Suppression of an invasive pine by a native shrub following a megafire

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Molina-Montenegro This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4433553/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Seedling density of the Chilean wineberry Aristotelia chilensis negatively correlates with the seedlings’ abundance of an invasive pine Pinus radiata , particularly in post-fire areas. This pattern emerged following a megafire in Chile’s Coastal Maulino Forest, a biodiversity hotspot facing increasing fire threats. This pattern, coupled with a high proportion of plots lacking pine seedlings, suggests that A. chilensis may play a role in limiting P. radiata invasion. The negative relationship was strongest in areas with moderate fire severity, likely reflecting differences in shade tolerance. A. chilensis , a light-demanding species with some degree of shade tolerance, can persist in partially shaded environments. In contrast, P. radiata , a more strictly light-demanding species, struggles to establish under significant shade. In high-severity fires, however, we found no significant relationship between these species, likely due to detrimental effects on both species, including potential microbiome dependence for A. chilensis . As A. chilensis shows successful establishment at low fire severity, enhancing its post-fire recruitment, particularly in moderately burned areas, could be a valuable strategy for mitigating P. radiata invasion and restoring fire-affected Mediterranean ecosystems. Invasion resistance Fire severity Post-fire establishment Soil microbiome Figures Figure 1 Figure 2 Introduction 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. Materials and methods Study Site The study was conducted at El Porvenir (35°42’ S, 72°22’ W), located at the northern edge of the Coastal Maulino Forest in central-south Chile (Gómez et al. 2022 ). El Porvenir is a fragment of native mesic forest type, surrounded by large stands of planted P. radiata and Eucalyptus globulus (Myrtaceae). The dominant tree species include Nothofagus glauca (Nothofagaceae), N. alessandrii , N. obliqua , Cryptocarya alba (Lauraceae), Aextoxicon punctatum (Aextoxicaceae), Gevuina avellana (Proteaceae), and A. chilensis . Study area have a Mediterranean climate with a mean annual precipitation of 918 mm and a mean annual temperature of 12.7°C (Becerra and Simonetti 2020 ). In January 2017, the Las Máquinas megafire affected El Porvenir, which experienced fire severity ranging from low to high (see Valencia et al. 2018 ; Gómez et al. 2022 ). Following the fire, several species exhibited regeneration at different levels, with high seedling recruitment for the invasive P. radiata and the native A. chilensis (Gómez et al. 2022 ). Plot establishment and seedling survey To assess the potential role of A. chilensis in limiting P. radiata invasion, we established twenty-three 625 m 2 plots across El Porvenir. These plots were randomly distributed within areas experiencing low (n = 8), moderate (n = 10), and high (n = 5) fire severity (see Gómez et al. 2022 ). Seedling surveys were conducted at 8 and 24 months following the Las Máquinas mega-fire (hereafter 2017 and 2019). In each plot, we searched for regenerating A.chilensis and P. radiata seedlings less than 60 cm in height. The average number of seedlings per plot was 21.98 ± 20.34 for A. chilensis and 7.46 ± 12.78 for P. radiata . We collected at least three random plant samples per species per plot for root system examination to verify that seedlings originated from seeds and not resprouts. Data analysis We performed a negative binomial Generalised Linear Mixed-effects Model (NB GLMM) to analyse the relationship between the abundance of A. chilensis and P. radiata seedlings. This statistical method is suitable for counting data with overdispersion, a common characteristic of ecological data. Here, we account for the potential influence of sampling time at each plot by including time since the fire as a random factor nested within fire severity. This nested structure considers the variation in fire severity across the landscape while acknowledging the potential influence of sampling time within each fire severity category (see above). Additionally, we conducted separate NB GLMM analyses for each fire severity level, including time sampling as a random factor. Results and discussion Our analysis revealed a negative relationship between A. chilensis and P. radiata abundance across the study site (ꭕ 2 (1,46) = 8.0707, p < 0.01) (Fig. 1 ). Thus, areas with higher numbers of A. chilensis seedlings have fewer P. radiata seedlings, potentially indicating a suppressive effect of native species on invasive tree establishment. Furthermore, our results suggest that the strength of this negative relationship varied depending on fire severity. A significantly negative relationship between A. chilensis and P. radiata was found in areas with moderate fire severity (ꭕ 2 (1,20) = 16.385, p < 0.01) (Fig. 2 ). In contrast, these two species had no significant relationship in plots with high or low fire severity (Fig. 2 ). This