Surveys are conducted in July and August so that pest "signatures" may be identified during the optimal period for symptom development of ocular estimation. The aerial survey is coordinated with known pest outbreaks so that the maximum extent of recent bark beetle damage (fading trees) and insect defoliation (discoloration, foliage loss) patterns may be determined. Aerial survey flights are termed as "local" if they can be completed within 1 day from the survey base and "regional' if more than 1 day is required to complete the survey reconnaissance.
More specific delineation of pest damage boundaries (polygons) may be obtained by later ground assessments or approximation of several individual years of mapping data. However, precise timing of the surveys for maximum symptom development is not always possible so that the aerial extent of damage generally cannot be accurately mapped for all pests. Also, many pest symptoms are delayed from the time of actual damage so that visual symptoms do not appear for several months after the initial damage. In the case of some bark beetle damage (e.g., spruce beetle) symptoms of "red-topped"
or "fading red" trees do not show until the season after initial attack. Precise estimates of the extent of bark beetle damage often required a corroborative ground assessment to determine the extent of current season attacks. Also, some defoliator damage is not readily apparent from the air or occur outside of the aerial survey widnow of time so that the actual extent (acreage) of damage cannot be accurately determined without extensive ground sampling
Any hardcopies or published datasets utilizing these data sets shall clearly indicate their source. If the user has modified the data in any way they are obligated to describe the types of modifications they have performed. User specifically agrees not to misrepresent these data sets, nor to imply that changes they made were approved by Alaska Department of Natural Resources.
The data is recorded at the time of capture on 1:250,000 scale USGS topographic-bathymetric series maps. Data on all surveys is collected from a Cessna 206 at 500 - 1000 ft. above ground level (AGL) or from a Beaver at 500-1000 ft AGL.
Damage areas on the base maps are transferred to georeferenced mylar overlays by FHP personnel. The mylars are verified by K. Matthews and D. Wittwer, FHP, and ADNR Forestry as to accuracy of rendition, location, and coding.
These files were interactively verified with the mylars for attribute and topological accuracy.
Areas of damage are delineated on the base maps as polygons and labeled with an agent code and for some insects a severity code. Inherent in many agent codes is the host species. The first three letters of each polygon label identify the damage, causal agent, and host species. The fourth letter, if present, identifies severity.
Acres for each polygon are calculated by dividing the area of a polygon by 4046.8564 which equals 1 square meter. Acres are rounded for display.
Damage/Causal Agent/Host Codes used in the 1999 data set are: ALD - Alder Defoliation - causal agent unknown BAP - Birch Aphid defoliation BHB - Black-headed budworm defoliation BID - Birch Defoliation - causal agent not identified CLB - Cottonwood leaf beetle defoliation COD - Conifer defoliation - causal agent & host not identified CWD - Cottonwood defoliation - causal agent not identified FIR - Fire mortality (note this is not all fire damage for the state) FLO - Flood or high water mortality - host not identified HCK - Hemlock Canker HSF - Hemlock sawfly defoliation IPB - Ips top kill and Spruce bark beetle mortality in same polygon IPS - Ips beetle mortality or topkill LAS - Larch sawfly defoliation LAT - Large Aspen Tortrix defoliation OUT - polygon with no damage inside of damage polygon POD - Porcupine damage - host not identified SBM - Spear-marked black moth defoliation - host not identified *SBR - Spruce broom rust discoloration SBW - Spruce budworm defoliation SLD - Landslide SMB - Spear-marked Black Moth defoliation SNA - Spruce needle aphid defoliation SNR - Spruce needle rust discoloration SPB - Spruce bark beetle mortality WID - Willow defoliation - causal agent not identified WIR - Willow Rust WNT - Winter discoloration - host not identified WTH - Windthrow mortality - host not identified
* Spruce broom rust is endemic to nearly all areas of the state, however mapping was not consistent nor representative.
Severity Codes used in this data set: Light = < 10% of the host species within the polygon were affected. Moderate = 11% to 30% of the host species within the polygon were affected. High = > 31% of the host species within the polygon were affected.