Tree trunks and branches are beautifully sculpted sinuous forms. Branches undulate toward and away from your viewpoint. Here is the simple trick to capture these shapes in your sketches: ( ) = toward, )( = away. Now let’s break it down.
Lines around the circumference of a curved cylinder will converge toward the inside of the curve and expand toward the outside edge. If you have a slinky around the house, bend it around and watch what happens.When you look at the slinky from the side, you will see the lines on the surface curves toward you bend like this ( ). The lines on a surface curving away from you bend like this )(.
Look closely at the lines that describe the curving oak branch at the top of this post. What is the orientation of the lines around curves that bulge toward you? How is this different than the way the lines converge on surfaces that curve away from you? How do ( ) and )( lines suggest curvature on this branch? Understanding these lines is extremely helpful to draw trees with dimension and accuracy.
Click on the first image below to watch an annotated step-by-step slide show.