Despite decades of research on plant drought tolerance, the physiological mechanisms by which trees succumb to drought are still under debate. We report results from an experiment designed to separate and test the current leading hypotheses of tree mortality. We show that piñon pine (Pinus edulis) trees can die of both hydraulic failure and carbon starvation, and that during drought, the loss of conductivity and carbohydrate reserves can also co‐occur. Hydraulic constraints on plant carbohydrate use determined survival time: turgor loss in the phloem limited access to carbohydrate reserves, but hydraulic control of respiration prolonged survival. Our data also demonstrate that hydraulic failure may be associated with loss of adequate tissue carbohydrate content required for osmoregulation, which then promotes failure to maintain hydraulic integrity. This study describes results of the first test of the leading, but controversial, hypotheses regarding how trees die during drought. Our results show that all of the hypothesized mortality mechanisms can occur in trees of the same, relatively isohydric species, but both the progress of symptoms and survival time during drought may vary with individual trees even in similar environmental conditions. The mortality process seems to be controlled by hydraulic limitations on carbohydrate transport and utilization, which determines plant survival time.