Bringing back the birch

On clear-felled slopes in Connacht's conifer forests, odd clusters of birch trees have been spared to lean together, more than usually slender and tremulous in the midst of all that space. Birches in lines and crescents fringe some of the younger spruce woods in a softening gesture to "amenity". And birches weep across the corporate lawns of city office blocks as a foil to man-made cliffs and canyons.

Birches are everywhere in Ireland, yet nowhere in any real number. They are widely enjoyed as native trees, yet are almost entirely banished to odd corners of ditches, bogs and forest margins. Only in the south-east of the country, and in the managed protection of big estates, is birch likely to reach its Irish optimum of 24 metres, or build a trunk of more than 30 cm in diameter.

So indifferent, indeed, have we been to the fate of the native birches that their original genetic diversity and potential has been dramatically eroded. A new willingness to look at native birch as a serious hardwood forest crop may have borne fruit just in time.

A year ago, a project aimed at improving the quality of Irish birch was launched jointly by UCD's Botany Department and the Forestry Unit at Teagasc, Kinsealy. It is funded by Coford (the National Council for Forest Research and Development) and has a double purpose. It will produce quality planting stock for an Irish birch timber industry, and increase the diversity and beauty of planted forests. This represents a considerable turnaround in forestry attitudes, part of the wider ecological change now gathering confidence within Coillte and the Forest Service.

Traditionally, foresters have seen the birch as a "weed", a pioneer opportunist sowing itself prolifically into newly-cleared land. This was how it spread across post-glacial Ireland before the primal oak forest formed and how it is spreading today in the new wilderness of abandoned cutaway peat-land in the midlands. The recent manual, Growing Broadleaves, published by Coford, mentions birch only as an "invasive species", and there are no grants for planting a tree that few foresters could imagine sawn into worthwhile planks.

There are actually two native species, Betula pendula, commonly called silver birch, and Betula pubescens, the downy birch. The first is uncommon in Ireland, but since the downy birch can be just as weeping and silver-barked when it wants to be, the difference may be safely left to botanists counting chromosomes in these difficult and variable species.

The trees mature after about 60 years and then go into decline, seldom exceeding 100 years. There's a magnificently-gnarled old veteran from Scotland, so huge you'd never guess it was a birch, in Thomas Pakenham's Meetings With Remarkable Trees. But solitary trees with picturesque forks and heavy, candelabra branches are not the kind that yield much profit at the sawmill.

Thus, as a first step in the birch improvement programme, Dr Niamh O'Dowd put out a call to people involved in forestry to help locate "elite" trees of superior form and vigour. The ideal tree has a single, cylindrical trunk without the fluting, the big and heavy branches and witch's broom outgrowths that characterise so many Irish birches. Of thousands inspected by the team from Kinsealy, trees at about 60 sites have seemed worth propagation, but none, even among these, could really be graded as excellent.

Indeed, the quality of the Irish birch populations is generally so poor that conventional ways of assessment by measurement are of little use. The team has had to develop an eye for the right genetic characteristics locked up in trees that environment has stunted or deformed. They have even trudged over wet raised bogs to visit slow-growing trees in ancient copses, taking seed from any whose trunks were somewhere near cylindrical. Given different conditions or bred in fresh crosses, surprising trees may yet be conjured from stock of this sort.

An indoor seed orchard was created last spring at Kinsealy, from scion-wood taken from the best Irish birches and grafted onto rootstocks. Within only three months, the female buds on the scions opened into catkins, which were dusted with male pollen from other "superior" trees. By August the seed was ripe. Given that one birch catkin can yield up to 800 seeds, even a 50 per cent germination rate could theoretically plant a whole hectare from just four or five catkins.

Now come the all-important field trials, to sort out the most suitable genotypes for timber production, and the best seed sources for particular types of site. Bord na Mona has been quick to offer a five-hectare site on cutaway peat-land, but O'Dowd is looking for others on mineral lowland, where birch can be grown to full advantage under forest conditions. From each trial, the top half-dozen trees will continue as seed-providers.

Other European countries are decades ahead of us in improving birch for timber. In Finland, it was considered a weed until the 1960s; today, 17 per cent of new plantations are birch. In Germany, a breeding programme began in the 1950s and is producing birches with a 50 per cent gain in volume. In both countries, the new trees have generated a flourishing industry for the pale, fine-grained wood, comparable to beech in strength and density and quite as good for furniture and crafts.

In that case, why not simply import the improved tree stock from Finland or Germany? Because (I feel pleased to say) birch has a sense of its proper place in the world, being very strongly adapted to local light and temperature. Moved more than three or four degrees of latitude to the south, it flushes into leaf too early and can be caught by late frosts and withering winds. Moved the same amount north, it goes into dormancy too late.

So, there are probably no short cuts, outside of genetic engineering or cloning, to patient improvement of our native stock. But as a fast and vigorous grower, with a rotation period comparable to Sitka spruce, birch could have a beautiful future in our countryside.