No matter how hard we cling to the long light, crisp mornings and golden trees, fall, like all good things, must eventually come to an end. Autumn is gasping its last breaths here in the boreal forest as the cold November winds sweep away the last of the colour and hard frosts condition us for the deep freeze to come.
Our last blaze of glory before the forests fade to the dull greys and bleached greens of winter comes from an unlikely source, a tree that should be an evergreen. I’m talking about the Tamarack (Larix laricina).
Also known as larches, tamaracks are conifers, needle-bearing trees; but unlike their boreal forest brethren, they are one of the only North American evergreens that don’t remain ‘ever-green’. Tamaracks are deciduous conifers, a beautiful paradox that bring one last flash of light to the forest before it’s extinguished by the wind scattering their needles all over the ground like a Christmas tree in January.
So, why do they do it? Did larches miss the ‘conifers are evergreens’ memo?
The jury seems to still be deliberating on the evolutionary history, costs and benefits of this strategy, but when you take a step back and think about it, larches are taking advantage of the best of both worlds. Broadleaf trees, like aspen and birch, create leaves that are relatively cheap to produce, with a large surface area-to-volume ratio that makes them high-efficiency photosynthetic factories. Unfortunately, that large surface area also makes them incapable of handling wild swings in temperature and moisture. So, deciduous trees cut their losses and lose their leaves when conditions no longer favour them.
Conifers take a different approach. Their needles are built to last, their low surface area-to-volume ratio and waxy covering make them much more resistant to temperature and moisture extremes. This allows the tree to keep them all year, which is necessary, because they don’t produce nearly as much energy through photosynthesis as their deciduous counterparts.
Tamaracks straddle the fence. Their needles are soft and long, with thinner cuticles and a little more surface area. This allows them to make the most of the summer sun and produce as much food as possible through photosynthesis, while protecting them from the wild swings in temperature and moisture typical of the northern boreal forests. Having needles also makes it possible to extend their season, turning sunlight into food right through to the end of October. Then, when the frosts set in and snow is in the clouds, the photosynthetic pigments shut down, leaving the needles a brilliant gold before they flutter to the ground. Without the added strain of maintaining their needles, the tree can survive harsh winters that can sometimes damage other conifers.
This strategy has allowed tamaracks to survive and even thrive in some pretty difficult habitats, from the edge of the Arctic treeline to the waterlogged and acidic soils of bogs.
As a field biologist, I’ve had sort of a love-hate relationship with tamarack. Whenever I spotted a stand of these trees towering in the distance along my survey line, I knew that I would soon find myself up to my knees in water and would spend the rest of the day trying to dry out my boots. Then, I would find myself in their midst, their soft, feathery limbs brushing me as I passed as though welcoming me into their world. Now, it’s a world a return to visit as often as I can.