Fruit and nuts on native British trees are ripening on average 18 days earlier than they were a decade ago, data from the Woodland Trust has shown.  Observations from Nature's Calendar, run by the Woodland Trust, in which members of the public record the timing of natural events, have suggested that the changing climate is altering the fruiting patterns of a range of trees.  The trend of earlier ripening has been seen across 12 different species, with acorns in Scotland ripening 18 days earlier than in the period 2000-2002, beech nuts 21 days earlier and rowan berries almost a month before they did a decade ago.  Experts believe the shift is down to the trees flowering earlier in the face of warmer springs.  Professor Tim Sparks, nature adviser for the Woodland Trust, said: "There is a suggestion that the average ripening dates have some correlation with mean temperatures recorded for april, so we presume that the link is through earlier flowering leading to earlier ripening.  "However, to see such a uniform advance across so many species is most unusual and we need many years' more data from the public to try to better understand the reasons for these changes."  The trust also said it had data showing that trees including oak, rowan and hazel had all produced increased crops of fruit and nuts over the past ten years.  and 2011, the trust said, was likely