Gleann na Muice Duibhe – The Black Pig’s Glen

Gleann na Muice Duibhe – The Black Pig’s Glen

More ravine exploring!

Fixed between the townlands of Edentober in Louth and Clontygora in Armagh, there is a steep-sided ravine running north from the Black Mountain. I first explored this glen in September and was delighted with a beautiful wooded ravine and some interesting plants and geology.

This glen is possibly linked to the former borders of the kingdom of Ulaidh, and seems to have a connection to the Ulster Cycle, since the black pig is a recurring character. Nevertheless, this river cuts deep through an interesting geologic interface: the brindled microgranite of the Ring of Gullion and the coal-black gabbro of the Cooley Mountains. The igneous geology is very complex here but can be seen very evidently along the stream.

Dark gabbro and lighter microgranite side-by-side

The greatest challenge was finding a way down. After crossing a field, I was met with a fresh landslide, scraping the ravine wall bare of any plants. After making it down in one piece I ventured upstream since this was easier to navigate. More landslides were evident (this was mildly terrifying), and I am not sure why this glen had so many considering its geology. Where woodland remained, it was an impressively rich hazel woodland. Situated in the uplands and in a steep and sheltered ravine, every surface (save the freshly exposed rock) was covered in bryophytes – this is when I got excited.

I had initially thought it would be a shallow ravine with mostly bracken possibly a few willow and birch; I was thankfully mistaken. Hazel was dominant, with occasional ash, rowan, willow and hawthorn. A few mature sycamore were here too, but largely free of invasives. Some of the hazels were huge and of considerable age, which made the place feel even more magical. I explored some of the rocky walls and without much surprise found a few oceanic bryophytes. Plagiochila spinulosa, Saccogyna viticulosa and Lejeunea lamacerina all growing together – all new sites for these species. I suspect there are many others. There were even some ancient woodland vascular plants like wood sanicle and wild strawberry. I suspect it is also a bluebell wood. Other ground flora included a bounty of ferns and carpets of wood-rush.

Plagiochila spinulosa growing among the larger Plagiochila porelloides

The combination of acidic granophyre and basic gabbro provides microhabitats for plants, especially mosses and liverworts. A trickling stream from the west had plenty of Pellia endiviifolia to show off which are slight calcicoles, preferring basic conditions. My search for filmy ferns however, was unsuccessful, despite it being perfect habitat for them.

Revisiting the site is difficult considering the danger of landslides and accessibility, but this is in part (maybe the whole part) why it has survived as intact woodland. Either side of the ravine is cultivated agricultural land and the ravine has been squeezed as thinly as possible. Livestock prevent any lateral expansion of the woodland, instead a perimeter of bracken marks the boundary between wild and managed. It will interesting to see how quickly plants colonise the newly exposed rock and if any other parts will succumb to the same fate. Though it is disappointing seeing woodland removed by landslides, it is a vivid example of the dynamic earth and the interplay between organisms and their environment.

I do NOT recommend visiting this ravine, namely because of how dangerous it is. If you are stupid like me, then I cannot stop you, but you’ve been warned.

Mature hazel trees on the eastern bank of the ravine