The Unexpected Connection Among Deer, Invasive Earthworms, and Tree Harvesting.

New research from the University of Minnesota shows that there is a surprising and very impressive relationship between invading earthworms, white-tailed deer, and tree harvesting in boreal forests.

The results, which were recently published in the journal, are open access EcologyInvasive earthworm numbers increase with the presence of deer and decrease with tree harvesting. Increased earthworm infestation is a cause for concern because the species is known to damage soil and regenerate trees.

“Invasive earthworms are ecosystem engineers that negatively affect basic ecosystem characteristics such as nutrient retention and diversity of native plant species. Deer exacerbate these negative impacts by increasing earthworm populations,” said Lee Frielich, assistant professor in the Department of Forest Resources and director. . Forest Ecology Centre.

The U of M team of researchers, in collaboration with the U.S. Forest Service, Wisconsin Department of Natural Resources and others, sampled earthworms in two long-running experiments in northern Wisconsin. Both experiment sites were set up in the mid-2000s and simulated deer extractions and tree harvesting – leaving behind a large canopy gap on the trailing floors.

Nearly 13 years after each experiment began, the team tested how deer droppings and tree canopy holes affected earthworm populations. The researchers also used earthworm data collected before the experiment was set up to test how earthworms changed over the course of 13 years. Earthworm samples were taken by pouring a slurry of mustard powder and water on the ground, which caused the earthworms to shoot to the surface—a method that anyone could use at home.

Researchers found:

• In both experiments, invading earthworms were lowest in areas that had no deer and had an umbrella gap above them.
• In addition, earthworms increased over 13 y in areas outside the deer enclosure and away from the center of the canopy vacuoles.
• The largest and most impactful earthworm species were increased by deer and decreased by canopy gaps.

These results suggest that reducing deer populations may be one of the management strategies to slow down earthworm infestations. In situations where deer numbers cannot be reduced, creating medium-sized canopy gaps may be another strategy to slow the invasion.

“Taking advantage of links between disturbances may be a real solution for protecting ecosystems, as controlling one disturbance can indirectly reduce the severity of another disturbance. However, we have to identify which disturbances are linked in the first place, highlighting the need for more research. about disturbances,” said lead author Sam Reid, Ph.D. Student at the College of Food, Agriculture and Natural Resources Sciences.

The research team has several theories about how these disorders may be linked. First, deer can alter the soil in a way that is favorable to earthworms, through fecal and urinary excreta. Another theory is that because deer greedily consume and kill plants, plants can redistribute nutrients underground to their root systems to avoid eating them, which may indirectly favor earthworms. When it comes to harvesting trees and canopy gaps, researchers believe that canopy gaps can reduce earthworm populations because there is less moist, nutrient-rich leaf litter below the canopy gap, which earthworms use for food and shelter.

Future research is needed to focus on the mechanisms underlying how deer and harvesting trees alter invasive earthworm populations. In addition, the disturbance ecology as a whole must extensively examine how disturbances can affect each other and how ecosystems respond to multiple and overlapping perturbations.