I'm skeptical. Having been to some areas of rural Japan, I'd suggest that the macro cycle established by humans was irrigation related and the removal of the same causes deep challenges to former human-presence-biome members. A novel and restored biome, more suited to the natural hydrosphere of the area, will likely take decades to a century to re-emerge assuming its species survive and its preconditions haven't been ruined by concrete.

Note also in my limited experience there is typically a severe and sudden difference between flat land and mountains, the former being human managed with extreme prejudice and the latter being typically degraded/unnatural/replanted ("Japan's forests are ~44% dense post-war cedar/hinoki plantations with barren understories"). This is one of the most striking features of the Japanese landscape relative to other nearby countries. I would assume the current study focused only on flatland, as the forests are not going to empty out when proximal humans desist: quite the opposite.

The unstated truth here is that Japan apparently raped its physical environment for its war machine.

https://japansociety.org/news/japans-forests-good-days-and-b...