Shiitake, of all the exotic gourmet mushrooms, is particularly of interest to forest landowners because it is commonly produced on small 10 to 20 cm diameter (4 to 8 inch) logs of hardwood trees (e.g., oak (Quercus spp.), beech (Fagus spp.), maple (Acer spp.), sweetgum (Liquidambar styraciflua L.)), which may be removed from a woodlot in the course of various forest management operations. Although shiitake have been successfully produced on a variety of hardwood species, its greatest success and highest level of productivity has been on oak logs (its common name "shiitake" means "mushroom of the shii tree" (a species closely related to oak) in Japanese). These mushrooms, normally larger than the supermarket variety white button mushrooms (Agaricus spp.), are honey-colored to chocolate brown in color and may be speckled with white spots along their perimeter or split along the top, looking something like overly-toasted marshmallows. The gills on the underside of the cap are white, as is the stipe or stem. Shiitake mushrooms have a distinctive, somewhat nutty or garlicky flavor and are high in B vitamins and essential amino acids. If exposed to sunlight, they will absorb vitamin D. Grown and used in Japan for centuries, they were introduced into the United States as a food commodity in the 70's (Harris, 1986). Interest in production and consumption of these mushrooms in the United States has grown steadily since then.
Spawn is the active ingredient, composed of mushroom spores, which have been germinated on a mixture of sawdust and grain under sterile conditions, assuring that the resulting medium will produce only the desired type of mushroom. Once the medium becomes completely infiltrated with the mycelia ("root" system) of the fungus, it becomes "active" and can be inoculated into logs. In addition to sawdust spawn, there is another form known as dowel spawn. In this case, the active material has been impregnated into wooden dowels which are then hammered into holes drilled in the logs for inoculation. Sawdust spawn is inoculated into the logs with some form of simple mechanical injector or directly by hand. Heavy duty high speed drills with wood bits create straight or diamond patterns of inoculation sites (8-9 mm (5/16-3/8 inch) deep) around the circumference and along the length of the logs to encourage the mushroom mycelia to spread throughout the log as quickly as possible. Log lengths are determined largely for convenience, as the logs are handled periodically throughout the production process. Shiitake may also be grown on sawdust or other high cellulose substrates, but that type of production is more capital- and labor-intensive than is log production. It does, however, yield more mushrooms per given surface area of substrate than logs.
As with any proposed new food commodity, production planning is essential. Logs for mushroom production are cut while hardwood trees are dormant - from a time when the trees are in full fall color and are beginning to lose their leaves, to late winter (late October/early November to February/early March in the midsection of the US). The objective is to cut living trees at a time when the sap is either translocating down from the leaves to the roots at the end of the growing season, or beginning to rise back up to the buds to nourish them just prior to budbreak. After a couple of decades of experience, experts now advise inoculating the logs as rapidly as possible after cutting. This ensures maximum moisture content in the logs, and minimum time for competing fungi or bacteria to invade the harvested logs.
Inoculated logs go through an incubation period which varies with the strain of spawn used, the species and sizes of logs, and the microclimates and macroclimate of their environment. Under normal circumstances, it takes from 6 to 12 months for the first flush of mushrooms to appear. Shiitake prefer a cool, moist environment, so forest landowners need to place the incubating logs in reliable shade (under conifers, for example), and near a water source if they are to be soaked.
Once it is possible to observe the whitish mycelia at the end of inoculated logs - but no earlier than 6 months and ideally after a year - shiitake can be forced to fruit by immersing them in water for 24 to 48 hours. "Shocking" the logs by thumping one end on the ground has also been known to initiate a fruiting flush. A more reliable production method than simply allowing the logs to produce at will, depending on local moisture and temperature conditions, is to soak the logs repeatedly to force fruiting. Once a log has completed a flush resulting from soaking, it must "rest" for about 10 weeks before it is rejuvenated enough to flush again. Shiitake survives by consuming the carbohydrates, cellulose and lignin in the logs. The total amount of "food" in the log is finite, so forcing the logs repeatedly tends to give them a shorter productive life in years, but probably the same number of pounds of mushrooms as if they had been allowed to fruit at will.
