Managing Piedmont Forests To Reduce Losses From the Littleleaf Disease

Managing Piedmont Forests To Reduce Losses From the Littleleaf Disease – Southern Pine Beetle Complex

R.P. Belanger – Principal Silviculturist, USDA Forest Service, Southeastern Forest Experiment Station, Athens, GA,
R.L. Hedden – Forest Entomologist, Clemson University, Clemson, SC, and
F.H. Tainter – Forest Pathologist, Clemson University, Clemson, SC.

Integrated Pest Management Handbook, USDA, Forest Service, Agriculture Handbook No. 649, March 1986.

In 1980, the Forest Service and the Cooperative State Research Service of the U.S. Department of Agriculture initiated the Integrated Pest Management Research, Development, and Applications Program for Bark Beetles of Southern Pines. This research/applications effort concentrates on pine bark beetles and associated tree diseases in the South. This is one in a series of Integrated Pest Management handbooks.

Preventive Cultural Treatments

Appropriate management practices can reduce or prevent losses occurring on problem littleleaf-SPB sites (Fig. 9). Preventive and direct control methods are intended to increase the productivity of susceptible stands (Belander and Malac 1980). A prime concern is to manage soil and stand conditions associated with the littleleaf-SPB complex in a manner that will minimize potential pest losses.

Stand Establishment
Planting or natural seeding is used to establish pine forests in the Piedmont. While planting offers the best opportunity to control species composition, seedling

Figure 9 – Silvicultural practices recommended to reduce the impact of pests in Piedmont forests.

quality, stocking, and culture of the stand, natural regeneration has the advantage of low establishment costs. Although the choice of natural or artificial regeneration is frequently decided by owner objectives, methods of preparing and regenerating problem areas are usually determined by soil and stand conditions specific to each site. The following considerations should be kept in mind in developing plans for regenerating high-risk littleleaf-SPB sites:

Regeneration methods should favor species most resistant to littleleaf disease and SPB problems. Probability of losses from these forest pests is likely to be high in pure stands of shortleaf pine. Thus, loblolly pine is recommended for most sites in the Piedmont. In addition to being less susceptible to littleleaf -SPB, loblolly grows well on a wide range of soil types and can be managed for multiple owner objectives.

Virginia and pitch pines commonly occur in natural stands in the northern Piedmont. Virginia pine is highly resistant to pest problems and can be managed to produce high yields of wood fiber on poor sites. However, natural pruning in Virginia pine is extremely slow; therefore, the species is not recommended for owners who wish to produce quality sawtimber. Pitch pine, although resistant to littleleaf disease, is highly susceptible to SPB.

The potential productivity of high-risk littleleaf-SPB sites is generally poor. The site index² for pest-prone stands surveyed in Georgia averaged 72 compared with 87 for healthy old-field plantations and about 76 for healthy natural stands. Proper management can rehabilitate problem sites in the Piedmont. These are eroded sites that have shallow surface soils and firm textured clays. Such sites have a high erosion potential, are poorly aerated, and restrict root development. Soils become excessively wet during rainy periods and extremely dry during periods of deficient rainfall. Trees growing on these sites are subject to varying periods of severe physiological stress.

²The average height in feet of dominant and codominant loblolly pine treees at age 50.

Burning, chopping, and the use of suitable herbicides are recommended practices for regenerating high-risk littleleaf-SPB sites. Mechanical site preparation should be avoided on slopes greater than 10 percent. Preplanting practices that scarify and expose the soil contribute to erosion and reduction of litter and organic matter considered essential for improving the site.

Long periods of time are normally required to improve soil conditions. Where special values are involved, this process can be accelerated by subsoiling and the addition of sewage sludge (Fig. 10). Subsoiling breaks any hardpan that may exist and increases water percolation. Sewage sludge acts as a slow-release fertilizer and produces a grass cover that protects the soil surface. Studies have shown that subsoiling results in better tree growth than disking and that sewage sludge is

Figure 10 – Subsoiling is one method of
improving compacted soils in the Piedmont.

superior to inorganic fertilizers (Berry 1985). These are expensive methods but show promise as a means of improving problem soils in the Piedmont. Caution: potential users should obtain guidelines from States regulating the application of sewage sludge.

Poor stocking is another characteristic of littleleaf-SPB sites. Most mortality in these stressed stands occurs during stand establishment and late in the rotation. Planting to achieve a stocking level of 500 to 600 seedlings per acre at the end of the first year is recommended for plantations. Stocking levels may vary depending on site quality and management objectives. Overstocking will increase the probability of attack and spot growth by the SPB; understocking will reduce the potential productivity of the site.

