Abstract
Nutrient release processes associated with needle litter decomposition were monitored for
2 yr after thinning in a 50-yr-old Sugi (Cryptomeria japonica D. Don) plantation in northeastern
Taiwan. Three thinning intensities [unthinned (T0), low (T28), and moderately low (T36)]
were applied. Litterbags were used to measure the Sugi needle litter decomposition. Results of
decomposition for 2 yr illustrated that the current thinning intensities in this study gave clear effects
on nutrient release and return of Sugi needle litter. C release from the litter was the fastest.
In addition to C, this study categorized nutrient dynamics of the decomposition litter into 3 types
based on the quantity correlation of nutrient loss and changes in the weight remaining and concentration
of nutrients: (1) N and P, (2) Ca and Mg, and (3) K. The overall relative mobilities of the
nutrients examined after 2 yr were as follows: C > (P, K) > Ca > Mg > N. In this study, only the
relative mobility of K and P changed with the different thinning intensities. The annual return of
all nutrients showed no significant difference between treatments T0 and T28. Significantly lower
nutrient return rates existed with treatment T36, and these may have contributed to the significantly
lower input of Sugi leaf litterfall. The quantities of C and other nutrients returned through litterfall
decreased with an increasing thinning intensity. Amounts of bioelements of Sugi needle litter that
were returned to the soil were as follows: C > Ca > N > K > P > Mg for the 3 thinning intensities
in this study. It is possible that the current thinning level was not high enough to produce very significant
changes in needle litter decomposition, nutrient release, or nutrient availability. For future
studies, we suggested that both higher thinning intensity treatment and long-term decomposition
studies of changes in temperate and moist environmental conditions are necessary.