by Greg Marley
• The acceleration of the process of wood decay and the associated nutrient recycling through:
• Opening up the bark, sapwood, and even the heartwood in living trees through the activities of feeding and cavity construction, resulting in the wood’s infection by decay fungi and insects
• Transfer of wood decay spores and mycelium from tree to tree in its beak and mouth
• Opening up bark and wood surfaces for the exploration and feeding of other species of woodpeckers, birds, and insects
• Creating resting, roosting, and nesting dens for other birds and animals
• Helping to mediate insect outbreaks through feeding on larvae and adults3
In some forests, deciduous trees are the preferred choice for feeding and nesting of keystone woodpeckers. Studies of aspen, Populus tremuloides, in the western United States have shown that a number of bird species rely on the tree for roosting and nesting sites and at least one, the red-naped sapsucker, is a primary or obligate aspen nester. Across the range of aspen, the aspen heart-rot fungus, Phellinus tremulae, infects the heartwood of mature aspen producing distinctive fruiting conks at the site of old branch stumps, and studies have shown that several species of sapsuckers prefer aspens as nest sites and appear to seek out trees where P. tremulae is fruiting. The fungus typically attacks older living aspen and rots the heartwood while the sapwood remains alive and intact. In one study plot in Wyoming, the average age of aspen with woodpecker cavities was 115 years. Researchers have hypothesized that the birds locate trees with heart rot either by noting the presence of fruiting bodies or by noting the difference in resonance of hollow versus solid trunks when pecked.4
Though the cavities in aspen are made by various species of woodpeckers, sapsuckers, and flickers, they then are used by a number of secondary cavity nesters, including chickadees, bluebirds, and smaller woodpeckers as well as birds that require trees of a larger diameter including barn, barred, and screech owls, and even wood ducks and buffleheads. The mammals that use large cavities include squirrels, opossums, raccoons, martens, and fishers.5
Big brown bats and silver-eared bats appear to prefer cavities in aspen to several other available tree species as a choice daytime roost.6, 7 The living trees offer firm sapwood for roosting and are five degrees cooler than conifers in the heat of summer. Other species of bats have been long associated with tree cavity roosts, as well. All forest-roosting bats are affected by the loss of large-diameter snags and old-growth stands. Some researchers recommend the preservation and restoration of cavity-promoting habitats as a management strategy for ensuring adequate populations of insectivorous bats in forest habitats.8
Managing Forests for Cavity Nesters
Decades of forest management practices that recommended the removal of older snags and harvest of wind-downed timber sites, along with other human interventions that remove large, old trees, have severely reduced the optimum habitat for cavity-nesting birds. This habitat loss has reduced populations of primary and secondary cavity nesters and it is thought that these management practices are responsible for dangerously reducing populations of species such as the endangered red-cockaded woodpecker in Texas, the once-assumed extinct ivory-billed woodpecker, and several primary and secondary cavity nesters known from old-growth forests in the Northwest, chief among them the spotted owl. With the disappearance of large-diameter snags and living trees, serious efforts are being made to determine strategies to increase the suitable habitat for cavity nesters.
A number of strategies have been suggested, attempted, and practiced. One challenge, however, is that there is an immediate short-term need for developed snags in many areas where a severe reduction in snags has resulted from decades of past management practices. In the absence of direct manipulation, it will be decades before the maturing forest naturally creates the needed snags sufficient to support optimal cavity users. Suggested short-term strategies include topping live mature trees just below the first main branches using saws or explosives, which is expensive in time, resources, and money; limbing or otherwise wounding trees to create openings for heart-rot fungal invasion (but that’s chancy and requires significant time to produce results); girdling mature trees with either chain saws or fire to kill the tree; and artificial inoculation of live or killed trees with selected hear-rot fungi. This last method is the strategy described in the fictional account of my grandfather, the duck hunter, that opened this story.
