Seasonal NDVI trajectories in response to disturbance: toward a spectral-temporal mixing model for tallgrass prairie

Natural and anthropogenic disturbance in tallgrass prairie communities can induce changes in plant species composition, including shifts in abundance of C/sub 3/ vs. C/sub 4/ lifeforms. The asynchronous seasonalities in greenness that C/sub 3/ and C/sub 4/ species exhibit should enable monitoring of their relative abundance using sensor derived vegetation indices, such as NDVI. The authors used close-range measurements made over 22 experimental. Plots at the Konza Prairie Research Natural Area (KPRNA) to evaluate seasonal trajectories in canopy greenness as a function of C/sub 3//C/sub 4/ ratio. NDVI data were collected from each plot at approximately ten day intervals throughout the 1995 growing season. Temporal trajectories were used to develop discriminant functions to model relative C/sub 3//C/sub 4/ abundances. The discriminant model yielded values of Kendall's /spl tau//sub b/ and Cohen's /spl kappa/ statistic of 0.794 and 0.781, indicating strong agreement between classes and an overall classification significantly better than random assignment. Results suggest the possibility of applying spectral-temporal mixture models derived from close-range sensing to larger scale monitoring of tallgrass prairie.