|The increase in the wild mushroom harvest in the province has led to complex and inter-related issues and concerns for mushroom pickers, buyers, sellers, managers and the general public. We will address some of the general issues here and discuss specific issues under each species.
It has been suggested that picking mushrooms is similar to picking apples. Picking apples one year doesnt affect future apple crops as long as the tree is not damaged. Likewise, picking mushrooms one year without damaging the mycelium should not reduce future mushroom production. However, there is insufficient information on the long-term effects of harvesting wild mushrooms to be able to substantiate such a claim.
Pilz and Molina (2002) identified five major concerns that must be addressed in order to understand and manage a sustainable wild mushroom harvest:
- mushroom biology, function and ecology;
- mushroom productivity;
- mushroom harvest techniques;
- habitat management; and
- people management
Mushroom Biology and Ecology
Although many different fungi produce fruiting bodies that are harvested and considered non-timber forest products, they all share certain biological similarities. All fungi obtain their nutrients and energy from external sources or substrates such as living trees or dead logs. Mushrooms and truffles are the fruits of the fungus, the structures in which reproductive spores are formed. The rest of the fungus is the vegetative stage, equivalent to the apple tree but composed of a network of hyphae (threads) or rhizomorphs (bundles of hyphae). Many interconnected hyphae or rhizomorphs are collectively known as mycelium, which lives often for many years in the substrate consumed by the fungus whether that is fine roots and surrounding soil or dead logs. Mycelia spread through their substrate, absorbing nutrients and waters. When conditions are right, the mycelium produces fruiting bodies on which spores are formed. Spores may germinate and develop into new fungal mycelia or they may fuse with existing mycelia. Either way, spores are the sources of new, genetically distinct individuals that can sometimes grow in previously unoccupied locations. One concern about mushroom harvesting is that the removal of so many mushrooms from the forest, often before spores have been produced, may imperil production of new individuals.
Functionally, the fungi that comprise harvested non-timber forest products (NTFP) can differ greatly from one another. Some NTFP fungi are saprophytic, absorbing nutrients and water from dead or decaying organic matter such as the twigs or logs. . Other NTFP fungi form mycorrhizae with living plant or tree hosts, acquiring carbon and energy from plant sugars formed by photosynthesis and in turn, supply soil nutrients such as nitrogen and phosphorus and water that the host plants need. Pathogenic mushrooms invade live hosts causing diseases.
To understand the ecology of forest fungi we must recognize that they interact with their environment in many ways that influence their productivity. Biological factors that influence mushroom production include host or substrate specificity and consumption by other organisms. For instance, some fly larvae consume only mushroom flesh and certain small mammals depend on forest mushrooms as important sources of food. Because many mushrooms are host or substrate specific, understanding the host or substrate is the first step towards understanding the mushroom. Mycorrhizal fungi must have an appropriate living host plant in order to survive. For some mycorrhizal fungi the age of the host is important in determining whether mushrooms will form, so although the fungal mycelium may occupy roots on a site it may not produce mushrooms until conditions, including host age, are ideal. Some saprophytic fungi are benign; invading the host after it is dead. Other fungi are aggressive and able to colonize weakened hosts.
Non-biological factors are also critical to NTFP mushroom production, triggering mushroom initiation by the mycelium and influencing mushroom development. Mushrooms fruit when appropriate water, temperature and light conditions exist.
Mushroom productivity is the total number or weight of fruiting bodies produced in a given area during the mushroom season. Mushroom productivity can vary tremendously from year to year depending on weather conditions such as precipitation and temperature. Fleshy or fragile mushrooms can be ephemeral, disappearing soon after their appearance, although many may produce multiple flushes at a given site. Tough, leathery mushrooms can fruit for extended times, but their onset of fruiting may be unpredictable. For all these reasons, multiple years of observing a given area are needed to establish and build a reliable database of mushroom productivity for the site. For important NTFP mushrooms, collaboration with local mushroom pickers and buyers is essential to estimate reliable annual productivity data. Highly productive areas tend to be quickly and extensively harvested, leaving little behind for data collecting. In B.C., little is currently known about productivity of any of the NTFP mushroom species. Estimates for pine mushroom and chanterelle productivity and value is now being established, but there is no such information for the other NTFP mushrooms.
