Document Type

Thesis - Open Access

Award Date

2022

Degree Name

Master of Science (MS)

Department / School

Natural Resource Management

First Advisor

Alexander Smart

Second Advisor

Lan Xu

Keywords

Bud Bank, Eastern redcedar, Mixed-grass prairie, Northern Great Plains, Seed bank, woody encroachment

Abstract

Grasslands historically covered 46 million km2 of Earth’s surface representing nearly 42% of the living vegetation. Encroachment of woody species onto grasslands and savannas is a widely researched global phenomenon, with eastern redcedar (ERC) (Juniperus virginiana L.) trees being the most prominent woody encroacher in the Northern Great Plains (NGP) due to the lack of prescribed fire and planted ERC escaping from shelterbelts. This encroachment poses a threat to native plant communities in terms of their reproduction, regeneration, and diversity. ERC are fierce competitors and can establish in most soil types, are drought tolerant, and prolific seed reproducers. These qualities coupled with their dense canopies that retain foliage year-round generate the perfect storm against native plant communities. The overall objective of this study was to determine how ERC encroachment in the NGP mixed-grass prairie is impacting plant communities. More specifically, we aimed to determine how ERC impact herbaceous species 1) biomass production, 2) composition and diversity, 3) the soil seed bank, and 4) the belowground bud bank. In addition, we classified, quantified, and weighed ERC seeds accumulated in the soil seed bank. Therefore, we attempted a holistic approach by assessing both the aboveground and belowground vegetation production and composition. This research was conducted in south-central South Dakota on two private ranches in 2020 and 2021. Biomass and foliar cover sampling were conducted during August whereas the soil seed bank and belowground bud bank were sampled in October following seed rain. We found ERC canopies to impact all of our objectives studied (1-4) compared to grassland control locations. However, impacts were limited to primarily underneath ERC canopies. We found exponential reduction in herbaceous biomass underneath ERC canopies based on canopy diameter (m) and a linear reduction in ERC stands based on stand canopy cover (%). Aboveground vegetation composition was negatively impacted underneath ERC canopies compared to the grassland control in terms of species richness, foliar cover, and frequency of native C4 grasses. The soil seed bank underneath ERC canopies was not altered in terms of seedling emergence, but exhibited higher proportions of annual/biennial and introduced forb species. We found a large quantity (52,000 seeds/0.1m3) of ERC seeds accumulated in the soil seed bank underneath ERC canopies and decreased in density with increasing distance from ERC stems. The belowground bud bank was significantly reduced underneath ERC canopies compared to other treatments with 70-99% fewer live buds produced and smaller proportions of native graminoid buds. This research contributes and builds upon previous literature, but also contains novel research conducted on the soil seed bank and belowground bud bank yet to be studied simultaneously to our knowledge in the NGP. Assessing the aboveground and belowground vegetation systems underneath and surrounding ERC canopies provides a holistic approach in determining current impacts of ERC encroachment and ideas for future management techniques or research needs. We recommend continued research on these topics post-removal of ERC on grassland systems.

Number of Pages

235

Publisher

South Dakota State University

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Rights Statement

In Copyright