This blender shader uses different textures that are blender over and over consider every red box as its own layer like in photoshop and the node after that is its blending mode
here is a preview of the different layers starting with the gradient layer that will make parts of the stem green, this will be used as a mask in node 8, the tree bark texture is blended with the green texture using the gradient mask so that white areas will show the bark texture and the black areas of the mask will show green areas
now these are the different preview for the layers that are blended to have the final back texture, take note that the first layer below has been scaled in away so that the texture details are really small to give us the high frequency detail and because of that you also see some tiling issues, this will not be visible after we blend it with another texture as that texture will overlap the tiling hiding it.
this is the second layer to give us some larger details you can see the scale is big and we are seeing some tiling but this will also go away after we blend it with the next layer
this preview below is a blend of the top one and a copy layer too this removes most of the visible tilling and gives us some rich details
this is a blend of all the textures that will be used to the brown areas of the back