Some thoughts on native trees

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by Andrew Clark, NI Forest Service

Recently I accompanied Pascal, Markéta and their merry band of helpers from the (Conservation Volunteers Northern Ireland) CVNI Tree Nursery in Clandeboye, Co Down, to an alder woodland, or carr, on the shores of Lough Neagh. I have also visited the Ulster Wildlife Trust’s nature reserve at Glenarm to inspect a collection of acorns for their tree nursery in Glendun. This was in my capacity as a Forest Service official operating under the Forest Reproductive Material Regulations (Northern Ireland) 2002 – or FRM Regulations for short.

The FRM Regulations supersede previous European legislation first introduced in the 1970s. In those days, the legislation was concerned solely with woodland for timber production and was a means of controlling the marketing of reproductive material (tree seed, plants and cuttings) of the principal timber species to try to ensure that the mature trees of the future had the potential to producer high quality timber. This was done by the registration of “seed stands” which were deemed to be of superior quality in terms of growth and form (i.e. straightness, lack of forks, light branching), from which material had to be sourced. Reproductive material from these stands was categorised as “selected” or “tested” to give some indication of the timber potential of the trees’ progeny, or offspring.

Native species are defined as trees that are naturally occurring within the local area. For example, those such as oak and ash are widely planted in new woodlands, and are among the most sought after hardwoods by the timber trade. But they will not be interested if the timber is bent or filled with massive knots caused by large branches. The potential for quality timber can be greatly enhanced by using the right seed source, planting the right species and managing the trees in the right way. And it does not have to be at the expense of other objectives such as the environment, biodiversity and landscaping. Forestry is the ultimate multi-purpose land use.

Exotic Species

Foresters have known for years that in the case of exotics such as Sitka spruce and lodgepole pine, the growth of plantation trees could be manipulated by selecting seed origins from different latitudes and environments within the species’ natural range. Hence seed might be labelled “Washington interior” or “coastal Alaskan”. Because it was known that widely distributed species had over time adapted to local environments, foresters were able to plant frost-hardy trees of more northerly origin in higher elevations or frost hollows, and faster growing trees of more southerly origin elsewhere. They had also learned that in the case of lodgepole pine, for example, the form of the trees could vary greatly from being practically bushes to fine straight-stemmed trees depending on where the seed originated.

The Return of the Native

In the case of native species, for generations seed had been collected and sown locally. During the great expansion of British and Irish forestry of the mid to late twentieth century, native species did not feature highly so little heed was paid to seed sources. In fact, of our native species ash and oak (sessile and pedunculate) were the only species covered by the old Regulations. However, with the increase in commercially available seed from further afield it gradually became clear during the 1980s and 1990s that there were some problems with imported seed.

For example, Hungarian hawthorn and Welsh hawthorn come into leaf at different times as they have been conditioned to different seasons. Hungarian hawthorn in Britain unfurls its first spring leaves too late to provide seasonable habitat and sustenance for the dozens of insects, including the Duke of Burgundy butterflies, yellow-tail moths, and hawthorn shield-bugs which rely on it. And some people believe that young oaks planted in Ireland from continental seed sources have poor form because they are not genetically adapted to our environment.

So the seed source may have negative implications for biodiversity and timber quality. The new Regulations are helpful as they recognise the concept of “nativeness” for the first time. Furthermore, the schedule of species has been extended to cover additional natives such as wild cherry and alder. For the first time also, a new category of seed source called “source identified” is introduced. Basically this means that the requirements for registration material exclude timber quality. This category now sits alongside the aforementioned “selected” and “tested”.

Origin or Provenance?

Put simply, if the trees from which the material is collected are directly descended from the natural forest which grew here before the arrival of humans, they are considered to be of local origin. If the trees are growing here, but we cannot be sure if they are directly descended from the early natural forests, the seed is considered to be of local provenance.
Now, when it comes to Irish forests, it is very difficult to be certain that they are of local origin. This is because there is not an acre of land that has not been modified in some way by mankind. Therefore if we look at a woodland we cannot be sure that the trees are directly descended from Irish stock, even if they are native species. The best we can do is to go to woodland sites which we can reasonably expect to be ancient, that is, there have always been trees growing there. These are often in remote places and on steep, rocky or marshy terrain, where the land was never cleared for agriculture. Even in these places we may well find many exotic species, some of which will have arrived naturally and some of which will have been deliberately introduced. We have to go to places where human influence has been much less than is generally the case in Ireland, for example in the remote glens of Scotland, to find trees which we can say with some certainty are of local origin.

