sorry,first time ,repeat

I think you may be mistaken in your view of garden history if I understand you correctly: Japanese gardens are a derivative of Chinese gardens, is that what you mean.

I am sure china is japanese garden root.1600 years ago,japanese begin to study chinese-style garden.

Here is a link that might be useful: share other some ideas

What were Japanese gardens like before the year 408? Did they have gardens?

They have nice garder,like small bridge,summerhouse,art shrub ect.there are new technic in japanese garden now,great.
but its root of garden,cloth,character is china.
chinese often is one of most rich before 200 years.

Here is a link that might be useful: share other some ideas