Another Life: Bluebells, boar and bracken

There's one view that sees a carpet of bluebells as a sin against biodiversity: just one species of plant crowding out everything else that might want to grow in a wood. Bring back the wild boar, it's urged, and see how its rooting snout, munching the bulbs of Hyacinthoides non-scripta like so many pickled onions, can restore a more natural variety of flora.

I'm rather more with Gerard Manley Hopkins and his "falls of sky-colour washing the brows and slacks of the ground with vein-blue", not to mention the way, as you close your fist to pick them, the stalks rub and click "in a juicy and jostling shock".

Peering for some reason around a corner of the tunnel, where ancient wheelbarrows go to die among the sheltering trees, I was dizzied with pleasure and surprise at, if not a carpet, then almost a couple of doormats of bluebells in bloom where I’d stuck in a few bulbs from a friend (who really has carpets under his oaks) some years ago.

I picked enough to fill a ceramic vase that I’d always seen as blue, but the flowers’ piercing violet suddenly turned it turquoise. I remembered the big, imitation cut-glass vase I stuffed with the sheaf of limply wilted bluebells, borne home on my handlebars from a distant Sussex wood – far too many and beginning to smell of tomcat.

It's in some of those woods now, apparently, that feral wild boar have established small populations, and enough people have grown worried for the local bluebells to warrant a scientific study of what boar actually do to biodiversity (Boar, Bluebells and Beetles, by three Forestry Commission researchers). It found that, even after 20 years of the boar, bluebells "are not unduly threatened" (although the number of flowers may decline) and that the rooting "can create a good seed bed in which other species can regenerate".

Ireland's introduced wild boar, denounced as an unwelcome and invasive species, have been reported thinly but widely across the country – 39 reports so far to biodiversityireland.ie, with a hot spot down at the southeast corner.

Their potential carriage of nasty, foreign swine diseases make it unlikely that we shall see them employed, as in experiments elsewhere, for rooting out invasive bracken, which continues to spread in Ireland by more than 3 per cent a year.

A decade ago I wrote of increasing concern about cancer-causing toxins in bracken and the threat to human water supplies sourced from fern-blanketed hillsides. The first studies came from the University of Wales, and then from a Danish scientist, Lars Holm Rasmussen. In 2003 he reported extremely high levels of the bracken carcinogen, ptaquiloside, in Danish and Swedish farm and village wells. The toxin is easily leached from the fronds, and Rasmussen thought it could explain concentrations of gastric and oesophageal cancer in many parts of the world.

This has now been followed by all-Ireland research, just published online, in Molecules, as Ptaquiloside in Irish Bracken Ferns and Receiving Waters, with Implications for Land Managers (at mdpi.com/1420-3049/21/5/543).

A 10-strong interdisciplinary science team, led by the Trinity College Dublin environmental engineer Connie O’Driscoll, studied nine bracken stands: two in the west, six in Northern Ireland and one in Co Louth.

The environmental load of ptaquiloside was highest in the densest bracken as its fronds flourished in June, with a rapid decline as the fern withered in autumn. Frond concentrations of the toxin were lower in the west, with its heavier rainfall, than in the north and east. It was high in water drawn from a hill stream in Co Mayo and lower in two groundwater spring wells. (All this in October.)

The report is the first to look at bracken management since the EU phased in a ban on the use of Asulam, the most effective herbicide in bracken control, becoming total next November. It refers to “an expectation of widespread bracken invasion” and concludes that spraying with herbicide, rather than cutting, is the most effective control. Indeed, it found, cutting “may increase the production of ptaquiloside in the short term and hence the potential risk to drinking water”.

It didn't, understandably, consider wild boar, but one study has reported on their experimental use, as at Dundreggan, the big Caledonian forest-restoration project in Scotland (An Evaluation of the Use of Pigs as a Method of Bracken Control", by Julia Henney, at grazinganimalsproject.org.uk/habitat_land_management.htm).

It seems that the boar do reduce the great networks of underground bracken rhizomes as well as increasing floral diversity. But too much bracken on its own may not be good for them, “leading to a thiamine deficiency exhibited as a nervous disorder and eventually leading to death.”

And wild boar with nervous disorders may not be the most amiable to meet while picking bluebells in the woods.

Michael Viney's Reflections on Another Life, a selection of columns from the past four decades, is available from irishtimes.com/irishtimesbooks