The present review has focussed on improvements in the methods for assessment and monitoring of forest damage by searching for more cause related criteria. The following parameters should be studied further in respect both to their applicability in a monitoring aspect, and because they are likerly to qive the most specific indications on the individual air pollutants: microscopical and ultrastructural changes in cells, antioxidants and changes in proteins, enzymes and lipids. The following parameters may also, through further research, appear to be descriptive of specific air pollutants and at the same time preliminary be applied in a monitoring aspect: emission of hydrocarbons and pigment ratios. The following parameters are found to be directly applicable for forest monitoring, partly being parameters giving a general picture of tree vitality: parameters describing tree growth/vitality, assessment of the root system and nutritional status in the plant. The effects of some air pollutants are reviewed here. Possible parameters describing the cause effect relationships between these and forest damage and their validity for forest monitoring are evaluated: Proteins, enzymes and lipids: Proteins, enzymes and lipids are tje first reaction sites for the action of ozone (2.4.1 and 2.4.2). Unbalanced input of nitrogen increases the content of argenine in plants (4.3.2). Microscopical and ultrastructural changes: changes in the cell structures are one of the early effects of air pollution (2.5 and 3.2.2.). It is stated that senescence and stress caused by air pollution inflict different changes, and that these can be recognized. Pigments: a promising parameter for assessing cell damage caused by oxidants. Antioxidants: numerous studies have shown that some air pollutants, especially oxidants, e.g. ozone, induce production of antioxidants (2.5.2). Emission of hydrocarbons: this is, like the production of antioxidants, an early indicator of stress in plants. This parameter may be useful in monitoring of stress induced by air pollutants (2.7 and ch.5). Root system: changes in the tree will be reflected in the root system. The following parameters picture the root vitality: root biomass, root morphology, development of young roots, colour of young roots and distribution of nutrients in the root (3.3.2. and 4.5.3). Tree growth and tree vitality: all the air pollutants mentioned here bring about changes in the growth pattern of the trees. Abundance of secondary shoots, 5-year-height increment, stem increment in 1.3m's height and in the upper half of the tree and dry weight to fresh weight ratio differences between current and two year old needles are found to be descriptive of tree damage (ch.5). Nutritional status: both natural factors and air pollutants influence the nutritional status in trees. The nutrient balance is a valuable and necessary param....
