Forest Practices

Alaska Forest Insect and Disease Surveys

Aerial surveys [map1_as2011_rfs.pdf 5.98MB] are an effective and economical means of monitoring and mapping insect, disease and other forest disturbance at a coarse level. In Alaska, Forest Health Protection (FHP), together with Alaska Division of Natural Resources (DNR), monitor 30 40 million acres annually [map2_as2011.pdf 605kb ] at a cost of to cents per acre. Much of the forest damage acreage referenced in the annual Forest Health Protection reports are from aerial detection surveys, so it is important to understand how this data is collected and the inherent limitations of the data. While there are limitations that should be recognized, no other method is currently available to detect subtle differences in vegetation damage signatures within a narrow temporal window at such low costs.

Aerial detection survey, also known as aerial sketch-mapping, is a technique used to observe forest change events from an aircraft and document the events manually onto a map base. When an observer identifies an area of forest damage, a polygon or point is delineated onto a paper map or a computer touch screen. Together with ground intelligence, trained observers have learned to recognize and associate damage patterns, discoloration, tree species and other subtle clues to distinguish particular types of forest damage from the surrounding undamaged forest areas. Particular damage attributable to a known damage agent is known as a damage "signature", and is often pest specific. Aerial sketch-mapping could perhaps be considered "real time photo interpretation" with the added challenge of transferring the spatial information from a remote landscape view to a map or base image. Sketch-mapping offers the added benefit of adjusting the observer's perspective to study a signature from multiple angles and altitudes, but it is challenged by time limitations and other varying external factors. Survey aircrafts typically fly at 100 knots and atmospheric conditions are variable.

During aerial surveys in Alaska, forest damage information has traditionally been sketched on 1:250,000 scale USGS quadrangle maps, a relatively large scale. At this scale, one inch represents approximately four miles of distance on the ground. Smaller scale maps are sometimes used for specific areas to provide more detailed assessments. A digital sketch-mapping system was first used in Alaska in 1999 and is now used in place of paper maps for recording forest damage. This system displays the plane's location via GPS input and allows the observer to zoom to various display scales. The many advantages of using the digital sketch-map system over paper sketch-mapping include more accurate and resolute damage polygon placement and a shorter turnaround time for processing and reporting data.

No two observers will interpret and record an outbreak or pest signature in the same way, but the essence of the event should be captured. While some data is ground checked, much of it is not. Many times, the single opportunity to verify the data on the ground by examining affected trees and shrubs is during the survey mission, and this can only be done when the landscape will allow the plane to land and take-off safely. Due to the nature of aerial surveys, the data provides rough estimates of the location and intensity of damage, and only for damage agents with a signature that can be detected from the air. Many of the most destructive diseases are not represented in aerial survey data because these agents are not detectable from an aerial view.

Unlike many other regions in the United States, the Alaska forest health specialists do not survey 100 percent of Alaska's forested lands. The short Alaskan summers, vast land area, high airplane rental costs, and the short time frame during which pest damage signs and symptoms are most evident, all require a strategy to efficiently cover the highest priority areas given the available resources. The surveys we conduct provide a sampling of the forests via flight transects. Each year we survey approximately 25 percent of Alaska's 127 million forested acres. Due to survey priorities, various client requests, known outbreaks, and a number of logistical challenges, some areas are rarely or never surveyed, while other areas are surveyed annually. Prior to the annual statewide forest conditions survey, letters are sent to various state and federal agency and other landowner partners for survey nominations. The federal and state biological technicians and entomologists determine which areas should be prioritized and plan accordingly. In order to establish trends from year-to-year mapping efforts, areas that have several years' worth of data collected are surveyed annually. In this way, general damage trend information for the most significant, visible pests, and is assembled and compiled in this annual report.

The sketch-map information is digitized and put into a computerized Geographic Information System (GIS) for more permanent storage and retrieval by users. No attempt is made to extrapolate infestation acres to non surveyed areas. The reported data should only be used as a partial indicator of insect and disease activity for a given year. Establishing trends from aerial survey data is possible, but care must be taken to ensure that projections compare the same areas, and that sources of variability are considered. For a listing of recent Alaska forest health protection report "highlights" and forest health protection reports and forest damage quadrangle maps of areas flown, please visit the U.S. Forest Service Region 10 (Alaska Region) Forest Health Protection website: http://www.fs.usda.gov/goto/r10/fhp/conditions. Data that resides there now links to some of the quadrangle damage base maps; however, specific forest damage data for individual survey years is available upon request. Digital data and metadata from the annual Alaska forest health protection surveys can be found at: http://agdc.usgs.gov/data/projects/fhm/.

Aerial Detection Survey Data Disclaimer: the USFS Forest Health Protection (FHP), the Alaska Division of Forestry and its partners strive to maintain an accurate Aerial Detection Survey (ADS) Dataset, but due to the conditions under which the data are collected, FHP and its partners shall not be held responsible for missing or inaccurate data. ADS are not intended to replace more specific information. An accuracy assessment has not been done for this dataset; however, ground checks are completed in accordance with local and national guidelines http://www.fs.fed.us/foresthealth/aviation/qualityassurance.shtml. Maps and data may be updated without notice. Please cite "USDA Forest Service, Forest Health Protection and its partners" as the source of this data in maps and publications.

Below are links to pdf versions of the most recent Alaska statewide forest health protection survey reports:


Submit aerial survey data and map information requests to:

Jason Moan, Forest Health Program Coordinator
DNR Division of Forestry, Anchorage

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