Mixed forests and wildfires

Mixed hashtag#forests play a fundamental ecological role in our landscapes, widely celebrated for increasing biodiversity and providing a broad range of essential ecosystem services. In forest hashtag#ecology and management, a prevailing assumption is that these mixed forests are inherently better and more resilient to natural disturbances, particularly wildfires, than homogenous pure stands. We often theorise that the higher structural diversity and varied morphological traits found in mixed species provide a natural, protective buffer against fire spread and severity.

However, to robustly check this hypothesis, we must move beyond theoretical assumptions and rely on extensive empirical evidence. This is exactly what we tried to do utilising a massive dataset from the Spanish National Forest Inventory (NFI) to examine post-fire tree mortality across 2,782 plots and over 30,000 trees over a two-decade period.

The main results of this analysis challenged our traditional expectations: mixed stands can actually suffer significantly higher post-fire mortality than pure stands. We found that combining tree species with differing fire-related strategies (such as mixing hashtag#fire-resistant species with fire-resilient ones like Pinus nigra and Pinus halepensis) often exacerbates stand hashtag#vulnerability rather than mitigating it.

This increased hashtag#damage occurs because combining different structural strategies can create a vertical "ladder effect" between the canopy and understory, accumulating higher biomass densities in intermediate layers and ultimately facilitating the spread of fire. While there are notable exceptions where mixing species actually helps, such as the introduction of Quercus robur which was shown to lower mortality in some pine stands, the overarching lesson is clear. We must reconsider the blanket assumption that "mixed is always better" and carefully tailor our management of mixed forests based on specific functional fire traits to truly build fire-resistant landscapes.

Find more: Peris‑Llopis, M., Mola‑Yudego, B., Berninger, F., Garcia‑Gonzalo, J., & González‑Olabarria, J. R. (2024). Impact of species composition on fire‑induced stand damage in Spanish forests. https://doi.org/10.1038/s41598-024-59210-4

Thanks to eco2adapt, Suomen Kulttuurirahasto / Finnish Cultural Foundation, European Forest Institute, European Research Executive Agency (REA), Marie Skłodowska-Curie Actions, Generalitat de Catalunya CERCA