Human beings are not the only living organisms vulnerable to ground level ozone. According to the Environmental Protection Agency, ground level ozone occurs as a result of chemical reactions between pollutants, such as those produced by cars, power plants and refineries, and sunlight. Humans exposed to ground level ozone may be vulnerable to respiratory problems, such as shortness of breath and chronic obstructive pulmonary disease, or COPD. But plants are vulnerable to ground level ozone, too. When sufficient ozone enters the leaves of a sensitive plant, it can slow the plant’s growth and increase its risk of disease and damage resulting from insects and make it more vulnerable to injury caused by severe weather. Ground level ozone also can reduce photosynthesis, the process in which plants convert sunlight to energy so they can survive and grow. Black cherry, quaking aspen, tulip poplar, and white pine are just some of the trees that are sensitive and potentially vulnerable to ozone exposure. When plants suffer because of ozone exposure, the result produces a ripple effect that impacts the entire ecosystem, adversely affecting species diversity, habitat quality and water and nutrient cycles.