Carbon and nitrogen dynamics in tropical ecosystems following fire

Aim Tropical ecosystems have grown increasingly prone to fire over the last century. However, no consensus has yet emerged regarding the effects of fire disturbances on tropical biogeochemical cycles. Location Tropics. Time period 1960-2018. Major taxa studied Tropical ecosystems: Above- and below-ground carbon (C) and nitrogen (N) dynamics. Methods We analysed the impacts of fire on C and N dynamics in tropical ecosystems through a meta-analysis of 1,420 observations from 87 studies. Results Fire reduced both above- and below-ground C and N pools, with greater reductions above- than below-ground. Fire decreased soil total carbon (TC), total nitrogen (TN) and nitrate nitrogen (NO3-) and increased ammonium nitrogen (NH4+) in surface mineral soil layers but did not affect those in deep layers. Fire decreased TC and TN in savanna but did not affect those in tropical dry and moist forests. Fire did not affect NH4+ and NO3- in savanna because of non-significant responses of N mineralization rate (N-min) to fire. Conversely, fire increased NH4+ and decreased NO3- in tropical dry forest, but did not affect NH4+ and increased NO3- in tropical moist forest owing to thermal decomposition of soil organic N and increased soil nitrification, respectively. Moreover, NH4+ declined and NO3- increased initially and then decreased with time after fire. Above- and below-ground response variables to prescribed fire were mediated largely by fire frequency and experimental duration, respectively. Main conclusions Our results suggest a high vulnerability of the above-ground C and N pools to fire, whereas the biogeochemical cycles below-ground are of high complexity. Fire effects on below-ground C and N pools, which are highly uncertain and vegetation specific, should be investigated further.