Fire regimes are experiencing major alterations globally due to the intensification and prolongation of fire seasons, increased occurrence and severity, as well as because anthropogenic effects of land use changes (Bowman et al., 2020; Kelly et al., 2023; Sayedi et al., 2024). Although fire is a natural disturbance that can act as a shaping agent in several ecosystems, there is growing concern about the effect on temperate forests less adapted to fires, since drier and warmer climatic conditions are catalyzing more severe and/or recurrent fires (Enright et al., 2015; Johnstone et al., 2016). As an example, burn areas in temperate forests of South America have increased by 17% annually, with a significant intensify in burn severity of 3.5% per year (Fernández-García and Alonso-González, 2023). In this context, the role of post-fire biological legacies, such as surviving trees, downed logs or understory canopy cover, in facilitating forest recovery and mitigating the negative effects of fire has become increasingly recognized (Franklin et al., 2000; Lindenmayer et al., 2019).

Plant species in fire-prone ecosystems that have co-evolved with more frequent fires often exhibit different functional traits that allow them to survive and/or quickly reestablish after fire (He et al., 2019; Vargas-Gaete et al., 2024). Functional and structural traits such as serotinous cones (seed protection from heat), thick bark (protection of living tissues: vascular cambium), shedding of lower branches (reduced vertical connectivity), apical, epicormic or underground resprouting (rapid species colonization), among others, confer to species the ability to persist after fire (Pausas et al., 2004; Keeley et al., 2011; Rodman et al., 2020). Conversely, ecosystems that have co-evolved with less fire pressure are characterized by a predominance of fire-sensitive species, i.e., species with functional traits less tolerant to a more frequent and/or severe fire regime (Whitlock et al., 2015; Tepley et al., 2018). Despite these adaptive responses, as well as the state of biotic factors that persist after a wildfire and facilitate the establishment of new cohorts (i.e., presence of biological legacies), the recruitment, growth, and ultimately the survival of species could be at risk in the face of altered fire regimes (Enright et al., 2015; Johnstone et al., 2016). Additionally, the post-fire effects of herbivore browsing and trampling (i.e., cattle use by local communities) can exacerbate the negative effects solely attributed to fire, hindering proper forest recovery (Raffaele et al., 2011; Lewis et al., 2024).

Southern temperate forests in southern South America are predominantly characterized by a mixed or low-frequency fire regime, with most of the forest dominated by tree species sensitive to fire. However, a smaller proportion of tree species possess the ability to resprout or withstand low-to-moderate fire intensities (Beard, 1990; Whitlock et al., 2015; Kitzberger et al., 2016). Mixed temperate forests dominated by Araucaria araucana (Mol.) K. Koch and Nothofagus spp. in the Andean region of Chile and Argentina (henceforth referred to as Araucaria-Nothofagus forests) are composed of species with varying levels of fire tolerance. Some species are highly susceptible to fire due to thin bark [e.g., Nothofagus dombeyi (Mirb.) Oerst., N. pumilio (Poepp. & Endl.) Krasser], while others exhibit adaptations such as thick bark and shedding of lower branches or the ability to resprout rapidly after fire (e.g., Araucaria araucana; Veblen, 1982; Burns, 1993; González et al., 2010; Arroyo-Vargas et al., 2024). This suggests that fire has been rather infrequent in these forests, generally with low-to-moderate severity (González et al., 2010; Fuentes-Ramirez et al., 2022). However, changes in fire frequency and severity in recent decades may indicate a shift in the fire regime of these ecosystems (González et al., 2020; McWethy et al., 2018). Furthermore, the introduction of agriculture and livestock in the early 18th century, which was intensified from the 1750s onwards, led to the use of fire to clear forest and habilitate land for these practices by Pehuenche communities, altering the historical fire regimes in forests dominated by A. araucana (Torrejón, 2001; González et al., 2020). Moreover, in Andean ecosystems, with the presence of seasonal winter and summer pastures, practices such as cattle transhumance have been carried out for centuries in these areas until the present day, even within areas affected by fire (Marchant, 2019). Therefore, the combined effects of more frequent fires and cattle herbivory may have significantly affected the survival and growth of tree species, posing a serious threat to the long-term recovery of burned forests (Arroyo-Vargas et al., 2024).

