The Vesdre River valley (province of Liège, Belgium) was historically home to an
important wool-processing industry. Raw wool was mostly imported from Australia, South Africa, and South America and contained numerous seeds and fruits. After cleaning the wool (“scouring”), the wastewater was discharged into the river, where the seeds germinated downstream of the mills, forming the so-called “wool aliens”. As a result of changed production processes (in particular: wastewater was no longer discharged) and the (almost) demise of this industry, the wool alien plants disappeared in the mid-20th century. In July 2021, the valley faced unprecedented floods, as a result of which the entire valley was destroyed. The banks of the river, for decades overgrown with the invasive weed Reynoutria japonica, were exposed again. In 2022 and 2023, seeds from the long buried sediment, which were thus introduced many decades ago, germinated. 178 wool alien taxa were identified, most of them from Australia and South Africa, the main suppliers of wool. Five families accounted for more than 87% of the taxa (in order of importance: Malvaceae, Fabaceae, Juncaceae, Geraniaceae and Convolvulaceae). Species-rich families like Asteraceae and Poaceae were completely lacking because their seeds likely did not survive the wool-processing or, more likely, were short-lived. The diversity of Malvaceae (71 taxa; 11 species of Abutilon and 15 of Sida) was quite remarkable. Almost 40% (68 taxa) of all taxa found had not been observed in
Europe before (or even outside their sometimes limited native range), despite the
fact that the wool alien floras were extensively studied in the past. More than 80%
(143 taxa) are considered weeds at least somewhere in the world. Wool therefore
appears to be a very efficient vector for the unintended introduction of foreign
seeds, including those of invasive species. Given the increasing use of wool waste
as fertilizer, inspection or certification measures may need to be considered to limit
the risk of introducing new weeds.