Data Sheet 1_Impacts of fire severity and exotic invasion of Pinus radiata on post-fire regeneration of relict Nothofagus alessandrii forests in central Chile.pdf

In Chile, wildfires caused mainly by human activity have led to substantial changes in forest composition and structure. These disturbances may promote irreversible forest degradation, particularly when critically endangered forests are affected by high intensity fires and invasion of exotic species. Understanding post-fire regeneration dynamics in endangered Nothofagus alessandrii forests, and the invasion of Pinus radiata under varying fire severities, is crucial to ensure the persistence of these ecosystems. This study examined the early post-fire response of N. alessandrii forest fragments embedded within a P. radiata plantation matrix following the 2017 ‘Las Máquinas’ megafire in central Chile. Fire severity was assessed using the differenced Normalized Burn Ratio (dNBR) derived from Sentinel-2 imagery. Post-fire vegetation dynamics were analyzed using time series of two spectral indices (NDVI and MSAVI2) from 2018 to 2021, applying linear mixed-effects models based on PlanetScope imagery. Early post-fire responses of N. alessandrii forests and P. radiata invasion were evaluated through establishment density and tree-ring radial growth across different fire severity classes. Results showed rapid vegetation recovery in areas affected by moderate and high fire severity. Post-fire regeneration of N. alessandrii occurred mainly through vegetative resprouting, with higher resprouting rates observed in moderately and severely burned sites (70%) compared to low-severity areas (48%). Radial growth of N. alessandrii did not differ significantly between moderate and high severity sites (p > 0.05), while P. radiata showed increased growth under high fire severity and greater growth than native species in areas severely burned (p <0.05). A direct relationship was observed between fire severity and the degree of invasion by P. radiata, with high-severity sites showing the highest levels of invasion (9,760 ind/ha). These results highlight the increased vulnerability of this already endangered ecosystem to severe fires and the invasion of P. radiata. Both processes induce irreversible forest degradation by reinforcing a positive fire feedback loop and intensifying competition with native species in severely burned areas. These results indicate the urgent need to effectively control the P. radiata invasion in the burned forests of N. alessandrii to avoid the loss of the last remaining fragments of this threatened species.