A day in Scotland’s most northerly native wood

For some years I’ve been keen to visit Berriedale Wood on the island of Hoy, one of the Orkney Islands to the north of the Scottish mainland. It’s the most northerly native woodland in the UK, and is therefore of considerable ecological interest, although similar woods flourish in the southwest of Norway at comparable latitudes, and indeed much further north as well. I’d made an attempt to see Berriedale when I was last in Orkney, about 9 years ago, but there had been no space on the ferry the day had I hoped to go, so I never reached it then.

This year, my wife and I had planned a trip to Orkney for six days in the middle of October, so this time I booked the ferry well in advance, to make sure that we would have an opportunity to visit the woodland. Berriedale Wood is contained within the RSPB’s Hoy Reserve, and is accessed from Rackwick Bay on the west coast of Hoy. A footpath from there leads northeast through Rackwick Glen to Moaness on the other coast of Hoy, and the wood can be reached by walking off the track across the glen and fording the Rackwick Burn.

The northern end of Hoy, where the RSPB reserve is situated, is unlike the rest of Orkney, which is mainly flat and green, and divided up into fields for sheep pasture. Instead, it resembles the northwest Highlands on mainland Scotland, with large hills and extensive areas of heather (Calluna vulgaris) and purple moor-grass (Molinia caerulea). As such, it is less visibly domesticated than most of the land in Orkney, but it still far from being a wild and natural landscape.

Most of Orkney would originally have been covered by forest, but the long history of human habitation on the islands resulted in the clearance of the trees thousands of years ago. Exposure to the near constant strong winds and the wide ranging use of domesticated livestock, particularly sheep, mean that it is very difficult for trees to get established again. Rackwick Glen is sheltered from the prevailing westerly winds by the high ground to the north and west. Its remoteness and challenging environment suggest that it has probably never been heavily utilised by people, and this has enabled a small remnant of woodland to survive there, seemingly against all the odds.

In fact, there are some scattered trees along quite a stretch of the Rackwick Burn, and the impression I gained is that they are relatively young, and spreading there. The trees are mostly willows, with grey willow (Salix cinerea) being commonest, although there are also some eared willows (Salix aurita) in places, as well as some rowans (Sorbus aucuparia), downy birches (Betula pubescens) and a few dog roses (Rosa canina). This growth of new young trees has apparently got underway since sheep were taken off the reserve as part of the RSPB’s management strategy, and this process should accelerate in future, as the existing trees begin to produce more seed.

We were following the footpath through the glen, assuming that at some stage there would be a track leading off from it to Berriedale Wood itself. However, the path just kept going further up the glen, without there being any obvious route across to the other side. When we’d passed the area where we were looking directly over at the wood, we realised that in fact there wasn’t a path to the wood itself and we’d have to find our own way across the open ground, and a place to ford the burn.

We had been seeing some signs of wildlife as we walked along, including a large ground beetle (Pterostichus niger) on the track itself. A couple of redwings (Turdus iliacus) kept just ahead of us for a while – they seemed to be looking for insects in the vegetation beside the footpath. Then, once we’d left the track and headed out across country, we began seeing the distinctive caterpillars of the northern eggar moth (Lasiocampa quercus callunae) on a number of heather plants.

As we’d been walking, we’d noticed that beyond Berriedale Wood itself, there was another smaller area of native woodland growing slightly further north, along a different burn, called the Burn of Segal. We decided to head for that first, and then visit Berriedale Wood on our way back down the glen, later on. We found a place to ford the Rackwick Burn and then entered the small band of trees that are growing along the Burn of Segal, just upstream from where it flows into the Rackwick.

It’s really quite a small pocket of trees in this location, but it is a real gem of a natural woodland. Stepping under the low canopy of the trees gave access to a completely different ecosystem from the open landscape all around. The trees were short in stature, and many had multiple trunks or branches close to the ground that were well-clothed in mosses. The woodland floor too was quite spectacular, with a dense growth of forest species such as blaeberry (Vaccinium myrtillus) and broad buckler fern (Dryopteris dilatata).

It felt like a remarkable green oasis of exuberant lush vegetation, in comparison to the heather- and grass-dominated surroundings in most of the glen. I had the impression it was one of Nature’s secret gardens, little known and seldom visited, except by those who have an active interest in, and great appreciation for, Scotland’s native woodlands. The moss and ferns gave the clear impression of this being a temperate rainforest, and birds (whose identity we weren’t able to ascertain) took off from the canopy of some of the trees as we approached.

Although it was a tiny area in its extent, there was a lot to see there, and the pulse or heartbeat of the verdant green life in the woodland was palpable and strong, radiating out from every patch of moss, ferns and trees alike.

 

 

 

 

 

 

 

Given how the rest of the Orkney Islands look today, it seemed like a miracle that this green grotto had survived and flourished, and now could be a nucleus from which native woodland can expand outwards again, to fill much of Rackwick Glen.

 

 

 

 

 

 

 

Another common plant on the forest floor was great wood-rush (Luzula sylvatica), and in some places it formed a solid carpet, covering the ground entirely. Because it was autumn, there were also a number of fungi fruiting under the trees.

