Forests: species composition as a factor in storm resilience?

Foster diversity and slow-growing species

In recent decades, Europe has experienced increasingly frequent and violent windstorms, considered to be the main cause of forest disturbance, both in terms of areas and volumes of wood affected. This threatens both timber production and other ecosystem services provided by forests, such as habitat and carbon storage.

The recent study published in Functional Ecology shows that the most storm-resistant European forests are those with the greatest diversity of tree species, dominated by slow-growing, high-density wood species. The impact of tree diversity on storm resilience is, according to the study, strongest in extreme climatic conditions, such as hot, dry conditions in the Mediterranean region and cold, wet conditions in northern Scandinavia.

According to Julien Barrere, researcher in forest ecology at INRAE: “Our study shows that monocultures of fast-growing species such as pine, while economically valuable, are more susceptible to storm damage. In a context of increasing storm losses across the continent, our study argues in favor of forest management practices that promote diversity and slow-growing species, such as oak.”

Modelling storm impacts

In order to reproduce the dynamics of hundreds of forests after a storm, the researchers have developed a numerical model based on field data from 91,528 forest plots in Spain, France, Germany, Sweden and Finland. The model forests vary in terms of climatic conditions, from the Mediterranean to the boreal forest, and in terms of composition, i.e. of tree species diversity and identity.

We were able to quantify the relationship between forest composition and its storm resilience, and to observe the evolution of this relationship along the European climatic gradient.

Following this model study, further field work is required to support the results, as Julien Barrere points out: “While model studies like ours are essential to draw conclusions about forest dynamics, due to the large natural timescales involved, the results must be evaluated against a clear understanding of the model assumptions and supplemented by field studies.”

Finally, according to Julien Barrere, this study focuses exclusively on the European forests response to a single storm. Although this is a first and necessary step, in today's context studies should focus on the resilience of forests to multiple disturbances rather than single disturbances.