Effect of fire on the regeneration of a keystone endangered conifer

Abstract

Disturbances such as fire influence population and community dynamics in forest ecosystems. Moderate-intensity disturbances can enhance diversity, while high-intensity events may disrupt ecosystems that have not evolved under such conditions. Fire shapes the mosaic of high-altitude grasslands and forests in southern Brazil, but its effects on forest vegetation and keystone species remain unclear. We evaluated the factors influencing the regeneration of Araucaria angustifolia, a keystone conifer of these mosaics, and assessed its response to fire severity. We hypothesized that fire contributes to Araucaria persistence by promoting resprouting at low severities and enhancing recruitment through reduced competition. Recruitment of Araucaria angustifolia declined with increasing distance from seed sources, indicating strong dispersal limitation, while fire severity did not influence recruitment, with similar recruitment levels in unburned and burned areas across a range of severities. In contrast, post-fire survival responses varied along the fire severity gradient. Mortality increased with increasing fire severity, whereas resprouting probability showed a non-linear response, peaking at intermediate fire severities and declining at higher severities. Fire severities above approximately dNBR 0.7 were associated with a marked increase in mortality. Our findings indicate that Araucaria angustifolia possesses mechanisms for post-fire persistence, with individuals surviving through both resprouting and recruitment, underscoring the species’ resilience to fire. More broadly, our findings help elucidate a previously understudied mechanism—resprouting—that may reconcile the apparent contradiction of fire simultaneously promoting forest persistence and limiting its expansion. This supports the view that fire has long been a key evolutionary and ecological force not only in shaping the traits and distribution of South American Araucaria species, but also in maintaining the dynamic balance of fire-prone montane forest-grassland mosaics.