EFFECTS OF TENDING PRACTICES ON NUTRIENT DYNAMICS IN A YOUNG STAND OF SUGI (CRYPTOMERIA-JAPONICA) AND HINOKI (CHAMAECYPARIS-OBTUSA)

The effects of three silviculture practices, fertilization, weeding, and pruning, on nutrient losses and cycling were investigated for 8 years in a young coniferous stand and compared with an established stand. On the basis of the results, the effects of three intensive operations on site productivity are discussed. The quantities of organic matter and nutrients supplied by weeding and pruning were large, these two operations having a beneficial effect on nutrient cycling and site productivity before crown closure in the young stand. Evapotranspiration was estimated to be high in the young stand before crown closure and water loss (precipitation - discharge) decreased after pruning to approximately 25% of the prepruning value. The effects of fertilization on stream-water quality were restricted to the period directly after clearcutting. There was a positive relationship between stream nutrient export and stream discharge except for the first 3 years after clearcutting and planting. To maintain site productivity it is important to prevent excess nutrient loss in stream discharge. © 1990.