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

Abstract

Biodiversity loss is a global concern, and maintaining habitat complexity in naturallypatchy landscapes can help retain regional diversity. A mosaic of prairie, savanna, andforest 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 plantcommunities originally surveyed in the 1950s to compare change in savannas to thatin remnant forests and prairies. Savanna community structure and compositionchanged substantially over the past 60 years. Tree canopy density nearly doubledand many prairie and savanna specialist species were replaced by forest and nonnative species. All three habitats gained and lost many species since the 1950s, resulting in large changes in community composition from local colonizations andextinctions. Across all three habitats, regional species extinctions matched that ofregional 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 extinctionsand colonizations were high over the past 60 years, and maintaining the presence ofall three community types-prairie, savanna and forest-on the landscape is critical tomaintaining regional biodiversity.