Shiitake's Medicinal Properties
The Japanese have been studying the medicinal properties of edible fungi, particularly shiitake for several decades. Some of these studies indicate that shiitake consumption reduces serum cholesterol levels (Harris, 1986). Other studies have isolated lentinan as an active ingredient of shiitake, now approved in Japan as an anti-cancer drug which seems to work by activating killer and helper "T" cells (Stamets, 1993). As a result of its known antiviral properties, scientists have been studying shiitake as possibly being effective against the HIV virus. Some Japanese studies indicate that it is effective, others that it is not, and American studies have not yet indicated what level of effectiveness lentinan or other active ingredients have against this particular virus. Major reviews of the nearly one hundred scientific papers on the medicinal effects of various edible mushrooms can be found in Fujii et al. (1978), Jong et al. (1991) and Mori et al. (1987). The antitumor, antiviral, and antithrombic activities of shiitake determined by scientific studies do indicate that it is a powerful stimulant of the immune system and therefore a valuable addition to one’s diet.
Given the level of forest resources available for the production of shiitake and other exotic gourmet mushrooms, there is considerable opportunity for growth in this cottage industry. Shiitake require little ground space per log. Over their productive lifetime (2 to 5 years if left alone, less if forced) each log may produce up to 300 g kg-1 of its initial dry weight in mushrooms (Przybylowicz & Donoghue, 1988). Many people may be interested in growing mushrooms on only a few logs (less than or equal to 10) in their back yards largely for personal consumption. Others may want to invest in a small commercial operation (100-500 logs). Still others may want to develop a business growing shiitake on logs (1000s of logs).
Economics of Shiitake Production
The important factors in growing shiitake at any level are availability and accessibility of markets for fresh and dried mushrooms, and availability and accessibility of raw materials, both logs and spawn. Logs are the critical factor and may be obtained from thinning operations or from accessing tops and other noncommercial parts of trees from a current logging operation. Spawn and other useful materials for a shiitake production operation are available from several reputable organizations in the United States. Although it is biologically possible to reproduce shiitake from mushroom spores produced on logs from spawn, this is not recommended. The companies that sell spawn are producing spawn under carefully controlled conditions, among which are those which ensure strong, healthy and consistently reproducible strains of the mushrooms desired.
Equipment needs for a shiitake operation are simple and relatively inexpensive. The highest priced item is a high-speed drill for inoculating hardwood logs. A regular wood drill can be used for small numbers of logs (< 10), but is impractical for larger numbers. The appropriate type of drill costs approximately $250. Spawn units, usually capable of inoculating 10 logs each, cost $15-20. Other equipment includes spawn inoculation tools (for sawdust spawn) at $25, and a deep fryer or other self-contained heatable container for melting cheese wax for sealing the inoculation sites on each log. An accurate scale, preferably digital, is another useful piece of equipment; prices vary and second-hand equipment may be available (Baughman, 1989).
Rathke and Baughman (1993) did an exhaustive economic analysis of shiitake production, comparing the economics of a 4000 log/year operation growing the logs both indoors and outdoors over a 15-year period. They estimated that each log would ultimately produce at least 100 g kg-1 of its original weight over a 3 (indoor) to 5 (outdoor) year production cycle. Assuming that the growers have good information about what they are doing, and that there are no catastrophic losses (attrition and normal losses are factored in), the authors expect that a grower could reap at least a 6% return on investment after taxes on such an operation.
