Site, Stand, and Host Characteristics of Southern Pine Beetle Infestations

Jack E. Coster and Janet L. Searcy - editors

Southern Pine Beetle Handbook U.S.D.A. Combined Forest Pest Research and Development Program Technical Bulletin No. 1612

In 1974 the U.S. Department of Agriculture initiated the Combined Forest Pest Research and Development Program, an interagency effort that concentrated on the Douglas-fir tussock moth in the West, on the gypsy moth in the Northeast, and on the southern pine beetle in the South. The work reported in this publication was funded in whole or in part by the Program. This technical bulletin is one in a series on the southern pine beetle.

Study Methods

All participants collected certain data in a standardized manner so that results could be compared Southwide. Nearly all of the data presented were collected from 1974 to 1977. In addition, individual investigators acquired data for which they had special interest, knowledge, or facilities. Only the coordinated data, however, are reported herein.

The complete ESPBRAP Coordinated Site/Stand Project data set has been archived on computer tape. Researchs in forest entomology, silviculture, forest pathology, and soils may find the data useful. Information on its availability and location is in the Appendix.

Data Collection

Soil/Site Characteristics

At each infestation the soil/site characteristics were described using the Soils Resource Guide, Southern Region (USDA Forest Service 1972). This guide provides descriptive keys for use in the Mountain, Piedmont, and Coastal Plains subregions.

Two soil samples were collected at each location for laboratory analysis: one composite surface sample (0-15 cm) and another of the subsoil. The subsoil sample was taken at the midpoint of the B horizon. In the absence of a recognizable B horizon, investigators took a sample from the 60-90 cm depth.

Laboratory analysis of surface and subsoil samples included mechanical analysis by either the hydrometer or the pipette method, and pH by glass electrode in a 1:1 soil to water mixture.

Researchers estimated site quality by site index based on the height of loblolly pine (Pinus taeda L.) at base age 50. They determined tree age and total height on three to five dominant or codominant pines in the immediate vicinity of the infestation center for use with the Schumacher and Colie (1960) site index curves. Where possible, they selected these trees from each quadrant surrounding the infestation center, and included at least one infested and one uninfested tree. In addition, slope percent and aspect (azimuth) were recorded.

Stand Characteristics

Basal Area and Composition of Stand.-Basal area (BA) was determined with a 10 BA factor prism positioned at the center of the infested area. When a single tree represented the center, the prism was positioned 5 ft. north. Field teams marked all "in" trees. Basal area was categorized as attributable to hardwoods or pine species.

Origin of Stand.-Stands were designated as plantation or natural (including artificially seeded areas).

Age.-Investigators determined the age of the stand from increment cores taken at breast height. Three to five trees were sampled in uneven-aged stands.

Stand Disturbances.-Plot disturbances that appeared to have occurred within the past 5 years were noted and categorized as follows:

1. No known distrubances
2. Logging activity within previous year
3. Logging activity 1 to 5 years ago
4. Ice and/or hail damage, severe-over one-half of stems affected
5. Ice and/ or hail damage, light-less than one-half of stems affected
6. Fire within previous year
7. Fire 1 to 5 years ago
8. Lightening strike evident
9. Chemical brush control within previous year
10. Chemical brush control 1 to 5 years ago
11. Wind damage

Stand Understory.-An estimation was made of the percent occupation of the site by woody understory vegetation that was not included in the BA assessment. Field teams made this estimation visually by vertically projecting understory crowns to the ground and estimating occupation tot eh nearest 10 percent.

Size of Infestation.-Total number of SPB-infested (dead or dying) trees in the infestation was tallied. Estimated size of infested area was recorded in 1/4-acre increments.

Stand Diameter.-The average diameter at breast height (d.b.h.) and the range in d.b.h. of those trees counted as "in" the BA plot was determined.

Stand Density.-The number of trees per acre was obtained from d.b.h. measurements taken (Avery 1967).

Tree Characteristics
The following characteristics were recorded for each individual "in" pine tree on the BA plot.

1. Species
2. Status
   1. Live (uninfested)
   2. Dead (SPB-infested)
   3. Dead (unknown causes)
3. Disease incidence based on visible evidence of
   1. Cronartium fusiforme (bole galls)
   2. Fomes annosus (conks or windthrown trees with stringy roots)
4. D.b.h. to nearest 0.1 inch
5. Total height to nearest foot
6. Height to live crown to nearest foot
7. Bark thickness measurements on site index trees for maximum thickness (from the ridges) and minimum thickness (from the base of the fissures). Measurements were taken to the nearest 0.1 inch at breast height.
8. Radial growth measurement of site index tree from increment cores at breast height. The radial growth in millimeters was determined for each of the last two 5-year periods.

Plot Selection Criteria

From aerial and ground surveys researchers randomly selected SPB infestations. The center point of each plot was established at or near the oldest infested pine. Field teams determined this point by assessing foliage color of the attacked tree, loss of needles, bark sloughing, and the occurrence of probable causative disturbance factors such as lightening strikes, logging damage, and other activities.

Nearly all plots were taken in infestations less than 3 months old, and no plots were selected from infestations more than 1 year old. The percent of total SPB infestations sampled in an area varied by project and year, but in all cases the sampled infestations taken can be considered representative of all infestations for the respective areas.

Basis for Comparison

A complete and detailed description of SPB infestations by region and Southwide is very useful. Such a description characterizes the type of sites and stands in which SPB attacks are most likely to occur. One question arises immediately, though: How much different are the infestations from unattacked stands? The forest manager must have some idea of the magnitude of these differences in order to determine priorities for stand treatment. Some assessment of unattacked stand conditions is therefore needed.

Two types of unattacked plot data were used in order to characterize unattacked stands. "Control" plots were established near the infestations. These plots were used to determined if differences between attacked and unattacked stands were due to microsite variation within the stand. That is, whether intrastand variability accounted for the major component of SPB susceptibility. The second type of unattacked data was obtained from "baseline" plots established randomly or in line-grid fashion across the individual study areas in order to characterize general forest conditions in each area. Typically, control plots were intermediate with regard to site/stand characteristics between SPB-attacked and baseline plots. Since the forest resource manager most commonly deals with entire stands as to susceptibility rather than intrastand or micro-environment effects, the baseline plots are the preferred standard for comparison.

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