Historical land-cover classification for conservation and management in Hawaiian subalpine drylands

We used aerial photography from 1954 and airborne LiDAR and imaging spectroscopy from 2008 to infer changes in extent and location of tallstature woody vegetation in 127 km² of subalpine dry forest on the island of Hawai'i (Phakuloa Training Area), and to identify 25.8 km² of intact woody vegetation for restoration and management. Total cover of woody vegetation was 54.7 km² in 1954 and 58.6 km² in 2008. Approximately 28.9 km² underwent woody vegetation change (22.7%) between 1954 and 2008. Increases in woody vegetation cover occurred in 16.4 km², and 12.5 km² represented reduction of woody vegetation cover (12.9% and 9.8% of the 127 km² study area, respectively). Our findings suggest that 3.9 km² (3.0%) experienced a net increase in woody vegetation cover between 1954 and 2008. Spatial patterns suggest that fires may be the primary driver of reductions in woody vegetation cover. Increases could be due to regeneration of dry forest trees or measurement errors associated with historical imagery. Areas remaining in woody vegetation cover over the 53-yr study interval can be targeted for restoration and management. We discuss challenges to integrating historical photography with contemporary conservation and management in Hawai'i and the Pacific and we outline additional studies that would help to improve estimates. The methods and analysis are general and could be applied to other dryland ecosystems with complex volcanic substrates in Hawai'i and the Pacific.