Large mammals alter soil chemistry and increase fertility in the Atlantic Forest

A recent study published in Ecological Monographs has revealed that large mammals in the Brazilian Atlantic Forest significantly impact the soil and litter chemistry, thereby increasing nutrient availability and potentially enhancing soil fertility. Conducted by researchers from the Center for Research on Biodiversity and Climate Change (CBioClima) at the Institute of Biosciences of São Paulo State University (IB-UNESP), the findings emphasize the vital role these animals play, despite facing heavy poaching and population decline.

The study's lead author, Letícia Gonçalves Ribeiro, explains that large mammals like peccaries, tapirs, deer, and agoutis contribute to altering the chemical composition of litter and soil through their trampling, rooting, and excretion activities. These behaviors increase nutrient availability, such as calcium and aluminum, and reduce harmful aluminum levels, fostering a balance crucial for soil fertility.

Additionally, the study found that the presence of large mammals leads to a decrease in leaf litter's lignin content, a complex molecule that hinders decomposition. This reduction promotes faster decomposition of leaf litter, thus enhancing soil fertility.

The research utilized camera traps to estimate mammal biomass, comparing plots open to free animal movement with those restricted by fences. Areas with large mammals showed lower soil acidity (pH) and higher nutrient availability compared to fenced-off areas. Furthermore, the study observed greater diversity in leaf litter from areas with roaming mammals, indicating improved decomposition processes.

Professor Mauro Galetti, the study's coordinator and principal investigator at CBioClima, highlights the crucial role of large herbivores as ecosystem engineers, influencing both plant community composition and soil chemistry. The research, part of the DEFAU-BIOTA project, has shown that the absence of these mammals negatively impacts soil nitrogen levels and plant diversity, potentially leading to forest homogenization dominated by a few resilient species.

Further analysis is underway to assess the impact of large mammals on nematode populations, which serve as vital indicators of ecosystem health. Preliminary results suggest a higher abundance of predatory nematodes in areas with large mammals, signaling a healthier ecosystem.