The slow-growing southern South American endemic conifer A. araucana is distributed between 37° and 40° S, mostly in the Andean region of central-south Chile and Argentina (Veblen, 1982; Sanguinetti et al., 2023). The species is currently protected under CITES by Chile and Argentina, and it is listed as endangered by the IUCN (Convention on International Trade in Endangered Species, 2001; Premoli et al., 2011). Moreover, the species holds significant ecological and cultural importance by local Pehuenche communities (Rozzi et al., 2012). Although A. araucana possesses traits that allow it to survive low-to-moderate severity fires (e.g., development of thick bark, shedding of lower branches in mature individuals, development of female cones in the upper crown; Burns, 1993), under severe and frequent fires, its mortality rate is practically 100% (Assal et al., 2018; Franco et al., 2022; Arroyo-Vargas et al., 2024). Additionally, A. araucana populations have declined by 50% from their original estimated distribution of 500,000 ha, largely due to selective logging for its valuable timber during the first half of the 20th century (Lara et al., 1999). In recent years, anthropogenic wildfires, cattle impacts, and an unsustainable harvest of its edible seeds have further exacerbated the situation (González et al., 2020; Donoso et al., 2024). This combination of pressures has raised significant concerns about the species’ ability to recover after severe fire events. Moreover, the importance of A. araucana in the territory and local communities from its evolutionary, biological and sociocultural perspective makes the species a key component of the ecosystems where it occurs (Rozzi et al., 2012; Sanguinetti et al., 2023).

As fire generally burns in a patchy manner, post-fire biological legacies that remain in the forest are thought to be crucial for facilitating seedling establishment, survival and growth over time (Turner et al., 1998; Seidl et al., 2014). These biological legacies may include surviving trees, downed logs or understory canopy cover. Moreover, the presence of herbivores [e.g., cattle (Bos taurus)] in burned areas greatly challenge the resilience of these forests and its ability to regenerate (Sanguinetti and Kitzberger, 2010; Zamorano-Elgueta et al., 2012; Arroyo-Vargas et al., 2019). In this context, restoration efforts are essential, and their success will depend on the interplay between the effects of fires, grazing pressure and the presence of biological legacies. These legacies provide essential advantages to seedlings, including shade, protection, and enhanced micro-habitats (Franklin et al., 2000; Rudolphi et al., 2014; Ferreiro et al., 2018). Currently, it is unclear how this interplay may affect the establishment of A. araucana seedlings in old-growth forests severely burned in the short-term. Thus, our study is specifically designed to answer the following questions:

(i) How does fire severity influence survival patterns of A. araucana seedlings in the presence of biological legacies and under cattle exclusion?, and (ii) How do the presence of biological legacies and cattle grazing affect the growth rate of A. araucana seedlings in different post-fire severity levels? We hypothesized that the presence of post-fire biological legacies and the exclusion of cattle lead to an increased survival and growth of Araucaria seedlings, especially in areas of high fire severity.

Understanding the complex interactions between fire, seedling survival and initial growth is crucial for designing more effective forest management and better conservation practices to canalize restoration efforts of this ancient, iconic forests in the Andean region of southern South America.

After 5 years of monitoring in the field, the survival trial of planted seedlings of A. araucana within burned areas did not exhibit significant differences across treatments (e.g., with vs. without biological legacies or with cattle exclusion) in areas affected by moderate and high fire severities. The survival rate reported in this research fluctuated between 72 and 85% across all the study conditions, which is considered quite good. A similar study of A. araucana seedlings, conducted in areas with no burns or biological legacies, found no significant differences in seedling survival comparing areas with and without cattle exclusion (Rechene et al., 2003). However, other studies on conifers have shown that seedling mortality rates can vary widely depending on the species, fire severity, post-fire conditions, climate, and/or site-level topographic conditions (Marsh et al., 2022; Andrus et al., 2022; Marshall et al., 2024). For example, in boreal forests, species like black spruce (Picea mariana) and jack pine (Pinus banksiana), often exhibit serotiny, a reproductive strategy that ensures seed dormancy until triggered by fire (Keeley et al., 2011). This adaptation provides a reliable seed bank for post-fire regeneration, but even serotinous species can experience high mortality rates if fires are too severe or frequent over time (Brown and Johnstone, 2012; Buma et al., 2013; Harvey et al., 2016; Turner et al., 2019). In contrast, many coniferous species in temperate forests of the southern hemisphere, including A. araucana, rely on dispersed seeds and post-fire seed germination, which is generally high for Araucaria (Fuentes-Ramirez et al., 2019). On this basis, biological legacies (i.e., fallen trees or standing snags) are thought to be important for improving post-fire site conditions at the micro-site scale by providing shelter and protection especially for the establishment of new seedlings after disturbances that may increase survival (Franklin et al., 2000; Arroyo-Vargas et al., 2019; Lindenmayer et al., 2019). What might explain why Araucaria araucana seedlings are able to survive well in burned areas with no aid of biological legacies, is the attribute of activating physiological mechanisms that allow them to tolerate short-term droughts (Papú et al., 2021), which is related to high survival rate even though post-fire biological legacies were absent.

