Seedlings of silver birch in a polythene tunnel were exposed to simulated acid rain at pH values of 2.5, 3.5, 4.5 and 5.6 while growing in pots of either John Innes No. 2 potting compost or an Arfon series soil. Measurements of visible and near infrared radiance were taken from the canopies of groups of plants exposed to each of the rainfall treatments, after 34 weeks for plants grown in John Innes compost, and after 75 weeks for plants grown in both soils. Plots of reflectance against wavelength revealed that only plants exposed to the control pH 56 treatment retained the shape of curve that is characteristic of healthy green vegetation. Discriminant analysis showed that the radiometer data could be used to distinguish between birch canopies which had been exposed to the different rainfall treatments after both 34 and 75 weeks.
The potential use of radiometry is discussed for identifying plants growing under the stress of acid rainfall in both controlled environments and in the field. It is apparent that further research using the more sensitive scanners now available will be required in order to improve the accuracy of this survey technique.