Tuber gibbosum and Leucangium carthusianum: ecology, harvesting and marketing
by Charles Lefevre, Dave Pilz, James Trappe, and Randy Molina.

Abstract
The culinary value of Tuber gibbosum (the Oregon white truffle) and Leucangium carthusianum (the Chartreuse truffle or locally known as the Oregon black truffle) has been recognized for three decades. However, little published information exists on the ecology or commercial harvest of these species. We reviewed herbarium records and compiled information from individuals who work with the truffles to gain an overview of the Oregon truffle industry. Tuber gibbosum has three varieties: var. gibbosum, var. autumnale and var. oregonense. Both vars. gibbosum and autumnale have commercial potential, but currently only var. autumnale is collected in significant quantities. Presently we recognize a single variety of L. carthusianum. Both species grow exclusively beneath Pseudotsuga menziesii var. menziesii, the coastal variety of Douglas fir, and their geographic ranges correspond roughly with that of their host (in Europe, L. carthusianum is associated with other host genera). Peak production of both species occurs in dense, young forests common throughout the region. Most harvesting takes place within a relatively small portion of the overall range of these species. The approximately 6,100 kg combined annual harvest likely represents a small fraction of available production. Most truffles are harvested surreptitiously by the controversial practice of raking the litter and surface layers of the soil. Raking frequently produces immature truffles that lack aroma and cause the reputation of Oregon truffles to suffer in comparison with other culinary truffle species. The wholesale price for T. gibbosum is approximately US$ 100 per kg. The average price for L. carthusianum is approximately US$ 140 per kg. The prices are slowly dropping because supply exceeds demand. However, the undeveloped potential market in the US may be much larger than current production. Our sources agree that the lack of good information regarding the harvesting, handling, and use of Oregon truffles and the consequent difficulty in marketing them hinders expansion of the industry.

Introduction
Tuber gibbosum Harkn., the Oregon white truffle, made its debut as a culinary delicacy in the late 1960’s. Somewhat more recently Leucangium carthusianum (Tul. & C. Tul.) Paol., known in France as the Chartreuse truffle and in the United States as the Oregon black truffle, was similarly discovered as a culinary treasure. Both species have won acclaim among North American chefs and are often favorably compared with the better known truffles of Europe (Czarnecki, 1995; Boyd, 1995; Sutton, 1998; Schneider, 1998). Nevertheless, little is known about these two truffle species or about the industry that has grown around their harvest and sale. The wild edible mushroom industry in the Pacific Northwest United States has received considerable attention in the last two decades, but mainly for epigeous species that are harvested in much larger quantities and generate far more income. All of the research undertaken to study wild edible mushrooms in the Pacific Northwest has therefore been devoted to other species, mainly Tricholoma magnivelare (Peck) Redhead, the American matsutake, Morchella species and various Cantharellus species. Thus, in spite of praise the Oregon white and Oregon black truffles have received and the fame of their European relatives, there is little scientific literature about them and one seldom sees them or encounters them on a menu, even in their native region (Boyd, 1995).

In this paper we will refer to Tuber gibbosum and Leucangium carthusianum collectively by the common term Oregon truffles. In the pages that follow, we provide an overview of the Oregon truffle industry. Given the near absence of literature we relied on herbarium records and knowledgeable individuals to obtain information concerning the habitat and commercial harvest of Oregon truffles. The overview we present suggests that several serious problems must be overcome if the Oregon truffle industry is to flourish.

Taxonomy and Distribution
Tuber gibbosum is comprised of three distinct varieties. Tuber gibbosum var. gibbosum as originally described by H. W. Harkness occurs from near San Francisco, California, to Victoria, British Columbia in winter and spring. It is characterized by a cinnamon to yellowish brown peridium, a dense, yellowish brown gleba, and ellipsoid to subglobose spores. A second variety, to be described elsewhere as T. gibbosum var. autumnale, fruits from northern California to southwestern Washington in autumn and early winter. It is white in youth, then develops areas of orange to brown and finally becomes dark orange-brown overall; the gleba is not as dense as the type variety, and the spores are ellipsoid to subfusoid. Both varieties have a peridium composed of interwoven hyphae. The third variety, to be described elsewhere as T. gibbosum var. oregonense, is known from only a few autumn collections in western Oregon. It resembles var. autumnale except it has an outer peridial layer of rounded, inflated cells rather than of interwoven hyphae. All three varieties produce emergent hyphal tips with distinctive, irregularly swollen walls. This character otherwise has been noticed only on Choiromyces alveolatum of western Oregon and California. Both vars. gibbosum and autumnale have commercial potential, but currently only var. autumnale is harvested in significant quantities.

