The aliens have landed
Native plants that we cherish in Ireland can become big problems abroad, and vice versa, as the experience of Bodega Marine Reserve, in California, shows
Invaded territory: dune ridges at Bodega Marine Reserve dominated by marram grass and (dark patches) Hottentot fig instead of native vegetation. Photograph: Jackie Sones
Invaded territory: the dune gilia, a rare California flower threatened by marram grass. Photograph: Jackie Sones
Bodega Bay, north of San Francisco, has got pretty used to living with threats of one kind or another. Most obviously, this natural harbour sits on top of the San Andreas Fault, where the Pacific and North American tectonic plates rub up against each other.
The San Andreas line runs under the housing at the Bodega Marina Reserve of the University of California Davis, where I am a guest.
In the brilliant Californian sunlight Bodega Bay is a kind of paradise. But when dense fog rolls in, as it does very frequently, and amplifies the pounding surf on the northern beaches to a booming roar, it can seem a little sinister. Which is probably why Alfred Hitchcock chose to film The Birds here, and why John Carpenter used it as a location for The Fog.
In the real world, the abundant wildlife in Bodega is unthreatening, with the exceptions of poison ivy and, perhaps, the occasional mountain lion.
The bay is lined with migrating shorebirds and pelicans, the sea sometimes seems to heave with seals, sea lions and cetaceans, and the landscapes of the headland, part college experimental reserve and part state park, are still strewn with the last of the summer flowers.
But it is here, on the great dunes and extensive coastal prairies that make Bodega Bay so special, that serious threats to the future of these ecosystems are making frightening headway.
The odd thing about this is that some of the most threatening life forms here are very familiar, and very welcome, ecologically speaking, at home. Our cherished native plants, it turns out, can become most unwelcome alien invaders elsewhere.
I was taken aback when a Californian scientist, visiting Wicklow recently, expressed concern that the dunes of Buckroney Nature Reserve, just south of Brittas Bay, were so “infested” with marram grass (Ammophila arenaria). But this plant should be here, I reminded him, and he quickly conceded that his response was coloured by his experience of marram grass in his own native place. In California marram grass is invasive, spreading extensively because the ecological forces that control it in Ireland do not exist on the west coast of the United States. And so it displaces the native plants that once carpeted Bodega’s dunes, such as sea lyme grass and sand verbena.
Indeed, more than a third of the plant biomass on Bodega Head is now made up of alien species. There is a danger of local extinctions of rare plants. There is also a danger that the whole system could tip over into a novel habitat that may become increasingly inhospitable to native animals as well.
The marram grass has not come to California by accident. It was systematically planted, in industrial rows, from the 1920s. It seems to have been introduced to stabilise the dunes,which were being trampled loose by cattle on the ranch that then occupied the headland.