Stand in your forest and count the overstory tree species you see. On the west side, this will likely include Douglas fir, hemlock, cedar and alder. On the east side, you are likely to tally Douglas fir, ponderosa pine and grand fir. Now, from that exact spot, count the shrubby understory, (or “brush”) species that you. This may include oceanspray, serviceberry, ninebark, salal, salmonberry, red or blue elderberry, cascara, beaked hazelnut, bitter cherry, chokecherry, evergreen huckleberry and so on. Nearly always there are two to three times as many species of native shrub, understory species on a site than there are tall trees. Wow!
Trees generally have a single stem and reach the highest levels of the canopy, while shrubs have multiple stems and grow in the understory. And yes, sometimes there are plants that confuse us. This rich, and often overlooked and underappreciated, layer of our forests contains some of the best wildlife habitat out there.
Benefits of Brush
Nearly 25 percent of our forest-dwelling wildlife rely on these plants for food or cover, and would not exist on our lands without these wonderfully dense thickets. Song sparrows, spotted towhee, warblers, chipmunks, deer and so. The critter list of those that thrive on this critical habitat element is long. In fact, the shrub layer may be the most important habitat feature for a high diversity of wildlife species in early forest successional stages. Systematic research in Oregon has shown that songbird abundance and diversity is increased when west side plantations are allowed to develop some shrub components.
When sunlight reaches the ground, even in small amounts, the various shrub species will take advantage of this niche and grow, sometimes for many years and to impressive mass. Who hasn’t seen a gap in the wet forest where the shrubs have come into create a little pocket of shrubs in the midst of an otherwise dark conifer overstory? These canopy gaps are a great source of habitat diversity. Mixed stands of mature trees, (conifer and hardwood), openings and substantial shrub components can provide some of the richest and most diverse habitats in our forests.
Many shrub species produce “mast,” or fruit, that is eaten by a wide array of wildlife, from birds to the smallest mammals and all the way up to the black bear. The wonderful flowers of our shrub species provide feeding opportunities for pollinators, including hundreds of species of native bees, hummingbirds and butterflies. Unlike the conifer, these flowers produce nectar, a rich draw for many animals including specialized insects. And most of our game species, those big charismatic megafauna, forage on these plants too. Shrubs usually carry these animals through the winter.
There are many shrub (“brush”) superstars. Here we highlight just a few of our best wildlife habitat shrub species.
Blue elderberry (Sambucus cerulea): This lovely plant grows in sunny spots east and west of the Cascades. It can take on a fairly large form if given enough time and light, reaching up to 25 feet high and across. Multiple stems produce lush, compound foliage that is preferred browse for deer, elk and other animals. The abundant purple berries are favorites of many birds and seldom last long. These same berries can even be made into wine or jam. If you want to enhance wildlife habitat by planting shrubs, this one is a great choice.
Red elderberry (Sambucus raesmosa): Wetter sites in western Washington grow the red elderberry, a very similar plant to the blue, with a branching brushy form and red berries favored by many wildlife species. These grow in small openings and in the dappled understory of mixed forest stands. In my observation these two plants usually don’t occur in the same locations, but both are great wildlife habitat plants.
Salmonberry (Rubus spectabilis): Dominating many understories across western Washington is the ubiquitous salmonberry. This plant features dense woody stems that can create a jungle of dense vegetation — perfect places for birds and small mammals to seek shelter. The berries resemble salmon roe (hence the name) and are eaten by most everything, including people.
Indian plum (Oemleria cerasiformis): Perhaps the earliest blooming shrub species in western Washington is the gorgeous Indian plum. This rich understory species occurs on many moist forest sites, providing early foliage and flowers for native pollinators. They produce lovely, tiny purple fruits and never last long, being eaten at first chance by many birds and mammals. Watch for the white flowers in the first blush of spring.
Indian plum foliage
Black hawthorn (Crataegus douglasii): The spiny hawthorn creates dense cover for birds and a great place for mammals to hide and rest. The fruits (called “haws”) are also eaten by many species. It prefers sun, but will get by in dappled shade. This plant occurs on both sides of the mountains.
Other shrub superstars worth mentioning include serviceberry, mock orange, ceanothus, cascara, salal, willow, dogwood, and even devil’s club. Each of these has great wildlife structure and bears fruit.
Sometimes the dense nature of shrub cover can prevent conifers from regenerating for many years, much to the frustration of those attempting to grow trees for harvest. Vast effort is made to eliminate this competition on lands dedicated to tree production, often by using aerial application of herbicides. This is hard on the shrub layer to say the least. The small landowner, however, usually has mixed objectives, wishing to provide quality wildlife habitat AND grow the next crop of trees. This can be accomplished by identifying the best wildlife shrub species growing on your property and actively maintaining them over time by allowing for space to grow these plants. Conifer competition can be dealt with by physically cutting the competing plants back, and/or strategically using herbicides on individual plants or clumps, thus allowing the conifers to get above the shrub layer and form a new canopy.
Sometimes individual plants are cared for. Planting can work if adequate care is made for each plant. Control competition and prevent browse on young plants. Desired shrubs that have become tall and “leggy” with extended stems and leaf and fruits out of reach of browsers, such as deer, can even be simply pruned back just as we might manage the bushes in our yards.
These are just a few thoughts and examples of the fabulous shrub species we encounter on our forest lands that are worth knowing and keeping on the landscape. Find out what shrubs you have on your place. Their value to wildlife as habitat is very great and definitely worth managing for.
Learn and enjoy your brush, or should I say, “shrub habitat.”
For more information or questions about managing small forest lands for wildlife, please contact me.
By Ken Bevis, DNR stewardship wildlife biologist, Ken.Bevis@dnr.wa.gov