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

Abstract

Global change is altering fire frequency and severity in many regions across the world. In this work, we studied the impact of different frequency and severity regimes on the soil biochemical properties in burned areas with different environmental conditions. We selected three sites dominated by pine ecosystems along a Mediterranean-Transition-Oceanic climatic gradient, where we determined the fire frequency, and severity of the last wildfire. Four years after the last wildfire, we established 184 4 m 2 plots. In each plot, we collected a composed soil sample from a 3 cm depth, and measured several ecological variables potentially affected by the fire frequency and severity (cover of bare soil, cover of fine and coarse plant debris, cover of vegetation, and vegetation height). From each soil sample, we analyzed the enzymatic activities corresponding to the biogeochemical cycles of carbon, nitrogen, and phosphorus (β-glucosidase, urease, and acid-phosphatase, respectively), and the microbial biomass carbon. The results indicated that fire frequency only played a significant role in soil biochemical properties at the Mediterranean and Transition sites. Specifically, we found that increases in frequency contributed to increased urease and phosphatase activities (at the Transition site), as well as microbial biomass carbon (at the Mediterranean and Transition sites). In relation to burn severity, we found opposite patterns when comparing the Mediterranean and Oceanic sites. Specifically, increased severity significantly decreased β-glucosidase, urease, and microbial biomass carbon at the Mediterranean site, whereas at the Oceanic one, severity significantly increased them. Burn severity also decreased microbial biomass carbon at the Transition site. Our results also indicated that, overall, fire frequency determined the studied ecological variables at the Mediterranean and Transition sites, but clear indirect effects on biochemical properties due to changes in ecological variables were not found. This study adds to the knowledge on the impact of shifts in fire regimes on soils in the current context of change.

Soil Resistance to Burn Severity in Different Forest Ecosystems in the Framework of a Wildfire

“…Soil biochemical properties showed no resistance after wildfire [99], decreasing with burn severity in all the ecosystems. Many authors found a decrease in enzymatic activity immediately after fire [2,88,[100][101][102], as well as a decrease in the activity of these extracellular enzymes with fire burn severity [30,31,46,64] due to the thermal denaturation of soil enzymes [2,66], which occurs above 60-70 • C [44]. The increase in soil pH has also been related to the decrease in β-glucosidase [103] and acid phosphatase [104] activities.…”

“…All these effects mainly occur in the first few centimetres of the surface horizon [2,26,43]. Nutrient cycles are influenced by soil enzymes [44,45], with βglucosidase, urease, and acid phosphatase being among the main enzymatic activities related to the C, N, and P cycles, respectively [2,46]. Enzymes in soils, which catalyse biological reactions [44], are of animal, plant, and microbial sources [45,47].…”

Soil Biological Responses under Different Vegetation Types in Mediterranean Area

“…An exception was C fung in P soils, which significantly increased after the fire, suggesting that the fire favored fungi as compared to bacteria [ 10 ]. Instead, the different behaviors of HA, extracellular enzymes, and DHA, and the intracellular enzymes between unburnt and burnt soils, suggest deep changes in different functional groups of microorganisms [ 53 ]. It can be supposed that after the fire, soil conditions are more disturbed, especially in H soils, as a conspicuous increase in BR and qCO 2 occurred [ 54 ].…”

Burnt wood management enhances soil multifunctionality at the medium term after a large wildfire in north-west Spain

“…Severe stand-replacing wildfires in Mediterranean fire-prone landscapes might involve substantial impacts on individual soil functions (e.g. Borgogni et al 2019;Fernández-García et al 2020;Huerta et al 2020) and plant community-level properties (e.g. Fernández-Guisuraga et al 2019;Etchells et al 2020), but also on ecosystem multifunctionality (Lucas-Borja et al 2021).…”