The underground architecture
In the vast savannas of central Brazil, the visible landscape of scattered, short trees is misleading. This is the Cerrado, called an "upside-down forest" because the majority of its plant life exists below the soil. For many woody species here, up to 70% of their total biomass is in their extensive root systems, which can penetrate the earth to depths of 15 meters or more. This subterranean network is a direct adaptation to the region's long dry seasons and frequent fires.
The plants have evolved specialized underground structures to survive. Many species, including 94 species found in a single hectare, possess a xylopodium. This is a thick, woody organ at the top of the root system that stores large amounts of water and carbohydrates. It also contains dormant buds, protected from the heat of surface fires. After a fire passes, these buds allow the plant to resprout rapidly. The deep taproots are important for reaching water stored far below the surface, allowing trees like Qualea grandiflora and those of the Byrsonima genus to maintain their leaves through the months-long dry season.
Fire, water, and carbon
The Cerrado is a fire-adapted ecosystem. Fires, often started by lightning, sweep through the grasslands every few years, clearing out old growth. The plants are prepared. Trees have thick, corky bark that insulates the living tissue from the heat. For many herbaceous plants and shrubs, the real survival strategy is their underground reserve. Protected by the soil, the root crowns and xylopodia enable swift regeneration, often just weeks after a burn.
This immense root network also helps the region's hydrology and carbon cycle. The deep roots of some trees can draw water from wet soil layers far below and release it into the drier upper soil layers at night. This process, known as hydraulic redistribution, can benefit neighboring, shallower-rooted plants.
The sheer volume of this underground biomass makes the Cerrado a globally important carbon sink. The soil and extensive root systems lock away enormous quantities of carbon, potentially more stable than the carbon stored in the aboveground biomass of other forest types. Recent studies indicate the biome's wetlands store carbon at a density six times greater than the Amazon's vegetation. This "upside-down forest" is under threat from agricultural expansion, which destroys the root systems and releases millennia-old carbon into the atmosphere.