Now that we have thought about representing trees in watercolor/pastel, let's look at applying what we know.

Pastel Drawing over Watercolor Underpainting

   When underpainting is thoroughly dry begin drawing your subject with pastel. 

 Bold Underpainting

Underpainting can be bold and abstract.  Think about your subject as you apply the watercolor.  In this case I am concerned to suggest the direction of growth, their posture and position of the tree to be drawn on the page.  I want to select colors that will complement my foliage color.  I am concerned to establish rhythm and balance. I keep my final idea in mind but am not dictated by it.

When the underpainting is dry, I can superimpose a finished image over the underpainting being careful to leave some of the underpainting color alone and free from pastel.

 Applying Foliage

 

Let's take a closer look at the application of pastel to represent foliage.

Here is a watercolor/pastel study of a massive oak tree that shades my patio.

 

Take a closer look at the foliage.

I have used a scumbling technique to create texture.  I have softened some edges.  But look how vibrant the areas are where I allow the watercolor color underpainting to remain untouched. The transparency of the watercolor allows the "white" of the paper to glow through. 

Outside edges can be secured with pastel.  This is especially useful for light value edges that were created with watercolor during the underpainting stage .

Note the green, white and yellow shapes on the right hand edge of the tree.  
By using lavender pastel and working around the light shapes the tree takes shape and form. 

The same technique can be used to secure the lightest side of trunks and branches. The light areas on the trunks of these trees have no pastel on them.  Their value and color is established with the watercolor underpainting which was applied at the beginning of the painting.