On this International Day for Biological Diversity, let us look toward the bark, the soil, and the treetops. A forest is not just a collection of trees, but a complex web of life that takes centuries to mature. We celebrate this day to remember that biodiversity is our true life insurance; protecting it is not an option, but the only guarantee for securing a resilient and functional future in the face of global change. Preserving this richness is not only a scientific task, but an ethical commitment to life in all its forms; because every species we manage to conserve is another thread strengthening the fabric that sustains us all.
The secret language of lichens
Epiphytic lichens and bryophytes play key roles in ecosystems by contributing to nutrient cycling, accumulating biomass, and providing food and shelter for countless organisms; they also act as “climate‑stress sensors”. Although they occur in almost all environments, it is in mature forests where they reach their greatest diversity and specialization. This is due to the high structural heterogeneity of these forests, which provides a wide variety of niches—deep fissures in the bark, rough surfaces, dead wood, cavities, bark‑free patches, aging branches, and a complex vertical stratification that creates more stable microclimates. These conditions allow the existence of late‑successional and specialist species, such as the genera Calicium or Chaenotheca, which are practically absent from young reforestations, as demonstrated by the recent study by Gregorio Aragón, Ana Isabel García‑Cervigón, Adrián Escudero, and Isabel Martínez, researchers at IICG‑URJC.
The mistake of underestimating the “old tree”
We often prioritize young plantations for their rapid growth, but science warns us: even reforestations more than a century old are still simplified structures that do not replicate the complexity of an old‑growth forest. Mature forests—old trees—are biodiversity reservoirs essential for maintaining life’s diversity.
Lichens and mature forests as foundations of biodiversity
The true wealth of our Mediterranean forests is measured by their diversity and by the variety of interactions that take place within them. A mature forest, clothed in lichens, ceases to be a mere grouping of wood and becomes a driver of biodiversity. This message adds to previous work on ants and birds within the BioFoRest project, which compared the attributes of old‑growth forest stands and plantations.
This International Day for Biological Diversity invites us to understand that restoring a forest is much more than planting trees; it is, in fact, about recovering multiple groups of organisms and their complex interactions to rebuild a vital infrastructure.
References of interest:
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- Aragón, G., García-Cervigón, A. I., Escudero, A., & Martínez, I. (2026). Beyond tree planting: The critical role of Mediterranean mature pine forests for epiphyte biodiversity. Forest Ecology and Management, 611(123723), 123723. https://doi.org/10.1016/j.foreco.2026.123723
- Conde, E., García-García, A., & Arnan, X. (2022). The value of old pine plantations in ants’ conservation in the Mediterranean: a comparison with well-conserved forests. Journal for Nature Conservation, 68, 126225. https://doi.org/10.1016/j.jnc.2022.126225
- López-Angulo, J., Conde-Raposo, E., Rojo-Valencia, M., Calvo-Donate, V., Martínez, I., Escudero, A., & García-Cervigón, A. I. (2025). Key structural attributes of Mediterranean reforestations for avian diversity conservation: comparisons with mature forests. Journal of Environmental Management, 394(127542), 127542. https://doi.org/10.1016/j.jenvman.2025.127542