Wednesday, November 24, 2010

The Dogwood Cousins

Sometimes, family get-togethers can try your patience. I was a wee small tyke when someone got the bright idea of gathering together about a dozen of my pre-teen cousins. As I recall, it only happened once.

These funny strangers were part of my family, it was explained, even though they had different last names and arrived in a wide array of sizes, shapes and colors. Over the years, the whole gang of us dispersed around the country, settling into our preferred habitats to sink roots and raise families.

It's a similar story for the dogwood family. The 40 or so different dogwood species that settled in specific habitats across the U.S. also grow in a wide array of sizes, shapes and colors. They have the same first names (Cornus) but different last names. 

Multiple stems of one Bunchberry Dogwood plant
During their ramblings in the northwest, Lewis and Clark crossed paths with at least three different dogwoods. In Oregon they met the Pacific Dogwood (C. nuttallii), and in Montana they noted two native dogwoods -- Red-osier Dogwood (C. stolonifera) and Bunchberry Dogwood (C. canadensis). Oddly, Bunchberry was the only one they collected.

At first glance, you might think these three dogwoods are unrelated. The coastal Pacific Dogwood forms a small tree with lovely, white flowers. Here in Montana, Red-osier Dogwood is a large, colorful shrub, while Bunchberry Dogwood is a wee small forb. But it's a set of very specific characteristics that defines a flora family. For dogwoods, these include botanist-arousing details like, "a lobed calyx that joins the pistol to form a two-seeded fruit." Well, okay.

But there is a characteristic shared by our two Montana natives that also appeals to non-botanists -- the color red. Well, sort of. Red appears in different seasons and on different plant parts, so be patient on this one.

Red-osier Dogwood

White Red-osier fruit
Red-osier Dogwood is a woody,  deciduous shrub, 3-19 feet tall, that is showy all year. Green buds in spring give way to large clusters of small, white summer flowers, which produce the waxy-white fruits of fall. In late fall, their green leaves turn to a rich burgundy for a few gorgeous weeks before dropping.

Fall is also when Red-osier begins earning its common name, and its keep. The new growth of summer started out red but slowly turned gray-green as it aged. But in fall, the stems turn into bright, eye-catching red. They'll go green again next summer, but these red stems provide some of the only color relief during the long months of cloudy winter white. The red branches appeal to travelling naturalists and other animals that pause to take note of this native.

Red-osier stems and leaves in fall
The red stems have been a favorite of basket makers for decades. Natives and early settlers also used the leaves and inner bark for tobacco (which is slightly narcotic). And these days, because it is fast-growing and easy to establish, Red-osier Dogwood is recommended for rehabbing road cuts and moist sites (e.g., abandoned placer mines) in Montana.

At some point during the year, Red-osier Dogwood is also important to many wild animal species. It is browsed by white-tailed deer in spring and mule deer in summer. The white fruits are a key food for both grizzly and black bears in the northern Rockies. This shrub often grows along stream banks, and even cutthroat trout eat the berries that fall into creeks. The burgundy leaves are a fall favorite for moose, and elk seek out the younger stems in winter. A bunch of other animals use Red-osier Dogwood, including rabbits, turkeys, grouse, ducks, ravens and beavers.

Bunchberry Dogwood

Compared to its gangly cousin, our native Bunchberry Dogwood is much shorter and, most of the year, much less colorful. That's because it has the unusual lifestyle (for a dogwood) of a creeping, perennial forb. It tops out at only 6-8 inches tall -- on a warm day.

In mid-summer, Bunchberry sprouts from long-lived rhizomes that lie just a few inches below the surface. It is a clonal plant that survives by growing a cluster of green, above-ground stems each summer for photosynthesis and flowering. In one study, one below-ground rhizome was 172 inches long and more than 36 years old.

The Bunchberry strategy relies more on vegetative regeneration than on seeds. Seedling survival is low due to low fruit set and germination, and slow growth. Three-year-old seedlings are only about 1" tall, and they don't begin growing the all-important rhizomes until after their fourth year.

Summer 's white flower cluster turns to fall's red berry bunch.
Bunchberry rhizomes can survive all but the most intense fires. In 1980, they resprouted stems within four months of the Mount St. Helens eruption. After a large-scale forest disturbance, Bunchberry can cover the forest floor for the first 40 years or so, until the canopy becomes dense and shades out the little dogwoods. Bunchberry increases in density again after about 150 years, when the forest matures and the canopy begins opening up. Interestingly, even though they grow faster in sunny spots, there is 2 to 3 times more digestible protein in Bunchberry leaves from forested areas than in Bunchberry leaves from sunny clearcuts.

Though short in stature, Bunchberry Dogwood is an important browse plant for mule deer and moose in summer, when it's growing above ground. Grouse eat the early buds while other birds eat the summer fruits. Mice and their kin rely on the fruits each winter.
In summer, each Bunchberry stem grows what looks like one white flower. But this is actually a cluster of many small flowers that are set within four white "bracts," or modified leaves. Bees and flies handle the pollination, and late summer or early fall is when these little dogwoods earn their common name. Each cluster of greenish-white flowers turns into a bunch of bright red berries, or berry bunches, or bunchberries.

So in our dogwood family, the tall Red-osier stems turn bright red during fall, and the short Bunchberry stems grow red berries in late-summer. See? I told you we would eventually tie them together with the color red. You just had to be patient enough to get through a summer and fall with Montana's native dogwood cousins.