Shelterbelt design.

By Andy Williams.

There’s no denying it, Caithness can be windy. Most of the croft houses in the area seem to have trees planted around them, but when we bought our croft it was bare fields. The only trees were in the front garden, and that was a jungle. The trees were close enough to the house for the roots to be affecting the foundations so unfortunately most of them had to go. The ones closest to the house have already gone, with the others earmarked for after the trees we planted have grown big enough to give us some shelter.

High winds can cause many problems for agriculture. It makes it harder for livestock to put on weight so increases feed costs. For growing plants, the sheer physical damage to plants can be an issue. It makes irrigation tricky, because it can dry out soil too quickly. There are advantages however. Sheep farming here can be easier because the wind keeps fly strike from becoming such a problem. After heavy rain, wind dries pasture faster than still conditions will. Overall however, we could certainly do with a fair bit less than we currently receive. We don’t have a huge amount of land, a shade over five acres, so need to use it very efficiently. A belt of sheltering trees around a field needn’t cost anything in yield however. Estimates vary depending on which authority you’re reading, but typically it’s estimated that 10% of the perimeter of your field planted to the right species can increase the effective yield inside the shelterbelt by over 20%, without even factoring in any yield from the shelterbelt itself. Yes please, we’ll have some of that!

Back when we knew we were going to be buying a croft but hadn’t zeroed in on one yet, I had certain preconceptions when visualising what ‘our’ croft would look like. The biggest of these was that it would of course be a south-facing slope. Designing a system on a south facing slope is a doddle. You can put your huge nut trees along the north edge of your land where they won’t cast any shade over the rest of your system. You can plant lines of full-sized trees on contour because the slope will allow every row access to the light. I knew exactly what it would look like, and there’s no denying that it affected my research into how to design agricultural systems. When we bought a northeast facing slope I had to go back to the drawing board in a lot of areas. I spent many hours thinking about the peculiarities of the site. The main ones were:

1. That loch view. Yes, it would be beneficial to plant dense, high, evergreen trees and shrubs to the northeast to block those cold winter winds but that’s the view that made us fall in love with the croft in the first place.
2. The southwest edge of the site is the natural ridge. The height of the trees there would determine the amount of solar gain the whole croft receives in winter. Full height trees would make the whole site colder, particularly evergreens.
3. When it’s windy, it’s *really* windy. While it would be lovely to plant a wonderfully productive shelterbelt entirely of fruit and nut varieties, until they grew big enough to provide at least a little shelter for each other we’d suffer heavy losses of expensive trees.
4. There is a large barn in the southwest corner of the croft. We don’t own it, but it does affect the site. It provides completely impermeable shelter from winds coming from the south and west, for the bit of land in its lee at least. It causes shade that varies according to the time of day and the season.
5. The site is wet. We hope to change the way water flows through the fields, but you can’t promise a tree it’ll be happier next year when it’s drowning. After rain the fields squelch underfoot, but after a couple of days of dry weather the water table can drop by over six inches.

I’ve approached the shelterbelt development in two phases. The first is the work we’ve already done, and the second phase will be implemented over the next few years as the plantings mature. One of the first things we did was remove the fence between the top and bottom fields. It was in a terrible condition but more importantly it’s more difficult visualising a piece of land as one system when it’s divided up by someone else’s straight lines. Nevertheless, because the design is different in what was the lower field because of the loch view we want to retain, I’ll stick to ‘top field’ and ‘bottom field’ for the time being. ‘The land formerly known as top field’ is a bit of a mouthful after all.

Northwest edge, top field.

This stretches from the house up to the barn in the southwest corner of the property. It receives the water running off the barn as surface water so has thick rush cover at the moment and is the wettest area of the whole site. Last year we stuck 147 willow cuttings along this edge after felling a tree in the front garden. At the time the pasture was knee-high in creeping buttercup so using the dilapidated fence as a guide has given us a somewhat wavy line. They’re just starting to put out shoots, so I’m going to remove them in the next couple of weeks because doing so later may damage the roots of the trees we’ve planted next to them since.

