Well, aren’t they all? Otherwise they wouldn’t be here..
There’s been a lot of interest lately in what plants might be adapted to our changing climate, so I’m going to toss in my two cents about what “climate-adapted” might mean. Climate-adapted plants are the ones that survive whatever the future climate throws at them, and by climate I mean long-term trends, including the frequency and amplitude of extreme events. It’s important to remember that plant populations are never perfectly aligned to their local environments, especially climate. Climate is always shifting, and since individual plants can’t themselves relocate when it gets hotter or colder or wetter or drier than they like, the only mobility they have is through casting their gametes, seed or vegetative propagules adrift and hoping that some of them land in hospitable spots. All plants can do is try to catch up to a moving target, the target being their ideal habitat. And since climate adaptation involves hundreds or thousands of genes regulating the expressions of multiple quantitative (and a very few qualitative) traits, no individual or population is ever perfectly attuned to its environment. Even the very best performer in a given habitat is going to have some deleterious alleles tucked away in, for instance, the 20-plus-gigabase genome of a ponderosa pine. So as they say, “ain’t nothin’ perfect.” And that’s true of plants as much as anything.
That said, plants are pretty darn good. The “heat-dome” event demonstrated clearly that most of our trees are freaking TOUGH customers. We hit 106, 107 and 114 here at the farm on 26, 27 and 28 June 2021. 114 is a hot day in Phoenix. In western Oregon it was unimaginable until it happened, with each successive day shattering what we thought was possible here. After getting smacked with 114 degrees and solar radiation near its maximum intensity, I would not have been surprised to see waves of mortality sweeping across the east slopes of the Coast Range, but by and large, that didn’t happen. The pattern of decline and mortality that we are seeing today on the periphery of the Willamette Valley wasn’t precipitated by single events even as extreme as the heat dome. It has, instead, unfolded slowly, the product of relentless heat and drought, summer after summer, over a period of many years.
I should note here that portions of the west slope of the Coast Range tell a different story. What very little is left of natural spruce-hemlock-cedar forest on the inland edge of the fog belt got absolutely hammered by the heat dome. Exposed crowns of hemlocks in particular got cooked off, and middle-aged and older individuals show little or no sign of recovery even now, over four years later. Many have finally died, and others are just standing there with a shell of dead branches and no leader. You can see this depressing legacy for a three-mile stretch along Highway 6, just east of Mills Bridge, which is the last bridge over the river before you enter the Tillamook valley. Spruce initially came through all of that seemingly remarkably well, but lately spruce all along the coast are looking terrible. After years of increasing summer temp and decreasing summer precip, the bell is finally tolling for them as well.
Back here in the Valley, we have not had a below normal summer average temperature since 2011. Also, during this period, average precipitation has been less than 40% of 20th century normals. This trend toward hotter, drier summers first emerged in the 1990’s and has accelerated every decade since. Summers in the 2020’s are on track to be the hottest and driest since record-keeping began. Here’s what the temperature trend looks like:
This now relentless upward trend in average summer T, combined with drought, is what is killing trees. Cedar, grand fir, red alder, even our local Douglas-fir population, all are showing signs of decline here in the Willamette Valley, along with dozens of other cool-adapted species and local ecotypes.
So what is doing better here in our now hot-box of a valley? Well, that is an interesting story. Garry oak is doing fine. Pinus ponderosa var benthamiana, the west side ponderosa that ranges from western Washington to central California, is doing fine. Incense cedar, the natural range of which extends north to Marion County, is looking good everywhere, including well north of its native range. Oval-leaf viburnum, a species we have grown for twenty years here at Scholls, continues to perform well. What gives?
HERE IS THE CRUX: The best clue we have regarding the “climate-adaptiveness” of species in the Willamette Valley currently is their ranges in California. Species and ecotypes that are doing poorly here now tend to have ranges that hunker down in the fog belt, immediately adjacent to the coast from Florence south to central or southern California. By contrast, the species that are doing well here now are extensively present throughout southwest Oregon and northern California, including the foothills of the Sierra Nevada. They are not restricted to California’s foggy, cool coastal strip. This is a pattern that we at Scholls Valley have been paying attention to for over twenty years. We want to provide you all with plants that have potential to survive what’s coming. In this and future posts, I will share information about plants that we think will perform well for you based on their natural ranges as well as their performance on the farm and on recent planting sites in our region. I’ll start with Viburnum ellipticum, which is a species we have grown since 1998.
Oval-Leaf Viburnum, also known as Oregon Viburnum, is among our finest ornamental natives. It is a long-lived, medium-size shrub with a tidy, compact form and dense, lustrous, deep-green foliage. Clusters of creamy flowers attract a wide variety of pollinating insects, and in late summer, purple-black fruits provide food for chipmunks, squirrels and fructivorous birds. By late fall, oval-leaf viburnum takes on a range of autumn colors, from gold to bronze to deep red.
The natural habitat of oval-leaf viburnum ranges from rocky, open slopes to well-drained streambanks. It is a valuable element of both Willamette Valley oak savanna and riparian woodlands. Its associates include Garry oak, tall grape, bigleaf maple, white alder and other elements of the floras of our natural levees and other well-drained sites.
As a restoration propagule, oval-leaf viburnum is extraordinarily resistant to heat and drought, tolerates transplanting well, and exhibits excellent survival even on harsh planting sites. Like many good drought tolerators, viburnum has a conservative growth pattern. It sets buds early in the growing season, and if things get hot and dry, it hardens off and stops growing. If the going gets really tough, it will begin to drop leaves, hanging onto just enough foliage to provision itself for fall root growth, whenever the rains finally come.
We currently have 12,000 of this exceptionally climate-adapted plant available for planting this coming season. You can order oval-leaf viburnum and many other truly sustainably grown plants (no methyl bromide!!) using our availability/order form, which you can access here: https://schollsvalley.com/availability/
It’s about to get HOT…ugh.