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Citizen scientists record novel leaf phenology of invasive shrubs in eastern U.S. forests

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Abstract

Invasive shrubs are an emergent concern in deciduous forests of eastern North America. Their extended leaf phenology (ELP)—earlier leaf emergence and later leaf off compared to native shrubs and the overstory canopy—can simultaneously provide photosynthetic benefits to invasive shrubs while negatively affecting native flora and fauna through producing novel understory shade when the overstory canopy is leafless. However, phenology varies geographically, and the degree to which ELP from local-scale studies applies across the range of forests experiencing shrub invasion is unknown. In partnership with the USA National Phenology Network, we developed a citizen science campaign to record broad patterns of species-specific ELP—an otherwise prohibitively large effort. Using 1500 observations of 14 species spanning 4 years, we found that the difference in leaf phenology between native and invasive shrubs can exceed 77 days within a growing season, a gap that decreases with increasing latitude by 2.9 [1.6, 4.2] days per degree latitude in the spring, and 2.2 [0.6, 1.9] in the fall. Geographic trends in ELP provide a context for interpreting local scale phenology research while bridging inconsistent findings between existing studies and can streamline management by targeting detection and removal of invasive shrubs with leaves while natives are dormant. Furthermore, even small changes to seasonal phenology can impact forest communities, especially if there is a differential response to climate cues by nativity. After exploring broad-scale environmental variables associated with leaf phenology, we find a similar correlation with pre-growing season warmth for native and invasive shrubs, but a different relationship with dormant chill days—a variable less frequently considered for modeling spring phenology for forest productivity.

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Availability of data and material

While publicly available for download via USA-NPN and PRISM, the specific data used herein are available at https://doi.org/10.5281/zenodo.3939230.

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Acknowledgements

The platform and technical assistance of the USA-NPN was instrumental for this research. We thank the USA-NPN Outreach Coordinator, Erin Posthumus, the many participants who contributed to the USA-NPN Nature’s Notebook program, and the Arbortetum at Penn State and Shaver’s Creek Environmental Center for allowing data collection at their sites. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Funding

Funding was provided by NSF DDIG proposal number 1701470.

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Authors and Affiliations

  1. Department of Ecosystem Science and Management, The Pennsylvania State University, University Park, PA, USA

    Erynn Maynard-Bean, Margot Kaye & Eric P. Burkhart

  2. Intercollege Graduate Degree Program in Ecology, The Pennsylvania State University, University Park, PA, USA

    Erynn Maynard-Bean, Margot Kaye & Tyler Wagner

  3. U.S. Geological Survey, Pennsylvania Cooperative Fish and Wildlife Research Unit, The Pennsylvania State University, University Park, PA, USA

    Tyler Wagner

  4. Shaver’s Creek Environmental Center, The Pennsylvania State University, University Park, PA, USA

    Eric P. Burkhart

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  1. Erynn Maynard-Bean
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Correspondence to Erynn Maynard-Bean.

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The custom modeling code is available at https://doi.org/10.5281/zenodo.3939230, and any additional R code is available upon request.

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Maynard-Bean, E., Kaye, M., Wagner, T. et al. Citizen scientists record novel leaf phenology of invasive shrubs in eastern U.S. forests. Biol Invasions 22, 3325–3337 (2020). https://doi.org/10.1007/s10530-020-02326-1

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  • DOI: https://doi.org/10.1007/s10530-020-02326-1

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