We’ve put in a double row of Italian alder, planted in a zig zag pattern, as the outer rows here. The outer row is four feet from the fence and planted four feet from each other. The inner row of alder is slightly inside this line, each planted between the trees in the outer line but still four feet from each of its pair of neighbours. Alders thrive in wet conditions, but as we’re going to divert the overland flow from the barn during the planned summer earthworks we needed to use a variety that can cope with drier conditions also. Italian alder can cope with occasional droughts as well as water logging, so should do fine here. It’s fast growing, putting on six feet in its first year, so should give us height quickly. It holds its leaves well into the autumn so should give plenty of protection from winds from the west for fruit trees that are finishing late. Like all alders it fixes atmospheric nitrogen as nodules on its roots via a symbiotic relationship with frankia bacteria, and these trees arrived ready inoculated. This nitrogen should encourage fast growth in the trees we’ve planted inside the alder. Italian alder has edible leaves. I’m rather curious to see how they taste to be honest.

Inside the alder we’ve planted a polyculture of bird cherry, crab apple, cherry plum and elder, all fruiting varieties. The area in the shade of the barn is elder-heavy because they crop well even in shade. There are also three small-leaved lime trees, which are reputed to have extremely tasty leaves.  They respond well to coppicing, so we can cut them in turn and always have one low enough to be easy to harvest. We’ve also planted some hazel on mounds to try to keep their roots out of the water-logging. Between and under the trees we’ve planted blackcurrant, redcurrant and sea buckthorn. The buckthorn doesn’t like waterlogged soils and some of them are struggling, but the earthworks should help that once they go in. Under all the fruiting species we’ve planted comfrey root cuttings. These will be divided and multiplied every year until they form a rhizome barrier to competing grass species and can be cut several times a year and left in place to feed the fruit trees and shrubs. No barrowing of fertilisers around the site, just a few minutes with a scythe. Between the trees and shrubs we’ve planted thousands of snowdrop and daffodil bulbs. They should have done their thing for the year before the trees and shrubs flower. We plan on having grafted, named cultivars of hazel, plums and apple inside the protection of the shelterbelt and all benefit from ‘wild’ pollen from seed grown trees. The mix of species should give a good nectar flow for bees over a sustained period as well as be attractive to humans. Who says beauty can’t be a yield too? An unexpected benefit of this area being covered with rushes is they’re providing excellent shelter for trees and shrubs nearby. Those planted near or among large clumps of rushes are leafing out significantly earlier than those in more exposed places. The Alder is the only species here that’s been planted in a straight line, in a double row. As vertical a face as possible to the wind has the best wind buffering effect, which is why we’ve planted the outer tree species in tight rows throughout the shelterbelt. Inside the protection of these we’ve intentionally kept things more random to look more natural and, hopefully, behave more like a natural ecosystem. We’ve left the areas of rushes bare of trees deliberately. After the water from the barn is diverted we’ll take the rushes out, and these areas will leave empty spaces for planting other species at a later stage.

Southwest edge, top field.

This is the driest part of the site, apart from the southernmost point where there is a dip in the ground full of rushes. It might lend itself to a pond at some point, but I’m not making that decision yet. Most of the outer row is hazel, four feet apart, but towards the wet corner we’ve used blackthorn. Inside this is a row of mixed blackthorn, bird cherry, elder, cherry plum, crab apple and rowan. Next to the barn is a single yew tree we grew from a seedling. Yew can be shade tolerant so should do well here. Under and between the trees we have more blackcurrant and redcurrant. All fruit species have comfrey root cuttings planted beneath them, that will need dividing next year to multiply. The hazel is more a multi-stemmed shrub than a tree, so should spread nicely to give good cover without getting too tall. Being deciduous it will allow some light through in winter when the sun is lower. It copes well with exposure and will itself produce a yield in time. We have deliberately left gaps in the inner rows of trees, for other species during the next phase of planting. We’ve planted many daffodils and snowdrops between the trees here also.

Northeast edge, top field.

