Comparing the impacts of continuous and rotational grazing on tallgrass prairie landscape using the National Agriculture Imagery Program imagery

Cattle grazing is an important disturbance on tallgrass prairie landscape in the Great Plains of the United States. However, evaluating the impacts of different grazing management practices (e.g., continuous and rotational grazing, C and R) on landscape is challenging due to the mismatch between pasture size and spatial resolutions of commonly available satellite datasets. Using the National Agriculture Imagery Program (NAIP) imagery, which acquires high spatial resolution aerial imagery (1-m at RGB and NIR bands) during the agricultural growing season of selected years in the continental U.S, we studied the impacts of C and R on tallgrass prairie landscape within two Replicates (Rep a and b) in 2010, 2013, 2015, and 2017. Land cover maps were generated by combining visual interpretation, support vector machine, and decision tree classifier. Landscape metrics (e.g. class area, patch number, and fragmentation index) were calculated from the FRAGSTATS. Both were then used to analyze landscape dynamics in the experiment pastures. Results showed that grass and shrub in different pastures differed largely in the same year and had significant annual dynamics controlled by climate. High stocking intensity delayed grass growth. A large proportion of bare soil occurred in sub-paddocks of rotational grazing just grazed or under grazing. Rep a experienced rapid shrub encroachment with large proportion of shrub at the beginning of the experiment. Shrub may occupy 41% of C and 15% of R in Rep a by 2030 revealed by the linear regressions analysis of shrub encroachment. In contrast, shrub encroachment was not significant in Rep b which only had a small number of shrub patches at the beginning of the experiment. This result indicates that the shrub encroachment is mainly controlled by the initial status of the pastures instead of grazing management.