Impact of burn severity on soil properties in a Pinus pinaster ecosystem immediately after fire

Abstract

We analyse the effects of burn severity on individual soil properties and soil quotients in Mediterranean fire-prone pine forests immediately after a wildfire. Burn severity was measured in the field through the substrate stratum of the Composite Burn Index and soil samples were taken 7–9 days after a wildfire occurred in a Pinus pinaster Ait. ecosystem. In each soil sample, we analysed physical (size of soil aggregates), chemical (pH, organic C, total N and available P) and biological (microbial biomass C, β-glucosidase, urease and acid phosphatase activities) properties. Size of aggregates decreased in the areas affected by high burn severity. Additionally, moderate and high severities were associated with increases in pH and available P concentration and with decreases in organic C concentration. Microbial biomass C showed similar patterns to organic C along the burn severity gradient. The enzymatic activities of phosphatase and β-glucosidase showed the highest sensitivity to burn severity, as they strongly decreased from the low-severity scenarios. Among the studied soil quotients, the C:N ratio, microbial quotient and β-glucosidase:microbial biomass C quotient decreased with burn severity. This work provides valuable information on the impact of burn severity on the functioning of sandy siliceous soils in fire-prone pine ecosystems.

Do Fire Regime Attributes Affect Soil Biochemical Properties in the Same Way under Different Environmental Conditions?

“…The term fire regime refers to the spatial, magnitude, and temporal attributes of fire in a given ecosystem [12][13][14]. Nowadays, much research investigates the importance of changes in fire regimes, most of which focuses on the fire frequency and severity [15][16][17][18][19]. Fire frequency is a temporal fire regime attribute defined as the number of fires in a given period [12].…”

“…Burn severity is a magnitude fire regime attribute defined as the loss of or change in ecosystem biomass that can be measured by remote sensing methods [20]. Both attributes have been shown to shape the ecosystem structure, composition, and resilience [12,20] and determine the fire impacts in relation to soil properties [16,17]. However, it is not clear whether the fire frequency and burn severity effects on soils are consistent across ecosystems with different environmental conditions, such as different climates and soil types [17].…”

“…Fire impacts on soils are particularly intense in fire-prone pine forests [7]. In these forests, which are the most affected by wildfires in Southern Europe [21][22][23], fire causes immediate changes in soils [16] that may persist for several years because of the direct impact and changes in the ecological variables, such as vegetation cover [17][18][19][20][21][22][23][24][25]. In the long term (>5 years), the effects of fire on soil properties are less evident [26,27].…”

“…In the long term (>5 years), the effects of fire on soil properties are less evident [26,27]. Many works have studied the impact of fire on soil physical properties, reporting decreases in the surface water repellency after frequent fires [19], and decreases in the size of soil aggregates at high severities [16,28]. Other studies have focused on soil chemical properties.…”

“…Other studies have focused on soil chemical properties. For instance, it has been demonstrated that frequent fires can decrease some nutrients, such as the total nitrogen (N) [29,30], whereas severe fires usually decrease organic carbon (C) and increase available phosphorus (P) concentrations [16,17]. However, although some studies have addressed fire frequency [31,32] and burn severity [15,[33][34][35] impacts on soil biochemical properties, to our knowledge, none of them have analyzed potential interaction effects between both attributes on soil enzymatic activities and microbial biomass.…”