Timber identification and selection tips
Species that have been evaluated for shiitake production in the PNW:
Red alder (Alnus rubra)
Suitability for shiitake: FAVORABLE
It has proven to be a very suitable PNW-native wood for producing shiitake on. As long as log moisture is well-maintained, red alder can promote a fast spawn run due to the wood having a high initial moisture content, ample sapwood, and moderately low density. It’s smooth bark has a favorable sheathing quality for protecting the wood and resisting sloughing, although it is relatively soft, making it vulnerable to damage from rough handling and becomes increasingly brittle with age. Conversely, the softness of the bark allows shiitake mushrooms to break through the bark relatively easily.
Accessibility: ABUNDANT
Red alder is the most abundant broadleaf tree species in the PNW. It often grows in thick stands as a pioneer species following clearcut logging, fires, and abandoned fields, or other similar clearing disturbances. Alder can also be a very efficient tree to cut for bolts, because there are often many trees of a desirable size within close proximity to each other, and because of it’s tendency to grow very tall and straight in thick stands that may commonly yield up to 10 bolts per tree.
Identification in winter:
Alder can generally look very different depending on the habitat it's growing in, but generally does not have many overt look-alike species that co-occur within it’s common habitats in the PNW. In dense stands it often grows tall and straight, whereas in more open areas, it can grow more stoutly with many branches of the main trunk. Branching of the main trunk is not common. Its branches are often long, thin, and often bear small seed cones and catkins that look like miniature pine cones during the winter. Alder very commonly does have a suite of moss and lichens growing on the bark, although less than other broadleaf trees found in the PNW. Usually the bark is a lighter gray with mottling, and furrows only develop on older trees, but are still rather sparse.
Winter look-alikes:
Pacific Dogwood (Cornus nuttallii); this species is most likely to be mistaken for Alder due to it’s smooth gray bark that is sometimes similarly mottled, but Pacific dogwood is rarely abundant in any mixed stand. Alder does not develop prominent suckers from the base of the tree, but Pacific dogwood will; this may help distinguish the two species in winter. Dogwood will also lack catkins and/or the “cones” that are found on the tips of alder branches in winter.
Buckthorn/cascara (Rhamnus purshiana); the bark is relatively smooth but less so than alder, and may develop short, small, shallow furrows. Buckthorn/cascara also often does not grow as straight, or as tall as red alder.
Birch species (Betula) Alder’s smooth, light-colored bark may resemble birch from a distance, although closer up, the differences are more distinct.
White alder (Alnus rhombifolia); these two species would be nearly indistinguishable in winter, although co-occurrence in the same habitat is not common.
Red alder bark is characteristically smooth with few furrows, and gray-colored with light gray/whitish mottling. Suites of moss and lichens are common on the bark but less so than other PNW broadleaf species with furrowed bark.
Red alder silhouettes illustrating it's typical tall, thin, straight trunks, thin branches and catkins hanging from the ends of branches.
Second-growth PNW forest showing a common scenario of thick stands of red alder as the dominant pioneer tree species.
Once cut, the exposed area of the wood and bark of red alder will soon thereafter develop a characteristic reddish/orange hue.
Garry oak (Quercus garryana)
Suitability for shiitake: FAVORABLE
In Japan and northeastern North America, oaks are considered to be a “gold-standard” species for shiitake production. In Japan, shiitake is near exclusively grown on two species of oak. In PNW trials, garry oak (aka Oregon white oak) has likewise proven to be a highly suitable PNW-native wood for producing shiitake on. One downside to oak is that spawn run is relatively slow due to the high density of the wood, but the high wood density also means that there is ample carbon for the shiitake fungus to consume. Some oaks may have limited sapwood though. Garry oak’s bark thickness helps protect the wood from damage during handling, and the furrowed quality of the bark allows shiitake mushrooms to grow through, but it does not inhibit oak logs from splitting as much other log species with a sheathing bark. It is harder to find straight, tall garry oak trees, but they are more likely to occur in crowded stands. Garry oak growth tends to be rather squat, and trees of the right diameter at the base of the tree (no greater than 6.5”) will yield no more than five bolts per tree.
