Vertex painting the different layers of bark to make the trees look unique and adding some wind.
Then baking the highpolys down to planes and using them as leaves in paint fx. The grass and bushes are also done with paint fx baked down to planes. This helped my to make different variations of trees and grass quick but it needed alot of tweaking of values to get it good.
Then making the bark materials in Substance Designer and using vertex painting with heightblend to blend them. Also using one more channel of the vertex paint to add some different colors to the white parts of the bark.