The problems connected with the dying of forests give rise to the checking of all components of pollutants. At present attention is concentrating also on the unfavourable effects of ozone, because ozone concentrations toxic for the wood species were measured in Europe, too. The purpose of our research was to produce visible damage to the assimilation organs of our principal economic wood species by the application of ozone, to characterize the symptoms observed and to document them photographically. Fumigation experiments were made with four years old plants in containers in a foil shed in June - July 1986. Ozone was generated by the LABO 76 ozonizer made by the firm of Trailigaz. The final ozone concentration was determined by the iodometric titration method. The mean ozone concentration during the experiments was 760 ppb. The following wood species were subjected to the experiment: Pinus nigra, Pinus strobus, Pinus mugo, Pinus cembra, Larix decidua, Populus canadensis in two varieties, Fagus silvatica and Quercus robur. According to the sensitivity of the individual species the symptoms of damage appeared gradually during the fumigation. The broad-leaved species and the larch reacted more sensitively than the coniferous species, the unfavourable effect of ozone manifested itself earlier in the former than in the latter. The damage to the leaves and needles began with chlorotic dwarfs which changed into point or surface necroses in the next phase. We succeeded in producing the damage symptoms in all wood species subjected to the experiment. Picea pungens resisted best to ozone impact. The damage symptoms were documented photographically in colour. The obtained data will be used in the next phase of research in which the influence of lower ozone concentrations on some internal changes in the needles and leaves of various forest wood species will be investigated.
