The legacy of pine introduction threatens the fuel traits of Patagonian native forests

Abstract

The introduction of non-native pine plantations and subsequent pine invasion are increasingly affecting native and high conservation value forests in the Southern Hemisphere. Pine invasion changes forest fire regimes, even in protected areas. However, most research evaluating the impact on fuel of this invasion on South American habitats has focused on steppe ecosystems; few studies have investigated whether pine-dominated areas are more flammable than native forests, how invasion age influences flammability, and whether areas dominated by mature pines from invasion and plantation have a similar impact on fuel. Here, we analyzed the fine fuel traits of the understory of different-aged post-fire invasions, plantations of Pinus radiata, and nearby native vegetation in a forest reserve (Patagonia, Argentina). Community composition shifts towards pine-dominated areas increased fire risk by affecting the quantity, distribution, composition, and condition (live or dead) of the fuel. Flammability levels increased with time since invasion. The oldest invasion had a higher load of the most flammable fuel than the adult plantation. Our results show that community composition shifts towards pine-dominated areas can increase fire risk by producing more pyrophytic habitats, and suggest that early removal of post-fire invasions can prevent increased fire risk on a landscape scale. Our results highlight the importance of considering the intrinsic characteristics of an invasion context when evaluating the impact of non-native species, and the need to be cautious when extrapolating the impacts of plantations to invasions.