Predicting Potential Loss
from Southern Pine Beetle in the
Coastal Plain of South Carolina

Forest insect and disease pests cause an estimated growth loss and mortality in excess of $8 million each year in South Carolina forests. An integrated pest management (IPM) approach on your forest lands could significantly minimize your potential losses.

Determining Stand Susceptibility to Southern Pine Beetle

The key to preventing forest pest problems is understanding the closely associated pest, tree, and site factors that make a stand susceptible to attack. In recent years, systems have been developed using this relationship, which easily and reliably determine where pest attacks are most likely to occur. These systems are commonly known as risk and/or hazard rating systems. Although the terms risk and hazard are often used interchangeably, they have distinct meanings from one system to another.

Forest managers concerned with southern pine beetle (SPB) impact may use an appropriate rating system to determine which stands are most susceptible. The results of such stand ratings will provide guidance in determining areas needing cultural treatment to prevent losses from the SPB. Before using any rating system, managers should be certain that the system applies to their specific situation.

SPB Rating System for the Coastal Plain

The following system allows users to rate both plantations and natural stands of loblolly and shortleaf pine in the Coastal Plain for the likelihood of a SPB spot (infestation) occurring, chance of a spot spreading, and potential for timber loss. Both natural stands and plantations can be rated. The system can be used in the field by taking a simple cruise, or in the office if appropriate stand records exist. Tables have been developed listing variables which need to be evaluated, instructions on how to measure these variables, and the relative need for cultural treatment. This publication describes in greater detail the variables measured, makes further suggestions on measurement technique, and demonstrates how the tables should be used.

Spot Occurrence

Four variables are used in determining SPB spot occurrence, spot spread, and potential loss in the Coastal Plain.

1. Landform - SPB infestations occur more often on dry ridged and wet low-lying areas than on other terrain. Landform classification in the Coastal Plain is subjective and reflects soil drainage condition rather than exact elevation. Therefore, the landform should be evaluated relative to local topographic condition. Landform evaluation can be done in the field or in the office using topographic maps. In the lower Coastal Plain, pine stands growing in low areas are more susceptible to SPB attack because of the adverse effect excess soil moisture has on tree vigor. In the lower Coastal Plain, moisture deficits occur on ridges and make pines in these areas more susceptible to attack. In both the upper and lower Coastal Plain, pine stands on the side slopes have the lowest susceptibility.
2. Total Basal Area - Overstocked stands with a high percentage of pine are more susceptible to SPB attack than low density stands. In dense stands high levels of between-tree competition occurs and results in reduced tree and stand vigor. Total basal area per acre in square feet can be determined from a prism cruise, visual estimate, or stand records. All merchantable-sized species should be included.
   
3. Pine Basal Area - The possibility of a SPB spot spreading is directly related to the density of the pine in the stand. Stands in which pine basal area is over 120 square feet per acre are very susceptible to spot spread. In dense pine stands, trees grow close together; this allow dispersing beetles to easily find a new host. Pine basal area can be determined by using a prism, visual estimate, or stand records.
4. Percent Pine - Pure pine stands are more susceptible to attack by the SPB than mixed pine-hardwood stands. Hardwood-pine stands have 25% to 50% pine and are generally less susceptible to attack than pine-hardwood (50-75% pine) and pure pine stands (>75% pine). Percent pine can be determined from stem counts, aerial photographs, or stand records.

RATING SPOT OCCURRENCE VARIABLES 1) LANDFORM (reflects drainage condition and should be evaluated relative to the local topography). Wet Lowland or Ridge Other Terrain 2) TOTAL BASAL AREA in sq.ft./acre (all merchantable-sized species, determined by using a prism, visual estimate or stand records). < 80 80-120 > 120 3) PINE BASAL AREA in sq.ft./acre (only pine species, determined by using a prism, visual estimate or stand records). < 90 90-120 > 120 4) PERCENT PINE (can be determined from stem counts, aerial photographs or stand records). < 25-50% 50-75% > 75%

DETERMINING SPOT OCCURRENCE (RISK) - Next, select the appropriate table based on the landform classification for determining risk value. Record the risk value(A) corresponding to the appropriate combination of total basal area and percent pine. The higher the risk value, the greater the chance of SPB attack.

Spot Spread

Determining Spot Spread (Hazard) - Pine basal area is used to determine the possibility of spot spread. Select the range in which your estimate falls.

Spot Spread

Potential Loss

Determining Potential Loss - Potential loss is based on the risk of a SPB spot becoming established in a stand plus the hazard of the spot spreading. To determine the potential loss value, simply add the risk value (A) and the hazard value (B).

Determining Potential Loss

Determining Need for Cultural Treatment - The potential loss value is used to determine the need for cultural treatment. The final table lists the potential loss values and the corresponding need for cultural treatment. Cultural treatments actually used will be based on the management objective of the owner. They may include converting stands to less susceptible species, thinning stands which have not reached maturity to promote stand resistance, and harvesting mature to over-mature stands.

Further Suggestions

When applying this rating system in the field, measurements should be made at several points. Then the risk, hazard, and potential loss calculated for each point should be averaged for the stand. When appropriate stand records exist, rating the stands in the office will yield a good estimate. If possible, ratings should be made when SPB populations are low, so that attention can be given to applying preventive cultural treatments rather than reacting to active infestations.

Additional Information

Keeping your pine timber stands healthy and vigorous, and having a good knowledge of the major disease and insect pests is essential to good forest management. Additional publications describing pest management techniques, as well as professional assistance, are available through the South Carolina Forestry Commission, Clemson University Cooperative Extension Service, USDA Forest Service, forest industry personnel, and private consulting foresters. Acknowledgment: USDA Technical Bulletin No. 1612.

C. Karpinski, Former Forester I
Roy L. Hedden, Professor

Department of Forest Resources