After the accident at Fukushima Daiichi Nuclear Power Plant (FNPP) in March 2011, high contamination levels in the environment suggest possible effects of radiation on nonhuman biota. In order to understand the effect on wild animals and plants, field investigations were conducted in the ex-evacuation zone where ambient dose-rate was particularly high. For the purpose of biomonitoring of the radiation effect, coniferous trees have been demonstrated to be suitable indicator organisms because of their high radiosensitivity, which was revealed decades ago by experiments using gamma irradiation facilities. Subsequently, radiosensitive damages in conifers became real after the Chernobyl nuclear power plant (CNPP) accident in 1986, where local coniferous species showed distinct biological damage in the radioactively contaminated areas. This review outlines the results obtained from the past radiation experiments and cases in surrounding forests after the CNPP accident for radiation effect studies of coniferous trees. By referring to them, the author explains the present situation and problems of the investigation on coniferous trees after the FNPP accident.