Where are the forests in the United States “not disturbed” over a quarter century?

Abstract:

Forests provide many important ecosystem services. Logging, fire, and other disturbances can disrupt or even diminish the provision of these services. Although many map products and inventory data can be used to estimate the total forested area in the United States, it is not clear how much of the country’s forest remained undisturbed in recent decades. Through the North American Forest Dynamics (NAFD) study, we have mapped both disturbed and undisturbed forests over the conterminous United States (CONUS) using sub-annual time series of Landsat observations. The results revealed that 33.6% of the land area of CONUS had forest cover during some or all of the years between 1986 and 2010. About two thirds of the nation’s forests remained undisturbed during the 25-year period. Most of these undisturbed forests were distributed in western and northern parts of the eastern US. The percentage of undisturbed forest in the southeastern states were lower, about 50% or less. In these states, much of the undisturbed forest was distributed along riparian zones or in protected areas, including national parks and national forests. In the northeastern and western US, riparian zones did not have a significantly higher proportion of undisturbed forests than non-riparian areas. While most protected areas had a high percentage of undisturbed forests, some of them had lower percentages than the average values of their surrounding regions. Topography may also have played a role in keeping forests “undisturbed”. Many ecoregions in the western and northern US had a substantially higher percentage of undisturbed forests at high elevations than at low elevations.