients that will be absorbed by the fern's roots. The roots are thus protected from drying out.

The Stag's Horn Fern also adapts by collecting rainwater in it's basket like structure in case of dry weather.

Bird's Nest Fern

The Bird's Nest Fern is another plant that adapts by growing on another. The leaf rosette traps fallen leaves which eventually rot and form humus which is then absorbed by the large mass of roots at the stem base.

How do leaves of plants adapt in a rain forest?

The main function of a leaf is to carry out photosynthesis, gas exchange and water transport. The structure of the leaf is divided into the leave blade, petiole (stalk) and vein (vascular tissue). The leave blade helps to harvest light for photosynthesis, the petiole (stalk) helps to hold the blade out to the light and the veins help to transport water and organic substrate.

Interestingly, the leaves of most rainforest plants have developed certain features to help them adapt to the environment.

Clidemia hirta

The Clidermia hirta (also known as the notorious weed) adapts to environment by producing fruits containing tannin which is poisonous to animals, particularly goats.

Thorny leaves

The plant copes with the threat of rainforest animals by growing thorns on its leaves to protect itself.

Image of an enormous leaf

Plants growing on the shady forest floor to adapts to the sunlight poor environment by producing large dark green leaves (almost the length of a human arm) with huge surface area. The precise combination of size and chlorophyll concentration ensures that the plant is able to harvest as much sunlight as possible, for photosynthesis.

A plant with waxy dark green leaves

Most plants adapt the rainforest conditions by producing leaves that are usually soft and waxy so that light will be better absorbed instead of being reflected. The leaves appear waxy due to the presence of wax substance (cutin) forming cuticle on the cell surface of the leaf. The waxy layer helps to protect the leaves from overhydrating.

The leaves in the picture also adapts to the sunlight poor environment by producing leaves that dark green. The colour of the leaves implies that there are more chlorophyll pigments for the efficient absorption of light

A plant with drip-tip leaves

Water shedding is an important form of adaptation. As is substantial amount of rainfall in rainforests, plants growing in rainforests often adapt to the environment by growing leaves with drip-tip. Leaves with drip-tip are mostly downward drooping and elongated. This is to ensure that excess water do not build up on leaves, resulting in fungi growth.


How do plant roots adapt?

Picture 1 - Adventitious roots

Picture 2 - More adventitious roots

Some plants adapts to the rainforest environment by making use of adventitious roots. Adventitious roots that are produced from the stems or leaves is used to support the plant. In certain species of plants, adventitious roots form on aerial stems, grow in the soil and helps to keep the stem upright. Besides providing support for the plant, adventitious roots helps the plant cope with its environment by allowing the vine to grow up to top of the canopy to secure sufficient sunlight for photosynthesis.

How do climbing plants adapt?

Climbing plants adapt to the environment by climbing towards the light using tendrils, spines or twinning stems.

Example 1 - A plant climber

Example 2 - Another plant climber





















Rattans

The rattan plant adapts and fights for sunlight by using its large thorny spines to scramble over other plants. The thorns also helps deter large climbing mammals preying on edible parts of the plant.

Picture 1 - Lianas

Picture 2 - Lianas
























Like a serpent, the lianas adapts by using trees to climb to the canopy in search of sunlight. These climbers often help to form above ground pathways, aiding animals such as monkeys in search of food which in turn help plants disperse their seeds.

How do fungi adapt?

Most fungi reproduces through spores. They do not possess chlorophyll necessary for the production of food. Fungi also play an important role in the ecosystem by decomposing organic material. They are also very important in cycling and exchange of nutrients.

Picture 1 - Fungus growing on a wooden structure

Picture 2 - Fungi growing on a log

Picture 3 - Fungi growing on huge fallen tree

Fungi adapting to its environment by growing in crevices of the forest floor, where it is dark and humid.

How do mosses adapt?

They can be easily found on the forest floor of the Bukit Timah Nature Reserve. Mosses are adapted to growing under dark and moist conditions and they can be easily found on rocks, logs and even on the ground.

Picture 1 - Moss growing on a fallen log

Picture 2 - Moss growing on stone steps

Unlike other plants, moss are unable to store water in their roots. Therefore, under harsh conditions, the moss will cope by stopping it growth. This is to protect its chorophyll from drying out. Furthermore, under bright sunlight, the moss will cope by folding and curling their leaves to protect themselves from the sun.

Videos for your entertainment!

Miss Lian speaking about adaptation

Miss Lian speaking about location

References

Tan, Hugh T. W., (2003). Growing at your doorstep : 35 native plants of Singapore, National Council on the Environment.

LaFrankie, James Vincent, (2005). Forest trees of Bukit Timah : population ecology in a tropical forest fragment, Simply Green.

Janzen, Daniel H., (1975). Ecology of plants in the tropics, Edward Arnold.

Veevers-Carter, W. (Wendy), (1984). Riches of the rain forest : an introduction to the trees and fruits of the Indonesian and Malaysian rain forests, Oxford University Press.