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Woodland‐to‐forest transition during prolonged drought in Minnesota after ca. AD 1300
Author(s) -
Shuman Bryan,
Henderson Anna K.,
Plank Colin,
Stefanova Ivanka,
Ziegler Susy S.
Publication year - 2009
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/08-0985.1
Subject(s) - woodland , ecology , climate change , fire regime , deciduous , ecosystem , disturbance (geology) , geography , fire ecology , vegetation (pathology) , biomass (ecology) , environmental science , dendrochronology , biology , medicine , paleontology , archaeology , pathology
Interactions among multiple causes of ecological perturbation, such as climate change and disturbance, can produce “ecological surprises.” Here, we examine whether climate–fire–vegetation interactions can produce ecological changes that differ in direction from those expected from the effects of climate change alone. To do so, we focus on the “Big Woods” of central Minnesota, USA, which was shaped both by climate and fire. The deciduous Big Woods forest replaced regional woodlands and savannas after the severity of regional fire regimes declined at ca. AD 1300. A trend toward wet conditions has long been assumed to explain the forest expansion, but we show that water levels at two lakes within the region (Wolsfeld Lake and Bufflehead Pond) were low when open woodlands were transformed into the Big Woods. Water levels were high instead at ca. 2240–795 BC when regional fire regimes were most severe. Based on the correlation between water levels and fire‐regime severity, we infer that prolonged or repeated droughts after ca. AD 1265 reduced the biomass and connectivity of fine fuels (grasses) within the woodlands. As a result, regional fire severity declined and allowed tree populations to expand. Tree‐ring data from the region show a peak in the recruitment of key Big Woods tree species during the AD 1930s drought and suggest that low regional moisture balance need not have been a limiting factor for forest expansion. The regional history, thus, demonstrates the types of counterintuitive ecosystem changes that may arise as climate changes in the future.