Size class structure, growth rates, and orientation of the central Andean cushion Azorella compacta

Catherine Kleier; Tim Trenary; Eric A Graham; William Stenzel; Philip W Rundel

doi:10.7717/peerj.843

Size class structure, growth rates, and orientation of the central Andean cushion Azorella compacta

PeerJ. 2015 Mar 17:3:e843. doi: 10.7717/peerj.843. eCollection 2015.

Authors

Catherine Kleier¹, Tim Trenary², Eric A Graham³, William Stenzel⁴, Philip W Rundel⁵

Affiliations

¹ Department of Biology, Regis University , Denver, CO , USA.
² Department of Mathematics, Regis University , Denver, CO , USA.
³ Nexleaf Analytics , Los Angeles, CA , USA.
⁴ Department of Computer Information Systems, Metropolitan State University , Denver, CO , USA.
⁵ Department of Ecology and Evolutionary Biology, University of California , Los Angeles, CA , USA.

Abstract

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.

Keywords: Andes; Cushion plant; Growth rate; Parque Nacional Lauca; Puna.

Grants and funding

This work was funded by a National Geographic Waitt Foundation grant W154-11. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.