Both Tuber gibbosum and Leucangium carthusianum fruit only in the presence of the coastal variety of Douglas-fir (Pseudotsuga menziesii var. menziesii), so we presume they are host-specific to Douglas-fir in Pacific Northwest ecosystems. Harkness originally described the type variety of T. gibbosum as occurring under oak at Mill Valley, Marin County, California. That area is now totally developed as suburbs, but the natural forest community was a mix of Quercus spp., Pseudotsuga menziesii, Lithocarpus densiflora, and various other species. Thus, "under oak" does not preclude the presence of Douglas-fir roots. Similarly, a small number of more recent herbarium collections are reported under Picea sitchensis or Tsuga heterophylla, both typically associated with P. menziesii. In Europe, L. carthusianum is associated with other host genera.

The geographic ranges of T. gibbosum and L. carthusianum extend between Northern California and southern British Columbia at relatively low elevations on the west side of the Cascades mountains (Arora, 1986, Molina, et al., 1993) corresponding roughly to the range of Pseudotsuga menziesii var. menziesii. Schlosser and Blatner (1995) suggest that both species are harvested commercially in Idaho approximately 500 km east of the main part of the range. We did not find herbarium collections from that region and none of the authors or our industry sources have expressed knowledge of Oregon truffles in that region. Idaho’s forests contain Pseudotsuga menziesii, but only the interior variety, var. glauca, which is not known to be a host for either species of Oregon truffle.

Ecology
 Both Oregon truffles fruit most abundantly in young Douglas fir forests, and unlike other wild edible mushrooms harvested commercially in the Pacific Northwest, the Oregon truffles tend to fruit on privately owned lands in easily accessible areas. Suitable habitat is common throughout the region, but most commercial truffle harvesting occurs in northwest Oregon and southwest Washington. Relatively few truffles are harvested in other parts of their range.

The two species are often found intermixed, but prolific patches for one species typically produce relatively few, if any, of the other species. Our industry sources report visible differences in soils producing the two species. Soils producing Leucangium carthusianum are frequently characterized by dark color and a very loose "fluffy" structure. Tuber gibbosum can be abundant in similar conditions, but it is also found in "heavy" red clay soils where L. carthusianum is uncommon.

No rigorous sampling of T. gibbosum or L. carthusianum productivity has been undertaken, but our industry sources and observations by the authors suggest that natural productivity can be quite high. In some patches Oregon truffle sporocarps may be more abundant than those of any other ectomycorrhizal species. Harvesters also commonly observe evidence of heavy rodent mycophagy and estimate that rodents consume a significant portion of the total crop.

A number of people are attempting to establish or enhance Oregon truffle production by inoculating existing stands of young trees, and in one highly publicized case the tree farmers claim to have successfully cultivated T. gibbosum. Their methods consist mainly of spraying inoculum on the soil surface beneath young Douglas fir trees. The inoculum is usually a slurry of macerated sporocarps diluted with water. Some people have reportedly fed truffles to animals, using their feces in the slurry. From the perspective of the authors and some of the sources we interviewed, there is no convincing evidence that these inoculation trials have succeeded in increasing truffle production or establishing new patches. In the best known case T. gibbosum existed on the site before it was inoculated and current production is good, but not dramatically better than some natural patches. Nevertheless, many people think that Oregon truffles are routinely cultivated.

Harvesting, Handling and Shipping
 There are relatively few truffle harvesters in the United States, and most of the truffles are gathered by a subset of them. Our industry sources estimate that fewer than 500 people currently harvest Oregon truffles. The number of harvesters is either static or growing very slowly as new harvesters replace others that move on to other sources of income.

Virtually all commercially productive truffle habitat is on privately owned lands. However, relatively few landowners harvest the truffles, either because they are not aware that they have them or because they are not aware of or interested in their commercial potential. Many people in the region are not aware that truffles of any kind exist in the Pacific Northwest, and Oregon truffle harvesters have successfully kept the nature of truffle habitat secret. Those who know the truffles exist typically do not know how or where to find them, even on their own land.

