The Southern Pine Beetle
The Southern Pine Beetle (Dendroctonus frontalis) has attracted the attention of foresters, natural resource managers, local and state government agencies, environmental groups, and private land owners.
[+ ZOOM] Examining the inner bark of an infected pine tree reveals the signature S-shaped egg galleries of the Southern Pine Beetle. © USDA/NRCS
The Southern Pine Beetle (SPB) has recently advanced north into the New Jersey Pinelands, killing pine trees in patchy but spreading areas. While the New Jersey Department of Environmental Protection (NJ DEP) has promoted a cut-and-leave approach to control the spread of the SPB, PPA is advocating for greater consideration of high-intensity prescribed growing season burns to both control current SPB infestations and prevent future ones in Pinelands forests.
On this site, you will find detailed information about the SPB, PPA's letter to the NJ DEP advocating further consideration of high-intensity prescribed burning, scientific research articles used as supporting sources of information, PPA newsletter articles, and links to further information from the NJ DEP and the NJ Pinelands Commission.
Southern Pine Beetle Facts
Links to More Information
[+ ZOOM] Sandy trail through a Pinelands forest. © Rachel Moore
When reviewing information about the SPB, it is important to keep in mind that the Pinelands is an ecosystem that is specially adapted to frequent fires. Being a low-nutrient ecosystem, natural fires are important in maintaining high rates of nutrient turnover consistent with the system's level of resource availability. The periodic burning of old trees and other vegetation allows the nutrients that are "locked up" in this biomass to be returned to the soil, promoting the regeneration of early successional plant species that require open habitats (i.e. Pine Barren Gentian and Wild Lupine). Fires also allow for the continued dominance of pine trees in these forests as they are better able to cope with frequent fires than are oaks and other hardwoods. In fact, in the absence of fire, the pine trees are replaced by the more competitive hardwoods. If pines are lost from the mixed pine-oak forests of the Pinelands - by way of the SPB or otherwise - and there are no subsequent fires to suppress the oaks, pine regeneration is not stimulated and the oaks limit the regrowth of early successional, shade-intolerant plant species.
[+ ZOOM] Young male cones. © Kevin Sparkman
Traditional forest management practices have disrupted the natural fire regime in the Pinelands, increasing its susceptibility to southern pine beetle attack.
It is also important to recognize the difficulty in predicting exactly how significant of a threat an insect pest poses to any particular area's natural environment and how long any negative effect will last. It is natural for pest populations to spike and plummet at regular or irregular intervals (gypsy moths, for example). When pest populations grow too large, they are eventually knocked back down by some sort of compensatory force - being preyed upon by a predator, attacked by bacterial, viral, or fungal disease, or simply depleting their own resources so much so that the population crashes. Factors independent of population size can also dramatically knock down a pest - for example, a particularly cold winter. After a pest population declines, the subsequent recovery of the ecosystem depends on a variety of factors: the scale of the disturbance; its intensity, duration, and frequency; its lasting effects; the dispersal potential of nearby sources of seeds to initiate regeneration.
Whether such a disturbance is viewed as harmful or beneficial to an ecosystem can vary with the scale of observation. For example, in the short term, a pest that destroys part of a forest will be seen as a negative disturbance that results in tree mortality. But, that disturbance can create forest gaps that provide new habitat for early successional plant species which have lain dormant in the soil seed bank for years. On a landscape scale, periodic and patchy disturbances allow for a more diverse biological community with greater stability and resilience to future perturbations. When a major disturbance affects an entire landscape within a short period of time, however, the fate of that landscape is less certain.
[+ ZOOM] A misty grove in the Pine Barrens. © Albert D. Horner
While we cannot predict the long-term effects of the SPB in the New Jersey Pinelands, we do know that these forests have adapted to and are highly dependent on fire for their continued existence. Restoration of a fire regime through well-designed high-intensity prescribed burning will likely increase the natural resilience of the Pinelands and allow it to respond more rapidly to a variety of disturbances, including the southern pine beetle.
