The devastating damage that deer can do, part 2

In August four colleagues and I spent three days on the West Affric Estate, a 10,000 acre area of land that encompasses the headwaters of the Affric River, and is owned by the National Trust for Scotland (NTS). We were there to look at some of the areas that we worked with NTS on between 1993 and 2000, when ten deer-fenced exclosures were erected, to kick-start the process of forest recovery on the estate. Some of those were for natural regeneration, protecting the few isolated clumps of trees that had survived there (mostly in remote gullies), while others were for areas of bare ground on the slopes of the hills, where our volunteers planted native trees.

On the middle morning of our three day trip, we set off from the Alltbeithe Youth Hostel to go to one of those planted areas, called Gleann Gniomhaidh, after the name of the glen it is situated in. The burn that flows through that glen, the Allt Gleann Gniomhaidh, joins with the Allt Camban, which flows through Fionngleann immediately to the south, and forms the Affric River itself about 700 metres upstream from the Youth Hostel. On our way, we passed several stock-fenced exclosures that our volunteers erected to protect naturally-regenerating eared willows (Salix aurita), and I wrote about one of those in part 1 of this blog.

These small exclosures contain virtually the only riparian trees and shrubs on the upper Affric River, and eared willows are the commonest species in them. Willows of course are highly palatable to red deer (Cervus elaphus), but are also a very good host species for large numbers of insects, which in turn attract insectivorous birds. Some of these solitary eared willows we’ve protected with the stock fences are supporting colonies of aphids (Aphis farinosa), which are being tended by meadow ants (Myrmica ruginodis), so the recovery of even a few bushes is providing a trophic cascade of benefits to other parts of the woodland ecosystem.

As we left the Affric River and headed west towards Gleann Gnionmhaidh, we crossed the Allt Beithe Garbh, and found some extensive groups of eared willows that were unable to grow because of the grazing pressure from the deer.

 

 

 

 

 

 

 

One of the fenced areas we erected on West Affric with NTS is higher up on the Allt Beithe Garbh, and the natural regeneration that has taken place in the exclosure since it was protected in 1995 is featured on our website. That area was one of those fenced for natural regeneration, and in addition to the new growth of trees such as rowan (Sorbus aucuparia), downy birch (Betula pubescens) and eared willow, there has also been a substantial change in the ground vegetation. This is due to the process of ecological succession, from grassland to dry heath and then pioneer woodland, being able to take place again in the absence of overgrazing by the deer, and is graphically illustrated by the difference between the two sides of the fence in this photograph.

Seeing the unprotected eared willows lower down the watercourse from the fence made me think we should approach NTS with the suggestion of extending the fence to protect them, thereby allowing the process of ecological recovery to continue further downstream, towards the burn’s confluence with the Affric River itself. Continuing westwards, the next protected area is the Gleann Gniomhaidh (pronounced ‘glen a-grievy’) exclosure, and we were going to look at it as we’d heard that the fence was damaged in several places, and that deer were inside, eating the trees there.

As we approached the fence we could see that a large section of it was flat on the ground, most likely the result of either a heavy snowfall or several posts rotting and breaking off at ground level. Stepping across the fallen fence it was also immediately obvious how much damage the deer had done. Numerous young trees had been stripped bare of all their leaves, and in some cases the stems themselves had been de-barked, leaving them as broken and lifeless stumps, sticking up above the ground vegetation.

 

 

 

 

 

 

 

We were at the eastern-most end of the exclosure, and there were very few trees left alive there at all, although further to the west we could see that some looked more healthy. However, it wasn’t just the trees that had suffered as a result of the intrusion by the deer.

Near some of the dead young trees, I spotted a cluster of blaeberry plants (Vaccinium myrtillus) that had been eaten as well – the living leaves were interspersed amongst twigs that had been bitten off and died.

 

 

 

 

 

 

 

We decided to spread out and look at different parts of the exclosure, to see the extent of the damage to the trees, and what condition the rest of the fence was in. My route took me across the central section of the hillside, more or less in the middle of the exclosure, looking at the trees as I went.

 

 

 

 

 

 

 

In some places the trees looked in better condition, mainly because they were larger, and as a result their leader shoots and main branches were out of reach of the deer. It was only their lower branches that had suffered any damage, and this took the form of the leaves all having been stripped off them. I also wondered if there was a correlation with the distance of these trees from the damaged section of the fence. Perhaps, because they were in the central part of the exclosure, the deer didn’t come to them as often, and concentrated their feeding on the trees they encountered when they first entered the exclosure?

Most of the trees in the exclosure were downy birches, but in one area my attention was drawn by a large willow, which was clearly more tree-like in its growth than the eared willows, which have a typical spreading, bushy form to them. As I approached it, I could see that it was either a goat willow (Salix caprea) or a grey willow (Salix cinerea), and when I reached it and looked at the leaves I identified it as the latter. My attention was drawn straightaway though by a large collection of feathers on top of a moss-covered boulder beside the tree itself – these can be seen at the bottom of the photograph here on the right. The feathers were obviously the remains of a bird that had been killed, most likely by a raptor that had used the mossy rock as a perch to dismember and consume its prey. I was unable to determine the identity of the unfortunate bird from the feathers that remained, but the kill looked very fresh indeed, as a section of the gut had been left, and it was still glistening and wet.

