Pacific Northwest Plant Profile: Pacific Madrone (Arbutus menziesii)

Arbutus menziesii bark

Though it looks exotic, Pacific madrone—a beautiful broadleaf evergreen tree with a captivating and distinctive presence that transforms with the seasons—is endemic to the Pacific coast. Its exquisite characteristics of fragrant flower clusters, brilliant berries, glossy leaves, twisting branches, rounded crown, and rich cinnamon-red bark that peels from a satin-smooth trunk, please all of our senses. And for the wild ones attracted to this unique gem, its ecological gifts never disappoint.

Madrona (after madroño, the Spanish name for a Mediterranean “strawberry tree”) is the name admirers in Washington give this member of the Ericaceae (heath) family, while those in California and Oregon call it madrone or Pacific madrone. British Columbians simply use the Latin genus name, Arbutus. (The epitaph, menziesii, is named after the naturalist Archibald Menzies, a naturalist for the Vancouver Expedition that explored the Puget Sound region in 1792.)

How it grows
Pacific madrone is a long-lived tree that naturally occurs in a climate with mild, wet winters and dry summers, although rainfall varies substantially within its range, from the east coast of Vancouver Island in British Columbia southward through Washington and Oregon (west of the Cascades) to San Diego County. It is often found on rocky soils and other coarse soils that retain little moisture, including the dry foothills, wooded slopes and canyons (at low to mid-elevations) of parts of California; within coastal redwood and mixed-evergreen forests; on dry ridge tops and slopes at low to moderate elevations along the east side of the Coast Ranges and in the Siskiyou Mountains; on warm, dry lowland sites west of the Cascades (within Douglas-fir and western hemlock forests); and—furthest north—near sea level on rocky bluffs and low elevation slopes. Within mixed hardwood forests—that may or may not have an overstory of conifers—its tolerance to shade varies with age. While madrone seedlings do best in partial shade and young trees can handle quite a bit of shade, tolerance decreases as trees age and for those at the northern end of this species’ range. Older trees need good light to survive and often can be found growing at an angle, twistily and desperately reaching for the sunlight that helps ensure a long life.

Wildlife value
Wild ones are drawn like a magnet to madrone trees year round. In springtime, lovely creamy white, waxy, urn-shaped blossoms provide nectar for hummingbirds, native bees, and other pollinators.

Arbutus menziesii in flower

 

Clusters of bright red berries—that ripen in autumn and may persist into early winter—feed many bird and mammal species, including American robins, varied thrushes, band-tailed pigeons, cedar waxwings, northern flickers, quail, raccoons,  squirrels, mule deer, and bears.

Arbutus menziesii (fruit)
Habitat is provided for a variety of insects, including echo blue and brown elfin butterfly caterpillars, who nibble on leaves and in turn provide dinner for insectivorous birds. Shiny, leathery leaves generally remain on branches for two years, after which they turn from vivid green to burnt orange and settle to the ground where they provide a natural mulch that protects soil microorganisms and little ground-dwelling creatures. Lofty roosting and nesting habitat is also supplied, and live trees with rotting wood offer cavities for insects as well as birds that nest in trees, such as woodpeckers.

Conservation
Unlike other trees, madrone’s fine roots have adapted to search deeply into rock fractures for stored water, making it an important plant for stabilizing slopes and cliffs and preventing landslides. In addition, it’s a valuable component of many vegetation types—for example, in mixed conifer forests like Washington’s Coast Range ecoregion (Douglas-fir/western hemlock/madrone), it provides a mid-canopy story, essential for the structural diversity of the forest. It ought to be preserved for its own sake, for the wildlife that use it, for the ecosystems of which it’s an indelible part, and, needless to say, for those of us who revere its spectacular beauty.

Tragically, the species is currently in decline throughout most of its range, for several reasons. First, sprawling development in its native habitat has stolen many mature specimens. Though tough and drought tolerant (or perhaps I should say drought dependent), its roots are extremely sensitive to drainage changes, compaction, grade alteration, and other soil disturbance. Because madrone belongs and successfully grows in regional arid soil conditions that many trees cannot, landowners and developers ought to protect and save these trees at all costs.

Under natural conditions, madrone depends on intermittent fires that limit the conifer overstory (typically Douglas-fir trees). Older madrone trees can survive fire and will sprout quickly and profusely afterwards due to carbohydrate reserves and existing roots. In addition, their fruit produces many seeds, which sprout on exposed soil readily after fire. But when humans suppress and prevent natural fires, the prolonged absence of fire and consequential shade—especially on moister sites—may cause madrone trees to die.

