Abstract
Savanna plant communities are highly diverse, characterized by an open-canopy structure with rich herbaceous diversity, and maintained by frequent low-intensity fire and grazing. Due to habitat loss and fragmentation, savannas are globally threatened, with less than 1% of former oak savanna land cover found in the Midwestern United States remaining. In remnant oak savannas, loss of fire and grazing has led to woody encroachment and canopy closure over the past century with cascading consequences for the taxonomic composition. Whether these taxonomic changes can be broadly predicted using species functional traits (morpho-physio-phenological characteristics that impact the fitness of a species) is a key question. We ask whether the impacts of woody encroachment on herbaceous species can be predicted from species’ abilities to persist (avoid extinction) and disperse (colonize new areas). Specifically, we pair persistence traits (e.g., clonality, belowground storage) and dispersal traits (e.g., seed mass, dispersal mode, flowering height) with a rare 60-year dataset from oak savannas in Wisconsin, USA to understand how the representation of these traits has changed in the herbaceous community over time. Over 60 years, change in species composition was explained both by dispersal abilities and persistence traits; small-seeded species reliant on unassisted dispersal and moderately clonal species experienced the greatest losses. These changes in functional composition are likely due to increased woody encroachment, which may impede propagule production and movement. Restoration efforts need to prioritize species that are dispersal limited and those that create fine fuels, which aid the persistence of fire-maintained open habitat savannas.
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Acknowledgements
Funding was provided by the National Science Foundation (DEB-1754764), the Vice Chancellor for Research and Graduate Education (VCRGE) at the University of Wisconsin-Madison with funding from the Wisconsin Alumni Research Foundation, and Bridge Funding from the College of Letters and Science at the University of Wisconsin-Madison. SJA was supported by the University of Wisconsin-Madison Department of Botany Undergraduate Research Fellowship, The Botanical Club of Wisconsin’s John Thomson Award, and University of Wisconsin-Madison Honors College Trewartha Undergraduate Research Grant. KTC was supported by the University of Wisconsin-Madison Arboretum Leopold Fellowship. JJH was supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. (DGE-1747503). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. We would like to thank the numerous students in the Damschen Lab for collecting the functional trait data used in these analyses and the Plant Ecology Lab (PEL) at the University of Wisconsin-Madison for collecting and preserving the historical survey data. We are grateful to Anthony Ives and Brett Melbourne for their assistance in developing the models and the Suding Lab at the University of Colorado-Boulder for their comments on preliminary manuscript drafts. Additionally, we thank The Prairie Enthusiasts, Wisconsin Department of Natural Resources, The Nature Conservancy, the Audubon Society, the University of Wisconsin-Madison Arboretum, and private landowners, for allowing plant community and trait collection on their properties.
Funding
Funding was provided by University of Wisconsin-Madison Department of Botany Undergraduate Research Fellowship, National Science Foundation (Grant Number DEB-1754764), University of Wisconsin-Madison Arboretum Leopold Fellowship, and National Science Foundation Graduate Research Fellowship Program (Grant number DGE-1747503).
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Author order is determined based on the first-last-author-emphasis approach with intermediate authors assigned using the sequence-determines-credit approach (Tscharntke et al. 2007). Sam J. Ahler (they/them): Conceptualization, Methodology, Formal Analysis, Investigation, Data Curation, Writing—Original Draft, Writing—Review and Editing, Visualization, Project Administration. Laura M. Ladwig (she/her): Conceptualization, Methodology, Investigation, Writing—Review and Editing. Katherine T. Charton (she/her): Methodology, Software, Formal Analysis, Investigation, Data Curation, Writing—Review and Editing, Visualization. Jonathan J. Henn (he/him): Software, Formal Analysis, Investigation, Writing—Review and Editing, Visualization. Ellen I. Damschen (she/her): Conceptualization, Methodology, Investigation, Resources, Writing—Review and Editing, Supervision, Funding Acquisition.
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Ahler, S.J., Ladwig, L.M., Charton, K.T. et al. Dispersal and persistence traits inform long-term herbaceous plant community change in encroached savannas. Plant Ecol 224, 361–371 (2023). https://doi.org/10.1007/s11258-023-01307-3
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DOI: https://doi.org/10.1007/s11258-023-01307-3