Quantifying the impact of grazing on ecosystem CO2 exchange in intensively managed pastures

Grazing alters ecosystem CO 2 exchange in pasture systems, but its short-term direct impacts on net ecosystem production (NEP) remain poorly quantified under real-world management conditions. Using eight years (2012–2019) of paddock-scale eddy covariance measurements from intensively managed dairy pastures in New Zealand, we quantified NEP responses to grazing, harvesting, and pugging. Across 168 grazing and/or harvest events, accumulated NEP ranged from −52 to 181 g C m −2 per event (median: 26 g C m −2 ; mean: 30 g C m −2 ). Average daily NEP in the 7 days before grazing (1.5 ± 0.4 g C m −2 d −1 ) was significantly higher ( p < 0.05) than in the 7 days after grazing (−0.6 ± 0.3 g C m −2 d −1 ). Grazing-induced NEP reductions (pre- vs. post-grazing difference) varied seasonally (1–3 g C m −2 d −1 ), with the greatest losses during mid-spring to early summer (October–December), when pre-grazing carbon (C) uptake potential was highest. From late winter to mid spring (August–October), NEP accumulation between grazing events exceeded the C removed in harvested biomass, suggesting that the additional fixed C was likely allocated to belowground pools or unharvested residuals. October emerged as a critical month, combining high C uptake with strong sensitivity to grazing timing. Limited case comparisons ( n = 3 each) indicated that spring harvesting sometimes supported faster short-term NEP recovery than grazing, while winter pugging consistently suppressed NEP. These findings highlight the importance of aligning pasture management with seasonal C dynamics and suggest that even small adjustments in grazing timing may enhance CO 2 uptake and contribute to climate-resilient pasture systems. • We compared grazing effects on net CO 2 exchange in a temperate pasture. • Grazing reduced carbon (C) uptake by 1–3 g C m −2 d −1 , depending on the season. • October (mid-spring) was key for C retention in grazed and ungrazed biomass pools. • Harvesting and soil conditions (e.g., pugging) can further impact C uptake.