Compounding negative effects of leaf litter absence and belowground competition from an invasive spring ephemeral on native spring ephemeral growth and reproduction

Abstract Restoring invaded communities requires understanding whether native declines are driven directly by invader competition versus changes to abiotic conditions associated with invader presence. In forest understories, declines in spring ephemerals could result from invasion or by loss of leaf litter layers (associated with invasive earthworms and shrubs) which native ephemerals evolved to emerge from annually. We investigate how native ephemerals ( Erythronium spp.) are affected by leaf litter absence with and without competition with the functionally similar invader lesser celandine ( Ficaria verna ). The absence of litter reduced Erythronium asexual reproduction (corm biomass) by 30%, with reductions magnified to 50% when celandine was also present. Celandine impacts occurred despite celandine having limited aboveground growth under common garden conditions, indicating belowground competition with celandine is sufficient to substantially impact Erythronium. This reduced clonal growth would eventually hinder Erythronium sexual reproduction because flowering only occurs in large individuals. Both Erythronium species responded similarly to treatments: in response to shading from litter, Erythronium produced larger and 72–93% 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, net benefits of litter on growth outweighed negative effects of this biomass allocation tradeoff. These results demonstrate how, although direct competition from invasive plants can impact co-occurring natives, invader-induced changes to local environmental conditions also have important indirect effects. Management supporting native spring ephemerals should prevent losses of or restore depleted forest litter layers as well as reduce invasive competition.