Spring no longer begins in March and the end of autumn now continues well beyond October, according to information gathered by almost 17,000 volunteers.

Naturally occurring events such as the arrival and departure of birds, the flowering and ripening of plants and fruits and the start of new life traditionally herald the change of the seasons.

But the Woodland Trust, the UK's leading woodland conservation charity, and the Centre for Ecology and Hydrology have warned the seasons are becoming increasingly muddled up.

The findings of thousands of volunteer phenologists- those who study the timing of natural events such as climate change - provide evidence that the seasons are changing.

Higher than average temperatures from January to April led to almost every characteristic of spring this year occurring up to three weeks earlier than in 2001.

On average, insects such as bumble bees and butterflies were three weeks early, while plants flowered two weeks ahead and many birds, including the turtle dove, arrived a week early.

Interconnected and other complex relationships between trees, insects and animals in woods are also affected by early spring arrivals.

Results from this spring show that some synchronous relationships between birds, insects and plants could become disturbed.

Crucially, for many species, this could have serious implications for their future survival, says the Woodland Trust.

As ancient woods become even more fragmented and isolated, some characteristic plants and animals might face further threats as the climate changes.