If diseases affecting trees take hold, the Isle of Man risks losing up to three-quarters of its tree population.
That was revealed in the House of Keys this week by the Environment Minister in response to concerns from North Douglas MHK Bill Henderson.
Mr Henderson had specific questions about the department's policy on dealing with the threat of Sudden Oak Death and Ash Die Back.
Phil Gawne said measures were in place to minimise the threat of them spreading, including importation limitations and certain restrictions in the countryside.
Mr Henderson hopes the department is being aggressive enough.
Mr Gawne says as soon as they realised there was a significant Ash Die Back threat in the United Kingdom, they acted very quickly.