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Title: Evaluating the impacts of continuous and rotational grazing on tallgrass prairie landscape using high spatial resolution imagery

Author
item MA, SHENGFANG - Chinese Academy Of Sciences
item ZHOU, YUTING - Oklahoma State University
item Gowda, Prasanna
item CHEN, LIANGFU - Chinese Academy Of Sciences
item STEINER, JEAN - Retired ARS Employee
item Starks, Patrick
item Neel, James

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2019
Publication Date: 5/9/2019
Citation: Ma, S., Zhou, Y., Gowda, P.H., Chen, L., Steiner, J.L., Starks, P.J., Neel, J.P. 2019. Evaluating the impacts of continuous and rotational grazing on tallgrass prairie landscape using high spatial resolution imagery. Agronomy. 9(5):238. https://doi.org/10.3390/agronomy9050238.
DOI: https://doi.org/10.3390/agronomy9050238

Interpretive Summary: The tallgrass prairie in the Great Plain provides nutritious forage for cattle grazing which is a major revenue stream for farmers in the region. Different cattle grazing treatments (e.g. continuous and rotational grazing, C and R) might exert different impacts on tallgrass prairie landscape ecosystem health and productivity can be quantitatively analyzed by landscape metrics. Evaluating the impacts of grazing on prairie landscape is challenging mostly due to potential mismatch between pasture size and spatial resolution of commonly used satellite datasets (e.g. MODIS and Landsat with a spatial resolution of 500-m and 30-m, respectively). However, the National Agriculture Imagery Program (NAIP) acquires high spatial resolution (1-m) multi-spectral (red, green, blue, and near-infrared) aerial imagery during the agricultural growing season in the continental US. The high spatial resolution of NAIP imagery provides us an opportunity to study landscape dynamics within paddocks not of sufficient size to be studied using medium to low spatial resolution data sets. This study used four NAIP multi-spectral images to generate land cover types and calculated landscape metrics to indicate landscape dynamics in C and R pastures. Results showed that high grazing intensity cause late growth of grass. Grass recovered faster from grazing in the years with good temperature and precipitation. Grass condition was jointly affected by grazing management (stocking intensity) and climate. Climate and initial status of shrub distribution (total area, percentage of landscape, fragmentation), instead of grazing management, were the controlling factors of shrub encroachment. Both high spatial and temporal resolution images are required to better monitor the impacts of grazing management on the tallgrass prairie landscapes.

Technical Abstract: This study evaluated the impacts of different grazing treatments (continuous and rotational grazing, C and R) on the tallgrass prairie landscape using high spatial resolution aerial imagery (1-m at RGB and Near Infrared bands) of experimental C and R pastures within two replicates (rep A and B) in the Southern Great Plains (SGP) of the United States. The imagery was acquired by the National Agriculture Imagery Program (NAIP) during the agricultural growing season of selected years (2010, 2013, 2015 and 2017) in the continental United States. Land cover maps were generated by combining visual interpolation, support vector machine, and decision tree classifier. Landscape metrics (class area, patch number, percentage of landscape and fragmentation indices) were calculated from the FRAGSTATS based on land cover results. Both of them were used to analyze landscape dynamics in the experiment pastures. Results showed that both grass and shrub of 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 Ca and 15% of Ra 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. However, the low temporal resolution of NAIP imagery (one snapshot in two or three years) limits us to compare the continuous and rotational grazing at annual scale. Future studies need to combine NAIP imagery with other higher temporal resolution imagery (e.g. WorldView) to better evaluate the interannual variabilities of grass productivity and shrub encroachment.