Top-Down Analysis of Forest Structure and Biogeochemistry across Hawaiian Landscapes

Technical and analytical improvements in aircraft-based remote sensing allow synoptic measurements of structural and chemical properties of vegetation across whole landscapes. We used the Carnegie Airborne Observatory, which includes waveform light detection and ranging (LiDAR) and high-fidelity imaging spectroscopy, to evaluate the landscapes surrounding four well-studied sites on a substrate age gradient across the Hawaiian Islands. The airborne measurements yielded variations in ground topography, canopy height, and canopy nitrogen (N) concentration more accurately than they could have been obtained by any reasonable intensity of ground-based sampling. We detected spatial variation in ecosystem properties associated with the properties of different species, including differences in canopy N concentrations associated with the native species Metrosideros polymorpha and Acacia koa, and differences brought about by invasions of the biological N fixer Morella faya. Structural and chemical differences associated with exotic tree plantations and with dominance of forest patches by the native mat-forming fern Dicranopteris linearis also could be analyzed straightforwardly. This approach provides a powerful tool for ecologists seeking to expand from plot-based measurements to landscape-level analyses.