Accessibility: MODERATE
The abundance of garry oak varies depending on where you are in the PNW. It is most abundant in low to mid-elevation areas with a dry season, predominantly throughout the Willamette Valley, and the region surrounding where the Columbia Gorge cuts through the Cascades. It can also be found throughout the Puget Sound and Chehalis basins, and down through southwestern Oregon into northwestern California east of the Coast range. In Washington, garry oak is classified as a priority conservation habitat, so garry oak timber harvest is discouraged unless it is enhancing the health of garry oak habitat through selective thinning. As awareness of native garry oak habitat has increased in the PNW in general though, garry oak land stewards are increasingly looking to restore habitat, which often includes selective thinning because oaks do not tolerate shading well, and thrive when the conditions mimic the “thinning” that fire would otherwise do to the forest understory.
Identification in winter:
Garry oak growth has a distinctive wavy growth pattern that can occur in both the trunk and the branches. This pattern can help distinguish it from other look-alike species in the PNW, because otherwise garry oak’s gray furrowed bark adorned with losses and lichens is not overtly distinctive from look-alikes. One aspect about garry oak’s bark though is that it is likely to be furrowed from a young age. It is often found growing in well-drained valley soils, but may also occur on well-drained low elevation hills (approximately < 1000’ elevation). It can withstand a degree of poor drainage, but oregon ash (Fraxinus latifolia) is more likely to be found in areas that commonly have standing water during the rainy season. Garry oak is also unlikely to be found in mixed species stands, because it is slow growing and does not tolerate shade well, and the understory is often relatively open.
Winter look-alikes:
Oregon ash (Fraxinus latifolia); most likely to be mistaken for garry oak as their habitats intermingle. This species has gray, furrowed bark but does not have a wavy growth pattern to the trunk and branches, and is more likely to be found in seasonally marshy areas. Young ash is more distinctive with a more greenish-colored, smooth bark.
Bigleaf maple (Acer macrophyllum); this species can have some habitat overlap with oak, but bigleaf will commonly be found in mixed species stands, being more tolerant of shade, even from conifers. Bigleaf maple will also be found at higher elevations than oak. Bigleaf maple also has gray, furrowed bark, but is more smooth and greenish when young, and will begin to get more brownish with age and will be much more heavily adorned with mosses than oak. Bigleaf maple growth is also much arching than wavy, with multiple arching trunks growing in a vase-like pattern or large arching branches off of the main trunk.
The bark of garry oak is light gray, with furrows that develop even from a young age. The bark is often laden with suites of moss and lichens.
A large garry oak in its more native open habitat illustrating the wavy growth pattern and large branching typical of this species. The openness of native PNW garry oak habitat was enhanced by periodic burning of understory vegetation.
Garry oaks growing in crowded stands such as this will grow straighter, which is favorable for shiitake bolts. Dense stands like this benefit from thinning, and can be a win-win for mushrooms growers needing straight oak bolts and land stewards doing oak habitat restoration.
Garry oak bolts showing the dense wood and thick, furrowed bark typical of this species.
Bigleaf maple (Acer Macrophyllum)
Suitability for shiitake: MODERATELY UNFAVORABLE
In northeastern North America, hard maples (ex: sugar maple, Acer saccharinum) are considered to be favorable for shiitake production and soft maples (ex: red maple, Acer rubrum) much less so. Bigleaf maple is more akin to soft maples, and has similarly been an underperformer for producing shiitake. Bigleaf maple *can* produce shiitake, but production may be either non-existent or low and variable until 2-3 years after inoculation. This is most likely due to bigleaf wood being not very dense, and the bark integrity being poor which leads to excessive moisture loss from bigleaf bolts. This can be exacerbated by the poor bark integrity allowing the log ends to split as they dry. Red alder also loses moisture easily as well, but bigleaf maple’s initial moisture content is notably lower than alder. This sub-par moisture circumstance appears to compromise spawn run in bigleaf bolts.
