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Study Finds Plant Diversity Not Reduced By Whole-Tree Logging
July 24, 2018

Timber harvesting or logging, like a number of other industries, faces a real dichotomy between public opinion and public desire. While society desires wood products such as lumber, paper, and toilet tissue, the general opinion regarding timber harvesting is mostly negative if not even hostile.

Michigan Tech silviculturalists expected that plant diversity would go down in logging stands where whole trees had been removed, perhaps because the tops and branches leave some nitrogen behind to fertilize the soil. That’s not what happened; there was no difference between whole-tree logging and leaving material behind. Credit: Sarah Bird/Michigan Tech.

Typically timber harvesting involves either selective tree removal or a process known as clear-cutting. The first method can either involve removing the whole tree, everything from the stump up, or the more old-fashioned method, which leaves tree branches behind in the woods. In contrast, the clear-cut method involves the removal of all the trees in an area of forest.

Over time, efficient forest management has undergone considerable scrutiny in many areas, not the least of which is the impact on flora biodiversity. Does whole-tree logging have a more deleterious impact on plant diversity than leaving tree tops and branches in the woods? According to information provided by Michigan Technological University (Michigan Tech), researchers are working to discover the answer.

“People think, ‘It’s bad enough to log, and now you are going to take away the branches that decay and then nurture the ecosystem?’” noted Robert E. Froese, Ph.D., associate professor in the School of Forest Resources and Environmental Science at Michigan Tech and Director of the Ford Center and Forest. “But we wondered, what really is the role of branches?”

With funding provided by the National Council for Air and Stream Improvement and Weyerhauser, Dr. Froese’s team undertook the challenge to find out. Published in the journal Forest Ecology and Management, the results of their study, “Vegetation Response to Logging Residue Removals in Great Lakes Aspen,” indicated that when it comes to plant diversity, harvesting the whole tree does not have dire consequences.

Along with PhD graduate Michael Premer, Dr. Froese studied plant communities scattered throughout 29 aspen stands in Michigan’s Upper Peninsula. All the stands had been logged at some point within the last 40 years. In some, only the logs had been taken, while in others the whole tree was harvested.

The researchers had anticipated finding that plant diversity would be diminished in stands where whole trees had been removed, but that was not what the study revealed.

“What we found is nothing, essentially,” Dr. Froese said. The study results showed there was no difference in the composition of the trees that grew back after logging. In fact, in stands where logging residues had been removed, the shrubs, grasses and other small plants were actually more diverse. According to Dr. Froese, “The difference was small, but it was measureable.”

The researchers have a theory to explain this difference. “We believe when you remove logging residues, you disturb the soil more, which increases nitrogen availability,” said Dr. Froese. “We’ve been asked if the diversity increased because of an uptick in invasive species, but we didn’t find that.”

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