Mounting evidence suggests spring is arriving early this year, according to Woodland Trust research.
Seasonal changes may affect the long term survival of some species
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."
This year I've noticed the dwarf narcissi in my garden (large pots in a North facing, overshadowed, concreted, back yard) are coming into flower. There are even tulip leaves coming up.
Last year they were flowering in time for St David's day, a month later.
Of course, the previous year they didn't flower til well into March as it was sooooo cold that year.
I've had a clump of snowdrops out for nearly three weeks now, and a couple of iris reticulata. These are, more or less, to time.
Sharon, Portsmouth, UK
Seasons have ceased to exist. The crocus's in my garden started to show a week ago and the rose bush only stopped blooming at the end of November. I barely have to time these days to administer some much needed pruning before my plants start to bud again.
Bring back the days of good solid frosts and decent snow-falls, I miss them.
Kiltie Jackson, Staffs, UK
I was amazed about a week ago when I was standing out on my back patio and a bumblebee buzzed lazily past my head. Bumblebees in January is something I've never seen before. It's so cold though, I bet they wish they'd stayed in bed!
I also spotted my elderly next-door neighbour wielding a camera at her laundry line. When I asked what she was up to, she said there had been a red admiral butterfly resting on her drying sheets. She had seen it a few days earlier and had kept the camera near the back door in case she spotted it again. She was amazed!
Anji, Portsmouth, Hampshire
We already have tadpoles in our wildlife pond, but this is the right time - February. The frogs will be spawning towards the middle of this month which is normal. They are certainly not early but within their time.
Penny Bright, Hullbridge in Essex