We all know and generally accept the truth that society needs wood, and by extension we also know and accept (some of us begrudgingly) that in order for this wood to benefit society, a tree must come down.
However, what happens after the tree comes down remains for many a mystery at best. Some believe that every severed tree is later replanted, while others think that every acre cut is an acre deforested, never to return to its former beauty. The truth, as always, is a bit more complicated than that and involves the long process of planning and implementing forest regeneration. While some might find discussing and monitoring the growth of trees as akin to watching continents drift, the question of regeneration is one to which foresters and landowners devote a great amount of time, research, and debate, as it is truly the heart and soul of the woods industry. In light of its importance and the common misperceptions, I hope to demystify the process a bit by explaining a few of the methods used to regenerate a forest after harvest.
Regardless of the method used, a tree’s ability to regenerate revolves largely around seed dispersal, and so one effective re-establishment is a type of harvest known as a “seed tree” cut. The premise of this method is just how it sounds: all trees are removed except for a few sparse trees designated to disperse seed and produce offspring. The wide spacing between residual trees allows for near full exposure of seedlings to sunlight while still enabling uniform regeneration of desirable species. Ideally, such seed trees will be of the best quality to improve chances of genetically advantageous traits being passed to the next generation. However, therein lies a problem: the trees used as seed trees are generally removed after seedlings become well-established, but often become considerably damaged in the line of duty as seed trees. Being so sparsely spaced makes them susceptible to lightning strikes, and wind can rustle the stems to such a degree that the wood develops what is known as windshake—the condition of having its growth rings physically separate from each other. Even if trees avoid damage, bringing heavy machinery back for such a low-yielding harvest may not exactly be profitable, so this method may effectively sacrifice commercially valuable wood. In any case, a seed tree cut is only suitable for certain species that can tolerate direct sunlight and high winds, so there are more options.
Similar to the seed tree cut is the “shelterwood” cut, which likewise involves leaving trees after a harvest to regenerate the stand. The difference here is that this method requires leaving a lot more trees and leaves them closer together. As the name suggests, it creates a shelter for seedlings that may need more shade and protection from the elements, but it also protects the parent trees themselves. The increased density of residual trees protects them from wind and lightning, and it provides enough wood to make subsequent removal cuts more commercially viable.
In addition to the “establishment cut” that opens the canopy up for regeneration, and the “removal cut” that takes out, sometimes incrementally, the parent trees to release the offspring, a shelterwood cut may also include a ”preparatory cut,” which is essentially a thinning designed to remove species and individuals that would provide suboptimal offspring. Leaving only optimal species provides more genetic control over the regeneration process.
By far the most controversial and probably well-known of the harvest prescriptions, “clearcutting” is essentially the removal of all trees from a given area. Counter-intuitive as it may seem, clearcutting can in fact be a legitimate means of regenerating a stand. Depending on site conditions, the scale of the cut and a few other factors, clearcuts may be left to regrow naturally, but often in the United States and around the world, this is the situation where planting (or artificial regeneration) can be advantageous. Genetically-selected and improved seedlings of desirable species can be cultivated in a nursery and transported to the harvested area where they are planted and tended to until they grow to maturity, at which point they are usually clearcut once again, and the cycle begins anew. While this method is utilized in Maine to some degree, it is exceedingly popular in the US south and west for softwood production. Internationally, it is practiced widely in Scandinavia to produce softwood, and even in South America it’s used to produce fast-growing species like Eucalyptus. Such systems are generally referred to as “intensive silviculture” for the many steps involved in bringing trees to maturity, including some form of chemical or mechanical site preparation and occasionally even the application of fertilizer. While it usually produces faster-growing trees, it does have the drawback of being the most expensive means of growing a forest.
The Forest’s Future
The methods mentioned here, it should be noted, are only used in even-aged management; which is to say they are used when producing trees of the same age. Uneven-aged and two-aged management include even more silvicultural systems that are arguably more nuanced. Though it may indeed seem like watching continents drift, regenerating a forest is a fascinating process full of risks and uncertainties. True, it’s not the material action movies are made of, but it is nonetheless exciting for all of us invested in forestry. Maine’s history, for better or worse, has been inextricably tied to the history of the forest. Even for those with no connection to the industry except the occasional hunt or hike through a carpet of green on the forest floor, that carpet represents the future forest our children and grand-children will be left with. That will be their forest economy, and if that isn’t exciting, I don’t know what is.