Somehow these dark grey trunks silhouetted against the winter afternoon sky brought to mind tombstones. The field sketch is below using conte crayon, charcoal and white gouache in tinted paper. Above, I tried to darken this with washes mixing burnt sienna with ultramarine or paynes grey, the watercolour scattering on the powdery surface. I have also turned down the exposure on the photo.
Below is the quick preliminary drawing, with the sun behind me. In reality that trunk is tiled with rich brown scales mortared in green. I need to have another try at capturing that.