National parks are among America’s most pristine and intact ecosystems. Understanding the dynamic character of park ecosystems in context of larger landscapes is essential to conserve their ecological integrity. Assessing attributes of landscape change across broad spatial and temporal scales provides insights into the dynamic nature of pristine and anthropogenic-affected ecosystems. Our study objective was to map and determine size, magnitude, frequency, and spatial distribution of landscape change over 25 years in three large Washington State National Parks (Mount Rainier, North Cascades and Olympic) and in ~ 16 km buffer around them. We monitored the occurrence and distribution of eight landscape change categories: Avalanches, Forest Clearing, Human Development, Fire, Mass Movement (e.g., landslides and debris flows), Progressive Defoliation (e.g., insect, disease or drought), Riparian (e.g., channel migration due to flooding), Tree Toppling (e.g., wind or root rot), and Winter Ice (e.g., foliage removal from heavy snow or ice). We used a pixel-based change detection algorithm (LandTrendr) to identify and track landscape change within a “temporal stack” of Landsat imagery from 1985-2009 and then combined like-adjoining pixels that changed in the same year into “patches” >0.8 ha. Manual and Random Forests classification methods were used to assign change categories to patches.
The annual rate of landscape change was 0.02% in Mount Rainier and Olympic National Parks, 0.09% in North Cascades; in the area surrounding these National Parks, the annual rate was 0.77%, 1.63%, 0.28%, respectively. The largest total area of landscape change detected was in Riparian category in Mount Rainier, Fire in North Cascades, and Fire and Tree Toppling in Olympic. Forest Clearing was the dominant landscape change type in the area surrounding all three National Parks. Comparing the first 13 years, 1985-1997, with the next 12 years, 1998 to 2009, the amount of landscape change increased 233% in Mount Rainier, 293% in Olympic, and 747% in North Cascades. The annual rate of landscape change was higher in North Cascades National Park, the driest of the three National Parks where fires are larger and more frequent. Changes due to individual extreme weather events affected the overall amount of landscape change detected within the three National Parks, whereas numerous, small, but widespread changes from Forest Clearing dominated the area surrounding the National Parks. Landscape-scale change occurred at a substantially slower rate inside the three National Parks compared to the area surrounding them.