How fungal inoculation can begin a tree hollow

A hollow is not damage to a tree but a habitat. It forms when a wood-decay fungus works inside the trunk for decades while the tree goes on living, because water and assimilates move through the outer layers. Bats, hole-nesting birds and a whole group of saproxylic beetles depend on that space.

The problem is time. A tree with hollows is usually a hundred and fifty years old or more, and managed landscapes hold few of them because they are felled earlier. A generational gap opens up: the habitat is missing now, and the trees that will make it are still young.

The paper by Jonathan Wainhouse and Lynne Boddy in Global Ecology and Conservation describes a technique for shortening that wait — introducing a wood-decay fungus into a living tree for the conservation of threatened taxa. The text is written as a guide for conservation practitioners rather than as a report of an experiment.

The technique sounds subversive, because the whole tradition of tree care rests on keeping wood-decay fungi away. The point of reversing that rule is that wood decay is not a disease of the tree but a habitat-forming process — and that what an impoverished landscape lacks is precisely the process, not the trees.

It is worth stating plainly what this entry does not claim. This is an intervention in a living tree, and the outcome depends on the tree species, the fungus and where the inoculation is placed. The authors describe it as a tool for conserving particular threatened taxa, not as something to try in any park.

Inoculation begins a process; it does not guarantee a hollow

Edman and colleagues inoculated living Scots-pine heartwood with Porodaedalea pini in 50-, 110- and 170-year-old stands. Seven years later, fungal DNA occurred in 67% of trees; stand age and three strains did not alter colonisation success. The study had not yet shown completed hollows or animal occupancy. In an older Washington experiment, after 8–9 years Fomitopsis pinicola conks occurred on 20.0% of inoculated trees versus 0.4% of controls, and woodpecker signs on 6.2% versus 1.2%. Inoculation can initiate decay and increase tree use, but outcomes depend on the fungus–tree pairing, protocol and decades of follow-up. It is a specialist conservation experiment, not a licence for the public to wound trees.