Over the past ten years as the market for shiitake has expanded, the prices for it have remained remarkably stable. Fresh mushrooms wholesale for $11-15/kg ($5-7 per pound) and retail for about twice that. Fresh mushrooms have a shelf life of two or three weeks under refrigeration. Dried mushrooms (at roughly a 7 to 1 ratio for fresh to dry) command $22-33/kg ($10-15 per pound) wholesale and closer to $77/kg ($35 per pound) retail. Drying shiitake can be done as any other fruit or vegetable is dried - either with warm forced air or in the open sunlight. Another option, though much more expensive, is freeze-drying (usually in a sliced form). This latter option yields a product that is almost as good as fresh, as the mushrooms reconstitute fully in water when ready to use. Any dried form of the mushrooms is much more stable than fresh mushrooms and has a reasonable quality shelf life of about six months. Success in the market for dried mushrooms is a more difficult one, however, because of competition from Chinese and Japanese producers, who market dried shiitake in the United States at very low prices. Marketing quality fresh mushrooms, then, is the most reliable and economically desirable option in North America. Poorer quality mushrooms can be dried and chopped for dry soup or dip mixes to make a value-added product.
Shiitake production is a good forest farming option for rural areas. If several people in a community wanted to grow mushrooms on a small scale (< 500 logs each), they could pool their marketing capability, and either take turns taking the mushrooms to market, or designate one person for this task. In this situation, some growers could force their logs and others not, so that the supply to buyers would remain more constant. Typical markets for these mushrooms include natural or health food stores, some supermarkets, restaurants, and farmers' markets or roadside stands. A good marketing device is to include recipes and/or make up a simple one for people to try (in a supermarket, for example). The flavor of shiitake is good enough that the mushrooms easily sell themselves.
Given the fact that more than 90 percent of our privately-owned forested lands have no professional management plan, there are millions of hectares on which gourmet mushrooms could be produced. The relatively high economic value of shiitake mushrooms in relation to other food commodities is reflective of supply and demand market factors. Mushroom production, like the other forest farmed products discussed here, probably will be most successful - economically and ecologically - when operated on a small, family-business sized scale.
Clearing small patches on the forest floor for morel or stropharia production, or using the products of a forest management operation for producing shiitake or one of the other log-grown gourmet mushrooms, are both options for increasing both the health and economic welfare of farmers and landholders of small woodlands through forest farming. These are not appropriate options for agribusiness, since mass production defeats the dual purpose of more sustainable forest management and the supplemental income realized from non-timber forest products for family farms and small woodlots.
The agroforestry definition emphasizes as the intentional mixture of tree crops with agronomic crops and/or animals. Typically the "animal" component of this definition is expected to refer to livestock, but in the case of apiculture in forest farming, the honeybee is the animal involved. Apiculture is the care and management of honeybees for various products, and/or for pollinating flowering agronomic or tree crops.
The common honeybee (Apis mellifera L.) (Fig. 8-6) is not native to North America, but rather was imported by Europeans when they first came to the western hemisphere. There are other, native, bee species and other flying insects, such as certain species of flies and moths, which also pollinate native flowering plants including tree species. None of these other insect species, however, is as efficient or effective as the European honeybee for pollination or honey production. Worker bees forage on one plant species at a time. This characteristic not only maximizes pollination efficiency, since worker bees go to multiple flowers of the same plant in one nectar collection foray, but also makes the flavor of honey from each flowering species unique.
Once the European honeybee became naturalized in North America, some escaped from managed hives each year, resulting in the development of feral populations, often in woodlands neighboring the farmland where bees were being raised. This worked in both directions, as beekeepers often brought "wild" swarms into their hives to crossbreed with their bees, thereby keeping the genetic pool diverse. Much of the pollination of forest flowering plants has been accomplished by these feral honeybee populations. Feral populations usually lived in cavities of deciduous trees, pollinating and producing honey just as efficiently as managed bees.
Bees and Trees
Honeybees are found associated with forests globally. Many commercially valuable forest tree species' flowers provide ample nectar and pollen for bee forage, some at times when other foraging options are limited. Combining apiculture and forest management provides forage as well as wind and sun protection for honeybees and their hives, while ensuring thorough pollination of the tree flowers, thus assuring a heathy seed crop for future regeneration of the forest. Forest management and beekeeping have each had a long history but have seldom been integrated or studied in a systematic fashion. Hives can be introduced into existing forest systems, or new tree plantings (orchard, Christmas tree, or otherwise) could be designed to favor bee forage and/or for hive protection.
