Aspen regeneration in riparian management zones in Northern Minnesota: Effects of residual overstory and harvest method

We examined aspen regeneration under different riparian management zone (RMZ) treatments in aspen forests in northern Minnesota. We also compared aspen regeneration in partially harvested RMZs to adjacent upland clearcuts. The four RMZ treatments included: (1) full control (no cutting in RMZ or upland; (2) riparian control (RMZ uncut; upland clearcut); and partially harvested RMZs cut to 54ft²/ac, with upland clearcut using (3) cut-to-length (CTL), or (4) tree-length harvesting. Three years after harvest, aspen sucker densities in the tree-length and CTL treatments were significantly higher than the full control, but did not differ from each other or the riparian control. Mean individual sucker heights (63-73 in) and aboveground biomass (2.4-3.4 oz) varied among the riparian treatments, but not significantly. Sucker densities were 62% higher in the adjacent clearcuts than in the partially harvested RMZs. Mean suckers heights did not differ between the two locations (71 in.), but aboveground biomass of suckers did differ significantly, averaging 3.4 oz in the partially harvested RMZs and 4.5 oz in the clearcuts. Our results indicate that 60% removal of basal area within RMZs increases density and size of aspen regeneration significantly, compared to uncut forest, but stocking is still below what is considered adequate for 3-yr-old stands. Suckering responses were similar with cut-to-length and tree-length harvesting, suggesting that harvest system has little effect on sucker development. While aspen likely will be a component of partially harvested RMZs, density and biomass increment will be much lower than in single-cohort stands and lower than what is considered desirable for commercial production.