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

Laura M Ladwig,Ellen I Damschen,David A Rogers

doi:10.1002/ece3.4251

Laura M Ladwig, Ellen I Damschen + Show 1 more

Open Access

https://doi.org/10.1002/ece3.4251

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Abstract

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.

Highlights

Biodiversity loss is a global concern (Chapin et al, 2000; Rockström et al, 2009; Steffen et al, 2015) largely caused by humans
A mix of prairie, forest, and savanna specialist species once co- occurred in the savannas of southern Wisconsin but over the past 60 years, sites lost many prairie and savanna species and more closely resemble forests
Fire was largely absent from both savannas and prairies (Alstad & Damschen, 2015; Ladwig personal comm.)

Summary

| INTRODUCTION

We use a unique legacy dataset from remnant savanna sites to ask: (Q1) How has the species composition of savanna communities changed over the past 60 years, and how does the amount of change compare to that of prairies and forests? To understand how relative contributions of local diversity in prairies, savannas, and forests contributed to regional diversity we examined the number of shared and unique species among the three habitat types in both the 1950s and 2010s. Based on the repeated- measures PERMANOVA comparing species presence/absence in habitats at both time points, communities were statistically different with regard to time, habitat type (savanna, prairie, forest), and the interaction between the two (Figure 3), and pairwise comparisons indicated that all three habitat types were different from one another (p = 0.001). Our measures of species richness are more comprehensive in forests, as sampling intensity was much greater in forests (85 sites) than in savannas or prairies (16 and 17 sites, respectively)

| DISCUSSION

Findings

CONFLICT OF INTEREST