Tree managers can improve the long-term ecological health of woods by "injuring" younger specimens to give them the characteristics of ancient trees, according to Vikki Bengtsson of Swedish consultancy Pro Natura.
She told the London Tree Officers Association Veteran Tree Seminar (31 January): "There is often a gap between old and young trees in a wood - you have 300-year-old trees and then 60-year-old trees. People value the old ones but the middle-aged ones less so, and that gives us an ecological problem."
The solution being pioneered by Pro Natura and the UK's Ancient Tree Forum is to "veteranise" trees that would otherwise be thinned out, increasing their habitat value for the specialist fauna typical of ancient trees.
"By 'veteranisation' we mean speeding up the natural ageing process in the tree," Bengtsson explained. "Pollarding already has that effect - in willows, you create hollows 50-70 years sooner than they would naturally arise."
Bengtsson began by injuring, in various ways, younger trees that were shading out the famous ancient trees of the National Trust's Hatfield Forest in Essex, where she used to work. Since then, she and colleagues have tried "around 20" techniques, from tearing bark with climbing spikes to setting off tree-mounted explosives.
"You would never do this on actual veteran trees - only on the boring ones that you would take out anyway," she stressed.
While monitoring is ongoing, she admitted that many unknowns remain. "Our results so far are quite anecdotal. There is a lack of robust data on which techniques work and which don't. We also don't know how many trees of today will reach ancient status, given climate change and tree diseases."
Veteran trees Educational programme
Pro Natura and the Ancient Tree Forum (ATF) are also partners in VETree (Vocational & Educational Training in Veteran Trees), a two-year largely EU-funded programme operating in the UK, Sweden, Belgium, Spain and Romania that runs until October.
ATF coordinator Helen Read told the seminar: "The situation in each country is very different. In Romania, where land use is changing very quickly, we are still at the stage of explaining why ancient trees are important, while other countries are more interested in risk management."
Videos and a range of other materials are now being made available on the VETree website - see vetree.eu.