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Due to anthropogenic pressures, only 3% of the historic extent of the biodiverse longleaf pine ecosystem remains, much of which is degraded. Fire is necessary for maintaining longleaf pine savanna structure, function, and biodiversity; however, it also creates resource constraints, as nutrients are volatilized, especially in the already nutrient‐depleted soils of many longleaf pine savannas. Nutrient limitation and subsequent competition between plants can lead to changes in species diversity and productivity. Using a multiyear, chronic nutrient addition experiment, we explore how resource limitation influences restoration outcomes in longleaf pine savannas by affecting (1) productivity, (2) biodiversity metrics, and (3) community composition. In the field, we established a factorial N and P nutrient addition (10 g m−1 year−1) experiment. Nutrient additions were administered for 4 years, and plant composition and biomass were collected yearly. We measured biomass each year by functional group and calculated diversity metrics and community composition changes. Understory productivity typically increased with N and P additions, with N × P together having no additive effect. There were several significant interacting effects of nutrient addition treatments with year on our biodiversity metrics; however, the main nutrient addition effects were not significant for any biodiversity metric. Finally, community composition was significantly different in nutrient addition plots compared to control. Our results show that xeric Sandhill longleaf pine savannas exhibit distinct responses to fertilization, as fertilization led to increased productivity of the groundcover without reducing biodiversity. Low‐level, chronic nutrient inputs could influence understory structure in ways that help meet numerous management objectives, such as promoting fire spread or increasing forage availability. However, this may also present challenges, such as encouraging woody encroachment or threatening rare species. Our findings highlight the need for context‐specific approaches to longleaf pine savanna management and a careful evaluation of how nutrient dynamics interact with long‐term conservation and restoration goals. Due to anthropogenic pressures, only 3% of the historic extent of the biodiverse longleaf pine ecosystem remains, much of which is degraded. Fire is necessary for maintaining longleaf pine savanna structure, function, and biodiversity; however, it also creates resource constraints, as nutrients are volatilized, especially in the already nutrient‐depleted soils of many longleaf pine savannas. Nutrient limitation and subsequent competition between plants can lead to changes in species diversity and productivity. Using a multiyear, chronic nutrient addition experiment, we explore how resource limitation influences restoration outcomes in longleaf pine savannas by affecting (1) productivity, (2) biodiversity metrics, and (3) community composition. In the field, we established a factorial N and P nutrient addition (10 g m−1 year−1) experiment. Nutrient additions were administered for 4 years, and plant composition and biomass were collected yearly. We measured biomass each year by functional group and calculated diversity metrics and community composition changes. Understory productivity typically increased with N and P additions, with N × P together having no additive effect. There were several significant interacting effects of nutrient addition treatments with year on our biodiversity metrics; however, the main nutrient addition effects were not significant for any biodiversity metric. Finally, community composition was significantly different in nutrient addition plots compared to control. Our results show that xeric Sandhill longleaf pine savannas exhibit distinct responses to fertilization compared to other grasslands and savannas globally, as fertilization led to increased productivity of the groundcover without reducing biodiversity. Low‐level, chronic nutrient inputs could influence understory structure in ways that help meet numerous management objectives, such as promoting fire spread or increasing forage availability. However, this may also present challenges, such as encouraging woody encroachment or threatening rare species. Our findings highlight the need for context‐specific approaches to longleaf pine savanna management and a careful evaluation of how nutrient dynamics interact with long‐term conservation and restoration goals.

