04/09/2026
AMAZING REBIRTH OF A TREE
Four days from dormant to flourishing
An absolutely stunning transformation took place in the great old oak tree on our lawn during the past week. On Monday it was completely bare after winter. By Friday it was in full green leaf. This year the oak has - most unusually - beaten the willows at the river to put on spring garb.
We live beside the Vaal River on the Highveld of South Africa which is cold and very dry in winter. The season we have just gone through was all browns and faded yellows. Suddenly everything is rupturing the stillness.
Summer seems to have arrived very early with the kind of hot days more typical of October than the end of August. The oak took this as its signal to get going.
But something else scientifically fascinating prompts me to ask a question: how does such a mighty tree find the energy to burst into leaf at the end of a long winter with no rain and harsh cold spells?
Part of the explanation - obviously - is that its underground root system finds water and "pumps" it up as lifegiving sap into the trunk, branches and twigs. But something else is involved. This is no mechanical pump.
I'm no botanist but I am curious about what's going on the tree, so investigated.
We need to understand what a strange substance water is. It is plentiful in the solar system but it has extraordinary properties that have made all life possible. Its molecules cling strongly to one another and to other surfaces, allowing an unbroken thread of water to be drawn upwards through the finest vessels of a tree against gravity.
These same unusual properties—along with its remarkable ability to dissolve substances and store heat—are among the reasons water makes life as we know it possible.
Water molecules stick to one another — cohesion — and to the walls of the microscopic xylem vessels in the tree — adhesion. Surface tension and capillary forces help maintain columns of water inside the tree.
But the main driving force begins at the top, not the bottom. Once leaves start developing, water evaporates from their surfaces through microscopic pores called stomata. This evaporation, or transpiration, creates negative pressure — tension — within the xylem.
Because water molecules cohere to one another through hydrogen bonding, water lost from the leaves effectively pulls the column behind it upwards, all the way down through the trunk to the roots.
So a great oak is less like a building with a pump in its basement than an extraordinary biological wick (as in a paraffin lamp) under tension, with evaporation from above pulling water upwards from below.
One puzzle is how a tree with no leaves can begin its rejuvenation to start with.
Before there are open leaves, the oak cannot generate much transpiration to pull through stomata. The initial awakening is powered and supplied differently.
During the previous summer and autumn, the oak stored carbohydrates—especially starch—in its roots, trunk and woody tissues. When winter dormancy ends, enzymes convert some of that starch back into soluble sugars. Those sugars provide both the energy and raw material needed for dormant buds to resume cell division and expansion.
From now on I will look at our oak tree with a good deal more respect for its scientific know-how. It is beautiful AND clever. So are all growing things.
The oak presents a lovely chicken-and-egg story: it needs leaves to operate its main water-lifting system, yet it needs water and energy to make those leaves. The solution is that the tree carries enough stored resources and has enough pre-formed machinery to get the first leaves open.
Then the solar-powered, evaporation-driven system takes over.
Would that we were so clever.
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