Interannual Climatic Variation Mediates Elevated CO sub(2) and O sub(3) Effects on Forest Growth

Relationships between interannual climatic variability and carbon dioxide and ozone effects on forest growth over a 7-year period were examined. Elevated increased three heights, diameters, and main stem volumes by 11%, 16%, and 20%, respectively, whereas elevated ozone decreased than by 11%, 8% and 29%, respectively. Responses similar to these were found for stand volume and basal area. The amount of photosynthetically active radiation and temperature during specific times of the year coinciding with growth phenology explained 20-63% of the annual variation in growth response to elevated carbon dioxide and ozone. The results indicated that a several-year trend of increasingly cloudy summers and cool autumns were responsible for the decrease in carbon dioxide growth response.