Although the light is natural, it seems flat. Consider shooting when the sun is lower in the sky and generating shadows. Taking steps to get a sharper picture and a composition with a stronger focus of interest might help.
Overlooking the fact for the moment that this DNMC, I'd recommend doing a landscape in landscape mode. Maybe you are considering it's a portrait because it's in portrait mode. Also, saturate the colors more to bring out the sky and forest.
Well, I am open to wide interpretation but however I wouldn't look at this image it is NOT a portrait... Technically, it's also too flat to my taste. I am sorry.
it was already a push to call this a natural light portrait and I prolly would have given you the benefit of the doubt, but you didn't even ahve anything in focus.