Lush forest floor with vibrant life amidst decaying logs.

Emerald Ash Borer's Aftermath: How Dead Trees Reshape Forest Ecosystems

Reese Marlowe in Science & Nature August 2025 • 4 min read.

"A deep dive into how the emerald ash borer transforms forests, affecting everything from ground beetles to overall biodiversity."

Biological invasions are dramatically reshaping ecosystems worldwide, causing widespread economic and ecological changes. Understanding these impacts is crucial, especially in forests facing threats from invasive species that trigger significant direct and indirect effects on community dynamics and ecosystem processes. One such invader is the emerald ash borer (EAB), Agrilus planipennis Fairmaire, an insect native to Southeast Asia that has devastated North American forests.

Since its accidental introduction and establishment in southeastern Michigan in the early 1990s, the EAB has killed hundreds of millions of ash trees (Fraxinus spp.). In areas surrounding the initial invasion sites, forests have experienced nearly complete ash mortality. This widespread death of ash trees has far-reaching consequences, influencing forest structure, function, and ecological succession.

The rapid die-off of ash trees due to EAB leads to increased canopy gaps and a greater accumulation of coarse woody debris (CWD)—fallen logs and large branches—on the forest floor. These changes alter the forest environment by modifying light availability, soil temperature, and moisture levels. While canopy gaps can change microclimates, the increase in CWD provides new habitats and resources for many species, especially forest floor invertebrates.

Decaying Wood: A Boost for Forest Biodiversity

Lush forest floor with vibrant life amidst decaying logs.

The increase in CWD significantly alters forest ecosystems, providing crucial resources and habitats for numerous forest floor invertebrates. These creatures utilize the downed wood for food, shelter, and breeding sites. As the wood decays, it enriches the soil and changes the dynamics of the local ecosystem. The type of invertebrate that benefits depends greatly on the stage of decay of the wood.

A study published in the 'Journal of Insect Science' examined how the different stages of decaying ash trees affected forest floor invertebrate communities. Conducted over two years in southeastern Michigan—close to where the EAB first took hold—the research focused on areas with almost total ash tree loss. The study aimed to understand how canopy gaps and the accumulation of CWD impact invertebrate communities during the later stages of EAB infestation.

Minimal Canopy Impact: The research found that canopy gaps had minimal impact on invertebrate communities in the late stages of ash mortality. This is likely because the gaps had already begun to close as other trees and vegetation grew to fill the space.
CWD is King: The accumulation and decomposition of CWD had a significant effect. Invertebrate activity, abundance, evenness, and diversity were highest near minimally decayed logs.
Moisture Matters: Soil moisture played a crucial role, often mediating how invertebrates responded to CWD and its various stages of decomposition.
Species-Specific Responses: The effects of CWD varied among different invertebrate taxa, influencing overall community composition.

These findings align with the prediction that CWD would have a greater impact than canopy gaps on invertebrate communities in the advanced stages of EAB-induced ash mortality. The study underscores the long-term ecological effects of invasive species and the importance of understanding how ecosystems adapt to such disturbances.

Implications for Forest Management

This research highlights the critical role of CWD in maintaining biodiversity within forests affected by invasive species. Forest management strategies should consider the importance of preserving a variety of decay stages in woody debris to support diverse invertebrate communities. Understanding these ecological dynamics can aid in mitigating the impacts of invasive species and promoting healthier, more resilient forest ecosystems. After all, even in death, trees continue to give back to the forest they once called home.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1093/jisesa/iex093, Alternate LINK

Title: Effects Of Late Stages Of Emerald Ash Borer (Coleoptera: Buprestidae)-Induced Ash Mortality On Forest Floor Invertebrate Communities

Subject: Insect Science

Journal: Journal of Insect Science

Publisher: Oxford University Press (OUP)

Authors: Kayla I Perry, Daniel A Herms

Published: 2017-11-01

Everything You Need To Know

What is the Emerald Ash Borer and why is it such a threat to forests?

The Emerald Ash Borer (EAB), scientifically known as *Agrilus planipennis Fairmaire*, is an invasive insect native to Southeast Asia. Its introduction to North American forests has been devastating. The EAB specifically targets and kills ash trees (*Fraxinus spp.*), leading to widespread ash mortality. This poses a major ecological threat because it disrupts forest structure, function, and the natural succession of the ecosystem, causing far-reaching consequences.

How does the Emerald Ash Borer's impact on ash trees affect the forest environment?

The EAB's destruction of ash trees causes several key changes. It leads to increased canopy gaps, as the dead trees no longer provide shade. It also results in a greater accumulation of coarse woody debris (CWD), such as fallen logs and branches, on the forest floor. These changes directly modify environmental factors like light availability, soil temperature, and moisture levels, creating new habitats and resources, particularly for forest floor invertebrates that rely on the decaying wood.

What role does decaying wood play in a forest affected by the Emerald Ash Borer?

Decaying wood, or coarse woody debris (CWD), becomes a crucial resource and habitat provider in forests impacted by the EAB. The increased CWD resulting from ash tree mortality offers food, shelter, and breeding sites for numerous forest floor invertebrates. These invertebrates are integral to soil enrichment and the overall dynamics of the local ecosystem. The type of invertebrate that benefits depends significantly on the stage of decay of the wood.

What were the key findings regarding canopy gaps and CWD in the study conducted in southeastern Michigan, and why are they important?

The research in southeastern Michigan revealed that canopy gaps had minimal impact on invertebrate communities in the late stages of ash mortality, likely because the gaps had already begun to close as other trees and vegetation grew to fill the space. However, the accumulation and decomposition of coarse woody debris (CWD) had a significant effect. Invertebrate activity, abundance, evenness, and diversity were highest near minimally decayed logs, with soil moisture also playing a crucial role. These findings are important because they highlight the long-term ecological effects of invasive species and underscore the significance of CWD in supporting biodiversity within affected forests.

How can forest management strategies be adapted to mitigate the effects of the Emerald Ash Borer and promote healthier forests?

Forest management strategies should prioritize the preservation of diverse decay stages in woody debris to support a wide array of invertebrate communities. Understanding the ecological dynamics, such as the impact of coarse woody debris (CWD) on forest floor invertebrates and the role of soil moisture, can aid in mitigating the impacts of invasive species like the Emerald Ash Borer. This approach helps promote the resilience of forest ecosystems, allowing them to adapt and recover from the disturbances caused by the loss of ash trees.