pattern hints that fire severity might play a role in mediating the interaction between A. chilensis and P. radiata . Wildfire severity plays a crucial role in shaping post-fire succession and ecosystem dynamics. Understanding the severity-specific effects of fires is essential for developing effective forest restoration and conservation management strategies. The observed negative correlation between the abundance of A. chilensis and P. radiata suggests that the former’s presence, as a component of the pre-fire native flora, can be considered a predictor variable influencing P. radiata establishment in post-fire areas. Given that 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 phenomenon, including the priority effect by pre-empting resources and habitat filtering (Byun et al. 2013 ; Byun and Lee 2017 ). First, A. chilensis is a fast-growing, light-demanding species. In areas with a higher abundance of A. chilensis , competition for light, water, or nutrients could be hindering the successful establishment of P. radiata seedlings. Future studies that quantify resource availability and seedling performance concerning A. chilensis density could provide stronger evidence for this hypothesis. Second, 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 ) (Fig. 2 ). 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 (Fig. 2 ). High-severity fires present a vastly different scenario, where most or all vegetation is fire-consumed and heat sterilises the soil, eliminating vital microbes and disrupting biogeochemical processes. These harsh conditions are detrimental to the establishment of both species, resulting in the lack of relationship observed in Fig. 2 . In this line, A. chilensis ’s lower establishment suggests a dependence on healthy soil microbes (Escobedo et al. unpublished), which are eliminated by high-severity fires. P. radiata , meanwhile, sometimes showed higher abundance in these areas, potentially benefiting from the open and A. chilensis -free conditions since its establishment and survival can be microbiome-idiosyncratic (Escobedo et al. unpublished). This resilience disparity highlights the threat of high-severity fires to the Coastal Maulino forest. Conclusion Our findings suggest that native A. chilensis might play a role in limiting P. radiata invasion, potentially through competition and/or habitat filtering. However, this beneficial effect might be compromised in high-severity fire areas, where A. chilensis establishment is hampered due to its dependence on a healthy soil microbiome. High-severity fires that disrupt soil microbial communities pose a significant threat to native plant communities and their ability to resist invasion. Promoting the establishment of native species like A. chilensis , particularly in areas with moderate fire severity, could be a valuable strategy for mitigating tree invasion and fostering the recovery of fire-affected Mediterranean ecosystems like the Maulino forest in central Chile. Declarations Acknowledgements PG was supported by the Global Botanic Garden Fund number 2022/022 (Botanic Gardens Conservation International, BGCI). 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Gayana Botánica 75:531–534. https://doi.org/10.4067/S0717-66432018000100531 Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4433553","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":322347599,"identity":"a35d8df6-cdb1-4b74-af4c-0948eb6c6d4e","order_by":0,"name":"Víctor Manuel Escobedo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+klEQVRIiWNgGAWjYDACZgSTDYTkgAzGAyAuH24tjA3IWoxB1AEoFxdA1ZLYQEiLwXHm5w8+7mGQk28/fOzBhzKb9A33mx8c+FHDII9Ty2E2w8YZzxiMDc6kpRvOOJeWu+EYm8HBnmMMhm04tEg28zA28xxgSNwgwWMmzdt2GKgFaA7QVQm4bIFpqZ8/A6jlb9vhdINj7B8OM/zDrYWfGaIlgeEGUAtj2+EEg2M8BocZ2/BpYTOcOeOAhOEGkF96zqUZzjyWU3Cwt08Cp1/Y+A8/+PDhgI08OMR+lNnI8x0+vvHBj2828vw4tECBBBEio2AUjIJRMAqIBwCdU1U7PEPrXQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-2673-3803","institution":"Universidad de Talca","correspondingAuthor":true,"prefix":"","firstName":"Víctor","middleName":"Manuel","lastName":"Escobedo","suffix":""},{"id":322347600,"identity":"cf11d2f7-d5bc-454b-be1e-c286223fe6b2","order_by":1,"name":"Persy Gómez","email":"","orcid":"","institution":"Universidad de Talca","correspondingAuthor":false,"prefix":"","firstName":"Persy","middleName":"","lastName":"Gómez","suffix":""},{"id":322347601,"identity":"1efcbb81-85ce-4081-82de-bcec45ce070d","order_by":2,"name":"Marco A. Molina-Montenegro","email":"","orcid":"","institution":"Universidad de Talca","correspondingAuthor":false,"prefix":"","firstName":"Marco","middleName":"A.","lastName":"Molina-Montenegro","suffix":""}],"badges":[],"createdAt":"2024-05-17 01:33:50","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4433553/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4433553/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":61233530,"identity":"2321bee5-0f0a-4361-95f5-15b869d13330","added_by":"auto","created_at":"2024-07-27 17:59:48","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":159523,"visible":true,"origin":"","legend":"\u003cp\u003eModel-predicted relationship between \u003cem\u003eAristotelia chilensis\u003c/em\u003e and \u003cem\u003ePinus radiata\u003c/em\u003eseedlings abundance for two sampling times (2017 and 2019). Line indicates a statistically significant negative relationship (p \u0026lt; 0.05) based on a negative binomial GLMM.