Wildfires pose a significant threat to biodiversity, disrupting ecosystem functions and threatening sensitive habitats worldwide. Their increased frequency and intensity are attributed to various factors, including climate change and land-use modifications (McLauchlan et al. 2020). The Coastal Maulino Forest, a biodiversity hotspot in central Chile (Myers et al. 2000), is facing more frequent and intense wildfires in last decades, driven by factors such as rising temperatures, a megadrought and the forestry plantations of non-native invasive species (González et al. 2018, 2023). Primarily, the invasive species is Pinus radiata (Pinaceae) which covers approximately 60% of the country’s 2.5 million hectares of forest plantations (Simberloff et al. 2002; González et al. 2018; Moyano et al. 2023). The devastating 2017 “Las Máquinas” megafire burned over 200,000 ha of the Coastal Maulino Forest, a stark reminder of the vulnerability of this ecosystem (Valencia et al. 2018). Despite ongoing active and passive restoration efforts in south-central Chile (Morales et al. 2021; Souza-Alonso et al. 2022), challenges persist, including the rapid arrival of post-fire pine regeneration that hinders restoration success (Gómez et al. 2019; González et al. 2020, 2023). This highlights the need for conservation and restoration practices tailored to this unique ecosystem.
Invasive species often display rapid resource utilisation, potentially outcompeting native species and promoting more frequent fire events. This can create a positive invasion-fire feedback loop (Contreras et al. 2011; Taylor et al. 2017). P. radiata is a light-demanding and shade-intolerant species known for its aggressive post-fire regeneration through serotinous cones, which release large amounts of viable wind-dispersed seeds after fire events (Franzese and Raffaele 2017). Studies have shown a higher probability of fire ignition in areas dominated by P. radiata plantations compared to native forests in south-central Chile (Contreras et al. 2011; Gómez-González et al. 2019).
Previous research suggests limited success in controlling P. radiata invasion through overall native species diversity (Gómez et al. 2019; González et al. 2020). However, recent field studies provide evidence that the native wineberry species Aristotelia chilensis (Elaeocarpaceae) efficiently recolonises burnt areas where P. radiata is scarce or absent (Promis et al. 2019; Becerra et al. 2022; Gómez et al. 2022). A. chilensis is a fast-growing, light-demanding, fleshy-fruiting bird-dispersed tree species with a semi-dioecious leaf habit. These traits allow it to not only colonise clearings but also persist after plantations replace native forests because it can exhibit some shade tolerance (Guerra et al. 2010; Salgado-Luarte and Gianoli 2012). This rapid establishment and fast growth of A. chilensis would align with the concept of the “pre-emptive resource effect” – a mechanism where early colonising native species can outcompete invasive plants by monopolising essential resources (Byun et al. 2013; Byun and Lee 2017; Delavaux et al. 2023). Additionally, studies suggest that P. radiata, being a shade-intolerant species, might struggle to establish into a darker understory dominated by A. chilensis and other native species (Gómez et al. 2019; Becerra and Simonetti 2020). The efficient colonisation and fast growth of A. chilensis suggest that it has the potential to act as a native plant competitor against P. radiata invasion in fire-affected ecosystems.
Building upon competition-based biotic resistance (Elton 1958) and the theory of limiting similarity, where native species can limit invasive plant establishment due to niche overlap, we hypothesised that P. radiata abundance would negatively correlate with increasing A. chilensis abundance. Specifically, we tested the relationship between the abundance of A. chilensis and P. radiata in plots affected by varying fire severity levels caused by the Las Máquinas mega-fire in the Maulino Coastal Forest. Additionally, we explored whether fire severity modulates this relationship. Moderate- or low-severity fires that increase light penetration while retaining understory vegetation could favour A. chilensis establishment, potentially strengthening its competitive effect on P. radiata (i.e., a negative relationship). In contrast, high-severity fires that create harsher conditions and potential soil disruption (i.e., depleting the soil microbiome) could hinder the establishment of both A. chilensis and P. radiata, obscuring any competitive effects. By elucidating these dynamics, we aim to provide valuable data to guide and enhance conservation and restoration efforts in fire-affected areas across the central Mediterranean region of Chile.