Habitats & Geology

Arran contains a fantastic array of habitats which are home to the island’s diverse plants and animals. These habitats are affected by the landscape and the underlying geology.

The landscape determines how exposed the environment is, and how well-drained the soil. The geology affects the chemical properties of the soil, like acidity and availability of nutrients. As these factors interact, different plants take root, providing food and shelter for a range of animals. Indeed, all of Scotland’s ‘Big Five’ are well-established on the island: golden eagles, red deer, red squirrels, otters and harbour seals.


Large areas of Arran, especially in the hills, are covered in heather moorland. These areas have acidic soils due to the breakdown of underlying igneous rocks including granite and rhyolite. Plants such as heather, bracken, juniper, and some grasses can withstand the acidic conditions and exposed environment. Heather moorland is a vital habitat for many of Arran’s important species, including red deer and hen harrier.

The volcanic rocks on Ard Bheinn in the centre of the island create conditions ideal for heather moorland. Granite is made up primarily of the minerals quartz, feldspar, and mica. When these break down they form acidic, nutrient-poor soils that many plants cannot grow on.

Arran has three endemic tree species which do like these soils: the Arran whitebeams. They are found on steep, rocky slopes in two northern glens, and are amongst the world’s rarest and most endangered tree species.

There are several herds of red deer – the UK’s largest deer – across the island. Listen for the stags roaring during the rut in September and October. Image: Terry Whittaker.

Peat Bogs

Peat bogs also form in places with acidic soils, and require poor drainage. They are widespread across hills and glens all over Arran. They occur when dead plant material doesn’t break down in the waterlogged ground, building up as more plants grow on top. The organic-rich material that is formed is called peat.

The most common plant in peat bogs is sphagnum moss, which forms a thick blanket across the landscape and soaks up huge amounts of water like a giant sponge. Other plants found in Arran’s bogs include sundew and butterwort: carnivorous plants which have adapted to the nutrient-poor soils by evolving to trap and digest small insects.

Cast your eyes upwards, and you may see the golden eagle soaring above: rural Scotland’s top predator. They hunt by flying low, and nest in remote crags. In the UK, only the white-tailed sea eagle is larger, having been reintroduced in the 1970s to the Isle of Rum – and we now get the occasional fly-past from them, too!

A pool in a peat bog, in the hills high above Laggan, North Arran.


Woodland and commercial forestry cover around a quarter of Arran, and provide vital habitat for countless mammals, birds, amphibians and invertebrates. Many of these areas are also popular destinations for walkers and cyclists. Arran’s woodlands exist predominantly on lower ground with less acidic soil, which has been formed by the breakdown of sedimentary rocks and basalt.

However, the idea that woodland cannot exist in Scotland’s uplands is a myth. Hardy scrub tree species were once abundant in Arran’s hills, but centuries of overgrazing by sheep and deer have seen montane scrub all but wiped out. Invasive species such as rhododendron can also ‘crowd out’ native plants. In response, the National Trust for Scotland’s Glen Rosa Project is seeking to restore these degraded habitats, through tree-planting, action on invasive species, and a newly-installed deer fence.

The island’s forests are already home to a thriving red squirrel population: all the squirrels you see on Arran are red squirrels! They are doing so well here because, unlike on the mainland, they face no competition from the non-native grey squirrel.

Sheep grazing amongst a mixed native woodland.


Arran’s rocky coastlines host a wealth of habitats for marine creatures. Mostly, the seabed comprises mixed sediments – sands, gravels, shells and muds – which were laid down during the Holocene, in the aftermath of our last ice age. This range of sediment provides the hard substrate on which living reefs can develop, building complex structures.

Reefs house wonderful spiny starfish, sea urchins, octopus, anemones and crabs, amongst quite literally hundreds of other species. Seagrass meadows lie both to the northwest and to the south of the island, acting as nurseries for fish and crustaceans. Both otters and seals take advantage of the varied diet this sea-life provides!

And, of course, farther out to sea you might spot basking sharks, dolphins, porpoises and whales – so keep your eyes peeled when you’re on the ferry!

The spectacular diversity of Arran’s coastal waters today is in large part a result of the Community of Arran Seabed Trust‘s successful campaign for the South Arran Marine Protected Area, which has led to a quite inspirational rewilding of an area that, very recently, was bereft of habitats and desperately depleted in fish stocks.

Oystercatchers strutting along a dyke at Kildonan. They dine on mussels and cockles, and tend to lay their eggs on pebbly shores.

Further information:

See the NTS’s Wildlife Spotter’s Guide for Goatfell to find out more about some of the exciting species in Arran’s hills!

A good overview of Arran’s plantlife is available, unsurprisingly, from Plantlife.

COAST – the Community of Arran Seabed Trust – led the successful campaign which resulted in Scotland’s first community-developed Marine Protected Area, with exciting and ongoing developments for Arran’s biodiversity. To learn about their ground-breaking work and Arran’s remarkable marine life, go to the COAST website.

To find out about Arran’s birds, go to Arran Birding where you can access the Arran Bird Atlas as well as see up-to-date information on sightings around the island.

Don’t visit Arran’s hills and wild coastline without an Ordnance Survey map! The whole island fits satisfyingly on to one sheet of an OS Landranger map, buy one here. Or for even more detail purchase an OS Explorer map. Buy using these links to help support local bookshops – Arran Geopark will be given 10% too.

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