Moving with the seasons: natural strategies for survival and growth
In the Netherlands, we are situated at 52 degrees north latitude, closer to the North Pole than to the equator! Brrr. And yet, for our northern location, we have a relatively mild climate, thanks to the warm Gulf Stream.
The farther from the equator, the more distinct the seasons and the greater the difference in daylight length between summer and winter.
The animation below clearly shows how, within a single orbit around the sun, warmth moves from the north to the south and back again. You can also see that the farther you are from the equator, the greater the difference between summer and winter – not only does it get colder or warmer, but the days also get longer or shorter. And to survive above the Arctic Circle, trees must be strong enough to withstand temperatures of minus 70 degrees Celsius and long dark periods.
Survival strategies
Even a bit of frost poses a significant challenge for plants. The process of photosynthesis requires a lot of water, and when it freezes, water cannot be transported from the roots to the leaves. Since ice can also evaporate directly (the phase transition from solid to gas is called sublimation), leaves slowly dry out in frost. To prevent frost damage, trees have found two solutions:
Withdraw as much sugar as possible from the leaves in the fall and then shed the leaf;
Minimize evaporation from the leaves.
Many tree species at our latitude follow the first strategy. They wait until the chance of prolonged frost has passed and then sprout again in the spring. Most conifers follow the second strategy (deciduous conifers such as the Larch and Metasequoia are exceptions). It is much easier to stop evaporation from small, thick needles than from thin leaves with a large surface area. An exception is the Holly. It is the only native evergreen deciduous tree. With a very thick, leathery skin combined with antifreeze compounds, this species manages to guide its leaves through the harshest winters.
Budding
Spring, that cheers everyone up, right? As soon as February arrives, you notice the days getting longer and nature slowly but surely awakening from its winter sleep. Yet, for trees at the beginning of the meteorological spring on March 1st, the 'frost danger' is not yet over.
March can still bring severe frost, April may occasionally wear a white cap, and even until mid-May, night frost can occur. Some tree species, such as the birch, bud early. Other, more frost-sensitive tree species like the albizia, play it safe and wait until early May. A single night of frost can be disastrous for the young leaves. Whatever the winter brings, every spring is a battle to catch as much sunlight as possible. Depending on the variation between the years, one survival strategy may work out better than another.
With the warming of the Earth, the growing season is getting longer and the sharp winter cold is disappearing (the coldest days warm up the fastest). A challenge for some species but favorable for vegetation in general. Who knows, maybe one day palms will grow above the Arctic Circle again?
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