BayCEER Workshop 2024

Volcanic eruption and wildfires as interacting drivers of first-year seedling establishment in Canary pine

On the island of La Palma, the Canary pine forest is largely unmanaged and depends on natural regeneration for sustainable population dynamics. Canary pine (Pinus canariensis C.Sm. ex DC.) has been continuously exposed to volcanic eruptions over evolutionary time scales. The species exhibits many adaptations to wildfires, but the current fire regime is likely not natural. While both volcanic eruptions and wildfires can devastate existing vegetation and unbalance ecosystems, they can also facilitate plant growth through mechanisms like nutrient release and increased light availability. Occasional successful regeneration events, driven by high first-year seedling establishment following a disturbance, could be essential to maintaining population structures. We investigated the interactions of volcanic eruption and past wildfires on first-year seedling establishment in the Canary pine forest after the 2021 Cumbre Vieja volcanic eruption. Decreasing distance to the eruption crater was significantly associated with finding high seedling abundance (> 50 per plot). Furthermore, the impact of the 2016 wildfire was a significant predictor in our model, indicating that patterns of first-year seedling establishment attributable to the eruption were negatively modified by fire history. We discuss the role of both wildfires and volcanic eruptions in the evolutionary history of Canary pine and highlight the task of disentangling the legacies of these two disturbances. Serotiny, traditionally considered to be a fire-specific adaptation, appears to also function after and increase the resilience of Canary pine to volcanic eruptions at the stand-level. Lastly, we raise the question of whether recurrent disturbances exceeding natural system dynamics could endanger the future demography of Canary pine by limiting infrequent but necessary forest regeneration events.