This photograph was made when a light marine fog was just barely higher than the tops of the (very tall) trees. This allows you to see where rays of sunlight make it past the trees. This effect is strongest when the sun is low in the sky however, in this picture, a wide-angle focal length is used making it appear as if the sun were low when, in fact, it was about as high as it gets for a winter day in Vancouver.
Photography notes:
This photograph was made with a wide-angle focal length and with the lens angled upwards. This makes the trees appear to lean into the centre of the picture, an effect called "convergence". In postprocessing, the top of the picture has been stretched out to reduce this effect. A picture from the original image is shown below. Note that the convergence wasn't eliminated entirely, just reduced to look more natural, as if the photograph was made with a "normal" focal length.
