Alabama landowners should be aware of another looming threat to the health of some Alabama forests; the Emerald ash borer (EAB). This insect is a member of the Buprestidae family of beetles in the order Coleoptera. This family is typically referred to as flatheaded borers and members have a metallic exoskeleton. Most species within this family are secondary pests that attack injured or dying trees.
Female emerald ash borers lay their eggs on ash tree bark. As the eggs hatch, larvae mine their way into the cambium. There, winding galleries are formed that effectively girdle the cambium of the host tree. A classic calling card left by this insect is the D-shaped exit holes in the bark of affected trees.
Unlike other forest pests, the emerald ash borer is not a secondary pest. It is fully capable of attacking and killing healthy ash trees, a consequence of a lack of evolutionary history between the Asian insect and North American ash trees.
Found in Alabama
In July 2017, the Alabama Forestry Commission collected the first documented EAB larvae from green ash trees on private property in Calhoun County. Only two weeks later, larvae were obtained from trees standing on a private residence in Talladega County. Larvae had chewed galleries through the phloem to approximately two feet above the base of the tree. Death of the main stem had already occurred, leaving behind many root sprouts. This indicates that the EAB has been present in those counties for several years based on the timeframes given from previous studies. It is possible that movement from this area may be stagnant for a brief time frame because Calhoun and Talladega counties are in the bottom third of counties concerning ash stocking.
Ash Trees in the State
The Forest Inventory and Analysis program (FIA) provides an array of forest statistics. Information pulled from the FIA indicates that ash comprises only one percent of the total tree species composition in Alabama. There is an estimated 224 million trees partitioned primarily on privately held lands. This number is somewhat misleading, as ash can comprise a sizable percentage of moist upland and bottomland sites in some localities.
In Lowndes County, ash species comprise 6.5 percent of all standing trees within the county. Outside of planted pine stands within the county, general observations have shown that ash is present along most of the creek drainages and moist flats surrounding black belt pastures and prairies. The greatest stocking of ash occurs in the Alabama, Cahaba, and Tombigbee river drainages in Clarke, Perry, and Sumter counties where over 24 million ash trees reside.
Private landowners bear the most substantial burden of the invasion and subsequent consequences of the EAB infestation. Consequences include ash mortality, timber revenue losses, and further occupation by invasive species such as Chinese privet.
EAB infestations begin in the upper crowns of ash and slowly move their way down the main trunk of the tree over a period of two to four years. By the time unmistakable signs of infestation are apparent, it is often too late to save the tree because the cambium has been compromised beyond the point of practical treatment. If conducted, treatment typically involves an injection of systemic insecticides into the cambium of high-value ash trees by certified arborists. Treatment is expensive and unreasonable to use on a forest scale.