Date of Award

9-1-2025

Degree Type

Thesis

Degree Name

Master of Science (M.S.)

Department

Agricultural and Environmental Sciences

First Advisor

Sarah Neumann

Abstract

Regeneration of many hardwood species, especially ectomycorrhizal-associated species like oaks, is inhibited under ericaceous thickets, but not much is known about how Kalmia latifolia inhibits seedlings. I explored this phenomenon using spatial analysis of a stem-mapped forested stand and two greenhouse experiments designed to detect plant-soil feedbacks, whether they are biotic, and light dependence. Spatial analyses confirmed that seedling abundance for most species is strongly, negatively correlated with K. latifolia basal area. Oaks that successfully recruit to the sapling stage are found in areas with less K. latifolia than those occupied by arbuscular (AM) or ericoid (ERM) associated saplings. In the greenhouse, Quercus alba showed no difference in emergence between conspecific and K. latifolia-conditioned soils, but emergence was higher in non-sterile K. latifolia soil, indicating a microbial benefit. Growth was greater in conspecific soil under low light, reflecting a positive, biotically mediated, light-dependent PSF. Oxydendrum arboreum experienced higher survival and growth in K. latifolia soil, but these negative PSFs were not consistently biotically mediated or stronger in low light. Microbial effects on O. arboreum survival were apparent only under low light, while growth was enhanced in nonsterile K. latifolia soil under high light. A second greenhouse experiment showed that Q. alba emergence was significantly reduced in soils conditioned by ericaceous species (Vaccinium spp., O. arboreum, and K. latifolia), suggesting that emergence suppression may be a broader pattern linked to ERM-conditioned soils. Collectively, these results indicate that K. latifolia and other ericaceous shrubs limit oak regeneration through complex, stage-specific PSFs that interact with light and microbial communities.

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