From canopy to seedling: Exploring the potential role of nurse plants on Santa Fé Island, Galápagos

Abstract

Island endemic species are highly susceptible to extinction by invasive species, which severely impact native plants and ecosystems. For over a century, feral goats (Capra hircus) on Santa Fé Island confined Scalesia helleri to cliff-sides and led to substantial decreases in Bursera graveolens juveniles prior to goat eradication in the 1970s. Ongoing restoration studies indicate that native species are slowly recovering, with anecdotal evidence suggesting that a nurse plant syndrome may be facilitating recovery of some native plants. Nurse plant syndrome facilitation occurs when an adult nurse plant creates a beneficial microhabitat that aids seedling survival and establishment, with little to no negative impact on the adult plant. To evaluate whether Opuntia echios, Bursera graveolens, and Scalesia helleri act as potential nurse plants on Santa Fé Island, data were collected on adult species, GPS coordinates, height, basal area, and canopy cover; juvenile species and height; and the distance between each juvenile and its associated adult. Results revealed a significant positive association between adult Opuntia and conspecific juveniles, while adult Bursera exhibited a significant positive association with heterospecific juveniles. Furthermore, Scalesia juveniles were found to be significantly closer to adults of any species than Opuntia juveniles. These results support nurse plant syndrome in Santa Fé’s recovery and may inform restoration efforts on other islands.