Autumn surprise in Strathfarrar

On 25th October I went out with my partner Pupak for the day to Glen Strathfarrar, hoping to catch the leaves of the trees there at the peak of their autumn colours. We’d been out in the glen at the beginning of the month, when some of the aspens (Populus tremula) were already brilliant gold in colour, but most of the trees had still been quite green then. Now, 3 weeks later, I knew that would have changed, and I was expecting the glen to look quite different, with all the deciduous trees in their autumn finery.

When we arrived in the glen however, I was surprised to find that some of the aspens were still bright yellow, standing out radiant, in the sunshine of the morning.

 

 

 

 

 

 

 

Aspen usually turns into its autumn colours earlier than the other broadleaved trees, and I hadn’t expected to see any of them still with their leaves on at this time of the month. It was a different group of aspens than those we’d seen 3 weeks previously – we’d driven past those ones already this day and they were leafless. This variation between leaf change highlights an interesting fact about aspens – that different clones (ie groups of aspens that are all the same organism, because they are part of the same root system underground) come into leaf in spring, and shed their leaves in autumn, at different times to each other.

Walking a little further into the glen from these aspens, I stopped to look at an oak tree (Quercus sp.) that was growing from the bank right out over the Farrar River.

 

 

 

 

 

 

 

The combination of mossy trunks, multi-coloured leaves and the still water seemed to me to evoke something of a Chinese or Japanese landscape painting …

The oak had leaves that were more elongated and less strongly-lobed than I’m used to seeing, so I wasn’t able to identify it as either sessile oak (Quercus petraea) or pedunculate oak (Quercus robur), the two species that occur in Scotland. However, hybridisation does occur between the two species, so it’s possible that this particular oak may have been a hybrid, as the leaves of those can be quite variable.

 

 

 

 

 

 

 

While I was photographing the oak, I realised that we were just below the site on the hillside to the north where we’re putting in a new 14 hectare fenced exclosure for both natural regeneration and planting trees there. The fence was about to be erected the next week, and we had two Conservation Weeks scheduled for tree planting in November, so I suggested to Pupak that we go up there and have a look around the area, as it was the last chance to see it before it was fenced.

We crossed the flat open ground on the valley bottom, between the river and the base of the hill, and as I started up the slope, a butterfly took off and flew away just in front of me. I was a little surprised to see a butterfly so late in the year, but I didn’t think anything more of it, until another one took off a few moments later. I was able to see this one more clearly and noted that it was a red admiral (Vanessa atalanta), and this made me think immediately that there must be a birch tree with goat moth larvae (Cossus cossus) in it nearby.

This is because the goat moth larvae, which live in the trunks of birch trees feeding on the wood of the trees, excrete frass that mixes with the tree sap to create a fermented, gooey, viscous, brown liquid that attracts a range of insects, including red admiral butterflies. We have several of these so-called goat moth trees at Dundreggan, and I’ve sometimes seen a number of red admirals on them in late summer. The fermented frass-sap mixture must be alcoholic, as the butterflies behave differently to normal when they are feeding, making erratic and unsteady movements, and it’s possible to approach them much more closely than usual.

It only took me a moment to note that the birch tree (Betula pendula) almost right beside me had the characteristic signs of goat moth larvae on it. These are brown areas that glisten with moisture from the frass-sap mixture that drips down the trunk from the holes where the larvae are feeding inside the tree.

There were also a couple of red admirals on the tree itself, and I realised that the two I had disturbed must have been feeding on it as well, before they flew off.  The goat moth is quite scarce, and is listed as a priority species for conservation in the UK’s Biodiversity Action Plan (UK BAP), so I was really pleased to find this tree here in Strathfarrar. As far as I know, we haven’t recorded any in the glen before.

