Could 2011 have two autumns?

The Woodland Trust is calling on the public to help them track the early signs of autumn to see if it is affected by the unusual seasonal events that have taken place so far in 2011.

With spring 2011 possibly being the earliest on record, one school of thought suggests that an early spring will be followed by an early autumn since leaves may have a “shelf-life”.

Another believes that trees will remain growing as long as temperatures remain high and water is available.

Data recorded by the charity over the past decade suggests that trees across the UK will on average be showing the first signs of autumn colour during late September, with so-called ‘full tinting’ appearing by late October.

Despite above average rainfall between June and August, according to the Met Office, the extremely dry spring has resulted in an overall water deficit and has caused many trees to show false autumnal colouring as they wilt and lose their leaves to help water retention.

As a result the Trust is asking 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 benchmark date for the UK’s most symbolic tree – the oak – to show the first signs of autumn colour is 25 September, with full tinting appearing by October 30.

Professor Tim Sparks, nature advisor to the Woodland Trust said: “Autumn is the best season to get out and make the most of our trees and woods, the beautiful reds, browns and golds are an awe-inspiring sight. We’re calling for the public to help us record the changing seasons, which helps inform scientists about the effects of climate change on our native flora and fauna.”

The onset of autumn occurs as the days get shorter, meaning plants and trees photosynthesise to a lesser extent and produce less chlorophyll – which provides the green colouring seen in leaves.

Sudden drops in temperature at night also destroy the chlorophyll, all of which leads to the appearance of the yellows, reds and browns of the season.

Preliminary results from nearly 40,000 volunteer observations recently compiled by the charity suggest that spring 2011 was the earliest so far this century, with some events earlier than in any year for which data is held – as far back as 1891. Records for autumn cover far fewer years; hence the importance of gathering data now.