Accessibility: ABUNDANT
Bigleaf Maple (Acer macrophyllum) is the second-most abundant broadleaf tree species in the PNW. it is found from the Pacific coast eastward to the western slopes of the cascades up to mid-elevations but more common in lower elevations and valleys. It is a mid-successional species that can be found in the understory, or as the dominant broadleaf species within mixed stands with conifers.
Identification:
Bigleaf maple has gray furrowed bark that looks similar to Oregon ash (Fraxinus latifolia) and garry oak (Quercus garryana) in the winter. Young bigleaf bark will begin smooth, with a light green-gray color and become more furrowed as it gets beyond ~4” in diameter, and then can become more brown-gray as it ages. Bigleaf is distinguished most readily by its tendency to grow in a vase-like pattern with long arching trunks and branches that are heavily laden with mosses and licorice ferns. The young shoots/branches are also notably long/lanky compared to oak and ash.
Winter look-alikes:
Garry oak (Quercus garryana) both species have gray furrowed bark and habitats that intermingle in lowlands and low-elevation hills where open areas meet second-growth forests and riparian areas. Bigleaf will be more common than oak in higher elevations with more precipitation, and in any mixed stand with conifers or other fast-growing tree species that would otherwise shade out oak. Bigleaf maple will also not tolerate as dry habitats as oak will. Young oak will have furrowed bark on trees under 4”, but this is more unlikely for bigleaf maple.
Oregon ash (Fraxinus latifolia); both species have smooth greenish-hued bark at a young age, that becomes gray and furrowed as it grows larger. Bigleaf maple may develop brownish hues to the bark later in life compared to Oregon ash. Bigleaf will tolerate some poorly drained lowland soils but ash is far more likely to be found in areas with seasonal standing water than bigleaf maple.
Buckthorn/cascara (Rhamnus purshiana); both species may be found tolerating shade in mixed stands with conifers. The growth patterns of younger bigleaf maple and buckthorn/cascara is not overtly distinct, but bigleaf will get much taller and larger. The bark texture and color is similar to middle-aged bigleaf maple but buckthorn/cascara lacks deep furrows.
Younger bigleaf maple bark showing greenish hues, before developing furrows.
Bigleaf maple bark is most commonly gray with furrows, and is often laden with mosses. Bigleaf maple bark can develop brownish hues as it gets older.
Typical vase-like growth pattern of bigleaf maple, with large arching branches, and trunks which will grow in a coppice like this (multiple trunks) if the main trunk is cut or damaged. Bigleaf maple will readily tolerate shading in mixed stands with conifers.
Some of the prominent downsides of using bigleaf maple for shiitake bolts is illustrated here, with poor bark integrity allowing splitting on the log end as it dries, which hastens critical moisture loss from the bolt.
Sweet Cherry (Prunus avium)
Suitability for shiitake: MODERATELY FAVORABLE
In Japan, cherry bolts are more commonly used to produce nameko mushrooms. North America, woods from the Rosa family (apple, cherry, plum, etc.) generally aren’t considered to be favorable for shiitake production when other species like oak and hard maple are otherwise available. In the PNW, cherry has some notable qualities that enhance it’s relative suitability for shiitake production. Trunks tend to grow tall and straight, and there's no other common broadleaf species found in the PNW with bark integrity greater than sweet cherry. It’s bark has a non-furrowed, sheathing quality similar to paper birch, but thicker. The bark therefore is therefore very resistant to damage from handling, and also helps retain the internal moisture of the log along with the relatively high density of the wood (less than oak, but greater than other common PNW-sourced species). On the downside though, cherry’s relatively high wood density can lengthen the spawn run period, but less than oak. Cherry also has distinctly limited sapwood, the amount of which can vary from tree to tree; because shiitake growth largely occurs in sapwood, this can limit the total amount of substrate available to the fungus. Also the strength of the bark unfortunately makes it nearly impossible for shiitake to get through, so fruiting is almost entirely limited to where holes were drilled during inoculation. In practice, shiitake yields on sweet cherry in the PNW have been relatively low to moderate, but steady and often of good quality.
