Importance of Early Season Conditions and Grazing on Carbon Dioxide Fluxes in Colorado Shortgrass Steppe

Morgan, Jack A.; Parton, William J.; Derner, Justin D.; Gilmanov, Tagir G.; Smith, David P.

doi:10.1016/j.rama.2016.05.002

Cited by 30 publications

(37 citation statements)

References 73 publications

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“…Morgan et al. () showed that MODIS‐derived NDVI values at the CPER site are highly correlated to the live biomass ( R 2 = 0.90 for seasonal patterns in live biomass vs. pasture NDVI during 2001–2003). We used the observed cumulative growing season NDVI (iNDVI, May to September) as an index of live biomass and plotted iNDVI changes from 1982 to 2016 (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…A recent paper by Morgan et al. () showed that April to June AET and precipitation‐controlled annual growing season net carbon uptake for the CPER site, while Derner and Hart () showed that cumulative April to June rainfall is highly correlated to ANPP for a nearby grassland site in Cheyenne, Wyoming. Morgan et al.…”

Section: Discussionmentioning

confidence: 99%

“…(), and Morgan et al. () papers showed that most of the grassland plant production occurs during the April to June time period and that live plant biomass ( R 2 = 0.80) and ANPP ( R 2 = 0.80) are highly correlated to iNDVI.…”

Section: Introductionmentioning

confidence: 99%

“…Morgan et al. () showed that live grassland plant biomass observations are well correlated to NDVI, while Hermance et al. () showed that ANPP is well correlated to iNDVI.…”

Section: Introductionmentioning

confidence: 99%

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The signature of sea surface temperature anomalies on the dynamics of semiarid grassland productivity

et al. 2017

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Abstract. We used long-term observations of grassland aboveground net plant production (ANPP, 1939(ANPP, -2016, growing seasonal advanced very-high-resolution radiometer remote sensing normalized difference vegetation index (NDVI) data , and simulations of actual evapotranspiration to evaluate the impact of Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) sea surface temperature (SST) anomalies on a semiarid grassland in northeastern Colorado. Because ANPP was well correlated (R 2 = 0.58) to cumulative April to July actual evapotranspiration (iAET) and cumulative growing season NDVI (iNDVI) was well correlated to iAET and ANPP (R 2 = 0.62 [quadratic model] and 0.59, respectively), we were able to quantify interactions between the long-duration (15-30 yr) PDO temperature cycles and annual-duration ENSO SST phases on ANPP. We found that during cold-phase PDOs, mean ANPP and iNDVI were lower, and the frequency of low ANPP years (drought years) was much higher, compared to warm-phase PDO years. In addition, ANPP, iNDVI, and iAET were highly variable during the cold-phase PDOs. When NINO-3 (ENSO index) values were negative, there was a higher frequency of droughts and lower frequency of wet years regardless of the PDO phase. PDO and NINO-3 anomalies reinforced each other resulting in a high frequency of above-normal iAET (52%) and low frequency of drought (20%) when both PDO and NINO-3 values were positive and the opposite pattern when both PDO and NINO-3 values were negative (24% frequency of above normal and 48% frequency of drought). Precipitation variability and subsequent ANPP dynamics in this grassland were dampened when PDO and NINO-3 SSTs had opposing signs. Thus, primary signatures of these SSTs in this semiarid grassland are (1) increased interannual variability in ANPP during cold-phase PDOs, (2) drought with low ANPP occurring in almost half of those years with negative values of PDO and NINO-3, and (3) high precipitation and ANPP common in years with positive PDO and NINO-3 values.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Morgan et al. () showed that live grassland plant biomass observations are well correlated to NDVI, while Hermance et al. () showed that ANPP is well correlated to iNDVI.…”

Section: Introductionmentioning

confidence: 99%

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The signature of sea surface temperature anomalies on the dynamics of semiarid grassland productivity

et al. 2017

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“…The high correlation of AET with ecosystem respiration, aboveground NPP, and GPP is also well documented in continental grasslands (Morgan et al 2016, Chen et al 2017, Del Grosso et al 2018). Rainfall is well correlated with annual changes and longterm average grassland aboveground NPP in the Great Plains of North America (Lauenroth and Sala 1992, Derner and Hart 2007, Chen et al 2017, and AET is well correlated with daytime and net plant carbon uptake in a Colorado grassland (Parton et al 2012, Morgan et al 2016. Rainfall is well correlated with annual changes and longterm average grassland aboveground NPP in the Great Plains of North America (Lauenroth and Sala 1992, Derner and Hart 2007, Chen et al 2017, and AET is well correlated with daytime and net plant carbon uptake in a Colorado grassland (Parton et al 2012, Morgan et al 2016.…”

