Tree Establishment During Dry Spells At An Oak Savanna In Minnesota
Affiliation
Minnesota Dendroecology Laboratory, Department of Geography, University of MinnesotaIssue Date
2008-06Keywords
Tree RingsDendrochronology
Oak Savanna
Drought
Palmer Drought Severity Index
Tree Establishment
Bur Oak
Quercus Macrocarpa
Northern Pin Oak
Quercus ellipsoidalis
Green Ash
Fraxinus pennsylvanica
Minnesota
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Copyright © Tree-Ring Society. All rights reserved.Collection Information
This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at editor@treeringsociety.org.Publisher
Tree-Ring SocietyJournal
Tree-Ring ResearchCitation
Ziegler, S.S., Larson, E., Rauchfuss, J., Elliott, G., 2008. Tree establishment during dry spells at an oak savanna in Minnesota. Tree-Ring Research 64(1):47-54.Abstract
Recent research has challenged the long-standing hypothesis that forests in the Upper Midwest of the United States developed during wetter periods and retreated during dry periods. We explored this debate by examining patterns of tree establishment on an oak savanna in east-central Minnesota within the context of variable moisture availability and fire suppression. We used superposed epoch analyses (SEA) to evaluate the mean moisture conditions for a 21-year window surrounding tree establishment dates. Before effective fire suppression (1809–1939), 24 of 42 trees with pith dates (62%) grew to 30-cm height during dry years (Palmer Drought Severity Index < -1), versus only 5 of 42 (12%) that established in wet years (PDSI > 1). Significantly more trees established during dry periods (negative PDSI values) than would be expected with the proportion of wet-to-dry years (x²= 10.738, df = 1, p-value = 0.001). Twenty of the complete sample of 74 trees with pith dates (27%) established during drought in the 1930s. We hypothesize that dry conditions limited plant productivity, which in turn decreased competition between grasses and tree seedlings and reduced rates of accumulation of fine fuels, enabling seedlings to grow tall enough to resist subsequent fires. We recommend SEA as a methodological approach to compare historical climate conditions with the timing of regeneration success in other regions of forest expansion.ISSN
1536-10982162-4585