 

 

 

 

 

 

While I had to rely on the expertise of Liz Holden to identify some of the fungi, one unmistakable species I saw was the birch polypore (Piptoporus betulinus). It produces distinctive brackets on the dead trunk and branches of birches, and there was one fruiting body in prime condition on the moss-covered fallen trunk of a birch. Because it was a fairly fresh specimen, the upper surface was a bright shade of brown; when the brackets get older they turn more of a dirty cream colour.

I spent a little while looking at the cap of this fungus, as it had a beautiful pattern of lines radiating out from its attachment point to the trunk. I suspect these were cracks in the ‘skin’ on the surface of the bracket, but they reminded me of the pattern of small streams that make up a river delta, when seen from the air. Over time I’m guessing that the cracks would widen more and more, revealing the lighter coloured fungal flesh underneath that would give the bracket its cream colour when it’s older.

There was another bracket of the same fungus nearby, but it had fallen off the tree it had been fruiting on, and was lying upside down on the ground. The underside is quite different in its appearance and texture, and my eye was drawn to a small brown shape on the otherwise off-white colour. I had to use my hand lens to see what it was because it was so tiny, and it turned out to be a seed from one of the downy birches. Resting on the fungus, it looked somehow almost like a miniature butterfly, with a wing on ether side of the seed, and two small stalks at the top, which did a good job of mimicking insect antennae!

We’d spent quite a while in this little patch of woodland beside the Burn of Segal, and although there was still much more to explore there, we had to move on, in order to have enough time to see Berriedale Wood itself. I had heard that there are some aspen trees (Populus tremula) in the main wood, and as we approached it, I spotted them straightaway. They had already lost their leaves and their distinctively branched trunks were clearly visible in amongst the birches and grey willows, which still had leaves on them.

I was disappointed to see that we’d missed the autumn colour display of the aspens, but they do tend to lose their leaves earlier than most other deciduous trees. I had to make do with finding some fallen aspen leaves on the ground, and one in particular was bright orange-red in colour.

 

 

 

 

 

 

Most of the woodland is on the steep slopes of the Berriedale Burn, which we’d approached from the northwest side. After a few minutes exploring the woodland edge, where we had come across some fungi that Liz Holden identified as being the black milking bonnet fungus (Mycena galopus var. nigra), we passed into the trees and down the slightly precipitous terrain.

Although it is still quite small in size, this patch of woodland is significantly larger than the other one along the Burn of Segal, and at least some of the trees here are larger in size as well. Almost immediately I noticed that there was a lot of honeysuckle (Lonicera periclymenum) growing amongst, and up, the trees. This was very interesting for me, as honeysuckle is quite rare in the Caledonian Forest remnants in Glen Affric and at Dundreggan. That’s most likely due to its palatability to deer, and in the absence of deer on Hoy, its occurrence is perhaps at a more natural density than in the woods on the Scottish mainland.

Some of the honeysuckle plants had ripe berries on them, which stood out as brilliant red clusters of fruit in the otherwise mostly green landscape. Looking at them made me think about the name of this woodland – Berriedale – and wonder if it had gained that because of the abundance of honeysuckle plants there? Blaeberry plants also occur in the wood, so they could also be the source of the name, or perhaps it was a result of both of these species producing abundant berries each autumn?

It was a bit of a scramble to get down the slope, and when we reached the bottom, we spotted a small bird’s nest, amongst some fronds of a broad buckler fern (Dryopteris dilatata). Beautiful in its carefully-crafted beak-work of woven twigs and moss, it had obviously been used earlier in the year, and now contained a few fallen leaves instead of the eggs it would have sheltered a few months previously. I didn’t know what bird would have made it, but when I consulted the friendly and helpful RSPB staff in Orkney, they said it was most likely the work of a blackbird (Turdus merula).

One of the most obvious features of the woodland was the abundance of plants on the forest floor. It was hard to walk amongst the trees without stepping on them, and in particular on the great wood-rush (Luzula sylvatica), which was prolific everywhere. The narrow, bright green strap-like leaves of this species made beautiful patterns as they criss-crossed each other, and they reminded me of the bromeliads of the tropical forests in Central and South America, which have a similar growth form to their foliage.

I suspected this density of plants on the woodland floor was another consequence of the absence of large herbivores, such as deer and sheep, that keep the understorey of most native woods in Scotland looking like closely-mowed lawns, as a result of overgrazing. Here instead, it felt like there was more of a truly wild character to the woodland, with the plants able to grow to their full potential size and abundance, unconstrained by hungry mouths.

Although it was the middle of October, there were still some signs of summer in the woodland, as exemplified when I found some wood sage plants (Teucrium scorodonia) still in flower.

 

 

 

 

 

 

 

I stopped to look at one particular grey willow (Salix cinerea), as I could see it had lots of other life growing on it. The first thing to catch my eye were some fungi that I recognised as being the bleeding broadleaf crust fungus (Stereum rugosum), on one of its trunks. This species gains its common name from the fact that if you break the surface of the fungus, a dark red liquid will ooze out,  looking just like blood.

