Can multi‐species plantings alleviate abiotic stressors to enhance Bald cypress restoration?

Restoration researchers and practitioners alike advocate for novel restoration approaches, informed by ecological theories and principles, to enhance the likelihood of meeting restoration goals. Forested wetland restoration has historically focused on creating abiotic conditions that support the tolerance thresholds of desired species, but the stress gradient hypothesis provides guidance for potential new strategies that use biotic interactions to ameliorate stressful abiotic conditions. In this study, we tested whether multi‐species planting approaches can be used to enhance the survival and growth of a target restoration tree species, Bald cypress, along multiple abiotic gradients. We conducted a fully factorial controlled greenhouse experiment which manipulated above‐ and belowground interactions between two species (Bald cypress and Soft rush), as well as light availability and depth of inundation. Our findings showed that co‐planting Bald cypress seedlings with Soft rush did not increase tree biomass production or growth metrics (e.g. stem height and leaf area) under any exposed stress combination. Importantly, we found that full‐sun irradiance negatively impacted functional traits associated with the tree seedlings' health and ability to photosynthesize. Our findings are important for consideration by practitioners as light is rarely the focus of wetland ecosystem restoration and degraded forested wetlands or restoration sites often have open canopies.