Prairie or Woodland? Reconstructing Past Plant Communities at Good Earth State Park Via Soil Core and Tree RIng Analysis

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The hills and ravines of Good Earth State Park, located in southeastern South Dakota, currently support extensive woodlands interspersed with small upland prairies. Analysis of stable carbon isotopes from soil cores suggests that the prairies were much more extensive in the past and that the woodlands have expanded in recent years. Soil carbon isotope values (δ13C) from forested ravines and upland prairie sites show a strong C4 native grass signature, around -16‰ at the deeper depths, suggesting widespread prairie dominance throughout the park in the past. At the forested sites, δ13C values decreased significantly towards the soil surface reaching average values from -23 to -25‰. Such values are characteristic of C3 woody plants, providing evidence that over time, woodlands have replaced the native prairies. By contrast, soil cores from the few remaining upland prairie sites showed consistent δ13C values from top to bottom, around -16‰, suggesting these sites have remained dominated by prairies for many years. Tree core samples taken from the larger bur oaks (Quercus macrocarpa) at Good Earth yielded maximum ages of approximately 125 years. The apparent absence of older trees in the park is consistent with the stable isotope analysis suggesting that the woodlands at Good Earth have appeared rather recently. The expansive prairies of the past were reliant upon frequent wildfires which, coupled with tree harvest by Native Americans, likely prevented forest encroachment. Following abandonment of the Blood Run site around 1700, the settlement by European immigrants throughout the region and subsequent suppression of prairie fires, the woodlands have expanded considerably. If recent trends continue, the few remaining tracts of native prairie at Good Earth will disappear within a few decades. We applaud recent efforts by park management to begin restoring some of the lost prairie habitat.

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Proceedings of the South Dakota Academy of Science



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South Dakota Academy of Science