Low solar grazing densities support beneficial insects in agrivoltaic systems

Abstract/Summary:

Solar grazing - the co-location of livestock grazing and photovoltaic energy production - is rapidly expanding globally to mitigate land-use conflicts. Solar facilities are increasingly sited on agricultural land, where both sheep grazing and the promotion of agriculturally beneficial insects are recognized as facilitators of multi-functional agroecosystems, yet how stocking rate shapes beneficial insect communities remains poorly understood. We conducted a replicated, three-year experiment testing six stocking rates (0–10 sheep ha⁻¹) at an operational 18MW solar facility, sampling bees and lady beetles across three years and four grazing rotations per year. Light grazing at 2 sheep ha⁻¹ supported 38% greater beneficial insect abundance than ungrazed controls, driven primarily by an 83% increase in honey bees. High stocking rates (≥8 sheep ha⁻¹) reduced bee abundance by 42–68% and significantly changed insect community composition. A companion study identified 8 sheep ha⁻¹ as the agrotechnological optimum, but our results identify 2 sheep ha⁻¹ as the agroecological optimum in our study region, where beneficial insect abundance and flock health are maximized. These optima did not coincide, indicating a clear tradeoff between ecological and operational objectives. However, at 4 sheep ha⁻¹, beneficial insect communities remained statistically indistinguishable from ungrazed controls while vegetation management effectiveness was greater than at 2 sheep ha⁻¹. Together these results define a synergy–tradeoff boundary with direct implications for targeting agroecological outcomes via the operations and maintenance of solar grazing facilities.