In a 2004 paper in the Western Journal of Applied Forestry, researchers reported on the results of artificial inoculation of conifers with two heart-rot fungi in forests located in the Coast Range of Oregon. They employed a hitherto untried delivery mechanism that was controversial and very cost effective. The vegetative mycelium of pine conk (Phellinus pini) and the rose conk (Fomitopsis cajanderi) were grown out onto small wood dowels or sawdust. This “spawn” was then delivered into the trunk of the tree using firearms. The dowels were fitted into specially made hollow slugs for a 0.45-70 rifle, and the sawdust spawn was packed behind 12-gauge shotgun slugs. The spawn was fired into carefully selected sites on live trees or recently artificially topped trees. In a five-year follow-up, all of the topped trees were dead and almost all of the trees showed the presence of decay and fruiting bodies of the target fungi and other species. Almost half of the trees showed evidence of use by primary cavity-nesting species of birds and other wildlife. The live inoculated trees showed little evidence of fungal growth and no sign of wildlife use, but samples of wood collected around the injury site showed that in most cases, fungal invasion was under way. The researchers concluded that topping (killing) a tree was a more rapid method for creating a cavity nester habitat, but use of living trees would likely be effective over a longer period of time.9 One difference in use of living versus topped trees is the cost. Topping involves either the risky use of chain saws high above the forest floor or, in some cases, the use of explosives to sever the tree high above the ground. Either method costs hundreds of dollars per tree versus the much cheaper and easily delivered firearm inoculation. A very realistic and more commonly used alternative to blasting a tree with a large-caliber slug involves the use of larger dowels colonized with a target fungus and tapped into predrilled holes in the trunk of a living tree. This technique has been used to increase nesting sites for the endangered red-cockaded woodpecker in the southeastern United States10 and as a general habitat restoration technique using the red-belted polypore in the Pacific Northwest.11
Certainly the use of explosives to create snags may be needless overkill, but the idea of infecting a living tree with a fungus that will lead to its eventual weakening and death has not been met with open criticism. The intentional use of fungi to perform the role they are naturally suited for is an effective way to undo the damage of narrowly focused forest management practices. Though the opening vignette about my grandfather Henry is fictionalized, the activity described would be a farsighted and effective way for hunters to look out for the overall health of the forest and ensure the long term availability of good habitat for their favored prey.
Man’s past intervention and management of forest environments has resulted in marked reduction in the habitat and presence of cavity nesters, a group of species of vital necessity to a healthy forest. If we can integrate recent lessons about the desirability of cavity nesters and the role of mature snags and wood-rotting fungi into wise management strategies, our positive manipulation of the forest might significantly increase the population of cavity nesters in the decades to come.
PART VI
TOOLS FOR A NEW WORLD
19
GROWING MUSHROOMS IN THE GARDEN
A How-to Story
Fungino genere est; capite se totum tegit.
He is of the race of the mushroom;
he covers himself altogether with his head.
TITUS MACCIUS PLAUTUS (254 B.C.–184 B.C.)
T he first time I encouraged mushrooms to fruit in a garden, it was an accident. My
friend Mark DiGirolomo and I had a small hobbyish business cultivating “exotic” mushrooms in the 1980s. We were part of an early wave of people cultivating wood-decay mushrooms on hardwood sawdust. The technology was coming out of Japan and China and being studied heavily at the University of Pennsylvania for use in the American mushroom industry. We started our business on a frayed shoestring budget by borrowing unused space beneath benches in a commercial greenhouse and using a decrepit 1940s concrete root cellar, located on a friend’s property, as a fruiting room. Our inability to finely control the environmental conditions needed to optimize fruiting in the Maine winters resulted in many “mistakes” and lots of painfully learned experience as we moved from the relatively easily cultivated oyster mushrooms to the more exacting shiitake and sulfur shelf varieties. At one juncture, we found ourselves in possession of a number of blocks of oak sawdust colonized with shiitake spawn but stubbornly refusing to fruit. Unfortunately, we needed to remove them from our root cellar to make room for a more promising crop. At the time, I was a caretaker on the property where the root cellar was located, property that also contained a bed of raspberries in need of mulching. We transferred several cartloads of the shiitake blocks onto the raspberries and called it good. Several months later, as spring turned to summer, I was quite startled to find a crop of shiitake mushrooms fruiting out of the thick sawdust layer on the raspberry patch following an extended period of wet weather. The sawdust mulch, acting as both a protective layer and soil amendment for the berry patch, was also playing the role of garden fungus patch as the mushroom mycelium broke down the wood waste, turning it into soil. There we were, in 1984, practicing permaculture gardening before the popular use of the term hit the media. We also enjoyed the collection and consumption of the shiitake from the garden. I have no doubt that their flavor was superior due to the serendipitous nature of their appearance.
