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Summary
Replacing Trees Killed by EAB: Seek Diversity to Avoid Future Problems (10/6/2009)
One of the most important lessons that have been learned from the widespread destruction of ash trees by the exotic emerald ash borer (EAB) is that diversity must be a key consideration when planting trees in various settings whether it is the home landscape, commercial parking lots or along city streets. Experts agree that tree diversity is an important buffer against catastrophic tree loss in natural and managed forest systems alike. Ash, for example, was a very popular shade tree, and in many cases it was the only tree chosen for landscape projects. In other words, it became a monoculture. So when EAB began infesting and killing ashes, entire communities and commercial establishments lost all of their trees at once. We didnt learn from the bad experience we had with Dutch elm disease, which wiped out elm trees in landscapes in the United States, said Kathy Smith, an Ohio State University Extension forestry program director. We just replaced one species with another. We need to learn that we need a variety of trees. Maybe this time we will be able to get away from that monoculture-street mentality. Forestry experts have come up with a formula to guarantee tree plantings achieve diversity and thus are better protected against devastating pests such as EAB. Its called the 10-20-30 Rule, and it advises that no more than 10 percent of the trees should be in the same species, no more than 20 percent in the same genus, and no more than 30 percent in the same family. One example of how to apply this rule to tree plantings is this: If you are planting 10 trees on your property, pick no more than three trees from the Fagaceae or beech family, no more than two trees from the Quercus or oak genus, and no more than one tree from the white oak (Quercus alba) species. Ideally, too, individual tree species should be scattered throughout the community or property to achieve both spatial and biological diversity. Age diversity should also be considered, avoiding having all of the trees in a particular setting be of the same age. To assist individuals and communities looking for options to replace felled or at-risk ash trees, OSU Extension has developed a comprehensive handbook, Ash Replacements for Urban and Woodland Plantings, that identifies tree species that can be used to replace existing ash or utilized in future plantings if ash species are not available or are not suited for planting. Authored by T. Davis Sydnor, professor of urban forestry, Randy Heiligmann, retired Extension state forestry specialist, and Smith (all with Ohio States School of Environment and Natural Resources), the 82-page publication lists different tree characteristics such as site requirements, ornamental features, wildlife value, flood tolerance and commercial availability for each of the 35 species recommended. This guide also includes full-color photos of each tree as well as its base, flowers, leaves, and other features such as nuts and fall foliage. The more than 100 photos featured in the publication make the selection process easier, especially for people who are unfamiliar with Ohio tree species. We have chosen native, hardy trees that occupy a space similar to that of ash in the canopy and serve a similar function, Smith said. Its not just replacing a tree with another. If you planted green ash around waterways because of its flood tolerance, youd want a replacement tree that works well in that particular environment. Ash Replacements was developed in response to the spread of EAB in Ohio, but the authors said its an excellent planting guide for anyone involved in woodland management. Theres nothing out there this detailed for Ohio, he pointed out. This is the probably the best single reference for photos available, and the tree requirements listed in the book are very helpful. In the past, foresters would take care of making planting recommendations. But because of emerald ash borer, a lot of different people Extension educators, Soil and Water Conservation District folks, etc. are going to be making planting recommendations, too. They now have a great resource to help them work with their clienteles. A free electronic version of Ash Replacements can be accessed at http://ashalert.osu.edu (look under Factsheets/Bulletins). The printed version is available through you local OSU Extension office for $7; it can also be purchased by contacting Media Distribution, Communications and Technology, at 614-292-1607 or online at http://estore.osu-extension.org (ask or search for Bulletin 924).
One of the most important lessons that have been learned from the widespread destruction of ash trees by the exotic emerald ash borer (EAB) is that diversity must be a key consideration when planting trees in various settings whether it is the home landscape, commercial parking lots or along city streets. Experts agree that tree diversity is an important buffer against catastrophic tree loss in natural and managed forest systems alike. Ash, for example, was a very popular shade tree, and in many cases it was the only tree chosen for landscape projects. In other words, it became a monoculture. So when EAB began infesting and killing ashes, entire communities and commercial establishments lost all of their trees at once. We didnt learn from the bad experience we had with Dutch elm disease, which wiped out elm trees in landscapes in the United States, said Kathy Smith, an Ohio State University Extension forestry program director. We just replaced one species with another. We need to learn that we need a variety of trees. Maybe this time we will be able to get away from that monoculture-street mentality. Forestry experts have come up with a formula to guarantee tree plantings achieve diversity and thus are better protected against devastating pests such as EAB. Its called the 10-20-30 Rule, and it advises that no more than 10 percent of the trees should be in the same species, no more than 20 percent in the same genus, and no more than 30 percent in the same family. One example of how to apply this rule to tree plantings is this: If you are planting 10 trees on your property, pick no more than three trees from the Fagaceae or beech family, no more than two trees from the Quercus or oak genus, and no more than one tree from the white oak (Quercus alba) species. Ideally, too, individual tree species should be scattered throughout the community or property to achieve both spatial and biological diversity. Age diversity should also be considered, avoiding having all of the trees in a particular setting be of the same age. To assist individuals and communities looking for options to replace felled or at-risk ash trees, OSU Extension has developed a comprehensive handbook, Ash Replacements for Urban and Woodland Plantings, that identifies tree species that can be used to replace existing ash or utilized in future plantings if ash species are not available or are not suited for planting. Authored by T. Davis Sydnor, professor of urban forestry, Randy Heiligmann, retired Extension state forestry specialist, and Smith (all with Ohio States School of Environment and Natural Resources), the 82-page publication lists different tree characteristics such as site requirements, ornamental features, wildlife value, flood tolerance and commercial availability for each of the 35 species recommended. This guide also includes full-color photos of each tree as well as its base, flowers, leaves, and other features such as nuts and fall foliage. The more than 100 photos featured in the publication make the selection process easier, especially for people who are unfamiliar with Ohio tree species. We have chosen native, hardy trees that occupy a space similar to that of ash in the canopy and serve a similar function, Smith said. Its not just replacing a tree with another. If you planted green ash around waterways because of its flood tolerance, youd want a replacement tree that works well in that particular environment. Ash Replacements was developed in response to the spread of EAB in Ohio, but the authors said its an excellent planting guide for anyone involved in woodland management. Theres nothing out there this detailed for Ohio, he pointed out. This is the probably the best single reference for photos available, and the tree requirements listed in the book are very helpful. In the past, foresters would take care of making planting recommendations. But because of emerald ash borer, a lot of different people Extension educators, Soil and Water Conservation District folks, etc. are going to be making planting recommendations, too. They now have a great resource to help them work with their clienteles. A free electronic version of Ash Replacements can be accessed at http://ashalert.osu.edu (look under Factsheets/Bulletins). The printed version is available through you local OSU Extension office for $7; it can also be purchased by contacting Media Distribution, Communications and Technology, at 614-292-1607 or online at http://estore.osu-extension.org (ask or search for Bulletin 924).
