“Haywire” seasons caused by global warming are having a worrying effect on flora and fauna, a leading conservation charity has warned.

In its annual wildlife and weather review, the National Trust said mixed-up seasons and warming seas in 2017 had led to a “freak” year for nature.

Flowers bloomed at unusual times, rare visiting birds were spotted and creatures of the deep appeared close to the British shoreline.

Wild daffodils in February. Photograph: John Malley/National Trust

Trust nature expert Matthew Oates said: “Looking at the bigger picture, 2017 has been one of – if not the hottest – years ever, and that’s led to more unusual occurrences in the natural world, globally and here in the UK.

“At times, it feels like the seasons are becoming less distinctive, and that makes it extremely difficult to predict how nature will react. Certain species are good at adapting, which is great, whereas others are struggling – some of them badly. We need to give wildlife the space, time and, where necessary, the support it needs, not only to survive, but to thrive.”

A mild start to the year led to bumblebees appearing in January and rampant vegetation growth, which can be damaging for some small annual plants that become choked.

The dry and mild winter also caused a low spawn count among amphibians such as natterjack toads, probably due to a lack of suitable breeding pools, the National Trust said.

Many spring flowers arrived early. Wild daffodils appeared in February while elder and dog rose, which usually flower in June, were blooming by April. Both continued to flower into the autumn months at sites from Cornwall to Surrey.

It was a good year for some insects with, for example, the heather colletes bee thriving on the Purbeck heaths in Dorset, while the elusive purple emperor, the UK’s second-largest butterfly, was spotted at Bookham Common, Surrey on 11 June – its earliest appearance for more than 120 years.

The warm weather was good for the rare willow emerald damselfly. Photograph: National Trust

The warm weather was good for the rare willow emerald damselfly, which was discovered along the Royal Military canal in Kent, while Atlantic Bluefin tuna have been drawn back to UK waters. Previously common off Britain, the Bluefin vanished in the 1950s after the herring and mackerel they eat were overfished. Now, rising sea temperatures have brought back their food source, and the Bluefin has followed.

Storm Ophelia, which swept across parts of the UK in October, brought with it an invasion of the beautiful – and venomous – Portuguese Man O’ War.

The latter months of the year saw an explosion of berries, nuts and seeds, while there was a good apple harvest and reports of a bumper year for acorns. The heavily laden boughs were the legacy of a fine spring, which also meant crops were harvested earlier than usual.

There were winners and losers among creepy-crawlies in the autumn. A diamond spider, not seen in the UK in half a century, was found at Clumber Park, Nottinghamshire. The annual emergence of the common autumn cranefly, otherwise known as daddy long-legs, largely failed again, which was bad news for birds and bats who feed on them.

Some other parts of Europe did not do so well for autumn fruits, which led an influx to Britain of the hawfinch, the largest UK finch, to the delight of British bird-spotters. Fifty-strong flocks were reported – in one go more than the most dedicated ornithologist could hope to see in a lifetime.

A Soay sheep at Cheddar Gorge. Photograph: Ben Costigan/National Trust

The late summer and autumn rains led to a prolific year for fungi and – until the cold snap in December – strong grass growth was keeping animals from deer and small mammals to the feral goats and sheep at Cheddar Gorge content.

Oates said: “These days, there are huge discrepancies between the winners and losers in the natural world. I’m extremely worried about some species – especially some of our insects – but also buoyed by success stories.”