Why are forests so scarce in subtropical South America? The shaping roles of climate, fire and livestock

• We modeled the notoriously low forest cover in southeastern South America (SSA).
• Tree cover increases with precipitation but is limited by fire and cattle density.
• In SSA grasslands, livestock likely limits the expansion of forests from rivers.

Forest cover is notoriously sparse across neotropical southeastern South America. In particular, the practically treeless landscapes of the Campos, as they are locally known, have puzzled ecologists since Darwin’s time. We used remote-sensing information and spatial regression models to relate tree cover to resource availability (i.e. climate, soil fertility, soil water holding capacity), disturbances (i.e. fire occurrence, cattle grazing) and landscape features that can mediate the effects of both (i.e. topography, distance to rivers). To better understand these relationships, we conducted the analysis at different spatial scales across non-cultivated areas of southeastern South America. Overall, tree cover in southeastern South America increases with precipitation but is limited by livestock densities and fire occurrence. Forests are concentrated close to rivers, especially in the Campos region, where cattle grazing seems to prevent tree expansion into the grasslands.