Forest Health: Southern Pine Beetle

Southern pine beetles (SPB), Dendroctonus frontalis, began initial attack on the Daniel Boone National Forest in late autumn of 1999, resulting in the most devastating insect assault ever documented on pine forests in Kentucky. Pine trees that once stood alive with lush green crowns now stand as bare skeletons across a vast landscape, as temporary monuments to a recent past. More than 70,000 acres of pine forests have been lost to SPB damage on the Daniel Boone National Forest.

WHAT IS A SOUTHERN PINE BEETLE

The southern pine beetle (SPB), Dendroctonus frontalis, is a small black beetle that is native to North and Central America. They are smaller than a grain of rice, measuring only 1/8 inch long. In spite of their tiny size, these insects are among the most destructive pests known to pine forests.

The SPB range occurs from Pennsylvania to Texas and from New Mexico and Arizona to Honduras. Documented outbreaks of SPB are periodic, occurring in cycles at various locations. The SPB will attack all species of pine, but they show a strong preference for southern yellow pine species such as shortleaf, Virginia and pitch pines.

The life cycle of SPB from egg to adult is about one month. New generations of SPB continue the cycle, typically emerging between April and September. The adult SPB invade pine trees by boring through the bark to lay their eggs. The winding S-shaped egg galleries that are developed eventually girdle the host tree resulting in its death.

The tiny white eggs of SPB hatch into larva, then the larva develop into pupa. Once pupation is complete, newly formed adults chew exit holes through the tree bark, take flight and repeat the cycle of reproduction and infestation of pines.

SPB populations can rapidly build to epidemic proportions under certain environmental conditions. Periods of drought and other factors that cause stress to pine trees are believed to contribute to SPB outbreaks. While the SPB relationship to pine is a natural occurrence, it is not one of mutual benefit. SPB are the predators, and pines are the prey.

THE INFESTATION

Southern Pine Beetles Attack the Daniel Boone National Forest

Southern pine beetles (SPB) began their initial attack on the Daniel Boone National Forest during the latter months of 1999. Early infestations were first recognized in mature pine stands on the southern end of the forest. Pine trees in these stands were found dead or dying, and closer observance revealed the culprit. SPB had set the stage for what would become the most devastating insect assault ever documented on the Daniel Boone National Forest in Kentucky. Neighboring states to the south were simultaneously documenting record outbreaks of SPB on their forests.

SPB continued their assault on the pine forests of the Daniel Boone throughout 2000 and 2001, working their way northward and spreading to epidemic proportions across the entire forest. More than 100,000 acres of pine forests have been lost to SPB damage on the Daniel Boone National Forest. It is estimated that at least 80% of pine habitat on the Forest has been lost.

The contributing factors that would launch a SPB outbreak had occurred on the Daniel Boone National Forest prior to 1999. Pine trees on the southern end of the forest had suffered stress from tornado, ice damage and fire. These conditions were followed by consecutive summers of severe drought. Many of the pine stands were overstocked, or too dense, causing added tree stress and competition for water supply. The summers of drought were followed by unseasonably mild winters that would allow for higher rates of SPB survival.
In Kentucky, prior outbreaks of SPB were documented in the mid-1950s and again in the mid-late 1970s. These outbreaks were non-significant, however, in comparison to the events that would unwind in 2000-2001. By the year 2000, most of the pine stands on the Daniel Boone had aged to maturity. SPB show a preference for older, larger pine trees that have weakened over time.

A GROWING DILEMMA

The New Millennium on the Daniel Boone National Forest

The stage was set. The SPB began their spread by developing small, scattered “spots” of infestation across the pine-forested landscape. These spots quickly began to grow as temperatures increased during the spring of 2000. The beetles were rapidly reproducing and increasing in number. Their spots grew from one to ten infested pine trees to hundreds at one location. The aspect of spread encompassed all directions, and the SPB spots began to converge with one another. Spots of SPB infestation eventually united, like connecting dots on a map, extending their reach across the dry sandy ridgetops and upper slopes where pine most typically occurs on the Daniel Boone National Forest.

