Abstract
The effects of deer overgrazing on soil nitrogen dynamics and streamwater chemistry were examined using deer exclusion fence established around a 13 ha watershed in a cool-temperate forest in Ashiu, Japan, in comparing to its adjacent 19 ha control watershed. Line transects along the valley and ridge lines in each watershed were established. At 339 quadrats along the transects, the soils were sampled and their water contents, FH layer thickness, ammonium and nitrate nitrogen contents, net mineralization and nitrification rates, and carbon: nitrogen ratio were measured. Streamwater was collected at the outlet of watershed. The FH layer in the ridge line was significantly thicker at the fenced watershed than at the control, suggesting that a decrease in understory vegetation accelerates the litter and soil movement to the lower slope. Nitrate concentration in mineral soil was significantly higher in the control watershed than in the fenced watershed both along the valley and ridge lines, whereas there was no difference in net nitrification rate between watersheds. Stream nitrate concentration was also higher in the control watershed than in the fenced watershed two years since the fence was constructed. These results indicate nitrogen uptake by understory vegetation plays a crucial role in nitrogen retention in the forested watershed. Deer overgrazing of understory vegetation can alter soil nitrogen dynamics and increase hydrological nitrate loss.
