Mounting evidence suggests spring is arriving early this year, according to Woodland Trust research.
The trust analysed the observations of more than 50,000 volunteers as part of its Nature's Calendar project.
The trust said some species of frogs, butterflies and plants have become "startlingly" active.
However, it says this phenomenon has left certain species vulnerable to wintry weather, calling their long term survival into question.
Volunteers observed that peacock and red admiral butterflies were on the wing, there have been 100 sightings of frog spawn and four sightings of tadpoles.
BBC Environment Correspondent Sarah Mukherjee said: "Researchers say that if the species regularly start their spring activities early, their long-term survival could be threatened as they become far more vulnerable to wintry cold snaps."
First appeared on the bbc news website|
Seasonal changes may affect the long term survival of some species