Age and population structure of Joshua trees (Yucca brevifolia) in the northwestern Mojave Desert

Authors

Kimberly D. Gilliland, Idaho State University, Pocatello
Nancy J. Huntly, Idaho State University, Pocatello
J. E. Anderson, Idaho State University, Pocatello

Abstract

Many desert perennials are long-lived, but there are few data on ages or population structures of desert plants. We used 2 methods to estimate ages of a population of Yucca brevifolia (Joshua tree) in southwestern Utah from a 14-year census of plant sizes. Plant height at the 1st census ranged from 0.08 m to 6.0 m, and trees grew in height at a mean rate of 3.75 cm · yr⁻¹. Plants also increased slowly in basal diameter (0.142 cm · yr⁻¹) and branch length (0.024 m · yr⁻¹), but basal diameter varied greatly from year to year, with many plants decreasing in diameter between sequential censuses. Forms of a nonlinear growth equation (the Richards function) did not fit the data on growth in height, but a simple linear relationship fit the data well. Using height as a linear predictor of age, we estimated that ages of a sample of 69 Joshua trees ranged from <20 to >300 years old, with 75% of the trees between 20 and 100 years and 11% over 150 years old. These data support the assumption that Joshua trees are indeed long-lived.

Recommended Citation

Gilliland, Kimberly D.; Huntly, Nancy J.; and Anderson, J. E. (2006) "Age and population structure of Joshua trees (Yucca brevifolia) in the northwestern Mojave Desert," Western North American Naturalist: Vol. 66: No. 2, Article 6.
Available at: https://scholarsarchive.byu.edu/wnan/vol66/iss2/6