We examined the effect of clear-cut and plantation of riparian forest (Japanese cedar) on stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) and radiocarbon natural abundances (Δ¹⁴C) of stream macroinvertebrates such as insect larvae. Macroinvertebrates and their potential food sources (periphytic algae and leaf litter of terrestrial plants) were collected from six headwater streams having similar geographic properties except for the stand age of riparian forest.

Both the δ¹³C values of periphytic algae and stream macroinvertebrates decreased with forest age. Except for grazers, most macroinvertebrates showed Δ¹⁴C values similar with those of terrestrial litter and modern atmospheric CO₂. The Δ¹⁴C values of grazers (i.e., aquatic primary consumers) were significantly lower than those of modern atmospheric CO₂ and other macroinvertebrates. Our results suggest that the forest rotation of clear-cut and plantation alters transfer pathway of energy and materials between terrestrial and aquatic ecosystems, but the impact on food web structure may be limited.