Autumn extravaganza in Glen Affric, part 1

Autumn is my favourite season in the Caledonian Forest and each year I like to spend some time camping out in one or more of the best woodland areas to make the most of the opportunities that the colour change of the leaves offers for photography. Thus it was that in mid-October I went to Glen Affric for a couple of days, hoping to catch the autumn colours at their best.

However, it has been a remarkably mild autumn in the Highlands so far this year, without any of the hard frosts that are necessary for the deciduous trees to produce the brightest and most vivid colours in their leaves before they fall for the winter. Instead, the very dry weather we had in September has been followed by a wetter and warmer October than usual. As a consequence, the colours of the trees have been more muted than in some other years, but as I discovered this day, the burns and watercourses were in spectacular spate, because of the prolific rainfall.

 

 

 

 

 

 

 

 

 

 

 

 

 

Stopping at the Allt na Imrich, one of the watercourses that flows from the north side of the glen into Loch Beinn a’Mheadhoin, I could see that the water level was well above normal, and what was usually a relatively gentle burn had become a raging torrent, cascading over the rocks as it rushed towards the loch.

The power and noise of the cascading water was quite impressive, and I watched it with awe and appreciation for a few minutes. This was a very brief experience of the millennia-long sculptural work of the water, to shape the rocks into more rounded, organic forms; to wear away their sharp edges and jagged outcrops, leaving them smooth and caressed into beautiful shapes by the relentless passage of the water.

The Allt an Imrich was larger, more powerful and in some uniquely river-like way more alive because of all the rain. Just above, it, the lichens growing on the branches of the rowan trees (Sorbus aucuparia) overhanging the watercourse were also benefitting from the increased moisture, both from the rain itself, and from the additional spray caused by the greater volume of water cascading over the rocks.

However, it was the flowing water itself that continued to draw my attention. At one place, a tiny rowan seedling, its leaves bright yellow before being shed, made a dramatic contrast with the raging torrent of the burn flowing just beside it.

 

 

 

 

 

 

 

 

 

 

 

 

 

Just upstream from there a cluster of golden-scaled male ferns (Dryopteris affinis) provided a much larger splash of bright yellow, with their fronds standing out in contrast to the dark, peat-coloured water behind.

 

 

 

 

 

 

 

Rather remarkably, it was quite windstill at the time, so I was able to take some long exposures to get the blurred effect of the rushing water, whilst retaining perfect sharpness in the ferns’ fronds because they were motionless.

While I was photographing the ferns I spotted some wood sorrel (Oxalis acetosella) growing nearby, and I noticed that some of them plants had seed capsules – it’s relatively rare that I come across their fruits.

 

 

 

 

 

 

 

The abundant rainfall that had swollen the burn so much had brought a lushness to all the vegetation, and this combined with the overcast conditions to create rich colours all around. The lichens in particular were thriving because of the moisture, swelling up to their full size (they shrivel in dry conditions) and radiant with life force. On one dead birch tree, the lichens and the fruiting body of a birch polypore fungus (Piptoporus betulinus) completely covered the trunk, so that not a single part of the bark was visible.

By this time, the weather was beginning to change and the sky was clearing, so I took that as my cue to move away from the burn and go to a small knoll nearby, where there are good views over the forest and Loch Beinn a’Mheadhoin. I’d been shooting some video of the water though, so here’s an edited compilation of that now, as a visual interlude between the two locations where I spent time this day.

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Reaching the knoll, the change in vegetation from the riparian area beside the burn was immediately obvious, and was characterised by swathes of blaeberry (Vaccinium myrtillus) with bright red foliage on the forest floor.

 

 

 

 

 

 

 

I’ve visited this particular patch of blaeberries in previous autumns, and the foliage there always turns a brilliant red colour. Most blaeberry leaves turn a yellow colour, but some patches like this one go red instead. I don’t know the reason for this, but I suspect it may be to do with different nutrients in the soil giving rise to a slightly different chemical composition in the plants, which in turn causes the specific colour change. In any case, this is a favourite area of mine, because of the autumnal colours on the forest floor, and I was pleased to see it at its best on this day.

