Managing ash woodlands: how to conserve ash-associated biodiversity given the potential implications of ash dieback. Common Ash Fraxinus excelsior is a common woodland and non-woodland tree throughout the UK. It is threatened by an emerging invasive fungal pathogen commonly called ash dieback or Chalara. The likely mortality rate is still unknown, but widespread death of ash trees within the UK would lead to impacts on populations of associated species that in some way depend on ash to complete their life cycle.