Alaska Forest Health Highlights 2020

The 126 million acres of forestland in Alaska represent a whopping 17 percent of the Nation's forests. In 2020, aerial surveys to detect active forest damage from insects, diseases, declines, and abiotic agents were grounded for the first time in decades due to the pandemic. In a typical year, our team aerially surveys around 20 million acres, or 15% of the forested area of the Alaska. An extensive ground survey approach in forests along roads and trails, along with remote sensing techniques utilizing high-resolution satellite imagery, enabled our team to gather the best forest health information possible. We also created an Alaska Forest Health project in iNaturalist to solicit observations from citizen scientists. The remote sensing methods and crowd-sourcing techniques developed to meet current challenges will undoubtedly enhance our forest health surveys into the future.

The main topics of this Story Map are listed across the top horizontal navigation bar. Throughout, follow links to our  Forest Health Protection website  for more detailed information about damage agents and to view our annual  Forest Health Conditions reports .

We conducted ground surveys along roads and trails, mapping major damage at regular intervals. These surveys covered approximately 2.5 million acres. Our goal was to capture major damage observations, approximating what would be mapped during our annual aerial survey, thereby providing damage locations to hone our remote sensing tools and techniques. As in recent years, we also recorded damage that is indecipherable from the air using the Survey123 app (displayed below in the Ground Survey Dashboard).

Based on locations with known forest damage, we evaluated damage signatures in high-resolution satellite imagery. This approach enabled us to map similar damage across broader and less accessible swaths of the landscape. High-resolution (< 1m) Worldview 2 and Worldview 3 satellite imagery captured June to September 2020 was requested through both  Digital Globe  and the USGS using their  CRSSP Imagery Derived Requirements (CIDR) imagery request tool . Available imagery was mosaicked (overlaid and positioned) in ArcPro software to create basemaps, which were then imported into our standard aerial survey mapping software on mobile tablets.

Finally, surveyors systematically scanned 4.8 million forested acres of imagery for forest damage. Using the same methods as aerial survey, they circled damage areas, attributing them with the damage agent, plant host, and damage severity. Imagery quality varied. Overall, damage was more difficult to see in imagery compared to what can be seen from the plane at 1000-1500ft above the ground. Some agents that cause relatively homogenous color change to the tree canopy (e.g., spruce beetle and hemlock sawfly) were easier to pick up in the imagery compared to more subtle or scattered damage that can be mapped from a survey plane. Using both road and remote sensing surveys, we mapped about 345,000 acres of damage across the 7.3 million acres surveyed, presented in the Remote Sensing Forest Damage Map. 

This year, we established a citizen science project in iNaturalist, a social media platform that allows users to upload biotic observations, called  Alaska Forest Health Observations . Now, we can tap into data that citizen scientists are already uploading from their backyards, roadsides, trails, remote islands, and even National Parks and Forests. We will continue to use this dataset to rapidly assess where forest damage agents have been observed and outbreaks may be building, and to keep a finger on the pulse of forest health concerns of the public. Remarkably, between April and December, 312 observers uploaded 2,471 forest health observations of 217 different species in Alaska to our Alaska Forest Health Project in iNaturalist! This year, iNaturalist observations of the previously undetected western tent caterpillar were crucial to assessing its current distribution.