Many scientists now believe that the direct and indirect impacts of acid deposition on vegetation are substantive, whether these effects are measured in a biological or an economic context.The growth rate of spruce trees in the Green Mountains of Vermont declined by 50% between 1963 and 1973.Tree ring analysis suggests similar reductions in forest growth in Europe. Acid precipitation has been implicated in these declines, but unambiguous cause effect relationships are lacking.
In addition to the extent of acid deposition (concentration or total deposition), the response of plants to acid deposition will depend on a number of factors including:
- Plant species, ecotype or cultivar.
- Plant age or stage of development.
- Characteristics of exposure (frequency, duration, period, form of acidity, time between exposures, and others).
- Other environmental factors that affect plant vigour.
- Buffering capacity/sensitivity.
- To address these challenges, many scientists have resorted to research in controlled environments such as greenhouses or growth chambers, using simulated acid precipitation.
Direct effects of acid precipitation on plants:
The acid rain affects the crops as well as the vegetation. The effect of acid rain on plants is grave. It not only damages the root, but also stops its growth and brings an end to the life of a plant. The nutritive value of the soil is reduced to a great extent as an effect of acid rain. Acid rain effects can be seen on the useful micro organisms which convert the decayed organic matter into essential nutrients for the soil. The consequence is that the micro organisms are killed resulting in reducing the availability of nutrients for the soil and plants. Also, the waxy layer of the leaves is damaged which make the plant more and more susceptible to diseases.
The havoc done by acid rain is not localised in the place where it is caused. The atmospheric emissions may travel for several days and over long distances depending upon wind and climatic conditions, before coming down as acid rain. The problem caused in an industrialised area may therefore result in acid rain in the surrounding forests or lakes, or even further away. It is believed that around 50% of the acid rain that occurs in Canada is due to pollution caused in the United States of America, and the effect of polluting industries in England can be felt in Norway