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4433553/v1/6fa208153f3007b3fb7841a5.jpeg"},{"id":61233529,"identity":"15ca529d-fc93-449b-b7fc-09278596708f","added_by":"auto","created_at":"2024-07-27 17:59:48","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":498552,"visible":true,"origin":"","legend":"\u003cp\u003eModel-predicted relationships between \u003cem\u003eAristotelia chilensis\u003c/em\u003e and \u003cem\u003ePinus radiata\u003c/em\u003eseedling abundance across fire severity levels (a, low; b, medium; c, high) for two sampling times (2017 and 2019). The solid line in the middle panel (b, moderate-severity fire area) indicates a statistically significant negative relationship (p \u0026lt; 0.05) based on a negative binomial GLMM. Relationships were not statistically significant in high- or low-fired-severity areas.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4433553/v1/3d2274a7b6c9940af8081c96.jpeg"},{"id":61607734,"identity":"8caec41d-cb5c-42cc-b085-862b4e19087b","added_by":"auto","created_at":"2024-08-01 22:52:13","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":942981,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4433553/v1/e2a7b754-3f7c-4e69-b951-e262120db9fd.pdf"}],"financialInterests":"","formattedTitle":"Suppression of an invasive pine by a native shrub following a megafire","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWildfires 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. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The Coastal Maulino Forest, a biodiversity hotspot in central Chile (Myers et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2000\u003c/span\u003e), 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 (Gonz\u0026aacute;lez et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2018\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Primarily, the invasive species is \u003cem\u003ePinus radiata\u003c/em\u003e (Pinaceae) which covers approximately 60% of the country\u0026rsquo;s 2.5\u0026nbsp;million hectares of forest plantations (Simberloff et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Gonz\u0026aacute;lez et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Moyano et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The devastating 2017 \u0026ldquo;Las M\u0026aacute;quinas\u0026rdquo; megafire burned over 200,000 ha of the Coastal Maulino Forest, a stark reminder of the vulnerability of this ecosystem (Valencia et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Despite ongoing active and passive restoration efforts in south-central Chile (Morales et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Souza-Alonso et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), challenges persist, including the rapid arrival of post-fire pine regeneration that hinders restoration success (G\u0026oacute;mez et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Gonz\u0026aacute;lez et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). This highlights the need for conservation and restoration practices tailored to this unique ecosystem.\u003c/p\u003e \u003cp\u003eInvasive 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. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Taylor et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). \u003cem\u003eP. radiata\u003c/em\u003e 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 \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Studies have shown a higher probability of fire ignition in areas dominated by \u003cem\u003eP. radiata\u003c/em\u003e plantations compared to native forests in south-central Chile (Contreras et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; G\u0026oacute;mez-Gonz\u0026aacute;lez et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePrevious research suggests limited success in controlling \u003cem\u003eP. radiata\u003c/em\u003e invasion through overall native species diversity (G\u0026oacute;mez et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Gonz\u0026aacute;lez et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). However, recent field studies provide evidence that the native wineberry species \u003cem\u003eAristotelia chilensis\u003c/em\u003e (Elaeocarpaceae) efficiently recolonises burnt areas where \u003cem\u003eP. radiata\u003c/em\u003e is scarce or absent (Promis et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Becerra et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; G\u0026oacute;mez et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). \u003cem\u003eA. chilensis\u003c/em\u003e 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. