IMPACTS OF TROPOSPHERIC OZONE AND AIRBORNE NITROGENOUS POLLUTANTS ON NATURAL AND SEMINATURAL ECOSYSTEMS - A COMMENTARY

Man's activities pose a number of threats to the functioning, structur e and diversity of natural and seminatural ecosystems. One of the main threats is the increase in concentrations in air pollutants in this c entury (Wellburn, 1988; Tamm, 1991). This paper is a commentary on the effects of tropospheric ozone (O-3) and airborne nitrogen deposition (both oxidized (NOx) and reduced (NHy) compounds) on natural and semi- natural ecosystems, based upon the oral presentations and the discussi ons during the Symposium, extended with a personal overview and some s uggestions about future challenges for research. The most important ef fects of these air pollutants on natural and semi-natural vegetation a re summarized and evaluated in ecological terms, with respect to the f unctioning and structure of unaffected systems. Air pollutants are tra nsported over both short and long distances (as far as a few thousand km) before being deposited on surface water, vegetation or soil. In th is way, vegetation over a large area or in remote regions can be influ enced by airborne pollutants (see Fowler et al. (1998); Asman, Sutton & Schjorring (1998)).