Out of bounds: Industrial forestry has changed forests

This blog focuses on how industrial logging can alter the age and species composition of forests harvested for wood products. It is part of a joint series between the David Suzuki Foundation (DSF) and NRDC exploring forest degradation in Canada. It was co-authored with Rachel Plotkin, boreal program manager at the DSF.

Forests are dynamic and complex. Sustainably managing them where logging occurs-meaning preserving their ecological integrity rather than merely regrowing trees for future logging-is a significant challenge.

In natural ecosystems, tree and forest regeneration follows a relatively cyclical pattern. When trees die, whether due to old age, forest fires or insect outbreaks, an ecological process known as succession occurs. During this process, different species gradually replace each other over time, each filling a specific role as the ecosystem evolves. As long as a forest is not converted to another use (i.e., deforested), natural forests usually continue this cycle and thus maintain their ecological structure, function, and composition over time.

In forests that are logged, an industry-accepted metric to manage them sustainably is to attempt to "emulate" natural disturbances such as wildfires. Since many forest species have adapted to natural disturbances, if forests are logged and regenerated in a way that mimics natural disturbances, it is assumed the diversity of fungi, plants, and animals originally found in an unlogged forest should also recover.

Unfortunately, a growing body of research suggests that in many forests that have been (and continue to be) logged, age classes (i.e., groups of forests by age) and species composition (i.e., the types of trees) are not returning as forests similar to what would be expected under natural succession. For example, where conifer tree planting and herbicide spraying is used, some managed forests become more conifer-dominated than their natural counter parts. Conversely, where some forests where tree planting and herbicide spraying has not been applied after logging, deciduous trees, such as poplars, are essentially taking over. These shifts can have direct impacts on birds and mammals.

The almost ubiquitous influence of fire throughout the boreal forest has fostered a false perception of unlimited resilience vis-a-vis these dramatic disturbances. However, this quality has been abused to justify the systematic use of clearcuts with relatively short rotations.

Dominic Cyr et al., 2009

In addition to changes in tree species composition, several studies have documented a dramatic decrease in mature and old-growth forests in Canada's southern boreal. Logging has resulted in more younger forest stands than would be expected with natural disturbance where the rate of logging has exceeded the rate of natural disturbance (i.e., logging frequently emulates a shorter fire cycle than what has typically occurred naturally). For example, many studies of eastern boreal shield forests in Canada have shown the following:

• Amount of forest more than 60 years old declined throughout the 20th century.
• Rotation ages averaged around 80 to 100 years, while the average fire return is closer to 166 years.
• Forests greater than 100 years old covered less than 15 percent compared to historic estimates of 30 to 80 percent.
• Remaining relatively old forest (more than 100 years old) was highly fragmented.

Generally, younger forests tend to lead to poorer habitat for caribou, American marten, flying squirrels, and boreal chickadees, to mention a few.

Our results highlight the failure of existing forest management regimes to emulate the effects of natural disturbance regimes on boreal forest composition and configuration. This illustrates the risks to maintaining ecosystem goods and services over the long term and the exacerbation of this trend in the context of future climate change.

Dr. Eliana Molina et al., 2022

As a case study, Ontario's Ministry of Natural Resources and Forestry's 2018 and 2019 Science and Information packages (that inform forest management) suggest that conifer regeneration in logged forests is lower than expected. For the most part, the analysis also shows that old and mature conifer forests, specifically, are in decline in landscapes where extensive logging has occurred. For 19 of the 35 forest management units within the provincial analyses, mature conifer is less than would be expected under natural disturbance (i.e., below the 25th percentiles). For nine of those forests, the extent of the difference could be considered to be of significant or severe concern (i.e., not within the modeled range of variation at all).

Almost all the forests in three of the four landscape regions in boreal Ontario were considered to be of significant or severe concern regarding the extent of loss of all-aged conifer forests. The decline in old and mature forests is because recruitment into these classes has not kept pace with the loss of these forests due to harvesting. The crises regarding extent of forest fires in the boreal forest now will likely exacerbate this situation.

Chris Wedeles, Ecologist, AVES Arborvitae

Ecoregion 3S4S (northern Ontario, Canada): Green dot shows the current (at time of analysis) forest composition. Green box represents the interquartile range (25-75%) expected if the forest was not influenced by industrial logging (i.e., based on models of natural variation), which are the targets used in forest management. Red and orange dots show the extreme high and low range of modelled natural variation. Source: Revised from Ontario's Landscape Tool and Science and Information Packages.

Despite the significance of these findings, these data are not highlighted in federal or provincial "state of the forest" reports. This is a disservice to the public, which has a right to know the state of managed forests throughout Canada, including the extent of their degradation. As the climate continues to change, forests will be "squeezed" between losses to natural disturbances and ongoing, and potentially increasing demand for forest products. Some jurisdictions, like British Columbia, have committed to adopting improved forest management practices. However, if only minor adjustments are made to existing frameworks, the results are likely to remain the same. To effectively manage and restore forests across Canada, it is crucial for jurisdictions to recognize the extent of current forest degradation, including changes in age classes and composition. Only then can the complexity and health of forests be truly safeguarded for the future.

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