Ozone can harm trees

The Tree Care Industry Association released a list of ozone-tolerant and ozone-sensitive species.

Sensitive
Yellow poplar
White ash
Hickory
Black cherry
Flowering dogwood
Eastern white pine
Sassafras
Aspen

Tolerant
Hemlock
Eastern and Colorado blue spruce
Yew
Rhododendron
Azalea
Oak
Most maples
Balsam fir
London plane

“Humans aren’t the only ones to be affected by recent ozone alerts in various parts of the country,” says Tchukki Andersen, BCMA, staff arborist with the Tree Care Industry Association. “Many of the most commonly planted trees in the nation’s urban forest also suffer during high levels of ozone pollution.”

Ozone pollution is the result of a chemical reaction that converts car exhaust into ozone, a colorless unstable toxic gas, in the presence of light. The regions that have the highest automobile traffic and sunshine are the most at risk. But even areas without congested traffic may suffer, since ozone is transportable over long distances. The pollutant acts as an oxidant that disrupts the chemical pathways in a plant’s photosynthetic powerhouse, the chloroplast. In response, the tree manufactures antioxidants such as vitamin E and C. This process may offer relief from low levels of ozone, yet are no match for repeated exposure to toxic levels.

Ozone injury on trees looks different on different species. On the leaves of poplar and black cherry, the homeowner may see brownish lesions on a leaf that appears water-soaked. On ash and hickory, however, the lesions are white. On other species, damage appears as a purple stippling all over the leaf. Evergreens appear to have burnt needle tips.