We watched the butterflies for a while, taking photographs as we did so, and I told Pupak about the life cycle of the goat moth. The larvae can live for up to 5 years inside a tree, before emerging to descend to the ground and find a place to pupate. It’s therefore very rare to see the larvae, although they do occasionally emerge for short periods before they are fully grown, and then re-enter the tree to continue feeding. I’ve only ever seen a larva once, and that was at Dundreggan in 2008, just a few days after we completed the purchase of the estate. I was out then with all the staff from our Findhorn office, and just after telling them how unusual it would be to see a goat moth larva, I spotted one, bright scarlet in colour and the size of my little finger, crawling on the ground near the base of the tree it had been living in. That was one of those magic moments that sometimes occur out in Nature, and it made a big impression on me, and all the staff, at the time.

I told this story to Pupak while we looked at the butterflies feeding on the tree, and then she noticed a pinkish-red movement in one of the crevices – it was a goat moth larva!

 

 

 

 

 

 

 

This was truly remarkable – a real surprise and a source of wonder to me, as it seemed exceptionally late in the year for one of the larvae to emerge like this. Usually I’ve heard of it happening in the summer, and my previous sighting of one was in August, but now this was almost the end of October.

 

 

 

 

 

 

This larva was not a mature one, as it was quite small in comparison to the one I’d seen before at Dundreggan, and was rather pinkish in colour, compared to the bright scarlet of the fully grown one. I’m guessing that it would probably spend another year or two feeding inside the tree, before it would be ready to pupate. There were other insects feeding on the larva’s frass-sap mixture as well, including some bluebottle flies and a couple of common wasps (Vespula vulgaris), which like the butterflies, didn’t seem to mind being approached very closely so that I could photograph them.

After spending about half an hour with the goat moth tree we continued further up the hill and into the birch woodland on the slopes there. I was heading for what would become the southwest corner of the soon to be fenced exclosure, as I knew from a previous visit that there were some aspen trees there. Before we reached them though, we decided to stop for lunch, near where there was a red fungus on the forest floor. I recognised this as one of the brittlegill fungi (Russula sp.), and I suspected that it was one called the sickener (Russula emetica). However, the fungi in this genus are notoriously difficult to tell apart, and although I collected the specimen, it rotted before I could dry it out and send it off to an expert for identification, so it will just have to remain as Russula sp.

We were quite close to the aspen stand, so after lunch I spent some time photographing it. The stand consisted of one main tree with several trunks, and a couple of smaller, younger trees nearby. The trunks of the main tree had the typical diamond-shaped lenticels that are a characteristic feature of aspens, and the bark was also quite green in colour. This is due to the presence of chlorophyll, the green pigment which enables plants to harvest the sun’s energy through the process of photosynthesis.

 

 

 

 

 

 

 

 

 

By this time the wind had begun to blow quite hard, so it became a challenge to take any photographs, because both the leaves and the trunks themselves were moving around a lot in the gusting conditions.

 

It reminded me of our previous visit to Strathfarrar, earlier in the month, when the wind had picked up during the day, and I’d spent a while taking long exposures of the aspens, to get the blurred effect of their leaves moving while the camera’s shutter was open. I did the same again now, and this photograph here, with the blurred leaves, makes an interesting comparison with the image at the top of this blog, of the same scene when it was briefly windstill.

While the wind was blowing I also decided to shoot some video footage, to illustrate the motion of the leaves, so here’s a brief compilation of that:

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Climbing up above the aspens, I reached a more open area, where we’re aiming to get natural regeneration of the trees inside the new exclosure. This provided some good views over the forest, looking westwards.

 

 

 

 

 

 

 

Up at this elevation on the hillside, Scots pines (Pinus sylvestris) are the predominant trees, but many of the old ones were killed by a fire several decades ago. The skeletons, or snags, of these dead trees still remain today, preserved by the high resin content in their wood. They provide a stark reminder of how much of the Caledonian Forest has been lost. No young trees have been able to grow in this area since the fire, because of overgrazing by red deer (Cervus elaphus), and it’s to address this situation that we’re fencing the area now.

By excluding the deer we’ll enable a new generation of young trees to grow there, by both natural regeneration and the planting of seedlings by our volunteers. These will be the first trees to grow in this section of the glen for about 200 years, and this project represents another step in our vision of restoring the Caledonian Forest to a significant part of its former range in the Highlands.