Pollution and plants

bioindicators such as trees take note of many changes in the environment and will thus soon become valuable recorders of contamination, very convenient for environmental monitoring, reports D K Pandey et al of the Forest Research Institute, Dehra Dun, Uttar Pradesh. Tree bark remains in the environment for many years. Therefore, it records very precisely any changes occuring in the environment. Tree bark works as an exceptionally sensitive indicator of environmental acidity. The increase of so2 concentration in the air is accompanied by the increase in acidity of the tree bark. However, the quantum of tree bark acidity depends on tree species, age and health of trees and the substrate upon which the tree is growing.

Among various trees, a deciduous tree bark is less acidified, so it acts as a more sensitive indicator of contamination than barks of coniferous and other trees.Deciduous tree barks record higher acidity. Pine barks among conifers, possess a good indicator value of environment acidity. They can be used to detect fluorine concentration in the air. Besides, using tree barks for monitoring air pollution has other advantages: the process takes less time and is apt for practical application, because of the low equipment requirement. Reports also show that plants can monitor air pollution by showing special symptoms. Some of the plants that can be used as air pollution indicators have been listed below ( see table: Tree species as indicators of air pollution ).

Trees also function as sinks of air pollutants because the large surface area of their leaves absorbs pollutants through numerous stomatal (pores on leaf surface that help in gaseous exchange) operations. They are the best dust collectors; average dust collection ranges from 1.44-5.35 grams per square metre on the leaf surface. However, this varies from species to species ( see table: Trees as dust collectors ).

Today, there is a need for round-the-year pollution monitoring of metropolitan cities and industrial areas, to lay down environmental quality standards for each pollutant and also reduce the extent and nature of the pollutant at source. Plants thus help us give specific details on morphological, physiological and biochemical studies, and enable us to devise injury control measures.

Tree species as indicators of air pollution
Tree species
Air pollutant Symptoms/effects

Adina cordifolia (Haldu)
Bauhinia racemosa(Kachanal)
Diospyros cordifolia (Bans)
Juniperus species (Junipers)
Thuja occidentalis (Morpankhi)
Populus delteoides (Poplar)
Quercus species (Oak)
Tamarindus indica (Imli)
Pinus roxburghli (Chir)
Mangifera indica (Mango)
Sulphur dioxide

Intervenial regions of leaf turn yellow (chlorosis) or brown (necrosis)

Cassia fistula (Amal tas)
Dalbergia sissoo (Shisham)
Picea glauca (White sprouce)
Juniperus persica (Aru)
Prunus cerasoides(Himalayan cherry)
Salix species (Willow)
Ulums species (Elm)
Hyerogen fluoride

Leaf tip and margine turn brown (necrosis)

Pinus roxburghii (Chir)
Juglans nigra (Black walnut)
Quercus species (Oak)
Picea species (Sprouces)
Juniperus species (Junipers)

Red and brown spots on leaf surface, folding of leaves if concentration increase, necrosis, chir needle tip burns
Azadirachta indica (Neem)
Mangifera indica (Mango)
Dust and smoke
Leaves turn yellow, photosynthesis rate decreases

     Tree as dust collectors
    Trees species Dust collected gm/sq m of leaf surface
    Tectona grandis (Teak) 5.35
    Shorea robusta (Sal) 4.50
    Terminalia arjuna (Behera) 4.49
    Mangifera indica (Mango) 4.05
    Bauhinia purpuria (Kachnar) 3.90
    Butea monosperma (Plaw) 3.05
    Azadirachta indica (Neem) 2.29
    Cassia fistula (Amal tas) 2.24
    Tamarindus indica (Imli) 2.08

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