The frequency and intensity of extreme climatic events such as heatwaves are predicted to increase under continued climate change and rising atmospheric CO2. Degraded and fragmented ecosystems are at particular risk of being greatly impacted by such extreme events. The longleaf pine (LLP) savanna ecosystem, once the dominant ecosystem throughout the Southeast Coastal Plains of the United States, has been reduced to a small percentage of its pre‐colonization range. While the effect of heatwaves on grassland systems has been well explored, less focus has been given to the legacy effects of previous climatic events. Through a greenhouse experiment using Schizachyrium scoparium (little bluestem), a dominant understory grass species in LLP savanna ecosystems, we aimed to study the legacy effects of heatwaves (i.e., higher temperatures and lower precipitation and humidity) across multiple plant performance metrics and stress responses. S. scoparium had a negative response to an early heatwave, showing increased mortality, smaller maximum leaf length, fewer leaves, decreased specific leaf area (SLA), decreased leaf thickness, and reduced belowground net primary productivity (NPP) when compared to plants that did not experience a heatwave. S. scoparium individuals exposed to a late heatwave had fewer leaves, reduced SLA, and thinner leaves when compared to plants that did not experience a heatwave. While plants exposed to both an early and late heatwave experienced an increase in some stress responses as observed by increased catalase activity and plant mortality, they exhibited no change in other stress responses studied (e.g., maximum leaf length, relative growth rate, productivity, leaf thickness, peroxidase levels, or fuel load). Overall, our study revealed that S. scoparium may show neutral‐to‐positive legacy effects in response to multiple heatwaves. This indicates that LLP savanna ecosystems dominated by S. scoparium may display resistance to the predicted increased frequency of heatwaves in the southeastern United States, an important outcome for the heavily degraded and endangered ecosystem.

The longleaf pine (LLP) savanna ecosystem once covered ∼ 92 million acres of the Southeast USA, but due to anthropogenic activities such as logging and fire suppression, only 3% of its once widespread historic range remains. While many restoration efforts are underway to conserve this biodiverse ecosystem, restoration must be done in the context of climate change. In the last few decades, heatwaves have increased in frequency and intensity across the Southeastern USA with further increases predicted. To expand our understanding of LLP savanna restoration in light of these changes, we ran a series of three simulated heatwave greenhouse experiments through a Course-based Undergraduate Research Experience (CURE) incorporating ∼ 150 undergraduate researchers per experiment. We measured plant growth metrics for four understory grasses commonly used in LLP savanna restoration efforts. We found that while most grass plug individuals survived heatwave conditions, aboveground production was reduced due to heatwaves. This productivity decrease could result in less biomass available for the essential vegetation fire feedback loop, where fire increases grass biomass, and in turn, more grass provides more fuel for fire. These results imply that land managers can proactively compensate for biomass loss due to heatwaves by planting more grass plugs during initial restoration.

Background Disturbance is a natural part of all ecosystems and often creates a balance of resistance-resilience among taxa. Grassland ecosystems, and in particular tallgrass prairie, are model systems for studying the outcomes of disturbance regime shifts because they are disturbance-dependent (i.e., maintained by fire, grazing, or climate). The effects of changing disturbance regimes, such as fire frequency in mesic grasslands, are often assessed based on one or a few taxa. However, to support diverse management goals, land managers must consider the effects of their choices on many taxa. In this study, we addressed this gap using a meta-analysis of 37 studies from tallgrass prairie to assess the effects of different fire frequencies on arthropods, birds, plants, small mammals, and soil properties (referred to here as ecological factors) and the interactive effects of fire frequency and grazing, another important disturbance. Results As expected, the abundance and diversity of taxa were affected by different fire frequencies. However, the directionality of the change varied among taxonomic groups, indicating that there is no “one-size-fits-all” fire-management strategy in tallgrass prairie. Annual fires promoted small mammal abundance but decreased plant abundance and diversity. Meanwhile, intermediate fire frequencies promoted plant abundance but at the cost of plant diversity, arthropod abundance, and soil total carbon and nitrogen. Grazing promoted plant abundance while reducing arthropod and obligate grassland-bird abundance. Conclusions Our study revealed research gaps, with critical data missing from small mammals, birds, soil properties, and eastern tallgrass prairie. However, quantifying the differential responses of ecological factors to fire frequency, as we did here, can inform tallgrass prairie management strategies, providing an example of the potential for land managers to manipulate disturbance frequencies to meet diverse management goals. We outline the important tradeoffs associated with management strategies using fire frequency and highlight the potential for fire to be used in unison with grazing to create a more heterogeneous landscape conducive to tallgrass prairie. Multi-taxonomic syntheses like this one are needed for land managers and ecologists to harness the power of prescribed fire in order to increase grassland sustainability and health worldwide.

