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Data for the study were acquired from thematic maps, aerial photographs, lightning-strike records, and forest management
records. The thematic map information included: ownership boundaries, roads, utility lines, hydrology, and forest
compartment boundaries. Locations of D. frontalis infestations were obtained by georeferencing and interpreting aerial
photographs, using a computer-assisted mapping system called MIPS (Map and Image Processing System). Aerial photographs
were provided by the USDA Forest Service. Once located on aerial photographs, the UTM coordinates for infestation
centers were collected and entered into the GIS (ARC/INFO) as point locations. Lightning strike data for the region were
purchased fi'om R-Scan Corporation. Again, UTM coordinates for lightning strikes were entered as point locations. Information
on tk_reststands was taken from a database (CISC-Continuous Inventory of Stand Conditions), which is maintained by
the Forest Service. These data sources were used to develop a sequence of three maps: the hazard, the modified hazard, and
the heterogeneity. Each map is described below.
The Hazard Map. First in the sequence is a general D. frontalis hazard map (Fig. 5). This map was developed by
hazard rating lorest stands in the study area. In this specific application, we used tree species and age as the principal
variables of hazard. We mentioned previously that several hazard rating systems have been developed (Lorio 1980). The
utility of this map is that it defines patches in the forest matrix that are suitable for the development of infestations, given the
presence of the insect (and acceptable weather conditions). The map also reflects habitat patches graded by host defense
capability, i.e., the high hazard stands have the lowest capacity for host defense. This rendition of the landscape will have
seasonal trend reflecting variation in host defenses associated with the normal physiological changes associated with tree
phenological development described by Lorio (1988). The general hazard map will change slowly, i.e., it will require
periodic updating, perhaps every 2 or 3 years, to remain an accurate portrayal of hazard.
5 ecies Ty e Hazard Rating
m_hortleaf _White [] No Hazarct
Pine /HiGkory
Loblolly Pine/ [] Low Hazar_i
ne mHardwo, [] Medium Hazar_
Mix
DSweetguml [] High Hazar_
Willow BWater
Figure 5._Maps of a :forestlandscape classified by species types and hazard to herbivory by D. fi'ontalis. Several systems
for hazard rating have been developed. All involve integration of a subset of variables: tree species, radial growth,
height, and DBH; stand basal area (pine, hardwood, total), species composition, site index, and degree of crown
closure; and landform classification. When applied to a forest landscape, the hazard rating systems provide a general
view of the distribution and abundance of host defenses against the insect.
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