“How did it get so late so soon? It's night before it's afternoon.” - Dr. Seuss
by Brendan McGarry
- The Capitol Hill Times -
Fall hit the northwest with a definitive jab, leaving us wet and groggy. We all know the feeling of trying to wake up to darkness and oppressive rain. Yet, we do get one final burst of color before total darkness sets in.
If you said “fall” to someone from the Midwest or New England, their mind immediately jumps to images of maples and oaks with resplendent yellows, oranges and reds. In the Pacific Northwest, however, our low diversity of these trees means that we see little color. We do live in the Evergreen State, after all.
Before we think about colors, I want to pose a question. Do you know why trees loose their leaves? It’s okay to say “no,” especially if you’re used to seeing evergreen conifers year-round. The annual shedding of all leaves in the temperate world is typically an adaptation to colder climates. Feel a leaf. It’s usually fragile and vascular, with obvious moisture to it; in a frozen environment, leaves would freeze because they contain water. Conifers get around this by having waxy needles and scales with freeze-resistant chemicals for all but the worst of conditions. They loose their foliage when it gets old and is replaced by new growth. A deciduous tree, instead, senses lessening daylight and begins to shut down photosynthesis in preparation to lose leaves.
In places where snow is common during winter (the Midwest or the Northeast), having year-round foliage would cause other problems, also. Leaves hold snow, and those loads can break branches. When you ascend our mountains, evergreen trees have decreasingly shorter branches that hold less snow. Our evergreen trees have the luxury of a mild climate to photosynthesize year-round, only needing to prepare for the occasional frost. Deciduous trees, though, with longer branches, are more at-risk in frost and snow.
A tree relies on the sugary carbohydrates that it creates via photosynthesis. Deciduous species, which lose their leaves to protect themselves from hard winters, also inhibit their ability to photosynthesize. Creating an extra store of sugars before going dormant is one fix for this. Dormancy can either mean halting new growth (such as in evergreens) or, after loosing leaves, existing in low gear, waiting for spring. Trees transport and store starches in vascular layers beneath their outer bark. When spring hits, these starches start to move to aid growth, (which is why maple syrup harvest is a late winter, early spring activity). When trees are preparing for dormant periods, their biological changes effect coloration.
No one has a full understanding of all of the working parts of fall coloration. The green colors that you see in leaves or needles are a result of chlorophyll, the essential molecule for photosynthesis, but that’s just one pigment. As the days shorten, energy needs to be stored and chlorophyll production declines, so the greens begin to fade. Underlying pigments like yellow and orange carotenoids begin to show up. Others, like the deep reds of vine maples (Acer circinatum), are only created during the fall when chlorophyll production is shut off and sugar production ramps up. Different species have a variety of colorations, and the annual show is condition-dependent, and, therefore, variable. Why the pigments, aside from chlorophyll, are there at all, however, isn’t fully understood.
Most Seattle streets and parks aren’t lined with native species. Native evergreens are often too massive, and there has always been a strong bias towards exotic deciduous plants, probably because of their variety and longer history of cultivation. Strong opinions exist about native versus non-native plantings, but if we didn’t have exotic species in our cities, we’d miss out on fall colors. Aside from a few plants, like blueberries, vine maples and western larch, our best colors are rather bland, mild yellows at best.
One of my favorite exotic species is the “Flame Ash” (Fraxinus angustifolia), which has been heavily planted along Broadway; they turn a beautiful dark auburn that transitions into deep red in the best of years. Norway and other maples display deeper yellows, oranges and reds than our similarly-sized bigleafed maples. I feel like I’m betraying the northwest when I say that I’d rather walk over the red leaves of a flame ash than the muddy yellows of a red alder.
I’m not surprised fall color isn’t completely understood because it’s so variable. Simply looking at my local bigleaf maples is a prime example. This year, they’re already dropping leaves, turning yellow and brown. At the same time last year, they were still around, just hinting at yellow. Several years before, they were deep yellow before leaves began to fall. Even if we don’t get to see the outrageous displays of other parts of the country, we can still take time to quietly contemplate the cycles of our own local flora.