Control of the Distribution of Giant Rosette Species of Puya (Bromeliaceae) in the Ecuadorian Paramos

This study examined the effects of vegetation cover, growth form, fire disturbance, and competition on the distributional limits of two species of Puya in the Ecuadorian paramos. Puya clava-herculis and Puya hamata are widely distributed giant rosette plants that occupy nonoverlapping elevational ranges (3700-4100 m and 3300-3700 m, respectively) and each shows a patchy local distribution. Under natural conditions, the lower elevational limits of P. clava-herculis is primarily determined by competition with shrubs. In areas near human habitation, the lower limit of P. clavaherculis and P. hamata is largely determined by constant burning. Above the distribution of P. clava-herculis, bare ground or cushion and mat plants predominate. On bare ground, solifluction, low temperatures, and moisture stress reduce the probability of Puya establishment. In areas dominated by cushion and mat plants, either species of Puya is outcompeted or seedling safe sites are absent. Seedlings of P. clava-herculis showed a stronger than expected association with grass tussocks, indicating the importance of tussock edges as seedling safe sites. The amount and type of ground cover, as well as the distance to and growth form of nearest neighbors, are important factors determining the local patchy distribution of P. clavaherculis.