Liz Studer

PhD Candidate

Current Research

Consequences of the Extirpation of Ash Trees in New England

The Emerald Ash Borer (Agrilus planipennis Fairmaire), an invasive phloem-feeding beetle from Asia, is rapidly becoming one of the most destructive invasive insects in North American history by threatening all members of the genus Fraxinus. The consequences of this invasion will have far-reaching effects on forest composition, resulting in ecological, economic, and conservation impacts. To better understand the magnitude of potential cascading effects due to the eventual extinction of ash, we need to elucidate the role of Fraxinus in the ecosystem. One major consideration for the conservation implications of the loss of ash are the potential effects to its sub-canopy organismal community. 
Ash have several unique traits compared to other trees in northern mixed hardwood forests. They (1) leaf-out later, (2) have increased nutrient availability in their leaf litter content, and (3) are associated with the less common mycorrhizal type. I am investigating how these traits impact the sub-canopy communities of plants and invertebrates below ash and other trees to better understand the potential negative effects of ash extirpation on other organisms.

1. LIGHT: As a ring-porous species, they leaf-out in the spring 1-2 weeks later than other similar trees, like beech and sugar maple
.  Late leaf-out means more light availability to sub-canopy species like spring ephemerals growing below ash during the vernal window.

2. NUTRIENTS: Ash leaves decompose rapidly in the litter layer due to their low lignin to nitrogen ratio (Melillo et al. 1982), suggesting a difference in nutrient availability for litter layer invertebrates to access. This is considered a fast nutrient economy, where turnover rate is high. Additionally, the litter layer below ash is thin due to the rapid decomposition rate.

3. DECOMPOSITION: Ash have arbuscular mycorrhizal associated roots. In addition to sugar maple, it is the only hardwood tree in this region to share this type of mycorrhizal association (others are ectomycorrhizal). This likely alters the microbial community composition in the soil and litter due to the increased availability of sugars provided by the arbuscular mycorrhizae present.


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