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Positive litter feedbacks of an introduced species reduce native diversity and promote invasion in Californian grasslands

Type of publication Peer-reviewed
Publikationsform Review article (peer-reviewed)
Author Mariotte Pierre, Spotswood Erica, Farrer Emily, Suding Katharine,
Project Exploring threshold dynamics in noxious plant invasion of Californian rangelands
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Review article (peer-reviewed)

Journal Applied Vegetation Science
Title of proceedings Applied Vegetation Science


Questions Californian grasslands have a long history of invasion, starting with the introduction of exotic forage species a century ago, and followed by newer waves of invaders. Both exotic and invasive species produce large amounts of litter, but the importance of litter accumulation on the growth and expansion of these species has not been rigorously assessed. We addressed the following questions: (1) Do litter type (exotic or invasive species) and litter quantity affect exotic and invasive plant performance? (2) At which plant life stages do litter accumulation effects occur? (3) Is litter accumulation impacting native species recruitment and diversity? Location Semi-natural grasslands of Northern California Methods We created litter quantity gradients (0, 62.5, 125, 250 or 500 g.m-2) of three litter types (exotic or invasive species litter or a mixture of both). We evaluated litter effects on the germination, recruitment, production of flowers and biomass production of the exotic Avena fatua, the invasive Elymus caput-medusae and a mixture of native species. We used litter depth as a proxy for litter accumulation and measured litter impacts on light availability at ground level, soil moisture, soil and microbial carbon and nitrogen. Results We found a significant litter depth impact on all species but no litter type effects. Litter accumulation principally reduced light availability at ground level and positively affected exotic and invasive species at different life history stages. Aboveground biomass production of the exotic species Avena increased with greater litter depth, suggesting a litter accumulation feedback. The invasive species Elymus responded to increased litter with increased seed production rather than biomass production. In contrast, litter negatively affected the recruitment and diversity of native species.