Hurricane “Lothar”, which raged in Switzerland on December 26, 1999, knocked over a total of 14 million cubic meters of wood. 19 people died during the clean-up work. Nevertheless, Lothar has apparently helped Switzerland to better prepare for such extreme weather events. Forest researchers have now determined – 25 years after the event – exactly how the hurricane affected the affected areas.
On December 26, 1999, hurricane “Lothar” left a path of destruction through northern France, southern Germany, Switzerland and Austria. With wind gusts of more than 170 kilometers per hour, 60 deaths and millions of dollars in property damage, it was one of the most devastating storms in recent decades. “Lothar showed us the damage that extreme events can cause. In the Swiss Plateau the scale was unprecedented, today one would say ‘unbelievable,'” says disturbance ecologist Thomas Wohlgemuth from the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) in Switzerland. He and his team have now examined how Lothar has changed the Swiss forest in the long term.
Spruces gave way to climate-resistant deciduous trees
In Switzerland, Lothar felled three times the amount of wood that would otherwise be felled there in a whole year. These approximately 3,500 truckloads of wood created such an oversupply that even wood prices fell by about a third in the spring of 2000. But how long-term has this widespread destruction changed the Swiss forest? And are these changes still noticeable today – 25 years later?
As part of their inventory, Wohlgemuth and his team found, among other things, that in the years after the hurricane and especially after the heat wave in 2003, harmful bark beetles additionally damaged an area about two-thirds the size of the storm damage. After Lothar raged, the team found that instead of pest-prone spruces, more climate-resistant deciduous trees such as oaks, cherry trees, sycamores and Norway maples grew in the forests that were originally used for wood production.
Because there are now fewer spruces and more deciduous trees growing in the Swiss plateau, bark beetles can no longer reproduce as easily. However, heat and drought can still encourage further bark beetle infestations. The WSL therefore recommends removing the bark from trees affected by windthrow and leaving them on the ground. In this way, the dead wood protects against falling rocks and avalanches and insects find a place to live.
Greater insect diversity through dead wood
Deadwood is a good keyword at this point. Although forest workers had cleared away many of the trees that had been brought down by Lothar, a lot of insect-friendly dead wood remained in the forests. “Uncleared storm areas are an outstanding habitat for endangered species, especially in later stages of decay,” explains Beat Wermelinger, who has studied insect diversity on storm areas for decades. After the storm, insect diversity increased sharply, as the WSL reports. The number of rare species in storm areas was a third higher than in undamaged forests. “It is impressive how, after 20 years, apocalyptic tree cemeteries have become dynamic and lush eco-paradises with otherwise rarely seen residents,” says Wermelinger.
Over time, however, this insect diversity has decreased again as trees and bushes have grown back in the areas. “Wind throw brings movement to the otherwise rather ‘sluggish’ forest vegetation. In areas that were initially easily accessible, it was sometimes impossible to get through after two to three years because the undergrowth was so overgrown,” explains botanist Michael Nobis from the WSL. “In some areas that had not been cleared, you could only walk on the tree trunks lying on top of each other at a height of two to three meters – as long as the bark was still holding.”
Source: Swiss Federal Institute for Forest, Snow and Landscape Research WSL