Suppressive effects: negative relationship between a native small tree and an invasive pine following a megafire at the Coastal Maulino Forest in Central Chile

Coastal Maulino Forest, a biodiversity hotspot, is increasingly threatened by frequent and higher-severity wildfires. Endangered tree species, including <i>Nothofagus spp.</i>, inhabit small, isolated native forest fragments surrounded by extensive <i>Pinus radiata</i> plantations, a non-native species that often colonises fire-affected areas. However, the seedling density of the native Chilean wineberry, <i>Aristotelia chilensis</i>, negatively correlates with the abundance of <i>P. radiata </i>seedlings in post-fire areas. This pattern emerged across areas burned at varying fire severities, sampled 8 and 24 months following the 2017 “Las Máquinas” megafire in Chile. The high proportion of plots lacking <i>P. radiata</i> seedlings, coupled with this negative relationship, suggests that <i>A. chilensis</i> may play a role in limiting <i>P. radiata</i> invasion. The negative relationship was most pronounced in areas with moderate fire severity, likely reflecting differences in shade tolerance between the species. While <i>A. chilensis</i>, a light-demanding species with some shade tolerance, can persist in partially shaded environments, <i>P. radiata</i>, a strictly light-demanding species, struggles under significant shade. In low-severity areas, no significant relationship was observed since the substantial native canopy remaining likely limits <i>P. radiata</i> establishment by shading. Conversely, in high-severity fire areas, the absence of a significant relationship might result from the detrimental effects on both species, including potential microbiome dependence for <i>A. chilensis</i>. Given the successful establishment of <i>A. chilensis</i> at low fire severity, enhancing its post-fire recruitment, particularly in moderately burned areas, could be a valuable strategy for mitigating <i>P. radiata</i> invasion and restoring fire-affected Mediterranean ecosystems.