The beetles attacked pine tree after pine tree, eating their way through the bark with a voracious appetite. Once through the bark, the SPB entered into the living cambium layer of a tree. The pine would develop “pitch tubes” of resin from the beetles’ points of entry, leaking small clumps of resin to the outside of the bark. Heavily infested trees looked like they were covered in popcorn from a distance.
Once infested by SPB, the journey of decline for a pine tree began. The needles soon began to fade, from yellow to red and then to brown. After turning brown, the needles soon dropped. Once the needles were gone, the tree was officially assumed dead. Within a few months, the crowning branches were weakened and began to occasionally drop. The bark began to loosen and slough off the trunk, eventually creating one of many dead snags across the landscape

THE HAZARDS

Watch for Dead Trees!

CAUTION! As a result of the southern pine beetle (SPB) epidemic on the Daniel Boone National Forest, thousands of dead pine trees across the landscape are creating hazards in the form of falling branches and tree snags. These “hazard trees” have the potential of causing severe personal injury or death. Hazard trees are especially cause for concern near campgrounds, trails, roads and powerline rights-of-way. The Forest Supervisor is urging the public to use extreme caution when visiting forest areas impacted by SPB.

Periods of high wind increase the chances for falling branches and dead tree snags. As a precaution, forest areas damaged by SPB should be avoided especially during high wind. Any snag can be dangerous any time, but dead pines tend to deteriorate more rapidly. Their wood is softer than deciduous hardwood trees, which makes them more susceptible to wind throw.

Forest managers are concerned about the debris from dead and dying trees that is now covering the forest floor. This debris dramatically increases the fuel load in these areas, which may create severe conditions in the event of a wildfire. Concern is heightened for firefighters, public safety and the lives and property on private lands adjacent to National Forest.   
Efforts to remove hazard trees from recreation areas and along roads are ongoing. Priority areas for treatment have been established across the Forest, targeting those areas with the most public use. While the task is daunting with a vast number of dead trees, Daniel Boone employees and contractors have been removing as many hazard trees as possible. SPB-infested stands adjoining private lands have also been identified for fuel hazards.

SPB CONTROL EFFORTS

The Methods Used

All efforts to control southern pine beetle on the Daniel Boone National Forest ultimately failed.

The beetles raged beyond control, spreading rapidly at an enormous pace. During the months of April through September 2000, hundreds of acres were being infested overnight on the southern end of the Daniel Boone. Treatments that were implemented on the forest only slowed the spread of the beetles for a brief time, sparing the lives of some trees for a few more months.  

Two types of treatment methods to control southern pine beetle were implemented on the forest:

   1). Cut and Leave – Infested pine trees were cut and left where they fell. A buffer zone of non-infested pine trees was cut in some areas where the direction of spread could be determined. The buffer zone went up to 200 feet.  

   2). Cut and Remove – Infested pine trees and non-infested pine trees in the buffer zone were cut and removed from the site. This method reduced the number of adult and maturing beetles that would likely emerge to attack more trees.

No other control methods were an option for SPB infestation on such a large scale. Spraying thousands of pine trees with pesticide over thousands of acres would not have been practical or environmentally sound. Burning infested areas hot enough to kill infested pine trees would have killed other trees in the area and possibly created air quality problems.

A natural predator of the SPB, the clerid beetle (Thanasimus dubius), has been steadily increasing in population since the SPB outbreak on the Daniel Boone. The clerid beetles are attracted to pine trees under attack by SPB. The clerid adults attack and eat SPB adults. In addition, the clerid beetle adults lay their eggs in pine bark crevices of SPB-infested trees. Their larvae enter the trees and feed on SPB eggs, larvae and pupae. This natural enemy to SPB is being reared in research laboratories to potentially help combat future attacks of SPB on National Forest lands.

RESULTS OF THE INFESTATION

Summing Up the Losses

The most obvious result of SPB infestation is the loss of thousands of acres of pine woodland across the Daniel Boone National Forest and Kentucky. Pine trees that once stood alive with lush green crowns now stand as skeletons across a vast landscape, as temporary monuments to a recent past. More than 100,000 acres of pine forest have been lost to SPB damage on the Daniel Boone, an estimated 80% of pine acres previously existing.   

As a secondary result to the loss of pines, the plant and animal species associated with pine forest habitat are being affected. The federally endangered red-cockaded woodpecker was one of the first species to suffer notable impact on the Daniel Boone. Fifteen of these rare birds had to be captured and relocated to other states where pine habitat was unaffected by SPB (more discussion below). The pine warbler is another bird species being affected. Its song is no longer heard in the same abundance as it once was on the forest.

