It is widely accepted that ungulates influence the nitrogen cycle within their ecosystem; however whether they accelerate or decelerate the cycle remains disputed and largely unexplored in tropical forests. With increasing rates of deforestation and subsequent extirpation of these animals, understanding their role has become increasingly pertinent. This study aims to model nitrogen within the forests of the Cerrado, Brazil, using the Century Soil Organic Matter model. Century is designed as an ecosystem-level model of the plant-soil relationship that simulates carbon and nitrogen fluxes within the system. Specifically, this project simulates the impact of white-lipped peccaries (WLP), an ungulate constituting 33% of the vertebrate biomass in the Cerrado. Biomass data for WLP in the Cerrado has been estimated and nitrogen outputs per kilogram for the species has been determined. Using this information, yearly nitrogen input by WLP has been calculated. Environmental parameters specific to the forests of the Cerrado have been gathered from published studies and have been input as ecosystem parameters within the model (i.e. temperature, precipitation, soil properties, etc.). Two simulations have been conducted, one of WLP presence and one of absence, in order to understand the role ungulate on forest nutrient dynamics.
Previously published WLP density estimates were used in conjunction with published nitrogen excretion estimates to calculate yearly input of nitrogen from fecal matter. Given their large presence in the Cerrado, it was determined WLP presence contributes .18 gN/m2/yr-1. Fecal matter directly deposits nitrogen in a form that is readily available to plants and helps stimulate decomposition, and is thus entered into the Century model as symbiotic nitrogen. A control simulation was run with the Cerrado Forest parameters and a WLP peccary simulation was run with the same parameters and the additional circulated nitrogen. Both simulations were run for 1000 years in order for each to reach equilibrium. Initial results show that once at equilibrium, WLP presence increases the nitrogen in forest biomass by 3.12 gN/m2 and in forest soil by 37.26 gN/m2, thus adding 40.48 gN/m2 to the ecosystem. Given nitrogen is a limiting element for forest systems, WLP presence also increases the carbon in the forest biomass by 228.53 gC/m2 and in forest soil by 133.93 gC/m2, thus adding 362.46 gC/m2 to the ecosystem. Results from these simulations indicate the important role of ungulates within forest systems through the deposition of available nitrogen.