The outer edge of this system is Bowles hybrid willow at fourteen inch spacings, four feet in from the fence. This hybrid is often grown as a biomass crop and grows incredibly fast. Ten feet in its first year, up to twenty-four feet at full height. It then spreads from the base to form a small clump. It leafs out early so should give excellent protection  from cold winds from the east for early blossoming species planted inside the shelterbelt, and is an early pollen source for bees. It also has a reputation for being very windfast, so I’m very curious to see how it performs. If it works as well as it should, the field should be much more sheltered by the end of this summer. Inside the willow we have a polyculture of bird cherry, blackthorn, cherry plum, rowan, sea buckthorn, blackcurrant, redcurrant, a couple of small-leaved lime, a couple of honey locust and a few radiata pine. The radiata are reputed to be one of the most windfast trees in the UK, a real pioneer species. They don’t like waterlogged roots, so we planted them on small mounds we dug for them. They’re suffering from severe wind burn at the moment, but of all the trees to suffer it could be worse. They were only ever intended to be for system establishment and eventually cut down, but I’m hoping some of them pull through. It’s nice seeing a little green in winter. This system hasn’t had comfrey planted for ground cover yet, but will early next year. It’s been the most exposed edge, so the trees are lagging behind the others. It seems likely that will change once the willow does its fast growth trick however. This part of the top field has been planted to have an inner edge that’s irregularly scalloped, to tie in with the approximate positions of the planned earthwork swales. The settling ponds dug inside these embrasures will create extremely protected microclimates that will hopefully allow us to grow things that would otherwise struggle here.

Northwest edge, top field.

This is the fence that we have removed. It originally divided the croft just uphill from the house and barn. The area between the house and the barn is being developed into a protected veg garden and will eventually have a greenhouse running along the approximate former fence line, but angled to face true south for maximum solar gain in winter. We’ve planted willow cuttings on six-inch spacing here as a temporary wind screen. The area between the barn and the northeast boundary will probably eventually become a perennial veg system, with the potential to develop some aquatics systems. We will plant a hybrid willow screen along the northeast edge of this section, between the barn and the southeast boundary. It will be several rows deep, so we can coppice a row each year for producing wood chip without reducing the wind buffering effect of the willow. We’re currently awaiting delivery of 200 cuttings for the initial planting.

View from the top field looking north past the house and barn.

 

Bottom field.

We’ve deliberately kept the trees here to a minimum, to keep the loch view open. The northwest edge has the phone line running above it, so we’ve limited it to a polyculture of smaller species. We have rowan, blackthorn, cherry plum, black locust, blackcurrant and redcurrant here. The southeast and northeast edges have a sparse planting of blackthorn and hawthorn with a few bird cherry and cherry plum. We’ve planted a couple of black locust with a couple of larger hawthorn behind them very specifically to screen our view from our house of the one house between us and the loch. We also have a radiata pine, a single spruce that was a freebie from a toilet paper promotion, and a single Korean pine that’s a retired living Christmas tree we’ve kept for years. We intend to add another couple of Korean pine eventually, they produce excellent nuts, but it’s one of the few species we intend to buy as older trees. They don’t start bearing nuts until they’re 20 years or so old, so it’s worth it for the head start. The Korean pine has a few blueberry planted under it, mostly to see how they develop.

Phase two.

Most of the species we’ve used in the shelterbelt have been relatively cheap to buy as cuttings or bare root trees. Other species that we intend to use however are expensive at £15 and upwards each. Because we want to use them in quantity they’re far beyond our budget. Instead we’ve bought bulk seed. We intend to establish a seedling tree and shrub area to grow our own for a fraction of the cost. A major advantage of this approach is we can grow enough plants to choose the ones that handle the local conditions the best rather than named cultivars. I’d rather hardy, high yielding plants than expensive ones that will struggle here.

Black locust. I love black locust. It’s a legume tree so fixes nitrogen. It’s a very attractive tree, with flowers that bees absolutely love. It has relatively open foliage so planted on pasture the grass still receives enough light to grow well. It burns green and coppices readily. Best of all though is how long its timber lasts. It resists rotting for anything from 500 to 2000 years depending on the environment. We plan on using it a lot. For example, I like wooden hurdles for fencing but don’t fancy having to remake them every few years. Using black locust I’ll only have to make them once. We’ll be planting plenty to go on the swales, but will also be using it to fill in odd gaps because it’s so useful.

Autumn olive. Another nitrogen fixer, this shrub also produces useable berries. We’ll use it to fill in some of the gaps in the top field shelterbelt, in particular the southeastern edge where there’s a lack of nitrogen-fixing support species so far. Particularly high yielding plants may be moved to the swale understorey planting.

