Bracken

A closer Look at Bracken -

Bracken evolved as a woodland species but has become invasive where there is full sun on hillside across the UK. It is seldom eaten by cows, deer and sheep as it is poisonous and contains known carcinogens.  Even the spores are carcinogenic.

Young fronds give off hydrogen cyanide and ptaquiloside when damaged. The ptaquiloside can leach into the soil and cause contamination of water supplies. Bracken has chemicals (tannins and cyanogenic gycosides) which act as insect repellents.

In addition Bracken can produce chemicals which mimic those use in moulting by insects. These chemicals lead to uncontrolled moulting and death for the insect.

Bracken crowds out other plants and deprives them of light. Its fronds decay to produce chemicals which inhibit the growth of other plants. This is called allelopathy.

Bracken and Ants

Bracken has extrafloral nectaries on the under surface of its fronds which produce a sugary nectar which attracts ants. Formica lugubris, Formica lemani and Myrmica spp. have been shown to feed at these nectaries. There could be an advantage to the Bracken as potentially the ants could reduce herbivore numbers but this has not yet been proved.

Insects which feed on Bracken are -

Moths
Moth caterpillars - Brown silver-line moth, Garden tiger moth, Small angle-shades moth, Orange swift moth and Gold swift moth.

Sawflies

The larva of the sawfly, Strongylogaster multifasciata feed on Bracken.

Bugs

The Bracken bug, Monalocoris filis feeds on the sporangia of Bracken and other ferns.

The Common froghopper feeds on Bracken.

The rare butterfly, The Pearl-bordered Fritillary benefits from Bracken as it gains shelter from the dead Bracken fronds in the spring. The butterfly is on the wing earlier than most other species.

Control of Bracken.

The herbicide, Asulox, has been used widely to kill bracken but is now no longer legal to use it in Scotland as it is toxic to aquatic life.

Planting trees is useful as the shade that they create inhibits the growth of Bracken.

Cattle may damage the rhizomes as their feet penetrate the ground and wild boar rooting around in the soil will do the same thing.

Burning actually encourages the Bracken as it removes competition from other plants and the Bracken sprouts up again from its underground Rhizomes In short burning is counter productive.

Cutting (or Bracken bashing) is very labour intensive and needs to be repeated many times to have a significant effect. In days gone by Bracken was used for bedding for animals and people and this helped reduce it.

Experiments with machine cutting and using the Bracken for biomass have been undertaken but only on a small scale. Hilly country makes it hard to cut the Bracken with machinery.

Industrial Uses

Bracken was widely cut and burnt to get the chemicals needed for the glass and soap industries.

Richard Paul