Commercially-Harvested Edible Forest Mushrooms
Productivity and Sustainable Harvest Research in the Pacific Northwest
David Pilz, Randy Molina, & Jane Smith.
Pacific Northwest (PNW) Research Station, US Department of Agriculture, Forest Service, Forestry Sciences Laboratory, 3200 Jefferson Way, Corvallis, Oregon 97331.
Pacific Northwest (PNW) Research Station, US Department of Agriculture, Forest Service, Siskiyou National Forest, Grants Pass, Oregon 97526.
Original Americans only collected a few edible forest mushrooms, but a wide variety of species have been collected in the Pacific Northwest since Europeans settled here and sought species they knew from their homelands. Commerce in these mushrooms has existed for decades, however, only since the late 1980's has the market really flourished. In the Pacific Northwest United States much of the best and most accessible forest habitat for wild, edible mushrooms exists on National Forest (US Department of Agriculture) and Bureau of Land Management (US Department of Interior) lands. Growing public demand for both recreational and commercial mushroom harvest opportunities has prompted the Pacific Northwest Research Station (a research unit of the US Forest Service) to institute a research program to address the concerns that managers and the public have about the vastly increased harvests.
Mushroom companies establish temporary buying stations in local towns during the harvest seasons. Fresh mushrooms are usually graded, cleaned, packaged and air-freighted to distant markets within several days.
Basket of commercially collected Tricholoma magnivelare (American matsutake).
Basket of commercially collected Morchella elata group (black morels).
Basket of commercially collected Boletus edulis (King Boletes).
Pacific Northwest mushrooms are marketed locally, regionally, nationally and internationally. These chanterelles were for sale at the Pike Street market in downtown Seattle, Washington.
The list of forest mushroom species that are commercially harvested in the Pacific Northwest is lengthy. Many are saprobes (for example, Morchella species or Laetiporus sulfureus) or parasites (for example, Sparasis crispa or Hypomyces lactifluorum). The most abundant and highly prized edible forest species are typically ectomycorrhizal. These include: the American matsutake (Tricholoma magnivelare), chanterelles (Cantharellus formosus and subalbidus), boletes (Boletus edulis and others), truffles (especially Tuber gibbosum and Leucangium carthusiana ), and hedgehogs (Hydnum repandum ). Currently, truffles are the only edible ectomycorrhizal fungus in widespread cultivation. As demand increases and cultivation technology improves, other species likely will be cultivated in plantations, or forests may be managed to enhance mushroom production. Because forest trees provide sufficient carbohydrates for abundant fruitings, wild harvests will probably also remain cost effective.
Pictured is a young Boletus edulis mushroom, commonly called the "King Bolete" or variously known as "Cep", "Steinpilz", or "Porcini" among many other common names used in Europe. This specimen was growing in a coastal sitka spruce (Picea sitchensis) forest of Oregon.
A tanoak (Lithocarpus densiflorus) mycorrhiza excavated immediately underneath an American matsutake (Tricholoma magnivelare) mushroom. T. magnivelare forms mycorrhizae with a wide range of host trees in the Pacific Northwest.
Pictured (courtesy of Eric Danell) are Cantharellus cibarius mycorrhizae synthesized in pure culture in the laboratory.
In situ study of forest fungi entails a variety of unique challenges:
PNW Research Station scientists are cooperating closely
with forest managers to address these challenges by designing and testing
inventory and monitoring protocols that are practical and efficient. In
combination with basic research into the biology and ecology of these fungi,
we intend to provide managers with the tools, information and understanding
needed to manage this resource effectively.
Baseline estimates of sporocarp production (numbers and biomass) are essential for insuring that mushroom harvests are sustainable and for determining the influence of forest management practices on fruiting and long-term population viability. Describing annual variation in productivity and correlating seasonal abundance to macro- or micro-environmental factors facilitates local, seasonal management of the commercial harvest. Characterizing productivity by habitat type allows long-term regional planning for continued mushroom harvests as the mosaic of forest ages and composition shifts across the landscape.