Southern Pine Beetle Facts
[+ ZOOM] Size comparison: Adult southern pine beetle on left, rice grain in middle, turpentine beetle on right. © New Jersey Pinelands Commission
- The SPB is native to the southeastern United States. Having recently advanced north into New Jersey due to recent warmer winters, its range expansion has likey been aided by the late 1990's drought and interstate commerce.
- In its native range, the SPB population fluctuates between being present in very low numbers and occasional outbreaks. It has historically been a consistent participant in natural southeastern pine forest dynamics.
- Research indicates that the last SPB outbreak in New Jersey, prior to the current one, occurred in 1939.
- The SPB feeds on all species of pine trees, but prefers pitch pine, shortleaf pine, Virginia pine and loblolly pine.
- The SPB prefers weakened, stressed, old and over-crowded pine trees.
- The SPB kills trees by feeding on the living tissue under the bark. Adult beetles bore galleries into the tree's inner bark and lay eggs inside. The eggs hatch into larvae, which feed on the tree's tissue. Larvae develop into adults, which leave and fly to a new tree to begin the process again.
- An infested tree's needles turn from green to yellow or brown as soon as two weeks after an initial SPB attack. Pitch tubes, exit holes, and egg galleries under the bark also indicate SPB infestation.
- In southern New Jersey, the SPB produces around two generations per year, but could produce up to four.
[+ ZOOM] Characteristic S-shaped egg galleries of the Southern Pine Beetle. © New Jersey Pinelands Commission
- Since 2001, the SPB has impacted about 26,600 acres in NJ. According to the NJ DEP, approximately 389 potential infestations totaling 14,100 acres were recorded in the Pinelands in 2010. In 2011, this number dropped to about 7,000 acres. In 2012, affected acreage reported by the DEP was 6,260 acres.
- Since its appearance in 2001, the SPB mainly affected pine forests in the very southern sections of NJ. In 2008, the SPB crossed the Egg Harbor River and entered the pine forests of Atlantic County.
- In addition to direct damage to pine trees through burying into and eating living tissue, the SPB also transmits blue stain fungi, which stops water from circulating in the tree.
- The Pinelands is an ecosystem that is highly adapted to frequent fires and depends on fire for maintenance of biodiversity and native plant regeneration. SPB prefers crowded, mature pine forests. Suppression of natural forest fires over the last several decades has resulted in this type of crowded forest throughout the Pinelands, increasing its susceptibility to SPB attack.
- Additionally, without subsequent fires to suppress the more competitive oak trees and stimulate pine regeneration following a SPB attack, there is less of a chance that forests affected by the SPB will reestablish as healthy pine forests.
[+ ZOOM] Current geographic range of the Southern Pine Beetle. © New Jersey Department of Environmental Protection
- The range of the SPB is most likely determined by winter temperatures. Because of the SPB's short generation time, high dispersal abilities, and wide distribution of host trees, changes in minimum annual temperatures can almost immediately alter the distribution of the SPB. Warmer winters allow the SPB to expand its range northward. Air temperatures of -16°C (3°F) result in almost 100% mortality. (Ungerer et al. 1999)
- In the southeastern U.S. coniferous forests within the SPB's native range, the SPB and fire historically interacted to maintain the structure and function of these forests. The interaction between fire and the SPB led to high community diversity and productivity by maintaining open, uneven-aged pine forests. Current forestry practices have disrupted this interaction and have created forests particularly susceptible to SPB infestation. (Schowalter et al. 1981)
- Land use trends over the past century, such as fire exclusion, conversion of pine forests to high density pine stands, and frequent cutting have increased pine susceptibility to SPB attack. (Boyle et al. 2004)
- Suppression of fires in forests affected by the SPB accelerates the transition from pine-dominated forests to hardwood (oak) forests. (Schowlater et al. 1981)
- In lodgepole pine forests in Canada (a forest type adapted to frequent fire), high-intensity prescribed burns were found to significantly reduce the population growth and attack rates of the mountain pine beetle (a northwestern analog to the SPB). While low-intensity prescribed burns had no effect on beetle survival, higher intensity burns reduced the beetle brood per tree. (Safranyik et al. 2001)
