Fire frequency drives decadal changes in soil carbon and nitrogen and ecosystem productivity

Abstract

Fire frequency is changing globally and is projected to affect the global carbon cycle and climate. However, uncertainty about how ecosystems respond to decadal changes in fire frequency makes it difficult to predict the effects of altered fire regimes on the carbon cycle; for instance, we do not fully understand the long-term effects of fire on soil carbon and nutrient storage, or whether fire-driven nutrient losses limit plant productivity. Here we analyse data from 48 sites in savanna grasslands, broadleaf forests and needleleaf forests spanning up to 65 years, during which time the frequency of fires was altered at each site. We find that frequently burned plots experienced a decline in surface soil carbon and nitrogen that was non-saturating through time, having 36 per cent (±13 per cent) less carbon and 38 per cent (±16 per cent) less nitrogen after 64 years than plots that were protected from fire. Fire-driven carbon and nitrogen losses were substantial in savanna grasslands and broadleaf forests, but not in temperate and boreal needleleaf forests. We also observe comparable soil carbon and nitrogen losses in an independent field dataset and in dynamic model simulations of global vegetation. The model study predicts that the long-term losses of soil nitrogen that result from more frequent burning may in turn decrease the carbon that is sequestered by net primary productivity by about 20 per cent of the total carbon that is emitted from burning biomass over the same period. Furthermore, we estimate that the effects of changes in fire frequency on ecosystem carbon storage may be 30 per cent too low if they do not include multidecadal changes in soil carbon, especially in drier savanna grasslands. Future changes in fire frequency may shift ecosystem carbon storage by changing soil carbon pools and nitrogen limitations on plant growth, altering the carbon sink capacity of frequently burning savanna grasslands and broadleaf forests.

A 55‐year‐old natural experiment gives evidence of the effects of changes in fire frequency on ecosystem properties in a seasonal subtropical dry forest

“…Although a significant increase in soil pH was observed in HF soils, the magnitude of this change was low (6.41 in LF vs. 6.75 in HF), suggesting that the time elapsed after the last fire was enough to dilute the immediate effects of fire and ash on the soil pH (Certini, ). In summary, it is possible that the repeated fire occurrence and the consequent loss of soil in HF could be the main limiting factors preventing forest recovery, at least at a multidecadal scale (Pellegrini et al, ).…”

Belowground community responses to fire: meta‐analysis reveals contrasting responses of soil microorganisms and mesofauna

“…Data available from the Dryad Digital Repository: < http://dx.doi.org/10.5061/dryad.19tb3dp > (Pressler et al ).…”

“…Changing fire regimes have become a significant component of global change (Flannigan et al , 2013, Moritz et al ) and have feedback potential that may exacerbate climate change (Levine et al ). Given that fire frequency is a long‐term driver of soil carbon (C) and nitrogen (N) stocks (Soong and Cotrufo , Pellegrini et al ), it is critical to understand the consequences of novel fire regimes for ecosystem structure, function and dynamics.…”

Inserting Tropical Dry Forests Into the Discussion on Biome Transitions in the Tropics

“…While cerradão is initially comprised of fire-adapted tree species from the cerrado, dry forest tree species colonize this environment if propagules are available, fire remains absent and soils are sufficiently fertile. These dry forest tree species may eventually outcompete cerrado tree species, since they do not invest in fire defense (Ratajczak et al, 2017), and in the prolonged absence of fire, cerradão may transition to a dry forest if there are positive feedback cycles between forest vegetation, lack of fire and soil fertility (Silva et al, 2013;Pellegrini et al, 2014Pellegrini et al, , 2018. However, if the underlying soils remain poor and/or if there are high aluminum concentrations in the soil that do not attenuate over time, then cerrado tree species, which are adapted to infertile, aluminum-rich soils may continue to dominate the vegetation.…”