Source: Drew La Pointe, Neal Pastick, Bruce Wylie, U.S. Geological Survey
 

Black Spruce forest near Yukon River

Fog along the Yukon River showing a Black Spruce dominated forest in the foreground, which is prone to wildfire. Photo credit: Bruce Wylie, USGS

Probability of land cover change in Alaska

Map of Alaska showing probability (%) of change occurrence. Insets show fire boundaries from the Bureau of Land Management (BLM) Large Fire Database and Landsat 8 imagery (bottom right; 2016) north of Fairbanks, Alaska.

spruce forest remnants

Remnants of a spruce forest complex following a severe wildfire in the Yukon Flats National Wildlife Refuge, Alaska. Wildfires are the dominant landscape-scale disturbance operating at annual time scales in Alaska, and fires play a major role in the rate and extent of vegetation growth and productivity of a site. Wildland fires typically result in the reduction of surface albedos shortly after occurrence and combustion of below and above-ground biomass results in the release of heat trapping gases to the atmosphere. Photo credit: Bruce Wylie, USGS.

erosion along Alaska's coastline

Neal Pastick – lead author of the study – investigating erosion along Alaska’s Arctic coastline near the village of Kaktovik. Permafrost-dominated coasts of Alaska have drastically changed as the result of coastal transgression and storm-surge flooding which can result in the loss of cultural sites and damage to infrastructure. Photo credit: M. Torre Jorgenson

May 29, 2018 • New research has revealed significant changes to Alaska’s landscape in recent decades. During the past 32 years, about 13 percent of the state — 67,000 square miles or an area larger than the state of Wisconsin — has changed, according to a new USGS-led study in collaboration with researchers from academia (e.g. University of Minnesota) and other federal agencies (e.g. NASA ABoVE [Arctic-Boreal Vulnerability Experiment]).

This is the first study to document more than three decades of land and water changes across Alaska, and it is the first study to quantify the underlying drivers of those changes, which is vital for understanding how these systems may continue to change.

Alaska has experienced glacial retreat, shrub and treeline expansion, wildfires, erosion, pollution disturbances, and other changes over the last 32 years. Most of that change occurred in boreal regions due to the residual effects of fires that are still apparent after 60 years.

To fingerprint the sensitivity of Alaska’s ecosystems to changing environmental conditions and disturbances, the team of researchers combined aerial photography, satellite imagery (e.g. Landsat) and climate data into an integrated modeling framework. As a result, according to lead author Neal Pastick, the study provided the most detailed and comprehensive reconstruction of modern-day landscape transformation in Alaska to date.

Renowned landscape ecologist, Professor A. David McGuire from the University of Alaska Fairbanks – and a co-lead investigator and author of a ground-breaking study in to carbon and greenhouse gas effects on Alaskan ecosystems – believes that this research “…fills a critical gap in the understanding of the historical and potential future trajectories of change not only in Alaska, but in other northern high latitude regions.”

The team discovered that Arctic and boreal landscapes have experienced unprecedented changes in recent decades, a trend that is expected to continue, with significant consequences for natural and man-made systems. Despite a legacy of studies that have documented the heightened sensitivity of northern high latitude regions to change, the characterization and prognosis of that ecosystem change has remained elusive.

As one example, rising air temperatures are found to have directly and indirectly promoted vegetation growth through vegetation expansion and the exposure of land surfaces as glaciers retreat. But warming has also increased evaporation, resulting in decreased plant productivity and drought that can increase the risk of disease, fire, and mortality for woody vegetation. These changes can have a substantial impact on animal migration patterns and subsistence hunting. This finding demonstrates that northern high latitudes are not responding in a simple, linear fashion as air temperatures increase.

Along with increasing air temperatures, the amount of surface water has generally increased across Alaska. Surface water gains have occurred predominately in areas with extensive permafrost (perennially frozen ground) that have experienced the largest increases in mean annual air temperatures. Melting permafrost can result in land subsidence and ground collapses that affect roads, as well as other infrastructure needed for natural resource extraction.

While these changes will continue to impact human and wildlife populations in Alaska, they also will influence ecosystem and climate processes which may have far-reaching consequences for communities outside of Alaska.

“The upshot is that combined effects could push systems past tipping points and impact large areas, especially after fires,” said USGS scientist Bruce Wylie, who co-authored the study.

Adaptation to climate change requires enhanced monitoring capabilities to detect and track changes in globally significant Arctic and boreal landscapes, and characterization and prognosis of change is an essential component for better understanding the vulnerability and resilience of northern high latitude regions to change. The continuation of the Landsat program, along with upcoming and related satellite missions (e.g. ICESat-2, Sentinel), will allow scientists to continue to fingerprint environmental and human-induced changes that affect human welfare and global ecosystems.

 
Reference
J., Pastick Neal, Jorgenson M. Torre, Goetz Scott J., Jones Benjamin M., Wylie Bruce K., Minsley Burke J., Genet Hélène, Knight Joseph F., Swanson David K., and Jorgenson Janet C. “Spatiotemporal remote sensing of ecosystem change and causation across Alaska.” Global Change Biology. doi: doi:10.1111/gcb.14279.