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Washington State University
WSU Puyallup Ornamental Plant Pathology

Bigleaf Maple Decline

Introduction

Decline 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 decline. 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 decline 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 decline.

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

Bigleaf Maple McKenzie Pass, Oregon

Bigleaf Maple

Bigleaf Maple growing along a street in Seattle

The Northwest Maple

Bigleaf maple is another iconic species of the Pacific Northwest. Where many maple species occur in other regions of the US, Bigleaf maple is the only native maple to the Northwest’s coastal regions.

The distribution of bigleaf maple generally reflects its adaptation to mild climates and sensitivity to cold temperatures. It grows abundantly on the west side of the cascades between sea level and about 1500ft, sometimes reaching as high as 4000 feet in California and Oregon.

As the name suggests, bigleaf maple is easily distinguished from other maples because of its large leaves. Look for the large hand shaped leaves with deeply cut lobes reaching up to a foot long.

Links to More Information

Identification

Biology and Ecology

Ethnobotany

Distribution

Pests and Disease

  • Leaf Spots, Pacific Northwest Pest Management Handbooks, Oregon State University
  • Powdery Mildew, Pacific Northwest Pest Management Handbooks, Oregon State University
  • Wood Decay, Pacific Northwest Pest Management Handbooks, Oregon State University
  • Verticillium wilt, Washington Department of Natural Resources
Leaf spots on Bigleaf Maple are caused by a variety of fungi

Importance

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.

Bigleaf maple stand in fall

Cultural Heritage

Bigleaf maple is known as the ‘paddle tree’ in many First Nation languages because of its superior quality as a strong and light wood for paddles and spindle whorls (Pojar and MacKinnon 1994). The wood is also important for crafting utensils and the inner bark was woven into baskets (Moerman 1998).

Seeds and sprouts are also edible and comparable to alfalfa sprouts (Arno & Hammerly 2007).

The enormous leaves have also been used as temporary containers and to cover food in cooking pits.

  • Arno SF, Hammerly RP. Northwest trees. Mountaineers; 2007.
  • Moerman DE. Native American ethnobotany. Timber press; 1998.
  • Pojar J, MacKinnon A. Plants of coastal British Columbia. Lone Pine Publishing; 1994.

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Concern

Summary

Unfortunately, many reports of decline 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 decline 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 decline remains unknown. However, research has revealed an association between decline and environmental variables such as temperature and the proximity to urban interface.

Photo credit: Dan Omdal, DNR
Photo credit: Dan Omdal, DNR

Unhealthy Bigleaf Maple

Healthy Bigleaf Maple

Photo credit: Dan Omdal, DNR
Photo credit: Dan Omdal, DNR

Reports of Decline Concerns

Theses

Posters

Book Sections

News Articles

Blog Posts

Declining bigleaf maple at Ravena park