Soundscapes, the combined sounds from natural and non-natural sources, are recognized as an important resource in national parks. The natural soundscape is generally comprised of two main sound categories—those from biological or those from physical sources.
Organisms such as birds, frogs, and plants, create biological sounds, while forces such as wind, rock fall, and rivers, create physical sounds. These two types of sounds can be used to characterize different habitats. The specific soundscape characteristics are an important attribute of Denali National Park and Preserve’s (Denali) natural systems, for non-natural sounds can obscure or disturb ecological functions, as well as adversely influence visitor experiences (NPS 1995).
Natural soundscapes are components of “the scenery and the natural and historic objects and the wildlife” as protected by the Organic Act (Public Law 64-235). They were specifically recognized and protected by the National Parks Overflights Act of 1987 (Public Law 100-91). Due to ongoing concern about aircraft overflight noise, the National Parks Air Tour Management Act was established, which requires the Federal Aviation Administration and the National Park Service to cooperatively develop air tour management plans for any park where commercial air tour operations exist or are proposed (Public Law 106-181).
Although Alaska parks were excluded from the act, they were not excluded from aircraft noise and other influences on the natural soundscape and visitor experience.
Start of Monitoring
By 2000, park managers recognized that the natural soundscape of Denali was increasingly affected by non-natural sounds. Because preserving the natural soundscape also helps preserve the associated wilderness values and visitor experiences, a soundscape program was initiated. The hope was to better understand, manage, and preserve the natural soundscape of Denali. In addition, soundscape measurements provide objective scientific data for future manag-ment decisions.
Each sound station records sound levels every second and collects five-sec-ond digital recordings every five minutes (288 samples per day). With this information we can identify the sound sources present at each sampling location, the sound levels of each sound source, and calculate the number of times per day each sound is audible. These data are used to compare the natural ambient sound levels to the sound levels of non-natural sounds. From the data analyzed to date, wind is the most widespread natural sound in all areas, and aircraft overflights are the most common human-generated sound.
Soundscape studies are relatively new for the National Park Service. The Denali Soundscape Program is developing new techniques and important information about soundscapes in Alaska parks. As identified in a new draft management plan, soundscape measurements are an important indicator of the level of human influence on park resources (NPS 2005). Information provided through this program will help managers protect natural soundscapes and preserve high quality visitor experiences in Denali.