In the boreal forest, air temperatures are increasing, and precipitation regimes changing, leading to amplified intensity and frequency of drought. These changes are projected to continue and the boreal forest will see complex and variable effects on local vegetation including drought-induced forest compositional changes, tree mortality and, in some places, forest loss. Drought causes stress in trees by reducing soil water available for plant uptake, and/or by increasing atmospheric loss via transpiration and evaporation. With soil and atmospheric conditions affecting drought, the specific drivers of water stress in trees can be difficult to disentangle. With this work, we paired environmental variables (soil moisture, soil temperature, rainfall, vapor pressure deficit, air temperature and solar radiation) with species-level tree water deficit (a measure of stem water content based on a plant�s relative hydration sate) to determine the drivers of water-stress in black spruce (Picea mariana) and tamarack (Larix laricina). Preliminary results suggest that vapor pressure deficit, and solar radiation drive daily water stress, while more prolonged tree water stress (weeks to month) is associated with soil moisture and rainfall. The relationship between environmental variables and tree water deficit varied across five sites spanning 2000 km from treeline to treeline. Finally, we examined the relationship between tree water deficit and evapotranspiration and determined that water stress in trees was not well coordinated with stand-level drought throughout the growing season, as measured by eddy covariance. Our results will enhance understanding of boreal forest vulnerability in the face of continued warming and drying.