Animals and Money: Spruce Bark Beetles - The Silent Invader of German Forests

The silent infestation of a tiny beetle is turning Germany's green forests into graveyards, giving rise to an alarming environmental crisis. All over the world, forests provide a home to over 50% of terrestrial species and combat climate by carbon sequestration, resulting in a reduction of greenhouse gases and preventing temperatures from rising [1]. They also regulate water levels, prevent erosion and can even lower blood pressure and stress of some animals [2]. The role of forests in achieving a sustainable future in the context of limiting global warming to 1.5°C is important. This goal can be achieved by halting deforestation and strengthening forest management and reforestation efforts [1].

Forests cover up to one third of Germany’s territory, which amounts to 11.4 million hectares with more than 90 billion trees. These forests are roughly balanced between deciduous and coniferous trees, with conifers like spruce and pine making up a slightly higher proportion at 54.2%. Spruce (𝘗𝘪𝘤𝘦𝘢 𝘢𝘣𝘪𝘦𝘴) is the most common species at 25.4% [2]. Forests face an ever-changing environment, leading to adaptions or - in the worst case - a loss of valuable forest territory. Unfortunately, forest loss in Germany is much higher than previously thought [3].

In German forests, the Bark Beetle (𝘐𝘱𝘴 𝘵𝘺𝘱𝘰𝘨𝘳𝘢𝘱𝘩𝘶𝘴) is a secondary pest, attacking mainly weakened or dying spruce trees, one of the most important woods in the European timber industry. The drought-weakened spruce is especially vulnerable to beetle infestation. Climate change is making this worse by increasing beetle outbreaks, often causing widespread devastation, even to healthy trees [4, 5]. Beetle attacks also introduce fungi into the trees, causing significant damage to the wood's physical and mechanical properties like strength, elasticity, coloration, and weight over time [6, 7]. The beetle population's sex ratio is typically 50% [8], however, during outbreaks the proportion of females can rise to 72%. More females in the population allows for a more rapid rise in reproduction, leading to more destruction in a short amount of time.

In Europe, the annual dieback of spruce caused by the European spruce bark beetle increased dramatically from 2-14 million cubic meters to 118 million cubic meters in 2019, mainly due to dry and hot summers [9]. Researchers at the German Aerospace Center (DLR) used satellites and discovered that from January 2018 to April 2021 about501,000 hectares forests have been destroyed in Germany. This is almost 5% of the total forest area and considerably more than previously estimated [3]. In 2019, Germanyharvested 83 to 85 million cubic meters of wood, including hardwood logs. Over 80% of this harvest was damaged coniferous wood, which had to be sold at a discount [10]. Spruce logs traded mostly between 105 and 110 euros per cubic meter, while beetle-damaged wood was selling 25-30 euro less [11]. Taking into consideration that 68 million cubic meters of wood were selling at 80 euro and only 17 million cubic meters of wood at full price, an overall loss of 2 billion euro can be calculated for the year 2019. Climate change scenarios suggest that damage from wind, bark beetles, and forest fires will continue to rise with an estimated increase of 0.91 million cubic meters of timber lost per year by 2030 [12]. To counteract this damage, Germany would need to reforest the affected areas and convert the remaining forests at a rate of 95,000 hectares per year, potentially costing up to €43 billion by 2050 [13].

Despite current high exports of softwood lumber, Europe may face local supply shortages in the future due to early harvesting caused by bark beetle damage. European sawmills are reaching capacity and exports of processed wood products are expected to decrease. As European supplies of logs decline, the United States may regain its share of exports to China and continue to supply European countries until their forests recover [14].

Arezou Aminizadeh

Issue 29