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Title: Examining the short-term impacts of diverse management practices on plant phenology and carbon fluxes of Old World bluestems pasture

Author
item ZHOU, YUTING - University Of Oklahoma
item XIAO, XIANGMING - University Of Oklahoma
item Wagle, Pradeep
item BAJGAIN, RAJEN - University Of Oklahoma
item MAHAN, HAYDEN - University Of Oklahoma
item BASARA, JEFFREY - University Of Oklahoma
item DONG, JINWEI - University Of Oklahoma
item QIN, YUANWEI - University Of Oklahoma
item ZHANG, GELI - University Of Oklahoma
item LUO, YIQI - University Of Oklahoma
item Gowda, Prasanna
item Neel, James
item Steiner, Jean
item Starks, Patrick

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2017
Publication Date: 2/10/2017
Citation: Zhou, Y., Xiao, X., Wagle, P., Bajgain, R., Mahan, H., Basara, J., Dong, J., Qin, Y., Zhang, G., Luo, Y., Gowda, P.H., Neel, J.P., Steiner, J.L., Starks, P.J. 2017. Examining the short-term impacts of diverse management practices on plant phenology and carbon fluxes of Old World bluestems pasture. Agricultural and Forest Meteorology. 237:60-70. https://doi.org/10.1016/j.agrformet.2017.01.018.
DOI: https://doi.org/10.1016/j.agrformet.2017.01.018

Interpretive Summary: Burning, grazing, and baling (hay harvesting) are common management practices for tallgrass prairie. However, the impacts of these management practices on grassland phenology and carbon uptake are not well understood. This study used canopy greenness (green chromatic coordinate, GCC) extracted from PhenoCam images, vegetation indices (VIs) extracted from satellite images (Landsat and Moderate Resolution Imaging Spectroradiometer (MODIS)), and eddy covariance data to investigate the impacts of different management practices on phenology and carbon uptake in a tallgrass pasture in El Reno, Oklahoma. Landsat images were used to assess the baling area and the trajectory of vegetation recovery. The MODIS-derived VIs were used in a satellite-based Vegetation Photosynthesis Model (VPM) to simulate gross primary production (GPPVPM) at the flux tower (baled) site. For comparison, VIs of the flux tower located pixel were substituted with VIs from a neighbor pixel (unbaled) and GPP was simulated. VIs and GPPVPM showed that the grassland recovered in one month after baling. The GPPVPM matched well (R2 = 0.89) with the eddy covariance-derived GPP (GPPEC). The reduction in GPP after baling was compensated by higher GPP after rain pulses in late July and early September, causing little differences in GPP between the baled and unbaled conditions (-0.002 g C m-2 day-1). Results indicate that different management practices and their interactions with climate complicate the understanding of the impacts of different land management practices on carbon dynamics and vegetation phenology of the pasture.

Technical Abstract: Burning, grazing, and baling (hay harvesting) are common management practices for tallgrass pasture. To develop and adopt sustainable management practices, it is essential to better understand and quantify the impacts of management practices on plant phenology and carbon fluxes. In this study, we combined multiple data sources, including in-situ PhenoCam digital images, eddy covariance data, and satellite data (Landsat and Moderate Resolution Imaging Spectroradiometer (MODIS)) to examine the impacts of burning, baling, and grazing on canopy dynamics, plant phenology, and carbon fluxes in a tallgrass pasture in El Reno, Oklahoma in 2014. Landsat images were used to assess the baling area and the trajectory of vegetation recovery. MODIS vegetation indices (VIs) were used in the Vegetation Photosynthesis Model (VPM) to estimate gross primary production (GPPVPM) at a MODIS pixel for the flux tower (baled) site. For comparison between baled and unbaled conditions, we used MODIS VIs for a neighbor MODIS pixel (unbaled) and ran VPM. Daily PhenoCam images and green chromatic coordinate (GCC) tracked canopy dynamics and plant phenology well. The grassland greened up immediately after burning in April. GCC values showed two peaks with the similar magnitude because of quick recovery of grassland after baling. Satellite-derived VIs and GPPVPM showed that the pasture recovered in one month after baling. The GPPVPM matched well (R2 = 0.89) with the eddy covariance-derived GPP (GPPEC). Grazing in the late growing season did not influence plant phenology (VIs and GCC) and carbon uptake (GPP) as plants were in the late growing stage. Neither did it affect GPP differently in those two conditions because of even grazing intensity. The reduction in GPP after baling was compensated by higher GPP after large rain events in late July and early September, causing little seasonal differences in GPP (-0.002 g C m-2 day-1) between the baled and unbaled conditions. Interactions of different management practices with climate make it complicated to understand the impacts of different management practices on carbon dynamics and plant phenology. Thus, it is necessary to further investigate the responses of tallgrass pastures to different management practices under different climate regimes at multiple temporal and spatial scales.