by Paul Hetzler
“If I knew for a certainty that a man was coming to my house with the conscious design of doing me good, I should run for my life.” David Henry Thoreau’s statement, funny on the surface, also brings to mind the incalculable harm done to cultures around the world by Western imperial powers in the guise of “helping” them. In a less horrific sense, it also applies to how we’ve “assisted” nature to disastrous ends. Cane toads in Australia, mongoose in Hawaii, Kudzu in the southeastern US, and the Asian harlequin ladybeetles that invade our homes each fall are but a few examples of good intentions gone wrong. On the heels of Canada’s 2021 National Forest Week of September 19-25 it may be good to ask trees what they need.
Given the Outaouais’ 11% population increase between 2016 and 2020 (l’Institut de la statistique du Québec), it’s not surprising that I get a lot of questions from residents who’ve recently purchased a few acres of forest, lakeside cottage, or home on a wooded lot and want to know if they should clear brush, thin trees, or do other things to improve the woods. It’s a fair question, and an important one. An honest answer would include “No one’s really sure,” and “It depends.”
Just to clarify, as an arborist I specialize in trees in the human landscape, whether they’re naturally occurring or intentionally planted. A forester is someone who manages tree communities on a larger scale for commercial ends. There’s enough overlap in training and skill sets, though, that I feel able to provide general guidelines.
While I recognize the importance of commercial forestry and have tremendous respect for it when done with integrity, its principles are often at odds with preserving or enhancing the well-being of small woodlots and backyard forests. One of its key concepts is known as Timber Stand Improvement or TSI, which encompasses things like pruning lower branches, removing unwanted species and thinning around high-value trees. At its best, TSI can increase the annual growth rate of desired trees from about 1% in most natural settings in the region to perhaps 9%.
This sounds great – and it is if you want to maximize profits. TSI improves timber value. However, it doesn’t necessarily make forests better. In fact, if not done carefully it can actually lower overall plant and animal diversity, degrade habitats, and remove genetically superior trees that should be left for seed production.
In and of itself TSI is not bad, but it has to be understood as a tool to achieve specific ends which must be defined before changes are made to any stand of trees, no matter how small. I’ve found it’s very hard to un-cut a tree. Just saying, in case you had it in mind as a backup plan.
If you have an acre or three of forest, in general the best way to improve it is to leave it alone. The older I get, the more appealing this strategy becomes. As long as they don’t pose a threat to houses or play structures, dead standing trees and trunks (snags) should stay – they’re vital habitat for roughly 30 species of native birds that either nest in cavities or take shelter in them. A lot of what appears to be brush is native and highly beneficial woody understory plants such as leatherwood, witch-hazel, moose maple and ironwood. Downed trees and branches decay at varying rates, gradually returning nutrients and carbon to the soil over time.
Leaving the forest alone applies to motor vehicles. In wet-soil conditions, all-terrain vehicles, trucks and tractors must stay out of the woods. Even heavy foot traffic can damage sensitive plant communities in springtime, so keep to designated trails. And it’s imperative that timber harvesting be done in dry conditions or when the ground is frozen. Today’s heavy skidders weigh three times what they did in the 1980s. I’ve seen waist-deep ruts left by these machines; damage of such magnitude will take centuries rather than generations to recover from.
Take heart all you vibrant young folk with infinite ambition who find leisure frustrating (yeah, I was there once) – there may yet be chores in your woodlot that cry out for attention. Not all “brush” is in league with puppies and Christmas. Invasive honeysuckle (Lonicera spp.) bushes lurk in vacant lots, city backyards, and increasingly in otherwise intact forest systems. If your back is OK you can easily uproot honeysuckle, the simplest way to eradicate it.
An understory tree called buckthorn (Rhamnus cathartica) is likewise moving north from urban areas into rural woodlands. Impossible to pull, you have to cut it low and cover the stump with black plastic for a couple years or apply the dreaded herbicide glyphosate (20% or higher) to fresh stumps. Neither invasive plant has fruit which is healthful for birds. In addition, buckthorn and exotic honeysuckles alter soil chemistry to disadvantage endemic plant species.
Garlic mustard (Alliaria petiolate), an invasive biennial, is a fragile and edible herbaceous plant. Doesn’t sound dangerous, but it’s a wily woodland adversary and managing it is not straightforward. Small infestations which have appeared within the last few years can be hand-pulled in early summer. Five to seven years of management are usually enough to wear out the soil seed bank.
On the other hand, widespread garlic-mustard patches that are well entrenched should be ignored. Seriously. One of the bad things about this plant is that it modifies the soil, making it hard for native plants to germinate or grow. Oddly enough it poisons itself to death in ten years, after which forests can recover. Removing established garlic-mustard not only prolongs each infestation, the resulting soil disturbance causes untold ecosystem harm. A large-scale invasion of garlic mustard is a call to action for the lazy, if that’s possible.
Helping nature can range from sweat to staring at treetops, but it begins with homework. As helpers, let’s tread lightly and with humility.
Paul Hetzler is an ISA Certified Arborist and a former Cornell Extension Educator. He lives in Val-des-Monts.