- Model simulations of pitch pine forests under the influence of both SPB infestation and fire have shown that with SPB infestation and fire combined, pitch pines maintain current levels of abundance. Without fire but still under attack from the SPB, pitch pines are removed from the forest. Fire needs to be reintroduced to maintain pine forests affected by the SPB. (Waldron et al. 2007)
- Fire, occurring after SPB infestation, is responsible for pine regeneration. (Knebel and Wentworth 2007)
- Fires occurring after SPB infestation and cut-and-leave suppression methods resulted in understory regeneration, maintenance of pine composition, and increased plant abundance and species richness in a Louisiana pine-mixed hardwood forest within 16 years after the initial SPB disturbance. (Coleman et al. 2010)
[+ ZOOM] Illustration of the cut-and-leave approach to controlling the Southern Pine Beetle. © New Jersey Department of Environmental Protection
[+ ZOOM] A pine cone releases its seeds following a fire in the Pine Barrens. © Kevin Sparkman
- Currently, the NJ DEP is implementing a cut-and-leave approach to control the SPB. This method involves mechanically cutting infested trees as well as a certain number of healthy trees along the perimeter of the advancing front of a SPB infestation. The trees are left on-site, orientated on the ground in such a way that confuses the SPB and prevents it from spreading further. This method helps control the SPB in spots with 10 to 50 infested trees. Expanding spots with more than 100 infested trees are more difficult to control with cut-and-leave.
- There have been indications that the NJ DEP is also considering a cut-and-take approach, in which infested and healthy trees within an affected forest patch are cut down and removed, the wood then being sold for economic gain. While this approach would help offset the cost of cutting trees in SPB-infested patches, there is concern that it could provide incentive to remove more healthy trees than is necessary.
- The cut-and-leave and cut-and-take approaches may help control the spread of the SPB in small, isolated spots of infestation, but are not practical in the long-term given the continuous and wide-ranging SPB threat. Also, this method of control was developed in southern pine plantations, where the primary concern is the cultivation of timber trees - not preservation of the shrub community, herbaceous community, or rare species. It has not been shown that this method is appropriate for ecosystem-level conservation in the Pinelands.
- PPA has communicated with the NJ DEP on this issue and has encouraged more consideration of the use of high-intensity prescribed growing season burns as a method of SPB control in combination with the cutting approaches.
- If warmer winter temperatures continue, we may not be able to completely resist the northern range expansion of the SPB and, in that case, we would need to accept its new role in our local ecology. The pine forests would likely benefit if we also accept that high-intensity fire through prescribed burning should be restored as a natural disturbance process.
- The observation that fire-thinned forests can keep the SPB in check in southern pine forests suggests that if it is to become a regular part of the Pinelands ecology, then fire-induced thinning may keep its populations in check here as well. Luckily, the Pinelands thrives with high-intensity fire, so we would not be introducing a new disturbance source solely to suppress the SPB.
- Between mortality due to SPB attacks and mortality due to mechanical cutting and felling, the abundance of pine trees will be reduced under the cutting approaches, but there is no subsequent fire to suppress oaks and jump-start pine regeneration. Cut-and-leave and cut-and-take will not suppress oaks, will not reduce the litter layer, and will not encourage pine regeneration if these methods are not followed by high-intensity prescribed fire.
- Routine high-intensity prescribed burns in forest areas not yet affected by the SPB would create forest conditions that are unfavorable to SPB outbreaks in the first place. Such a strategy would be large-scale and preventative, rather than small-scale and reactionary like the cut-and-leave and cut-and-take approaches. Prescribed burning can be likened to a medical analogy, in which a person works to stay in good health as a means of preventing disease, instead of treating the symptoms only after illness occurs.
