Occasionally, one can find in nature a kind of a frame within the scene that is being photographed. If one is in the Arches National Park, they are prevalent. Other times one might look for tree limbs or rock structures hanging over the scene.
I might suggest not to base ones style on this but an occasional image with a strong sense of originality is used.
When used properly it gives completeness to the image.
This is because the frame is natural as being in the scene itself. Because of the natural frame now contains the scene instead of the viewfinder. there is a kind of formality added to the image. The emphasis is contained within the frame instead of the aspect of the scene flowing beyond the edges of the image.
Another reason this works well is because the frame now becomes a strong foreground. This then tends to give the image a sense of depth and the viewer that they are looking from one scene into another.
All sorts of things can be used as natural frames
Trees are most often used, caves, rock arches, gaps in fences and gates, windows, and whatever else the creative mind can find. The strongest types are when the foreground is used as a silhouette, and the scene beyond is brightly lit. However, if the tree has a unique texture in the bark it maybe used with both the foreground and background in bright light as this will add to the image.
Spacing becomes critical, thus the size of the frame in relationship to the size of the image( do not leave much space between the edge of the image and the natural frame and /or the natural frame and the scene within.) is critical.
Now create your style of natural frames, using all the things available…..The hardest part is seeing these natural frames. They are there.