"Veteranization" of trees explained

Ancient trees provide different microenvironments from young or typical mature trees.

Oak polypore fungi and stag beetle larvae feast on the dead heartwood, adult stag beetles sup the sugary liquid from the "sap runs", the living layers of wood which transport water and minerals throughout the tree. Hover flies lay eggs in water-filled rot holes, rat-tailed maggots devour leaf litter and violet click beetles eat up wood mould that is rich with faeces and other remains, accumulating over a century. Knothole moss and pox lichen cling to the bark in rainwater channels. Barbastelle bats hibernate in crevices and under loose bark. Woodpeckers and nuthatch enlarge holes for nesting, while owls, kestrels, marsh tit and tree-creeper move in to ready-made cavities...

The ancients of our forests provide essential food and shelter for more than 2,000 of the UK's invertebrates species. In Savernake Forest alone, these trees are home to nearly 120 species of lichen, more than 500 species of fungi, and other important wildlife such as the elusive white-letter hairstreak butterflies.

We face losing these micro-worlds as, one by one, the ancient trees of today are dying and there are not enough ready to replace them.

It takes many human lifetimes to "replace" an ancient tree, but it may be possible to replicate the microenvironments artificially.

It can take up to 300 years before heart-rot, the decay at the centre of an ageing tree, is established enough that insects can start moving in and laying their larvae, says Rutter. "It becomes a complex ecosystem. The ancient trees that we have today, ones that are 300-900 years old – perhaps older – support an incredibly wide range of species."..

Veteranisation is the practice of damaging younger trees in order to initiate decay sooner than it would occur naturally. The hope is that habitats usually seen in older trees will begin to develop much earlier. Veteranisation is not new, explains Rutter, but it is not well documented. Only recently has research been initiated to monitor the success of veteranisation techniques.

An international trial, started in 2012 and set over 20 sites in Sweden, England and Norway, is in the process of evaluating the veteranisation of almost 1,000 oak trees. The methods applied include creating woodpecker-like holes, breaking or ringbarking lower branches or the trunk to mimic damage from animals such as deer or horses, and creating nest boxes for birds and bats. The project is planned to take 25 years, until 2037, so the results have yet to be fully analysed...

"Heart-rot species are key," says Rutter. "These fungi are able to break down the lignin, the very hard part of the wood which is normally incredibly indigestible. Many heart-rot fungi happily eat the central dead wood without harming the living tissue on the outside – and can co-exist with a tree for 600 or 700 years. We want a tree to live a long time so the habitats can continue for as long as possible."

To try and mimic this process in younger trees, Ancients of the Future is growing heart-rot fungi on blocks of wood in the lab, inserting the blocks into holes cut in young trees and recovering them with bark. They are left that way for a few years, then the blocks are removed to see if the fungi have taken hold inside the tree...

She explains that the hollowing of ancient trees by fungal decay, previously seen as detrimental, is a natural part of the ageing process and can even prolong the lives of trees, feeding them nutrients from the inside...

"We need to think beyond our own lifetimes and look after the trees we’ve got now, to give them a chance to grow into ancients," says Rutter. "Trees are fragile, complex chemical factories and major hubs for biodiversity. Without them, many species won’t survive."

Fascinating.  More details at the BBC source article.  You learn something every day.