A Plague of Black Locust

I’ve recently returned from a trip to Italy where we learned about how the population of Rome plummeted during various plague events. In evidence this time of year was a whole different kind of plague - an infestation of black locust (Robinia pseudoacacia), a plant that was brought to Europe in the 1600’s from explorations to North America.

Black locust in Rome near Villa Borghese

I first noticed black locust as we were driving away from the Rome airport. While occasionally I’d see trees that were deliberately planted (large, standalone trees in a park), the majority of trees were in vast thickets along roads. Their growth pattern looked suspiciously like weed infestations of non-native trees in Georgia (like tree of heaven, mimosa, and privet). These trees were in full bloom, and their dangling white clusters of flowers made them all the more noticeable.

When we took a train from Rome to Florence, passing through rural areas, I was dismayed to see how widespread the growth reached into what appeared to be natural areas (although I am not sure how much natural area exists in a small area that has been heavily human-dominated for many thousands of years). I'm sorry I wasn't able to take a good picture of the infestation from the train, and I can't seem to find any representative pictures on the web.

Upon reaching home, I did a little research and found that some people are happy with the tree and are enjoying positive economic impacts from it (“fast growth, valuable and resistant wood, suitability for amelioration, reclamation of disturbed sites and erosion control, honey-making and recently dendromass production”). People concerned about nature conservation have those points to battle in their arguments that it is invasive, “threatening especially dry and semi-dry grasslands, some of the most species-rich and endangered types of habitat in the region, causing extinction of many endangered light-demanding plants and invertebrates due to changes in light regime, microclimate and soil conditions.”

I know that black locust is also considered invasive in North America; USDA shows it present in all the lower 48 states, some of which is surely due to man’s hand in moving it around. The flowers are beautiful and fragrant, a trait that surely convinced many a settler to take a piece to his new land just as he took other favorites. We know that many North American native plants were transported back to Europe by early explorers, but I’m shocked to see how much it has spread (but why should I be given the spread of some invasive plants here?). I guess 300+ years and the hand of man can accomplish a lot.