The shelterwood method can be used to regenerate pines on littleleaf-SPB sites (Society of American Foresters 1981). Stands are usually harvested by the two-cut method. The first cut removes all but 20 to 30 mature seedbearing trees per acre. Parent trees should be healthy, 10 inches or greater in diameter, and well distributed over the area. (Healthy trees may incorporate genetic resistance in the future stand.) The final removal cut should be made as soon as reproduction is established.

The seed tree method is not recommended for high-risk Piedmont stands. Conditions on these severe sites are unfavorable for seed production, seed germination, and seedling establishment. There is also the possibility of losing seed trees to lightening, wind, and ice storms. Deterioration of root systems by littleleaf disease further increases the susceptibility of the residual seed trees to storm damage.

Intermediate Cuttings
Intermediate cuttings can be made as the stands develop and mature to reduce losses and to increase the amount and value of residual timber on littleleaf-SPB sites. Thinning stimulates growth and vigor in young stands and reduces the probability of SPB spot occurrence and growth (Fig. 11). Salvage cutting may be used to minimize losses from littleleaf disease and bark beetles in mature stands. The most important factors to consider in selecting stands for intermediate cutting are (1) the percentage of diseased trees in the stand and (2) susceptibility to SPB attack.

Figure 11 – Thinning reduces the probability of
southern pine beetle attack and spot growth.

Figure 12 – Guidelines for managing littleleaf
disease-southern pine beetle stands.

Stands that are low to moderate risk for SPB and contain only a small percentage of littleleaf trees can be managed utilizing prudent silvicultural strategies and long rotation harvesting schedules (Fig. 12). For high-risk littleleaf-SPB sites, a combination of adequate spacing, salvage-sanitation cutting, and harvest rotations of 25 to 35 years will minimize timber losses. Stands with high levels of littleleaf disease should be harvested and regenerated as soon as practical. Such stands deteriorate rapidly and require frequent salvage cuttings to utilize dead and diseased timber. Clearcutting followed by planting with loblolly or Virginia pine is also recommended for high-risk SPB stands with moderate levels of littleleaf disease.

Frequency and intensity of thinning – Thinning is most effective and economical as an SPB prevention technique when management used 35+ year rotations to produce sawtimber and veneer. Stands should initially be thinned at the onset of root and crown competition. This occurs in pine plantations at approximately 10 to 15 years of age, but may start even earlier in dense natural stands. Thinning is not recommended for pulpwood stands being managed on 20- or 25-year rotations. Growth in these stands is generally good and fairly high stocking is needed to get full production from the site.

Intensity of cutting will depend upon the age of the stand, total stand density, site index, and management objectives. In the Piedmont, basal areas of 80 to 100 feet² per acre are recommended to reduce the potential for SPB problems. The risk of beetle outbreaks will increase considerably when stand density exceeds 100 feet² per acre.

It is also important to consider climatic conditions when selecting a method and intensity of cut. Severe ice storms occur frequently in the Piedmont, and pulpwood-size stands are extremely vulnerable to glaze damage after thinning. Tree mortality and stand decline result from bole breakage, uprooting, severe leaning, and bending beyond recovery. The damaging effects of ice storms can be minimized by early and frequent thinning. No more than a third of the basal area should be removed at each cut. Row thinning should be avoided as much as possible.

Other considerations – Intermediate cuttings should remove all trees with symptoms of littleleaf disease, and those highly susceptible to SPB attack should be cut next. These include trees that are damaged or weakened or with crowns that are overtopped or surrounded by taller trees. Taller (dominant and codominant) trees are then cut to obtain the desired spacing. The residual stand should contain healthy trees that are free to grow.

Intermediate cuttings will not completely eliminate stand stress or associated SPB problems on littleleaf sites. Losses are still apt to occur toward the end of the rotation period. However, the magnitude of damage is less than for untreated stands being grown for the same product.

The impact of southern pine beetle is greatest in pure pine stands. A mixture of pines and hardwoods (Fig. 13) reduces the risk of spot occurrence and growth because the continuity among pines is disrupted by the intervening hardwoods. Hardwoods also benefit littleleaf-SPB sites by building humus and increasing nutrient levels. These measures are slow but progressive means of amending problem sites.

Final Harvest Cuts
The susceptibility of pines to littleleaf disease and associated SPB attack increases with age. Volume and value losses are greatest in dense pure stands 30 years or older. High-risk stands seldom respond to intermediate cuttings and should be replaced with the most resistant pine species or a mixture of species suited to the area. In managed stands, final harvest should be timed to occur before the growth and vigor of the stand starts to decline. Maintaining a healthy, free-to-grow stand of established pines and shortening rotation lengths are effective means of reducing losses resulting from littleleaf and SPB attack.

Figure 13 – A mixture of pine and hardwoods reduces the risk of spot occurrence and growth by disrupting continuity between host trees.

[ Contents ] [ Back ] [ Forward ] [ Home ]