The Woodland Trust's chief executive has said increasing people's access to green spaces could cut billions of pounds from the NHS healthcare bill.
Sue Holden said it had been calculated that the NHS could save £2.1bn a year if everyone had access to green spaces.
She made the comments at an event to mark the culmination of the five-year VisitWoods project.
Ms Holden added that only an estimated 14% of the UK's population had "easy access to trees".
She told an audience of invited guests at the Houses of Parliament that the link between "healthy woods and healthy lives" was a "connection that really has to be made much more and much more often".
She added: "It is a connection that we know intrinsically, we believe it to be true but - increasingly - it is something that evidence is backing up as well.
"It has been calculated, for example, that £2.1bn of healthcare costs could be saved if everyone had access to green spaces."