Each fall deciduous trees, ice-cream stands, and marinas close for the same reason: as daylight dwindles and cold creeps in, they become less profitable. When income dips down to equal the cost of doing business, a wise proprietor will turn off the lights and lock the doors until spring.
Some enterprising holdouts stay solvent longer than others who are in the same business. Perhaps they have less competition or a better location. Conversely, a few businesses close
their shops at the first whiff of autumn. Those are the ones that just barely scrape by at the height of summer.
I’m talking about trees here, of course. Trees whose leaves show color ahead of their same-species peers are doing so because they are barely breaking even. In fact, they are probably not long for this world.
The solar-powered sugar factories we call trees are prudent savers and meticulous accountants. As a rule, they run a tight ship and don’t live beyond their means. In addition to sunlight, they need carbon dioxide, enough water and nutrients, and their roots need to breathe.
A tree’s income is sugar, which is converted to starch and deposited in the equivalent of a savings account – trunk and root tissues. Each spring, a deciduous tree withdraws money from the bank and invests in a solar-panel array, known as leaves. Over the summer, trees replenish their starchy bank accounts for the cost of making leaves, and then sock some extra away for emergencies.
Ongoing tree expenses include respiration, and maintenance like the synthesis of antimicrobial compounds in response to injury. As summer wanes, costs remain the same, but the solar panels can’t make as much sugar due to shorter days. Income falls as the hours of daylight continue to shrink, eventually forcing hardwood trees close for the season.
However, if a tree has problems getting water or nutrients, or if root respiration is hindered because its root zone is compacted, it struggles even in the best of times. Compared to other trees, it is disadvantaged. As a result, that tree’s solar-powered sugar factory will be less efficient compared to others of its kind, and less profitable overall. Poorly drained soils, deicing salt exposure, and mechanical damage also compromise root function.
Landscape trees experience high soil temperatures, restricted root zones, and intense competition from grass. Waterfront trees have other challenges: fluctuating water levels tax
root systems, and those soils tend to be nutrient-poor. Stressed trees reach the break-even point earlier than robust ones, and they will show color first. This is why you often see the first leaf colored leaves on the edges of ponds, lakes, in addition to along roadsides.
Early color is a reliable sign of critical stress, but palette gives information as well. Orange (carotenes) and yellow (xanthophylls) are already within the leaves, masked by green
chlorophyll. First a little background: In autumn, trees make a waxy layer at the point of attachment between twigs and leaves to seal off the vascular connections. This is to protect the tree from freeze injury. It’s kind of like winterizing a camp – you can’t leave the water spigot on. As leaves are thus choked off, the chlorophyll dies, revealing yellow and orange.
The red-purple range (anthocyanins), though, is another story. Red pigments are manufactured in the fall by some species, maples especially, at significant cost. Science has yet to come up with a plausible explanation for this. The point about red is that a maple showing lots of red color is strong enough to “waste” energy making anthocyanins. But maple that only has orangey-yellow leaves is in real deep doo-doo.
If one of your trees turns color early, or your sugar or soft maple is devoid of red fall foliage, that’s a clear message in tree sign-language that its health is in free-fall. If that is the
unfortunate case, it would be a good idea to hire an arborist for an evaluation to see what actions, if any, may be appropriate to help prolong its life.
Paul Hetzler is an ISA-Certified Arborist and a former Cornell Cooperative Extension educator.