Legume ground covers alter defoliation response of black walnut saplings to drought and anthracnose

Growth and premature defoliation of black walnut saplings underplanted 5 or 6 years earlier with six different ground covers were quantified in response to a summer drought or anthracnose. Walnut saplings growing with ground covers of hairy vetch, crownvetch, and to a lesser extent sericea lespedeza continued to have more rapid height and diameter growth than saplings in resident vegetation. Walnut saplings in a dense cover of sericea lespedeza had more rapid defoliation during a summer drought than saplings growing in a ground cover of resident vegetation. During the following year with nearly normal precipitation, walnut saplings growing in ground covers of resident vegetation had more rapid defoliation than walnut saplings underplanted with hairy vetch, crownvetch, and sericea lespedeza. Walnut saplings that had been underplanted with annual legumes that had failed to reseed themselves (crimson clover or Korean lespedeza) had defoliation rates similar to walnut saplings in resident vegetation. Regression analysis with a full first and second-order polynomial indicated that approximately 50 to 70 percent of the variation in the subsequent annual growth increment was a function of premature defoliation and sapling stem diameter, trunk cross-sectional area, or stem volume.