Microsite requirements, population structure and growth of the cushion plant Azorella compacta in the tropical Chilean Andes

In the altiplano of northern Chile, we investigated the microsite habitats, adult population structure and growth rates over 14 months for the giant cushion plant Azorella compacta. The majority of plants (52.0%) were found growing downslope of large (>50 cm diameter) boulders and on north-facing rocky slopes with a slope angle greater than 10degrees inclination (44.4%). Size was used as a surrogate for age. The youngest size class was most common; remaining size classes were roughly equal in frequency; but very large cushions were scarce. Growth rates were expressed as height, diameter and perimeter over a 14-month period. Height increased an average of 1.40 cm, perimeter increased an average of 10.28 cm and diameters actually decreased 2.30 cm, although this was not a significant difference. Using perimeter averages based on mean plant size, we estimated a radial growth rate of 1.70 cm per 14 months. Trenches 4 cm wide were cut over the length of five plants, and these trenches were nearly repaired after 1 year, indicating that growth is overall and not just on the perimeter of the plant. These findings indicate that although Azorella compacta populations may be recovering from past exploitation, future monitoring is still necessary to ensure viable populations.