Maple trees are naturally found across Ohio. Their vibrant fall colors and fast growth rates make them popular in urban areas. In forests, they provide important products such as lumber and syrup, along with wildlife habitat, water quality, and aesthetics. Maple trees, however, can be attacked by beetles, tapped for maple syrup, or otherwise injured. These injuries often result in the tree’s wood becoming an ambrosia color, resulting in a wood that is called “ambrosia maple.” The ambrosia colors are not signs of fungal infection or decay (as is the case with many softwoods) but are the tree’s defense mechanism to prevent further damage from decay following the wounding. This fact sheet describes what ambrosia coloration is, the species in which it occurs, and ways in which landowners and homeowners can capitalize on it.
Maple (genus Acer) are among the most common tree species in Ohio forests and cities. Maple species found in Ohio include red (A. rubrum), sugar (A. saccharum), black (A. nigrum), silver (A. saccharinum), and boxelder (A. negundo). Brilliant red, orange, and yellow colors exhibited by maples in the fall, combined with fast growth rates, make them favored species in urban landscapes. Silver, red, and sugar maple can grow to become large shade trees. However, any number of insects and diseases affect the trees. Among the most important insects attacking maple are ambrosia beetles.
Ambrosia does not refer to any given species of maple, rather it’s a discoloration that affects the wood of many Ohio maple species, primarily red maple (Acer rubrum). Ambrosia colors are usually a combination of greens and browns. This discolored wood is called ambrosia due to the beetles that burrow into the tree. It is also called wormy maple or ghost maple. The ambrosia coloration can also be present in maples that have been tapped for maple syrup production, with the ambrosia discoloration appearing around and below the tap holes.
Unlike the blue and black stain found in southern and western conifer species, ambrosia coloration in maple is not caused by a fungus. Rather, it is the tree’s defense mechanism against injury. Ambrosia stains in maple are not associated with decay. The colors are made by different phenolic compounds produced in the area of the wound to prevent fungal and bacterial infection. These compounds are sterilants, which prevent further injury resulting from decay. This discoloration does not reduce physical wood properties, nor does it fade over time. From a mechanical standpoint, ambrosia maple and non-ambrosia maple are similar. The presence of the insect bore holes and the discoloration typically remove ambrosia maple from use for things like flooring, furniture, and cabinets. However, woodworkers and craftspeople like the color combinations it provides.
Another member of the maple family that exhibits this ambrosia behavior is boxelder (Acer negundo). However, the ambrosia color in boxelder is red, instead of the greenish brown color found in red maple. Boxelders with a strong ambrosia coloration are often called “flame” boxelder. As with other maples, the red ambrosia color (flame) in boxelder is caused by the same decay-preventative process. Instead of brown and green, the colors are pink to red. This pink/red color fades over time when exposed to UV radiation in light.
Boxelder typically grows in wetter areas across Ohio but usually doesn’t reach the size where it’s commercially viable to harvest. Its relative softness compared to other maples and lack of grain pattern make it less desirable for most uses. However, woodworkers like it for the red color and easy machining.
Management of Ambrosia in Maple
Most landowners do not want insect infestations in their forests and do what they can to prevent infestations. While not reported in the scientific literature, it’s commonly believed that ambrosia beetles attack stressed and weakened trees. This stress is often caused by factors such as overcrowding, slow growth rates, poor locations, and more. Active forest management can help reduce these stressors. However, insect populations can reach levels that result in attacks on even well-managed stands of healthy trees.
In conversations with a number of sawmill owners across Ohio, boxelder always seems to have the red ambrosia, or flame, coloration. The degree of coloration present dictates the potential value of the wood. Boxelders seldom reach the size where it would be financially viable to cut them. Once cut, value is largely determined by the degree of flame present in the wood. To maximize value, the landowner must be familiar with local markets and woodworkers who may be interested in the wood. Having an understanding of the value of the wood helps increase timber harvest revenue.
Ambrosia maple offers landowners a possible premium product to sell to woodworkers and craftspeople. This potential avenue for increasing returns on harvesting operations does not require an increase in stand management activities. However, it does require the landowner, logger, and consulting forester to communicate clearly and understand local markets.
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