Researchers and managers must distinguish between "commercial" and "total" (biological) production. Commercial production is the portion harvested for sale and is often divided into quality grades of differing value. Total production is useful for examining the importance of non-harvested mushrooms in spore dispersal or the diets of forest animals. Collected specimens must be sorted, weighed, and dried promptly at the end of each day's sampling.
Sampling a strip plot for matsutake mushrooms in the Siskiyou Mountains of southwestern Oregon.
Most forest mushrooms absorb moisture rapidly with rainfall and dry quickly in the sun. Even fluctuations in relative humidity can swiftly alter their moisture content. Valid comparisons of mushroom productivity (biomass) depend on accurate dry weight measurements. Home food dryers with good air circulation and adjustable temperatures dry specimens quickly without excessive heat.
Harvesters and managers alike are interested in how subsequent fruiting is affected by the harvest of sporocarps, the method of harvest (pulling, cutting or digging), and associated activities such as raking, trampling or moving woody debris. The impact of reduced spore dispersal on fungus reproduction is also of concern.
Researchers studying the impact of harvesting must estimate the weight of mushrooms in non-harvested "control" areas because both numbers and size may be affected. The size and weight of similar mushrooms are used to develop regression equations that allow the weight of the mushrooms from the non-harvested patches to be estimated from measurements of their size.
Harvesters who are unfamiliar with an area will sometimes move leaves, forest duff, or soil organic layers to find the valuable, young "buttons" of the American matsutake, Tricholoma magnivelare. Concern that raking might reduce or eliminate future fruiting has prompted studies of its impact. Pictured is a research plot on the Umpqua National Forest in Oregon where the duff layer of a matsutake patch (mapped with flags) has been experimentally raked.
Forest management goals differ widely among landowners in the Pacific Northwest. Even on federal lands, objectives vary for a given portion of the landscape. Integrated management of forest ecosystems provides landowners with the means to enhance the production of commercial products while conserving important forest amenities. An understanding of how forest management activities affect edible fungi is needed for sustaining or enhancing their production while conserving their viability and functional roles in the ecosystem.
Much of the original Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) forest of the Pacific Northwest has been harvested and replanted. As dense new stands of trees are beginning to mature, they are producing abundant crops of chanterelles (Cantharellus species). Foresters intend to thin many of these forests by commercially harvesting suppressed trees. Mushroom researchers are monitoring how chanterelle fruiting will respond to changes in the forest environment when logging leaves fewer, but more vigorous, trees.
Wildfires often create prime habitat for the commercial collection of the black morel (Morchella elata group, including M. angusticeps and M. conica.) in the high elevation (1500-2500 meters) forests of the inter-mountain west. Pictured is a burned forest consisting of white fir (Abies concolor), western larch (Larix occidentalis), Douglas-fir (Pseudotsuga menziesii), Engelmann spruce (Picea engelmannii), and lodgepole pine (Pinus contorta v. latifolia). Throughout much of the region, decades of fire suppression allowed unusually dense forests to develop . Dry years during the 1980's lead to high tree mortality from insect infestations. Soil disturbances from efforts to restore forest health through salvage logging and prescribed fires may temporarily enhance morel crops.
Much remains unknown about the physiology, habitat requirements, reproductive biology, genetic diversity, population dynamics, ectomycorrhizal host interactions and ecosystem roles of edible forest fungi. Further understanding is essential to their management in natural ecosystems.
This researcher has excavated two American matsutake (Tricholoma magnivelare) mushrooms to examine the ectomycorrhizal root tips that develop in the dense hyphal mat this fungus forms. The fungus grows in arcs or "fairy rings" through the soil. During mycorrhiza formation, it aggressively invades host roots, eventually resulting in necrosis and death of fine roots to the rear of the migrating fungus mat. Understanding the unique biology of this species is essential to its proper management.
The PNW Research Station edible forest mushroom research program encompasses a variety of specific projects. These include:
These initial studies are laying the foundation for future work by establishing baseline estimates of productivity, providing comparisons of sampling designs and procedures under various forest conditions, and supplying managers with preliminary information about the mushrooms they need to manage immediately. Future research activities are likely to include: