Population dynamics and orientation of the central Andean cushion Azorella compacta 1 2

12 Azorella compacta (llareta; Apiaceae), a large woody cushion plant, is a remarkable 13 species forming dense cushions and characterizing the high elevation rocky slopes of the central 14 Andean Altiplano. Field studies of an elevational gradient of A. compacta within Lauca National 15 Park in northern Chile found a reverse J-shape distribution of size classes of individuals with 16 abundant small plants at all elevations. A new elevational limit for A. compacta was found at 17 5250 m. A series of cushions marked 14 years earlier showed either slight shrinkage or small 18 degrees of growth up to 2.2 cm yr -1 . Despite their irregularity in growth, cushions of A. compacta 19 show a strong orientation, centered on a north-facing aspect and angle of about 20 o from 20 horizontal. This exposure to maximize solar irradiance closely matches previous observations of 21 a population favoring north-facing slopes at a similar angle. Populations of A. compacta appear 22 to be stable, or even expanding, with young plants abundant and recolonization of disturbed 23 habitats. 24