Close to nature forestry, an efficient tool to reduce the vulnerability of Mediterranean mixed forests to drought

Oct 2, 2023

In response to the increase in drought events, the Joint Research Unit from Agrotecnio and the Forest Science and Technology Centre of Catalonia (CTFC), in collaboration with the University of Lleida, has studied innovative approaches to improve the drought resilience of Mediterranean mixed forests.

The research, carried out within the framework of the LIFE MixForChange and ONEforest projects, has been reflected in the study “Effects of close to nature management on tree growth and soil moisture in Mediterranean mixed forests”, published in the scientific journal Forest Ecology and Management. This work highlights the potential of close-to-nature forest management to promote ecosystems resilient to drought and other disturbances exacerbated by climate change.

Currently, a common characteristic of Mediterranean forests is a high density of trees, due to a decades-long lack of management. This leads to high competition for water and light, and a loss of tree vitality. The paper examines how different close-to-nature silvicultural actions affect tree growth and soil moisture.

“Implementing naturalistic forest management in Mediterranean forests has the potential to produce more vigorous and drought-tolerant trees, especially in the first years after the interventions, while generating a future increase in high-value wood. However, this strategy requires more effort and deeper knowledge of the forest ecosystem, such as in the selection of trees of high interest, to obtain good results,” explains Eduardo Collado, lead author of the article and CTFC researcher.

For the study, the researchers worked in 18 forest plots in Catalonia (Montnegre-Corredor, Montseny, Bellmunt-Collsacabra, and Ripollès), which represent a variety of competition intensities and various types of forests, dominated by oaks, chestnuts, and pines. The plots studied were divided into nine pairs, where some served as control plots, leaving them to evolve without intervention, while in others naturalistic forest management treatments were carried out.

The forestry actions carried out included both low-intensity thinning to favor trees with greater economic or ecological value, and selective clearing of undergrowth to avoid vertical continuity of fuel and thus reduce structural vulnerability to large forest fires. These types of treatments require frequent interventions to ensure that both the understory and the trees are maintained in the conditions necessary to achieve the objectives set (in this case, conservation of biodiversity and productivity of high-value wood).

Once the interventions were carried out, multiple variables of the forest dynamics were measured, such as annual growth and soil water content. The results show that the treatments implemented reduce competition for water, light, and nutrients, thus contributing to tree growth and increasing the water content in the soil.

Comparing the managed plots with the control ones, the treatments showed an average increase of approximately 10% in soil water content for stands dominated by holm oaks, oaks, chestnuts, and pines. This improvement was especially notable during spring, the season of most intense vegetation growth.

The results indicate that close-to-nature forest management practices can effectively reduce drought vulnerability to drought by increasing tree vitality and preserving soil moisture, at least in the short term (three years). This new silvicultural approach may help forest owners generate higher-value forest products in the future, and therefore, increase the profitability of the forest. The findings provide valuable information on sustainable forest management approaches and hold great promise for fostering more multifunctional forests, well adapted to Mediterranean regions.