Forest trees represent one of many varieties of flowering plants. Bee foraging is an important part of the biology of both young and established forests. Commercially valuable trees found in central North America which have flowers that produce nectar and pollen attractive to bees include paulownia (Paulownia tomentosa (Thumb.) Steud.), tulip-poplar (Liriodendron tulipifera L.), basswood (Tilia americana L.), persimmon (Diospyros virginiana L.), black locust (Robinia pseudoacacia L.), blackgum and tupelo gum (Nyssa sylvatica Marsh.) (Fig. 8-7). Early spring forage for bees is critical because the colony requires the nutrient income at this time for population growth and hive viability. The role of bees in pollinating forest trees has not been widely studied, but the loss of feral honeybee populations is likely having a negative impact on forest tree seed production.
If managing a forested area in part for bee forage is desirable, it may be important to thin the existing trees enough to expose more of the trees' crowns to sunlight. If bees are to be part of a plantation, it is easier to space the trees appropriately initially. A sugarbush, for example, is managed to give the sugar maple trees maximum space for their crowns, where their leaves can make more photosynthate to produce greater volumes of sap for syrup. In a similar manner, exposed tree crowns provide a greater surface area in relation to the volume of the crown to produce flowering bee forage (Ayers, 1993).
Perhaps the greatest economic benefit of raising bees is their service in pollinating agricultural crops, though it is difficult to estimate accurately the value of this service. In 1973, the USDA estimated that 1.4 million hectares (3.5 million acres) of fruits, vegetables, oilseeds and legume seed crops depended on bee pollination and another 25.5 million hectares (63 million acres) received some benefit from insect pollination activities. More recently, the USDA has estimated that at least 150 g kg-1 of the plant-derived part of the human diet comes from plants dependent on insect pollination (Jones, 1985).
Like nectar, pollen is often a floral reward for pollinators, especially bees which depend almost entirely on it as a protein and vitamin source. Pollen consumption by bees leads to colony growth, which is essential to honey production later in the season. Thus, pollen abundance and nutritional quality are variables important to bees and beekeeping. The honeybee is considered the best insect pollinator because:
1. individual worker bees show species fidelity to single species of flowering plants;
2. each bee will make multiple trips daily to the same species of flower in order to meet the need of feeding 50,000 to 80,000 bees per hive;
3. honeybees overwinter in colonies, so they start in the springtime with a large resident population of foraging bees (Hill & Webster, 1995).
A better understanding of tree pollen production would contribute valuable information about bee-tree dynamics and forest farming options in apiculture.
Today pollinator populations are threatened by a variety of problems: forest fragmentation, land use conversion from forest or farmland to highways and/or urban or suburban development, industrial pollution and overzealous pesticide use (Rompf, 1991; Time, 1996). Gary Paul Nabhan and Stephen Buchmann lead the Forgotten Pollinator Project at the Arizona-Sonoran Desert Museum, and are conducting studies on Africanized honeybees, among others. They estimate that one out of every six invertebrate pollinators is currently threatened with extinction. They further express fear that the loss of native pollinators will cause greater than five billion dollars in losses to fruit and vegetable crops (Buchmann & Nabhan, 1996).
In the past several years, parasite and disease problems, such as infestations of mites (Acarapis woodi (Rennie) and Varroa jacobsoni Oudemans) have hit both managed and feral populations (Webster, 1995a, 1995b). It is estimated that, by the middle of 1996, 90% of the feral bee population had disappeared, and, even with medication, up to 50% of managed hives did not survive the winter of 1995 (Buchmann & Nabhan, 1996). As a result, the future status of European honeybees in North America is unclear.