- In short, high-intensity prescribed growing season burns could:
[+ ZOOM] Fire in the Pinelands. © NJ Natural Lands Trust
- Reduce tree density, which (1) decreases competition and associated stressed trees which are more vulnerable to SPB attack, and (2) creates a more open forest in which the aerosol pheromones produced by the SPB are not as concentrated, reducing communication efficacy among the SPB.
- Directly kill SPB adults and brood.
- Suppress the oaks which would otherwise dominate following destruction of pines.
- Stimulate regeneration of pines following a SPB attack.
- Reduce forest fuel loads, thereby preventing uncontrolled wildfires.
Drawbacks of high-intensity prescribed burning include the increased costs of planning and labor, as well as safety concerns. However, experience in other states shows that high-intensity prescribed fires can be conducted safely in forests like those of the Pinelands. For example, a particularly well-managed prescribed fire plan has been followed for 20 years at the Albany Pine Bush Preserve in Albany, New York. This inland Pine Barrens, though it is much smaller in area than the New Jersey Pine Barrens, is surrounded by development and has been routinely subjected to high-severity prescribed burns without posing a significant threat to the surrounding development and without violating EPA Clean Air Act standards. The management plan for the Albany Pine Bush preserve can be found as a PDF file on their website.
Links to More Information
Download PPA's letter to the NJ DEP:
Download the NJ DEP Southern Pine Beetle Fact Sheet or visit their Southern Pine Beetle website
Visit the NJ Pinelands Commission Southern Pine Beetle page
Read PPA's Southern Pine Beetle article in our October/November 2011 Newsletter
Read PPA's Southern Pine Beetle article in our August/September 2011 Pinelands Watch
View a great resource on the Southern Pine Beetle and methods of Southern Pine Beetle control
Support legislation for prescribed burning in New Jersey
Boyle, M.F., R.L. Hedden, and T.A. Waldrop. 2004. Impact of prescribed fire and thinning on host resistance to the southern pine beetle: preliminary results of the national fire and fire surrogate study. Pgs 60-64 in: Proceedings of the 12th Biennial Southern Silvicultural Research Conference, February 24-28, 2003, Gen. Tech. Rep. SRS-71. USDA Forest Service Southern Research Station. Asheville, NC.
Coleman, T.W., A. Martin Jr., J.R. Meeker, S.R. Clarke, and L.K. Rieske. 2010. Disturbance from southern pine beetle, suppression, and wildfire affects vegetation composition in central Louisiana: A case study. Gen. Tech. Rep. SRS-129, Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station.
Knebel, L. and T.R. Wentworth. 2007. Influence of fire and southern pine beetle on pine-dominated forests in the Linville Gorge Wilderness, North Carolina. Castanea 72:214-225.
Lafon, C.W. and M.J. Kutac. 2003. Effects of ice storms, southern pine beetle infestation, and fire on table mountain pine forests of southwestern Virginia. Physical Geography 24:502-519.
Safranyik, L., D.A. Linton, T.L. Shore, and B.C. Hawkes. 2001. The effects of prescribed burning on mountain pine beetle in lodgepole pine. Information Report BC-X-391. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, BC.
Schowalter, T.D., R.N. Coulson, and D.A. Crossley, Jr. 1981. Role of southern pine beetle and fire in maintenance of structure and function of the southeastern coniferous forest. Environmental Entomology 10:821-825.
Ungerer, M.J., M.P. Ayres, and M.J. Lombardero. 1999. Climate and northern distribution limits of Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae). Journal of Biogeography 26:1133-1145.
Waldron, J.D., C.W. Lafon, R.N. Coulson, D.M. Cairns, M.D. Tchakerian, A. Birt, and K.D. Klepzig. 2007. Simulating the impacts of southern pine beetle and fire on the dynamics of xerophytic pine landscapes in the southern Appalachians. Applied Vegetation Science 10:53-64.
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