Changes in photosynthesis and water relations of remaining leaves and regrowth over the first 50 days following shoot decapitation were studied in Populus deltoides Bartr. ×nigra L. I-262 (DN22) and Populus maximowiczii×nigra L. MN9 to determine if these changes were correlated with the reinvigoration of growth that occurs after shoot decapitation. There was a 7-fold increase in net photosynthesis of the remaining leaves 5 days after shoot removal, indicating a rapid, substantial reinvigoration. Diurnal photosynthetic patterns of retained stump leaves and new coppice leaves showed that decapitation increased the photosynthetic potential of tissue by increasing net photosynthetic rates in the early afternoon, thereby eliminating the post-midday reduction typical of intact plants. The retained stump leaves exhibited lower midday xylem pressure potentials than comparable leaves on intact plants due to higher stomatal conductance, suggesting that an alleviation of plant moisture stress was not the cause of enhanced net photosynthesis of retained leaves. The results suggest that leaves of intact plants typically photosynthesize well below their capacity and that growth of new stump sprouts coincides with higher photosynthetic rates of coppice foliage.