Understanding determinants of plant invasiveness: a case study on tree mallow Lavatera arborea

We have found the media to be extremely keen to report on our initial studies on tree mallow in Scotland, partly because of its impact on puffins, a popular conservation icon. Hence, we have chosen to present the proposed work in this light, using it as an effective platform to reach people and subsequently inform them about the proposed study on determinants of plant invasiveness. In other words, the text below could be a typical press release send out upon initiating the study. One of Britain's best known seabirds, the puffin, is being forced out of a number of Scottish seabird island colonies by an invading fast-growing alien plant species. Scientists have discovered that dense stands of tree mallow, growing up to 3 metres tall, are choking puffin breeding sites and have warned that the plant could soon start affecting other coastal breeding birds such as cormorant, eider duck, herring gull and fulmar. Tree mallow, Lavatera arborea, an Atlantic-Mediterranean plant native to coasts, is believed to have escaped into the wild in Scotland after being planted in coastal gardens. Whilst present in confined places for several hundreds of years, the plant has suddenly become invasive, taking over island ecosystems and thereby suppressing ground breeding birds and native vegetation. The reasons for this rapid expansion are milder winters and, ironically, an increase in the number of breeding seabirds who fertilise the soil and disturb the vegetation through burrowing and trampling. Manure-rich, bare patches in seabird colonies are now the places where tree mallow establishes and from which they gradually invade island ecosystems. The problem occurs not only in Scotland, but islands in Australia and New Zealand are also having their seabirds squeezed out as tree mallow takes over. Despite being a superior competitor in parts of its non-native range, tree mallow is not invasive in the southwest of the UK, where it survided the last ice age and lives among other plant species in harmony. This 'Dr. Jekyl-style' change in behaviour seems to occur in many plants, with only their invasive character shown when introduced to new environments. Understanding why plants can be invasive in one place whilst not in another has become essential. Once established, the negative effects of invasive plants on native plants and animals, and the associated costs of operations to control them, rise steeply, so a better strategy is to identify high risk species and take measures to prevent this from happening. However, we need to know where and how the problems are likely to arise so that these preventative measures can be targeted precisely. Rather than discussing problems from behind a desk, scientists from the University of Aberdeen propose to study both invasive and non-invasive ranges. Parallel experiments will be set up in Scotland and Cornwall in which conditions that seem to favour tree mallow are being mimicked: guano from birds will be added, and the vegetation disturbed just like seabirds do in their breeding colonies. Moreover, half of the sites will be protected from grazers such as rabbits and sheep as their appetite for the grazing-intolerant tree mallow seems also to play a critical role. In both places, the growth of tree mallow plants from Scotland and Cornwall will be compared to reveal whether Scottish plants are something special, or whether the conditions under which tree mallow grows determines whether or not it will actually turn invasive and cause biodiversity loss. Invasive plants are a major threat to global biodiversity, and their economic costs are estimated to be far in excess of $87 billion U.S. per year worldwide. We hope that our research on this single plant species will give us insights that help finding ways how best to limit further spread of invasives, to the benefit of our natural environment.