Wildfires pose a significant threat to biodiversity, disrupting ecosystem functions and threatening sensitive habitats worldwide. Their increased frequency and severity 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), has experienced more frequent and higher-severity wildfires in recent decades, driven by rising temperatures, a megadrought, and extensive forestry plantations of non-native species (González et al., 2018, 2023), some of which become invasive after fire disturbances. These fires are particularly concerning for the survival of endangered species such as Nothofagus alessandrii (Nothofagaceae) and N. glauca, which are confined to small, isolated forest fragments surrounded by vast Pinus radiata (Pinaceae) plantations. The invasive P. radiata, which covers approximately 60% of the country’s 2.5 million hectares of forest plantations (Bustamante and Simonetti, 2005; González et al., 2018), often rapidly colonises post-fire areas, further endangering these native species. The devastating 2017 “Las Máquinas” megafire burned over 200,000 ha of the Coastal Maulino Forest, underscoring 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; Gómez and Garrido, 2018). 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) can efficiently recolonise burnt areas, often where P. radiata seedlings are sparse or absent (Promis et al., 2019; Becerra et al., 2022). A. chilensis is a semi-dioecious, fast-growing, light-demanding, fleshy-fruiting, bird-dispersed, evergreen small tree species. 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 Coastal Maulino 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.

Our analysis revealed a negative relationship between Aristotelia chilensis and Pinus radiata abundance across the study site (χ² _(1,46) = 8.0707, p < 0.01; Figure 1 ). Areas with higher numbers of A. chilensis seedlings had fewer P. radiata seedlings, suggesting a potential suppressive effect of native small tree species on the establishment of the invasive tree.

This negative relationship between A. chilensis and P. radiata was especially pronounced in areas with moderate fire severity (χ² _(1,20) = 16.385, p < 0.01; Figure 2 ), whereas no significant relationship was observed in plots with high or low fire severity ( Figure 2 ). These findings suggest that fire severity may mediate the interaction between A. chilensis and P. radiata, with moderate fire severity favouring the competitive advantage of native species. Fire severity is known to shape post-fire succession and ecosystem dynamics, making it crucial to understand these effects for both effective forest restoration and conservation management strategies.

In addition to A. chilensis, other native species, particularly the endangered Nothofagus alessandrii and N. glauca, are acknowledged components of the Coastal Maulino Forest. These species, such as A. chilensis, are part of the pre-fire native flora, and their presence may contribute to post-fire regeneration dynamics. However, both N. alessandrii and N. glauca face particular challenges in regenerating after fires, especially in areas with high-severity burns (Gómez et al., 2022). The severe disruption of soil conditions and the elimination of key microbial communities could limit their recovery (Certini, 2005; Warneke et al., 2023; Escobedo et al., 2024), further threatening the ecological integrity of these fragmented populations (Gómez et al., 2022; González et al., 2023). Given their importance, restoration efforts must consider the regeneration of fast-growing species like A. chilensis, which may support strategies for the recovery of slow-growing, fire-sensitive species such as N. alessandrii and N. glauca.

The observed negative relationship between A. chilensis and P. radiata suggests that the former’s presence, as a component of the pre-fire native flora, may influence P. radiata establishment in post-fire areas. As A. chilensis was already present in these ecosystems before the fires, its abundance at the time of the fire event likely influenced the available resources and habitat conditions for P. radiata establishment. Several mechanisms could explain this, including the priority effect by pre-empting resources and habitat filtering (Byun et al., 2013; Byun and Lee, 2017). Given that A. chilensis is a fast-growing, light-demanding species, it may pre-empt light, water, or nutrients in areas where it is abundant, hindering P. radiata establishment. Future studies quantifying resource availability and seedling performance in relation to A. chilensis density could provide stronger evidence for this hypothesis.

Moreover, fire can have profound and different effects on plant community assembly depending on its severity (McLauchlan et al., 2020). The environmental conditions created by moderate fire severity may be more favourable for the establishment of native compared to invasive species. Specifically, these fires create a more open canopy with increased light availability in the understory, typically forming a patchy mosaic of burned and unburned areas rather than eliminating the entire canopy. While A. chilensis is a light-demanding species with some degree of shade tolerance (Guerra et al., 2010; Salgado-Luarte and Gianoli, 2012), P. radiata is a strictly shade-intolerant species (Gómez et al., 2019). Thus, this variation in light availability could favour A. chilensis over P. radiata establishment in suitable microsites within the burned landscape. In low-severity fires with more remaining canopy cover, P. radiata pine showed very low establishment (only two plots with 9 and 15 seedlings), likely due to limited light availability for germination and seedling growth. In contrast, A. chilensis, which can exhibit some shade tolerance, could persist and thrive, with an average of 16 seedlings per plot and up to 67 in one case ( Figure 2 ). Consequently, the lingering native canopy foliage after low-severity fires probably limits light availability, thus restricting the establishment of P. radiata seedlings.

