Treating Old Forests with New Tricks

Primary Source: Sohrabi, H.; Jourgholami, M.; Lo Monaco, A.; Picchio, R. Effects of Forest Harvesting Operations on the Recovery of Earthworms and Nematodes in the Hyrcanian Old-Growth Forest: Assessment, Mitigation, and Best Management Practice. Land 2022, 11, 746.

Old-growth forests are one of the most important environments on the planet. The massive, aged trees that define them act as storage for tons upon tons of carbon that would otherwise take the form of CO2 in the atmosphere. Additionally, the many structures formed by trees, living and dead, offer a habitat to many diverse forms of life. Aside from these ecological benefits, they act as a major natural resource. Wood from old-growth forests is especially sturdy, as years upon years of growth compress into a much denser wood than younger trees.That being the case, many of the world’s old-growth forests have been logged to near-annihilation. While these forests can handle controlled levels of logging, historic attitudes towards these forests, as well as resource crises, led to irresponsible over-logging of these rare and precious ecosystems. With modern issues compounding the issues brought about by this historic decline, many scientists are researching new ways to rehabilitate, manage, and protect the remaining old-growth forests while they recover their historic losses.

Loggers make various temporary roads such as this one from Australia, called skid trails, to transport equipment and materials to and from the logging site. Credit:”Corrugated road in wet season” by John Hill, licensed under CC BY-SA 3.0
Starting from the Ground Up

While completely abandoning current logging efforts in the remaining old-growth forests would be best for their recovery, this would be too impractical to put into practice. Given this situation, researchers from University of Tehran and University of Tuscia worked together to find means of making the logging industry less disruptive to the organisms living in the soil of the Hyrcanian Old-Growth Forest in Iran. To do so, researchers looked at three different logging operations, harvested at 6, 10, and 20 years prior to the study. These harvesting operations leave behind skid trails, makeshift roads to a logging site for the transport of logs and equipment. For each of these operations, researchers designated skid trails as high, medium, or low traffic based on how frequently they were used for transport, and sampled the earthworm and nematode populations from sites along these skid trails. Furthermore, sampling sites were further divided by the different species-makeup of the tree litter in the area, either as beech, beech-hornbeam, or mixed beech. By studying the effects of these various factors on the soil-bound earthworm and nematode populations, researchers can determine which choices in the logging industry have the biggest impact on soil health, which in turn affects the rate of recovery for the rest of the old-growth forest.

Understanding Underground

Researchers found that skid trails from 6,10, and 20 years ago had an insignificant difference in their populations of earthworms and nematodes. Compared to samples taken from undisturbed soil, the population of earthworms and nematodes were significantly lower at samples from skid trails 6 and 10 years old. Additionally, the population of earthworms and nematodes from medium traffic and low traffic skid trails were significantly larger than those from high traffic skid trails, though still smaller than those from undisturbed soil. Finally, earthworm and nematode populations were significantly larger for each increase in the number of tree-litter species present, with the largest populations found at sites with mixed beech, followed by beech-hornbeam, and then beech on its own.

Earthworms and other soil-dwelling species digest various materials that other organisms can not utilize and return the nutrients contained within back into the ecosystem as soil. Credit: “Earthworms” by Petr Kratochvil, licensed under CC0 1.0
From Topsoil to Treetops

These findings tell us that the soil quality of this old-growth forest is dependent mostly upon species diversity, amount/ intensity of anthropogenic disturbance, and time since disturbance. With these factors in mind, changes can be made to the way logging is handled in these historic and few-remaining ecosystems. By limiting the length and usage of each skid trail, as well as replanting with species diversity in mind, the foundation of these scarce but valued forests can maintain their quality. By protecting the base layer of these ecosystems, the unique resources and organisms they contain can be preserved and allowed to recover from harvesting. Hopefully, as further research guides our understanding of these historic, resource-rich environments, the day these forests extend back to their historic ranges comes closer and closer.

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Cypress Novick

Cypress Novick

I am a recent graduate of Occidental College in Los Angeles, California, where I studied for my Bachelor's in Biology. My main research interests are wetlands ecology, mycology, estuary ecosystem interactions, and plant-based trophic interactions. I have always been passionate about making science more available and understandable, and am always trying to improve my writing so I may help myself and others be better understood.

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