Topographic heterogeneity and woody plant seedlings on Santa Fé Island, Galápagos

Abstract

In arid and disturbance-prone ecosystems like the Galápagos Islands, understanding seedling establishment at the microsite level is critical for effective conservation. Island systems are resource-limited and host highly endemic vegetation due to isolation, making them especially vulnerable to disturbances such as invasive species. Santa Fé Island, Galápagos, experienced centuries of habitat degradation following the introduction of feral goats (Capra hircus), leading to biodiversity loss and shifts in the abundance and distribution of dominant woody species, including Scalesia helleri, Bursera graveolens, and Opuntia echios var. barringtonensis. Although the goats have since been eradicated, vegetation recovery is ongoing, underscoring the global need to understand post-disturbance regeneration processes. Topographic heterogeneity plays a key role in shaping microtopography - defined as small-scale (<1 m) terrain variation - which in turn influences abiotic factors critical for seedling establishment. This study (1) describes microtopographic features on Santa Fé Island; (2) identifies relationships between abiotic variables and topography; and (3) compares environmental conditions associated with seedlings of the three dominant woody species. Measurements of soil depth, volumetric water content (VWC), rugosity, canopy cover, and elevation were collected at seedlings of each of the species across nine locations using GPS, soil probes, and image analysis. Results indicate Opuntia echios seedlings were associated with the lowest canopy cover, Scalesia helleri with the lowest soil VWC and highest canopy cover, and Bursera graveolens with higher soil VWC. Soil depth differed significantly among species, and principal component analysis identified soil moisture, depth, and elevation as the strongest contributors to variation in seedling microsite conditions. These patterns suggest species-specific spatial associations likely shaped by dispersal strategies and regeneration niches. Findings underscore the importance of topographic heterogeneity impacts on seedling establishment and understanding plant community recovery to inform restoration planning following the eradication of feral ungulates on degraded arid islands globally.