Why focus on leaf litter?

The upper few centimeters of soil and the accumulated leaf litter and rotten wood that lies on it is a compressed region of intense biological activity. Biodiversity is far more concentrated there than anywhere else in terrestrial ecosystems. Almost all the biomass of the forest eventually falls to this thin layer where it is transformed to other forms in the carbon cycle. A highly diverse fauna of mostly very small arthropods lives in this layer. For example, at La Selva Biological Station in Costa Rica, a lowland rainforest site, 270 species of ants, 60% of the entire ant fauna, lives in this litter layer.