Abstract

Beaver dams substantially reshape peatland hydrology, yet their influence on plant phenology, a key driver of ecosystem carbon dynamics, remains poorly understood. We used UAV‐based RGB imagery to quantify seasonal changes in greenness (GCC) of sedge (Carex spp.) across three hydrological treatments in a Canadian Rocky Mountain peatland: flooded beaver pond, drained beaver pond and unimpacted fen. Repeat imagery captured from May to September 2023 revealed that beaver damming, whether current or legacy, significantly altered sedge phenology. Phenology in the flooded beaver pond followed a similar trajectory as the unimpacted fen but delayed green‐up by 2.5 weeks. Interestingly, the drained beaver pond exhibited the earliest green‐up, beginning 12 days earlier and reached a 12% higher peak greenness while having a similar length of season as the unimpacted fen, likely due to warmer peat and later‐season water stress. The flooded beaver pond maintained a high, stable water table which delayed senescence and extended the growing season by 6 weeks. These hydrological legacies created a patchwork of phenological responses across the peatland. Our findings highlight how beaver engineering via manipulation of water table elevation controls plant phenology, with potential indirect downstream effects on carbon cycling and forage availability in montane peatlands.