The Ecology of Spring

David Beeson, February 2023

Brimstone butterflies emerge in late winter.

Our chunk of rock we call Earth and it sits in space, some lucky distance away from our star.  We neither freeze nor fry at this distance. Our planet had a minuscule chance not to rotate and a near 100% chance to turn on its axis and this rotation gives us our day and night sequence. Any other rotational speed would not give us our 24-hour days. In a similar way, we had a very small chance that our axis was square to the Sun and a near 100% chance that it would be angled … and that ensures we have seasons. In summer the northern hemisphere is angled towards the energy source and warms, and in winter it is turned more away and our country receives less solar input and is cooler.

In Southern England, I am experiencing the phased warming of my environment as I’m turned to gain more solar radiation … spring is coming! About time, as I’ve had enough of a cold winter, thank you. Forgetting for a moment global warming, I’m looking forward to a warmer environment and a bursting of plant life.

We all understand that sunlight energy is the driver of life on Earth. That energy warms the soil, seas, organisms and the air as well as being partly absorbed by photosynthetic plants.

The universe is about gradients. Cars move down hills, without using their engines, along an elevation gradient. Currents (electrons) move in a circuit, from a battery, along an electrical gradient. Oxygen moves into our blood along a chemical gradient. Energy flows from the Sun to us along a gradient. Indeed, heat energy moves from our planet into space along a gradient … but can be delayed by carbon dioxide (and methane etc) in the atmosphere, giving us atmospheric warming. Some warming is vital to life as we know it, too much is an issue. A very worrying issue.

Native green hellebores at Forest Edge.
Woodland plants usually store resources underground and can grow as soon as the temperature is suitable for them.

All solar radiation is not equal. It arrives in a wide spectrum of wavelengths, with only the red and blue aspects capable of being used by most green plants. Of course, green plants look green because they cannot absorb green light, just as a red jumper can absorb all wavelengths except red, which is reflected into our eyes. So, it is the red and blue wavelengths that drive the food chains on Earth and cause the release of oxygen.

(Incidentally, our planet’s atmospheric oxygen is from the photosynthesis carried out by non-decayed plants – our fossil fuels. If they were fully decayed the process would use up all our atmospheric oxygen. A good reason for leaving them underground.)

Here, in late 2022 a few hazel leaves still held. By February the winter frosts had encouraged them to be shed. With low temperatures and a lack of solar energy the woodland floor is bare. But, the bluebell bulbs have stored supplies and growth will soon commence.

So, with spring approaching the energy input to my local environment, Harewood Forest, is increasing. Here the dominant vegetation is deciduous trees, mainly oak and ash. They have lost their leaves when their roots were too cool to absorb replacement soil chemicals and their flimsy leaves lack protective chemicals to inhibit leaf freezing. With freezing conditions, water molecules in leaf cells change from liquid to solid, and expands. Under these circumstances, the cells would burst and the resources both be lost, and their extracellular availability would encourage bacterial and fungal disease. So, the plant is better to shed its vulnerable leaves and cut the losses, having first hidden away useful resources in roots or trunks.

With February moving to March, sunlight energy now increasingly reaches the ground and warms it. The few surviving green leaves can potentially capture this in photosynthesis and use it. The question now is, how best to use this? There are options, including a) growing new leaves, b) reproducing, c) protecting themselves chemically or d) storing the energy chemically as starch or oils. And, as you already know, each species will make different choice packages. Dog’s mercury will use it, with previously stored resources, to flower. Woodland grasses will grow new leaves and leave reproduction until later. Ferns may build up protective cyanide in their cells. Those species with better strategies for that site will increase in numbers, and the less well-adapted will slowly vanish. Survival of the fittest, extinction for the rest.

We all know sites where fires or human management have changed the environment with a resulting change in the ground-level plant species. Change the environment, change the successful species.

With warming soil, and the promise of more input energy to come, some plants use up stored resources from last year. Plants with bulbs, corms, tubers or rhizomes can mobilise these and generate new leaves very early in the season. These are the species that often dominate in dense summer-shaded places. Early flowering is also a possibility as pollinators will be keen to get involved, so enhancing their own resources.

Native daffodils at Forest Edge. They occur wild in the adjacent woodland.

Locally we already have bulbous snowdrops and daffodils and crocuses, together with green and stinking hellebores all in bloom. In more open locations common daisies have been flowering for some time. (And gardens will be filled with the odd plants that buck the trend to flower in cold conditions – forsythia, witch hazel and some viburnums.)

As spring approaches, plant chemistry is speeded up by the elevating temperatures. The growth rush begins as enzymes ramp up plant metabolism. Even a small raise in the environmental temperature can double the speed of plant activity. Meanwhile, enhanced fungal activity will break down the autumnal leaves releasing their growth-stimulating nutrients. Life ramps up.

Soon deciduous trees and shrubs will produce their leaves, causing wind speed in woodlands to drop and put an end to easy wind pollination. Hazel catkins will fall away, their task completed. The light at the soil level will soon fall as it is captured in the canopy, soil moisture may decrease, and the woodland floor will become comatose again. But, until then, those of us who enjoy ecology will relish the delight that is spring.

Snowdrops and crocus at Forest Edge.
On warm days the bees take advantage of early-year flowers.

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