Death or damage may be also caused by several pathogens, including a foliar fungus (Nattrassia mangiferae) commonly called “madrone canker,” that reproduces via spores and causes dieback, blackening of branches, and cankers that may spread to the trunk. A root rot, Heterobasidium annosum, can also cause serious damage. Unlike fire, “disease decreases starch accumulation in the root burl, so that declining trees are less able to resprout after the aboveground portion of the tree is killed by disease.” But prevention is possible: Susceptibility to disease is exacerbated by unnatural environmental stresses such as regular summer irrigation and the use of fungicides and fertilizers. Essentially, spores are carried by water, fungicides kill beneficial mycorrhizal fungi (symbiotic associations between the roots of most plants and fungi, which protect roots from pathogens), and studies suggest that increased soil nitrogen disrupts the mycorrhizal associations between beneficial fungi and tree roots, which in turn reduce the supply of micronutrients and water to trees, thereby increasing susceptibility to disease. Madrone trees host a large number of types of mycorrhizal fungi and have been called “a major hub of mycorrhizal fungal diversity and connectivity in mixed evergreen forests” that play a large role in forest regeneration by promoting resilience to disturbance below ground.

Madrone is also affected to a small extent by sudden oak death, a disease caused by a water-borne, fungus-like pathogen, Phytophthora ramorum, which arrived in the U.S. via live plant imports of exotic ornamentals to nurseries; it is increasingly spread by human actions, including climate change.

Try it at home
Despite all these threats, a madrone in the wild can live hundreds of years and may grow very large—over 100 feet tall. In cultivation they rarely exceed 50 feet after many decades. Young trees often grow fast (up to several feet per year), while older trees typically grow at a much slower pace. In the southern, drier and warmer part of its range, it grows more slowly and stays smaller.

Supplemental water after establishment is highly detrimental: Madrone cannot tolerate slow drainage, standing water, or regular irrigation during summer, which make it susceptible to disease (as will fertilizer applications). While it has a bad reputation for being difficult to establish and isn’t for the fussy gardener, knowing what this tree needs and can’t tolerate will help ensure success. In my experience, there are five essentials to successfully growing this tree:

1. Figure out if it historically occurred in your area. Though it’s not absolutely essential that this species likely grew in your immediate area 200 years ago—especially since much change has occurred since then—because this tree can’t just be stuck in the ground anywhere, look to nearby natural areas to see if it might have naturally occurring relatives nearby in similar soil. In its northern range, it’s usually found growing on soils derived from glacial sands or till and gravels, while in the southern and middle parts it reportedly grows on soils derived from a variety of materials.

2. Be sure your site has the right conditions: Fast-draining, slightly acidic soil (pH a little less than 7), noncompacted soil, and a bright location with at least a half day of sun in northerly locations. However, seedlings need partial shade to establish; if you have mostly sun, shield them from hot afternoon sun until established. Site plants on a slope or area that’s elevated (even slightly) above the surrounding area to facilitate drainage. In my yard I tried twice to grow one-foot-tall saplings in the lowest part of my yard with sad results, despite digging in extra small rocks and gravel to increase drainage. My third attempt, which I grew myself from seed, I planted atop a short, south-facing slope, again with extra rocks and gravel. I believe that the increased drainage was what was needed; however, the seedling was also very small—only three inches tall—so that also may have helped. Note: If you live in a warm, dry area (such as parts of California) be sure to plant this tree on a north-facing slope, rather than in direct sunlight.

3. Start with very small saplings, no more than a foot tall, as older trees do not transplant well. Once they “take,” however, young trees grow quite fast—in my yard, over a foot a year.

4. Plant saplings in the fall, just as winter rains begin, since they establish best when they can establish roots first, then put on aboveground biomass. Also, you won’t need to worry about how much or how often to water—just let nature decide. Do not dig large amounts of organic matter into the soil that could inhibit the moisture-seeking roots from penetrating to mineral soil, and do not add fertilizers that can disrupt the mycorrhizal associations between beneficial fungi and roots. Never apply fungicides.

Baby madrone

Baby Madrone, just 4 months after planting as a 3-inch-tall sapling.

