Left: Acacia monoculture which we wrongly do. Right: Mixed forest that we can recreate through polyculture.

THE term "sustainable development" seems to have reached a stage of sustainability after having been used for long. Sustainability is a word most suited, perhaps, for describing an ecosystem constituted of biota like plants, animals and microbes living in any area of the earth. But unfortunately, we -- the most destructive animal species -- did not let ecosystem thrive sustainably, rather we caused extinction of much of the biodiversity in the world, resulting in large-scale environmental degradation.
Bangladesh tries to reforest its barren land, but there are some areas where trees are still being cut down. The government inaugurates the tree plantation season in June every year, and it continues till September. Tree fairs are arranged all over the country; thus tree plantation receives due importance. But what does not receive due attention is the importance of choosing the right kind of trees that can contribute both to plant-biodiversity and harbour plant-dependent biota including animals. To help provide food and shelter to the existing animal species, polyculture of indigenous plant species should be the way.
Does our reforestation comply with indigenous polyculture? I don't think it is. I have seen patches of land in Madhupur and Bhawal forests where only lines of eucalyptus or acacia trees were planted. Such monoculture forestry is seen to be the trend also in the deforested areas in Chittagong.
We have also committed similar mistakes in selection while planting saplings by the sides of highways and city roads (and also road islands). We make acacia (that rarely has a straight trunk) jungles by the sides of national highways, and eucalyptus (which contributes to dryness through transpiring water) saplings are still planted on both sides of roads.
The forest department seems to be counting the total forested area, which is around 8%-9% but should be about 25%. Only counting will not replenish the natural ecosystem, rather the forests should contain many types of plant species, especially indigenous ones so that animal species specifically dependent on certain plants can survive. Due to growing population, Bangladesh does not have enough scope to regain about 25% as forested area, so we have to choose the best kinds of trees for planting.
The following kinds of trees should be planted:
Trees having fruit-bearing and timber quality together.
Trees having appreciable timber value.
Trees that grow fast.
Trees that spread over large areas.
Trees that produce fibre and/or cotton.
Trees having medicinal value.
There are many trees famous for both timber and fruits, like blackberry, jackfruit, mango and palmyra palm (tal). Blackberry is famous for its tall straight trunk. Jackfruit is our national fruit and the tree, though not very tall, has timber of very high quality. Some mango trees by the roadsides can provide fruits as well as shade. Palmyra palms are a source of fruits, sugar and hard wood, and a row of them along the sides of roads can also prevent vehicles from going off the road.
Trees grown mainly for timber are wood-oil tree (gorjan), teak (segun), redwood (shishu), Indian lilac (jarul), mast tree (debdaru) etc. Debdaru and jarul usually grow 10-15 meters high, while gorjan and segun may reach even 30-40 meters. Our indigenous silk flower (shilkoroi) yields good timber as well.
Fast growing trees like rain tree (rendi koroi) and mahogany (mahogoni) are found all over the country and rain tree alone provides the bulk of timber for low-cost furniture. Another fast growing tree, almond, has a tall trunk and is famous for its medicinal value.
Banyan (bot) is, perhaps, the largest and most spread-out tree in the world. If grown to its proper size a banyan tree can provide extensive shade. The small fruits not edible for humans, but are food for many birds, and the bushy top is an excellent niche for nesting. So banyan is very bird-friendly.
Red silk cotton tree (shimul) is becoming rare in Bangladesh. Its timber is of low quality, but its fruit produces silk cotton that is now scarce and much more valuable than other cotton varieties. 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.
We were rich in medicinal plants just few decades back. Tree varieties (many are shrubs or herbs) of the medicinal plants are arjun, bahera and the well-known neem. These plants can be grown by the sides of all the highways. The forests can also have a mixture of these trees, and some areas can be sorted out in every village and moholla to establish medicinal plant gardens.
Every attempt at reforestation should aim at establishing polyculture forests consisting of the best kinds of trees. The highways can have 3-4 rows of trees on either side. To contain more trees of the right kind, saplings should be planted following a good plan. The lowest ebb of the roadside may have jarul saplings along with some babla and hijal. These plants can thrive in water. Aam, mahogoni, gorjan, debdaru, rendi koroi, jaam etc. may be planted in the middle. Kathal, shimul, segun, redwood etc. cannot withstand water, so they should be planted along the highest ebb. Besides, a few banyan trees and medicinal plants can be planted at some distance along the highways.
Abdus Sattar Molla is a biologist and a PhD candidate in NIE, Singapore. E-mail: [email protected].