Abstract
Restoration of keystone species is a primary strategy used to combat biodiversity loss and recover ecological services. This is particularly true for oceanic islands, which despite their small land mass, host a large fraction of the planet’s imperiled species. The endemic Opuntia spp. cacti are one example and a major focus for restoration in the Galápagos archipelago, Ecuador. These cacti are keystone species that support much of the unique vertebrate animal community in arid zones, yet human activities have substantially reduced Opuntia populations. Extreme aridity poses an obstacle for quickly restoring Opuntia populations though water-saving technologies may provide a solution. The aim of this study was to evaluate current restoration efforts and the utility of two water-saving technologies as tools for the early stages of restoring Opuntia populations in the Galápagos archipelago. We planted 1,425 seedlings between 2013 and 2018, of which 66% had survived by the end of 2018. Compared with no-technology controls, seedlings planted with Groasis Waterboxx® water-saving technology (polypropylene trays with water reservoir and protective refuge for germinants) had a greater rate of survival in their first two-years of growth on one island (Plaza Sur) and greater growth rate on four islands whereas the “Cocoon” water-saving technology (similar technology but made of biodegradable fiber) did not affect growth and actually reduced seedling survival. Survival and growth rate were also influenced by vegetation zone, elevation, and precipitation in ways largely contingent on island. Overall, our findings suggest that water-saving technologies are not always universally applicable but can substantially increase the survival and growth rate of seedlings in certain conditions, providing in some circumstances a useful tool for improving restoration outcomes for rare plants of arid ecosystems.
Highlights
The restoration of previously abundant keystone species is one way to combat loss of biodiversity and ecological services (Grime, 1998)
Our study focused on measuring the utility of water-saving technologies for enhancing cactus growth and survival of four endemic Opuntia taxa within the archipelago: Opuntia echios var. echios Howell, Opuntia echios var. gigantea Howell, Opuntia megasperma var. megasperma Howell, and Opuntia megasperma var. orientalis Howell (Hicks & Mauchamp, 1996)
We evaluated two technologies: Groasis Waterboxx R (Groasis), a protective polypropylene box that collects rainwater that it provides to the plant (Hoff, 2014); and the Cocoon system, a 99% biodegradable box that contains and provides water to the plant similar to Groasis, but Cocoon is only filled with water at the time of planting (Land Life Company, 2015; Faruqi et al, 2018; Appendix S1)
Summary
The restoration of previously abundant keystone species is one way to combat loss of biodiversity and ecological services (Grime, 1998). Several factors have been attributed as the primary threats to Opuntias including herbivory by introduced mammals (Grant & Grant, 1989), extinction of keystone predators that once regulated numbers of cactivores (Sulloway & Noonan, 2015), and the increased intensity of El Niño events likely driven by climate change (Snell, Snell & Stone, 1994; Hicks & Mauchamp, 1996). Opuntia declines on Plaza Sur Island, for example, are especially pronounced (60% reduction since 1957) despite the eradication of introduced goats since the populations are likely too low to successfully regenerate in the presence of native herbivory (Grant & Grant, 1989; Snell, Snell & Stone, 1994; Sulloway & Noonan, 2015)
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