A mass die-off of trees could happen in the next 50 years unless action is taken, warn experts.
"Ecosystem collapse", where trees suddenly fade and die, could happen within 50 years, they warn.
But the 42 experts said if we act now we can avert the catastrophe.
The large-scale loss of forests hit by "wind, fire, pests and disease" has already happened in continental Europe and North America.
"A collapsed forest would be heart-breaking, devoid of its essential life and all the joy and benefits it gives to humanity," said Dr Eleanor Tew of Forestry England and Cambridge University.
But she said we have time to make a difference and we know what to do to make our forests more resilient "so they can continue to thrive for future generations".