Tunnels can occur in a couple of ways, as you’ll see below. However, they work best when there are two sides of the image which are darker, tunnelling toward the background. The background does NOT need to be an open area/open sky/field etc – in fact, it could be more forest! But having some kind of “sides” to the image will give us much the same effect as a frame image.
Tunnels can also occur when you position the subject on a very narrow track, meaning you’ll have a tunnel of the foliage either side of them, too.
These are usually a lot more similar to “open” images, however we have the added benefit of some light and dark tones on either side of the image at least, giving us a little more flexibility in editing. By selectively darkening these edges, we can really draw attention to the subject within, without applying a fake vignette.
Many of the images below were taken on a wider path, or a path without foliage. Or, I looked for a space through the trees where they were dense either side of the dog, and had small narrow gaps behind him.
Be on the lookout for curves in nature. These can give us interesting options, as we can pose our dogs to reflect the same shape as the curve, use the curve to direct the dog’s gaze. or, they can accidentally block the gaze or the flow of the image, if rising in the gazing direction. Curves are usually going to also use elements from the other sections (eg., a curved tree-tunk becomes a frame) but it’s worth looking out for them in nature.