It may be important to reintroduce bee populations into our woodlands to fulfill the need for tree flower pollination and to attempt to reestablish feral honeybee populations. A potential solution for the mite problem is crossbreeding Oriental species with the European species. Varroa mites occur in the Chinese bees also, but they have adapted to the presence of the mites by developing a grooming behavior which removes the mites before they can harm the bees. If a bee cannot reach an invading mite on its own body, it will "dance" for grooming assistance from other bees (Buchmann & Nabhan, 1996). Apistan is the chemical that is used to control mites in beehives, but like many human medications (such as antibiotics) this chemical is beginning to lose its effectiveness (Libby Fox, 1997, personal communication). Some beekeepers have had some success in combating tracheal mites with herbal repellents, such as bee balm (Monarda didyma L.), fennel (Foeniculum vulgare L.), peppermint (Mentha piperita L.) and other members of the mint family, planted around the bases of the hives to keep the mites away. At least one beekeeper has found that mixing oil from fennel plants into the Crisco and granulated sugar patties placed in the hives for bee food has been successful in controlling mite problems (Fox, 1997). Tracheal mites appear to be sensitive to camphor and menthol (Webster, 1995a). Forest ecosystem management and apiculture in forested or agroforested areas must include an understanding of both managed and feral populations of honeybees.
Products From the Hive
Honey has been a source of sweetness in the diets of humans and other animals since the beginning of recorded time. Honey is the product of worker bees' digestion of the nectar of flowers and its subsequent concentration in the cells of the hive. Because its sugars are digested in the process of honey-making, it is a food which is easy for other animals to absorb and assimilate, and can restore oxygen to the human body rapidly, especially when the muscles are fatigued. Honey also has natural antiseptic, antibiotic and antimycotic characteristics (Lee & Lee, 1995).
Beeswax is probably the second most widely known of beehive products. It is the waxy coating that bees use to seal off the honey-containing cells as well as the brood cells for new queens and new worker bees. Beeswax has been used for candle-making and in a wide variety of domestic and industrial applications.
Honey and beeswax are produced in all 50 states, but the amounts vary both regionally and from state to state. Honey production depends on climatic factors that regulate flowering such as temperatures and rainfall, and on human-caused factors such as cropping patterns, soil conditions and farm or forest management techniques. In the United States, honey production peaked in 1951 at 113 million kg (250 million pounds) and has dropped since the 1970s to a fairly consistent 91 million kg (200 million pounds) per year. Most honey is produced by many thousands of what are termed "hobby" beekeepers - those managing 25 or fewer hives. Much of that honey is not sold commercially, but rather is used for personal consumption or distributed locally to neighbors, family and friends. Consumption of honey has remained relatively stable, but has declined from a level of about 0.7 kg (1.5 pounds) per capita per year in the 1960s to a current level of about 0.4 kg (1 pound) per capita (Jones, 1985).
Propolis, a less commonly known product of the hive, is the sticky resin which oozes from the bark of several tree species, notably poplars (Populus spp.) and conifer species. Foraging bees collect it in the pollen baskets on their legs and bring it into the hive for various protective purposes. Worker bees mix the resin with saliva and wax and use the resulting material to seal and reinforce passageways, brood chambers, and the inside walls of the hive. It also protects the bees from bacterial and viral infections. For human consumption, this material also has antibacterial, antibiotic antifungal, antiviral, and antiseptic properties. In addition, it has been noted by Dr. John Diamond of the International Academy of Preventive Medicine that propolis activates the thymus gland and thus boosts the human immune system (Lee & Lee, 1995).
Royal jelly is a glandular secretion produced by young female bees which, with one exception, is exclusively for the queen bee’s use. The exception is a three-day supply of this extraordinary material in the brood cell of each larva at the beginning of its development. Royal jelly is what makes a queen bee a queen bee. Without a solid diet of this material, the larva which becomes a queen would have developed into an ordinary worker bee. An exclusive diet of royal jelly allows a queen to live up to 5 years, in contrast to the average bee lifetime of three months or less. The queen is also 40 percent larger and 60 percent heavier than the other bees and can lay up to 2000 eggs per day. Royal jelly has strong antimicrobial and anti-inflammatory properties, aids skin regeneration and increases resistance to disease (Lee & Lee, 1995). It is widely available in natural and health food stores for human use (Fig. 8-8).