 

The day was now quite different from the morning, as the wind had picked up, blowing away most of the clouds and leaving much of the sky blue. The clouds that remained were passing from west to east quite quickly, so there were intermittent periods of bright sunshine, interspersed with duller cloudy spells. I took advantage of the former to take some photographs of clusters of Scots pines (Pinus sylvestris) and birches against the blue sky, making for very different images from those in the morning beside the burn.

 

 

 

 

 

 

 

 

 

Under the canopy of the trees it’s not so easy to take photographs when the sun is shining, as the mottled patches of bright sunlight contrast with the areas of deep shade and make it hard to get an exposure that works for the light levels of both. In these situations I often tend to concentrate instead on smaller subjects, where I can control the light fully, and on this day I began to focus on invertebrates that I spotted on the vegetation.

There area a number of young eared willow bushes (Salix aurita) growing near Loch Beinn a’Mheadhoin in this area, and when I looked closely at those I came across several with conspicuous galls on the undersides of some leaves. These are induced by a sawfly (Eupontania pedunculi), and I noticed that the leaves they were on were more advanced in their autumn coloration than the other leaves with no galls on them. I wondered if this is due to the fact that the sawfly larva inside each gall was diverting the bush’s nutrients to itself, and therefore triggering an earlier leaf fall? I’ll have to do some research in my gall books to see I can find out if this is the case …

These sawfly-induced galls on willow leaves are some of the larger galls that occur in our area, so I carefully cut one of them open, in order to see and photograph the larva that was feeding inside. The remarkable thing about the gall causer-plant relationship is that in many cases such as this one the inducing organism (ie the sawfly in this instance) not only forces the plant to produce the abnormal growth that is the gall, but also somehow stimulates it to provide special nutritive cells that the larva feeds on.

As is often the case, while I was looking at the galls on the eared willow bush, I noticed something else of interest too –  a stonefly resting on one of the leaves. Stoneflies are a distinctive group of insects classified as the order Plecoptera and are characterised by their generally linear body shape and the fact that they hold their wings folded flat along their backs. This makes them relatively easy to identify as a group, but I’m waiting to get confirmation from a former colleague on the exact species of this one – from the photo he thinks it’s most likely Leuctra fusca.

 

 

 

 

 

 

 

With it being autumn, there were plenty of fungi fruiting on the forest floor, and I noticed a couple of common ceps (Boletus edulis) close together near the eared willows.

One of these was very young and fresh-looking, just pushing up through the soil and not completely opened yet. The other was fully-formed, but had suffered from the attentions of slugs and other invertebrates that had feasted on it – the common cep is not only edible for people, but highly attractive to a range of insects and other little creatures. Indeed, if anyone wants to eat one of them, it’s essential to collect them when they are very young, otherwise they are usually infested by the larvae of fungus gnats.

Fungus gnats are small two-winged flies whose larvae live in plant roots and the fruiting bodies of fungi. I spotted several white larvae in this cep, and when I sent a photograph of one to Peter Chandler, a specialist in fungus gnats who’s done surveys for them at Dundreggan, he confirmed that this was indeed a fungus gnat larva. He replied that a white legless larva with a black head was typical of a fungus gnat, but that rearing it to adulthood would be necessary to identify the actual species.

There are many species of fungus gnats (139 have been recorded by Peter on Dundreggan so far) and they can be quite abundant, so there are also many predators and parasitoids of their larvae. There were several predatory rove beetles in the genus Lordithon hunting for larvae in the underside of the cep’s cap, as well as a number of female ichneumonid wasps ovipositing, or laying their eggs, on the larvae of the fungus gnats. The wasp larvae feed on the fungus gnat larvae as they develop, eventually killing their hosts.

There was a whole miniature ecosystem contained within the body of this one cep fungus, and I marvelled at the complexity of relationships that existed there for the brief period of time (only a matter of days at most) that the mushroom would be fruiting before it decomposed and rotted away. It reminded me again of the tremendous privilege of being human, with our long lives and ability to see, document, understand and photograph the wonders and interconnectedness of the natural world all around us.

By this time it was late in the day, and I was planning to camp for the night, before continuing my explorations the next morning – watch out for Part 2 of this blog, coming soon!