Estimated Impacts of Emerald Ash Borer on Ash Timber Supply in Texas, USA

We estimated annual timber growth, removals, and mortalities under various scenarios of the spread of emerald ash borer (Agrilus planipennis Fairmaire; EAB) within Texas. Future annual ash EAB-induced mortalities were simulated to follow either a normal or beta distribution over 25, 50, or 75 years, with five percent of the original inventory remaining at the conclusion of each projection. Discounted present values of future ash growth, harvests, mortalities, salvage, and beginning and ending annual inventories were calculated, and economic impacts to timber receipts were determined from average real prices. The present net effects of timber product output, mortalities, and salvage resulted in benefits ranging from lows of (delivered/stumpage) $37.6/$12.8 million over 25 years when assuming a normal distribution to highs of $247.8/$97.2 million over 75 years under a beta distribution. Salvage intensity exceeded mortality accumulation by a factor of at least 2.00. Regardless of length chosen, mortality that skewed toward later years led to lower discounted volumes and less value lost to EAB. Results were sensitive to discount rate selection (constant, increasing, distributional) with the constant and increasing rates having the most similar results. Longer time horizons led to far smaller losses of overall economic returns allowing more typical harvest management despite EAB. Study Implications: Literature is lacking that could inform managers and policymakers on the economic impacts of emerald ash borer (EAB) from a production forestry perspective and how those impacts could affect forest management and use strategies in the southern portion of ash species' home ranges. Our analysis concerned the 15.7 million tons of ash timber currently residing on Texas forestlands. Model simulations showed that, depending on assumptions, net economic benefits accrued via timber receipts. Greater importance was placed on mortalities when shorter projection periods (and mortality distributions) were considered, which subsequently lowered net benefits. Government participation will likely be critical to achieving socially acceptable salvage conditions. Policymakers and forest administrators should consider the management, use, and logistical differences that EAB's relatively slower, yet persistent, influence will have on regional supply chains versus the immediate and widespread mobilization efforts more commonly employed in response to regional natural catastrophes, such as storms and southern pine beetle (Dendroctonus frontalis Zimmermann) epidemics. From an economic perspective, the results support policies for slowing the spread of EAB even if full control is not feasible. The results consistently indicated that longer time horizons led to increased discounted values for removals, less need for salvage of dead/dying trees, less wood left in the forest, and larger positive net returns.

Automated summary

The study estimated the impact of emerald ash borer (EAB) spread on timber growth, removals, and mortalities in Texas, showing that longer time horizons lead to increased net economic benefits. Government participation is crucial for achieving socially acceptable salvage conditions, and shorter projection periods emphasize the economic impact of mortality.