## 3 Results
### Forest Loss Severity and Recovery
#### 3.2.3 Recovery  
Of the fifteen high-disturbance sample sites selected for the vegetation recovery analysis, eleven of the locations were confirmed as wildfire sites based on the MTBS fire severity and MODIS burn area data. Of the seven spectral indices tested using the LandTrendr model (NBR, NDVI, NDMI, TCB, TCG, TCB, and TCA), the NBR performed best on temporal segmentation fitting with lower RMSE values. The 15 sites showed variable rates of NBR recovery following forest loss events (Figure 8). The NBR values remained lowered for many years after disturbance, with an average NBR of 0.6 pre-event, \(-0.04\) immediately following the event, and 0.31 five years later. For the six sites that fully recovered the pre-disturbance NBR values, the average time until total recovery was 10.8 years, as some locations rapidly improved (e.g., Figure 8k,o) and other locations took 15-20 years to recover the NBR values (e.g., Figure 8a,c).  
Figure 8: Forest loss impact and recovery for selected disturbance sites on the PCT (**a–e**), CDT (**f–i**), and AT (**k–o**) based on the Landsat-derived NBR spectral index values and LandTrendr temporal segmentation, where higher NBR values indicate more vegetation. The average NBR values decreased from 0.6 pre-event to 0.31 five years later.  
Figure 7: Dual-axis time series showing the relationship between the monthly MODIS burned area and CHIRPS average monthly rainfall for (**a**) the PCT, (**b**) the CDT, and (**c**) the AT. Note the different y-axis values for rainfall on each trail. Wildfires along the PCT are frequent and highly seasonal, occurring during dry summer months.  
The more arid western PCT and CDT trails exhibited slower recovery and more frequent changes in land cover after forest loss. Notably, four of the CDT sites (Figure 8f,g,i,j) had not fully recovered the pre-disturbance spectral index values more than 15 years after the disturbance event. The sites that changed vegetation more permanently include the PCT sample site (Figure 8c), which burned in the August 2009 Station Fire in the Southern and Baja California Pine-Oak Mountains of California (Figure 9). Analysis of the MODIS MCD12Q1 data at this location demonstrates the transition from a dominance of evergreen needleleaf forests before 2009 to grasslands and subsequent savanna-dominated systems after the wildfire and continuing through 2023 (Figure 9a). The National Agriculture Imagery Program (NAIP) high-spatial-resolution 1 m aerial imagery from 2009 and 2010 show the fire impact on the PCT trail and surrounding vegetation (Figure 9b,c). Comparison of the spectral index performance and the LandTrendr temporal segmentation shows the slow vegetation recovery captured by most spectral indices (Figure 9d). The TCB index did not effectively capture the impact of the Station Fire event and the TCB failed at 12 of the other sample sites, as well. While the NDVI was able to capture the Station Fire, the NDVI did not capture forest disturbance at four of the sample sites.  
Figure 9: Vegetation recovery analysis at PCT trail site C (34.379, \(-\)118.164) following the 2009 Station Fire. The MODIS MCD12Q1 land cover analysis for the study site (**a**) shows a transition from abundant evergreen needleleaf forest (2002–2008) to grassland (2009–2011) and savanna (2012–2023). The NAIP aerial imagery from (**b**) 22 June 2009 and (**c**) 7 June 2010 shows the loss of vegetation resulting from wildfires. The LandTrendr temporal segmentation with various spectral indices (**d**) reveals the impact of wildfire on the study site and the gradual revegetation over time.