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 variability in foliar stable carbon (δ13C) and nitrogen (δ15N) isotope ratios of koa (Acacia koa) across 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 transects. Analysis of resultant δ13C and δ15N isotope ratios from multiple individuals across ecoregions indicated certain regions exhibited a correlation between carbon and/or nitrogen content, isotope ratios, precipitation, and elevation however, many comparisons 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 might have contributed to a lack of definitive data. Our results identified several areas within the Waiakea Forest Reserve and Volcanoes National Park where, based on isotope analyses, reforestation efforts could be most successfully initiated.