Wildland fire ash enhances short-term CO2 flux from soil in a Southern African savannah

Chemical Characteristics of Wildfire Ash Across the Globe and Their Environmental and Socio-Economic Implications

“…For example, for the NAUS site (temperate eucalypt forest, Table 2), Santín et al (2015b) reported 4 and 3.8% (40.0 and 38.1 g kg -1 of total C) for unburnt and burnt soil, respectively, while 24.7% (247 g kg -1 of total C) was observed in the ash from the same fire. Similarly, for the study sites from the subtropical savanna in South Africa (SAPB1, SAPB3 and SAMB), we observed total C contents in the ash an order of magnitude higher than in the pre-and post-burn soils (Sánchez-García et al, 2021). This is because the main contributor to ash is usually vegetation and highlights the important role of ash in mobilizing and redistributing C in the landscape after fire (Bodí et al, 2014;Santín et al, 2012).…”

“…This is partly due to its high mobility, and hence rapid redistribution after fire, which makes wildfire ash more challenging to collect than other components of the post-fire environment, such as fire-affected soils or the eroded sediment (Bodí et al, 2014). Over the last few years, however, research interest in wildfire ash has gained traction, with studies assessing ash chemical characteristics in a diverse range of ecosystems such as tropical and sub-tropical savannas (Brito et al, 2017;Brito et al, 2021;Caumo et al, 2022;Oliveira-Filho et al, 2018;Sánchez-García et al, 2021), tropical broadleaf forests (Audry et al, 2014), temperate eucalypt forests (Campos et al, 2015;Campos et al, 2016;Costa et al, 2014;Santín et al, 2012;2015b;2018;Silva et al, 2015;Wu et al 2017), Mediterranean and temperate conifer forests (Balfour & Woods, 2013;Harper et al, 2019;Pereira et al, 2012;Simon et al, 2016;Tsai et al, 2015;Quigley et al, 2019;Wang et al, 2015), temperate heathlands (Marcos et al, 2008), boreal forests (Kohl et al, 2019), and wetlands (Liu et al, 2010). This previous research indicated that ash chemical composition is highly heterogeneous even for ash from the same or similar ecosystems (Table 1).…”

Postfire Phosphorus Enrichment Mitigates Nitrogen Loss in Boreal Forests

“…After forest fires, a portion of N from ash and charred organic matter leachates is lost through runoff and wind erosion, regardless of N form . The remaining N leaches to the subsoil horizons, − where it may be retained by biological uptake and mineral adsorption or lost by gaseous emission (NH 3 , N 2 O, NO X , and N 2 ) and leaching [i.e., dissolved inorganic N (DIN) and dissolved organic N (DON)]. ,,,, We found that soil DIN content showed a depletion during postfire recovery in the Greater Khingan Mountains (Figure S3E,F; R 2 = 0.118, p < 0.05 in O horizon; R 2 = 0.180, p < 0.01 in A horizon). In contrast, soil DON content gradually increased during postfire recovery (Figure S3H,I; R 2 = 0.086, p < 0.05 in O horizon; R 2 = 0.221, p < 0.001 in A horizon).…”

Soil Respiration and Bacterial Changes after a Wildfire in Mediterranean-Type Ecosystems

“…Variables affecting soil respiration are associated to either positive or negative microbial responses due to fire. The thermal shock could kill microorganisms and reduce soil respiration whereas increased nutrient availability in deposited ash would favor microbial activity and CO2 release (Sánchez-García et al, 2021;Zhang et al, 2021b). Increases in pH and dissolved organic carbon, especially in low severity fires may enhance microbial respiration, whereas the formation of material characterized by high aromaticity and recalcitrance would result in a drop of microbial activity (Hu et al, 2020).…”

“…Better nutrient status was often used as an explanation for the proliferation of some microbial groups and the increase of saprophytic and decrease of autotrophic microorganisms after fire (Vázquez et al, 1993). The important role of ash in post-fire soil respiration was also emphasized by Sánchez-García et al (2021) working in a savanna environment. Adding wildland fire ash enhanced CO2 emissions by up to 3 times compared with pre-and post-fire soils without ash, suggesting that this was the result of the high content of readily available nutrients in the ash.…”