In the years following the raspberry shiitake patch, I left the mushroom cultivation field and turned to other, more lucrative pursuits in my quest to cobble together a living wage in rural New England. I never left behind my interest in mushroom cultivation, however, and over the ensuing years, continued to read the scientific literature and popular press about trends in mushroom growing. Occasionally I delved into cultivating mushroom varieties on my in-town property. Early in my research into growing mushrooms, I came across a reference to Hungarians growing oyster mushrooms in their home gardens using logs infected with the fungus. The image I conjured was of a utopian setting with a 2-foot-diameter log of maple tucked into a shady corner of the rustic garden and covered with succulent clusters of fruiting oyster mushrooms. I now find there are many enthusiasts seeking to create their own slice of mushroom utopia by growing mushrooms in their gardens. Unlike the 1980s, today there is an industry in place to aid the home cultivator in the pursuit of knowledge, equipment, and mushroom spawn for planting in the appropriate substrate. Mushrooming in the garden is coming of age in the United States as it has in parts of Europe and Asia. Growing exotic varieties in the backyard represents an opportunity for the person too anxious to collect their own “wild” mushrooms in the forest. He or she still can enjoy interesting varieties of fungi picked fresh and cooked up on the day of collection.
Today’s home mushroom cultivation in the United States has its roots in the efforts of our grandfathers to grow a crop of button mushrooms (Agaricus bisporus) in beds of composted horse manure in the basement. Starting in the 1920s and continuing through the Depression days of the 1930s, mushroom cultivation on trays of composted manure in farmhouse basements became a relatively common rural pastime. Fueled by the growing taste for mushrooms brought to the United States by soldiers returning from the World War I, mushroom cultivation took hold in America. However, the current movement also owes a great deal of credit to those growers with the primary motivation of securing a predictable and trustworthy source of hallucinogenic mushrooms. Several of the most significant innovators in the field of exotic mushroom cultivation and the sale of cultivation equipment and products began their careers in the 1970s by learning to grow Psilocybe cubensis and other magic mushrooms. The subsequent transfer of these skills to edible mushrooms was a natural response to their own growing interest and the questions and needs of their fellow enthusiasts. The same basic techniques and skills are needed for growing edible, medicinal, or hallucinogenic mushrooms; the fungi have no interest in how we plan to use their fruit after we coax them into growth. So don’t be surprised when you come across lots of references and information on hallucinogens as you do your homework on edible mushroom cultivation. We stand on the shoulders of these pioneers and are grateful for the paths they have laid for us to follow.
Basic Cultivation Tips
Today many call the integration of mushrooms into the home and garden landscape permaculture gardening and recognize it as one vital component of creating an intentional sustainable ecosystem in a home or commercial setting. The thoughtful use of saprobic fungi assists in the breakdown and recycling of plant mulches to release nutrients for the growing crops. The fruiting mushrooms are another crop to be used as food. There is an increasing interest in growing our own food, and mushrooms are a logical addition to tomatoes, squash, and beans. Some kinds of mushrooms are easily grown on the average suburban house lot. Just as the vegetable gardener helps to ensure success by learning the techniques for how plants grow best, the mushroom gardener is in need of basic knowledge about the life cycle and growing needs of his or her fungal target species before setting forth outdoors. So, before you run out to buy a new sauté pan for cooking your homegrown mushrooms, there are a few basic cultivation tips to consider. These include:
1. Develop a working understanding of the life cycle and growing needs of mushrooms in general and the specific needs of the mushroom you want to grow; this is vital to the success of the enterprise.
