Unexpected earthworm effects on forest understory plants.

Area of Science:

• Ecology
• Invasive Species Biology
• Plant Science

Background:

• Introduced earthworms are prevalent in North American forests, causing ecological disruption.
• Previous studies often confound earthworm impacts with other environmental stressors.
• Field research struggles to isolate earthworm effects on individual native plant species.

Purpose of the Study:

• To isolate and assess the impact of the earthworm Lumbricus terrestris on native plant seedlings.
• To differentiate earthworm effects from other confounding factors in forest ecosystems.

Main Methods:

• A mesocosm experiment was conducted to control environmental variables.
• Seedlings of 14 native plant species were exposed to Lumbricus terrestris.
• Plant survival, fertility, biomass, and growth metrics were monitored over 17 weeks.

Main Results:

• Earthworm presence did not significantly affect the survival, fertility, or biomass of any tested seedling species.
• Lumbricus terrestris significantly reduced the growth of two sedge species, Carex retroflexa and Carex radiata, by decreasing culm numbers.

Conclusions:

• Mesocosm findings contradict field observations of widespread negative impacts on forbs and positive impacts on sedges.
• Earthworm impacts on native plants appear to be specific to plant age and environmental context.
• Generalizing earthworm effects without considering associated factors may be misleading.