The Karp Lab’s goal is to better understand how feedbacks between changing fire, climate, and biotic (i.e., floral and faunal) interactions lead to abrupt landscape transitions on a variety of spatial and temporal scales. To examine these processes today and in the geologic past, we use a combination of statistical, remote sensing, field ecological, and geochemical techniques. We also work to ground-truth and improve organic geochemical and isotope geochemical proxies that can be applied in unique ways to better understand ecological disturbance in the past. Our ultimate goal is to resolve how grassy biomes and their fire regimes may respond to global climate change, informing future management decisions by extending temporal context.

Paleo-herbivory proxy development 

To study how herbivores have shaped ecosystem functions in the past, we must be able to reconstruct how herbivore densities and communities have changed through time. We are working to explore and develop organic geochemical proxies (fecal biomarkers) for paleo-herbivore communities. To accomplish this, we have deployed a multi-scale calibration framework in Kruger National Park, South Africa, where we measured the concentrations and distributions of these compounds in dung, soils and sediments.

Publications: Karp et al., 2023

Fire response to African Humid Period rainfall shifts

The African Humid period (14.7-5 Ka) was a time of increased rainfall in northern and subtropical Africa. This period provides an opportunity to test if savanna fire activity responds to long-term shifts in rainfall in predictable ways. We generated new organic geochemical records of paleofire from East African lakes, and synthesizing them alongside existing charcoal records to examine if hydrologic controls on paleofire fuel dynamics varied across the savanna rainfall gradient (200-1500 mm/yr). We are also using model-proxy comparisions to examine how herbivory may have complicated the relationship between fire and climate.

Publications: Karp et al., 2023

Herbivore-fire interactions in grasslands

Consumer feedbacks (i.e., fire and herbivory) play important roles in stabilizing grasslands biomes. However, how these factors interact with each other on long timescales, and how they may respond to our currently changing climate is unknown. This project combines remote sensing, herbivore exclusion experiments, and Quaternary paleoecological reconstructions to examine if and how herbivory may impact fire activity in grasslands and savannas.

Publications: Karp et al., 2021;  Staver et al., 2021; Karp et al., 2024

Pyrogenic Carbon: Today and in the Past

Fire-derived organic carbon (PyC; black carbon) is recalcitrant is potentially an underappreciated carbon sink. PyC can be used to reconstruct paleofire, and is an important part of the organic carbon cycle. We have improved our ability to identify the fiery origin of molecular forms of PyC (Polycyclic aromatic hydrocarbons [PAHs]) through multivariate statistics and compound specific isotopic measurements of both modern burned samples and sedimentary samples (i.e. lake, marine sediments). We are currently working on a project measuring PAHs, Pyrosugars, charcoal and bulk PyC from controlled burns in Kruger National Park (KNP), South Africa to calibrate these proxies specifically for grasslands. We are also comparing PyC in temperate (IL) and subtropical (KNP) savannas to better understand how PyC contributes to global C storage in soils.

Publications: Karp et al., 2020; Vachula et al., 2022; Hernadez et al., 2023

Testing the Fire Hypothesis for Neogene Grassland Expansion

Today grasslands are responsible for up to 30% of global terrestrial primary productivity and are important to maintaining subtropical biodiversity across five continents. Fire has been hypothesized as one of the potential drivers for the expansion of these ecosystems in the Neogene. We have worked to reconstruct fire alongside shifts in vegetation and climate to test this hypothesis. Our research has generally focused on the grassland expansions in South Asia and Australia, but we have worked with colleagues who are interested in other regions as well. Results indicate the role of fire in grassland expansion differs between continents.

Publications: Karp et al., 2018; Karp et al., 2021a; Karp et al., 2021b; Polissar et al., 2021