overpopulated without it, leading to vegetation degradation from overgrazing elk herds. Opponents cite that there has been an increase of predators such as the wolf and grizzly bear in Grand Teton National Park, rendering the annual hunt unnecessary and exposing hunters to attacks by grizzly bears as they become accustomed to feeding on remains left behind from the hunt. Fire ecology The role of wildfire is an important one for plant and animal species diversity. Many tree species have evolved to mainly germinate after a wildfire. Regions of the park that have experienced wildfire in historical times have greater species diversity after reestablishment than those regions that have not been influenced by fire. Though the Yellowstone fires of 1988 had minimal impact on Grand Teton National Park, studies conducted before and reaffirmed after that event concluded that the suppression of natural wildfires during the middle part of the 20th century decreased plant species diversity and natural regeneration of plant communities. One study conducted 15 years before the 1988 Yellowstone National Park fires concluded that human suppression of wildfire had adversely impacted Aspen tree groves and other forest types. The majority of conifer species in Grand Teton National Park are heavily dependent on wildfire and this is particularly true of the Lodgepole Pine. Though extremely hot canopy or crown fires tend to kill Lodgepole Pine seeds, lower severity surface fires usually result in a higher post-wildfire regeneration of this species. In accordance with a better understanding of the role wildfire plays in the environment, the National Park Service and other land management agencies have developed Fire Management Plans which provide a strategy for wildfire management and are expected to best enhance the natural ecosystem. Air and water quality Grand Teton National Park is more than air distance from any major urban or industrial area, and localized human activities have generally had a very low environmental impact on the surrounding region. However, levels of ammonium and nitrogen have been trending slightly upwards due to deposition from rain and snow that is believed to originate from regional agricultural activities. Additionally, there has also been a slight increase in mercury and pesticides that have been detected in snow and some alpine lakes. Ozone and haze may be impacting overall visibility levels. Grand Teton National Park, in partnership with other agencies, erected the first air quality monitoring station in the park in 2011. The station