Surface mining in the Athabasca Oil Sands Region (AOSR) disturbs vast landscapes of boreal forest, which must be reclaimed to functional ecosystems. This study analyzes 16 years (2008-2023) of growing season eddy covariance (EC) data from a constructed aspen-spruce-dominated boreal forest and evaluates evapotranspiration (ET) dynamics and the factors driving ET and energy partitioning with time. The study site, South Bison Hill, is a saline clay-shale overburden deposit capped with glacial till cover of ~1 m and a surface peat mineral mix of ~0.2 m. Annual growing season ET for the study period was 264 ± 20.3 mm – similar to estimates reported for boreal coniferous forests. Evapotranspiration increased by 15% from the early (2008-2012) to middle (2013-2017) stages of forest development and declined in the late stage (2018-2023), nearing early period rates. Air temperature, vapor pressure deficit, and net radiation combined explained 70% of ET variability in the early and late stages, with canopy conductance emerging as a crucial driver in the middle stage. Interannual climate variability mainly resulted in an increase in ET during wetter and warmer growing seasons and a decrease in ET during dry years with reduced soil moisture. No prolonged drought periods were observed, although ET exceeded rainfall in 85 % of growing seasons. A multi-year increase in site greenness, particularly evident during winter, and decreased ET in later years are attributed to an increase in coniferous species (white spruce). Therefore, understanding long-term forest transformations is essential for successful reclamation efforts in a changing climate.