Volcanic Eruption and Wildfires as Compounding Drivers of First-Year Seedling Establishment in Canary Pine
Written by: Christopher Shatto
Science is not always straightforward. Soon after completing a study where we found that wildfire may actually enhance the recovery of the pine forest, we found that this may not always be the case, particularly in the case of new tree seedlings!
How did we do it?
Canary Island pine is a unique species that has adapted to both volcanic activity and wildfires over evolutionary timescales. Using a combination of field data and remote sensing, we examined how the 2021 Cumbre Vieja eruption and past wildfires (2012, 2016) influenced first-year seedling establishment in La Palma's forests. Through traversing the entire island, we managed to count seedlings in over 100 field plots. We then used satellite imagery to quantify the impact of past fires, and the volcanic eruption, on the pine forest across the region.
Key Findings
Eruption-Driven Growth: Areas closer to the eruption site showed a significant pulse in seedling establishment🌱, likely due to favorable conditions like increased light and nutrient availability.
Impact of Overlapping Disturbances: Seedling densities were much lower in areas impacted by both the eruption and past wildfires🔥, highlighting how compounded disturbances can limit regeneration.
Outlook
Interestingly, while our earlier research suggested that the 2016 wildfire enhanced stand recovery in Canary Island pine, this new study indicates it hindered seedling establishment after the eruption. These contrasting findings point to the differing needs of forests at various growth stages🌱🌲—what benefits mature stands may not always support regeneration at its earliest stages.
This study sheds light on the challenges forests face under shifting disturbance regimes, especially with the growing influence of climate change. It also raises important questions about the balance between natural resilience and the limits of regeneration when disturbances occur too frequently.
Figure 1. (a) This photo (March 2013) shows a group of Canary pine trees growing together on the steep slopes in northern La Palma, at about 1500 meters above sea level. In these fire-prone forests, there isn’t much undergrowth or new tree growth. (b) Taken in April 2022 near the Tajogaite Volcano, this image shows a Canary pine tree sprouting new shoots from its trunk and branches after a fire. (c) After fires open up the forest canopy, small plants start to grow. In this picture, herbaceous plants and legumes become common until a drought hits or the ash washes away the nutrients. (d) This photo, taken eight months after the 2023 wildfire in northwestern La Palma, shows Canary pine trees and young pines sprouting new shoots at a site that was moderately affected by fire. (e) In contrast, this image (also eight months after the 2023 wildfire) shows young Canary pines that have been badly burned, with no visible new growth. (f) Here, a group of young Canary pine seedlings is growing on a fresh layer of volcanic ash. You can also see opened cones and fallen needles nearby.Photo credits: C. Beierkuhnlein (a, c, f); F. Weiser (b); V. Wilkens (d, e).
Figure 2. This map displays our model’s prediction for the chance of finding seedlings in the southern Canary Island pine forest. The area is divided into hexagons, each 250 meters across. We’ve also marked the approximate areas that burned during the 2012 and 2016 wildfires (data from EFFIS Emergency Services Management). Additionally, the map shows the extent of the lava flow and the location of the eruption crater from the Tajogaite Volcano.
Figure 3. These boxplots compare the average number of young Canary pine trees (seedlings) in three types of areas:Areas affected by both wildfires and a volcanic eruption.Areas affected only by the volcanic eruption.Areas with no disturbances.Panel (a): Shows all 117 study plots. Panel (b): Shows only the plots where at least one seedling was found.The symbols at the top right of each boxplot tell us if the differences are statistically significant:n.s. means not significant.* means the result is significant (p < 0.05).** means p < 0.01.*** means p < 0.001.Letters above the boxplots come from extra tests comparing the groups, adjusted to account for multiple comparisons.
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