• The Low Down

Tree sign language: early fall colour

Deciduous trees, ice-cream stands and marinas close each fall for the same reason: as daylight dwindles and cold creeps in, they become less profitable. When their income dips below the cost of doing business, a wise proprietor turns out the lights and locks the doors until spring.


Some holdouts stay open longer — perhaps they have a better location. But the establishments which just scrape by at the height of summer will close shop at the first whiff of autumn.


Trees whose leaves show colour ahead of their same-species peers are doing so because they are barely breaking even. The solar-powered sugar factories we call trees are prudent savers and meticulous accountants. As a rule, they don’t live beyond their means. In addition to sunlight, they need carbon dioxide, enough water and nutrients, and their roots need oxygen.


Each spring, deciduous trees withdraw money from the bank – starches out of trunk and root tissue – and invest in a solar array, known as leaves. After replenishing its starch-bank for the cost of making leaves, tree expenses include respiration, and producing protective chemicals in response to injury. Income is sugars; savings account, starches.


As summer wanes, longer nights drive up respiration costs, while shorter days bring down income, eventually forcing hardwood trees to close for the season. However, if a tree’s root zone is compacted, root respiration is hindered and they’re less efficient.


That tree’s sugar factory will be less profitable compared to others of its ilk. Poorly drained soils, deicing salt and mechanical damage also compromises 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 will colour first. This is why you often see the first leaf colour on roadsides or the edge of ponds and lakes.


Early colour is a reliable sign of tree stress, but palette gives information as well. Orange (carotenes) and yellow (xanthophylls) are already in the leaves, masked by green chlorophyll.


Trees make a waxy compound in autumn to block water and nutrients to their leaves, equivalent to winterizing a camp — it protects the plumbing. As leaves are thus choked off, chlorophyll dies, revealing yellow and orange.


The red-purple range (anthocyanins), though, is different. Red pigments are manufactured in the fall by some species like maples at significant cost. The point about red is that a maple showing lots of it is strong enough to “waste” energy making anthocyanins.


If one of your trees turns early or your maple is devoid of red fall foliage, that’s a clear message in tree sign-language. It would be a good idea in that case to hire an arborist to evaluate it.


Paul Hetzler is a Val-des- Monts resident and ISA-certified arborist.