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Salgado-Luarte and Gianoli \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). This rapid establishment and fast growth of \u003cem\u003eA. chilensis\u003c/em\u003e would align with the concept of the \u0026ldquo;pre-emptive resource effect\u0026rdquo; \u0026ndash; a mechanism where early colonising native species can outcompete invasive plants by monopolising essential resources (Byun et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Byun and Lee \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Delavaux et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Additionally, studies suggest that \u003cem\u003eP. radiata\u003c/em\u003e, being a shade-intolerant species, might struggle to establish into a darker understory dominated by \u003cem\u003eA. chilensis\u003c/em\u003e and other native species (G\u0026oacute;mez et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Becerra and Simonetti \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The efficient colonisation and fast growth of \u003cem\u003eA. chilensis\u003c/em\u003e suggest that it has the potential to act as a native plant competitor against \u003cem\u003eP. radiata\u003c/em\u003e invasion in fire-affected ecosystems.\u003c/p\u003e \u003cp\u003eBuilding upon competition-based biotic resistance (Elton \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1958\u003c/span\u003e) and the theory of limiting similarity, where native species can limit invasive plant establishment due to niche overlap, we hypothesised that \u003cem\u003eP. radiata\u003c/em\u003e abundance would negatively correlate with increasing \u003cem\u003eA. chilensis\u003c/em\u003e abundance. Specifically, we tested the relationship between the abundance of \u003cem\u003eA. chilensis\u003c/em\u003e and \u003cem\u003eP. radiata\u003c/em\u003e in plots affected by varying fire severity levels caused by the Las M\u0026aacute;quinas 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 \u003cem\u003eA. chilensis\u003c/em\u003e establishment, potentially strengthening its competitive effect on \u003cem\u003eP. radiata\u003c/em\u003e (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 \u003cem\u003eA. chilensis\u003c/em\u003e and \u003cem\u003eP. radiata\u003c/em\u003e, 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.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy Site\u003c/h2\u003e \u003cp\u003eThe study was conducted at El Porvenir (35\u0026deg;42\u0026rsquo; S, 72\u0026deg;22\u0026rsquo; W), located at the northern edge of the Coastal Maulino Forest in central-south Chile (G\u0026oacute;mez et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). El Porvenir is a fragment of native mesic forest type, surrounded by large stands of planted \u003cem\u003eP. radiata\u003c/em\u003e and \u003cem\u003eEucalyptus globulus\u003c/em\u003e (Myrtaceae). The dominant tree species include \u003cem\u003eNothofagus glauca\u003c/em\u003e (Nothofagaceae), \u003cem\u003eN. alessandrii\u003c/em\u003e, \u003cem\u003eN. obliqua\u003c/em\u003e, \u003cem\u003eCryptocarya alba\u003c/em\u003e (Lauraceae), \u003cem\u003eAextoxicon punctatum\u003c/em\u003e (Aextoxicaceae), \u003cem\u003eGevuina avellana\u003c/em\u003e (Proteaceae), and \u003cem\u003eA. chilensis\u003c/em\u003e. Study area have a Mediterranean climate with a mean annual precipitation of 918 mm and a mean annual temperature of 12.7\u0026deg;C (Becerra and Simonetti \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn January 2017, the Las M\u0026aacute;quinas megafire affected El Porvenir, which experienced fire severity ranging from low to high (see Valencia et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; G\u0026oacute;mez et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Following the fire, several species exhibited regeneration at different levels, with high seedling recruitment for the invasive \u003cem\u003eP. radiata\u003c/em\u003e and the native \u003cem\u003eA. chilensis\u003c/em\u003e (G\u0026oacute;mez et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003ePlot establishment and seedling survey\u003c/h2\u003e \u003cp\u003eTo assess the potential role of \u003cem\u003eA. chilensis\u003c/em\u003e in limiting \u003cem\u003eP. radiata\u003c/em\u003e invasion, we established twenty-three 625 m\u003csup\u003e2\u003c/sup\u003e plots across El Porvenir. These plots were randomly distributed within areas experiencing low (n\u0026thinsp;=\u0026thinsp;8), moderate (n\u0026thinsp;=\u0026thinsp;10), and high (n\u0026thinsp;=\u0026thinsp;5) fire severity (see G\u0026oacute;mez et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Seedling surveys were conducted at 8 and 24 months following the Las M\u0026aacute;quinas mega-fire (hereafter 2017 and 2019). In each plot, we searched for regenerating \u003cem\u003eA.chilensis\u003c/em\u003e and \u003cem\u003eP. radiata\u003c/em\u003e seedlings less than 60 cm in height. The average number of seedlings per plot was 21.98\u0026thinsp;\u0026plusmn;\u0026thinsp;20.34 for \u003cem\u003eA. chilensis\u003c/em\u003e and 7.46\u0026thinsp;\u0026plusmn;\u0026thinsp;12.78 for \u003cem\u003eP. radiata\u003c/em\u003e. We collected at least three random plant samples per species per plot for root system examination to verify that seedlings originated from seeds and not resprouts.