Radiocarbon ages of macroscopic charcoal fragments found in Hawaiian drylands

This data publication contains radiocarbon ages (RCA) of charcoal fragments obtained from five soil pits excavated to a depth of ≤ 1.5 meters on the leeward flanks of Mauna Loa and Mauna Kea on the Island of Hawaii. Fragments were collected and radiocarbon-dated between 2012 and 2015. RCA of fragments ranged from less than 200 years RCA (2 pieces) to 7,730 years RCA (1 piece), with 13 pieces greater than 1,500 years RCA. We also obtained genus identities for four macroscopic charcoal fragments. Data also include measurements such as charcoal weight, depth below the surface, Δ¹³C, Δ¹⁴C, and Δ¹⁴C age. These findings indicate the existence of fires before humans are known to have occupied the Hawaiian archipelago and contributes to our understanding of prehistoric fires in shaping primary succession in Hawaiian drylands.
Primary succession in forests is characterized by stages of ecosystem development and decline, whereby systems accumulate biomass and vertical stature early in primary succession, but then enter a stage of long-term decline during which biomass and vertical stature are lost. The most typical cause of these changes is persistent phosphorus (P) limitation that occurs with substrate aging. Available P increases soon after the formation of parent material due to geochemical weathering, but later becomes limiting and decreases when demand and losses due to leaching outstrip supply. However, few studies of primary succession and ecosystem development have been conducted in drylands–those receiving < 500 millimeters (mm) of precipitation annually. Unlike wet systems, dryland ecosystems are likely to increase in vulnerability to fire over the course of primary succession. We know fires have well-known impacts on ecosystems that are associated with successional changes, but our understanding of primary succession in dryland ecosystems is limited, because weathering is slow and the impact of fire across scales of space and time is difficult to quantify. We used measurements from airborne imaging spectroscopy and LiDAR to characterize changes in the structure and composition of vegetation on a volcanic substrate-age gradient on the leeward flanks of Mauna Loa and Mauna Kea on the Island of Hawaii. We show a progressive increase in the vertical stature of vegetation on younger substrates where the lateral distribution of vegetation is sparse followed by a collapse in vertical stature on Pleistocene-aged flows where the lateral distribution of vegetation is dense. We then ask whether histories of fire frequency inferred using radiocarbon dates of macroscopic charcoal excavated from these sites implicate prehistoric and pre-human fires in the pathway of primary succession.
For more information about these data, see Kinney et al. (2015).