The adverse effects of smog are not limited to humans alone. As it turns out, plants are perhaps more sensitive to air pollutants than humans. In particular, acid rain has left areas barren or with severely damaged vegetation. Yet, perhaps the greatest damage has been from ground-level ozone and PAN. Entering leaves of plants from the stomata during normal gas exchange, both ground-level ozone and PAN can cause discoloration, damage, and loss of leaves-reducing photosynthesis by as much as 50% (Munster; Gow and Pidwirny). Plants also become more vulnerable to attacks by pests, disease, and other environmental disasters (Shaw). Consequently, the plant's ability to store food, grow, and reproduce is hindered (ibid).