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eData analysis\u003c/h2\u003e \u003cp\u003eWe performed a negative binomial Generalised Linear Mixed-effects Model (NB GLMM) to analyse the relationship between the abundance of \u003cem\u003eA. chilensis\u003c/em\u003e and \u003cem\u003eP. radiata\u003c/em\u003e seedlings. This statistical method is suitable for counting data with overdispersion, a common characteristic of ecological data. Here, we account for the potential influence of sampling time at each plot by including time since the fire as a random factor nested within fire severity. This nested structure considers the variation in fire severity across the landscape while acknowledging the potential influence of sampling time within each fire severity category (see above). Additionally, we conducted separate NB GLMM analyses for each fire severity level, including time sampling as a random factor.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eOur analysis revealed a negative relationship between \u003cem\u003eA. chilensis\u003c/em\u003e and \u003cem\u003eP. radiata\u003c/em\u003e abundance across the study site (ꭕ\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e(1,46)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;8.0707, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Thus, areas with higher numbers of \u003cem\u003eA. chilensis\u003c/em\u003e seedlings have fewer \u003cem\u003eP. radiata\u003c/em\u003e seedlings, potentially indicating a suppressive effect of native species on invasive tree establishment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurthermore, our results suggest that the strength of this negative relationship varied depending on fire severity. A significantly negative relationship between \u003cem\u003eA. chilensis\u003c/em\u003e and \u003cem\u003eP. radiata\u003c/em\u003e was found in areas with moderate fire severity (ꭕ\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e(1,20)\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;16.385, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In contrast, these two species had no significant relationship in plots with high or low fire severity (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This pattern hints that fire severity might play a role in mediating the interaction between \u003cem\u003eA. chilensis\u003c/em\u003e and \u003cem\u003eP. radiata\u003c/em\u003e. Wildfire severity plays a crucial role in shaping post-fire succession and ecosystem dynamics. Understanding the severity-specific effects of fires is essential for developing effective forest restoration and conservation management strategies.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe observed negative correlation between the abundance of \u003cem\u003eA. chilensis\u003c/em\u003e and \u003cem\u003eP. radiata\u003c/em\u003e suggests that the former\u0026rsquo;s presence, as a component of the pre-fire native flora, can be considered a predictor variable influencing \u003cem\u003eP. radiata\u003c/em\u003e establishment in post-fire areas. Given that \u003cem\u003eA. chilensis\u003c/em\u003e 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 \u003cem\u003eP. radiata\u003c/em\u003e establishment. Several mechanisms could explain this phenomenon, including the priority effect by pre-empting resources and habitat filtering (Byun et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Byun and Lee \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). First, \u003cem\u003eA. chilensis\u003c/em\u003e is a fast-growing, light-demanding species. In areas with a higher abundance of \u003cem\u003eA. chilensis\u003c/em\u003e, competition for light, water, or nutrients could be hindering the successful establishment of \u003cem\u003eP. radiata\u003c/em\u003e seedlings. Future studies that quantify resource availability and seedling performance concerning \u003cem\u003eA. chilensis\u003c/em\u003e density could provide stronger evidence for this hypothesis. Second, fire can have profound and different effects on plant community assembly depending on its severity (McLauchlan et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). 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 \u003cem\u003eA. chilensis\u003c/em\u003e is a light-demanding species with some degree of shade tolerance (Guerra et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Salgado-Luarte and Gianoli \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), \u003cem\u003eP. radiata\u003c/em\u003e is a strictly shade-intolerant species (G\u0026oacute;mez et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Thus, this variation in light availability could favour \u003cem\u003eA. chilensis\u003c/em\u003e over \u003cem\u003eP. radiata\u003c/em\u003e establishment in suitable microsites within the burned landscape. In low-severity fires with more remaining canopy cover, \u003cem\u003eP. radiata\u003c/em\u003e 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, \u003cem\u003eA. chilensis\u003c/em\u003e, 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 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). High-severity fires present a vastly different scenario, where most or all vegetation is fire-consumed and