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Abstract In the southern Great Lakes Region, North America, between 19,000 and 8,000 years ago, temperatures rose by 2.5–6.5°C and sprucePiceaforests/woodlands were replaced by mixed‐deciduous or pinePinusforests. The demise ofPiceaforests/woodlands during the last deglaciation offers a model system for studying how changing climate and disturbance regimes interact to trigger declines of dominant species and vegetation‐type conversions.The role of rising temperatures in driving the regional demise ofPiceaforests/woodlands is widely accepted, but the role of fire is poorly understood. We studied the effect of changing fire activity onPiceadeclines and rates of vegetation composition change using fossil pollen and macroscopic charcoal from five high‐resolution lake sediment records.The decline ofPiceaforests/woodlands followed two distinct patterns. At two sites (Stotzel‐Leis and Silver Lake), fire activity reached maximum levels during the declines and both charcoal accumulation rates and fire frequency were significantly and positively associated with vegetation composition change rates. At these sites,Piceadeclined to low levels by 14 kyr BP and was largely replaced by deciduous hardwood taxa like ashFraxinus, hop‐hornbeam/hornbeamOstrya/Carpinusand elmUlmus. However, this ecosystem transition was reversible, asPiceare‐established at lower abundances during the Younger Dryas.At the other three sites, there was no statistical relationship between charcoal accumulation and vegetation composition change rates, though fire frequency was a significant predictor of rates of vegetation change at Appleman Lake and Triangle Lake Bog. At these sites,Piceadeclined gradually over several thousand years, was replaced by deciduous hardwoods and high levels ofPinusand did not re‐establish during the Younger Dryas.Synthesis. Fire does not appear to have been necessary for the climate‐driven loss ofPiceawoodlands during the last deglaciation, but increased fire frequency accelerated the decline ofPiceain some areas by clearing the way for thermophilous deciduous hardwood taxa. Hence, warming and intensified fire regimes likely interacted in the past to cause abrupt losses of coniferous forests and could again in the coming decades.
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Global acceleration in rates of vegetation change over the past 18,000 years
Global vegetation over the past 18,000 years has been transformed first by the climate changes that accompanied the last deglaciation and again by increasing human pressures; however, the magnitude and patterns of rates of vegetation change are poorly understood globally. Using a compilation of 1181 fossil pollen sequences and newly developed statistical methods, we detect a worldwide acceleration in the rates of vegetation compositional change beginning between 4.6 and 2.9 thousand years ago that is globally unprecedented over the past 18,000 years in both magnitude and extent. Late Holocene rates of change equal or exceed the deglacial rates for all continents, which suggests that the scale of human effects on terrestrial ecosystems exceeds even the climate-driven transformations of the last deglaciation. The acceleration of biodiversity change demonstrated in ecological datasets from the past century began millennia ago.
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- PAR ID:
- 10230248
- Publisher / Repository:
- American Association for the Advancement of Science (AAAS)
- Date Published:
- Journal Name:
- Science
- Volume:
- 372
- Issue:
- 6544
- ISSN:
- 0036-8075
- Page Range / eLocation ID:
- p. 860-864
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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