Beware Himalayan climbers getting a foothold on a bank

ANOTHER LIFE:THE PLANT THAT burst into bloom in our gateway a few years ago was new to my eye, certainly pretty, and grown, perhaps, from a seed thrown off a passing lorry. Picking it to paint it was, perhaps, a lucky impulse. Left to produce its own seeds, it could have sprayed them explosively, raining little black ball-bearings for several metres all around.

The banks of the stream that ducks through a hollow at that corner of our acre could now be choked with thickets of Impatiens glandulifera, or Indian (Himalayan) balsam, joining the existing jungle of Fuchsia magellanica, the alien from Argentina.

Both plants have beautiful flowers and each can be invasive, given the chance. Of the two, however, the annual, easily-pulled balsam is an international villain, while fuchsia, a much-admired shrub, is a devil to uproot and resprouts from any fallen branch. Such little quirks abound in the war against invasive aliens, now among humankind’s more costly and urgent undertakings.

The lush Indian balsam, for example, the tallest annual plant in Ireland, is beloved by bumblebees. They nuzzle into its pink bells for nectar and back out, gilded brightly with pollen (“bee-bums” is, reportedly, one of the plant’s folk names in Britain). That may be all right for bumblebees, cry balsam-bashers, but the bees might then not bother to pollinate the native plants next door.

"Balsam bashing" before the plants flower and seed is now a well-established rite of early summer among voluntary conservation groups in the UK. In one recent exercise, some 1,800kg of the plant were cleared from the banks of rivers in southeast London. Similar "balsam bashes" will be held along Irish rivers during Fisheries Awareness Week (May 12th to 20th). The website of Inland Fisheries Ireland, fisheriesireland.ie, invites teams of volunteers to sign up for a day's labour in wellies and gloves which should end, the group recommends, "with a hearty barbecue, some cold drinks and a rousing sing-song". Indian balsam was one of the spectacular waterside plants imported to these islands by Victorian gardeners in the 1800s. Heracleum mantegazzianum, the dreaded giant hogweed of inflammatory sap, was another.

Its biggest advances are on rivers in Northern Ireland, but those of Leinster, the southeast and southwest are also widely affected.

As an annual, balsam can propagate only by seeds, but ejecting hundreds per plant as far as seven metres, its growth can take over large areas of bank, smothering native vegetation. Perennial nettles and briars might be less friendly, but at least their roots bind the earth. When the shallow-rooting balsam dies away in autumn, the banks are left bare and open to erosion.

Thus runs the case against the plant as widely agreed by fishery and wildlife-conservation groups and, in Britain, justifying a control bill of more than £1 million (€1.2 million). But some voices seem less sure. In a recent broadcast, Richard Mabey (author of Flora Britannica) suggested that balsam germinates most readily on bare soil – provided, perhaps, by the dredging of rivers. He had yet, he said, to read hard science on the loss of native riverbank vegetation.

Some eradication schemes have clear-cut ecological benefits and finite costs – clearing rats from small islands with especially rare birds or mammals, for example. Others are weighed up economically for the damage to human interests. Still more, inevitably, are candidates for control in the hope of finding future solutions – some Himalayan bug, for example, that feeds on balsam but won’t spread to native Irish plants, or a contraceptive for American mink that won’t affect fellow mustelids, such as native stoats or otters.

Without voluntary effort, as in “balsam bashing”, finance is the key to control and research. The most studied aquatic invader in Ireland is the zebra mussel, Dreissena polymorpha, an “ecosystem engineer” of profound impact on human and natural infrastructure, still advancing in our lakes and rivers. The bloody red shrimp, Hemimysis anomala, has emerged as another menace. Discovered in Lough Derg and Lough Ree on the Shannon in 2008 and 2010, and, like the zebra mussel, a native of eastern European waters, its powerful predation on other invertebrates and its appetite for fish eggs has aroused some serious concern.

Last year’s expert research report to the Environment Protection Agency, Alien Invasive Species in Irish Water Bodies, noted the shrimp’s arrival and offered some ominous speculation. Our lakes and rivers are being invaded by several high-impact aliens at once (Lough Corrib, for example, now has the zebra mussel along with invasive waterweeds and non-native fishes). Among the unpredictable effects, suggest the authors, “interactions among invaders may well lead to accelerated impacts on native ecosystems, in an ‘invasional meltdown’ process”. The report can be downloaded from the EPA website.

Eye on nature

In the last week of March I watched a clump of insects swooping and diving near the top of a 30ft macrocarpa tree. Were they swarming or mating?

Anne McCormick, Carrowmore-Lacken, Co Mayo

It was a swarm of male midges or mosquitoes into which females would fly to select a mate.

My garden, near the Dodder, is full of small, shrimp-like, black creatures in the soil and especially under stones. When exposed they jump frantically.

Penny Tyndal, Dublin 6

They are springtails, which are harmless and indicate good soil health.

I have just planted 400 native bare-root plants of whitethorn, blackthorn, spindle, dog rose, guelder and holly. Our wildlife corridor enchants us as we watch the early-morning leverets nibble away at the plants.

Anne Hutchinson, Cloughjordan eco-village, Co Tipperary

I hope you have protected your trees and shrubs from hares, because they will eat the tender growing points and ruin your plantation.

I saw a fox in Bromley, London, last year put his head into snow and run the length of the garden, leap into the air, turn around and repeat the action.

Ann Hall, Marine Green, Dublin 3

Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, or email viney@anu.ie. Please include a postal address.