Section: Discussionmentioning

confidence: 81%

Photodegradation accelerates ecosystem N cycling in a simulated California grassland

et al. 2018

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Photodegradation accelerates litter decay in arid grasslands where plant growth and litter decay are strongly controlled by precipitation and evapotranspiration. However, the effects of photodegradation on ecosystem C and N dynamics are not well understood. We examined the effects using an ecosystem biogeochemical model DayCent-UV with photodegradation explicitly represented and validated. The model was parameterized for a California grassland where photodegradation was documented to release CO 2 from litter. The model was parameterized with an inverse modeling approach using an extensive data set of six years of daily observed carbon and water gas exchange (gross primary production, ecosystem respiration, and evapotranspiration), soil temperature, and soil moisture. DayCent-UV correctly simulated the seasonal patterns of the observed gas exchange and closely simulated the inter-annual variation in the gas exchange and biomass production rates. The simulations suggested that the inter-annual variation is driven more by actual evapotranspiration than by precipitation because a large portion of precipitation is lost as runoff during wet years. Photodegradation in DayCent-UV accelerated C and N cycling, decreasing system C and N by 9.2% and 9.5% and C and N residence times by 9.4% and 18.2%. Accelerated N cycling made a greater fraction of system N available for plants, increasing net N mineralization and plant production for a given amount of system N. Increased net N mineralization was due to decreased immobilization by microbes in the aboveground organic matter. Photodegradation did not alter the control on plant production by evapotranspiration. These results suggest that at the ecosystem level, the central effect of photodegradation is to suppress microbial activity. We conclude that photodegradation accelerates N cycling at the expense of microbes in this grassland, making it more efficient in supporting plant growth for a given amount of N in the system.

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Assessing precipitation, evapotranspiration, andNDVIas controls of U.S. Great Plains plant production

et al. 2019

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Productivity throughout the North American Great Plains grasslands is generally considered to be water limited, with the strength of this limitation increasing as precipitation decreases. We hypothesize that cumulative actual evapotranspiration water loss (AET) from April to July is the precipitation‐related variable most correlated to aboveground net primary production (ANPP) in the U.S. Great Plains (GP). We tested this by evaluating the relationship of ANPP to AET, precipitation, and plant transpiration (Tr). We used multi‐year ANPP data from five sites ranging from semiarid grasslands in Colorado and Wyoming to mesic grasslands in Nebraska and Kansas, mean annual NRCS ANPP, and satellite‐derived normalized difference vegetation index (NDVI) data. Results from the five sites showed that cumulative April‐to‐July AET, precipitation, and Tr were well correlated (R2: 0.54–0.70) to annual changes in ANPP for all but the wettest site. AET and Tr were better correlated to annual changes in ANPP compared to precipitation for the drier sites, and precipitation in August and September had little impact on productivity in drier sites. April‐to‐July cumulative precipitation was best correlated (R2 = 0.63) with interannual variability in ANPP in the most mesic site, while AET and Tr were poorly correlated with ANPP at this site. Cumulative growing season (May‐to‐September) NDVI (iNDVI) was strongly correlated with annual ANPP at the five sites (R2 = 0.90). Using iNDVI as a surrogate for ANPP, we found that county‐level cumulative April–July AET was more strongly correlated to ANPP than precipitation for more than 80% of the GP counties, with precipitation tending to perform better in the eastern more mesic portion of the GP. Including the ratio of AET to potential evapotranspiration (PET) improved the correlation of AET to both iNDVI and mean county‐level NRCS ANPP. Accounting for how different precipitation‐related variables control ANPP (AET in drier portion, precipitation in wetter portion) provides opportunity to develop spatially explicit forecasting of ANPP across the GP for enhancing decision‐making by land managers and use of grassland ANPP for biofuels.

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Importance of Early Season Conditions and Grazing on Carbon Dioxide Fluxes in Colorado Shortgrass Steppe

Cited by 30 publications

References 73 publications

The signature of sea surface temperature anomalies on the dynamics of semiarid grassland productivity

The signature of sea surface temperature anomalies on the dynamics of semiarid grassland productivity

Photodegradation accelerates ecosystem N cycling in a simulated California grassland

Assessing precipitation, evapotranspiration, andNDVIas controls of U.S. Great Plains plant production

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