A collection of 5,000 pressed flowers, gathered by Italian naturalist Ulisse Aldrovandi in the hillsides of Bologna 500 years ago, has emerged as a resource for understanding the impacts of climate change and human migration on landscapes in northern Italy.

The dried specimen, catalogued in Aldrovandi’s herbarium, were initially collected to identify plant species for pharmaceutical purposes. Today, they aid modern botanists in documenting the landscape changes that have unfolded over the past five centuries in this region.

The hills of Bologna were once teeming with a diverse array of plant species. Some species became threatened or extinct. While the total number of plant species has increased over time, the quality of the flora has notably decreased, especially concerning rare species. The 560% increase in the Italian population during this period is believed to have played a substantial role in these ecological shifts.

Ulisse Aldrovandi’s herbarium is a historical treasure comprising 15 books. Each book holds up to 580 specimens affixed to sheets. What makes it stand out is its early inclusion of detailed notes on species’ frequency, abundance, ecology, local names, and folk medicine uses, making it one of the oldest herbaria with such extensive documentation.

The herbarium’s significance in shedding light on ecological changes over time is highlighted in a recent research paper. The study compared Aldrovandi’s flora with collections by Girolamo Cocconi in 1883 and records from the Emilia-Romagna region between 1965 and 2021. The focus was on the plains around the River Po and its tributaries for dataset comparisons, revealing a staggering 1,000% increase in non-native American flowers.

The increase in non-native American flowers reflects the growing importance of American-European trade routes since the Renaissance. Dr Fabrizio Buldrini, the lead researcher from the University of Bologna, expresses concern about these findings, as they clearly indicate a profound human impact on the ecosystem over centuries.