29 pieces by Enrico (a mixture of digital, pencil & watercolor, acrylic, and mixed media). 28 pieces by Ronnie (an equal mixture of digital, watercolor, pastel, and gouache, with a few pieces in other media). 24 pieces by Tadahiro (primarily digital, with 2 watercolor and 1 gouache).

From the publisher:

The three artists featured in Three Trees Make a Forest are professional illustrators with a penchant for travel and ambitious side projects in books and comics. Ronnie Del Carmen is a story artist, character designer and illustrator at Pixar Animation Studios. Del Carmen has also worked in comics with DC and Dark Horse. Tadahiro Uesugi is a world renowned Japanese illustrator who creates intuitive drawings of landscapes, characters and urban scenery, all with an amazing sense of color and texture. Enrico Casarosa is also a story artist at Pixar and is the founder of Sketch Crawl, a worldwide marathon sketching event.