标题：Role of dispersal timing and frequency in annual grass-invaded Great Basin ecosystems: how modifying seeding strategies increases restoration success
摘要：Seed dispersal dynamics strongly affect plant community assembly in restored annual grass–infested ecosystems. Modifying perennial grass seeding rates and frequency may increase perennial grass establishment, yet these impacts have not yet been quantified. To assess these effects, we established a field experiment consisting of 288 plots (1 m2) in an eastern Oregon annual grass–dominated shrubsteppe ecosystem. In this study, the amount, timing, and frequency of perennial grass seeding events, soil moisture availability, and annual grass seed bank density were manipulated. We found that more frequent perennial grass seeding events combined with high perennial grass seeding rates produced the highest perennial grass density and biomass 2 years following seeding. However, we also found that if annual grass seed density was 1500 seeds ⋅ m−2 or higher, perennial grass density and biomass decreased, regardless of seeding strategy. Because of this finding, it appears that a threshold is crossed between 150 and 1500 annual grass seeds ⋅ m−2. Adding water in the first growing season initially facilitated perennial grass establishment but only produced higher perennial grass density following the second growing season when annual grass density was lowest. Assessing the existing annual grass seed bank prior to seeding can likely forecast restoration outcomes because high annual grass seed densities likely interfere with and reduce perennial grass recruitment. In addition, if annual grass seeding density is 1500 seeds ⋅ m−2 or lower, modifying the temporal patterns of perennial grass seed arrival will increase the likelihood that a perennial grass seed finds a safe-site.La dinámica de dispersión de semillas afecta considerablemente el ensamble de la comunidad vegetal en los ecosistemas restaurados e infestados por pasto anual. La modificación del ritmo y la frecuencia de siembra del pasto perenne pueden incrementar el restablecimiento del mismo; sin embargo, el impacto aún no ha sido cuantificado. Para evaluar tales efectos, establecimos un experimento de campo que consistió de 288 parcelas (1 m2) en un ecosistema de estepa herbácea, al este de Oregon, dominado por un pasto anual. En este estudio manipulamos la cantidad, el ritmo y la frecuencia de eventos de siembra de pasto perenne, así como la disponibilidad de la humedad del suelo y la densidad del banco de semillas de siembra de pasto anual. Encontramos que la mayoría de los eventos de siembra de pasto perenne, en conjunto con tasas altas de siembra de tales pastos, producen la densidad más alta de pasto perenne y de
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