Reduced growth and reproduction in native spring ephemerals from key drivers of forest change: invasive ephemeral competition and leaf litter absence

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The Ohio State University

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Net effects of co-occurring invaders on native performance must be assessed to understand invasion mechanisms and impacts. We used a common garden experiment to investigate how two widespread native spring ephemerals (Erythronium albidum and E. americanum (Liliaceae); trout lilies) are affected by direct competition with invaders and by indirect effects of invader-induced habitat alteration. We examined impacts of competition with invasive Ficaria verna (lesser celandine), itself a spring ephemeral forest herb, and simulated forest litter layer reduction associated with invasive shrubs and earthworms. Lastly, we investigate the dynamic wherein shading causes Erythronium to elongate petioles, which may reduce biomass allocation to leaf blades. The absence of a litter layer reduced corm and offspring weight, with even greater reductions when celandine was also present. Celandine impacts occurred even despite celandine having limited aboveground growth due to a planting delay. Therefore, belowground competition with celandine is an important driver of its impacts on Erythronium. We also conclude that invaders could reduce the frequency of sexual reproduction in Erythronium; because only large Erythronium flower, reduced biomass caused by these invaders could reduce flowering. In response to shading from litter, both Erythronium species produced larger, heavier petioles and invested less in leaf blade tissue as a proportion of total shoot tissue. Though reduced leaf blade investment was correlated with reduced corm growth, the net benefit of litter on growth outweighed any impact of this trade-off. In sum, this study demonstrates how the impacts of an invader on natives can increase when multiple invasive species co-occur in a site. Preventing the loss of forest litter layers and reducing invasive competition are key to supporting spring ephemeral populations.



invasion impact, competition, spring ephemerals, functional traits, Erythronium, Ficaria verna