Forestry Commission Plant Health Service head Dr John Morgan said: "The UK's trees, woods and forests face unprecedented levels of threat from non-native pests and diseases, many of which have entered the country on internationally traded products.
"These pests and diseases are usually kept in check by indigenous predators and environmental conditions in their natural ecological niches in other parts of the world. However, partly because we are an island nation, these natural checks and controls are often not present in the UK, allowing the pests and diseases to be much more destructive when they arrive here.
"The warming climate is also increasing the risk that some of these organisms may find it easier to become permanently established here.
"Our first line of defence is to try to prevent them from entering the UK in the first place, but we need to be prepared for the fact that some will get in. When that happens we must do everything we can to eradicate them or, if that proves impracticable, to contain and control them as best we can.
"This guidance should prove an invaluable aid to many people who have to visit woods and forests in the course of their duties or recreation, by giving them useful advice on steps they can take to avoid accidentally spreading these damaging organisms on their clothes, footwear, vehicles and by other means."
The document is available on the Forestry Commission website at www.forestry.gov.uk/pestsanddiseases