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Vol. 5 No. 4 - October 1999

Bioremediation of Urban Environmental Pollution by Ornamentals

By: S. C. Sharma and R. K. Roy

Earth was a beautiful landscape but man has ruthlessly exploited for his greed specially in the present century. With rapid industrialisation and random urbanisation environmental pollution has become a serious problem. Over exploitation of open spaces, ever-increasing number of automobiles and demographic pressure have further aggravated the problem. There are various ways and means to mitigate the urban environmental pollution. Planting of trees and shrubs for abatement of pollution and improvement of environment is an effective way and well recognized throughout the world. Earlier, the purpose of planting trees in urban areas was purely aesthetic. The incessant increase of urban environmental pollution has necessitated to reconsider the whole approach of urban landscaping and its orientation in order to achieve duel effect i.e. bioaesthetics and mitigation of pollution. Proper planning and planting scheme depending upon the magnitude and type of pollution, selection of pollution tolerant and dust scavenging trees and shrubs should be done for bioremediation of urban environmental pollution. Pollution, the major problem in cities is compounded by the fact that there is no exhaust for the polluted air to escape. Landscape architects can solve the pollution problems related to urban landscape by creating a micro-climate.

Planting along the road:

Roads are the important sites of the urban areas which contribute significantly in mitigating pollution by planting trees on both sides. Unfortunately, in most of the old Indian cities and towns, there is hardly any provision of sufficient space for the same. However it is necessary to study the type of road, overhead electrical cables, space available on both sides, central verge, traffic triangles, round abouts, squares and other open space available before taking up any plantation. It has been observed that trees and shrubs which are drought / frost resistant are generally tolerant to pollution.

Selection of trees is another important task. Before selecting any plant species, it is necessary to consider following characters : agro-climatic suitability; height and spread; canopy architecture; growth rate and habit (straight undivided trunk); aesthetic effect (foliage, conspicuous and attractive flower colour); pollution tolerance and dust scavenging capacity. Some of the ornamental trees which have aesthetic effect and tolerant to pollution have been screened and recommended for planting along the roads. Acacia auriculiformis, Ailanthus excelsa, Alstonia macrophylla, A. scholaris, Albizzia lebbek, Bauhinia acuminata, B. purpurea, Butea monosperma, Cassia fistula, C. marginata, C. siamea, Casuarina equisetifolia, Crataeva religiosa, Drypetes roxburghii, Ficus benjamina, Lagerstroemia duperreana, L. flosreginae, L. rosea, Mimusops elengi, Polyalthia longifolia, P. longifolia 'Angustifolia', P. longifolia 'Pendula', Peltophorum ferrugineum, Tectona grandis, Terminalia arjuna, T. muelleri, Thespesia populnea etc. Emphasis should be given to the native plant species which are comparatively well acclimatised, stress and pollution tolerant.

Central Verge:

Central verge of the two way roads in the cities and towns are often found neglected and devoid of any planting. It is recommended that this area should be well utilized by planting dwarf trees and shrubs. This will not only serve aesthetic purpose but also functional being physical barrier for the glare of head lights of the vehicles which is essential for effective and safe operation of the roads during dark hours. Planting may be done either in single or double row depending upon the space available. Since these plants are more close to the automobile exhaust, their capacity for pollution tolerance should be considered before selection. Following plant species have been reported as pollution tolerant and recommended for plantation: Acalypha wilkesiana, Bougainvillea 'Chitra', 'H.C.Buck', 'Lady Mary Baring', 'Mary Palmer Special', 'Partha', 'Shubhra', 'Zulu Queen'; Caesalpinia pulcherrima, Callistemon lanceolatus, C. polandii, Cassia surattensis, Duranta plumeri, Euphorbia milli, Hamelia patens, Hibiscus rosa-sinensis, Ixora coccinea, Jatropha panduraefolia, Lantana camara, L. depressa, Malpighia coccigera, M. glabra, Murraya paniculata, Nerium oleander, Phyllanthus niruri, Rosa'Gruss an Teplitz', Tabernaemontana coronaria, Thevetia neriifolia, Vinca rosea, Wadelia lacinata etc.

Traffic Island:

Traffic islands at the main road intersections vary in shape and size from square, triangle to round. Whatever may be the shape, these islands should be property planted with the dwarf trees, shrubs and ground covers recommended for planting along the road and central verge which will contribute effectively in mitigating the air pollution.

Greenbelt:

Greenbelt is defined as the mass plantation of pollution tolerant trees and shrubs in an area for the purpose of minimizing air pollution by filtering, intercepting and absorbing pollutants in an effective manner for improvement of the environment. Every town and city must have certain area earmarked for the development of greenbelts. The effectiveness of the greenbelt depends on the several factors viz. climatic conditions, design, selection of plant species and its characters and type of pollutants. The importance of greenbelt can be ascertained from the estimate of cleansing capacity of 3.7 tonnes of CO2 from atmosphere and supply of 2.5 tonnes of oxygen from one hectare of woodland. Following trees and shrubs are recommended for planting in the greenbelt which have aesthetic effect as well as pollution tolerant capacity: Acacia auriculiformis, Albizzia lebbek, Azadirachta indica, Bougainvillea cultivars, Bauhinia purpurea, Butea monosperma, Cassia siamea, C. surattensis, Dalbergia sissoo, Ficus infectoria, Diospyros embryopteris, Lagerstroemia duperreana, Melia azedarach, Millingtonia hortensis, Murraya paniculata, Nerium oleander, Nyctanthes arbortristis, Parkinsonia aculeata, Polyalthia longifolia, Putranjiva roxburghii, Terminalia arjuna,T muelleri, Thevetia neriifolia etc.

Considering the present scenario of urban environmental pollution, there is a growing need for changing the approach of planting trees and other plant species. Inclusion of the ornamental plants having pollution mitigating ability in the landscape plan will serve the duel purpose in the long way for making the cities green and pollution free. Proper planting scheme will bring life and colour in the cement concrete jungle and healthy environment to the urbanities.

Dr. S. C. Sharma is an Emeritus Scientist (CSIR) and Dr. R.K.Roy is a Scientist in Botanic Garden at National Botanical Research Institute, Lucknow, India.


This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.


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