Disturbances impose a state of disequilibrium on ecosystems, often leading to the maintenance of ecosystem type and prevention of state shifts. Grasslands serve as a model system for assessing disturbance regime shifts, as they are disturbance-dependent ecosystems. Fire, climate, and herbivory are key disturbances in maintaining grasslands, but these regimes are shifting due to anthropogenic activity. Fire intensity is increasing while frequency is decreasing, and precipitation is becoming more variable, with longer and more intense droughts projected. Moreover, grasslands are being exploited for agricultural use, often resulting in a shift of primary herbivores from native species to cattle grazers while terrestrial arthropods—globally important herbivores—are decreasing in abundance. Thus, we must work to understand how shifts in these regimes will affect future biodiversity and ecosystem function in grasslands.To explore ecosystem changes as disturbance regimes shift, I focused on the Great Plains of North America where I performed a meta-analysis exploring the effects of fire frequency across multiple abiotic and biotic ecological factors (Chapter II) and used experimental and observational approaches to determine drought effects on plant communities (Chapter III) and assess the effects of cattle grazing and precipitation regime shifts on arthropod communities (Chapter IV). In Chapter II, I found that there is no “one-size-fits-all” fire management strategy to benefit all ecological factors in tallgrass prairie, however fire in unison with grazing creates a heterogeneous landscape, which benefits many ecological factors. In Chapter III, I provide evidence that plant communities in northern mixed-grass prairie are resistant to drought, likely due to shifts in plant species traits; however, this outcome is variable based on site and environmental factors. Finally, in Chapter IV, I demonstrated that precipitation mediates the effects of cattle grazing on arthropod communities, with diversity of arthropods increasing with cattle grazing intensity only in drought years. Overall, my work advances scientific knowledge on how anthropogenic and climate change driven shifts in disturbance regimes impact community dynamics and ecosystem function in Great Plains grasslands. As grasslands make up 40% of the earth’s ice-free surface and contribute to the livelihoods of more than 800 million people worldwide through agricultural goods and services, providing evidenced-based information to land managers about how novel disturbance regimes impact grassland biodiversity and function will be critical to promote long-term sustainability of the ecosystem and will increase global food security.

Anthropogenic biodiversity decline threatens the functioning of ecosystems and the many benefits they provide to humanity1. As well as causing species losses in directly affected locations, human influence might also reduce biodiversity in relatively unmodified vegetation if far-reaching anthropogenic effects trigger local extinctions and hinder recolonization. Here we show that local plant diversity is globally negatively related to the level of anthropogenic activity in the surrounding region. Impoverishment of natural vegetation was evident only when we considered community completeness: the proportion of all suitable species in the region that are present at a site. To estimate community completeness, we compared the number of recorded species with the dark diversity—ecologically suitable species that are absent from a site but present in the surrounding region2. In the sampled regions with a minimal human footprint index, an average of 35% of suitable plant species were present locally, compared with less than 20% in highly affected regions. Besides having the potential to uncover overlooked threats to biodiversity, dark diversity also provides guidance for nature conservation. Species in the dark diversity remain regionally present, and their local populations might be restored through measures that improve connectivity between natural vegetation fragments and reduce threats to population persistence.

Anthropogenic biodiversity decline threatens the functioning of ecosystems and the many benefits they provide to humanity1. As well as causing species losses in directly affected locations, human influence might also reduce biodiversity in relatively unmodified vegetation if far-reaching anthropogenic effects trigger local extinctions and hinder recolonization. Here we show that local plant diversity is globally negatively related to the level of anthropogenic activity in the surrounding region. Impoverishment of natural vegetation was evident only when we considered community completeness: the proportion of all suitable species in the region that are present at a site. To estimate community completeness, we compared the number of recorded species with the dark diversity—ecologically suitable species that are absent from a site but present in the surrounding region2. In the sampled regions with a minimal human footprint index, an average of 35% of suitable plant species were present locally, compared with less than 20% in highly affected regions. Besides having the potential to uncover overlooked threats to biodiversity, dark diversity also provides guidance for nature conservation. Species in the dark diversity remain regionally present, and their local populations might be restored through measures that improve connectivity between natural vegetation fragments and reduce threats to population persistence.