Relationships between recruitment of perennial seedlings in 2018 and litter abundance. Litter abundance was measured by a litter cover for treatments representing native or naturalized annuals and controls, b litter biomass for the invasive annual treatment, and c a principal component combining both litter metrics to visualize the unimodal relationship across all treatments (this relationship was also significant when we ran a parallel model using 2017 data: F1,97 = 17.5, P < 0.001). Photo shows a perennial forb (Balsamorhiza sagittata) seedling emerging amidst sparce litter in a naturalized plot. Note that recruitment was modeled with a negative binomial distribution in all cases and associated predicted relationships have been back-transformed to the original scale.