Accessibility: MODERATELY ABUNDANT
Sweet cherry is not a native PNW species, but it is commonly found growing in mixed forests in regions west of the Cascades that have a history of agriculture. Sweet cherry seeds are readily dispersed by birds and mammals who eat their fruit, and sweet cherry trees thrive in the climate west of the Cascades. This species generally can be found in habitats similar to those favored by bigleaf maple and red alder, and seems to tolerate shade similarly as well. It is not uncommon to find sweet cherry throughout mixed second-growth forests in amounts that exceed some native species like buckthorn/cascara, pacific dogwood, or even bigleaf maple. It can grow in small clusters where it may the dominant broadleaf species, but tends to not dominate or proliferate to the degree that red alder can.
Identification:
In winter, sweet cherry is one of the more readily identifiable PNW broadleaf tree species. The bark is often a graphite/charcoal-gray color, darker than most other PNW broadleaf species. Older cherry may develop some furrows near the base of the tree where the diameter is thickest. Branches are distinctly opposite and often long like alder, but sweet cherry branches often can become much larger than what is typical for alder. The bark is rougher to the touch than birch, even though the sheathing quality is similar.
Winter look-alikes:
Bitter cherry (Prunus emarginata); this PNW-native cherry is the most common look alike species to non-native sweet cherry. The bark of these two species is largely indistinguishable. Bitter cherry is a species that is frequently found in riparian areas, but in areas where sweet cherry is common, sweet cherry can far outnumber bitter cherry. Bitter Cherry is a much smaller tree, with a large shrub-like growth character, whereas sweet cherry will commonly be a standalone tree that get very large, with trunk diameters that can readily exceed 12”, and grow to a height of 50-90’.
Paper birch (Betula papyifera); although paper birch bark is associated with the color white, paper birch bark can vary considerably in color, with some bark having near black or reddish-purple tones on some parts of the tree. Darker colored paper birch can look very similar to sweet cherry bark especially because they are both a sheathing type of bark with horizontal lenticels, but paper birch bark tends to be smoother and shinier than cherry bark, and the entire tree is less likely to be completely dark-colored. Paper birch will also have much more noticeable natural peeling of the outermost bark layer.
Characteristic sweet cherry bark, darker charcoal/graphite gray, with horizontal lenticels and an absence of vertical furrows.
Typical sweet cherry growth pattern, with a straight main trunk, and prominent opposite branching.
Sweet cherry can grow in clusters within mixed stands, but tends to not dominate as much as alder. From a distance the growth resembles alder with straight trunks and long thin branches, but sweet cherry is more likely to develop larger diameter branches or forks in the main trunk.
Although sweet cherry has many positive attributes as a shiitake bolt, yields tend to not be much larger from any one shiitake harvest than what can be seen on the bolt in the center of the image. Often cherry will regularly produce well-sized, good quality mushrooms, but in lower numbers. This may be partly due to it being very difficult for shiitake mushrooms to break through cherry bark except for where the inoculation holes are drilled.
Birch species (Betula populifolia , papyifera)
Suitability for shiitake: MODERATELY FAVORABLE
Birches are not commonly used in other regions of the world that produce forest-cultivated shiitake, but trials in the PNW have illustrated that this genus is a favorable option for shiitake production if you are able to source it. Birches typically have an ample initial moisture content that is retained very well by the robust integrity of it’s sheathing bark. The wood is also moderately dense (greater than red alder, but less than garry oak), and often contains an ample proportion of sapwood for shiitake growth and consumption. These characteristics reliably lead to a fast, predictably strong spawn run in birch bolts. In PNW trials this fast spawn run has also translated to considerably more reliable fruiting within a year after inoculation compared to other species that are more vulnerable to critical moisture loss during summers with more pronounced drying weather. Birches also tend to grow tall and straight, making them efficient trees to commonly harvest 5-10 bolts from, and efficient to work with in a shiitake production system due to their straightness. On the downside, in PNW trials with gray birch, strong initial yields have been frequently followed declining, more variable yields in the beginning in the second to third year of production. The cause of this yield decline is unknown but may be 1) in part due to the bark inhibiting infux of water to initiate fruiting, or 2) the bark conversely holding an excessive amount of water in the log, and/or 3) shiitake not being able to reliably grow through the bark.
