My first chance this year of botanising away from home was a much anticipated trip to the Burren region of Co. Clare on the west coast of Ireland. The area is famous both for its otherworldly, glaciated ‘Karst’ landscape and the unique and diverse flora this supports.
The 800 m deep layer of early Carboniferous limestone which makes up most of the visible rock in the landscape was laid down in shallow, tropical seas 325 million years ago and is stuffed full of colonial corals and other fossils.
The special thing about the landscape here is the way it has been shaped by both glaciation, which stripped off more recent, protective deposits from the limestone and the subsequent erosion of the fractured limestone by carbonic acid in rainwater. This karstification has produced extensive areas of limestone pavement and underground drainage systems with sink holes and caves and means there is precious little surface water in summer.
The thin, alkaline soils which form on top of limestone, the high levels of light reflected by bare rock and the sea and a very temperate maritime climate produced by the gulf stream give rise to a diverse flora with an unusually long growing season. A large proportion of all the 2196 species of flowering plants in the Irish flora are found in the area, along with many mosses, liverworts and ferns. These, in turn, support a multitude of insects, birds and small mammals. Coming from Co. Durham, I am not short of good limestone flora but in the Burren species such as Bloody cranesbill, widespread further south in Europe, jostle for space with remnant artic-alpine flora such as the Spring gentians I find in Upper Teesdale creating a unique assemblage of plants.
Spring gentian, Gentiana verna (left) and Bloody cranesbill, Geranium sanguineum, (right) on Black Head
The range of different habitats in the Burren is a key reason for its diversity. Limestone pavement areas provide deep fissures or grikes, which stay shady and retain water in the driest weather, allowing ferns and dwarf versions of shrubs such as Blackthorn, Alder buckthorn and Dwarf willow to flourish as well as rampant Limestone bedstraw.
Much of the land in the Burren is protected and carefully managed to support this biodiversity. Though the National Park itself is relatively small area (1500 hectares) in the centre of the Burren, a larger area falls into the Burren and Cliffs of Moher Geopark, which includes the vertical sandstone and shale sea-cliffs to the south, which are the highest in Europe.
Of course, as a botanist, there is always a bit of the twitcher about me which wants to find scarce plants, so being introduced to a rare Flecked marsh orchid by a man with a serious botanical camera by Lough Gealáin was a joy. As was finding my first Fly orchids on Slieve Carron nature reserve.
Another favourite for me was Mountain avens, Dryas octopetala, as beautiful in seed as in flower.
Dryas octopetala is a name to conjure with for anyone with even a passing interest in the vegetation history of the British Isles – its pollen is so abundant in peat cores as a marker of recent cold spells in our current glacial-interglacial cycle that these are named after the plant (imaginatively, the Younger, Older and Oldest Dryas periods!) I’ve never seen Mountain avens growing in abundance before, though it has a circumpolar distribution and is found in mountains as far south as Italy. It is a tough cookie, despite the pretty flowers, with leathery leaves resistant to both drought and freezing. Although it produces abundant seeds, each with a plume of silky hairs which carry it long distances in the wind, Dryas mainly reproduces by runners spreading and rooting from the original parent plant. A large clonal colony has a single deep tap root, rather than having to rely on multiple shallow roots – a distinct advantage in this dry landscape and the biggest plants can be up to 500 years old!
Like Wood anemones, Mountain avens’ flowers track the sun and the parabolic shape focuses the Sun’s rays onto the developing seeds in the centre – an important feature in regions further north than the Burren, where the growing season is short. Reproducing vegetatively can be a real advantage in a harsh environment but is a risky strategy when that environment changes in any way. Unlike some artic-alpine plants, whose distribution is threatened by our warming climate, D. octopetala seems to thrive when spring and autumn are warmer. The leaves stay green all winter and last for two or more years so are well able to capitalise on a lengthening growing season. It also seems that the relatively warm climate of the Burren has improved the chances of seeds germinating and new plants establishing themselves, compared with colder regions to the north.
For me the real thrill of the Burren was the abundance and diversity of flowering plants, particularly where shallow grassland has formed over the limestone landscape. Here you see a colourful mosaic of Bloody cranesbill, Bird’s-foot trefoil, Kidney vetch, Tormentil, Mountain everlasting, Wild thyme and Milkwort, alongside the Mountain avens.
This diversity is apparent even when cattle are being grazed in the fields, which speaks to careful management of livestock density and also, I suspect, to the almost total absence of sheep in the landscape.
The collage below gives just a taste of that diversity….
The really good news, from my point of view, is that a repeat trip next year might be on the cards if @Basilosaurus is invited to do some more teaching in Galway….