Tree planting is still a win for climate and biodiversity goals, writes forest scientist Alice Palmer.
A tree planter at work in BC. Photo from the CBC.
The Canadian government has pledged to plant two billion trees by 2031, as a means of fighting climate change and biodiversity loss. However, large-scale tree planting has increasingly come under question. What is the reason behind this controversy, and is tree planting still a good idea?
This summer’s extreme fire season provided a catalyst for the discussion. For example, in a recent New York Times op-ed, author Claire Cameron reflects on her experience tree planting in Northern Ontario thirty years ago. She and her crew planted mostly black spruce, a species which burns readily. By planting a monoculture of spruce, without also including any hardwoods such as aspen, she wonders whether she had been inadvertently increasing the risk of wildfire in the area.
In BC, where logging has long been subject to public criticism, tree planting has usually escaped without comment. However, the phrase “monoculture tree plantations” is increasingly working its way into the discussion here too. For example, recent letters-to-the-editor have suggested forests are being converted into “short-rotation monoculture plantations” with “modified, nursery seedlings.”
Why Do We Plant Trees After Logging?
Although tree planting is common in Canada, it actually isn’t 100% necessary. In nature, if a forest burns down, blows down, or is logged, it usually grows back on its own. In the newly-established sunlight, pre-existing seeds will sprout, and new seeds will blow in from adjacent forests. With less overhead competition, surviving understory trees “release” and grow more quickly.
However, the process of natural regeneration can take a long time. Often, the first species to establish themselves after a disturbance are what are known as “pioneer” or “early seral” species: sun-loving species such as grasses, shrubs, and rapid-growing (yet less commercially valuable) trees such as alder and aspen. These pioneer species can initially out-compete the slower-growing “climax” species that existed in the forest before the disturbance. Also, if dense brush prevents trees from getting established, there can be gaps in the tree cover.
The benefit of planting trees versus waiting for natural regeneration is that planting speeds up forest reestablishment and ensures that harder-to-reestablish species are included in the mix. While this is obviously advantageous from a commercial perspective, planting also ensures that other forest benefits such as carbon sequestration and soil stabilization occur more quickly.
How Do We Choose What to Plant?
In BC, we typically aim to regrow the tree species that were on the ground before an area was logged. Prior to logging, the site is surveyed, and a detailed reforestation plan is created, based on the site conditions and the existing tree species.
As mentioned above, foresters recognize that naturally-regenerated trees often join those that were planted. Some species, such as western hemlock, regenerate so abundantly that foresters often leave them out of their planting prescriptions, even though they anticipate the species will dominate the mature forest. Thus, even if only a single species is planted, the second-growth forest will often contain more.
The (False?) Controversy Over “Monocultures”
The dictionary definition of “monoculture” is “the cultivation of a single species in a given area.” According to this definition, monoculture forests are in the minority in BC. However, the term has frequently been stretched. For instance, this article in The Tyee defines monocultures as “tracts of trees of a similar species and age.” The expression has lately been used to contrast coniferous forests (regardless of species mix) with forests that have a mix of conifers and deciduous trees.
Since we primarily log conifer species in BC, these are the species we typically aim to have in our second growth forests. If we didn’t seek to reestablish the same species we log, over time, the composition of our forests would likely change. This has been observed in logged-over areas of Siberia, where forestry laws were, until recently, much laxer than they are in Canada. When Russian companies left their forests to regenerate naturally, vast swathes of forestland were converted to early seral species like aspen. Planting conifers is therefore part of good forestry practice.
However, Claire Cameron does have a point: we are now seeing an increase in extreme wildfire behaviour in Canada. With climate change occurring, this pattern is likely to continue. As our climate changes, policies that served us well in the past may need to evolve.
For example, because hardwood stands are less flammable than softwoods, they can act as firebreaks. Consequently, our policy of always regrowing the same tree species we logged may deserve a rethink. The same could be said of a host of other forest management and fire mitigation policies. How can forests be better managed to be more fire resistant than if left on their own?
Intervening to manage forests before fires occur may be part of the solution. Nonetheless, tree planting as currently practiced in BC plays an important role in promoting both biodiversity and carbon mitigation. But those concerned about the risks of wildfires and biodiversity loss may be surprised to find more tree planting (not less) playing a role in the future of sustainable forest management.
Alice Palmer is a forest scientist and consultant based in Richmond, BC. To follow her work, check out her Substack here.