Stable isotope ratios and reforestation potential in Acacia koa populations on Hawai’i

Abstract

Stable carbon and nitrogen isotopes can be influenced by a multitude of factors including elevation, precipitation rate, season, and temperature. This work examined the variability in foliar stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope ratios of koa ( Acacia koa ) for 17 sites on Hawai’i Island delineated by elevation and precipitation gradients. Sites were identified and grouped with respect to mean annual precipitation (MAP), mean annual temperature (MAT) and position along three elevation ranges. Analysis of the resultant δ 13 C and δ 15 N isotope ratios from multiple individuals at these sites indicated that certain sites showed a demonstrated correlation between carbon and/or nitrogen content, isotope ratios, precipitation, and elevation however many sites showed no correlation. We used publicly available temperature and moisture data to help eliminate confounding effects by climatic drivers and capture possible points of contention. At sites where the temperature, precipitation, and elevation data were not significantly different we compared stable isotope information to determine if additional variables could have contributed to the lack of more correlative data. Our results note several areas within the Waiakea Forest Reserve and Volcanoes National Park where, based on isotope results, reforestation efforts could be most successfully initiated.