The effects of the aggressive species Pteridium caudatum on the vegetation of Socorro Island: Restoration challenges and opportunities

Abstract

Humans’ impacts on natural environments have become pervasive, and natural regeneration is often hampered by extreme soil degradation. This situation is exacerbated in insular habitats where introductions of non-native grazing mammals have left behind completely barren areas. Once mammals are removed, aggressive native or non-native plant species can grow vigorously. This leads to the question of whether biodiversity can return through native succession, or if other actions are needed to prevent invading pioneer species from causing successional arrest. This occurs on the remote Socorro Island, in the UNESCO World-Heritage Revillagigedo Archipelago, Mexico. To understand whether native plants are establishing at sites invaded by Pteridium caudatum, we evaluated natural regeneration in sites with different Pteridium cover in two contrasting zones of the island (dry and mesic). We also calculated plant stress indicators (midday leaf water potential, chlorophyl content and maximum quantum yield) for two native species—Dodonea viscosa and Psidium socorrense—growing in open areas and under Pteridium. Our results showed that Pteridium is a significant barrier to seedling establishment. Thus, restoration actions such as seeding and/or plantings should focus on areas without Pteridium cover. Certain local species can be used to restore degraded areas: P. socorrese and Waltheria americana could be used in dry zones, while D. viscosa could be sown in either dry or mesic zones. For adult plants of the two dominant shrubs, Pteridium cover neither imposes or ameliorates stress. Our results suggest that the restoration of plant diversity in the vast Pteridium-invaded areas of Socorro Island will require management actions, including progressive physical removal of Pteridium cover to activate natural regeneration. Pteridium removal can be accelerated by nucleation, planting adults of native shrubs to generate shading. This strategy could be viable if restoration programs involve conservation institutions and government agencies, who currently have critical human and technological resources on the Island.