Late frost

There was a frost on Saturday night.

Night frosts are nearly always followed by early morning sun. The frosted tender foliage and flower buds of developing plants thaw too rapidly in the sunshine and their cell walls burst. It can take a few days for this to become evident but the leaves and flowers turn brown and die.

While climate change is bringing us earlier and warmer springs, it doesn’t seem to have much changed the date or frequency of the last frosts. This can make them particularly damaging to trees which are beginning their spring growth earlier every year.

Leaf buds and oak flowers

Oak trees are usually very resilient to frost damage. They always have dormant leaf buds in reserve for just such an emergency; these dormant buds will be activated as the frost-damaged leaves die, and will make new leaves. By midsummer it will be difficult to see that there ever was damage. But a late frost can damage or kill the flowers of an oak, particularly the female flowers which form the acorns and are usually higher in the tree; the flowers have no recovery mechanism and this will mean fewer acorns in the autumn.

Winter moth caterpillar, knopper gall on an oak, and a blue tit

The caterpillars of the winter moth feeding on new oak leaves have a built in anti-freeze so will have survived the frost; the blue tits feeding their young on winter moth caterpillars will also be OK. But the knopper gall wasps that lay their eggs in developing acorns may have a harder time of it and the hornets and wasps that prey on the newly hatched gall wasps later in the year will also suffer.

The squirrels, ever the generalist feeders, will be fine; a poor crop of acorns will hardly affect them. They will move on to the hazel, which have already set their fruit and will have suffered no damage from the frost – but the specialist dormice, which rely on the hazel nuts, will suffer from the competition.

The park is an ecosystem; a blow to one part of it can travel through the whole of it.

Header and footer pictures by DKG


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