Dilemmas of dealing with invasive species

The rest of nature, too, revels in heat and light. The fragrance of coumarin from new-mown hay, in fields restored to meadows once again, mixes with the heady scent of honeysuckle, frothing in pink and cream across the fuchsia hedges of the west. Our exotic shrubberies have really come into their own: not for years have the spiky palisades of New Zealand flax hoisted such splendid masts of blossom, their sheaths of gold and purple bursting into flames of crimson flowers, the anthers tipped with vivid orange pollen.

Phormium tenax is one of those exotically "architectural" plants whose lateral growth can, at length, seem exponential. Ours, a pink-washed hybrid bought in a pot a couple of decades ago, must now be hacked back every few months to allow swift passage in and out to postman Dave. Elsewhere along the coast, Phormium is a common windbreak of farmhouse shelter belts, defying the saltiest of gales. Since these must date from long before the first Mayo garden centre, one can only conjecture on a neighbourly traffic of offsets from some distant estate.

Botanically a giant relative of the day lily, the plant’s natural habitat Down Under is in lowland swamps, which makes its success along Ireland’s coastal hillsides a little strange. But at least, even uncorseted, it stays more or less where it’s put, unlike another swampy triffid in the west, the equally “architectural” but invasive gunnera, from South America, that waves great umbrellas rather than swords.

While the fibres of New Zealand flax may never find in Ireland the myriad uses of its native history (now, even surfboards), it does make occasional offerings to our wildlife. At home, and called the harakeke, its generous supply of nectar is food for the tui, a glossy and voluble bird (“the nightingale of New Zealand”) whose beak nicely matches the curve of the flax’s flowers. Ireland’s birds might be thought to lack both an interest in nectar and the right sort of beak. Yet, earlier this month, a Dublin reader on a visit to Achill, Frank Barton, saw a flock of some 20 young starlings busy at the flax blossom, their foreheads brightly dusted with the orange pollen. He thought the curve of their beaks “ideal for extracting nectar, some of which was spilled in the jostling and highlighted by the sunshine.” This recalled past reports from Wicklow, both of starlings and a great tit, in similar behaviour. So we do have birds to match the tui in fertilising viable seeds. The plant’s long pods hold hundreds and release them into the wind.

A recent national survey of Ireland's 900-odd alien plants by Sylvia Reynolds did list "apparently self-sown" Phormium plants at Dunmanus Bay in Co Cork, and others on a cliff at Ballybunion, Co Kerry "were unlikely to have been planted". If more little Irish birds catch on to Phormium as a food source, its presence in likely habitats could grow, joining the current sparse scattering of wild New Zealand cordylines, hebes, willowherb and hairy pennywort. These are nothing, of course, compared to the spread of Japanese knotweed, Himalayan balsam and giant, corrosive hogweed from the Caucasus, all garden escapes into the wild. A picture of the balsam in massed and seductively lovely pink flower along the banks of the lower river Barrow was a dramatic, if familiar, prompt at the Invasive Species Ireland forum that was held in Belfast recently.

More speakers showed the impact of alien water plants, dumped from garden ponds or aquariums and now carpeting the surface of lakes and rivers. Alien freshwater molluscs and fish, alien mammals and insects, alien seaweeds and ocean invertebrates: Ireland is beset by incoming species at a pace never equalled in the island’s history and boosted by human hobbies, travel and trade.

Where do we draw the line in resisting alien species, and is the effort and cost of controlling them becoming a hopeless rearguard battle? After the last ice age, our bare and soggy island was steadily colonised by species, both naturally and in the course of human settlement. Those we now call native have been the most successful in making themselves at home as part of evolving but stable ecosystems.

There was a time in conservation when ecologists could afford to be quite chauvinistic in protecting or restoring prized Irish habitats. Thomas Pakenham once described as “a kind of ethnic cleansing” the move to eradicate naturalised trees, such as beech and sycamore. Today, ecologists have had to sort their priorities. “Conserve biodiversity and sustain human livelihoods” is the widely accepted global aim.

The invasiveness of species, not their origin, is already the measure of conservation campaigns in Ireland, whether to protect the future of tourist angling or save native vegetation from being overrun. As costs mount, and climate change offers survival to yet more alien arrivals, sustaining human livelihoods will become the more immediate claim. The slow surrender of the countryside to new mixes of plants and associated wildlife will do no more to nature than human agriculture, forestry, industry and infrastructure have done to this world already.