Southern Pine Beetles (SPBs) are predators of pine trees (Longleaf, Loblolly, and Shortleaf) in East Texas. In the National Forests and Grasslands in Texas (NFGT) and on private lands, landowners often control SPBs after they have attacked pine trees. Areas where these attacks occur are called “spots”. The last significant SPB predation in the NFGT occurred in 1991-1994. Since that time (24 years) SPBs have been at low population levels. In the future there is concern that population levels will rise and economic losses of pine trees will grow.
SPBs are a natural solution to dense pine tree growth caused by humans or Nature. SPBs act as natural thinning agents when they kill pine trees. Pine tree death creates new habitats and biological legacies like standing dead trees (snags), downed trees (coarse woody debris), thickets, rootwads, etc. These habitats and biological legacies are important for the ecological health of forest ecosystems because they provide shelter, food, and nutrients. Oftentimes humans overstock pine plantations, farms, and forests which creates unhealthy forest conditions that SPBs like.
Methods to reduce SPB attacks usually include 1) Spray trees with pesticides; 2) Cut and leave pine trees with SPBs and a buffer of green trees around the “spot”; 3) Cut and remove (salvage logging) pine trees attacked by SPBs and a buffer of green trees around the “spot”; and 4) Monitor “spots” to determine their rate and direction of growth.
The Sierra Club is concerned that many SPB reduction methods can result in soil erosion, damage to vegetation, stream siltation, loss of nontarget hardwood trees, pesticide pollution, and loss of wildlife habitat.
The Sierra Club favors an alternative SPB control strategy (CS) implemented over the long-term which causes less environmental damage. The Sierra Club CS is a combination of methods that are available and will reduce, not eliminate, SPB predation.
The Sierra Club CS is a type of Integrated Pest Management (IPM). IPM is a combination of cultural, biological, and other treatments which reduce pest numbers to levels where economic damage is acceptable.
Each tree species has a range of conditions (maximum and minimum) under which it can grow successfully. Trees often survive in a weakened condition in many areas. The set of conditions that each tree species must have for optimized growth includes sunlight, water, soil (minerals, nutrients, and organic matter), topography, and space (tree density).
Research has shown that SPBs attack weakened pine trees. This is how “spots” begin. This often means that pine trees that are attacked grow under less than optimal conditions. Less than optimal conditions for pine trees include dry soils, wounded trees, wet soils, nutrient deficient soils, and areas with overly dense pine trees. Growing pine trees in these areas is an invitation for SPBs. Too often pine trees are grown under suboptimal conditions to maximize economic returns.
Conversion from hardwood forests and mixed hardwood-pine forests to pine forests or pine-hardwood forests is often based upon economic and not biological reasons. After such conversions, pine forests grow in densities and areas where they normally would not naturally have survived. Competition from hardwood trees normally reduces or eliminates pine trees from these unsuitable areas.
In East Texas, Southern Red, Bluejack, Blackjack, and Post Oaks are found on dry ridges. In wetter areas, oaks like Willow, Water, Shumard, Cherrybark, and other bottomland hardwood tree species grow naturally. Many of these dry or wet areas have been planted in dense stands of Loblolly Pine with little consideration about optimal growing conditions.
In wet areas, root rot is prevalent which can weaken pine trees and make them more susceptible to SPBs. Traditional hardwood or other unsuitable areas and increased hardwood tree density creates natural barriers or screens where hardwood trees surround pine trees and make SPB attacks more difficult. An increase in hardwood trees in these areas has beneficial wildlife impacts due to increased soft and hard mast and den trees. White-tailed Deer, Eastern Wild Turkey, Gray and Fox Squirrels, rodents, and other animals will benefit from more hardwood trees and the food and shelter they provide.
Planting more Longleaf Pine trees can reduce the susceptibility of a forest to SPBs. Longleaf Pine trees have greater resistance to SPBs due to thick bark and more resin which pitches out or drowns SPBs. Longleaf Pine trees used to be the dominant upland pine tree in many areas in East Texas. Unfortunately, many of these uplands have been planted to Loblolly Pine trees which are not as resistant to SPBs.
Increased populations of hardwood and Longleaf Pine trees increase habitat for woodpeckers. Some woodpeckers, like the endangered Red-cockaded Woodpecker, like old Longleaf Pine trees in more open upland areas. Woodpeckers are prime predators of SPBs. Increased woodpecker habitat means more woodpeckers to feed on SPBs. Longleaf Pine trees generate additional snags, cavities, and large downed wood on the forest floor. This provides more nesting and perching sites for hawks, owls, and other birds and shelter and food for raccoons, opossums, reptiles, amphibians, insects, and other animals.
Improved pine tree genetics can play a role in the reduction of SPBs. Insect resistance can be bred into pine trees (increased resin production and thicker bark) so that trees can resist and survive SPB attacks better.
Natural factors like droughts, floods, hurricanes, windstorms, lightning strikes, etc. can wound and weaken pine trees. These weakened pine trees can be girdled and left in the forest to serve as snags and downed trees for the benefit of wildlife. Current spacing of pine trees in the NFGT, 20 to 25 feet between trees, is done to reduce SPB attacks. The growth of variable densities of pine trees scattered over the landscape better represents the original growth of pine trees and should act to interrupt or reduce SPB movements.
Pine trees with scraped bark produce odors that attract SPBs. Improved logging practices that reduce the number of wounded trees due to logging equipment helps reduce the number of SPB target trees.
The use of pheromones to disrupt and disturb SPB attacks should be quickly implemented on a wide scale when a SPB attack is discovered. Areas of pine trees should be thinned (logged) to reduce their density so they are not desirable targets for SPB attacks. Prescribed burning prepares pine forests for better growth and thus improves their health against SPB attacks.
The increased “edge effect” that SPBs cause is beneficial to some wildlife. These smaller forest openings allow for different successional stages in random forest growth. These smaller openings are more beneficial for wildlife than large areas that are clear-cut and simulate natural openings due to storms. SPB “spots” allow forests to grow in a mosaic of tree species and ages by naturally thinning out overstocked pine trees. When this occurs, remaining pine trees grow better due to reduced competition.
Taken together, these methods, applied systemically over East Texas, reduce economic damage due to SPB attacks. We must accept that SPBs are a valuable part of dynamic pine forest ecosystems in East Texas. When we accept that we must live with SPBs and when we give up thoughts of their eradication, we will learn to appreciate and take advantage of the healthy forest ecosystems that SPBs create.
Brandt Mannchen
July 28, 2018