Croatian Oak Forests Devastated by Oak Sawfly

Croatia is renowned for its rich oak forests, primarily dominated by Quercus robur (Slavonian oak) and Quercus petraea. Among these, Slavonian oak is particularly prized across Europe for its slow growth, dense grain, and exceptional durability. Its light golden-brown hue and fine, even texture make it a sought-after material for high-quality wood products, while its mild flavour has made it a favourite for wine barrels and spirits aging.

Croatia had a devastating windstorm in the summer of 2023, which left many oak forests damaged and vulnerable to infestation by the “oak sawfly” (Agrilus biguttatus). In response, contractors swiftly harvested affected areas, salvaging high-quality logs for sawmills. Unfortunately, this left behind a massive volume of low-grade, infested logs that are commercially unviable due to their poor yield.

To combat the crisis, the Croatian government has implemented emergency measures, including a temporary halt on harvesting in non-infected forests until the infested timber is processed. Additionally, they raised the price of oak logs to incentivize the industry. However, sawmills are struggling to turn a profit, as the infested timber holds little commercial value and is largely suitable only for firewood. Many Croatian sawmills are at risk of closure, threatening not only the local economy but also the broader European market since Croatia is one of the largest suppliers of oak logs and lumber in the EU. The effects of this crisis are being felt by oak producers in Italy, Germany, Austria, and Bosnia, who rely heavily on Croatian oak resources.

While traditional methods like fumigation and kiln-drying can mitigate the infestation, they do not guarantee the complete eradication of bark beetles and their larvae. Other solutions are urgently needed to salvage “wormy oak” and restore its commercial viability. One possible approach is thermo-modifying the wood at higher temperatures, which effectively kills all pests and could potentially make the wood suitable for higher-value applications.

As Croatia is the largest oak log and lumber supplier in the EU, the aftermath of this disaster will be felt across the continent, underscoring the urgent need for sustainable solutions to protect and restore these invaluable forests.