## 3 Results
### Duff Ignition Probability  
We estimated the 50% ignition probability (P\({}_{50}\)) in all the duff samples (N = 15) and in six soil samples taken close to the surface (F 0-5 cm, N = 15) from the area exposed to low-intensity burning. All the surface soil samples (C 0-5 cm, N = 15) taken from the control zone, in contrast, do not present a P\({}_{50}\) of ignition. The separate linear regression model between percentage of soil moisture content (% MC) at P\({}_{50}\) and percentage inorganic matter (% IM) has a very high magnitude (\(F=104.5\), \(p<0.001\)) and a  
Figure 5: Box plots showing the variability in the physicochemical properties of the duff layer (Oe + Oa) with distance along the transects (D0, D8, D16, D24 y D32): (**a**) depth (cm); (**b**) bulk density (BD (kg/m\({}^{3}\))); (**c**) inorganic matter content (IM (%)); (**d**) organic matter content (OM (%)). Error bars represent the variability of data and indicate the error or uncertainty in each case. coefficient of determination (\(R^{2}\) = 0.846) (Table 6a). In the separate linear regression model between % MC at an ignition of P\({}_{50}\) and BD expressed in kg/m\({}^{3}\), the magnitude (\(F\) = 70.9, \(p\) \(<\) 0.001) and the coefficient of determination are also high (\(R^{2}\) = 0.789) (Table 6b). The mean moisture threshold for P50 is 81.22 \(\pm\) 20% and 23.08 \(\pm\) 31% for the control and burned zone respectively. The inorganic matter content means are 35.52 \(\pm\) 11% in the duff and 66.40 \(\pm\) 16% in the F\(-\)0-5 cm (Figure 6a). The organic matter content means are 64.48 \(\pm\) 11% in the duff and 33.6 \(\pm\) 16% in the F\(-\)0-5 cm. The mean bulk density is 156.76 \(\pm\) 135 kg/m\({}^{3}\) in the duff and 373.90 \(\pm\) 114 kg/m\({}^{3}\) in the F\(-\)0-5 cm (Figure 6b). In the burned zone, the minimum moisture estimated is 0.12% corresponding to sample D\({}_{32}\) from T6. The next lowest value is 6.80%, corresponding to sample \(D_{24}\) from T5. These two results mark the maximum limit of inorganic content and density for P\({}_{50}\) (76.36% and 74.26% of IM, 478.31 kg/m\({}^{3}\) and 439.87 kg/m\({}^{3}\) of BD, respectively). In the duff layer of the control zone, soils can reach P\({}_{50}\) when moisture content is as lower as 33.60%, IM is 19.16% and bulk density is 580 kg/m\({}^{3}\) (sample \(D_{16}\) from T3), although the sample is not an extreme that can be considered representative of the whole layer. The next lowest moisture content 55.62% recorded in sample \(D_{24}\) from T1 associated with an IM of 55.61% and a BD of 193.33 kg/m\({}^{3}\). This value can be considered as being more representative of the duff layer. The highest bulk densities are recorded in samples \(D_{32}\) from T2 and D\({}_{8}\) from T3 with 290 kg/m\({}^{3}\) each. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & \(B\) & \(SE\) & \(t\) & \(p\)-Value \\ \hline \multirow{2}{*}{(a)} & (Constant) & 141.432 & 8.110 & 17.440 & 0.000 \\  & IM (\%) & \(-\)1.743 & 0.170 & \(-\)10.222 & 0.000 \\ \hline \multirow{2}{*}{(b)} & (Constant) & 109.271 & 6.387 & 17.108 & 0.000 \\  & BD (kg/m\({}^{3}\)) & \(-\)0.196 & 0.023 & \(-\)8.42 & 0.000 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Results of the analysis of the two linear regressions. (a) Moisture (%) at P\({}_{50}\) of ignition and mineral content (IM (%)): \(R^{2}\) = 0.846, \(N\) = 20; (b) humidity (%) at P\({}_{50}\) and bulk density (BD (kg/m\({}^{3}\)): \(R^{2}\) = 0.789, \(N\) = 20. Figure 6: (a) Relationship between the moisture content (MC) at an ignition probability of 50% (P\({}_{50}\)) and inorganic matter content (IM) \(R^{2}\) = 0.846, \(SE\) = 8.11, \(N\) = 20. 6. (b) Relationship between moisture content at an ignition probability of 50% and bulk density (BD): \(R^{2}\) = 0.789, \(SE\) = 6.39, \(N\) = 20. Values expressed by distance (\(D_{0}\) = 0 m, \(D_{8}\) = 8 m, \(D_{16}\) = 16 m, \(D_{24}\) = 24 m, \(D_{32}\) = 32 m, \(D_{40}\) = 40 m) along the transect (T1, T2 and T3 located in the control zone, T4, T5 and T6 in the burned zone).