Many gardeners are now seeking climate ready trees as the causes of global warming begin to affect our ecosystems. What are climate ready trees? And could ponderosa pine be Portland’s best hope for climate resilient urban forests?
Climate Ready Trees in Urban Forests
Land managers are taking interest in the subject of climate ready trees & urban forests. This article from Green Seattle describes Portland’s northern neighbor’s approach to thinking about climate resilience for urban forests.
First it’s critical we make the changes necessary to avoid warming over 1.5 C of pre-industrial temperatures. Without limiting CO2 emissions & other causes of climate change, our urban forests will have a harder time adapting. We need to monitor climate change until we have a better idea of how we’re going to mitigate it’s effects.
What Are Climate Ready Trees?
Oregon white oak and Pacific madrone are adapted for drought and flood conditions like many of Portland’s native plant species. Others such as Western red cedar and Oregon ash are much more specialized for our cooler, moist local climate.
However, many urban forest professionals are also getting eager to recommend other non-native tree species. Across the globe, many tree and shrub species have incredible ability to withstand extreme temperatures & conditions. It is our inclination to want the best urban street trees. So the opportunity to utilize the amazing resilience of all street tree species will certainly be left on the table.
Selecting Climate Ready Trees
We should always favor native tree and shrub species for resiliency in our urban forests. Native species have symbiotic associations with microbes and other organisms that create habitat function. In some cases, it may be appropriate to use seeds & genetic varieties of native plants originating from more Southern areas.
Pinus ponderosa is an amazing tree species that can withstand a wide array of extremes. To identify Ponderosa pine, simply sniff the bark on a warm day. If you experience a delightful vanilla or butterscotch aroma, then you’ve got a Ponderosa. Here’s a few quick facts about Ponderosa Pines:
- They range from Canada to Mexico North to South, and from The Pacific Northwest all the way to Nebraska and Oklahoma.
- In the plateaus and mountains of Arizona & New Mexico, these lush forest trees stand tall & perfectly spaced among nothing but rocks & dry grass.
- Their needles provide critical canopy shade and a source of organic biomass in dry desert places.
- They are incredibly well adapted for drought tolerance and fire resistance.
Ponderosa pine also happens to be one of the plants we use in native habitat restoration in Portland. The same year I enjoyed seeing Ponderosa pines throughout Arizona, I planted them along the floodplains of the Tualatin river near Beaverton. Unbelievably, I noticed some of the Ponderosa pines my predecessors planted were often completely submerged under turbid Tualatin river water. Sometimes for weeks at a time.
This is the Willamette Valley Ponderosa Pine aka pinus ponderosa var willametensis. The Valley Ponderosa is a subspecies of Ponderosa pine native to the Willamette Valley of Oregon. I would bank on Valley Ponderosa as a champion of climate adaptation and sustainabile landscapes.
What Makes A Tree Climate Ready?
From drought tolerance to flood tolerance, Valley Ponderosa as a high degree of plasticity. Plasticity refers to the tree’s ability to thrive under a variety of flood, drought or unseasonable hot or cold termperatures. When I think of plasticity I think of Ponderosa pine. These trees are as rugged as they are tough.
Temperature extremes, even from negative forty to well over a hundred degrees, do not appear to limit them. Apparently Ponderosa pine seedlings are even more drought resistant than Douglas Fir, California white fir & sugar pine. Will the Valley Ponderosa or just ponderosas in general have enough plasticity and resilience to be a climate change champion?
Another species of focus from some habitat restoration professionals is California Bay Laurel. The leaves of this fragrant are famous for spicing up soups and stews. In fact, bay laurel grows across the middle-elevation areas of California. However it seems to stop just short of crossing the Oregon border. Oftentimes Portland gardeners use California bay laurel as a landscaping plant.
Indeed some restoration professionals myself included have noted probable California Bay Laurel volunteer seedlings appearing in the Portland Metro area. Should we plant resilient native species? Or should homeowners & urban foresters consider other species? It also indicates similarly adapted species from southern climates may be finding their way here on their own.
Climate Change Resilient Landscaping
For Portland climate change resilient landscapes, we should bet on native species like Ponderosa Pine and Oregon White Oak. Indeed, we should try to engage and restore native plant and soil microbes to restart our ecosystem’s natural defense mechanisms. And we should use serious caution when introducing non-native species even with the intent to conserve the environment.
Making Existing Trees Climate Ready
It is worth paying close attention to what species are doing well. But let’s also recognize local conditions & health history are usually the primary factor. In fact, living microbes in the soil largely determine soil health. Microarthropods (tiny insects), fungi, bacteria, protozoans, nematodes all feed each other and digest nutrients. So the soil food web helps make nutrients bioavailable to your plants and soil.
Feed The Soil Food Web
Feeding the soil is a concept that’s picking up major steam in organic agriculture and backyard gardening. And for good reason. Since a healthy soil teeming with beneficial microbes creates an environment that’s resistant to pests & disease. Surely, in healthy soil, insect predators find a home. Additionally, beneficial microbes outcompete pathogens in the invisible food web around the root zone, also called the “rhizosphere.”
So remember to amend any new trees or shrubs responsibly. And more gardeners & homeowners choose an appropriate mycorrhizal inoculant product. Even just transplanting a scoop of soil from a similar healthy forest species can help.
For habitat regeneration, adding soil amendments like alfalfa, kelp, oyster shell powder, biochar or mycorrhizal inoculant is a no-brainer. These additions reduce nutrient deficiency for the plant and for the soil microbes. Soil amendments boost plant growth and beneficial soil life creating healthier stronger plants faster. For pest, disease, drought and climate-change resistant backyard landscapes in Portland Oregon don’t hesitate to call us.