At the Root: Trees Rule
By Guest Blogger: Eileen Stark, Portland, Oregon
Although the region’s unique wetlands and grasslands carry the greatest diversity of species, it is the forests that dominate and most distinctly characterize the Pacific Northwest. Structurally complex, dense, and immense ecosystems, forests sustain trees that substantially outgrow and outlive other plants and tolerate temperature variation and soil differences better. When the first European settlers arrived, conifers covered nearly the entire landscape of western British Columbia and Washington, and northwestern Oregon–from coast to Cascade crest–including the Puget Trough and parts of the Georgia Basin and Willamette Valley.
These conifers (and other dominant species) are known as keystone species because of their strong and often unique effects on their ecosystem. Though they are greatly outnumbered by smaller plants in the forest, their contributions are mammoth. Cool, wet winters and mild, dry summers, along with rich soils, have made for optimum evergreen growing conditions.
Conifers are able to photosynthesize during much of the year and are essential for watershed stabilization. Some species are the most massive on earth, often growing over 200 feet tall and living for more than 500 years. Worldwide, conifers represent the largest terrestrial “carbon sink,” where carbon is packed away in plant tissue above and below ground. The wettest forests–those on the west side of coastal mountain ranges–were once especially complex, with lush layering and much variation in tree age. Logging has eliminated much of the original, most productive old-growth forests, and massive clearcutting has resulted in severe fragmentation. Today, much forested land is “second growth” that has followed logging and wildfire.
Garry oak (or Oregon White oak) ecosystems, where these oaks grow naturally, have become rare, with only a very small percentage remaining. The loss of these unique ecosystems puts all the species that rely on them in jeopardy, and indeed, some species have already been lost, while many of the remaining are at risk. If you live on land that was once part of a Garry oak ecosystem and are starting with a blank slate, consider planting Garry oaks and associated species like madrone (Arbutus menziesii), oceanspray (Holodiscus discolor), tall Oregon grape (Mahonia aquifolium), and baldhip rose (Rosa gymnocarpa). If your site is too small for large trees, grow the smaller associated species in a meadowlike garden or rock garden. Spring ephemerals include white fawn lily (Erythronium oregonum), Henderson’s shooting star (Dodecatheon hendersonii), and camas (Camassia quamash). Mid-bloomers include tiger lily (Lilium columbianum), nodding onion (Allium cernuum), stonecrop (Sedum spp.), harebell (Campanula rotundifolia), and western columbine (Aquilegia formosa); for late blooms try yarrow (Achillea millefolium var. occidentalis), showy fleabane (Erigeron speciosus), and goldenrod (Solidago canadensis).
Most yards can support more trees, whether evergreen or deciduous, than they do. If you have the space, grow large trees–the oaks, the pines, the firs–that are quintessential to our region and will help replace some of the habitat that has been lost to development and logging. Just one Western red cedar (Thuja plicata) will provide dense shelter and nesting sites for various birds and small mammals, bark that can be used as nesting material, food for seed-eating birds and browsing mammals, and, as the trees mature, cavities for roosting and cavity-nesting birds.
In urban areas, street trees that grow in parking strips could be native species (as well as the other plants you grow there). Some good choices for narrow parking strips (not less than 4 feet wide) include cascara (Rhamnus purshiana), Douglas maple (Acer glabrum), and black hawthorn (Crataegus douglasii), and for wider strips (greater than 6 feet wide) and without overhead utility wires, Garry oak (Quercus garryana), and Oregon ash (Fraxinus latifolia). Always check with your city’s urban forestry office before planting.
Excerpt from Real Gardens Grow Natives: Design, Plant, & Enjoy a Healthy Northwest Garden by Eileen M. Stark (Mountaineers Books, 2014)
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