PARENT SESSION
Poster Session #37: Plant Ecology: Populations.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Age and growth rate determination of threatened tropical dry-forest trees in Hawaii.

Walcek, Jennie^*,1, Sandquist, Darren¹, ¹ Department of Biological Science, Fullerton, CA

ABSTRACT- As part of a larger project to quantify the effects of an alien grass species (Pennisetum setaceum) on native dry-forest trees in Hawaii, we are examining changes in stable carbon isotope ratios of tree cross-sections. Doing such requires the establishment of a time sequence for these tree cross-sections and an estimate of tree growth characteristics. The age of temperate trees is easily found by counting the annual rings, however, there is no set method for aging tropical trees, which produce rings on a continual, non-annual basis. In order to find appropriate samples for our study, natural-abundance radioactive ¹⁴ C isotopes (¹⁴ C) were used to date trees and determine their growth rates. This method relies on detection of the enrichment of atmospheric ¹⁴ C due to bomb testing in the early 1960s. Tree samples yielding ¹⁴ C results revealed that most trees were not ideal for use in this study due to slow growth rates; tree ages greatly exceeded the time frame of the grass invasion. Nonetheless, information on tree ages and growth were attained. For example a regression of age (based on ¹⁴ C ) vs. distance from tree core was used to calculate the total age of a Metrosideros polymorpha tree of 25 cm diameter. The estimated age was 218 years old, assuming a linear growth rate. Additional samples have shown similar ages for other species in this forest.

KEY WORDS: ¹⁴ C isotopes, Hawaii, growth rate, tropical trees