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.

Summary and Conclusions

The rationale for the coordinated data collection procedures was to provide standardized information on a wide range of variables that could be used to detect conditions associated with SPB infestations in the several study areas.  The wide variability of climatic, edaphic, physiographic, and biotic factors in southern and southeastern pine forests suggested that variables important in one place may be less so in another.  And differences also exist in levels, and kinds, of human activities in these forests.

Nevertheless, some factors were consistently related to SPB activity.  Stand stocking level and mean radial growth rate were the most apparent, especially in the Coastal Plain.  Basal are per acre of pine at the point of origination of infestations was 1.4 to 1.9 times higher than in the surrounding baseline stands (tables 1, 6, 11, and 20).  And as would be expected, the highly stocked stands were generally growing slower, especially during the most recent 5 years (table 1, 6, 11, and 20).

Stand disturbances were more common in SPB-attacked stands, and the most prevalent factor was lightning.  Recent logging activity (less than 1 year old) was also somewhat more common at the point of origination of the infestations.  Interestingly, the incidence of beetle infestations was generally reduced in stands that had been logged 1 to 5 years earlier.

In addition to these general relationships, some conditions were peculiar to a geographic subregion, or to an individual project area.

Coastal Plain

This subregion, and especially its West Gulf portion, was the most intensively studied.  In the lower areas of Mississippi, Louisiana, and Texas, infestations occurred more often than expected on wet, low-lying sites of higher site index.  High volume and BA typify all Coastal Plain infestations.  Shortleaf pine was the preferred species in Arkansas, but loblolly pine was preferred elsewhere in the Coastal Plain.  In general, stand conditions appear to be more important than site conditions in determining susceptibility in this subregion.  Proper stand management practices (e.g., thinning and cull tree removal) would, therefore, reduce the incidence of SPB damage in these stands.

Piedmont

Shortleaf pine stands, with reduced radial growth, were more susceptible to SPB in the Piedmont.  In contrast to conditions in the Coastal Plain, site factors appeared to be more related to infestations in the Piedmont.  Surface soil depth, soil pH, and eroded heavy clay soils were more important.  Though treatments to improve growth rate of pine stands may reduce susceptibility to attack, the importance of site characteristics and the greater susceptibility of shortleaf pine stands are most useful.  These facts permit the identification of sites and landforms most likely to be attacked, and these can be more intensively monitored for SPB.

Mountains

The data base for the Mountain subregion was quite limited.  In general, though, attacked stands seemed to have relatively high volume and lower-than-normal growth rate.  Attacked stands were on sites that would be subject to extreme stress during droughts.  In the Georgia Mountains, shortleaf and pitch pines were preferred hosts but Virginia pine, the most abundant pine species in the area, was attacked less frequently than expected.

Clearly, certain site, tree, and stand characteristics are associated with SPB attacks.  Some of these relationships have been known for years by "woods-wise" foresters.  The ESPBRAP Coordinated Regional Site/Stand Project has a quantified these variables in a manner that can be used to develop stand hazard-rating models and management recommendations.  The resource manager can begin to do more than simply react to SPB after timber is destroyed.  He can manage his lands to lessen the chance of beetle attack in the future.

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