Suitable trees for national highways

The monsoon is time for planting saplings. The common varieties of timber trees planted on the roadsides are rain tree, mahogany, redwood (Shishu), cedar (Debdaru) etc. Acacia and eucalyptus are also planted. But many botanists and environmental scientists say eucalyptus takes in a large amount of water and makes the area drier. So this tree is suitable for waterlogged areas only. Acacia does not have such bad impacts on the environment. But what is good with this plant species? Acacia usually does not grow straight, it produces a bent shoot and the quality of timber is also not very good.

Therefore it is suggested that we avoid planting eucalyptus on the sides of our national highways that are known for dryness and not waterlogged anyway. And very few acacia saplings can be planted with other better timber or fruit trees but so many acacia planting should not continue.

Most suitable tress
Now the question arises -- what trees are better to plant along our national highways? The plants to consider should be those occupying less space and are economic including the timber value, production of fruit, providing shade, shelter for animals, especially birds and so on.

We know Wood-oil tree (Dipterocarpus turbinatus: Garjan in Bangla) is a very good timber species growing usually 30-40 meters straight.

The second timber tree of choice can be the well-known teak (Tektona grandis: Segun). Teak trees grow about 10-15 meters straight shoot and the timber quality is high. We do have a number of these trees grown on roadsides. We need more of this high quality timber.

Redwood (Dalbergia sisso: Shishu) is another high quality timber tree. But this rarely produces a long straight shoot. However, its planting should continue for the timber's high polish taking quality.

Mahogany (Swietenia mahagoni) is well known for timber value having a straight shoot of more than 10 meters long. For its quality it has won the 'avenue tree' status. Planting its saplings should continue.

Indian lilac (Lagerstroemia speciosa: Jarul) is a very good timber tree producing over 10 meter long shoot and it also produces a reddish beautiful flower once a year. The timber is famous for making watercrafts like boats, launches and ships. The added quality of this tree is that it can grow in water and can be planted at the lowest ebb of the roadsides in place of the less important Babla (now being planted largely).

Cedar (Polyalthia longifolia: Debdaru) produces the shoot usually about 10-15 meters long and the timber is also fairly good. This tree looks very beautiful with its short branches and long serrated leaves. This has attracted the city fathers' attention much earlier and most of our road island trees are of this beautiful species with evergreen leaves producing much oxygen round the year.

Rain tree (Samanea saman: Rendi koroi) is a fast growing timber tree and most of the ordinary furniture in Bangladesh is made of this timber. However, it takes much space on the roadsides. So its saplings should be planted at some more distance so that narrower trees can grow in between.

Our indigenous silk flower (Albizzia lucida: Shilkoroi) yields a better timber though is not so fast growing. It can grow and live in water for some months.

Apart from these trees grown only for timber, we can turn to some trees famous for both timber and fruits. Black berry (Syzygium cumini: Jam), jackfruit (Artocarpus heterophyllus) and mango (Mangifera indica) are some of them.

Black berry is famous for its tall straight shoot. The fruit it produces is smaller in size and no man can pluck all the fruits. So some are left out for birds and this plant can act as a good source of food and shelter for our dwindling bird community.

Jackfruit is our national fruit. The tree, though does not grow as tall as those described above, its quality of timber is very high. The large fruits can be protected if leased to the local people. Mango is termed the king of fruits. The shoot grows almost the same length (3-5 meter) as jackfruit. The timber, however, is not as good as of jackfruit. But the shade produced by a mango tree is much better and can act as shelter for the passers-by.

Banyan (Ficus bengalensis) is, perhaps, the largest and most spread tree in the world. We have our own variety of this. Banyan saplings are conventionally planted in bazaars to provide shades to the people. If grown to its proper size a banyan tree can serve not only for the shades, the small fruits not edible for humans, are a source of food to many birds and the bushy top is an excellent place for nesting of birds. So banyan is very bird-friendly. May be the sides of national highways, would, also not be very suitable for planting many banyan trees, but some planted at some specific distance can serve the two purposes described above.

Red silk cotton tree (Bombax ceiba: Shimul) is now becoming rare in Bangladesh. Its timber is of low quality. But its fruit produces silk cotton that is now scanty and much more valuable than corpus cotton. Therefore planting some saplings of this species is of utmost importance both for the sustenance of this plant species and for the pillow filling cotton.

Growing some medicinal plants is also very much emphasised these days. We were rich in those just few decades ago. Thanks to our policy makers (including the PM) for their realisation of the need for the medicinal plants. Of the medicinal plants very few are tree varieties (most being shrubs or herbs). Two of the tree varieties are Arjun (Terminalia arjuna) and the well-known Neem (Azadirachta indica). Arjun is not so well known as neem. Some such plants can be grown by the sides of all the national highways of the country.

I don't understand why the people planting saplings on the either side of national highways have no choice at all. They plant any tree and still many eucalyptus saplings have been planted on the sides of the 48-kilometre long new road from Kodda in Gazipur to Modonpur in Narayanganj along the eastern side of Dhaka (known as the eastern by-pass road) joining the North-west to the South-east. Some acacia and mahogany are also seen. But no Gorjan, teak, Jam, Jarul or cedar is found along this potential tree growing new highway.

A specific plan for the Dhaka Eastern By-pass
It is hoped that many more saplings would be planted this year. Large number of Garjan, Jam, teak, cedar, mahogany and Jarul saplings should be planted because these take less space but produce the high quality timber. Some rain tree, silk flower, silk cotton, mango, jackfruit and banyan saplings can also be planted maintaining distance. Some neem and arjun saplings should be planted for their medicinal value.

The narrow common timber trees like Garjan, Jam, teak, cedar and Jarul are planted at 3 meters (about 10 feet) distance. One row along one side only of the 48-kilometre new highway would number at 16000 trees. There can be at least two and at best four rows of such trees on either side of the highway. Usually one side of the highway has plain (high) land and the other lowland. The lowland side is suitable for planting four rows of trees, the highland side may be suitable for two rows.

On the lowland side of the highway, mahogany (beautiful and straight) saplings can be planted on the highest ebb, followed by redwood, Garjan and Jarul (at the lowest ebb). Every row can have over 16000 plants. On the other side (presumably highland side) teak (that does not thrive in water), Jam and cedar can be planted. If this side is also a slope, then Jarul saplings can be planted at the lowest ebb again.

Besides these narrow straight trees, jackfruit, Shimul and medicinal plants can be planted on the highland side at a certain distance (say 100 meters) in between the teak, Jam and cedar. Some mango, rain tree and Shilkoroi saplings can be planted in between the second and third row of plants listed earlier for the lowland side. Thus about 500 such spreading trees can be planted in one row, certainly decreasing the number (16000) of narrower trees on the row. Banyan trees can be planted at more distances (say one in 500 meters) on any side, preferably along the second row. The number of banyan trees planted at half kilometre distance on both sides would count about 200 (96 x 2 = 192, to be precise).

If the roadsides are divided into some parts and those parts are leased out to local people for some specified time period (say 20-30 years), the fruit-harvesting sharing problem can be solved. Besides, the plants would receive maximum care from these owners.

If the chosen best varieties of trees are planted and supplemented by compartmentalisation and leasing, the sides of all national highways can support a good number of human families too.

The writer is a specialist, National Curriculum and Textbook Board (NCTB) and Life Member Zoological Society of Bangladesh.