The other day I made a garden bench from a tree that I had planted in 1990 – a larch tree, felled by Storm Arwen on November 27th 2022. The notion of home-made artisan furniture never entered my head while planting those alternating rows of pine and larch. In theory one can imagine a tiny sapling becoming a fifty-foot specimen, though when the baby tree is no higher than the surrounding vegetation it requires a degree of optimism to dismiss the ridiculous idea that the planters never get to see the results of their labour. A solid, functional artefact derived from such labour substantially destroys the myth.
We planted our small woodland to achieve several ends: to provide shelter from the Aberdeenshire winds, to enhance cover and food supply for wildlife and to sequester carbon. On a global scale it is this last objective which fuels the drive to plant trees.
The 1.5 degree target will almost certainly be breached and several tipping points have already been passed, with predictable consequences. Though on an almost positive note, one climate expert maintains that every fraction of a degree of temperature increase that is prevented can reduce the possibility of further, and more serious, tipping points from being reached.
Thirty-two years on our objectives have been realised, though of course the occurrence of violent storms can upset the apple cart. As noted in a previous blog we lost more than seventy trees in last winter’s shocking onslaught, though twelve months on we approve of the changes involuntarily forced upon us – more light in the wood which favours the shrub layer, and more planting space for yet more interesting subjects; plus a barn-full of firewood.
Tree planting is still very much worthwhile, for all the reasons highlighted, and more (sea-grass is considerably more effective at sequestering carbon, but not an option for most gardeners). The sowing of seed is always a demonstration of hope, a commodity in increasingly short supply.
One of the numerous delights to be derived from establishing a small piece of woodland is that after a number of years your trees start producing their own seed. So now, in addition to the hundreds of ash and sycamore seedlings derived from much older trees that germinate in our ubiquitous woodchip mulch we can now lift oak, alder, gean, holly, birch and rowan saplings from beneath the trees that we planted; and in much greater numbers than we can use in our own patch. Thus recently we were able to donate a hundred trees to community gardens in Aberdeen – after making it clear to the recipients that a certain amount of hybridisation, particularly amongst the rowans and birches, will likely prevent a crop of purely native trees, given the diversity of species that we are growing here. Does this matter?
Despite the abundance of ‘free’ planting material we also collect seed from favourite trees in order to provide extra plants for our own garden and to generate subjects for selling to visitors, which enables us to support Fauna and Flora International.
One of our favourite genera is Sorbus – the rowans – a large group of relatively compact trees that produce showy crops of glistening berries in a range of colours, making them an excellent choice for any size of garden. The native rowan, Sorbus aucuparia, is by no means the only species or variety that produces fruit attractive to native wildlife. The first one here to be cleared of its crop, mostly by blackbirds, comes from an island off the coast of Korea – S. ulleungensis ‘Olympic Flame’. By the time that the winter-visiting redwings and fieldfares arrive, Olympic Flame has been denuded and it is the other red-berried rowans, including the native, that attract their attention. Once those have been stripped the yellow fruit is raided – as from S. ‘Joseph Rock’ and S. ‘Wisley Gold’; while white-berried rowans, such as S. cashmeriana and S. setchwanensis are more or less left alone. Colour of food appears to be more important to these thrushes than country of origin.
Some species of Sorbus are apomictic, meaning that they produce seed without any sexual recombination of genes. While this habit might have adverse evolutionary consequences it is a boon for the amateur propagator who wants an identical duplicate of the parent plant, something ‘normally’ only possible through vegetative propagation, using cuttings or layers. The extremely attractive, though dubiously edible, white-berried S. cashmeriana is an apomict, as is the purple-pinkish S. vilmorinii. A few winters ago a large specimen of this tree was defended against all comers by a very aggressive mistle thrush who had designs on the entire crop.
