Effects of harvesting on nitrogen and phosphorus availability in riparian management zone soils in Minnesota, USA

Riparian management zones (RMZs) protect streams from excess nutrients, yet few studies have looked at soil nutrients in forested RMZs or the impacts of partial harvesting on nutrient availability. We investigated the impacts of upland clearcutting in conjunction with uncut and partially harvested RMZs (40% basal area reduction) on soil nutrients in forests in Minnesota, USA. Nitrate, ammonium, and phosphorus were measured using exchange resins. Upland clearcutting increased dormant and growing season nitrate, ammonium, and total inorganic nitrogen in the upland 2 to 5 times compared with uncut upland. Upland clearcutting increased dormant and growing season nitrate and total inorganic nitrogen just inside the RMZ boundary 2 to 5 times compared with this location adjacent to uncut upland. Dormant season nitrate and total inorganic nitrogen were 2 times higher in the entire RMZ adjacent to upland clearcut. Phosphorus was not affected by treatment. Partial harvesting of the RMZ did not increase nutrients compared with the uncut RMZ. Results suggest that nitrate is transported into the RMZ from adjacent clearcuts but partial harvesting of the RMZ does not increase nitrate availability.