Potential of Digital Color Imagery for Censusing Haleakala Silverswords in Hawaii.

Spatially explicit, high spatial resolution remotely sensed imagery offers a largely untapped potential for censusing and monitoring rare plant populations that exist in remote, exposed environments. Using digital color imagery acquired over the Haleakala Crater on Maul, Hawai'i, we evaluated the accuracy of photointerpretation and automated censuses by imaging nine silversword census plots characterized by individuals of known size, life cycle status, and location. Due to spatial resolution limitations, both methods tended to omit small individuals, but omissions varied by size class and type of omission. Omission rates were low for demographically important medium and large plants; however, the automated method often failed to segment and census tightly clustered plants. The photointerpreter commission error rate was lower than that of the automated method, and both methods tended to overestimate mean silversword size. These data outline the issues and challenges that will likely emerge as spatially explicit, high spatial resolution aerial censuses become more common. [ABSTRACT FROM AUTHOR]