Everybody knows autumn is on its way when the leaves begin to turn, but it appears Scotland is to have two versions of the season thanks to the phenomenon of "fool's gold".

Leaves on many trees are changing colour ahead of schedule and Woodland Trust Scotland says it is because of this year's dry summer. According to Met Office records, August 2013 was the driest in Scotland since 2003.

This has resulted in many trees not getting enough water, causing species such as sycamore and birch to show early autumnal colouring and begin to drop their leaves.

Conservationists are now looking for volunteers to help chart the phenomenon. Rory Syme, from the Woodland Trust Scotland, said: "When we have a particularly dry summer this can lead to early autumn colour in some tree species, and in effect we'll experience two autumns.

"True autumn colour is triggered by fading sunlight and cold temperatures. Leaves lose the chlorophyll that makes them green, revealing spectacular yellow and red pigments.

"Fool's autumn colour is different. It's caused by trees still struggling to cope with a dry summer. They wilt and drop their leaves early to save water."

He said people might notice that the colouring seems especially early or out of character compared to other trees of the same species nearby.

Data recorded by The Woodland Trust over the past decade suggests that trees across Scotland will on average show the first signs of 'true' autumn colour during late September, with 'full tinting' appearing in mid-late October.

The trust is appealing to the public to use its VisitWoods website to find their nearest wood and record dates of true autumn colour - vivid reds, golds and browns. The onset of autumn occurs as the days get shorter, meaning plants and trees photosynthesise to a lesser extent and produce less chlorophyll.

Sudden drops in temperature at night also destroy chlorophyll, all of which reveals the yellows and reds of the season, that in fact were present - but hidden - in the leaf all year.