Facilitation of Agave potatorum: An ecological approach for assisted population recovery

• Agave potatorum is significantly associated to specific nurse plants species.
• Protection from solar radiation is the main factor determining facilitation of establishment.
• Seed provenance influences performance of seedlings and nurse plant quality.
• Association of agaves and nurse plants has to be considered in managing populations’ recovery.

Extraction of Agave potatorum from forests for mescal production is a main cause of its populations’ decline and extinction in central Mexico. Sustainable harvest of agaves and populations’ recovery actions are needed for protecting this and other agave species similarly threatened. Our study aimed to identify mechanisms determining seedling establishment and sapling plants growth of A. potatorum in order to generate information helpful for enhancing populations’ growing and reforestation strategies. We hypothesized that (1) A. potatorum plants are spatially associated, probably species-specific, to shrub species, the frequency of facilitation being higher in the earlier stages of life cycle, varying among sites under different stress conditions, (2) germination and seedling survival are higher beneath nurse plants canopy compared with open areas, seeds and plants from a particular site performing better in the original conditions than in others, (3) nurse plants have a positive effect in the net balance of the growth rate of A. potatorum despite the negative effects of shade on carbon gain. We studied the association of A. potatorum with shrub and tree species by analysing their distribution patterns in two sites with contrasting environments (one relatively more xeric than the other). In these site we conducted experiments for testing seedling establishment and growth of agaves. Reciprocal transplanting experiments tested seed germination and seedling survival of agaves in open areas and beneath nurse plants. Two-years-old saplings were planted in open areas and beneath nurse plants to analyse their relative growth rate. We found a significant association of both young and adult plants to nurse plants, some of them being markedly specific. Germination and survival were higher under nurse plants, we also found negative effects of shade in carbon gain, but growth was higher there than in open spaces. We suggest that protection against solar radiation is a main factor influencing the association. Provenance of seeds was significant for germination success and early establishment. Nurse plants are crucial for the establishment of A. potatorum; however, several species may play the role of nurse plants and these may be different among sites. Therefore, rapid identification of nurse plant species in different vegetation types would allow agile actions for successful reforestation. Manual dispersion of seeds beneath canopies of shrubs that are high quality nurse plants, as well as producing sapling agaves in nurseries and transplanting them after two years associated to nurse plants are recommendable techniques for populations’ recovery.