Access Type

Open Access Thesis

Date of Award

January 2016

Degree Type

Thesis

Degree Name

M.S.

Department

Biological Sciences

First Advisor

Daniel M. Kashian

Abstract

Abstract

AN ANALYSIS OF BLUE ASH (FRAXINUS QUADRANGULATA) REGENERATION IN SOUTHEASTERN MICHIGAN IN THE PRESENCE OF EMERALD ASH BORER (AGRILUS PLANIPENNIS)

by

BENJAMIN A. SPEI

May 2016

Advisor: Dr. Daniel M. Kashian

Major: Biological Sciences

Degree: Master of Science

Since the introduction of the invasive bark beetle emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae) to southeastern Michigan, most native ash species (Fraxinus spp.) such as white ash (F. Americana), black ash (F. nigra), and green ash (F. pensylvanica) have suffered mortality rates exceeding 99% after infestation. This has led to the loss of seed sources resulting in a depleted seed bank and thus a loss of potential future regeneration. These trends suggest that these species will soon no longer function as important canopy species in North American hardwood forests as EAB continues to spread. Blue ash (F. quadrangulata) is thought to be the most resistant of all native ash species to EAB with observed mortality rates between 30% and 40%. This reduced mortality may be sufficient for mature blue ash trees to persist and maintain a seed bank robust enough to evolve even higher resistance to EAB. While several studies have quantified declining regeneration of other ash species, little research exists describing blue ash regeneration in the presence of EAB. A total of 18 blue ash stands were sampled at 6 different sites in southeastern Michigan near the EAB introduction point. For reference, 18 white ash (F. Americana) stands within the same 6 sites were also sampled. Observed overstory mortality for blue ash ranged between 7.1% and 31.6% and was significantly lower than white ash across all sites. Overstory blue ash was on average significantly older and larger than white ash across all sites and maintained a higher frequency of healthier crowns. Blue ash regeneration densities were found to be abundant at all sizes within all stands. New seedlings (< 3 yrs old) were significantly more abundant for blue ash than white ash across all sites suggesting blue ash has not experienced the same depletion of its seed bank as white ash. Blue ash seedling growth rates were equal to or significantly greater than associate non-ash species at all size classes and at all sites; and equal to white ash seedling growth rates at the majority of sites and size classes with few exceptions. My results show blue ash maintaining a relatively healthy and dominant position in the canopy of several forests in southeastern Michigan. Furthermore, my results suggest that blue ash is still regenerating in a capacity that shows a high probability of canopy replacement by blue ash and thus its continued persistence in the presence of EAB.

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