## 3 Results
### Forest Loss Severity and Recovery
#### 3.2.2 Wildfire  
The MTBS wildfire data indicate a total of 1073 km\({}^{2}\) burned at moderate or high intensity (levels 3 and 4) during the study period. While the Hansen Forest Loss data include many burn area boundaries, 330 km\({}^{2}\) of additional wildfire locations were not  
Figure 4: Scatterplots comparing the PhenoCam GCC estimates and the Landsat-derived GPP for (**a**) PCT Sagehen PhenoCam site (39.431\({}^{\circ}\), \(-\)120.239\({}^{\circ}\)), (**b**) CDT Butte PhenoCam site (45.95\({}^{\circ}\), \(-\)112.479\({}^{\circ}\)), and (**c**) AT NEON D02.SERC.DP1.00033 PhenoCam site (38.89\({}^{\circ}\), \(-\)76.560\({}^{\circ}\)).  
Figure 5: Time series (**a**,**b**) and heatmaps showing the density of the (**c**) Hansen Forest Loss events and (**d**) MTBS moderate and high severity burns 2001–2023.  
captured in the annual Hansen Forest Loss dataset. This includes fires on unforested lands, such as grassland, and wildfires within landscapes with rapid recovery.  
Most of the moderate and high-intensity wildfire burn areas occurred within the PCT corridor (66% of the fire area), with 33% within the CDT and less than 1% of burned areas within the AT. The annual wildfire burn area is significantly correlated with the annual forest loss along the PCT (r\({}^{2}\) = 0.68), with the correlation exceeding the 99% confidence level. However, the relationship between the burn area and the forest loss is less significant along the CDT and AT (Figure 6). The drier conditions in the western U.S. and the seasonal occurrence of winter precipitation create a strong seasonal cycle of wildfire occurrence during the summer months on the PCT and CDT (Figure 7). Along the southern portion of the PCT, the Station Fire burn in 2009 occurred in the Southern and Baja California Pine-Oak Mountains near Los Angeles, CA, USA [99]. Additional significant wildfire hotspots on the PCT center on the 2020 and 2021 wildfires in California's Sierra Nevada mountain range (e.g., 2020 Claremont fire, 2020 Lionshead fire). The 2021 Dixie fire burned over 100 trail miles of the PCT [100]. The PCT wildfire hotspots then extend northward into the Klamath Mountains of northern California and up through the Cascades of Oregon and Washington, which experienced severe burns in 2017 [101].  
The MTBS and MODIS burn area data along the CDT indicate major wildfire events in the northern portion of the trail along the Canadian Rockies of Montana in multiple years, including the 2006 Red Eagle fire in Glacier National Park, the Fool Creek Wildfire of 2007 [43], and the Meyers Wildfire of 2017 (Figure 5c). The Idaho Batholith ecoregion was also prone to persistent wildfires, with burn events occurring repeatedly in the past four years. A third hotspot of CDT wildfire activity is in the Southern Rockies near Rocky Mountain National Park, Colorado. The wildfires in this area include the 2020 East Troublesome Fire, Colorado's second-largest wildfire on record [44]. Finally, in the southern portion of the CDT, the 2022 Black Fire in New Mexico was the largest in the state's history and directly burned more than 45 miles of the trail path [49].  
While the AT experienced relatively few wildfires directly along its 2 km corridor, a significant event occurred in late 2016 within the Great Smoky Mountain National Park in the southern Appalachians [45] and is visible on the MODIS burned area time series (Figure 5c) and map (Figure 5d).  
Figure 6: Scatterplot comparing the annual Hansen Forest Loss (km\({}^{2}\)) and MODIS-derived burned area (km\({}^{2}\)). The annual wildfire burn area is correlated with the forest loss area along the PCT (R\({}^{2}\) = 0.68) but the relationship is less significant along the CDT (R\({}^{2}\) = 0.13) and AT (R\({}^{2}\) = 0.13).