In many mountainous regions, such as the European Alps and the Rocky Mountains, natural hazards threaten infrastructure such as roads, buildings, and railways. These natural hazards have globally increased by almost 70% in the last 30 years because of climate change. Triggered by harsh rainfall and storms, these hazardous events include rockfalls, landslides, floods, and debris flows, or a large mass of loose material moving down a slope.
However, it is well established that forests protect mountainous regions from natural hazards. Tree roots can decrease the availability of loose material by stabilizing the soil in steep terrain. In addition, forest canopies catch and collect rainfall, reducing surface water runoff. Getting rid of that forest canopy, either by human timber harvesting or natural causes like bark beetles, also reduces the protective function of forests.
Recently, Austrian researchers performed a large-scale study based on a large Landsat satellite image database, documenting 3768 torrential hazards that occurred in the Eastern Alps during a period of 31 years. They confirmed that an increase in forest cover decreased the probability of torrential hazards, like floods. It also turns out that regularly reducing forest canopy, such as small-scale logging interventions to regenerate forests, is actually more detrimental for natural hazards than singular, occasional disturbance events.
Unmanaged forests – where human intervention is absent or minimized – may better help protect human infrastructure against natural hazards than managed forests. And that could be important to know in a future where we want mountain regions to become more resilient to increasing heavy rainfall events and canopy reduction predicted under climate change.