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The UK Government has imposed a ban on import of Ash trees (Fraxinus excelsior), in response to the spread of the fungus Chalara fraxinea in UK trees.  100,000 young trees have been destroyed in an attempt to curb the spread of the fungus, which causes ash dieback.  The disease was first described in Poland in 1992, and has spread through Europe, with 90% of Ash trees in Denmark now having succumbed.

The fungus is an anamorph of a newly-discovered species Hymenoscyphus pseudoalbidus, which has been categorized as an invasive species within Europe, and so is considered a less welcome addition to our knowledge of biodiversity.  There are estimated to be as many as 1.5million species of fungus on the planet, and only a small minority – around 70,000 – have been described by scientists.

It’s not surprising, therefore, that a previously unknown species has come to prominence in the last two decades.  Current events do beg the question, however, of what has led to the fungus spreading so devastatingly through european trees; its virulence could be a symptom of increased environmental stresses in forest ecosystems, for example.  As official agencies scramble to contain the spread of the fungus (amid claims of prior incompetence), it remains to be seen if significant damage to the UK’s forest ecology can be limited.