concept

Ash bed effect

The sudden nutrient pulse a fire leaves on the ground. When vegetation burns, the calcium, magnesium and potassium in the biomass do not go up the plume; they settle as oxides and carbonates, in forms roots can take up at once rather than after slow decomposition. Being alkaline, they also neutralise acid topsoil, lifting pH by roughly 1-3 units and unlocking minerals that low pH had held tightly bound. This is the regenerative half of fire's nutrient ledger, the counterweight to the losing half where nitrogen volatilises into the smoke - fire takes nitrogen away and hands back cations.