I wondered how the bird had died? Had it been roosting in the willow when it was surprised and taken, or had the predator caught it elsewhere, and brought it to this sheltered spot, partially underneath the tree, to eat it without being disturbed? I’m not knowledgeable enough about birds to know the likely answers to these questions, so the story behind this pile of feathers will have to remain a mystery. However, it was intriguing to see that this had occurred beside one of the largest trees in the exclosure, and I suspect that there must have been some reason or purposefulness about that …

Turning my attention to the tree itself, I had a quick look at its leaves to see if I could find any invertebrates feeding on them. After a couple of minutes, I turned one leaf over and spotted a sawfly larva on the underside. While the larvae of sawfly can be mistaken for the caterpillars of moths or butterflies, they are distinguishable from the latter by having six or more pairs of prolegs, whereas lepidopteran larvae have 5 or fewer pairs. (prolegs are the fleshy legs that exist in the larval form of invertebrates, but do not appear in the adult forms). This sawfly larva looked familiar to me, but I didn’t know what species it was. When I sent the photo to Guy Knight, a sawfly specialist, he replied that it was probably an immature larva of a Trichiosoma species, possibly Trichiosoma vitellinae, but also stated that the larval forms of this genus of sawfly are not well-studied or known.

Continuing westwards, the trees thinned out again, and more and more of them had been badly damaged by the deer. The eared willows in particular had suffered because of their greater palatability, and many of them had been reduced to small stumps, virtually at ground level, with a few leaves struggling to survive at the base of the stems. It was sad to see what had happened to these trees, which had been planted carefully by our volunteers, bringing new life, and a three-dimensional structure to the vegetation community, that probably hadn’t existed in this part of West Affric for hundreds of years.

After walking a little further I found a deer skull in the grass. Stripped clean of all skin and flesh, it had obviously been there for a while, and indicated that deer had been getting into this exclosure for at least a year or more. Because the skull was there, it implied that the deer had died of natural causes, rather than being shot, when its carcass would have been extracted and the meat sold as venison. The carrion provided by this dead deer would have been a source of food for a range of scavengers and invertebrates that breed in decaying flesh.

Although this may sound unpleasant, it’s a key part of the nutrient cycle in nature, whereby the nutrients held in an animal’s body are returned to the soil and other organisms when it dies. That cycle is broken when carcasses are extracted for their meat, as no nutrients are ever returned to the ecosystem to replace those are exported through the sale of venison.

 

 

 

 

 

 

 

Continuing further on, I came across a real surprise – a primrose (Primula vulgaris) in flower. This was remarkable not only because it was flowering in the middle of August (when the normal season for primroses to bloom in the Highlands is April or early May), but also due to its distance from any other primroses that I know of in Glen Affric. Those are much further to the east, in the woodlands around Loch Beinn a’Mheadhoin, at least 15 kilometres away. Like the bluebells I wrote about in Part 1 of this blog, this primrose plant here seemed like a little miracle. Somehow, a seed must have found its way there, against the prevailing winds that come from the southwest, enabling this plant to grow and bloom.

Spring and summer have both been late in the Highlands this year, but even so finding a primrose in bloom in the middle of August seemed exceptional to me. I wondered if it was somehow another consequence of the climatic changes being caused by all the carbon dioxide we’re pumping in to the atmosphere by burning ever increasing amounts of fossil fuels? However, despite those thoughts, my discovery of this primrose in flower was a very welcome counterpoint to the damage I’d seen to the trees in the exclosure.

Like the bluebells, this primrose plant seemed to symbolise the resilience of Nature, and how the irrepressible life force of plants will bounce back as soon as they are given a chance to grow. In my mind I imagined what more of West Affric would look like, if it was protected from overgrazing by deer. How extensive would the areas of primroses and bluebells be? What other flowering plants would recover, and what insects would they attract as pollinators etc? In fact, later this same day I found some of the answers to those questions in another fenced exclosure we erected with NTS on West Affric further west in Gleann Gniomhaidh, and I’ll write about that in another blog. However, after passing the primrose plant I soon came to the western fence line of the exclosure, and found that much of that was down flat on the ground, providing ready access for the deer. It seemed to me this was also why I’d seen fewer and fewer living and healthy trees as I’d crossed from the centre of the exclosure westwards. As with the eastern end, the deer had eaten all the trees close to where they could gain entry to the exclosure, and it was only in the middle section, furthest from their entry points, that any significant number of trees had survived.

It was distressing to see the damage that had been done to all the trees that our volunteers had planted in this exclosure, often in challenging weather conditions, and to realise how vulnerable the remaining ones were, given how easily deer can reach them now. I rendezvoused with my colleagues at the western edge of the exclosure, and by comparing notes for what we’d seen, we agreed that the existing fence was beyond repair. It would be too costly to replace it all, and too difficult to maintain it against the snow drifts of winter that had probably contributed to its collapse in various places.

However, we also agreed that the area where the trees had grown better, and were still relatively untouched by the deer, was definitely worth protecting. That would allow those trees to continue their growth, and to provide a future seed source for further native forest recovery. This could be done by establishing a new fence around a smaller part of the original area, and we will be making a proposal to NTS about this in the near future.

We sat together there for a while and had our lunch, which gave us time to contemplate the situation and what had happened to the area once the deer had got into it. From where I was sitting, I was looking directly at two bare stumps (in the bottom of the photo here at the right) – all that remained of the trees that had grown from the seedlings planted by our volunteers there. Looking across the glen, I could see the two solitary trees growing high up in the gully on the north slope of Beinn Fhada that featured in a photo earlier in this blog. With that came the realisation that the fate of the former forest on this part of West Affric, of which those two solitary trees are the only living reminder, had probably been repeated with the dead ones in front of me. I suspect that over time the forest frontier was pushed further and further into remote locations as the human population grew and spread, and at some stage the last accessible trees would have been destroyed by deer, just as these two in front of me had been. This is a situation that was probably repeated all over the Highlands over the course of centuries or even thousands of years. It was galling to see that it had occurred again here now, but I took heart from the living trees that still survived, and the flowering primrose, and I hope that we can help the trees and flowering plants recover once more in this area.