# Habitat Loss and Other Threats to the Survival of _Parnasius apollo_ ([PERSON], 1758) in Serbia
## 3 Results
### Vegetation Index-Based Burn Scar Detection on Stol Mountain (Luka, Bucje and Bucje 2 Site Location)  
Table 2 presents the temporal variation in three vegetation-related spectral indices--Burned Area Index (BAI), Normalized Burn Ratio (NBR), and its modified version NBR2--over the study area during the period from 29 July to 14 October 2024. This time frame includes the pre-fire, active fire, and immediate post-fire phases. In the pre-fire period (July 29 to August 25), the values of all indices indicate healthy and dense vegetation cover. BAI values remain relatively low (mean values between 9.30 and 10.93), which is typical for areas without recent burning. Correspondingly, NBR values are consistently positive (mean values from 0.09 to 0.17), suggesting vigorous vegetation. NBR2 also maintains stable values around 0.17-0.18, confirming the presence of undisturbed plant biomass. A significant drop in NBR and NBR2 values begins on September 12, coinciding with the detected fire event, indicating rapid loss of live vegetation. To assess whether spectral changes associated with the wildfire were statistically significant, we applied the non-parametric Mann-Whitney U test to compare pre-fire (July 29-August 25) and post-fire (September 12-October 14) values of BAI, NBR, and NBR2. All three indices showed statistically significant differences between the two periods (BAI: \(U\)= 0.0, \(z\) = \(-\)2.24, \(p\) = 0.036, \(r\) = \(-\)0.79; NBR: \(U\) = 15, \(z\) = +2.24, \(p\) = 0.036, \(r\) = +0.79; NBR2: \(U\) = 15, \(z\) = +2.24, \(p\) = 0.0314, \(r\) = +0.79), confirming the spectral signature of fire-induced vegetation loss. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Year 2024** & **Date** & **29.7** & **8.8** & **13.8** & **23.8** & **25.8** & **12.9** & **27.9** & **14.10** \\ \hline \multirow{8}{*}{_BAI_} & Minimum value & 2.97 & 3.24 & 2.47 & 2.22 & 1.67 & 3.42 & 3.47 & 2.15 \\  & Maximum value & 25.09 & 73.53 & 30.62 & 34.77 & 24.33 & 120.54 & 91.83 & 85.82 \\  & Range & 22.12 & 70.29 & 28.15 & 32.55 & 22.66 & 117.12 & 88.35 & 83.66 \\  & Mean value & 9.9\({}^{\circ}\) & 10.32\({}^{\circ}\) & 10.09\({}^{\circ}\) & 10.93\({}^{\circ}\) & 9.30\({}^{\circ}\) & 27.90\({}^{\circ}\) & 27.95\({}^{\circ}\) & 21.55 \\  & Standard deviation & 1.72 & 6.42 & 2.01 & 2.42 & 2.02 & 15.31 & 13.62 & 9.78 \\  & Minimum value & \(-\)1.00 & -1.00 & -1.00 & -1.00 & -1.00 & -1.00 & -1.00 & -1.00 \\  & Maximum value & 1.00 & 1.00 & 1.00 & 1.00 & 1.00 & 1.00 & 1.00 & 1.00 \\ \multirow{2}{*}{_NBR_} & Range & 2.00 & 2.00 & 2.00 & 2.00 & 2.00 & 2.00 & 2.00 & 2.00 \\  & Mean value & 0.17\({}^{\circ}\) & 0.15\({}^{\circ}\) & 0.14\({}^{\circ}\) & 0.11 & 0.09\({}^{\circ}\) & \(-\)0.10\({}^{\circ}\) & \(-\)0.11\({}^{\circ}\) & \(-\)0.10\({}^{\circ}\) \\  & Standard deviation & 0.18 & 0.18 & 0.17 & 0.16 & 0.17 & 0.21 & 0.19 & 0.17 \\  & Minimum value & 0.11 & 0.10 & 0.11 & 0.12 & 0.11 & -0.05 & -0.04 & \(-\)0.01 \\  & Maximum value & 0.23 & 0.23 & 0.23 & 0.22 & 0.21 & 0.20 & 0.18 & 0.17 \\ \multirow{2}{*}{_NBR_} & Range & 0.12 & 0.13 & 0.12 & 0.09 & 0.10 & 0.24 & 0.23 & 0.19 \\  & Mean value & 0.17\({}^{\circ}\) & 0.17\({}^{\circ}\) & 0.18\({}^{\circ}\) & 0.18\({}^{\circ}\) & 0.17\({}^{\circ}\) & 0.07\({}^{\circ}\) & 0.05\({}^{\circ}\) & 0.06\({}^{\circ}\)Figure 9 illustrates the vegetation loss and structural change following the wildfire, particularly the reduction in low vegetation and increase in woody regrowth. A marked shift in spectral index values is observed starting from September 12, which aligns with the assumed fire event. BAI values increase sharply, reaching a peak mean of 27.95, accompanied by a noticeable rise in standard deviation, indicating spatial variability in fire severity. Simultaneously, NBR values drop into the negative range (\(-0.10\) to \(-0.11\)), which is a strong indicator of burned surfaces.