Field Margin Vegetation Structure Buffers Microclimate Extremes in Temperate Agricultural Landscapes.

Field margins in agricultural landscapes range from herbaceous strips to tree-rich hedgerows, influencing microclimate and wildlife habitat quality. Despite their ecological importance, the microclimatic properties of structurally diverse field margins remain poorly quantified. We investigated how local field margin vegetation structure and landscape context influence microclimatic conditions and assessed how temperature measurement methodology, specifically the use of shielded versus unshielded sensors and the choice of temperature reference, affects estimates of thermal buffering. From June to September 2018, 180 paired shielded and unshielded sensors recorded temperature across 30 fields in 20 one-kilometre2 landscapes located in a temperate Canadian agricultural region, where field margins varied from short herbaceous cover to tall woody canopies. This paired design explicitly quantified how vegetation mediates solar radiation effects and how radiative processes contribute to apparent thermal buffering. We quantified daily maximum and minimum temperature offsets between field margins and adjacent crop fields and compared these measurements to regional weather station data. Linear mixed-effects models showed that tree-dominated margins strongly buffered thermal extremes, reducing maximum temperatures and elevating minimum temperatures, while herbaceous and shrubby margins provided limited thermal buffering. Margin width and landscape-level natural vegetation cover had no detectable effects. Although shielding reduced the magnitude of temperature offsets, the direction of buffering effects remained consistent. Temperature differences between margins and fields were substantially larger when compared to local in-field sensors rather than regional weather stations. Our findings demonstrate that both vegetation structure and measurement methodology substantially influence estimates of microclimate conditions, with implications for quantifying thermal buffering in agricultural landscapes.