The growth of seedlings in terms of height was constant over time independently of the treatment (i.e., with vs. without biological legacies or with cattle exclusion) and burn condition (i.e., moderate or high fire severity). Although there were some significant differences in growth after 24- or 54-months post-plantation, the fitted models did not show a significantly better performance when considering any of the explanatory variables (biological legacies or absence of cattle activity). Nonetheless, number of shoots and diameter at root collar of seedlings showed a trend of improving when biological legacies were absent instead. On a previous study, Rechene et al. (2003) also measured diameter at root collar and height of A. araucana seedlings that were planted in the field with and without exclusions. However, they only found statistical differences in the growth of the diameter at root collar between seedling groups with different years when planted in the field, which is expected. Nonetheless, seedling survival can be low because of herbivory, trampling, competition with weeds, and an increase in the severity and frequency of fires in burned areas (Sanguinetti and Kitzberger, 2010; Crovo et al., 2021; Lewis et al., 2024). In addition, our study only considers the early establishment of seedlings in a period of 5-years, and longer measurements are needed to better understand plant growth and the potential long-term effects of biological legacies and cattle exclusion in a long-lived conifer such as A. araucana. In this context, a wide range of studies have demonstrated that the presence of biological legacies and the exclusion of cattle improve the performance of seedling establishment of A. araucana from temperate forests in southern hemisphere (González and Veblen, 2007; Blackhall et al., 2008; Zamorano-Elgueta et al., 2012), which can ensure the success of seedling establishment in harsh conditions when the forest is subjected to disturbances. Nonetheless, these findings are seldom taken into account when restoration actions are designed or implemented at larger operational scales (Stanturf et al., 2014; Köbel et al., 2021). Despite these practice challenges, our results highlight the remarkable resilience of A. araucana in burned forests, demonstrating its ability to survive and grow even under the harsh challenging conditions imposed by severe anthropogenic fire events, presenting a significant opportunity to tackle down restoration bottlenecks and support ecosystem recovery more efficiently (Bannister et al., 2018).

Our study shows that while A. araucana can establish in burned areas, its slow early growth as a seedling may be affected by predicted warmer and drier conditions. In addition, shifts from natural successional trajectories may be exacerbated by the combined effects of fire severity, cattle pressure, and other disturbances, highlighting the need for strategic restoration actions to support ecosystem recovery (Bannister et al., 2022; Donoso et al., 2024). Furthermore, and despite harsh post-fire conditions in burned areas, A. araucana displays key evolutionary characteristics that allow it to survive and grow well without biological legacies or under cattle exclusion management, which would make it easier for restoration efforts to be undertaken at broader scales.

The results show that planted A. araucana seedlings exhibit high survival rate and good initial height growth during the first 5 years post-fire, which could be auspicious for post-fire restoration plans. One of the main issues on these forests is that severe wildfires importantly affect the natural regeneration of A. araucana due to the lack of surviving female trees in burned patches (Arroyo-Vargas et al., 2024). Although the species has some fire adaptations (Burns, 1993; González et al., 2006), the mortality of mature trees is high in large severely burned areas, and seedling establishment is practically absent within these burned patches (Arroyo-Vargas et al., 2024; Assal et al., 2018; González et al., 2010). Our study reports that A. araucana is well capable of surviving and growing with no specific management, such as using biological legacies as protection or preventing cattle into burned areas. Considering these results and previous studies, when planning planting programs and management, large areas affected by severe fires should be prioritized for restoration due to the lack of natural regeneration. Thus, using nearby biological legacies does not appear to increase seedling establishment in the short-term, nor does avoiding cattle in burned areas. Yet, these practices may benefit post-fire vegetation recovery in the long run (Arroyo-Vargas et al., 2019; Blackhall et al., 2008; Zamorano-Elgueta et al., 2012), and could be considered when feasible.

Survival of Araucaria seedlings reached an overall rate of 75% after 5 years of assessment, with no significant effects of biological legacies nor the exclusion of cattle. Neither of the fire severity conditions assessed in this research had an effect on seedling survival over time. Thus, in absence of further disturbances, seedling survival with no improved micro-site conditions caused by biological legacies, would be enough to properly recover Araucaria after fires. Plant growth did show a significant and positive response only for height in areas of high fire severity when seedlings were planted nearby biological legacies and were protected from cattle. This, however, was marked in the first 2 years post-planting, and then the effect tended to weaken as plants grew over time. Furthermore, these findings were not consistent for other growth variables such as number of buds nor for root collar diameter. In summary, A. araucana is well capable of surviving and growing in absence of biological legacies or when preventing cattle into burned areas, highlighting a great resilience capacity that exceeds expectations under fire and grazing pressure to face its recovery after severe forest fires.