2. Explore your property with an eye to evaluating the overall environment where you live and the microclimates created by tree cover, slopes, and the shading of buildings. Learn what you can modify easily (and cheaply) to make the site more mushroom friendly.
3. Investigate potential organic food sources for your hungry fungi; what is easily available, inexpensive, and in need of being recycled?
4. Ensure access to water.
5. Cultivate a patient attitude and be comfortable with failure in the pursuit of knowledge.
1. Understand the saprobic mushroom life cycle.
A mushroom is the fruiting body of a fungus, one large enough to be seen easily with the naked eye. Mushrooms take on many forms; the round-domed cap, complete with an intricate radiating set of gills attached to a central stalk-growing on the ground is what most people hold as the classic form. The mushroom is analogous to an apple or tomato or any other fruit from a plant. The reason for its existence is to make, display, and distribute the spores of the next generation. And, just like an apple hanging from its tree in the orchard, a mushroom is a very small portion of the whole fungal body. Where the entire apple vegetative body (tree) is composed of the roots, branches, twigs, fruit, and leaves, the fungus also has a vegetative body, the mycelium. It generally is not visible, so it would be easy to believe that the visible mushroom is the entire organism. This is not the case. For this discussion, I am focusing specifically on the saprobic fungi that live by decomposition of organic matter rather than the mycorrhizal species discussed in the previous chapter. Let’s look at the oyster mushroom as an example.
The classic oyster mushroom presentation of multiple fleshy caps fruiting in a cluster on that old sugar maple in late October is the end result of a great deal of life work by Pleurotus ostreatus, the formal species name. The current generation of mushrooms began when a spore, the microscopic “seed” of P. ostreatus, was released from the parent mushroom and landed in a wound on the maple tree trunk, found the proper amount of moisture and warmth, and germinated. The germinating spore developed into a microscopic thread of hyphae that grew and branched
to form the vegetative body of the fungus. Most people know hyphae as the cotton-like fuzz they find on bread wrapped in plastic left too long in their breadboxes. These one-cell-wide hyphal threads grow through the substrate, colonizing the heartwood of the sugar maple, and, as they elongate, they produce enzymes that break down the wood of the tree. These very powerful enzymes flow out of the cell and into the surrounding environment where they do the work of breaking down the complex carbohydrates, such as cellulose and lignin, into simple sugars. These carbohydrates are then brought back into the hyphae as food. The fungus can be said to literally eat its way through its host with the heartwood being the main course.
As the hyphae grow through the maple heartwood (in the case of the oyster mushroom), they are colonizing it. The network of hyphae formed in this process is known as mycelium. The mycelium functions to support the growing fungus through storage of nutrients and water, transport of nutrients and, as the conditions are right, to carry out the formation of the mushroom fruiting body. Before this can happen, fungal sex must occur. This fleeting moment happens when the haploid hyphae originating from one spore meets and combines with the hyphae of another compatible strain of the same species. This doubles the genetic material in the cell and, afterward, the fungus is capable of forming a sexual fruiting body, the mushroom. The combined (diploid) mycelium continues to grow as it colonizes its food source and when the fungus has gained enough food energy (biomass) and the environmental conditions of temperature, moisture, and light (yes, some fungi require specific levels of light to fruit) are conducive, the mycelia will begin to form thick hyphal knots, the precursors to the actual mushroom.
The oyster mushroom does require low levels of light to set fruit, as my mushroom farming partner and I found out. When our bags of sawdust and straw were left too long in near darkness while the fungus colonized the substrate, they started to set fruit. In the absence of adequate light, the mushrooms produced were spindly, almost all stalk and very tiny caps. Consider the adaptive reason for this. If the mycelium that colonized the maple heartwood produced a mushroom deep in an enclosed cavity in the log, one that had no access to the outside air, the resulting spores would never be launched into the wind for dispersal to another possible site to grow. Therefore, low levels of light signal the mycelium that it is near the open air, but not in direct sunlight. The expanding mushroom will be out in the open, but not in the direct drying sun.
