Paleorecords of the middle Holocene (MH) from the North American mid-continent can offer insights into ecological responses to pervasive drought that may accompany future climatic warming. We analyzed MH sediments from West Olaf Lake (WOL) and Steel Lake (SL) in Minnesota to examine the effects of warm/dry climatic conditions on prairie-woodland ecosystems. Mineral composition and carbonate δ18O were used to determine climatic variations, whereas pollen assemblages, charcoal δ13C, and charcoal accumulation rates were used to reconstruct vegetation composition, C3 and C4 plant abundance, and fire. The ratio of aragonite/calcite at WOL and δ18O at SL suggest that pronounced droughts occurred during the MH but that drought severity decreased with time. From charcoal δ13C data we estimated that the MH abundance of C4 plants averaged 50% at WOL and 43% at SL. At WOL C4 abundance was negatively correlated with aragonite/calcite, suggesting that severe moisture deficits suppressed C4 plants in favor of weedy C3 plants (e.g., Ambrosia). As climate ameliorated C4 abundance increased (from ≈33 to 66%) at the expense of weedy species, enhancing fuel availability and fire occurrence. In contrast, farther east at SL where climate was cooler and wetter, C4 abundance showed no correlation with δ18O-inferred aridity. Woody C3 plants (e.g., Quercus) were more abundant, biomass flammability was lower, and fires were less important at SL than at WOL. Our results suggest that C 4 plants are adapted to warm/dry climatic conditions, but not to extreme droughts, and that the fire regime is controlled by biomass-climate interactions.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Jan 13 2004|