Other species associated with upland pine habitat are expected to suffer decline. At least one fourth (1/4) of the terrestrial plant and animal species occurring on the Daniel Boone National Forest in Kentucky are directly or indirectly associated with upland pine or mixed pine-hardwood forest types. The loss of pine habitat causes concern for these species and their ability to sustain viable populations in this region.

An estimated monetary loss from SPB damage on the Daniel Boone National Forest has not been determined. The dollar value of all the pine trees destroyed would undoubtedly sum into the millions. A dollar value, however, cannot be placed on the diverse plant and animal species associated with pine and mixed forest habitats. Their value is priceless. The potential for loss or decline of some pine-associated species is expected over the forest.

RED-COCKADED WOODPECKER

Extirpation in Kentucky

The red-cockaded woodpecker (RCW), Picoides borealis, is a federally endangered species that is dependent upon mature pine forest habitat. These birds require mature pine for cavity nesting, roosting and foraging for insects. As a result of the southern pine beetle epidemic on the Daniel Boone National Forest, Kentucky’s population of RCW was lost.

Prior to SPB infestation, extensive management efforts on the forest for RCW were proving successful. A critical population decline of RCW was being turned around. A habitat management area for RCW was established on the southern end of the Daniel Boone. Management efforts were being implemented within this 54,000-acre area to restore a viable population of RCW in Kentucky.

By 1995, Kentucky’s population of RCW had declined to only three known birds. Between February 1995 and September 1999, a total of fifty RCW were moved from other states and released within the habitat management area on the Daniel Boone. These “translocations” were conducted to recover RCW and prevent extirpation of this species in Kentucky. The population of RCW in Kentucky gradually increased from three known birds to twenty-three in 2000.

As SPB activity began to spread on the Daniel Boone, attempts were made to control their infestation within or near the active cluster sites of the endangered RCW. SPB-infested trees were cut from the active RCW sites and surrounding areas. While the cutting activities slowed the spread of beetles into the RCW sites, the pine trees would eventually succumb to SPB. The southern pine beetles have destroyed nearly all of the pine habitat that was once available for RCW on the Daniel Boone.

It became apparent by the early months of 2001 that RCW could no longer survive the degraded pine habitat conditions on the Forest. In consultation with the U.S. Fish and Wildlife Service, fifteen RCW that could be found on the Daniel Boone were successfully relocated out of Kentucky. Thirteen birds were moved to Arkansas and South Carolina in March 2001. The remaining two birds were moved to Georgia in September 2001.

PINE RESTORATION

Rebuilding the Future of the Forest

The restoration of yellow pine on the Daniel Boone National Forest will be a long-term endeavor but one that is worthwhile as a disappearing ecosystem is revived. Forest employees continue to conduct surveys and take inventory of SPB damage within the general forest area to determine future restoration needs.

Pine restoration may be accomplished in various ways. The use of prescribed burns, or controlled fires, is one of the tools that may be utilized during restoration efforts. Fire may be used to prepare a site for planting pine by exposing the mineral soils and reducing woody debris on the forest floor. Fire would aid in restoration by opening the forest canopy and allowing more sunlight for pine seedlings to grow.

Some pine planting has already occurred on the forest, and more is being planned for the future. The upcoming revision to the Daniel Boone National Forest Land and Resource Management Plan will address pine restoration on a larger scale.

Natural regeneration of pine is occurring at some locations across the forest. This natural regeneration is a result of 1). pine seeds that fell prior to the death of their parent tree or 2). the few remaining green pine trees that are providing a nearby seed source.

Unless pine recovery efforts are implemented, areas that were once pine forests would likely be replaced by hardwood. Plant and animal species that depend on a pine ecosystem for habitat and food supply would be negatively impacted and possibly lost in this region of the country.

Insect Threats

Chestnut Borer | Gypsy Moth | Hemlock Woolly Aldegid | Sudden Oak Death

Other Forest Health Topics

Four Threats to Forest Health | Forest Health Initiative | Red cockaded woodpecker | Invasive Species | Prescribed Burning

Last Updated: July 27, 2009