Ecology of an ungrazed island

The island in Loch nan Eun on the Hilton Estate offers the geographically closest example to Dundreggan of what a more natural vegetation community might look like at higher elevations in the Highlands. At 0.74 hectares (1.8 acres) in size, it is too small to support any resident deer, and although the loch may be frozen over completely in very cold weather, theoretically allowing deer access to it, there wasn’t any evidence of recent grazing during the visit we made to the island in November.

The species of plants growing there are the same as those on the lands surrounding the loch, but because of the lack of grazing, the balance has shifted between them. Heather predominates on the island, whereas elsewhere it is suppressed and grasses are more abundant. This is true for much of the western Highlands, and the natural process of succession, that would see wet heath and grassland gradually replaced by dry heath in suitable sites, is prevented. This is known as arrested succession, and is the result of excessive grazing by the artificially high deer population in the Highlands today. In the drier, eastern parts of the country, the practice of muirburn, whereby heather is burned on a regular basis to provide a supply of new growth to benefit grouse, has a similar effect. Burning prevents the succession of dry heath into young woodland, which occurs when pioneer species such as birch and rowan grow amongst the heather.

On the island, heather covers most of the land, and some trees have become established, despite the distance from the nearest seed source. Rowan seeds arrive in bird droppings, while the seeds of birch and eared willow can travel considerable distances by wind. All of those trees, plus a large area of low-growing juniper, are growing successfully, albeit to a small stature because of the elevation (505 metres) and exposure to the wind and cold.

Other features on the island also illustrate the growth of vegetation that can take place in the absence of grazing by deer. These include abundant lichens on the low branches of trees, extensive beds of reindeer lichen and a greater profusion of cloudberry than I’d seen in the Highlands before. Both of those latter features reminded me of landscapes I have visited in Norway and Sweden, where there is less grazing pressure on the land and forests than in Scotland. Even in winter, the island was lush and abundant in comparison to the surrounding land, and it felt like a small sanctuary - a refuge where plant life could still flourish as it must have done throughout more of the Highlands in the past.

This island is not alone of course in providing an example of how different vegetation communities can be when they are not subjected to excessive grazing. There are a number of other islands in the middle of lochs that are noted for their vegetation. The best-known perhaps are those in Loch Maree, which contain some of the least-disturbed native woodlands in the UK.

Alan Watson Featherstone

 

Click on an image below to view the gallery.

Looking east from the centre of the island, the juniper (Juniperus communis) patch, with reindeer lichen (Cladonia portentosa) in the foreground and birch (Betula spp.) and rowan (Sorbus aucuparia) trees behind, provides an indication of what a healthy montane landscape could look like in the Highlands.
This tiny fungus (Cordyceps militaris) seen here in a mossy hollow between two of the trunks of a rowan tree, is notable because it grows out of the pupae of moths while they are overwintering.
Gall induced by a sawfly (Euura atra) on the stem of one of the eared willows (Salix aurita) on the island.
There are some good patches of this reindeer lichen (Cladonia ciliata) on the island.
Tristan Dougan and Badger Pigott doing a quadrat survey on the island. Birch (Betula spp.) can be seen in the background, while heather (Calluna vulgaris) is abundant.
This dog lichen (Peltigera membranacea) was abundant on some parts of the island.

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