heat sterilises the soil, eliminating vital microbes and disrupting biogeochemical processes. These harsh conditions are detrimental to the establishment of both species, resulting in the lack of relationship observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. In this line, \u003cem\u003eA. chilensis\u003c/em\u003e\u0026rsquo;s lower establishment suggests a dependence on healthy soil microbes (Escobedo et al. unpublished), which are eliminated by high-severity fires. \u003cem\u003eP. radiata\u003c/em\u003e, meanwhile, sometimes showed higher abundance in these areas, potentially benefiting from the open and \u003cem\u003eA. chilensis\u003c/em\u003e-free conditions since its establishment and survival can be microbiome-idiosyncratic (Escobedo et al. unpublished). This resilience disparity highlights the threat of high-severity fires to the Coastal Maulino forest.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eOur findings suggest that native \u003cem\u003eA. chilensis\u003c/em\u003e might play a role in limiting \u003cem\u003eP. radiata\u003c/em\u003e invasion, potentially through competition and/or habitat filtering. However, this beneficial effect might be compromised in high-severity fire areas, where \u003cem\u003eA. chilensis\u003c/em\u003e establishment is hampered due to its dependence on a healthy soil microbiome. High-severity fires that disrupt soil microbial communities pose a significant threat to native plant communities and their ability to resist invasion. Promoting the establishment of native species like \u003cem\u003eA. chilensis\u003c/em\u003e, particularly in areas with moderate fire severity, could be a valuable strategy for mitigating tree invasion and fostering the recovery of fire-affected Mediterranean ecosystems like the Maulino forest in central Chile.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003ePG was supported by the Global Botanic Garden Fund number 2022/022 (Botanic Gardens Conservation International, BGCI).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e \u003cp\u003eThe data supporting this study\u0026rsquo;s findings will be available in a repository upon manuscript acceptance.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBecerra PI, Figueroa C, Meza A (2022) Din\u0026aacute;mica post-incendio de la vegetaci\u0026oacute;n en la localidad de Rastrojos, Chile central. 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Gayana Bot\u0026aacute;nica 75:531\u0026ndash;534. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.4067/S0717-66432018000100531\u003c/span\u003e\u003cspan address=\"10.4067/S0717-66432018000100531\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Invasion resistance, Fire severity, Post-fire establishment, Soil microbiome","lastPublishedDoi":"10.21203/rs.3.rs-4433553/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4433553/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSeedling density of the Chilean wineberry \u003cem\u003eAristotelia chilensis\u003c/em\u003e negatively correlates with the seedlings\u0026rsquo; abundance of an invasive pine \u003cem\u003ePinus radiata\u003c/em\u003e, particularly in post-fire areas. This pattern emerged following a megafire in Chile\u0026rsquo;s Coastal Maulino Forest, a biodiversity hotspot facing increasing fire threats. This pattern, coupled with a high proportion of plots lacking pine seedlings, suggests that \u003cem\u003eA. chilensis\u003c/em\u003e may play a role in limiting \u003cem\u003eP. radiata\u003c/em\u003e invasion. The negative relationship was strongest in areas with moderate fire severity, likely reflecting differences in shade tolerance. \u003cem\u003eA. chilensis\u003c/em\u003e, a light-demanding species with some degree of shade tolerance, can persist in partially shaded environments. In contrast, \u003cem\u003eP. radiata\u003c/em\u003e, a more strictly light-demanding species, struggles to establish under significant shade. In high-severity fires, however, we found no significant relationship between these species, likely due to detrimental effects on both species, including potential microbiome dependence for \u003cem\u003eA. chilensis\u003c/em\u003e. As \u003cem\u003eA. chilensis\u003c/em\u003e shows successful establishment at low fire severity, enhancing its post-fire recruitment, particularly in moderately burned areas, could be a valuable strategy for mitigating \u003cem\u003eP. radiata\u003c/em\u003e invasion and restoring fire-affected Mediterranean ecosystems.\u003c/p\u003e","manuscriptTitle":"Suppression of an invasive pine by a native shrub following a megafire","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-27 17:59:43","doi":"10.21203/rs.3.rs-4433553/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a4a1e18e-e6ad-4967-ab05-68f6caafd6e7","owner":[],"postedDate":"July 27th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-08-01T22:44:06+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-27 17:59:43","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4433553","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4433553","identity":"rs-4433553","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}