Typically, “tree aging” is done by counting annual growth rings, either on a stump or on a sample core taken by a special tool. But the phrase can also refer to veteranization, a process whereby trees are prematurely aged through targeted injury and stress in order to create specialized habitats. It’s much like the ageing of parents, a treatment administered by one’s children to produce worry lines, grey hairs, and character.
We humans whistle past the cemetery, as it were, with refrains like “50 is the new 40,” apparently hoping to trick death into giving us a free decade somewhere along the line. For trees, there is no single definition of old. A mountain-ash is decrepit by fifty, while a bur oak of that age is a mere adolescent. Every species has a lifespan range beyond which no amount of wishful thinking or supplements can help.
Among long-lived trees such as hard maple, oaks, hickories, and white pine, veterans which are past their prime and beset with internal decay from lightning strikes, logging injuries or storm damage may still have centuries of life remaining. They are of little commercial value, though, and standard forest-management norms would dictate that they be removed. Yet those sylvan elders play a unique and essential role in the ecosystem.
Flying squirrels love to nest in mid-size branch or trunk cavities, and I’ve seen large trees which have clearly sheltered many generations of porcupines. Raccoons are just as likely to den inside a spacious cavity, and even black bears have been known to squeeze into a hollow tree for the winter. Bats often roost inside “defective” old trees, and many cavity-nesting bird species require trees with rooms in their hearts.
But just as importantly, trees in their senescent years are crucial to the survival of myriad insects, most of which are pollinators, and all of which are important food for wildlife. Our planet is in the midst of a precipitous die-off of arthropods. In Denmark, for example, insects have declined by 97% in the past 30 years. In the UK, biologists documented 2,000 insect species that live exclusively inside ancient trees. Some of these insects are now only found at two or three sites on Earth.
Even decay fungi can be specific to the heartwood of a particular kind of tree. Fungi have given us cancer treatments, antibiotics and more, yet humans have only begun to catalog the health benefits of fungal species.
But ancient trees are vanishing. Exotic pests and diseases have decimated some of eastern North America’s largest and longest-lived species: American chestnuts have been all but extirpated by chestnut blight, and while Dutch elm disease hasn’t entirely purged our native elms, the leviathans of old are gone. Beech bark disease, butternut canker and the emerald ash borer, grim reapers all, continue to march through our forests.
In addition, more frequent droughts exact a greater toll on elder trees, which are less resilient than youngsters. The trend toward vast agricultural fields has destroyed millions of tree-lined fencerows, and transformed countless acres of forested wetlands into cropland. And in some places, it is now common practice to raze whole forests and chip trees of all sizes and ages.
It has long been known that damaging a few trees in a forest can benefit endangered species. In the late 1980s, a friend of mine worked for the US Forest Service out West, dynamiting the tops out of Sitka spruce to make nesting sites for northern spotted owls. But modifying young trees to replicate the conditions found in forest elders has not been tried on a large scale until recently.
In 2012, Ancients of the Future, an ambitious project involving several UK-based nonprofit nature groups, was launched. On the twenty different sites in England, Norway and Sweden that were chosen, biologists “surgically” harmed 874 oak and beech trees to mimic natural events such as lightning strikes, wind breakage, and woodpecker damage.
In some cases, fungal samples taken from veteran trees were transferred to trees in the study. This may help preserve unique fungal strains. Curiously, there is evidence that decay fungi inside old trees can actually help prolong their life. Kind of like fecal transplants for humans, I guess.
Although a final evaluation of the Ancients of the Future project is planned for 2037, an interim assessment and report were made in 2020.
Researchers found that many of the artificial cavities they made are now home to bats, birds, and mammals. Tree mortality was much lower than anticipated, but it seems that in a lot of instances, biologists were too gentle with their chainsaws, as trees had callused or “healed” over some of the openings. But most if not all of the fungal inoculations had taken hold, a good sign for purposes of the experiment.
Veteranization of healthy trees may not be practical everywhere. At the very least, though, landowners should do all they can to protect hollow, decaying, or otherwise “flawed” old trees as long as possible. Increasingly, the natural features we judge as useless or unsightly are found to be vital in ways we never imagined. In light of this fact, I’m going to let my eyebrows grow wild in case the shelter they provide ends up rescuing some tiny critter from extinction.
Photo of American elm tree courtesy Wikimedia user Msact.