Cultivating an understorey on the forest's ferny floor

ANOTHER LIFE:THE WESTERN MOUNTAIN landscape is emerging from a dark cloak of conifers as the great peatland forests are shaved away. Above the raw stumps of Sitka spruce, some of it planted almost half a century ago, whole valleys, hillsides and streams are opened to the sun and wind.

As Coillte clearfells the plantations to carpets of tangled brash and waving ferns, Mayo and Connemara will yield more than 200,000 cubic metres of felled timber in this year alone. Some of the cleared ground will go to windfarms, notably at Cloosh, between Spiddal and Oughterard, Co Galway. But, generally bound to replant by its licence from the Forest Service, the company will go on to sow again – 3,440 hectares by 2015.

The historic compulsion to plant tall, shallow-rooting Sitka on agriculturally “unusable” land – namely, the bogs and mountainsides – has been drastically revised. Two-thirds of future seedlings will be of lodgepole pine, the tough, undemanding pioneer conifer that clothes so many of the poorest, windiest soils of the west.

Left unthinned, lodgepole sprawls and seeds itself freely, so that many old and unthinned plantings have become impenetrable. Coillte now plans a “Wild Nephin Project” for its mountain forest beside the new Ballycroy National Park in north Mayo. It cites the National Wilderness System established in the US to help people engage in “primitive” recreation, and the 2009 call from the European Parliament for restoring land to wilderness “where man has the opportunity to engage closely with nature”. Making, perhaps, a virtue of necessity, Coillte is setting aside “a large area that would be initially managed to create the conditions where natural processes will begin to prevail and where opportunities will be provided for visitors to experience challenging and adventurous recreation”. One imagines the thrills of orienteering through a jungle of wet lodgepole pine.

The ugly swathes of clearfell have been inescapable, given the vulnerability of peatland Sitka to windthrow once the forest canopy is opened. But the execution has sometimes gone disastrously wrong. On some denuded hillsides, residues of decades of rock phosphate – a slow-release organic fertiliser – have been washed into streams, menacing the pearl mussel, Margaritifera, and other freshwater life.

All this steps up the arguments for switching to an entirely new planting system – that of “continuous cover forestry” (CCF). In this the soil is never exposed. Only single or small groups of selected trees are felled, at planned intervals, so that an understorey of trees is developed, each growing to take its place in the light. This stops erosion of soil and defacement of landscape, preserves continuous habitats for forest plants and wildlife, and – especially important as climate changes – better protection against the wind.

A switch to continuous cover is the common ideal of the nine or so NGOs now active in Irish woodland development, plus the State-funded agency of the Heritage Council. In Britain, CCF is under serious discussion by the Forestry Commission, and Ireland’s Forestry Service has funded Pro Silva Ireland, the leading proponent of CCF, in a booklet describing the system.

Coillte itself has brought varying prescriptions for CCF into 34 of its woodland sites and made it management policy for all broadleaf mature forest in its estate. It will also make it “the favoured system” in amenity areas such as Gougane Forest in Cork. A number of large estate owners, mostly active members of Pro Silva, have decided to transform their forests to CCF and more mean to follow suit.

Coillte itself has taken part in trials to test ways of transforming existing conifer forests through progressive CCF underplanting.

In a study published last year by Coford, the State’s forest research agency, a team led by Dr Áine Ní Dhubáin of University College Dublin reported on eight years of experiments to see how six kinds of seedling trees would grow in thinned areas of a mature 40-year-old Sitka forest in Co Wicklow.

It was a complex piece of research, monitoring what happened not only to the trees (Sitka, larch, western red cedar, beech, downy birch and sessile oak) but to sunlight and shade, temperature, moisture and state of the soil. It used cameras with fish-eye lenses to keep track of the surrounding conifer canopy. My drawing, below, is based on such a hemispheric view.

The conclusions were not promising. To use this “shelterwood” approach in transforming a stand of mature Sitka spruce, said the team, would need bigger gaps in the canopy to let in more light – and that would bring the risk of wind damage. The best option, it concluded, is to start the process much earlier. Heavier thinnings among young conifers would offer the CCF seedlings more light and give them more room to grow.

An Evaluation of Continuous Cover Forestry in Ireland can be downloaded at coford.ie/publications/projectreports

Eye on nature

While walking up Bray Head recently my son, Leon, and I discovered a family of guinea pigs on the side of the path. I had no idea wild guinea pigs had colonised this area.

Ivan and Leon Fitzgerald, Killiney, Co Dublin

The guinea pigs must be escaped pets. They are unlikely to survive in the wild as they are not equipped to forage for food or protect themselves against predators.

There are large, pale, misshapen acorns among the normal ones on an oak tree in our garden. Is this caused by a parasite?

Florence Shields, Clogherhead, Co Louth

From the photograph you enclose, your oak tree has been attacked by the tiny knopper gall wasp, which lays her eggs in the embryonic acorn, triggering growth that encases the larvae in a large, woody gall. The all-female gall wasps that emerge from the knopper galls do not need males to reproduce, but need to lay their eggs in the flower buds of a Turkey oak. Male and female wasps hatch from the cones of this oak, and after mating the female lays her eggs in native oak acorns, causing knopper galls. They cause a poor acorn crop.

Diver and photographer Brendan Moran recently filmed a 40cm scorpionfish (bull rout) off Greystones, in Co Wicklow, and a large curled octopus off Dalkey, in Co Dublin.

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