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Identifying Susceptible Stands
Figure 2. - Hazard ratings indicate where SPB infestations are most likely to occur.
Figure 2. - Hazard ratings indicate
where SPB infestations are most
likely to occur.		 The SPB occurs across all geographic regions of the South. Site conditions, tree species, and size classes associated with SPB attacks differ somewhat between the Coastal Plain, the Piedmont, and the Southern Appalachian Mountains (table 1). But slow radial growth and dense stocking are common measures of high-hazard stands.

Several rating systems have been developed that provide an evaluation potential risk (see Selected References). Hazard ratings indicate where beetle outbreaks are most likely to occur (fig. 2), and, if they do, where losses and beetle activity are likely to be greatest. Testing and implementation of the ranking systems have been limited to stand, site, and insect conditions associated with selected areas in the geographic subregions, however.

Rating systems can also be used to evaluate the effectiveness of silvicultural treatments in reducing susceptibility of stands to beetle attack. Information regarding hazard-rating systems for specific localities can be obtained from State forestry agencies.

 

The Southern Coastal Plain

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Natural stands susceptible to SPB attack in the Coastal Plain are characterized by high stand densities, a large proportion of pine sawtimber, and declining radial growth. Outbreaks occur most frequently in stands located on poorly drained soils and low-lying areas. Trees on dry or droughty soils are less commonly attacked. Rating systems have been developed for east Texas; the Kisatchie National Forest in Louisiana; corporate timberland in Texas, Louisiana, and Mississippi; and forests in south Arkansas.

The Piedmont

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Natural stands susceptible to endemic SPB attack in the Piedmont are well-stocked pine stands with a large percentage of the host component in shortleaf pine, slow radial growth during the last 10 years, and a high clay content in surface and subsurface soils. Two systems have been developed for ranking the susceptibility of natural stands to SPB attack in the upper Piedmont of Georgia. The first is a predictive equation that includes variables easily measured or often contained in existing inventories; the second is a system designed for use in the field by service foresters.

 

Table 1. - Characteristics of stands susceptible to SPB attack.

Southern Coastal Plain Piedmont Southern Appalachians
Densely stocked stands Well-stocked stands Densely stocked natural stands
Large proportion of sawtimber Small sawtimber Large proportion of overmature sawtimber
Declining radial growth Slow radial growth during last 10 years Slow radial growth
Poorly drained soils and low-lying areas High percentage of clay in surface and sub-surface soils Dry, south-facing slopes
High percentage of shortleaf and/or loblolly pine in the stand High percentage of shortleaf pine in the stand High percentage of shortleaf and/or pitch pine in the stand


The Southern Appalachians

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Studies in the mountains of Georgia, North Carolina, South Carolina, and Tennessee have shown that stands severely attacked by the southern pine beetle were densely stocked, slow growing, and had a large proportion of overmature pine sawtimber. Shortleaf pine and pitch pine were more susceptible to beetle attack than Virginia pine and eastern white pine. Systems are currently being developed to rank the susceptibility of natural stands in the mountains.
 
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