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Cold weather has stalled the critical wake-up process for trees

April soakers are needed to ensure a lush, green summer
2018-04-01 hawkes ugar Maple flowers.jpg
Sugar maple flowers. David Hawke for OrilliaMatters

A spring thaw of sorts has finally happened. Not the hoped-for blast of hot air that melts icy snowbanks into puddles over the course of a day, but at least a warming trend that gets above the freezing point for a couple of hours a day. A slow and steady crawl into springtime.

As glad as I am to see terra firma showing its face again, I do worry about the snow reduction process we are going through. All that knee-deep snow was retained moisture that should now be going into the ground, saturating the soil and starting the wake-up process for trees. Not happening. Not good.

The previous two weeks of clear blue sky and plus three degrees may have been a delight to us sun-seekers, but it didn't really melt the snow, it just evaporated it! And the minus 10 degree nights kept the surface frost intact, continuing to act as a barrier. Instead of tiny rivulets of water seeking and saturating low spots, the frozen liquid went straight to gas vapour and drifted away, leaving our soils rather dry.

All plants need water to grow, a valuable lesson we should have learned before graduating from Grade 2 science. What is interesting about trees, is how much water they need to sustain themselves. A bit of an internet search revealed that a single corn stalk needs about 200 litres of water over a growing season, whereas a large tree in a rainforest will process 1,200 litres a day! The water needs of our local oaks and maples sits somewhere around 200 litres a day. That is a lot of water for each tree, every day.

Apparently a tree retains only about 5% of its daily moisture intake, the other 95 per cent being released almost continuously via transpiration. So what's up with this high demand of intake that is balanced by such a high rate of discharge? The answer lays within the soil... and the leaves. Let's start at the bottom and work our way up.

Soil is gritty, made from ground-up rock particles, and in between each soil particle is a gap, a space. When a water droplet first enters this space it pushes the particles apart and loosens the soil, then the minerals and nutrients held within the soil particles dissolve and mix with the water. This is known as tree food. And to get this wet food inside itself, a tree needs to use its rootlets.

One other thing about soil, before we get carried away with the functions of root systems, is that the natural litter found on a forest floor must somehow become broken down and mixed with the soil. That layer of leaves, twigs, animal scat, and tiny carcasses can add up to about one ton per acre. (And now you know why you are so tired after raking leaves!)

A wide array of bacteria and fungi begin the dismembering of a cast-off leaf, breaking the nutrients apart. Along comes an army of centipedes, springtails, mites, snails, worms and dear knows what all else to mush the rotting leaves into the soil, perhaps even carrying it downwards via tiny tunnels.

That water solution seeping between the soil particles now contains both earth minerals and organic nutrients. And here come the roots.

Any tree worth its name has a wide assortment of roots, some growing deep down to anchor the structure in place, others spreading outwards, seeking new frontiers, to boldly grow where no other roots have grown before!  Okay, so I'm overemphasizing a bit. Live long and prosper, eh?

The very tippy tip of a new rootlet is soft and porous, allowing moisture to seep inside. Cool fact: The dry side of a root grows long thin cells, and the damp side has shortened cells, thus causing the root to bend towards moisture, a process called hydrotropism. The absorbed nutrient-rich moisture then begins to travel through the root, passing into larger sections that have now grown a thick protective bark-like coating. A couple of twists, bends, and curves, and up the trunk it flows!

The wood of the tree trunk only needs moisture within the new growth cells, called the inner bark. While moisture is needed, only a small amount is retained, the rest travelling upwards to the leaves.

Leaves collect sunlight as part of photosynthesis, that amazing ability to convert solar radiation into sugars. Part of this complex process involves small pores (called stomata) opening on the underside of the leaf to collect carbon dioxide from the air. And here the tree has a problem. As the stomata open for CO2 intake, a great amount of water exits as vapour. Since the stomata are open for most of the day, water is continuously lost from the same openings.

As all this water goes whoosh and away, it creates a bit of a vacuum for the next bit of water to move into place until it too disappears to be replaced by the droplet behind it. And so it goes all down the tree, right down to the roots, right out to the rootlets. Water is absorbed and then flushed straight through and out the leaves, with the good stuff being extracted along the way.

In my long-winded story it comes back to show that growing trees need moisture, and lots of it. If the snow evaporates, and the spring rains are slow to appear, tiny waiting rootlets begin to desiccate, dry up and become useless. Too much of that nonsense and the tree may be in peril of dying or being stressed.

On that 'happy note', let's hope for a few real soakers in April to ensure a lush green summer. Until then, just enjoy the sunshine.