Eucalyptus and Mimosa – Portugal’s Australian problem

Just had two weeks in central Portugal, near Coimbra. The Iberian peninsula is not somewhere I am that familiar with, but would increasingly like to be. It is home to some 6,000 native flowering plant species, scattered over an amazingly wide range of habitats. A brief foray into Spain last spring made me feel very optimistic about spending more time in the region. Central and northern Portugal however been a bit of a reality check. It seems to be home to one of the biggest accidental experiments in ecology I have ever seen. One which looks disastrous and which has had amazingly little publicity, at least outside the country.
The problem is Australians. Not the people I hasten to add, but eucalyptus and Acacia dealbata – the familiar mimosa and Acacia melanoxylon. And a New Zealander – Pittosporum undulatum, and increasingly the South American Cortaderia selloana – pampas grass. I have, as many of you may be aware, often been pretty sceptical about much of the currentdiscussion of invasive aliens. I have always felt that people in Britain who worry about impatiens or Japanese knotweed have very little idea of the damage that really invasive aliens can do; and that many ‘invasives’ are actually not so bad. Increasingly there is evidence that alien species can even play a positive role in the development of novel ecosystems. Portugal is a good example of where things can go really really wrong, but also just how complex these issues are.
To start with the deliberately spread alien, the eucalyptus, mostly E. globulus. Almost any vista in the region between the mountainous east and the coast, north of Lisbon, that we drove through included it, in vast quantities, the distinctively bunchy growth of the outermost branches being particularly conspicuous in silhouette. Almost all the hills are covered with it – nearly all planted as a forestry crop for the paper pulp industry, although it also has some capacity to spread by seed too. The story is that much of this region has granite or other acidic soils, and is not much good for the pastoral agriculture that one might expect in hilly regions, or indeed for cork oak, which is a major form of land use in the warmer and more calcareous south which the tree prefers. Historically, these hills were dominated by oak and chestnut but centuries of deforestation resulted in them being covered in scrub: gorse, heathers, cistus and suchlike. Economically pretty useless. Pine was often planted or spread naturally. But during the 20th century eucalyptus was introduced and promoted under the Salazar regime (always nice to have a fascist dictator to blame!). The paper pulp industry continues to promote planting the tree. The result is an oppressive monoculture, which with the decline of the pulp industry (now moving to South America), is going to be increasingly worthless. To say nothing of the fire risk, posed by this infamously inflammable tree. A eucalypt fire can turn whole landscapes to ash.
Eucalyptus is a controversial crop. One can’t blame poor rural regions for wanting to earn money from forestry. And in fact in terms of the big environmental picture it is actually a good thing. The vast area under the tree here must have soaked up a huge amount of CO2, done much to help reduce soil erosion and hold water in the ground. There is a widespread belief in much of the world that the trees dry the soil out, but in fact there is little evidence that this is the case. In very poor regions their presence can actually help protect native forests by being a superior source of firewood and timber, e.g Bolivia.