For their analysis, the research team led by Prof. Dr. Rupert Seidl from the Technical University of Munich used a deep learning-based simulation framework, which was trained with 135 million data sets from forest simulations for around 13,000 locations in Europe and combined with satellite data on forest disturbances. This approach allowed the scientists to calculate the development of forests as well as the occurrence of fires, storms and bark beetle infestation up to the year 2100 with high spatial resolution and across a large spatial extent.
Climate change increases risks
Simulated disturbance regimes in the 21st century under the RCP2.6 scenario. The values show the mean disturbance rate across all simulation years (2021–2100). The size of the dots corresponds to the share of forested area in each hexagon with a side length of 25 km. Gray areas indicate hexagons without forests. © Marc Grüning et. al.
The results show that climate change will increase the risk of disturbances in Europe’s forests throughout the entire 21st century. Rising temperatures, in particular, increase the risk of wildfires. While these have mostly affected the Mediterranean region so far, they could become more frequent in temperate and boreal regions in the future.
Under scenarios of unabated climate change, involving a warming of +4°C (scenario RCP8.5), the study predicts a 122% increase in disturbed forest area due to bark beetles, storms and wildfires compared to the period 1986 to 2020.
Simulated disturbance regimes in the 21st century under the RCP8.5 scenario. The values show the mean disturbance rate across all simulation years (2021–2100). The size of the dots corresponds to the share of forested area in each hexagon with a side length of 25 km. © Marc Grüning et. al.
According to the researchers, predicting future forest disturbances is difficult as the various disturbance factors interact in complex ways, and feedback loops between the development of vegetation and disturbance dynamics can either mitigate or intensify the effects of climate change. In scenarios involving the effective reduction of emissions, the disturbance intensity will reach its peak by the middle of this century, after which a recovery phase for forests should set in.
At a regional level, the effects will vary. Forests in southern and western Europe are considered to be particularly vulnerable, while changes in northern Europe are expected to be somewhat less profound overall. Nevertheless, researchers expect regional hotspots with a substantial increase in damage in the north as well.
Forests under increasing pressure
Trees with visible bark beetle damage © Rupert Seidl, TUM
The increasing occurrence and extent of disturbances are not only changing forest landscapes but also their structure. The share of young forests could increase by up to 14% by 2100, especially in the Mediterranean region. Meanwhile, the share of old forests is expected to decrease slightly by 3% relative to simulations without changing climate and disturbance regimes. This shift has repercussions on carbon storage, biodiversity and the ecosystem services provided by forests.
As temperatures are rising, the composition of forests will change by the end of the century. Tree species such as spruce and beech will grow on smaller areas. The researchers advocate for considering the costs of forest disturbances in future forest planning. Possible countermeasures include the planting of less disturbance-prone tree species, structurally diverse mixed forests, and shorter rotation periods.
According to the authors, political decision-makers have to respond, and forest management practices needs to be changed. “We must prepare ourselves for the significant damage to forests that we will certainly see in the coming years. On the one hand, this means that we will have to buffer greater fluctuations in the services provided by forests. On the other hand, disturbances are also an opportunity for establishing new, more climate-resilient forest stands. They act as a catalyst for change,” Seidl explains. “Large forested areas will still exist in Europe in a few decades from now, but forests will be more open, with smaller trees that can better withstand heat and drought,” Professor Dr. Henrik Hartmann from the Institute for Forest Protection at the Julius Kühn Institute in Quedlinburg/DE is quoted as saying on tagesschau.de.
Climate change will increase forest disturbances in Europe throughout the 21st century | Science
