Bigleaf Maple Dieback

Dieback of bigleaf maple has been observed throughout the region during the past decade. A recent study out of University of Washington indicated that 22% of the maples sampled from 59 randomly selected sites in western Washington had symptoms of dieback. This finding is of enormous concern given the importance of this species economically, ecologically and culturally.

Unfortunately, a definitive cause has not been identified, although pests and pathogens have been widely considered (see PNW Handbook webpage). However, the dieback is known to be associated with several environmental variables such as vapor pressure deficits and higher temperatures, which is expected for most tree species. Still, more research is needed to confirm whether recent changes in these variables are the primary drivers of the dieback.

More information about the importance of bigleaf maple, the symptoms of dieback and the available resources for understanding the trends are listed below.

Bigleaf maple is an important species to the Pacific Northwest because of its commercial, ecological, cultural value.

Commercially, bigleaf maple is coveted by craftsman and woodworkers for fine furniture and custom products such as guitars and pianos. As the largest growing hardwood species in the region, slabs of bigleaf maple are highly prized because of its size, immaculate grain patterns, and common fungal compartmentalization and discoloration known as spalting.

Ecologically, the abundant leaf litter dropped from bigleaf maples each fall enriches the soil and the trees provide substrates for substantial growth of mosses, lichens, and even ferns. The characteristic helicopter seeds also provide valuable nourishment for many invertebrates living in our forests. In urban environments, it is an valuable source of shade, sometimes growing as wide as it is tall in open areas such as parks.

Summary

Unfortunately, many reports of dieback have been noted during the past decade (see below). Observations of declining maples have been made throughout western Washington and Oregon since 2010.

Symptoms

Symptoms of dieback include thinning and entire crown dieback. Branches sometimes have clumps of unnaturally small leaves and heavy seed crops. Leaves may appear chlorotic (yellow-ish) and with tips and edges that resemble leaf scorch.

The Cause

The precise cause of the dieback remains unknown. However, research has revealed an association between dieback and environmental variables such as temperature and the proximity to urban interface.