Estimate of coarse root biomass and nutrient contents of trees in a subtropical broadleaf forest in Taiwan

We studied the biomass and estimated the nutrient content of coarse roots (≥ 5 mm) of trees (dbh ≥ 10 cm) in a subtropical broadleaf forest at Fushan, northeastern Taiwan. The results from excavating 8 trees of 7 species indicated that the biomass of coarse roots accounted for 13.4~30.2% of the total tree biomass. This percentage was not correlated to the diameter at breast height (dbh). Based on the natural logarithmic regression established by sample trees, the biomass of each category and the total biomass of coarse roots were highly significantly related to dbh. In the coarse roots, the stump and ≥ 100-mm roots had the highest percentage of biomass, each accounting for approximately 30.0% of the coarse root biomass. Comparatively, the biomass of coarse roots accounted for 21.9% of the total tree biomass and 28.0% of aboveground biomass. The biomass of coarse roots of trees was 65.1 Mg ha-1, which is higher than the average root biomass of tropical evergreen forests reported in the literature. The root/shoot ratio calculated from coarse roots was 0.28, higher than those for both tropical forests and the global average. The higher root/shoot ratio of the Fushan forest is likely a result of severe branch and leaf damage caused by frequent typhoons, leaving the forest with lower aboveground biomass. The nutrient allocation of coarse roots in trees of the Fushan forest is similar to that of temperate broadleaf forests.