By Alex Kirby
BBC News Online environment correspondent
The landscape of much of the southern UK will be altered forever by climate change, a gardening expert believes.
Blackcurrants may not survive in southern Britain (Image: RHS Herbarium)
Dr Simon Thornton-Wood of the Royal Horticultural Society told BBC News Online orchards would vanish, and some fruit varieties would no longer thrive.
But as they move northwards, he thinks, peaches and other fruit from southern Europe may move in and replace them.
He says he also expects "significant" drops in yields of several summer fruit like pears, cherries and blackcurrants.
Too warm to fruit
Speaking before the RHS Science Exchange Dr Thornton-Wood, the society's head of science, said the UK Climate Impacts Programme showed there would be some frost-free winters during this century.
Warmer winters would fail to provide the chill that some plants need if they are to produce flowers and fruit.
Orchards are likely to move north
Dr Thornton-Wood said: "We've lost a lot of orchards in the UK, but apples are still an important crop.
"I think the climate will mean it becomes harder to get a decent crop in the south of England, and apples may head north to find a cooler place to grow.
"Other fruit crops will be affected too, but I imagine it will be easier to grow crops like peaches instead. It'll be a matter of swings and roundabouts.
"Our members are becoming more aware. In these last few years we've seen some quite significant variations in what people regard as the norm.
"We're getting many more queries now about waterlogging, and last year about drought as well."
Usurped by aliens
A study on the possible implications for commercial fruit growers of warmer winters has been commissioned by the Department for Environment, Food and Rural Affairs.
The RHS is giving priority to two other climate-related problems which it says are of particular interest to gardeners:
Dr Thornton-Wood told BBC News Online: "Giant hogweed has already gone haywire, and we think other invaders may do the same.
The need to find ways to offset the effects of winter flooding on what are known as "Mediterranean" plants, which will thrive in hotter summers
The possibility that climate change may encourage some exotic weeds to become problematic invaders.
"Japanese knotweed is a problem, but we don't really know where the next crisis will come from, so we're calling on gardeners to be observant.
"You never know how species like these are going to affect the ecology of the British countryside, but they always do. They out-compete the native fauna and flora and change what has become familiar."
Japanese knotweed could become a bigger problem
The RHS Science Exchange, being held at the Darwin Centre in the Natural History Museum in London on 16 March, brings together leading horticultural scientists to discuss the future of gardening in the 21st Century.