Characteristics of each sub-basin in the study.

Freshwater fish communities in New York State, USA, have been impacted by a variety of threats over the last century, including changes in land cover. Land cover exerts a powerful influence on aquatic communities at multiple spatial scales, and alterations to systems can persist even after restoration actions are taken. Our research examines how land cover changes were correlated with changes in fish species richness in a nearly 100-year dataset from New York’s Oswego River Watershed. The watershed was heavily agricultural in the early 1900s and was modified by both reforestation and urbanization in the subsequent century, two changes which we may expect to have opposite effects on biodiversity. Linear mixed effects models showed that species richness correlated positively with natural and urban land cover and negatively with agricultural land cover, with increases in the richness of sediment-tolerant, temperature-tolerant, and nonnative species driving the urban increase. Understanding how historical changes in land cover have affected species richness can help inform predictions about future changes to fish communities as formerly agricultural regions experience the conflicting effects of reforestation and urbanization.