Siberian pea tree. Again, a nitrogen-fixing legume. This is a bush that is extremely wind hardy and produces seeds that can be used much like lentils. It’s often used over and around chicken yards for the birds to self forage the seeds. We plan on using it a lot in the lower field, where we’ll be planting forage crops for a pig and chicken system, as well as filling some of the gaps in the understorey of the top field shelterbelt.

Juniper. This needs no introduction of course, we just haven’t found a supplier of cheap trees that won’t hammer us on the postage. I’ve observed natural polycultures in Scotland of pine over juniper over raspberry over herbaceous ground cover. We plan on using it in a similar role here and it should do well.

General design elements.

We’ve deliberately not used hawthorn in the top field because it can cause problems for pear trees when they’re planted too closely. There are hawthorn hedges up wind in neighbouring fields so we may struggle with pear here anyway, but it makes sense to at least maximise our chances.

The leaf fall from nitrogen-fixing species is extremely high in Nitrogen. Some of the leaf litter will remain below the trees that grew it but much of it will be wind-driven. Leaves tend to collect in swale ditches, so once they’re installed they’ll passively collect fertility from the shelterbelt using the remaining breeze to do the work. We’re deliberately going light on nitrogen fixing trees in the southwest shelterbelt. Nitrogen encourages fast, sappy growth in trees and we want them to grow slowly until the swales are installed and planted in their lee.

New trees typically have guards around them for a couple of years. They’re not cheap at £3 to £4 each (particularly when the trees have cost around 60p each) and nobody would ever describe them as attractive, but they’re a necessary evil to keep the trees from being browsed. Deer are often the biggest problem, a few deer can wreak havoc among a young woodland in very little time. Here however we’re surrounded by agricultural land. Five miles to the south we’d need deer fencing around the whole property but here they’re rarely a problem. Another major issue is usually rabbits. They ring bark young trees and kill them. When we were planning the system I realised we’d not seen many at all, so I hit the internet. A virus came through in 2016 and wiped out rabbits in the area. They’ll return of course, but at the moment we don’t have to worry about them. The only thing that’s even a possibility here is rodent damage. So far we’ve had no damage whatsoever, and considering the cost of replacing a couple of trees versus the cost of guarding them we’re taking a calculated gamble and leaving them unguarded.

The instructions you receive from tree nurseries all recommend mulching around new trees to a metre all around the trunk. When you’re planting over 650 trees however it’s not so simple, that much mulch would cost as much as the trees. We started with cardboard as mulch. We’ve had to order a lot of things online, and that means boxes. The trouble with cardboard mulches is they need weighing down with stones, and the cardboard under the stones rots very quickly. We soon got tired of adding to mulch constantly. We recently picked up over 500 stone slates that were going cheap locally. The bulk of them are earmarked for slabs and roof repairs, but the most damaged ones are being used for mulch around the trees and shrubs. Not even ceeeping buttercup can grow through Caithness stone.

Yield.

We’ve tried to design the shelterbelt system to stack functions as much as possible. The inner sections are mostly composed of bee forage species, and the outer rows too as much as possible. We will get diverse yields of fruit and nuts, as well as pole timber from some of the hazel, locust and willow. It will have huge benefits to wildlife, which will generally benefit the whole site. The design divides the site into four different climates. The veg garden will be the most protected, with buildings completely enclosing it eventually. It will be the most labour intensive system on the croft, requiring the most inputs. This is the main reason it lies directly out of the back door. Almost as sheltered will be the area between the barn and the southeast boundary. It’s bigger than the veg garden, and a little further from the house but requires less labour and fewer inputs. Next in terms of shelter is the top field, which will be the swale system with rotational grazing between. This is the biggest part of the croft and will be the main food production systems. The lower field will be the least sheltered, but is easily accessed from the house and veg garden so will hold the pig and chicken forage systems. The only moderately buffered wind should help to keep insect populations at bay, but the wind hardy shrubs should provide localised shelter.

That’s it: our shelterbelt design. Writing it has been a challenge, producing over 3000 words on shelterbelt without mentioning breaking wind just once isn’t easy as I’m sure you can appreciate.