Nutrient budgets in four Japanese forests based on short- and long-term methods

Abstract

Estimation of the nutrient accumulation rate in tree biomass is important for understanding the nutrient budgets of forest ecosystems but choosing a suitable method can be challenging. In this study, we compared the nutrient budgets of four forest ecosystems in Japan (Oyasan, Kamigamo, Kiryu, and Takatori) and estimated the nutrient accumulation rates in tree biomass using two methods. For short-term estimates, the nutrient content of tree biomass was measured at two points in time over several years; for long-term estimates, the nutrient content was divided by forest age. The nutrient accumulation rates estimated using the long-term method was lower than those using the short-term method. Weathering rates for potassium, magnesium, and calcium estimated using the long-term method were lower than those using the short-term method. Weathering rates determined using the short-term method were high and could be overestimates in nutrient-limited forests. Soil nitrogen release values were lower with the longterm method than those with the short-term method and could be overestimated when using the latter method in nitrogen-limited watersheds. In conclusion, weathering rates and soil nitrogen release values determined using the long-term method are useful for assessing the sustainability of nutrient cycling in forest ecosystems although the rate of nutrient accumulation in tree biomass is assumed to be constant.