When the Ancient Woodland Inventory for Northern Ireland is complete, we may have some justification for being reasonably certain that a given seed source is of local origin. It is being carried out by the Woodland Trust and Queens University, with results expected in 2005/6. In the meantime, organisations such as CVNI and the Ulster Wildlife Trust are collecting seed from woods such as the alder carr on the shores of Lough Neagh, and the oak woodland at Glenarm. They are then propagating this seed and selling young trees which are classified as “source identified” and of Northern Irish provenance under the FRM Regulations. This gives an assurance to anyone buying and planting out these trees that they are of local provenance.

But perhaps the issue of whether a seed source is of local origin or local provenance does not matter anyway, because there is evidence to suggest that trees have adapted to their environment in relatively short timescales. This is provided by the trees conservationists love to hate, sycamore.

Everyone knows that sycamore is a foreign introduction. We think it has been here for around 500 years. However, when seed is collected from sycamore stands around Ireland and grown together in one place, the individual trees behave in different ways that may be due to their climatic adaptation – they flush, flower, seed and enter winter dormancy at different times of year. Although this theory must be treated with caution, because the genetic variation may result from the parent trees own parents originating from different climatic zones within continental Europe, it is clear that seed sources matter.

Given the possibility that trees may adapt over a relatively short timescale of just a few tree generations (which for early seeders such as alder and birch may only take a few decades), it is arguably better to plant trees grown from material collected locally. It means that we can infer that they are likely to be suited to the local conditions and will thrive better as a result, and benefit the wider biodiversity associated with the species which has evolved similarly to be “in tune” with the seasons.

How local is “local”?

This is a tricky one. So far as the Regulations go, it refers to the regions of provenance. European member states have defined these according to geographical boundaries such as mountain ranges or seas, on the basis that discretely different genetic populations will have evolved in areas cut off from one another by physical barriers, or regions with different climatic conditions. Indeed this has been proven to be the case for the remaining native Scots (or Caledonian) pine forests of Scotland, which have been tested for genetic variation. In Northern Ireland we lack any substantial physical barriers, and it could be argued that there isn’t any great climatic variation. Indeed the whole of Ireland could be regarded as one climatic zone, although for legislative purposes the North and the South are considered separate. Northern Ireland therefore constitutes a single region of provenance.

Forests for All Reasons

As a professional forester, I understand the importance of the original 1970s FRM Regulations. It is in the interests of anyone growing timber to ensure that their timber is of the highest quality. I would also argue that anyone planting trees should not dismiss the possibility that those trees could one day produce valuable timber.
The Forest Service manages its woodland along the principle of sustainable forest management and this woodland is independently certified under the UK Woodland Assurance Standard which means that in today’s State forests, there is a place for timber alongside recreation, amenity and biodiversity. No one knows what the future holds for timber markets and the global availability of timber, so we should not miss the opportunity to develop a resource which is valuable in economic, social, and environmental terms. This should be the same for state and private owners.

What about the exotics?

Sycamore has its place. Granted, that place is not adjacent to or in ancient woodland. However, as a plantation tree grown for timber it can excel, being resistant to disease and rapid in growth, as well as showing reliable form once established. It is known for being more resistant to exposure than other broadleaves, principally through its capacity to produce new shoots from dormant buds when terminal buds are damaged. In comparison with ash, sycamore is more frost hardy and less prone to forking in the establishment phase. Sycamore is also not the ecological desert many would suggest – although it does support a smaller range of biodiversity than many other species. Unfortunately it is another exotic – the grey squirrel – that poses the greatest threat to the production of quality sycamore timber.

Room for Improvement

Currently the British and Irish Hardwoods Improvement Programme (BIHIP) is working to improve the timber potential of seven species – ash, oak, wild cherry, silver birch, walnut, sweet chestnut and sycamore. This is being done by identifying the best quality stands and individuals (“plus trees”) which will be used for breeding programmes. With the possible exception of sweet chestnut and walnut, all these species have the potential to produce excellent timber in Northern Ireland, and I believe that BIHIP deserves the support of all those working to use and promote hardwoods – and that includes the growers!

If we are not too concerned about how local “local” is in a particular woodland, and we cannot find a suitably good quality stand in natural woodlands, we should consider sourcing our seed from planted forests which have shown that they are well adapted to our climate, as well as those from further afield that share a similar climate i.e. in Ireland or GB. Indeed, there are those who argue that because of climate change we should aim to avoid restricting the gene pool too much because if we do, we may find in future that our native trees cannot adapt quickly enough and will die out.
Unfortunately there is a dearth of native woodlands in Ireland as a whole. And the timber quality in those where we might consider collecting native provenance seed is often poor. Furthermore, the trees that are easiest to collect seed from are usually the misshapen, bushy specimens, rather than the tall, straight finely branched individuals whose seed is borne so high. But should we not be aiming to collect seed from the best trees, so that the forests of the future at least have a chance of producing fine, straight, healthy, vigorous trees? Then we will be getting the best of all worlds.