Asymmetric vegetation responses to mid-Holocene aridity at the prairie–forest ecotone in south-central Minnesota

Abstract

The mid-Holocene (ca. 8000–4000 cal yr BP) was a time of marked aridity throughout much of Minnesota, and the changes due to mid-Holocene aridity are seen as an analog for future responses to global warming. In this study, we compare the transition into (ca. 9000–7000 yr ago) and out of (ca. 5000–2500 yr ago) the mid-Holocene (MH) period at Kimble Pond and Sharkey Lake, located along the prairie forest ecotone in south-central Minnesota, using high resolution (∼ 5–36 yr) sampling of pollen, charcoal, sediment magnetic and loss-on-ignition properties. Changes in vegetation were asymmetrical with increasing aridity being marked by a pronounced shift from woodland/forest-dominated landscape to a more open mix of grassland and woodland/savanna. In contrast, at the end of the MH, grassland remained an important component of the landscape despite increasing effective moisture, and high charcoal influxes (median 2.7–4.0 vs. 0.6–1.7 mm2 cm− 2 yr− 1 at start of MH) suggest the role of fire in limiting woodland expansion. Asymmetric vegetation responses, variation among and within proxies, and the near-absence of fire today suggest caution in using changes associated with mid-Holocene aridity at the prairie forest boundary as an analog for future responses to global warming.

Climate change and ecosystems dynamics over the last 6000 years in the Middle Atlas, Morocco

“…P ann decreases progressively by ca. 100 mm, which is in line with the aridity trend that has been observed in other fossil records (Risacher and Fritz, 1992;Brooks, 2006;Hastenrath, 1991;Anderson and Leng, 2004;Umbanhowar et al, 2006) and particularly in the Mediterranean area (Pons and Reille, 1988;Julià et al, 2001;Burjachs et al, 1997;Yll et al, 1997;Roberts et al, 2001;Valino et al, 2002;Jalut et al, 2009) and northern Africa (Ritchie, 1984;Ballouche, 1986;Lamb et al, 1989). At a more regional scale, reconstructed P ann is coherent with that obtained from Lake Tigalmamine (Cheddadi et al, 1998) which shows a decreasing trend over the last ca.…”

Rapid responses of the prairie-forest ecotone to early Holocene aridity in mid-continental North America

“…the Holocene, the prairie-forest ecotone was highly mobile, shifting position in response to regional changes in aridity and fire regime (McAndrews, 1966;Grimm, 1983;Webb et al, 1983;Wright, 1992;Baker et al, 2002;Nelson et al, 2004;Umbanhowar et al, 2006). Understanding these Holocene dynamics has long been of interest to ecologists, as a way of gaining insight into the physical, biological, and cultural processes that regulate the position and structure of the ecotone (Gleason, 1922;Transeau, 1935), to synoptic paleoclimatologists documenting the spatiotemporal patterns of long-term hydrological variability (Bartlein et al, 1984(Bartlein et al, , 1998Harrison et al, 2003), and to atmospheric scientists interested in the effects of land-cover change upon atmospheric circulation and climate variability (Claussen et al, 2001).…”

Fire in upper Midwestern oak forest ecosystems: an oak forest restoration and management handbook

“…These stages also occurred in mixed pine-oak and northern hardwood-oak forests further north (Heinselman 1996), but were less accentuated due to the overall lower human populations, less conversion of land to uses other than forest, and colder climate with a shorter fire season. Although aridity alone can preclude trees from grasslands, paleoecological studies show that frequent fires can also exclude trees from sites that are mesic enough to support tree establishment and persistence (Umbanhowar et al 2006). …”

“…However, as the climate has warmed and cooled over the last 11,000 years since glaciers left the region, this band has shifted to the south and west during periods of relatively cool, moist climates, and to the north and east during times of relatively warm, dry climates (Umbanhowar et al 2006). Fire has been a major contributor to the development and maintenance of oak forests for thousands of years (Abrams 1992(Abrams , 2002.…”