Understanding the interplay between environmental factors and operational practices is essential to overcoming the bottlenecks that often hinder post-fire restoration success. Selecting favorable microsites can enhance initial seed establishment by offering conditions conducive to survival and growth, although these same sites may also increase vulnerability to seed predation. Practical interventions, such as adjusting the timing of sowing, can help mitigate this risk. This is particularly relevant for endangered, large-seeded gymnosperms with limited post-fire dispersal, such as Araucaria araucana in southern South America. These forests face major regeneration challenges due to increasingly severe wildfires, highlighting the urgent need for effective restoration strategies. This study evaluates how two sowing seasons (spring and autumn), fire severity (unburned, low, and high), and microsite characteristics (proximity to fallen logs) interact to influence the early post-fire establishment of A. araucana seedlings following direct sowing. We sowed 2400 seeds in spring and autumn across unburned and burned stands of varying burn severity, distributing seeds either close (0.1 m) or far (2 m) from fallen logs in 60 plots. Over two growing seasons, we monitored seed predation, seedling emergence, seedling survival (live seedlings from those that emerged), annual height growth, and successful establishment (live seedlings relative to seeds sown at the beginning). We also recorded temperature, relative humidity, and soil moisture near and far from fallen logs in 30% of the sowing plots. Seed predation was 50% lower, and height growth rate and successful establishment were nearly twice as high in spring compared to autumn sowings. Successful establishment was greater in high-severity stands when seeds were sown in spring. These high-severity stands experienced higher temperatures, higher vapor pressure deficits, and lower soil moisture compared to unburned stands. However, at the microsite scale, proximity to fallen logs buffered microclimatic extremes, lowering temperature and vapor pressure deficit, and promoting seedling establishment in the high-severity stand. We demonstrate that proper microsite selection and timing of sowing significantly improve seed establishment, especially in adverse environments following a wildfire. Our study offers valuable guidance for managing other large-seeded species threatened by global change.
Castro et al. (Sun,) studied this question.