Long term monitoring of a site establishes the baseline data on the productivity of a specific site, allows an evaluation of changes in productivity. With baseline productivity data at hand, attempts to manipulate the site by adding inoculated hosts, irrigating the site or spreading decomposing mushrooms onto the site can be assessed. In Japan, there are reports of successful manipulation of environmental factors in forests to increase the productivity of the Japanese pine mushroom, the Matsutake (Tricholoma matsutake), but there are no reliable reports of similar success in North America.
Mushroom Harvest Techniques
As commercial and recreational NTFP mushroom harvest increases, there is mounting concern that over-harvesting of particular mushrooms will lead to the decline in mushroom fruiting. Methods of picking the mushrooms may also contribute to mushroom decline. For instance, some mushroom pickers suggest that cutting the mushroom at its base, rather than pulling or digging up the mushroom, should be the preferred method especially when the mushroom is an ectomycorrhizal one. However, there is no evidence that this particular difference affects mushroom productivity.
A 10-year study on the effects of harvesting chanterelles (Cantharellus formosus) by the Oregon Mycological Society (Norvell 1995) found that there was no decline in chanterelle productivity regardless of the picking method. However, the picking method is critical for commercial NTFP harvesting. Buyers insist that pickers cut chanterelles at the base of the stem to keep the mushrooms clean. In contrast, buyers demand that pine mushrooms be harvested with the stem intact. In addition, pine mushrooms are more valuable when they are young, which has resulted in irresponsible pickers raking the forest floor in pursuit of the young, intact fruiting bodies. There is real concern that raking the forest floor in search of pine mushrooms can irreparably harm mushroom harvest, since the vegetative stage or mycelium that forms the mushrooms can be destroyed. There is little information on harvesting techniques for other wild mushrooms.
One impact of simply visiting a mushroom site again and again is the compacting of the moss layer and forest floor. Studies have shown that fruiting of the yellow or funnel chanterelle (Cantharellus lutescens Fr.) declines due to trampling. This decline, however, has been attributed to injury of the buttons or primordia because once trampling was stopped, fruiting returned to previous levels. Similar concerns have been expressed for other forest litter mushrooms..
Both commercial and recreational pickers and buyers suggest that leaving a mature cap or tapping a harvested mushroom cap to encourage spore discharge onto the forest floor will ensure that spores are available for future colonization. They also speculate that carrying a mature mushroom through a site will help distribute mushroom spores. There is no scientific evidence to support such speculations but it is reasonable to believe that spores play an important role in the life of NTFP mushroom species and that leaving some mature mushrooms in harvested stands will help perpetuate the species.
The mushrooms included in this web site are found in forests, disturbed areas, and lawns and other turf areas. Management of these habitats can impact mushrooms in many ways. These effects depend on the specific mushrooms reproductive strategy and the goals of the management strategies.
Application of pesticides and fertilizers can affect mushrooms, although we know of no scientific research that has investigated the impact of pesticides on wild forest mushrooms. Herbicides are sometimes used on regenerating forest sites to prevent competition for the newly planted tree seedlings. However, most herbicides are applied when the vegetation is actively growing during the spring and summer, while mushrooms fruit predominantly during the autumn and are most likely not affected by the herbicides. Additionally, most mushrooms of economic importance usually begin to fruit many years after out-planting, so only persistent compounds or recent drifts are potentially hazardous to mushrooms. Mushrooms growing on lawns, other grassland and turf areas are often treated like invasive pests. There are a number of fungicides available and other control measures have been developed to prevent these mushrooms from fruiting. Encouraging these mushrooms means that the manager must curtail the use of such fungicides. Application of pesticides and herbicides is suspected to negatively affect mushroom edibility.
Different mushrooms respond differently to various fertilizers. Phosphorus fertilizers have minimal effects on mushroom productivity, while nitrogen fertilizers can have significant effects on mushroom productivity. Generally, ectomycorrhizal mushroom diversity and productivity is reduced when nitrogen is added to the soil.
In Europe, air pollution has been implicated in the decline of wild mushrooms, especially chanterelles (Cantharellus cibarius). In affected areas there has been an increase in the acidification of forest soils and an increase in nitrogen precipitation because of the air pollutants as well as feedlot runoffs. Forest management activities such as clear-cut logging, fire management and site preparation also can adversely affect forest mushrooms. Clear-cut logging removes the tree host essential to ectomycorrhizal mushrooms, which severely impacts the life cycle of the mushroom. However, once sufficient time has passed to permit re-establishment of the ectomycorrhizal relationship, mushroom production should resume. Research has shown that smaller timbers cut blocks have more diverse and abundant ectomycorrhizal mushrooms compared to larger timber cut blocks.
