- 2130 - 
  
2,5 Y) to yellow-red (7.5 YR) hues. Healthy pines usually have up to 5 years 
of needle retention, wheregs smog affected foliage may have only the current 
growth of needles, many bare branches are visible to the photo-interpreter and 
permit the positive identification of damaged trees. : 
2,5 Fluoride Pollution 
Serious pollution today comes from brickworks and aluminium smelters. The two 
main pollutants are sulphur dicxide and fluoride gas. Sulphur dioxide from 
older brickworks with insufficiently high chimneys may damage crops in the vicinity. 
Newer works dispose of the gas more efficiently. However, fluorides, evea at 
levels of 0.1 ppm or less can cause serious damage to plants. Fluorides are 
emitted in two forms, as hydrogen fluoride gas (HF) and particulate fluorides 
(Ca, A1, Si and Na). They are formed in the production of steel, bricks, elay- 
pottery, aluminium, ironstone, vitreous enamel and china clay. 
In Norway, aluminium smelters were once built at the bottom of fiords, near the 
site of hydro-electric power and were surrounded by many square kilometres of 
dead and dyirg coniferous trees. The restricted topography concentrated the 
pollution effects in areas up to 30 kms from the source, with death of pine trees 
withinô kms and a 25% death rate of up to 15 kms distance. Very near to the 
source of pollution only tall herbs and grasses exist and often with signs of 
lead chlorosis. In Britain there have been reports of fluoride damage io 
agricultural crops but the most serious effects have been on cattle. When 
fluorides are deposited on pastureland, the grass concentrates the pollutant 
leading to poisoning of the grazing animals, in the mild form present as mottled 
teeth, while in severe cases the skeletal bones are softened and eventually the 
animals die. 
Most modern smelters have very high chimneys so local damage is prevented. Thev 
are usually built on undulating and well ventilated land with the folloving adjacent 
land uses - urban, residential and some horticultural cultivation. Tbe plani 
species to be avoided include Pinus, Picea, Populus, Acer pseudoplatanvs, Tilia, 
Prunus and spring bulbs. Genotypes show a degree of resistance and this permi*s 
possibilities in breeding resistant plant species. 
Colour infra-red films at 1/5,000 scale are favoured for identifying various levels 
of damage to Picea (spruce) species. For example, on colour infra-red healthy 
spruce appears purple-pink or pink, heavily damaged spruce appears grey or green- 
grey and dead spruce appears blue-green. As many of the older needles nave 
fallen off from earlier fumigations, dark shadows appear on affected spruce. 
This is emphasised by the high contrast characteristics of colour infra-red 
film. Hildebrandt and Kenneweg (1968) noted that interpretation on colour 
infra-red iransparencies along the edge of the Ruhr Valley indicated that the 
intensity of damage to spruce stands appeers to be related to altitude, even at 
long distances from the source of pollution. Thus, the vitality of Norway spruce 
could be used as an indirect indicator of the distribution of oxidants. The 
colour infra-red film depicted alilevcls of damage from old dead snags to less 
severely damaged t.ees. Darkenings of foliage of a moderately affected spruce 
can be seen on black and white infra-red prints, but are hardly detectable on 
panchromatic prints. 
The silvicultural intensity and multiple use of most European forests has 
necessitated information about all air-pollution injuries for almost every 
small planning unit, in addition to estimated damage for large areas. In 
Fast Germany, where more than 5% of the entire forest area suffers sevevely 
from air-exidant damage, detailed inventories are an essential part of the ten 
year forest management plans in some forest regions. In most cases these air 
pollution surveys are carried out with two stage probability sampling (Wolff, 
1970, Lux, 1965). fhe first stage involves the interpretation of multiband 
aerial photography at a scale of 1/5,000 to 1/8,000. The second stage is a 
ground check of randomly selected plots.