Most harvesting is therefore done by individuals who do not own the land and who frequently do not have permission to harvest. In the United States landowners have the right to deny access to their land. Consequently, many excellent patches are untouched because they are close to private homes and harvesters try to avoid attention. Landowners do frequently notice and are upset by damage caused by truffle harvesters on their land, but many apparently do not know what the harvesters are collecting. Knowledge of the truffles and their habitat is spreading among landowners and some are beginning to lease access to truffle harvesters, but many harvesters are not eager to pay for truffles that they have obtained freely in the past.

The damage caused by truffle harvesters results from the controversial practice of using rakes to remove the litter and surface layers of the soil rather than using dogs or pigs to locate individual truffles. By raking, harvesters can rapidly collect all or most of the truffles in a given area. They can also see whether or not a patch has been searched and avoid spending time in areas with no truffles remaining. The disadvantages include potentially harming the truffle patch or the host and the fact that truffles harvested in this way are frequently unripe and lack aroma. The rakes also break or gouge many of the larger truffles.

Opinions differ regarding the impacts of raking, but there is a consensus among our industry sources that the potential for harm depends on the depth of raking. Commercial truffle harvesters do return to patches annually, but many people are aware of areas that stopped producing truffles after a year or two of heavy raking (e.g. Trappe, 1989).

No studies have examined the effects of raking on truffle production. However, rakes are occasionally used to harvest Tricholoma magnivelare, the American matsutake mushroom, and a study is nearing completion that measures the effects of raking and raking methods on matsutake production (Hosford et al, 1997). Preliminary results suggest that raking does reduce subsequent production, but replacing litter layers significantly speeds recovery to pre-raking production levels.

Though there are individual truffle harvesters that replace litter disturbed by raking, it is clear that relatively few do so. Some truffle harvesters intentionally rake the litter into heaps or windrows to promote production of larger truffles beneath the piles.

The effects of raking likely differ by species. Tuber gibbosum sporocarps are usually at the interface of the mineral and organic layers of the soil and most are exposed by relatively gentle raking. Leucangium carthusianum sporocarps often grow deeper in the soil profile and harvesters excavate for them. Truffle harvesters have reported finding L. carthusianum as deep as 50 cm below the soil surface. Raking to this depth severs host roots, kills truffle mycorrhizae and alters soil profiles.

Another serious problem with raking is the inability of harvesters to selectively harvest mature truffles and leave immature truffles to develop. Because truffles develop over a period of months, harvesters using rakes can collect them well before they ripen. Harvesters and distributors recognize that chefs want aromatic truffles, but because harvesters compete for well-known sites, truffles are sometimes collected early to prevent competitors from harvesting the patch first. Also, some buyers prefer slightly under-ripe truffles to prevent spoilage during handling and shipping.

Few chefs in the US have experience using and judging the maturity of Oregon truffles so harvesters and buyers have less difficulty selling immature truffles than they might if chefs were more discerning. As a result, chefs may conclude after an initial trial that all Oregon truffles lack fragrance when the truffles they purchased were simply harvested too soon. Many people suspect that sales of immature truffles have given Oregon truffles a bad reputation that continues to hurt the industry.

A solution to problems associated with raking would be for harvesters in the US to employ dogs. However, given the relatively low prices for Oregon truffles harvesters need to collect large quantities to earn a living and they feel they could not gather enough using dogs. Unfortunately, the practice of raking yields lower quality truffles that sell at lower prices and the use of rakes becomes self-reinforcing. Some collectors use evidence of rodent diggings to locate patches, particularly for L. carthusianum which tends to be more dispersed, but that is the only way animals currently contribute to the harvest of Oregon truffles.

Most Oregon truffles harvested by raking lack a strong aroma for a time after removal from the ground and must be ripened in storage (Czarnecki, 1995). After several hours to several days in proper storage conditions the aroma of mature or nearly mature truffles intensifies. At peak ripeness the truffles soften slightly and within a day or two begin to exude visible surface moisture. The appearance of surface moisture is an indication that they are about to spoil and they must be used within a day. The period of time during which truffles may be ripened and used is therefore very short.