5. Irrigate sparingly, and preferably only during the first summer or two. During my little tree’s first spring and summer it was unusually warm and dry, and I noticed some wilting of leaves on especially warm days. I carefully (and nervously!) watered it in the mornings around its base and outwards a few feet, keeping the leaves and stem dry. I did this only a couple of times a week when heat was predicted, and by the end of the summer it was in fine shape and had grown well over a foot in height. During the second summer I left it on its own and when no wilting of leaves occurred, it became clear that the little tree was self-suffient. After another foot of growth was added, I was able to fully exhale.

Grab a partner
It’s best to match madrones with other species that are compatible below ground—those that have similar needs and mycorrhizal associations and that would naturally occur together in nature (if you already have some non-natives that you want to keep, be sure not to grow any that need summer irrigation nearby!). Which native “associated species” you choose depends on what part of the region you live in. 

Madrone most commonly rubs shoulders with mixed-hardwood tree species that often have some overstory of conifers.  A member of the Douglas-fir/tanoak forest, madrone makes up the secondary canopy, while Douglas-fir (Pseudotsuga menziesii) with tanoak (Lithocarpus densiflorus) typically create an overstory. Less commonly, madrone mingles with coast redwood (Sequoia sempervirens) along the northern California and southern Oregon coast, and with western hemlock (Tsuga heterophylla), Oregon white oak (Quercus garryana var. garryana), and Pacific ponderosa pine (Pinus ponderosa var. ponderosa) throughout much of its range. Washington’s San Juan Islands’ open woodlands support madrone with Douglas-fir and fescue (Festuca spp.), as well as other species such as lodgepole pine (Pinus contorta), Oregon white oak (Quercus garryana), and Rocky Mountain juniper (Juniperus scopulorum). In British Columbia, Pacific madrone grows alongside lodgepole pine. Other tree species associated with madrone include sugar pine, white fir, California black oak, giant chinquapin, bigleaf maple, bitter cherry and California laurel, according to the U.S. Forest Service. Small trees commonly associated include vine maple, black hawthorn, red-twig dogwood, willow, hazelnut, and red elderberry. Shrub associates include manzanitas, Oregon grape, ceanothus, salal, oceanspray, poison-oak, gooseberry, wood rose, snowberry, huckleberry, and thimbleberry.

A. menziesii with oaks

Madrone mingles with Oregon white oak, aka Garry oak (Quercus garryana), in parts of its range.

 

As always, buy plants propagated from source material that originated as close as possible to your site. Using such “local genotypes” helps ensure that you get plants that are well adapted to your area and that genetic diversity—which helps plants (and animals) adapt to changing conditions—is preserved. Ask growers and nurseries about their sources if you’re unsure.

Propagation
Pacific madrone are fairly easy to grow from seed. Collect fruit soon after it ripens, generally early to mid-fall. Because one berry can have more than a dozen seeds, you won’t need more than one or two if you just want to grow a few trees.

Separate the seeds from the pulp of a ripe (red) berry (if they have dried, soak them overnight to help release the seeds from the pulp). Place them in a small bowl of water for 15-20 minutes; discard those that float and allow those that sink to dry in a cool place out of sunlight. (Dry seeds may be viable for a couple of years if stored properly in a cold, dry place.) Place seeds on top of a fine seedling mix, either in a pot outdoors or in the spot where you want a tree to grow, and cover just slightly.  I like to grow them in pots so I have a little more control, but I’ve had success both ways. If you choose to use pots, keep them moist but don’t allow them to fully dry out, and keep them away from slugs and snails.

Madrone seeds reportedly are able to maintain dormancy for long periods (“scores of years”) in the soil, but when conditions are just right—cold but above-freezing temperatures and adequate moisture—dormancy is broken In early spring after cold stratification has weakened the seed coat. At that point they should be moved into a somewhat warm, bright location, but not direct sunlight—seedlings establish best in partial shade and grow fairly slowly. Keep them moist, but not saturated. After they have developed their second or third set of true leaves they may be moved to bigger pots with fast-draining soil (I like to use a mix of sterilized potting soil and small gravel), handling them by their expendable first set of leaves, not their delicate stems. Water them when the top inch of soil is dry; I find it’s hard to overwater with fast draining soil, but do give them time to dry out slightly. Plant them out when they’re 3 to 12 inches tall, in the conditions described above.

 

© 2017 Eileen M. Stark

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