The exotic emerald ash borer, Agrilus planipennis, (Coleoptera: Buprestidae) is established in a number of states, including Michigan, Indiana, Ohio, and Ontario. At high population densities, all green, black, and white ash trees are apparently susceptible to attack and can be expected to die. Emerald ash borer larvae develop in the phloem of ash trees in stems and branches above approximately 2.5 cm in diameter. Removal of ash from high priority areas such as those stands in close proximity to outlier populations will reduce the population density of this insect. Measurements of ash trees suggest a strong relationship between diameter at breast height and calculated surface area of the tree. Other relationships between diameter, surface area and volume of phloem are being determined. These relationships, in addition to others involving tree vigor, form, and growing conditions, have been integrated into models characterizing the amount of ash phloem in a forest stand. Using these models, it is possible to determine diameter limits for cutting to meet prescribed ash phloem reduction targets. By reducing emerald ash borer populations through phloem reduction, and decreasing the removal of the smaller trees in a stand, this model will enable the genetic diversity of ash to be optimized in light of ash reduction efforts. Forest resource managers will be able to access the models online at www.ashmodel.org and find the diameter limit for removal of ash to achieve the phloem reduction target.