Not All Forestry Is Equal: How High Retention Logging Might Protect the Understory

Source Article: Bartels, S.F. and Macdonald, S.E. (2023), Dynamics and recovery of forest understory biodiversity over 17 years following varying levels of retention harvesting. J Appl Ecol. Accepted Author Manuscript.

Featured Image Caption: Clear-cutting is the logging practice of removing all the trees from a forest. Image Source: Pixabay Free to use under the Pixabay license. No attribution required.

What is Retention Logging? Does it Help Forests?

We all rely on logging for housing, furniture, paper, etc., but typical logging practices are often entirely destructive to forest ecosystems. When the forest canopy trees are suddenly gone, life dramatically changes for animals and the understory, the plants that live under the canopy, like shrubs and non-woody plants. The good news is that scientists think logging can be more sustainable.

The understory is the shady area near the ground under the tree canopy in a forest, pictured here in a conifer-dominated forest in Banff National Park, Alberta. Image Source: Self, Julia Bebout 2022

Retention logging is the practice of harvesting trees while leaving some fraction of the forest in place. Retention logging may reduce the impact of logging on the forest understory and animals and speed recovery of the whole forest ecosystem by maintaining aspects of the original habitat. Because the forest canopy shapes life in the understory, greater retention of standing trees should protect the understory from dramatic changes in response to logging.

But forests, especially boreal forests, can take decades to recover from disturbances. In boreal forests almost all plants are perennials, that is, they live for many years. No one knows how retention logging affects forest recovery over the entire time scale of recovery because only short-term effects have been studied. Does retention logging actually benefit forests in the long run? If so, how much of the forest must be left in place to reap the long-term benefits of retention logging?

Experimental Logging

To answer these questions, researchers in western Canada conducted a large-scale experiment. The researchers retention harvested 10-hectare areas of forest, retaining six different fractions of the trees in the various areas: 2% (clear-cut), 10%, 20%, 50%, 75%, and 100% retention (unharvested). Before logging, and then over the course of seventeen years following (1999-2016), they studied the understory plants, observing which species were present and the abundance of each species. They repeated this experiment in three areas in each of four different types of boreal forest in northwestern Alberta: deciduous-dominated, deciduous with conifer understory, mixed deciduous-conifer, and conifer-dominated.

Then, the researchers used statistical models to understand how their observations of the understory in these experimental forests changed over time depending on the amount of harvest retention and forest type.

An aerial view of the various retention treatments. Image Source: from Bartels & Macdonald (2023). J. Applied Ecology. Open Access Article.
Answers in the Understory

After logging, understory plants in logged areas generally increased in abundance due to increased sunlight. Then, their growth plateaued as time went on, stabilizing by 17 years after logging. However, the understory responded differently to logging depending on the fraction of the forest that was retained and depending on the forest type.

Three years after logging, the different retention treatments still had similar plant abundance, but then differences started to appear. In most of the forest types, the areas with a higher fraction of the forest logged had greater increases in understory plant abundance, at least temporarily. After seventeen years of natural recovery, the effects of different amounts of retention on plant abundance had disappeared.

However, in areas of all forest types, the types of understory plants differed among various retention treatments; areas with more retention (less logging) saw increases in shrub and sapling abundance, while areas with little retention (more logging) saw increases in grassy plant abundance. Across the board, logged areas had different species than the unharvested reference areas, especially for logged areas with low retention. Areas with 20% or less retention generally differed in their mix of species compared to areas with 75% or more retention.

In all forest types, the number of different species in each area increased after logging and then declined. Surprisingly however, this pattern was almost the same for areas with different retention treatments. The researchers also did not observe consistent patterns of species diversity over time or between the different retention treatments.

The understory in a deciduous-dominated forest. Image Source: PxHere Public Domain
Lessons for Logging

Overall, the understory in mixed deciduous-conifer and deciduous-dominated areas seemed to be less seriously affected by logging than the understory in conifer-dominated or deciduous with conifer understory areas. Additionally, differences among retention treatments did not appear until year 6. This may be because of lingering seeds in the soil from the original plants, or because it simply takes time for the original, perennial species to die out and for new species to colonize the area after logging.

This experiment found that understory plant abundance, the number of species present, and diversity generally did not differ much between the different retention harvested treatments, which suggests that retention does not have much effect on understory recovery. Yet, many more of the original species present remained in plots with 50% and 75% retention, so these high levels of retention may still be helpful for understory recovery and protecting other forest life. However, recovery is very slow, and all understory plant communities remained different from the unharvested reference areas after 17 years.

What Does This Mean for Me?

While most of us cannot choose to employ sustainable logging practices, many of us can choose to act as informed, conscious consumers! You have probably heard the phrase, “reduce, reuse, recycle.” Reduce harm to forest ecosystems by purchasing used wood products instead of new and limiting your use of paper products. For the protection of forest ecosystems, it is best simply to decrease the need for logging. If reusing is no longer possible, wood and paper can be recycled into new paper, fiber, or construction products. For certain purposes, bamboo may also be a socially and environmentally sustainable alternative to traditional hardwoods. Bamboo is highly renewable, affordable, and strong.

If you find yourself in need of new wood products, seek out wood that was harvested sustainably, using practices including high retention logging. Keep an eye out for FSC (Forest Stewardship Council) or SFI (Sustainable Forestry Initiative) certification labels on products, which indicate that the wood was most likely harvested according to certain sustainability standards. While wood-based products are currently key for many aspects of our lives, we can still act as conscious consumers to mitigate the impacts of logging on forest ecosystems!

Global logging is currently a roughly $540 billion industry. Experts expect that the industry will grow to be worth $956.71 billion in 2030. Image Source: Pixabay Free to use under the Pixabay license. No attribution required

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Julia Bebout

Julia Bebout

I am a PhD student at the University of California San Diego studying how the timing of germination and flowering shapes plant communities. I'm fascinated by how past environments can affect present and future ecosystems, especially faced with climate change. My favorite things to write about are community ecology, wetland and alpine ecosystems, and regenerative agriculture. I also love hiking, climbing, baking, and dancing! Twitter: @BeboutJulia

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