Assessing Emergence of a Long-Lived Monocarpic Succulent in Disturbed, Arid Environments: Evaluating Abiotic Factors in Effective Agave Restoration by Seed

Abstract

Agave palmeri Engelmann is a semelparous perennial succulent thought to provide a critical food source for the endangered species, Leptonycteris curasoae Miller. Concern over impacts to existing A. palmeri populations has accelerated interest into reestablishing populations after disturbance. Little is known about its early life history and potential for restoration by seed in its arid habitat. In a greenhouse we measured emergence for 5.5 months across treatments with four variables: simulated precipitation (low: 170 mm, average: 285 mm, high: 390 mm), shade (present, absent), surface mulch (straw, gravel, bare soil), and soil type (sand, sandy loam, loamy sand). The highest emergence was associated with high simulated precipitation (33%), straw mulch (42%), shade (38%), and the loamy soils (mean: 30%). High simulated precipitation on shaded, straw mulched treatments had the highest overall emergence (63%). Lowest emergence involved low simulated precipitation (11%), bare soil (9%), absence of shade (10%), and sandy soil (10%). Low levels of simulated precipitation, combined with unshaded, bare soil treatments—conditions common in heavily disturbed arid environments—had zero seedling emergence. Our results indicate that microsite conditions play a crucial role in the emergence of this species, and manipulation of these conditions may significantly increase emergence, even when water availability is low. This is critical information for land managers attempting to recover populations, as duration and frequency of rainfall are characteristically variable in regions A. palmeri inhabits. Thus, the use of surface mulches and shade may effectively facilitate restoration in large-scale disturbances when unfavorable conditions cannot be controlled.