28 November 2019

Fires combined with climate change may convert forests into open landscapes

Mediterranean forests at risk

Climate change is expected to increase the chance and intensity of drought around the Mediterranean basin. According to the collaborative work developed by a group of empirical and theoretical scientists from Utrecht University, the University of Alicante and other Dutch and Spanish universities, the increased aridity will make Mediterranean forests more vulnerable to wildfires, and shrubs and grasses could permanently replace hardwood and pine forests.

A Holm oak rises from the ashes of a previous fire. Credit: CEAM Foundation

The most common hardwood species in the Mediterranean area, the evergreen Holm oak, is very well adapted to withstand fires. It is not very flammable, as its humid understory prevents fire spread. It is also incredibly resilient to fires, as individual trees can regrow quickly out of their roots after a fire. However, even these very strong species have an Achilles’ heel. Climate change is expected to hit the Mediterranean basin especially heavily, and these evergreen oaks will suffer from the drier and hotter conditions and thus will grow back less strongly after fires.

Planting hardwood trees to prevent forest fires

“This decreased growth will possibly prevent the forest survival in the future”, says Susana Bautista of the University of Alicante. Their model results indicate that planting hardwood trees such as Holm oaks can help preventing forest fires, accelerating the otherwise slow establishment of these trees. However, even these less flammable hardwood forests may be at risk given the ongoing expected changes in climate in the future decades.

Mediterranean shrubs burning during an experimental fire. Credit: M. Jaime Baeza

Crucial for all ecosystems across the world

The researchers used decades of field data to parameterize a mathematical vegetation-fire model that includes the specific response to fire of dominant Mediterranean tree, shrub, and grass species. “To predict fire and plant’s fate in a changing world we need to represent full plant-fire responses in our models”, says Dr Mara Baudena from Utrecht University. This is likely crucial not only for the Mediterranean, but for all ecosystems across the world where fire occurs, and should be considered for global-scale models such as those used by the IPCC, the UN Intergovernmental Panel for Climate change.”

Publication

Baudena, M. et. al. (2019), Increased aridity drives post‐fire recovery of Mediterranean forests towards open shrublands. New Phytol. doi:10.1111/nph.16252