Above-ground competition by Nephrolepis brownii inhibits tree seedling recruitment in a tropical restoration experiment

Nephrolepis brownii (Desv.) (Nephrolepidaceae) is an invasive fern species in the Neotropics. In a restoration experiment in southern Mexico, N. brownii was common in the understory where it hindered native seedling recruitment. To inform management plans in similar contexts, we investigated whether its mechanism of interference was by above-ground or below-ground competition. Using a 2 × 2 factorial design, we sowed seeds of two non-pioneer, large-seeded tree species, Sapindus saponaria (L.) (Sapindaceae) and Cymbopetalum baillonii (R.E. Fr.) (Annonaceae), under conditions that restricted or allowed above-ground and/or below-ground competition with N. brownii. Growing under fern cover for 2 years negatively impacted S. saponaria, yielding seedlings with lower values of every biometric variable measured except seedling establishment and root-to-shoot ratios. Cymbopetalum baillonii also showed lower diameters, seedling mass, and leaf mass, with less pronounced differences. Below-ground competition increased S. saponaria diameters and, in combination with above-ground competition, lowered C. baillonii moisture content. Probability of survival was not influenced by presence or suppression of competition. Differences in performance between species suggest that S. saponaria exhibits light-demanding traits. Above-ground competition was the main mechanism of interference, but further research with a broader set of species representative of the diversity of life histories and seed sizes is needed to ascertain how N. brownii impacts tree recruitment. Synthesis and applications. As Nephrolepis brownii primarily interferes through above-ground competition, management of above-ground tissues may mitigate its impact. However, additional research on the efficacy of this management strategy and potential allelopathic traits is needed.