High-severity fires present a vastly different scenario because nearly all vegetation is fire-consumed and heat sterilises the soil, eliminating vital microbes and severely disrupting biogeochemical processes. In these harsh conditions, the establishment of A. chilensis and P. radiata is hindered, resulting in the lack of relationship observed in Figure 2 . In this line, A. chilensis’s lower establishment suggests a dependence on healthy soil microbes (Escobedo et al., 2024), which are eliminated by high-severity fires. P. radiata, meanwhile, sometimes showed higher abundance in these areas, potentially benefiting from the transiently increased nutrient availability and A. chilensis-free conditions since its establishment and survival are less reliant upon microbe communities (Escobedo et al., 2024). This resilience disparity in high-severity fire areas poses a significant threat to the already vulnerable Coastal Maulino Forest, especially for endangered species such as N. alessandrii and N. glauca that are less adapted to such extreme and changing conditions. Although the general trends observed in areas of high fire severity are consistent with our expectations, we acknowledge that the small number of high-severity plots (n=5) may limit the statistical power to detect finer-scale interactions between A. chilensis and P. radiata in these areas. This limitation should be addressed in future studies with a larger number of high-severity plots to confirm the patterns observed. Furthermore, more extensive sampling could improve our understanding of how fire severity impacts post-fire recovery dynamics in native and invasive species.

To expand on the implications of long-term competition dynamics at the Coastal Maulino Forest, it is important to consider that the competitive interactions between A. chilensis and P. radiata may shift over time. While our study captured early successional processes in the first two years post-fire, we speculate that as A. chilensis continues to establish and grow, it may increasingly outcompete P. radiata in the coming years due to its superior shade tolerance. Conversely, in areas where P. radiata manages to establish initially, its rapid growth may enable it to outcompete A. chilensis over time. Active management strategies that include the removal of P. radiata seedlings in the early stages, combined with the promotion of A. chilensis, could provide a highly effective restoration approach. Restoration techniques promoting A. chilensis recruitment—such as direct seedling planting with native soil microbiomes, boosting seed dispersal, and optimizing environmental factors like light and soil conditions—could be pivotal in encouraging its establishment post-fire. This dual strategy may not only suppress invasive P. radiata populations but also support the long-term recovery of native ecosystems, fostering the establishment of fire-sensitive species like N. alessandrii and N. glauca. Long-term monitoring of these interactions would be essential to confirm whether the trends observed in the short term persist or evolve in different fire severity scenarios.

While our study focused on the Las Máquinas 2017 megafire, the findings possess broader implications beyond the Coastal Maulino Forest, particularly in regions experiencing increased fire frequencies where P. radiata is invasive. Similar interactions between native and invasive species have emerged in other Mediterranean-type ecosystems, such as those in California (Dimitrakopoulos and Papaioannou, 2001; Alexander and D’Antonio, 2003) or Australia (Grice, 1997), and South Africa (Van Wilgen and Richardson, 1985; Holmes et al., 2000), where variable fire frequencies and species compositions influence competition dynamics. In areas such as Hawaii, Australia, and New Zealand (Mandle et al., 2011; Hynson et al., 2013), the spread of P. radiata and resultant fire-induced disturbances present parallel challenges. These comparisons underscore the necessity of factoring ecosystem-specific characteristics into our understanding of post-fire recovery. The competitive dynamics observed between native species such as A. chilensis and P. radiata could inform management strategies aimed at controlling pine invasions across diverse regions. Although our study concentrated on the Coastal Maulino Forest, the mechanisms of native species pre-empting resources and moderating invasive species establishment (e.g., competition for resources, shading effects) might be applicable to other ecosystems with similar invasion and fire dynamics (e.g., Grace, 1998; Brooks et al., 2004). Further research is essential to comprehensively understand how native species can be leveraged to manage P. radiata invasions effectively in varying fire-prone environments.

Our findings suggest that promoting the establishment of native species like A. chilensis, particularly in areas with moderate fire severity, could help limit the invasion of P. radiata. Thus, restoration strategies might consider A. chilensis as a targeted support species for the recovery of fire-sensitive species such as N. alessandrii and N. glauca, which are crucial for maintaining the ecological integrity of the Coastal Maulino Forest. Moreover, this study highlights potential applications beyond this region, offering insights into managing P. radiata invasions in other fire-prone ecosystems worldwide. Efforts focused on enhancing post-fire recruitment of A. chilensis, especially in areas of moderate fire severity, could offer a pathway to mitigating invasive tree spread and promoting ecosystem recovery in this unique biodiversity hotspot.