Zaricor, M. 2026. Context-dependent effects of herbivores and management on plant and soil dynamics during grassland restoration. Dissertation, Michigan State University, East Lansing, MI.

Grasslands cover a large portion of Earth’s terrestrial surface and provide critical ecosystem services, including biodiversity support, forage production and carbon storage. However, they are among the most degraded and least protected ecosystems globally, requiring the need for restoration. Despite restoration efforts, many restored grasslands often fail to recover the diversity and ecosystems functioning of non-degraded systems, suggesting key ecological processes, such as top-down control, are missing or altered. Because grasslands coevolved with large herbivores such as bison (Bison bison) their reintroduction has been promoted as a “natural climate solution” to aid in restoration recovery, especially through top- down effects on plant diversity. However, bison reintroduction has shown inconsistent responses in restored plant communities. In addition, small mammals, which are also common in grasslands, can influence plant communities through selective foraging, but their role in restoration outcomes remains understudied. Previous research suggests that herbivore effects on plant and soil processes can be context dependent through interactions with management practices (e.g., prescribed fire) yet few studies explicitly investigate how these interact with herbivores of different sizes. Because both large and small mammals are present in restored grasslands, and because restorations are managed using multiple practices, understanding how these factors jointly influence plant communities and ecosystem processes is critical for adaptive management and predicting restoration trajectories. In this dissertation, I used a manipulative field experiment in an early stage grassland restoration to examine how herbivores and management jointly shape plant communities, biomass allocation, and soil carbon dynamics.
Specifically, I compared the independent and interactive effects of large herbivores (bison), small mammals, and their exclusion across multiple management treatments (i.e., prescribed fire, mowing, herbicide, and no management). In Chapter 2, I examined how herbivores and management treatments influenced plant community composition and diversity. In Chapter 3, I quantified how these same treatments affected above and belowground biomass pools. In Chapter 4, I evaluated how herbivores and management influenced seasonal soil carbon dynamics using active and intermediate soil carbon pools, as well as total carbon and nitrogen relationships. Across chapters, I found that herbivores and management interacted in important and context dependent ways. The strongest positive diversity responses occurred in plots with
prescribed fire and bison grazing, while small mammals generally reduced plant diversity. Notably, the exclusion of all mammals reduced diversity further. Bison also had the most consistent and strongest effects on aboveground biomass pools, whereas small mammals had weaker effects. Belowground biomass responses did not respond similarly to aboveground responses, suggesting that belowground dynamics may not be reliably predicted from aboveground measurements alone. Finally, soil carbon pools were sensitive to season and some herbivore interactions, but short term responses were variable, highlighting the need for long- term evaluation to detect consistent trends. Overall, this dissertation reinforces the need to understand how herbivores and management together shape restoration outcomes and demonstrates the importance of understanding their interactive effects across multiple ecosystem processes for predicting and improving grassland restoration success.

Associated Treatment Areas:

• Cross Site Synthesis
• LTER Research Context

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