Accessibility: LIMITED/REGIONAL
Paper birch is the only birch that is native to the PNW, and it’s range is largely limited to north of the Skagit river west of Cascades, and to the northeastern inland PNW in Washington and Idaho panhandle. In other regions of the PNW, mostly non-native birches can sometimes be found as escaped ornamentals from urban/residential areas. Some birches like gray birch (native to northeastern North America) will thrive as a pioneer species in the PNW climate, forming dense clusters of birch-dominated stands if seed is distributed into an open area, but will otherwise be limited within a mixed stand.
Identification:
Close up, birches generally look visually distinct amongst other PNW broadleaf tree species that may be present in the same habitats, due to their whitish, smooth sheathing bark and characteristic peeling of the outermost layer(s) of the bark. Birch bark can also develop furrows in it though once it begins to exceed ~6” in diameter. Birch bark has horizontal lenticels and dark colored chevron-shaped “frowns” where branches or branch buds occur on the trunk. If birch is found in far northwestern Washington (Whatcom or Skagit Counties) or the northeastern PNW, it is most likely native paper birch unless it is found in an urban/residential area. In the latter case it could be gray birch or another eurasian-native birch species. The latter situation also applies if birch is found in other parts of the PNW where paper birch does not naturally occur.
Winter look-alikes:
Other birch species (Betula); many species of birch look very similar in winter. Gray birch typically has more limited peeling of the bark compared to paper birch, and will often be more reliably white in color. While this maybe a non-issue if birches all generally perform well for producing shiitake, not all birch species have been evaluated.
Quaking aspen (Populus tremuloides); this species most resembles birch of any other species due to the growth habit, smoothness and whitish color of the bark. Paper birch and aspen are the only species with any likelihood to co-occur in the PNW though. Both birches and aspen have dark colored “frowns” where branches or branch buds occur on the trunk, along with horizontal lenticels. Up close though, aspen bark will lack peeling, and is more likely to have a dull luster.
Black Cottonwood (Populus trichocarpa); this species shares some of the similar likenesses described above for quaking aspen, except the bark will tend to be darker, and more commonly furrowed. Black cottonwood will also get much larger than birches, and largely will not occur outside of riparian areas.
Cherry species (Prunus); both non-native sweet cherry and native bitter cherry have sheathing bark with horizontal lenticels, which can resemble darker variations of paper birch bark. Cherry bark will tend to have far less or absent peeling, and will generally not look as shiny as paper birch can be.
Red alder (Alnus rubra); these two genuses belong to the same family (Betulaceae) and have a similar growth habit and habitat. The light color of alder bark can resemble birch from a distance, but a distinction becomes more pronounced up close, where red alder bark completely lacks bark peeling and will have a uniformly dull luster compared to birch.
Typical white, smooth sheathing birch bark with horizontal lenticels, as shown here on gray birch (a non-native that may occur in the PNW as an escaped ornamental near urban/residential areas).
The variability in color of native PNW paper birch bark ranging from white to much darker colors can be seen on these logs.
Ample initial moisture content and sapwood, and robust sheathing bark in birch often leads to a fast spawn run, as can be seen here where shiitake mycelium is already beginning to show on the end of this paper birch bolt only ~2 months after inoculation.
The fast spawn run that occurs on birch often in-turn leads to birch bolts being the first to fruit, as can be seen here where the bulk of shiitake fruiting is occurring on the birch logs compared to more spotty or absent fruiting on other species. Birch's outstanding bark integrity also helps retain critical amounts of water even in smaller than average diameter logs (<4") such as shown here, which are more vulnerable to excessive drying.