Scrub/forest environment in Denali.

The dominant tree species in the scrub/forest acoustical zone in Denali is spruce on the north side of the Alaska Range and a mixture of deciduous and coniferous trees on the south side. Willow, birch, aspen and alder also grow to heights that play a large role in attenuating sounds. The natural soundscape is less dominated by wind in this zone due to the presence of trees and tall shrubs that block and reduce wind speed. Compared to the other two zones, animal sounds are more frequently audible. A greater diversity of birds, insects and mammals occupy this scrub/forest zone than the other two acoustical zones. With the exception of aircraft sounds, audible sounds are usually generated by nearby sources rather than carried from distances. Red squirrel chatter replaces the sub-alpine zone’s arctic ground squirrel whistles, and woodland birds such as thrushes and warblers replace tundra bird species. Streams have turned into rivers in this zone, which then dominate the acoustics in the riparian and surrounding areas. Human-generated sounds originate from developed areas of the frontcountry and from travel corridors near roads and railways. Aircraft are often heard overhead throughout this zone. Again, the distinction between the natural soundscapes of the acoustical zones becomes blurred during the winter months when flowing water sounds have either stopped or are muffled by snowcover and animal sounds are reduced in diversity and number. The remaining difference between the three zones in winter is mainly determined by human-generated sounds.