The conservation charity is counting the cost of fires on its sites over the past five years, which have caused millions of pounds worth of damage and had a devastating effect on rare woodland and wildlife.
Many summer wildfires are started accidentally by lighting fires or disposable barbecues. But one stray spark or an abandoned pile of dying embers can have horrendous consequences for the countryside, decimating wildlife and causing long-lasting damage.
Nick Hall, head of health and safety, said: “Fires have huge implications - both in terms of the financial burden and the effect on our woods and wildlife, which can be catastrophic.
“One spark really can spell disaster. You’re gambling with the lives of people and animals by taking one on your summer outings.”
With the potential for prolonged periods of dry spells, the risk of wildfires significantly increases and they can easily get out of control.
The “be cool, stay fire-free” message is part of the trust’s Love Your Woods campaign which is encouraging people to enjoy their visit but help protect woods and nature for the future.