This is obvious to me in Southern California. I contribute nutrients to the land near me that would otherwise not be here at all. The compost alone has nutrients from fruit and vegetables that don't even grow here. I maintain fruit trees that the squirrels and rabbits eat and in turn the coyotes and red tailed hawks are able to sustain their population. It's pretty simple really. We add more energy into the system and it has more biodiversity in turn.

I wonder if this is somewhat specific to Japan or has been observed elsewhere

In your face depopulators!

this will inevitably prompt the usual litany of "without immigration, Japan will not survive", so I'd like to point out the elephant in the room: no one wants to live in the countryside anymore, for a number of good reasons. those reasons are mostly cultural, and there's nothing any government can do about it.