The influence of prehistoric fire on the succession of Hawaiian sub-alpine dry forest ecosystems is poorly understood. Our study investigates the record of macroscopic charcoal preserved in soils where plant communities dominated by the low statured native shrub (Dodonaea viscosa) and native grass (Eragrostis atropoides) exist. This dry forest plant community type is known commonly as the Dodonaea shrubland (DVS) and is primarily located on Pleistocene age substrates.
We used a suite of remote sensing technologies and field approaches to locate and extract macroscopic charcoal fossils in DVS areas of interest. A high- resolution digital terrain model derived from LiDAR and maps of vegetation cover from airborne imaging spectroscopy were used to distinguish topographic features conducive to stable soil accumulation. We established 5 soil pits <1.5m in depth from a pool of randomly selected soil accumulation zones accessible to field study. After an exhaustive search for charcoal was performed in the soil pits, charcoal samples were sent to the Center for Accelerator Mass Spectrometry at the Lawrence Livermore National Lab for standard pre-treatment, graphitization and dating procedures. We quantified the frequency of charcoal samples collected in the soils as an index of prehistoric fire.
Results/Conclusions
We identified 18 pieces of macroscopic charcoal. Radiocarbon ages of charcoal fragments ranged from modern (2 pieces) to 7730 yr B.P. (1 piece), with 13 pieces > 1500 yr B.P. Most of the charcoal dates occur prior to estimates of human arrival (830 +/- 50 yr B.P.) in the Hawaiian Islands. The results suggest that natural fire events have been a persistent feature of the DVS landscape. These findings provide valuable insights about the natural history of fire in this region with regard to the ecosystem structure and community composition we see today. The implications of these results may be realized in adaptive restoration planning approaches and protected area designs that account for prehistoric vegetation dynamics.