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.
Four variables are used in determining SPB spot occurrence, spot spread, and potential loss in the Coastal Plain.
RATING SPOT OCCURRENCE VARIABLES
1) LANDFORM (reflects drainage condition and should be evaluated relative to the local topography).
2) TOTAL BASAL AREA in sq.ft./acre (all merchantable-sized species, determined by using a prism, visual estimate or stand records).
3) PINE BASAL AREA in sq.ft./acre (only pine species, determined by using a prism, visual estimate or stand records).
4) PERCENT PINE (can be determined from stem counts, aerial photographs or stand records).
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.
Table 1. Wet Lowland or Ridge
Table 2. Other Terrain
Determining Spot Spread (Hazard) - Pine basal area is used to determine the possibility of spot spread. Select the range in which your estimate falls.
|Pine Basal Area||Hazard class||(B) Hazard Value|
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
|Potential Loss Value||=||(A) Risk
|+||(B) Hazard Value|
|__________||=||(A) _______||+||(B) _______|
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.
|Potential Loss Value||Need for Treatment|
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.
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