Thinning a forest allows more light, heat and rain to penetrate the soil. If enough ectomycorrhizal hosts are retained on a site, their associated mushrooms are minimally impacted. Pilz et al. (2003) provide data from Oregon has showing that a heavily thinned Douglas-fir (Pseudotsuga menziesii) forest stand resulted in a 90% reduction in chanterelle fruiting in the year following thinning. There may have been some difficulties in seeing the ground because the forest floor was so shaded and identifying fruiting bodies may have been missed. Reports suggest that frequent, light thinning will impact mushroom productivity less than infrequent, heavy thinning.
Some ectomycorrhizal mushrooms are host specific, while others have a broad host range. Therefore tree selection on a site will influence the ectomycorrhizal mushroom community. Sites dominated with ectomycorrhizal hosts such as fir (Abies), alder (Alnus), birch (Betula), larch (Larix), poplar (Populus), spruce (Picea), pine (Pinus), Douglas-fir (Pseudotsuga) and hemlock (Tsuga) can share mycorrhizal fungi, so these sites will have a rich ectomycorrizal mushroom community. However, if non-ectomycorrhizal hosts such as maple (Acer), yellow cedar (Chamaecyparis), yew (Taxus) or cedar (Thuja) dominate a site, there will be a reduction in the ectomycorrhizal mushroom community.
Use of heavy machinery on a site under inappropriate soil conditions can cause soil compaction problems, which could impair mycelial growth and result in depleted fruiting body development. However, in B.C. scientific data are lacking concerning the long-term effects of repeated use of heavy machinery on mushroom productivity. Helicopter or cable logging is more likely to have less impact on mushroom productivity compared to ground-based logging. In B.C., the greater risk to mushroom productivity is clear-cut logging which removes the ectomycorrhizal host entirely.
Managed or wild fires can cause a shift in mushroom communities. Fires that destroy the soil litter layer will cause a reduction in mycorrhizae and fruiting body development, but less invasive fires may impact the fungi less. In the longer term, fire may play an important role in mushroom productivity; it has been observed, for instance, that many pine mushroom forests are even-aged stands of fire origin. In the short term, some morels are known to fruit abundantly in the spring the first year after a fire. There is a need for research to define the parameters that might be used to predict morel crop productivity on forest sites that are burned.
With more people now harvesting mushrooms for commercial, recreational and traditional purposes, there are opportunities for conflicts to develop among the different users of the forest resources. To minimize actual conflict, it is imperative that the different groups understand one another. One road to understanding lies in the motivation for harvesting mushrooms. For some people, it is economic gain, for others it may be the independence, the pursuit of something elusive, being surrounded by beautiful natural landscapes, or the social aspect of living in a camp.
On crown lands managed by the Ministry of Forests or forest companies, an issue that contributes to conflict and uncertainty is the lack of NTFP policy and tenure. Many people believe that some sort of policy and management is necessary to sustain all NTFP resources. In the Nass Valley for instance where pine mushroom harvesting is an important activity, the Nisgaa First Nation government has issued permits to mushroom harvesters on Nisgaa Lands. There are no easy resolutions to these issues for there are as many people opposed to government intervention in NTFP as there are in favour of it.
With the integration of greater understanding from research, knowledge developed from field studies, and the application of a sensitive program supported by the diverse users of the resource, the achievement of a sustainable mushroom harvest will become possible.
Vital features of this program will include:
- An understanding of the biology and ecology of the mushroom;
- The establishment of baseline data on the productivity of the mushroom on a site;
- The development of techniques that minimize the impact of harvesting on both the habitat and the long-term production of wild mushrooms;
- The development and enhance the habitat in which the mushroom is found; and
- A vigorous educatational plan directed at everyone involved in a commercial or recreational wild mushroom harvest.
Arnolds, A., 1991. Decline of ectomycorrhizal fungi in Europe. Agriculture Ecosystem and Environment 35: 209 - 244.
Norvell, L., 1995. Loving the chanterelle to death? The 10-year Oregon chanterelle project. McIlvanea. 12: 6 -25.
Pilz, D., and R. Molina. 2002. Commercial harvests of edible mushrooms from the forests of the Pacific Northwest United States: issues, management and monitoring for sustainability. Forest Ecology and Management 155: 3 16.
Pilz, D., L. Norvell, E. Danell, and R. Molina. 2003. Ecology and Management of Commercially Harvested Chanterelle Mushrooms. Gen. Tech. Rep. PNW-GTR-576. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 83 pp.