T. Eric McConnell, Curtis L. VanderSchaaf and Shaun M. Tanger

The invasive insect Agrilus planipennis, more commonly known as the emerald ash borer, is a relatively recent arrival to the North American landscape. That, however, has not slowed its impact on changing that landscape in a profoundly negative way, killing tens of millions of ash trees (Fraxinus spp.) since its detection in 2002 in Michigan.

Like many other states, Louisiana has a history of conservation efforts that included planting ash trees as ornamentals in rural and urban areas because of their superior survival traits. Those traits, though, have created a large target, and the entire species is threatened by extinction, similar to what happened to elm and American chestnut trees. In a strange twist, ash trees gained in popularity after replacing elm trees lost to the Dutch elm disease outbreak, which had become a popular replacement for American chestnut trees decimated decades before by the chestnut blight. The emerald ash borer recently was found to have parasitized the white fringe tree, which is not in the same genus as ash trees but is in the same family, Oleaceae. This family also includes olive, jasmine, privet, forsythia and lilac.

The potential economic and ecological impacts of emerald ash borer are staggering. National inventory data show more than eight billion ash trees in U.S. forests and woodlands, with a value estimated at more than $280 billion. Unfortunately, the emerald ash borer has now been discovered in several north Louisiana parishes (Figure 1). After first being detected in southern Arkansas in July 2014, the first official identification in Louisiana came in February 2015 in Webster Parish. Louisiana is the 25th state to be infested, and according to the Louisiana Forestry Association, the emerald ash borer had spread to eight other parishes as of July 2017.

Emerald ash borer is a bark- boring beetle, with one generation per year being typical. The larvae are the primary culprits that lead to tree death, where they tunnel in S-shaped galleries to feed in an ash tree’s inner bark (phloem) and outer sapwood (xylem) through summer and into fall (Figure 2). The persistent tunneling in the vascular system over multiple generations eventually limits the tree’s ability to transport water and nutrients and leads to death. A key identifier of emerald ash borer infestation is the insect’s distinct D-shaped exit holes.

Louisiana is likely to take a huge blow economically and ecologically from an emerald ash borer infestation because ash is a significant part of Louisiana forests. This is particularly true along the Red, Atchafalaya and Mississippi rivers (Figure 3). The most recent U.S. Department of Agriculture Forest Inventory Analysis data show ash trees represent around 5 percent of all hardwood species in the state at 20 million tons in rural Louisiana. These numbers do not include ash trees in cities and suburban areas. The Louisiana ash inventory is not as large as the levels in the northern U.S. where the infestation originated. There, ash was a significantly greater component of the regional forest, and its depletion occurred rather rapidly.

Five species of ash are found in Louisiana. In relative order of total volume, they are green ash, white ash and Carolina ash followed by pumpkin ash and blue ash. White and green ash have the most commercial use, including for furniture and lumber, while pumpkin ash has some commercial value. Carolina and blue ash have little commercial value.

Experts estimate a mortality level of nearly 100 percent when emerald ash borer parasitizes ash species. Given this grim prognosis and ash tree abundance in the Louisiana landscape, Louisiana Tech and LSU faculty members have developed an economic trade flows model to estimate the effect on the timber industry and larger economy in Louisiana from losses of ash species due to an emerald ash borer infestation. This article focuses specifically on the effects emerald ash borer could have on trees classified as sawtimber, using 2016 timber and harvest data for the state as an example. Sawtimber is the term for harvested logs converted into either appearance-grade lumber for flooring and cabinets or industrial-grade products, such as ties, pallets and mats.

Results

The total contribution of hardwood sawtimber harvesting in Louisiana in 2016 was $83.1 million. This included the delivered mill gate value of $46.9 million plus an additional $36.2 million of additional contributions from other sectors and institutions with activities linked to the logging sector. Of the $36.2 million, industries contributed $21 million and households added $15.2 million.

The particular economic scenario in this model shows that an emerald ash borer infestation could cause average harvest volumes to decline by 4.15 percent, falling to 94.7 million board feet from 98.8 million board feet.

Average local purchasing also declines by 4.15 percent, which means the state forest industries would need to import 4.1 million board feet to maintain current sawlog levels. The average mill gate value falls to $45.0 million, a decrease of $1.95 million; however, harvest levels could fall by as little as 3.46 million board feet or as much as 4.67 million board feet. This could directly contribute to a loss of hardwood sawtimber product value in the range of $1.64 million to $2.22 million.

The total economic contribution of annual hardwood sawtimber harvests under an emerald ash borer scenario in 2016 could have ranged from $75.4 million to $77.5 million. Compared to that year’s actual harvest contribution, this represents a decline of $5.68 million to $7.70 million. Beyond the loss in timber revenues are the losses that would be felt in other sectors throughout the Louisiana economy. Supplier industries could suffer output losses of $3.00 million to $4.07 million. Declines in household activities could range from $469,000 to $1.04 million. The grand total could range from $9.15 million to $12.81 million in losses to the Louisiana economy.

What do these findings mean?

It is important to establish baseline scenarios for economic damage estimates related to natural resources and agricultural commodities in Louisiana. Having these estimates allows policy-makers to establish a hierarchy of priorities. Further, the results, in more detail, show which industries would be hit hardest by the outbreak and those to target for assistance. Relatedly, the number of jobs lost due to the outbreak can be quantified and used as justification for targeting unemployment benefits related directly to disaster relief. Ultimately, this model suggests how timber markets may react to a change in ash availability.

Figure 1. Map of emerald ash borer detection in Louisiana.

FIGURE 2. An illustration of emerald ash borer damage. The tree’s outer bark has been peeled to expose the larval galleries. Photo by T. Eric McConnell of a tree in Ohio

FIGURE 3. Ash inventory (basal area) in Louisiana and surrounding states. Larger dots represent a greater presence of ash inventory. Source: USDA Forest Service