Date of Award

December 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

Jason Fridley

Keywords

ecophysiology, invasive, productivity, storage, tradeoff, woody plant

Subject Categories

Life Sciences

Abstract

Non-native woody plants from Europe and East Asia have invaded intact, low-light forest understories in Eastern North America. Compared to co-occurring native species, invasive species exhibit greater productivity and resource use efficiency, but the extent to which plants are subject to tradeoffs between productivity and survival is unknown. Herbivory and freezing events are common sources of damage in the forest understory, and non-structural carbohydrates (NSCs) and defense compounds support resilience and resistance to damage. In this dissertation, I evaluated the hypothesis that invasive species maintain high productivity at the expense of storage and defense, reducing their survival under severe damage. In the first chapter, I identified differences in seasonal NSC concentrations in 39 species of native and invasive plants and evaluated whether a tradeoff exists between growth and storage. I found no evidence of a growth-storage tradeoff, but native species tended to maintain greater soluble sugar concentrations than invasive species in both stems and roots. However, invasive species had greater root starch during the growing season. In the second chapter, I investigated defense investment in 20 native and invasive species, coupling generalist herbivore feeding trials with leaf defense trait assays. I found that invasive species have higher leaf lignin and nitrogen concentrations than native species, but generalist caterpillars showed no nativity preference, suggesting that invasive species do not benefit from enemy release. In the third chapter, I compared growth and survival responses to varying levels of defoliation in two pairs of native and invasive tree species in the field. Over three growing seasons, I subjected saplings of each species to each of the following treatments: no defoliation control, half defoliation over three years, full defoliation over one year, and full defoliation over two years. Native and invasive species had similar responses to treatments: half defoliation reduced radial growth but did not affect survival, while full defoliation caused greater growth reductions and severe decreases in survival. NSCs in living saplings were not affected by defoliation, suggesting that plants prioritize storage over growth in response to damage. Taken together, these studies show differences in carbon storage and defense in native and invasive woody species, but contrary to my hypothesis, I did not find evidence for direct tradeoffs between growth and survival. Additionally, native and invasive species are equally targeted by generalist herbivores and exhibit similar responses to damage in the forest understory.

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