One of our favourite rowans is a red-berried variety of S. aucuparia, named ‘Ravensbill’ on account of its black, beak-shaped leaf buds. This is not an apomict though a row of twenty Ravensbills have all come true to type. This may be partly due to the location of our single parent tree which grows isolated from other relatives with which it could cross-pollinate. The other salient factor is that some members of the genus are self-compatible – they can pollinate themselves – whereas others are not. The yellow-berried S. esserteauana readily hybridises with other species, pointing at self-incompatibility; so vegetative methods of propagation are required to guarantee replication of this species. Another excellent yellow is S. ‘Joseph Rock’, itself a hybrid (possibly between a white-berried plant and a red-berried one) which produces viable seed that may or may not come true to type.
Perhaps all this detail is a tad arcane, though I consider it to be yet another benefit of planting trees, a process which in time reveals the intricacies of plant evolution.
Visitors to Airdlin Croft will have noticed that two other genera are well represented in the garden: Hosta and Rhododendron, both morphologically dissimilar from Sorbus but equally fascinating to the propagator. Hosta is a small genus of around fifty species of herbaceous plants native to Japan and nearby bits of Korea and China, remarkable for their propensity to produce sports that derive from mutations within the leaf mesophyll that affect the location and quality of plastids, thus giving rise to endless forms of variegation. At least 10,000 cultivars of Hosta have been named – and yes, some look remarkably like others – but even within a relatively small collection we have been able to isolate three ‘new’ ones, including a very promising plant derived from the all-green H. ‘Stir Fry’ , which has yellow variegation – tentatively named ‘Stir Crazy’. Perhaps this will appear on the market one day. But even if it doesn’t, its discovery and subsequent propagation has brought much enjoyment.
Returning to trees, genus Rhododendron produces even more surprises, but here it is sexual promiscuity rather than vegetative mutation that gives rise to seemingly endless variety. As noted elsewhere, even the best-known rhododendron nurseries struggle to replicate ‘species’ that come true to type, which, for the adventurous gardener isn’t necessarily a bad thing. Growing rhododendrons from seed may be a slow process but as with rowans and hostas, the non-predictability of results can be exciting.
Incidentally, when sowing seeds from berrying trees we have found that germination occurs more quickly if they are extracted from their fleshy fruit and rinsed off in a sieve under running water, and then sown in a free-draining compost mix and allowed to over-winter in an unheated polytunnel. They are also less likely to be dug up by mice or voles.
Another genus that we have been propagating this year is Salix – the willows; and these grow very easily from stem cuttings that can be rooted in a jar of water before potting up. We are using willows – mostly native – to thicken up the shelterbelt along the marshy western edge of the garden. It is worth noting that they have the potential to attract more insect species than any other native tree.
While on the face of it restricting oneself to native trees might be in the best interests of native wildlife, climate change has moved the goalposts, to the extent that several of our iconic tree species are severely threatened, for example by bark-munching insects that can thrive in the absence of severe winters. Ash dieback has arrived in our garden but so far the centenarian examples are still standing proud. But we are reluctant to plant any of the annual seed crop while their future looks threatened. And while climate breakdown is a visible reality it appears difficult to predict the consequences for Scotland. It may continue to get warmer here, favouring the more tender introductions like the glamourous, large-leaved rhododendron species. Or the melting of Arctic ice could affect ocean currents in such a way that it becomes much colder, in which scenario the rowans might continue to thrive.
Insects are not the only creatures responding pragmatically to environmental change. In the last twenty years several Mediterranean bird species have started breeding in the UK. It wouldn’t be surprising if the annual influx of winter thrushes became a thing of the past. Are we humans alone in burying our heads in the sand?
The genie is out of the bottle both in respect to climate breakdown and the introduction of plant material from around the world, a process accelerated by human activity but by no means the only way it has occurred. Ocean currents move viable propagules between continents, and humans are not the only animals to plant seeds. This observation does not excuse gardeners from allowing invasive subjects to escape from their patches, let alone wild planting in areas where management is insufficient or absent.
The planting of trees is a worthwhile endeavour for all the reasons so far suggested, and still more. Many gardeners will recognise a need to favour food plants over aesthetics, and a warming climate will, for a while, allow a much bigger range of edible fruiting trees to flourish. In that context it should be mentioned that a fig tree growing outside here has produced fruit for the second year in a row.