The genus Fraxinus, commonly known as the ash tree, has long been a fixture in North American forests and urban landscapes. These deciduous trees gained a reputation as fast-growing, adaptable species that provide excellent shade and a stately appearance. Historically, their resilience across a wide range of soil and climatic conditions made them a preferred choice for planting projects. However, the decision to plant a new ash tree today is complicated, requiring a careful balance between the tree’s inherent value and a severe, ongoing ecological challenge that has fundamentally altered the long-term viability of the species.
The Appeal of Ash Trees
Ash trees were celebrated for their rapid growth rate, allowing them to quickly establish a mature canopy and deliver shade benefits sooner than many other hardwood species. Their foliage is composed of graceful, pinnate leaves that create an airy, dappled shade. This leaf structure also minimizes the amount of heavy debris created during the autumn leaf drop.
The aesthetic value is enhanced by their vibrant seasonal color change, often shifting from bright green to striking yellows or deep purples. The wood of Fraxinus species is highly prized for its exceptional strength-to-weight ratio and elasticity, making it a staple in manufacturing for items like baseball bats and tool handles. Ash species are also notably hardy and adaptable, thriving in conditions from moist riverbanks to drier, well-draining soils.
The Primary Ecological Risk
The widespread popularity of ash trees has been curtailed by the arrival of the Emerald Ash Borer (EAB), Agrilus planipennis. This small, metallic-green beetle is an invasive pest native to Asia, first detected in North America in Michigan in 2002. The EAB poses a severe threat because North American ash species have no natural resistance, leading to catastrophic mortality rates.
The adult beetles cause minimal damage by feeding on foliage, but the destruction is caused by their larvae. The larvae burrow into the tree’s vascular system, feeding on the phloem layer just beneath the bark. This feeding activity effectively severs the tree’s ability to transport water and nutrients, starving the tree.
Infestation is difficult to detect early on, but once symptoms appear, the timeline to tree death is swift, usually ranging from one year for smaller trees to four years for large specimens. In areas where EAB is established, mortality rates have exceeded 99% of all ash trees. The beetle attacks all 16 species of North American ash, threatening the functional extirpation of the entire genus across the continent.
Long-Term Management and Associated Costs
For property owners with existing ash trees, the presence of EAB introduces a permanent and expensive management commitment. Protecting an ash tree in an affected area requires the repeated application of systemic insecticides. The most effective treatment involves trunk micro-injection, using a potent insecticide like emamectin benzoate distributed throughout the tree’s vascular system.
This treatment must be reapplied periodically, typically every two or three years, to maintain protection. The cost is usually calculated based on the tree’s diameter at breast height (DBH), often running around $11.00 per inch of trunk diameter. Economic analyses show that the cumulative expense of repeated treatment is significantly less than the eventual cost of removing a large, dead tree, which can range from hundreds to thousands of dollars.
Early detection is essential for treatment success, as insecticides cannot reverse existing damage. Property owners must monitor for signs of infestation, including D-shaped exit holes left by emerging adult beetles and noticeable crown dieback. A tree whose canopy has already suffered more than 50% dieback from EAB is unlikely to be saved, even with treatment.
Advisability of Planting an Ash Tree
Given the ecological threat and the resulting maintenance commitment, planting a new ash tree is discouraged in regions where the Emerald Ash Borer is established or likely to arrive soon. The decision to plant one should only be made within a long-term, managed plan that explicitly includes the financial commitment for biennial or triennial systemic insecticide treatments. Planting an ash without this ongoing chemical protection is essentially planting a tree destined to die within a few years of the pest’s arrival.
Specialized breeding programs are working to develop cultivars that exhibit natural resistance to EAB, but these are not widely available for general planting. If the unique characteristics of the ash tree, such as its tolerance for challenging site conditions, are desired, several alternative species can fulfill similar landscape roles without the associated risk. Selecting a diverse range of species for planting is the most prudent strategy to ensure the long-term health and resilience of the local tree canopy.
Alternative species that can fulfill similar landscape roles include:
- Certain species of Oak (Quercus).
- Disease-resistant American Elms (Ulmus hybrids).
- Hackberry (Celtis occidentalis).
- Various Maples (Acer), such as the Miyabe Maple.