Mixed forests are gaining ground over single species

An investigation conducted by the UCM observed a general trend of change in the composition and dominance of Iberian forests with the increase in the area of ​​mixed forests, where there is no clear dominance of one species over another, to the detriment of monospecific forest species where a single species dominates.

The increase in extreme weather events, combined with the abandonment of the traditional uses of the territory, intervene in the recovery of these forest masses rich in species compared to the monospecific ones where only one dominates.

These results, from a study conducted by the Complutense University of Madrid, can be considered in current nature conservation and management policies.

The intensive use of the territory through agriculture, livestock and forestry has shaped Spanish forests for centuries, favoring monospecific tree formations over mixed ones.

Due to global change factors such as the abandonment of traditional uses and the increase in extreme weather events such as droughts and forest fires due to climate change, mixed forests are gaining ground. For this reason, they must be taken into account in nature management and conservation policies.”, justifies Rut Sánchez de Dios, researcher at the Department of Biodiversity, Ecology and Evolution at the UCM.

At the to studypublished in ecosystemsThe National Institute of Agrifood Research and Technology (INIA-CSIC) also participates. Based on a work of mapping forest habitats commissioned by the Ministry of Ecological Transition, the UCM researchers warned that an important part of the Spanish forest area could not be included in the classic classifications of Spanish forests, which are mostly referred to as monospecific forests ( holm oaks, cork oaks…) because they were mixed forests.

Atlantic region, more frequent changes in mixed forests

To demonstrate the increase in mixed forests in relation to monospecific ones, the researchers used the National Forest Inventory database, which periodically collects detailed information about our forests from 1990 to the present day.

The work indicates which types of forests and areas of the Iberian Peninsula have undergone the most changes. For example, it confirms the long-term shift from forests dominated by a single pine species to forests where pine shares dominance with other hardwood species.

Furthermore, the Atlantic region – north and northwest of the peninsula – is identified as the territory where these changes are occurring more frequently.

Almost all scientific studies consulted point to greater resilience of mixed forests in the face of global changes. However, new global change drivers, such as the increase in invasive species and extreme weather events, could disrupt this natural trend.”, recalls Laura Hernández, researcher at UCM and INIA-CSIC.

Are these mixed masses mere stages of transition in ecological succession to more mature phases of monospecific forests, as advocated by some authors? “The next step in the research would be to demonstrate that these mixed forests are, in many cases, stable mature stages and that they are here to stay.”, concludes Hernández.


Sánchez de Dios, R., DeSoto, L., Cortón, B. et al. “The Renaissance of Mixed Forests? New insights into changes in tree dominance and composition after centuries of human-induced simplification in Iberian forests”. ecosystems (2023)


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