Forester inspecting Pine Stand

Predicting Potential Loss
from Southern Pine Beetle in the
Piedmont 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.

 

 

 

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Forestry Leaflet 11
Revised October 1997


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 Piedmont

The following rating system is appropriate for natural pine stands in the Piedmont region of South Carolina. It allows the user to rate a stand for the likelihood of an SPB spot (infestation) occurring, chance of a spot spreading, and potential for timber loss. It can be used in the field by taking a simple cruise, or in the office if suitable stand records exist. Tables have been developed to organize variables which need to be evaluated, give instructions on how to evaluate these variables, and determine the 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

Three variables are used to evaluate spot occurrence.

  1. Pine Component - Shortleaf pine is among the most susceptible of all pines to SPB attack. Where it occurs in a high percentage relative to other species, chance of attack is increased. Stands with 50% or more shortleaf pine have been shown statistically to be very susceptible to attack. The percentage of shortleaf pine can be determined by visual estimates, conducting a simple cruise, or by using appropriate stand records.
  2. Slope - In the Piedmont, over 60% of all SPB infestations occur on slopes greater than 10%. On these sites, erosion may be a factor in stressing the trees, making them more susceptible to SPB. Slope can be determined with a clinometer, Abney level, visual estimate, or with Soil Conservation Service soil survey information. The figure given in the soil survey is an average figure for the area.
  3. Clay Content - Clay soils are often found where slopes are steep or where sheet erosion has occurred. Littleleaf disease is common on these sites. This disease is known to stress trees, making them more susceptible to SPB attack. The easiest way to determine clay content is through the use of a soil survey. Estimates given in a soil survey are average and may contain up to 10% of a different soil type. Any uncertainty on soil type variation in the stand can be checked with a field visit. Pine stands, especially shortleaf, growing on soils with a clay content of 28% or greater have been shown statistically to be susceptible to SPB attack.

RATING SPOT OCCURRENCE VARIABLES

1) PINE COMPONENT (determined from stand records, ocular estimate, or cruise)

Is more than 50% shortleaf pine?

___ YES
___ NO

2) SLOPE (use a clinometer, Abney level, ocular estimate, or SCS soil survey)

Are slopes greater than 10%?

___ YES
___ NO

3) CLAY CONTENT (use a field test, SCS soil survey, or stand records)

Is clay content greater than 28%?

___ YES
___ NO

Determining Spot Occurrence (Risk) - In the following table, find the combination of results from the first three questions which matches your evaluation. Record the corresponding risk value. The higher the risk value, the greater the chance of SPB attack. After determining the risk of spot occurrence, proceed to spot spread.

Pine
Component
Slope Clay
Content
(A) Risk Value
Yes

Yes

No

Yes

No

Yes

No

No

Yes

No

Yes

Yes

No

No

Yes

No

Yes

Yes

Yes

No

Yes

No

No

No

3

3

3

2

2

1

1

1

Spot Spread

Determining Spot Spread (Hazard) - The possibility of an SPB spot spreading is determined by one variable: Pine Basal Area. The probability of an SPB spot increasing in size once it is established is directly related to stand density. Stands in which basal area is over 120 square feet per acre are very susceptible to spot spread. In dense stands, trees grow close together, allowing dispersing beetles to find a new host easily. Pine basal area can be estimated by using a prism, visual estimate, or stand records. In the next table, select the range in which your estimate falls and note the corresponding hazard value (B) .

Spot Spread

Pine Basal Area (B) Hazard Value Hazard Class
more than 120

90-120

less than 90

3

2

1

High

Moderate

Low

Potential Loss

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

Determining Potential Loss

Potential Loss Value = (A) Risk
Value
= (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 describes potential loss values according to their corresponding need for cultural treatment. Cultural treatments should be based on the management objective of the owner. They may include converting shortleaf pine stands to other species, harvesting over-mature stands, and thinning stands which have not reached maturity to promote stand resistance to SPB.

Potential Loss Value Need for Treatment
6

5

4

3

2

Extremely High

High

Moderate

Low

Extremely Low

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 necessary 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 southern pine beetle habits and symptoms is essential to effectively deal with this destructive pest. Professional advice and assistance is available through the South Carolina Forestry Commission, Clemson University Cooperative Extension Service, U.S.D.A. 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