Invasive Buckthorn Reduces Forest Leaf Litter

A recent study by DePaul University professor Liam Heneghan and Lake Forest Open Lands Association has revealed that buckthorn leaf litter has high nitrogen content and decomposes more rapidly than the litter of most of Chicagoland's dominant native species.

Buckthorn chokes out healthy plant communities by blocking sunlight. But that's only part of the story. Though nitrogen is a critical soil nutrient, the excess nitrogen from decomposing buckthorn leaves causes a significant increase in the rate of decomposition. Heneghan found that, as buckthorn spreads and dominates a preserve, the rate of decomposition of all forest floor material increases dramatically, adding large amounts of nitrogen to the soil very quickly and modifying the soil composition. He concluded that the increase in nitrogen content could have serious negative effects on the survival of many native plants, even after the buckthorn is removed.

Heneghan found that forest leaf litter virtually disappears each year in the high-nitrogen conditions found in dense buckthorn thickets. As buckthorn encroaches still further, the disappearance of the leaf litter may cause local extinctions of several invertebrate animal species. "This loss in turn may have implications elsewhere in the food chain — affecting the diversity of mammals and birds, for instance," suggests Heneghan.

Heneghan and his research team conducted their buckthorn leaf litter research in Shaw Woods, a preserve of the Lake Forest Open Lands Association.