Effects of Chronic Exposures to Gaseous Pollutants on Primary Production Processes Photochemical Oxidant Impact on Mediterranean and Temperate Forest Ecosystems: Real and Potential Effects

Photochemical oxidants Cprimarily ozone) a s a i r po l lu tan ts pose a more ser ious problem t o f o r e s t s of t he United S t a t e s than any o ther s ing le a i r po l lu tan t . Temperate and Mediterraean fo r e s t s elsewhere have most l i k e l y been s imi l a r l y impacted and current inves t iga t ions of such e f f e c t s a re being pursued. Ozone Land i t s photochemically reac t ive precursors) has been demonstrated t o occur a t cons iderab le dis tances downwind of major urban sources. Ozone has induced pertubat ions t o vegetation over la rge areas and has therefore impacted innumerable and diverse fo r e s t ecosystems. Direct i n ju ry due t o ozone has been documented t o occur on numerous individual f o r e s t vegetation species but d i r e c t a l t e r a t i o n s of f o r e s t ecosystems a s r e l a t ed t o ozone induced e f f e c t s have only been extensively documented i n the San Bernardino Mountains of Cal i fornia; t o a l e s se r degree s imi la r s tud ies have been done i n the Blue Ridge Mountains of Virginia . Due t o t he current su l fu r dioxide (SO?) problems confronting European f o r e s t s and due t o the planned increased u t i l i z a t i o n of f o s s i l f ue l s i n much of t he North American Continent, the influence of ozone i n combination with SO2 must be f u l l y considered. The influence of o ther photochemical oxidants such a s nitrogen oxides and peroxyace ty l n i t r a t e on fo r e s t vegetation has remained r e l a t i v e l y unknown.