Flourishing in the freeze

OVER the past few weeks I’ve listened to a lot of people complaining about the weather.

I’ve grumbled a bit myself, particularly the day I attempted to go fishing from an open boat on Lough Ree and was driven ashore by the bone-chilling cold.

Temperatures have been at least 10 degrees lower than they were in March and early April last year. Uncomfortable but there were compensations. There are two main factors controlling the arrival of spring at these latitudes —- temperature and day-length. In some species of plants, insects, birds and amphibians temperature is the dominant factor, in others it’s the amount of daylight.

So far this spring we’ve had unusually low temperatures but the light levels have been normal, or even better than normal. This has given nature watchers an opportunity to separate the temperature dependent species, which are behind schedule, from the light dependent ones, which are on time.

Air temperature, of course, is only one part of the equation. Soil temperature is what counts for many plant species and some insects. As spring advances soil temperature lags behind the daily average air temperature, often several weeks behind. When it does start to catch up it warms from the top down. This means that shallow rooted plants, like grasses, get the benefit before more deep-rooted plants like trees and shrubs.

For many plant species, and some invertebrates, particularly those with larvae that over-winter in the soil, the crucial temperature seems to be between six and eight degrees. As far as aquatic life is concerned its obviously the water temperature that’s vital and this also lags behind air temperature. In deeper water things are complicated by the fact that water is at it densest at four degrees. When the surface water reaches that temperature in the spring sunshine it sinks to the bottom —- this is why ice floats —- and it’s replaced by colder water.

So in my local canal some complicated processes are going on that control when the dormant water lily rhizomes in the mud will stir into life and send up shoots towards the bright light at the surface. The same processes are controlling when fish will spawn, frogs will mate or dragonfly larvae will turn into winged insects.

But evolution does not like putting all its eggs into one basket and many species will do what they’re supposed to do despite exceptionally cold weather. At the height of the cold snap my free range hens all came into lay. Their pineal glands were stimulated by the extra daylight and they ignored the low temperature.

Nature table

HAWTHORN (Crataegus monogyna)

The hawthorn, also known as white thorn and sometimes as May bush, is the commonest native Irish tree. It grows everywhere except at high altitudes or in pure sand or peat. It’s often only a shrub or a trimmed hedge plant but it’s capable of growing into a long-lived tree up to 15 metres in height.

The bright green, lobed leaves appear around now and are edible. The flowers are white, often fading to pink, and appear in mid May. They are followed by fruits called ‘haws’ which have a single pip and ripen to a red colour. They are also edible, though not very appetising, but they stay on the tree well into winter and are an source of food for birds and small mammals.

The dense, reddish timber makes good firewood but the principal use for hawthorn, from prehistoric times until the availability of cheap wire, has been as stock-proof hedging. Most ‘fairy trees’ are hawthorns.