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For wildlife, not all trees are equal. Large old trees have many for perching, and many fissures or hollows for sheltering. By contrast, younger trees have far fewer such features or lack them entirely. More than 300 species of Australian mammals, birds, reptiles and amphibians habitat structures in older trees.

Pygmy possums use small hollows to form. Black cockatoos need larger hollows that might take 200 years, and bigger birds such as powerful owls need still older hollows. Many species also need found only in older trees.

But these large old trees are getting rarer . Australia has many of and they're due to farming, logging and urbanization.

Birds and animals centuries for new hollows to form. In response, land managers are experimenting with , where younger trees are the features of older trees. If done carefully, veteranization may have promise.

Making young trees older

Artificially aging trees isn't new. The ancient practice of trees to promote growth also encourages hollow formation.

But there's in exploring veteranization to boost habitat, either by damaging trees or adding structures or supports.

Most commonly, veteranization is done by damaging younger trees to encourage decay. Using chainsaws to cut off a limb can open up the dead heartwood inside a tree to wood-rotting fungi, which can deepen smaller hollows.

Veteranization can also involve adding structures resembling natural hollows or cavities. Nesting boxes are well known, but animals can avoid artificial-looking structures, find them too hot or struggle to climb smooth walls. Our research has found and can avoid this. Mimicking natural complexity can trick wildlife into using younger trees.

Removing limbs, causing damage

In Europe, managers have cutting off the crown of the tree, breaking or pruning branches, scorching surfaces with fire, ringbarking limbs, using "" cuts to trap water, drilling holes to expose internal decay and bruising stems. Swedish researchers found increased decay and created more microhabitats but didn't affect formation of large dead branches.

In Australia, researchers have trialed or to carve hollows into living wood. These hollows are rapidly by as well as . Informal reports suggest hollows made by skilled arborists in Tasmania were rapidly used by critically endangered .

Supporting branches, adding features

It's not essential to damage younger trees. Another approach is to add missing features, such as by:

• installing to provide nests and shelters
• repositioning to
• as food for wood-eating organisms
• making to house plants and small animals.

Our research suggests another possibility: constructing able to stand on their own or attach to younger trees.

We should think of these human-made features as rather than a temporary tweak. They should be carefully designed, safely installed, maintained as needed and their use monitored. At the end of their life, they should be retired and an equivalent type of habitat installed or grown.

Another approach is to preserve existing veteran trees by branches likely to fall.

Techniques worth exploring?

To date, Australian trials feathertail gliders, sugar gliders, brown antechinuses, long‑eared bats, white‑throated treecreepers and other species using features created by both damaging and feature-adding techniques. can also benefit.

Many other species could benefit, including hollow‑nesting and perching , , arboreal marsupials and the which eat dead and decaying wood.

It will take more research to find out which techniques work best. Approaches such as aren't very effective in hollow development, while other approaches can or the lives of damaged trees.

Similarly, some fissures close soon after , while modifications such as inoculation with tree-rotting fungi in producing these features.

Applying veteranization in Australia will require adaptation. Bushfires can to trees temporarily weakened by veteranization or augmented by artificial structures. Eucalypts have distinct wood chemistry allowing them to .

Overall, we should think of veteranization as a supplement rather than substitute for large old trees.

This is because artificial features aren't the same as natural. The communities of fungi and invertebrates that live on tree surfaces, in cracks and within hollows can differ from their .

Protect large old trees first

It can be alluring to come across new ideas such as veteranization. But the thrill of the new can make it hard to see the situation clearly.

For land managers, the priorities are clear. Protect large old tree and ensure younger trees can grow old safely.

If this is done, it may be worth experimenting with veteranization to mimic old trees in areas where there are shortages. Testing will . Run trials, make adjustments to find improvements, share data openly about what works and what doesn't, and make advanced methods to everyone.

Tree-damaging methods are worth exploring, but they should not be our first choice. It doesn't seem right to damage young trees to make up for the damage humans have done to their ancestors.