|Drawing by Toki Oshima|
By Andy McEvoy
Weeding a garden seems intuitive. Unwanted weeds impinge on the ability of vegetable crops to absorb water and nutrients from the soil and energy from the sun, so we weed. Likewise, after carrots sprout, we thin them; otherwise the crowded roots will twist around one another in odd and comical shapes.
Pine trees and carrots have this in common: Growing densely among competitors results in undesirable shapes and weaker plants. An acre of dense, weevil-ridden pine will yield little more than pulp and lots of dead woody material.
We hear little talk of weeding a forest. Terms such as “pruning,” “thinning” and “timber stand improvement” may be familiar, but their importance in promoting healthy, viable woodlots cannot be overstated. Pruning and thinning can greatly increase the economic value of standing timber. White pine saw logs are priced according to their grade, which is determined partly by the number of knots in the wood. Strategic pruning can reduce knots and increase value.
Likewise, trees remaining after proper thinning will have access to more water, nutrients and sun, resulting in faster growth and greater economic value.
“Pre-commercial” work benefits ecosystems as well. In most biological systems, overcrowding promotes disease. Maine has many acres of overcrowded stands of pine that are susceptible to pine weevil infestations. Weevils kill the pine leader, or growing tip, causing side branches to take over as growing tips. This results in the characteristic J-shaped crook common in many trees.
Unmanaged and mismanaged hardwood stands can also suffer from overcrowding. For instance, crowded stands of beech are more susceptible to blight and cankering.
Species diversity is another important aspect of forest ecology and management – and pruning and thinning allow more sunlight to reach the forest floor, facilitating a multi-level forest that supports new and old growth. Dominant and shade-intolerant species will thrive in the upper canopy, while shade-tolerant small trees and shrubs fill in below. Such diversity is generally what our local ecosystems evolved to look like. Wildlife thrives in diverse forest ecosystems due to the plethora of food and shelter. Natural monocultures do occur in Maine, but they are few.
Exotic invasive species, akin to unwanted garden weeds, are another concern in forests. They consume soil water and nutrients and, if unmanaged, proliferate wildly, choking out native flora – and the fauna that depend on the native flora. Most of us understand the threats that invasives pose to our forest economies and ecosystems, but few recognize the cost of managing such tenacious growers. Little to no market exists for honeysuckle, buckthorn and bittersweet, so most folks ignore these species when the problem is small. Although the problem starts small, it is also likely growing and may reach the point eventually where the only reasonable options seem to be chemical treatments and clearcuts. No one wants to have to make that choice.
As a culture we have no problem understanding that a garden must be tended fastidiously long before the first vegetable is picked and marketed, and that the removed weeds generally have no cash value. Yet who is willing to pay someone to mechanically remove honeysuckle, or to prune and thin pines?
Pruning and thinning forest trees and managing invasive species do not yield immediate cash return but are essential to an eventual return on investment and to maintaining viable, productive forests.
A garden produces food for our table, and the woods produce fuel and shelter to keep us warm and dry. Managing a garden differs in many ways from managing a woodlot, but they share essential value and the need for good stewardship.
Andy McEvoy was MOFGA’s Low-Impact Forestry program coordinator in 2012.