Surveys are conducted in July and August so that pest "signatures" may be obtained 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.
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 so that the actual extent (acreage) of damage cannot be accurately determined without extensive ground sampling
Any hardcopies 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 on the hardcopy map. 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 is collected from planes flying at 500 - 1000 ft above ground level (AGL).
Damage areas depicted on the base maps are transferred to georeferenced mylar overlays by FHP personnel. The mylars were verified by R. Wolfe, FHP as to accuracy of rendition, location, and coding. The mylars were digitized and converted to Arc/Info files.
These files were plotted and 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. Inherent in many agent codes is the host species. The three letters of each polygon label identify the damage, causal agent, and host species.
Damage/Causal Agent/Host Codes used in the 1993 data set are: 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 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 SNA - Spruce needle aphid defoliation SNR - Spruce needle rust discoloration SPB - Spruce bark beetle mortality WID - Willow defoliation - causal agent not identified 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.