 

 

 

 

 

 

 

On another of the trunks of the grey willow there was a large patch of tree lungwort (Lobaria pulmonaria) – an arboreal lichen that occurs in wet areas, mainly in western parts of Britain and Ireland. It also occurs in the Pacific Northwest of North America, where it is considered to be an indicator species of temperate rainforest ecosystems, and its presence here in Berriedale confirmed the impression I’d gained earlier in the day, along the Burn of Segal, when I felt it looked like a temperate rainforest. Tree lungwort is notable because in addition to the fungal and algal partners that are characteristic of all lichens, it also contains a cyanobacterium (Nostoc sp.) that absorbs nitrogen from the atmosphere, fixing it in the lichen thallus, and thereby adding nutrients to the soil when the lungwort dies.

One of the trunks of the grey willow had died, but ironically it had more life on it than the other living ones. There was a patch of tree lungwort flourishing next to the twisted climbing stems of honeysuckle, and several bracket fungi that were a rich brown colour and which Liz identified as being a polypore fungus (Polyporus badius).

 

 

 

 

 

 

As their common and genus names indicate, polypore fungi do not have gills like most common mushrooms, but instead have a dense concentration of pores on their undersides. These serve the same function as gills, namely to facilitate the dispersal of the fungus’ spores, but I don’t know if any comparative studies have been done to determine whether gills or spores are more effective at that.

Nearby, on the moss-covered stem of a small dead tree, I spotted evidence of another fungus. This took the form of several dark brown stems sticking out horizontally through the moss, about 30 cm above the ground. I recognised these as being the dead stems, or stipes as they are more properly called, of a honey fungus (Armillaria sp.). This must have fruited some weeks previously, and the caps had already decomposed, leaving just the stipes behind. It’s been a prolific autumn for honey fungi, with an abundance of them fruiting in places such as Glen Affric and Glen Strathfarrar, and as a result I’ve learned to recognise the stipes, which remain after the rest of the fungus has already disappeared.

Moving on again after spending about half an hour with the grey willow, I came across another fungus on the woodland floor. Like the birch polypore I’d seen earlier, this one also had the tiny seed of a downy birch tree on its cap. Birches produce large quantities of seeds in the autumn, and they are dispersed by the wind, coming to rest in all sorts of places when they land. This fungus was past its prime condition, so Liz was not totally certain of its identification, but said that it is likely to be the grey milkcap (Lactarius vietus).

As I wandered through the woodland, my route took me closer to the Berriedale Burn itself. Several trees had fallen across the burn, and were completely covered in moss, adding to the feeling of being in a temperate rainforest.

 

 

 

 

 

 

 

 

Like so much of the woodland area, the banks of the burn were covered with great wood-rush, and I liked the contrast between the bright green of the leaves and the dark, almost black colour of the water, highlighted by some yellow leaves on a rock.

 

 

 

 

 

 

 

Moving on again, I walked for a short distance until I came to an eared willow bush, where a small shape on one of its leaves caught my eye. It was a spider, and when I looked at it closely it seemed to me to be one of the Metellina spiders that are common throughout Britain. This was confirmed when I sent the photos to Edward Milner, the spider recorder for Orkney and Shetland, who identified it as a male Metellina segmentata.

I hadn’t seen much evidence of invertebrates in the woodland during my time there so far, but that changed now, as I looked at this eared willow. Willows in general host a large diversity of insects and other invertebrates, being second only to oaks in that regard, and this eared willow was a good case in point. While I was looking at the spider I noticed some discoloured leaves that looked familiar to me, and when I turned them over I found some galls there that I recognised as having been induced by a midge (Iteomyia capreae).

These take the form of raised pustules that protrude downwards on the underside of the leaves, while on the upper surface there’s usually a discoloured area indicating where each pustule is located. On a couple of the leaves with these galls I noticed that sections of the leaf edges had been curled downwards, and this is the work of a different invertebrate. From visiting the British Leafminers website I  suspected that these were made by the larvae of a sawfly, but I wasn’t able to determine the species responsible for them.

When I contacted Rob Edmunds, one of the people who run that website, he said that the leaves had most likely been curled by a sawfly in the genus Phyllocolpa, but that it wasn’t possible to identify which species it was without examining the larva itself. The fact that there were two different insects using these leaves of the eared willow exemplify the ability of trees to host a diversity of species. Thinking back to how little forest there is in Orkney now, and the fact that studies have shown that woodland covered most of the islands several thousand years ago, gives an indication of how much biodiversity has been lost there, and indeed throughout Scotland, most of which has suffered similar near-total deforestation.

However, thanks to the management that is now underway in the RSPB’s Hoy Reserve, the woodland is expanding and increasing its extent again, boding well for the return of at least some of the island’s lost biological abundance. That was a positive note to end the day on, as time had gone by quickly and we still had to walk back down Rackwick Glen. As it turned out, we just made it back to the road before it got fully dark, bringing a satisfactory conclusion to what had been a very interesting, inspiring and beautiful day in this precious jewel that is Scotland’s most northerly native woodland.