If you’re looking for ways to counteract — in a small but significant way — the relentless destruction of the natural world and want to turn your yard into a place that supports the wildlife community, or you already garden for biodiversity, you probably know that appropriate habitat — food, water, space, cover — is essential. Food is best supplied by regional native plants that produce insects, nectar, pollen, fruit, and/or seeds, while water comes either from natural sources or human-made birdbaths or ponds. Adequate space is important to prevent competition for food, cover, and nesting sites. Cover, or shelter, is as crucial as the others because wild fauna need places that not only shield them from inclement weather, but also hide them from predators (and people). Predatory animals themselves often need cover to successfully obtain prey. A lack of cover is a limiting factor for many wildlife populations.
Increased biodiversity comes with careful planning and placement of cover habitat supplied both vertically and horizontally with small and large native shrubs and trees. Those with particularly dense foliage may also provide valuable nesting habitat, as well as privacy for you, or even a windbreak if strategically placed.
Thickets are a great way to provide cover for relatively small animals, due to their tendency to be impenetrable to large species. They may be dense groups of trees or shrubs, usually dominated by one or a few species that tend to be multi-stemmed and often densely twiggy, or they may be formed by a single species that either enlarges via underground suckering stems or sheds large numbers of seeds that have the ability to grow beneath or close to the parent plant. Thickets of the latter type may also be spread by human disturbance.
Because thickets tend to fill quite a bit of space, they usually are not suitable for very small gardens, since they will tend to “take over” a small space, either fairly quickly or over many years, depending on the species. But if you have a fairly large yard or an acreage, native thickets create mini-ecosystems within which essential food and cover are supplied for a large number of beneficiaries, from insects and birds to reptiles, amphibians and mammals, depending on the location. They’ll also conserve soil moisture and may slow — or even prevent — erosion on slopes. And, when well established, thickets keep out many invasive weeds (note: always remove weeds well before planting any type of native plants). Many of these plants also can provide food for us, but I suggest you share with wild visitors.
Thickets often get a bad rap because they don’t look particularly neat and orderly, but if you garden for wildlife you know that messy and naturalistic is much better for the wild ones. To tidy up shrubs that tend to develop into thickets, gardeners often clip out suckers and sprouts for appearance’s sake, but that’s to the disadvantage of wild visitors.
Although thickets (especially thorny ones) may not be suitable for most front yards, in back yards or other areas, they can be wonderful wildlife magnets. And when located as far from human activity as possible, they also lend tranquility in an urban environment. Though my yard is just one sixth of an acre, I have several thickets—one that’s composed of snowberry and clustered rose, several of tall Oregon grape, and a large clump of thimbleberry. It seems there’s almost always something going on: A little bird or two flitting around branches looking for food, a ground feeding bird foraging within fallen leaves, pollinators hard at work, or — during nesting season — a bird vocally establishing his territory. Flowers’ pollen and nectar attract a variety of native pollinators in springtime, fruits or seeds become available later in the year, and the rose offers a place for mourning cloak butterfly larvae to develop.
Choosing thicket species
In nature, thicket-developing plants grow in forested areas, as well as open areas such as historic savannas (a grassland with trees scattered at least 100 feet apart), upland prairies (another type of grassland) or wet prairies. Needless to say, savanna/prairie plants require more sunlight than forest thicket species. Since humans have converted most savanna and prairie habitat to agriculture and livestock grazing, those thicket species aren’t having an easy time; they’re mostly forced to live on forest edges and fence rows and are threatened by invasive species.
Prairie or savanna thickets naturally would be surrounded and complemented by native herbaceous plants and grasses that are members of a plant community, which together would create a highly supportive ecosystem. Forest species also would naturally occur with ‘associates’ that interact and flourish together.
Here are some plants that typically will form thickets in the Pacific Northwest, west of the Cascades (but it’s not an exhaustive list). Choose species that would naturally occur in your area; check native status to county level here.
For sun to part sun: Douglas hawthorn (Cragateus douglasii), Red-twig dogwood (Cornus sericea), California hazelnut (Corylus cornuta var. californica), Western crabapple (Malus fusca), Western serviceberry (Amelanchier alnifolia), Ninebark (Physocarpus capitatus), Tall Oregon grape (Mahonia aquifolium), Bitter cherry (Prunus emarginata var. mollis), willows such as Salix scouleriana, S. lucida, S. hookeriana, and S. sitchensis, red-flowering currant (Ribes sanguineum), wild roses (Rosa nutkana, R. pisocarpa), Douglas spiraea (Spiraea douglasii*), white spiraea (Spiraea betulifolia var. lucida), Thimbleberry (Rubus parviflorus*), Salmonberry (Rubus spectabilis*).
For part shade to shade: Red elderberry (Sambucus racemosa), Snowberry (Symphoricarpos albus), Osoberry (Oemleria cerasiformis), Salal (Gautheria shallon).
* may spread rapidly.