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 10 Њ 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.

The environmental relationships and ecophysiology of Azorella compacta, a giant cushion plant, were investigated in Parque Nacional Lauca, Chile (18°10′–18°25′ S and 69°16′ W, 4400 m asl). The diurnal temperature range can reach 42 °C on some days of the year. The surface temperature of A. compacta was 13 °C below that of the air temperature of −7 °C at dawn, but from midmorning to late afternoon, the plant surface temperature remained within a few degrees of the air temperature. Soil surface temperatures did not differ between north‐ and south‐facing slopes, but a model showed an increase in radiation reception by north‐facing slopes throughout most of the year. Gas exchange measurements of A. compacta measured at the onset of the wet season ranged from −0.6662 to 11.4 μmol·m−2·s−1, and maximum stomatal conductance (Gs) was 410 mmol·m−2·s−1. The estimated light compensation point was 89 μmol·m−2·s−1 and estimated light saturation occurred at about 1280 μmol·m−2·s−1. Diurnal water potential measurements for A. compacta ranged from −1.67 to −2.65 MPa. This is one of the first ecophysiological studies of a tropical alpine cushion plant.

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We investigated biotic and abiotic associations for four growth forms in Chile's Parque Nacional Lauca, a tropical alpine puna ecosystem. We determined the biotic associations between Parastrephia lucida (Meyen) Cabr. [Asteraceae] and Festuca orthophylla Pilger.[Poaceae]. To determine if F. orthophylla was acting as a nurse plant for P. lucida, we used chi-square analysis to test for nurse plant effects. Our results indicated that F. orthophylla roots more often on bare ground and that P. lucida grows more often in association with F. orthophylla than would be expected. In testing for abiotic associations, we observed that both a tree, Polylepis tarapacana [Rosaceae], and a cactus, Tephrocactus ignescens [Cactaceae], showed positive abiotic associations with large boulders. These studies indicate that in an extreme environment, such as the South American puna, abiotic and biotic associations are important for plant survival.

Azorella compacta (llareta; Apiaceae) forms dense, woody, cushions and characterizes the high elevation rocky slopes of the central Andean Altiplano. Field studies of an elevational gradient of A. compacta within Lauca National Park in northern Chile found a reverse J-shape distribution of size classes of individuals with abundant small plants at all elevations. A new elevational limit for A. compacta was established at 5,250 m. A series of cushions marked 14 years earlier showed either slight shrinkage or small degrees of growth up to 2.2 cm yr−1. Despite their irregularity in growth, cushions of A. compacta show a strong orientation, centered on a north-facing aspect and angle of about 20° from horizontal. This exposure to maximize solar irradiance closely matches previous observations of a population favoring north-facing slopes at a similar angle. Populations of A. compacta appear to be stable, or even expanding, with young plants abundant.