This study assessed the application of airborne imaging spectroscopy to monitor α-diversity in restored grassland plots. The study site was located within the Central Platte River ecosystem, south of Wood River in Central Nebraska, USA, and consisted of two sets of plots (young and old). Exotic species had recently invaded the old plots, confounding the original study design, while the young plots did not have significant invasion by weeds, reflecting the original study design. We used spectral variation (i.e. spectral diversity, expressed as the coefficient of variation) as a proxy for α-diversity (expressed as species richness and Shannon index). Airborne data collected at two flight altitudes and two flight directions tested the validity of “spectral diversity-α-diversity” relationship at different sampling scales and flight directions. Our results showed a strong relationship between spectral diversity and α-diversity in young, non-invaded plots exhibiting strong differences in α-diversity. However, in the old, invaded plots, the spectral diversity-α-diversity relationship was non-significant. Factors likely contributing to this failure in the old plots included the spatial mismatch between airborne and field-based sampling, the convergence in diversity levels over time, and the unique reflectance signatures of the invasive species related to their different structural and phenological properties. Unlike previous airborne studies in manipulated experimental prairie plots, but similar to results in more natural settings, the strong spectral diversity-α-diversity relationship in the young plots remained even at the spatial resolution of 1 m, demonstrating the potential of airborne remote sensing to assess diversity patterns in prairie grasslands. These findings demonstrate the importance of experimental remote sensing in evaluating spectral diversity, and provide insight for the development of operational airborne methods to assess biodiversity.
Bibliographical noteFunding Information:
Many thanks to two anonymous reviewers and the associate editor for providing feedback and insightful comments on this manuscript. We acknowledge The Nature Conservancy, its staff, and all the people who helped us during our field campaign. We specifically thank Nelson Winkel (TNC) who provided valuable information about the study area at the early stages of this experiment and assisted us during field data collection. We express our sincere gratitude to Rick Perk (Center for Advanced Land Management Information Technologies at UNL) for collecting the airborne data. We thank Kim Helzer for providing the plant diversity inventory, Bryan Leavitt (UNL) and Katherine Hogan (TNC) for their invaluable field assistance. We also express our gratitude to Dr. Zheng Xu (UNL) for his advice on statistical analysis. Special thanks to Dr. Craig Allen (UNL) for helping us to improve the design of our experiment. We also thank Donnette Thayer for assistance in preparing the spectral diversity maps. This work was supported by NSF/ NASA Dimensions of Biodiversity Program grant DEB-1342823 to J.A.G. and A.I.Z., DEB-1342872 to J.C.B., and DEB-1342778 to P.A.T. Mention of trade names does not imply endorsement by the authors.
- Airborne remote sensing
- Restored prairie
- Spatial scale
- Spectral diversity