Flower Bush (IMAGE) American Society of Agronomy Caption High elevation spruce-fir forests have a mix of evergreen and deciduous plants. Shown, a rhododendron bush in bloom. Before the Clean Air Act of 1970, the morning fog could have contained acidic particles from air pollution. These acids were hurtful to humans, plants and soil. Credit Jennifer Knoepp Usage Restrictions For use with story only. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.