Sixty years of community change in the prairie-savanna-forest mosaic of Wisconsin.

Biodiversity loss is a global concern, and maintaining habitat complexity in naturally patchy landscapes can help retain regional diversity. A mosaic of prairie, savanna, and forest historically occurred across central North America but currently is highly fragmented due to human land conversion. It is unclear how each habitat type now contributes to regional diversity. Using legacy data, we resurveyed savanna plant communities originally surveyed in the 1950s to compare change in savannas to that in remnant forests and prairies. Savanna community structure and composition changed substantially over the past 60 years. Tree canopy density nearly doubled and many prairie and savanna specialist species were replaced by forest and non-native species. All three habitats gained and lost many species since the 1950s, resulting in large changes in community composition from local colonizations and extinctions. Across all three habitats, regional species extinctions matched that of regional colonization resulting in no net change in regional species richness. Synthesis-Despite considerable species turnover within savannas, many species remain within the broader prairie-savanna-forest mosaic. Both regional extinctions and colonizations were high over the past 60 years, and maintaining the presence of all three community types-prairie, savanna and forest-on the landscape is critical to maintaining regional biodiversity.