Most Oregon truffles are shipped overnight, but they frequently spoil en-route or shortly after arriving. Thus, perishability may be the single greatest difficulty in selling Oregon truffles. As the season advances and overall maturity of truffles increases their shelf life decreases, reaching a length of about one week after harvest during the final month. In addition to initially screening the quality of freshly harvested truffles, handling and storage conditions can have a dramatic impact on shelf life. Most buyers prefer to leave adhering soil on the truffles in order to preserve their shelf life, allowing chefs to wash them immediately before use. The truffles are also occasionally packed in uncooked rice to extend shelf life by as much as a week, but rice ultimately dehydrates the truffles and reduces their quality.

The two common varieties of T. gibbosum may require different storage conditions to ripen properly (Lefevre, unpublished observation). The late fall and winter fruiting T. gibbosum var. autumnale seems to ripen in one of two ways. If refrigerated soon after harvest it develops the aroma that has made it a culinary delicacy. If it is kept at room temperature for as little as one day it develops an aroma resembling toluene or diesel fuel. Marin and McDaniel (1987) found that toluene is a component of the aroma of T. gibbosum var. autumnale. The spring fruiting T. gibbosum var. gibbosum requires somewhat warmer temperatures in storage to ripen properly. If it is refrigerated it fails to develop a strong aroma, but it does ripen properly at spring soil temperatures which are generally between room temperature and refrigeration.

Buyers can freeze truffles that they are unable to sell. Frozen Oregon truffles maintain the quality of their flavor, but they loose intensity and value. Some harvesters and buyers have experimented with various preserved and value-added products, but we are not aware of anyone selling such products.

Business and Marketing
Current prices for Oregon truffles are half or less than they were 10 to 15 years ago. Current wholesale prices to restaurants for T. gibbosum are approximately US$ 100 per kg. Wholesale prices for L. carthusianum are approximately US$ 140 per kg. Prices to harvesters estimated in 1992 were US$ 71 per kg for T. gibbosum and US$ 170 per kg for L. carthusianum. (Schlosser and Blatner, 1995). Prices paid to harvesters for L. carthusianum in 1992 were higher than current wholesale prices, indicating a dramatic decline between 1992 and the present. According to our industry sources, prices have leveled somewhat since falling in the early 1990s, but the general trend is toward further decline. Their reasons to explain the decline are poor quality control, poor marketing, and supply exceeding demand.

Schlosser and Blatner (1995) estimated that 1992 production of Oregon truffles was 3,400 kg for T. gibbosum and 2,700 kg for L. carthusianum. Our industry sources believe that growth in the industry is very slow and that production quantities have not changed dramatically since 1992.

in spite of slow growth, our industry sources estimate that the potential market for Oregon truffles in the US is much larger than current production. Since the bulk of the US population lives outside of the Pacific Northwest it is likely that a relatively small proportion of US chefs have ever had an opportunity to use Oregon truffles.

Almost all Oregon truffles are sold within the United States and our sources believe that this is not likely to change. Obstacles to exporting Oregon truffles include their perishability and established preferences for European species.

The exalted image of European truffles may also hinder marketing of the native species within the United States. We are not aware of large marketing efforts to promote Oregon truffles in the US. The most active efforts to market Oregon truffles are currently by individual harvesters selling directly to restaurants. Several small companies advertise Oregon truffles on the Internet at substantially higher prices than other sources.

Conclusions
 The potential supply of Oregon truffles is much greater than the current harvest. Three factors contribute to that conclusion: most commercial collecting takes place within one portion of the geographic range, appropriate habitat is common throughout the range, and the surreptitious nature of the harvest deters searching in many patches near private homes. The potential market is similarly undeveloped. Current marketing efforts are minimal and relatively few fine restaurants in the United States have ever used Oregon truffles, though the popularity of culinary mushrooms is growing.

Nevertheless, the Oregon truffle industry remains small in spite of a potentially large supply and high prices that would appear to present a good business opportunity. Several factors hinder growth in the Oregon truffle industry. Foremost is the short shelf life. Oregon truffles are inherently difficult to handle; they are sensitive to storage conditions and spoil quickly. Existing business models built around other wild mushrooms may need to be modified for these species. Additional obstacles include ensuring ripeness of truffles harvested by raking, developing a market for a product with unpredictable supply, and overcoming a sullied reputation. The Oregon truffle industry also faces competition with the exalted image of European truffles and the task of educating chefs about the idiosyncrasies of Oregon truffles.

Growth in the Oregon truffle industry will require solutions to these problems, but if they are overcome, Oregon truffles may become an important part of the larger wild edible mushroom industry in the Pacific Northwest and a distinctive element in North American cuisine.

Literature Cited
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